High-Power 1.5 μm Tapered Distributed Bragg Reflector Laser Diodes for Eye-Safe LIDAR

A high-power InAlGaAs/InP tapered distributed Bragg reflector laser diode with narrow linewidth emission at 1.5μm is reported. The laser has a monolithic waveguide architecture comprising a third-order grating section for longitudinal mode selection, an index-guided gain section for lateral mode filtering, and a gain-guided tapered section for power scaling. An output power of 770 mW is reported for continuous wave operation at room temperature. In pulsed mode, the laser delivered a peak power of 4.6 W with a full width at half-maximum spectral linewidth of only 250 pm. In addition to the narrow linewidth and high-power features, the emission wavelength exhibits a temperature dependent shift of only 0.1 nm/°C. The parameters achieved suggest that these laser diodes would enable the realization of compact LIDAR systems with improved signal-to-noise ratio, owing to the high output power and the possibility to use narrow passband filters at receiver side, which is enabled by the narrow and temperature-stable emission spectrum. The wavelength range around 1.5μm also enables LIDAR systems with high output powers while maintaining eye safety, ultimately leading to improved system performance.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC
Contributors: Aho, A. T., Viheriälä, J., Koskinen, M., Uusitalo, T., Reuna, J., Guina, M.
Number of pages: 4
Pages: 1249-1252
Publication date: 1 Oct 2020
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 32
Issue number: 19
ISSN (Print): 1041-1135
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Diode lasers, distributed Bragg reflector, high power, LIDAR

Bibliographical note

INT=phys,"Koskinen, Mervi"

Source: Scopus
Source ID: 85091098269

Research output: Contribution to journalArticleScientificpeer-review

Tree species classification using structural features derived from terrestrial laser scanning

Fast and automated collection of forest data, such as species composition information, is required to support climate mitigation actions. Recently, there have been significant advances in the use of terrestrial laser scanning (TLS) instruments, which facilitate the capture of detailed forest structure. However, for tree species recognition the structural information from TLS has mainly been used to complement spectral information. TLS-only classification studies have been limited in size and diversity of plot forest types. In this paper, we investigate the potential of TLS for tree species classification. We used quantitative structure models to determine 17 structural tree features. These features were computed for 758 trees of five tree species, including two understory species, of a 1.4 hectare mixed deciduous forest plot. Three classification methods were compared: k-nearest neighbours, multinomial logistic regression and support vector machine. We assessed the potential underlying causes for structural differences with principal component analysis. We obtained classification success rates of approximately 80%, however, with producer accuracies for three of the five species ranging from 0 to 60%. Low producer accuracies were the result of a high intra- and low inter-species variability. These effects were, respectively, caused by a high size-dependency of the structural features and a convergence of structural traits across species as a result of the individual tree position in the forest canopy and shade tolerance. Nevertheless, the producer accuracies could be improved through sensitivity vs. specificity trade-offs, with over 50% for all species being obtainable. The high intra -and low inter-species variability complicate the classification. Furthermore, the classification performance and best classification method greatly depend on its targeted application. In conclusion, this study proves the added value of TLS for tree species classification but also shows that TLS opens up potential for testing and further development of ecological theory.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Inverse Problems, Universiteit Gent, National Physical Laboratory, University of Oxford, CSIRO Energy Centre, NERC National Centre for Earth Observation (NCEO), UCL Department of Geography
Contributors: Terryn, L., Calders, K., Disney, M., Origo, N., Malhi, Y., Newnham, G., Raumonen, P., Åkerblom, M., Verbeeck, H.
Number of pages: 12
Pages: 170-181
Publication date: 1 Oct 2020
Peer-reviewed: Yes

Publication information

Journal: ISPRS Journal of Photogrammetry and Remote Sensing
Volume: 168
ISSN (Print): 0924-2716
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Computer Science Applications, Computers in Earth Sciences
Keywords: Machine learning classifiers, Quantitative structure model, Structural tree features, Terrestrial laser scanning, Tree species classification
Source: Scopus
Source ID: 85089603514

Research output: Contribution to journalArticleScientificpeer-review

Fusionsense: Emotion classification using feature fusion of multimodal data and deep learning in a brain-inspired spiking neural network

Using multimodal signals to solve the problem of emotion recognition is one of the emerging trends in affective computing. Several studies have utilized state of the art deep learning methods and combined physiological signals, such as the electrocardiogram (EEG), electroencephalogram (ECG), skin temperature, along with facial expressions, voice, posture to name a few, in order to classify emotions. Spiking neural networks (SNNs) represent the third generation of neural networks and employ biologically plausible models of neurons. SNNs have been shown to handle Spatio-temporal data, which is essentially the nature of the data encountered in emotion recognition problem, in an efficient manner. In this work, for the first time, we propose the application of SNNs in order to solve the emotion recognition problem with the multimodal dataset. Specifically, we use the NeuCube framework, which employs an evolving SNN architecture to classify emotional valence and evaluate the performance of our approach on the MAHNOB-HCI dataset. The multimodal data used in our work consists of facial expressions along with physiological signals such as ECG, skin temperature, skin conductance, respiration signal, mouth length, and pupil size. We perform classification under the Leave-One-Subject-Out (LOSO) cross-validation mode. Our results show that the proposed approach achieves an accuracy of 73.15% for classifying binary valence when applying feature-level fusion, which is comparable to other deep learning methods. We achieve this accuracy even without using EEG, which other deep learning methods have relied on to achieve this level of accuracy. In conclusion, we have demonstrated that the SNN can be successfully used for solving the emotion recognition problem with multimodal data and also provide directions for future research utilizing SNN for Affective computing. In addition to the good accuracy, the SNN recognition system is requires incrementally trainable on new data in an adaptive way. It only one pass training, which makes it suitable for practical and on-line applications. These features are not manifested in other methods for this problem.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Auckland University of Technology, University of Los Andes, Aalto University
Contributors: Tan, C., Ceballos, G., Kasabov, N., Subramaniyam, N. P.
Number of pages: 27
Publication date: 17 Sep 2020
Peer-reviewed: Yes

Publication information

Journal: Sensors (Switzerland)
Volume: 20
Issue number: 18
Article number: 5328
ISSN (Print): 1424-8220
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Biochemistry, Atomic and Molecular Physics, and Optics, Instrumentation, Electrical and Electronic Engineering
Keywords: Evolving Spiking Neural Networks (eSNNs), Facial emotion recognition, Multimodal data, NeuCube, Spatio-temporal data
Source: Scopus
Source ID: 85091041249

Research output: Contribution to journalArticleScientificpeer-review

Optically induced crossover from weak to strong coupling regime between surface plasmon polaritons and photochromic molecules

We demonstrate optically induced crossover from a weak to a strong coupling regime in a single photonic system consisting of propagating surface plasmon polaritons (SPPs) on a planar silver film and ultraviolet (UV)-switchable photochromic molecules. A gradual increase is observed in the vacuum Rabi splitting upon increasing UV exposure, along with intriguing behavior, where the reflectivity initially decreases due to increased losses at the weak coupling regime, and then increases due to the emergence of strongly coupled modes and the associated band gap formation at the resonance frequency of the uncoupled states. This work explicitly demonstrates the optical tunability of the degree of hybridization of the SPP and exciton modes, spanning the range from weak to intermediate and finally to the strong coupling regime.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Research group: Chemistry & Advanced Materials, Ita-Suomen yliopisto
Contributors: Asamoah, B. O., Mohamed, S., Datta, S., Karvinen, P., Rekola, H., Priimagi, A., Hakala, T. K.
Number of pages: 10
Pages: 26509-26518
Publication date: 31 Aug 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 28
Issue number: 18
ISSN (Print): 1094-4087
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

EXT="Rekola, Heikki"

Source: Scopus
Source ID: 85090383053

Research output: Contribution to journalArticleScientificpeer-review

ClothFace: A Batteryless RFID-Based Textile Platform for Handwriting Recognition

This paper introduces a prototype of ClothFace technology, a battery-free textile-based handwriting recognition platform that includes an e-textile antenna and a 10 × 10 array of radio frequency identification (RFID) integrated circuits (ICs), each with a unique ID. Touching the textile platform surface creates an electrical connection from specific ICs to the antenna, which enables the connected ICs to be read with an external UHF (ultra-haigh frequency) RFID reader. In this paper, the platform is demonstrated to recognize handwritten numbers 0-9. The raw data collected by the platform are a sequence of IDs from the touched ICs. The system converts the data into bitmaps and their details are increased by interpolating between neighboring samples using the sequential information of IDs. These images of digits written on the platform can be classified, with enough accuracy for practical use, by deep learning. The recognition system was trained and tested with samples from six volunteers using the platform. The real-time number recognition ability of the ClothFace technology is demonstrated to work successfully with a very low error rate. The overall recognition accuracy of the platform is 94.6% and the accuracy for each digit is between 91.1% and 98.3%. As the solution is fully passive and gets all the needed energy from the external RFID reader, it enables a maintenance-free and cost-effective user interface that can be integrated into clothing and into textiles around us.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Research group: Wireless Identification and Sensing Systems Research Group, Computing Sciences, Research group: Machine Learning Group MLG, Research group: Vision, Research group: Inverse Problems
Contributors: He, H., Chen, X., Mehmood, A., Raivio, L., Huttunen, H., Raumonen, P., Virkki, J.
Number of pages: 12
Publication date: 28 Aug 2020
Peer-reviewed: Yes

Publication information

Journal: Sensors (Basel, Switzerland)
Volume: 20
Issue number: 17
Article number: 4878
ISSN (Print): 1424-8220
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Biochemistry, Atomic and Molecular Physics, and Optics, Instrumentation, Electrical and Electronic Engineering
Keywords: deep learning, human–machine interaction, passive UHF RFID, textile electronics, user interface, wearables
Source: Scopus
Source ID: 85090182156

Research output: Contribution to journalArticleScientificpeer-review

High-Power 760 nm VECSEL Based on Quantum Dot Gain Mirror

We report high-power second-harmonic generation of 760 nm laser light from optically-pumped vertical-external-cavity surface-emitting laser based on quantum dot active medium. The laser generates 1.2 W in fundamental transverse mode with fixed linear polarization. The emission wavelength can be continuously tuned from 738 to 778 nm by using an intra cavity birefringent filter for fundamental radiation without readjustment of phase-matching angle of the nonlinear crystal. The result constitutes a viable alternative for applications requiring broadly tunable high brightness lasers in the 700-800 nm range.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, LakeDiamond SA, Ecole Polytechnique Fédérale de Lausanne, Universite de Rennes
Contributors: Nechay, K., Mereuta, A., Paranthoen, C., Brevalle, G., Levallois, C., Alouini, M., Chevalier, N., Perrin, M., Suruceanu, G., Caliman, A., Kapon, E., Guina, M.
Number of pages: 4
Publication date: 1 Aug 2020
Peer-reviewed: Yes

Publication information

Journal: IEEE journal of quantum electronics
Volume: 56
Issue number: 4
ISSN (Print): 0018-9197
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Optical harmonic generation, quantum dot lasers, semiconductor growth, surface emitting lasers
Source: Scopus
Source ID: 85087421916

Research output: Contribution to journalArticleScientificpeer-review

Edge-enhanced optical parametric generation in periodically poled LiNbO3

We demonstrate enhanced optical parametric gains occurring at the edge of periodically poled LiNbO3 (PPLN) regions. Experiments performed in MgO-doped PPLN samples, pumped at 532 nm with parametric signal outputs around 800 nm and 1550 nm, exhibit good agreement with numerical simulations of the nonlinear wave dynamics in the system, based on the assumption of an average refractive index increase ∆n = 5.3×10−5 in the PPLN region. Excitation in proximity to the PPLN edge with a pump power of 8.1 mW results in a 3.6-fold output power increase with respect to parametric generation inside the PPLN area.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, KTH Royal Institute of Technology
Contributors: Prytz, N. B., Qvarngård, D., Härkönen, A., Guina, M., Gallo, K.
Number of pages: 9
Pages: 20879-20887
Publication date: 6 Jul 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 28
Issue number: 14
ISSN (Print): 1094-4087
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85087787954

Research output: Contribution to journalArticleScientificpeer-review

Selective hydrogen production at Pt(111) investigated by Quantum Monte Carlo methods for metal catalysis

This rapid communication gives the salient points and results of the theoretical investigation of a chemical reaction for efficient selective hydrogen production. The clean fuel produced is a sustainable energy source. Accurate methods based on quantum theory are used because the changing electronic structure is a probe that monitors reactions. The reaction between water and carbon monoxide is used industrially with metal catalysts, usually platinum. There is a considerable economic and environmental challenge underpinning this fundamental investigation where bond dissociation plays an essential role. A bond dissociation process is often the limiting step of reaction rates for industrial catalysis. Most mainstream quantum approaches fail to a greater or lesser degree in the description of this process. The present work advocates a promising alternative: the initial analysis of statistical data generated by the Quantum Monte Carlo (QMC) method demonstrated very stringent statistical accuracy for essential information on hydrogen production via the water-gas shift reaction with platinum catalyst. The transition state structure is obtained from QMC force constants and illustrated here. It corresponds to water OH-stretch concerted with Pt-H bond formation, whilst the OH oxygen atom begins to interact with the CO carbon. The present QMC evaluation of the corresponding activation barrier is low: 17.0 ± 0.2 kcal/mol. It is close to the experimental apparent activation energy of 17.05 kcal/mol. This method is applicable to a wide range of similar systems.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Institute Pascal
Contributors: Sharma, R. O., Rantala, T. T., Hoggan, P. E.
Publication date: 5 Jun 2020
Peer-reviewed: Yes

Publication information

Journal: International Journal of Quantum Chemistry
Volume: 120
Issue number: 11
Article number: e26198
ISSN (Print): 0020-7608
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Physical and Theoretical Chemistry
Keywords: heterogeneous catalysis, low activation barrier, metal surface, quantum Monte Carlo calculation
Source: Scopus
Source ID: 85083688806

Research output: Contribution to journalArticleScientificpeer-review

Low-noise octave-spanning mid-infrared supercontinuum generation in a multimode chalcogenide fiber

We demonstrate the generation of a low-noise, octave-spanning mid-infrared supercontinuum from 1700 to 4800 nm by injecting femtosecond pulses into the normal dispersion regime of a multimode step-index chalcogenide fiber with 100 µm core diameter. We conduct a systematic study of the intensity noise across the supercontinuum spectrum and show that the initial fluctuations of the pump laser are at most amplified by a factor of three. We also perform a comparison with the noise characteristics of an octave-spanning supercontinuum generated in the anomalous dispersion regime of a multimode fluoride fiber with similar core size and show that the normal dispersion supercontinuum in the multimode chalcogenide fiber has superior noise characteristics. Our results open up novel perspectives for many practical applications such as long-distance remote sensing where high power and low noise are paramount.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Ultrafast Optics, Research group: Nonlinear Fiber Optics
Contributors: Eslami, Z., Ryczkowski, P., Salmela, L., Genty, G.
Number of pages: 4
Pages: 3103-3106
Publication date: 1 Jun 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 45
Issue number: 11
ISSN (Print): 0146-9592
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85085675757

Research output: Contribution to journalArticleScientificpeer-review

Zinc-indiffused MgO:PPLN waveguides for blue/UV generation via VECSEL pumping

We present the design and characterization of a zinc-indiffused periodically poled lithium-niobate ridge waveguide for second-harmonic generation of ∼390 nm light from 780 nm. We use a newly developed, broadband near-infrared vertical external-cavity surface-emitting laser (VECSEL) to investigate the potential for lower-footprint nonlinear optical pump sources as an alternative to larger commercial laser systems. We demonstrate a VECSEL with an output power of 500 mW, containing an intracavity birefringent filter for spectral narrowing and wavelength selection. In this first demonstration of using a VECSEL to pump a nonlinear waveguide, we present the ability to generate 1 mW of ∼390 nm light with further potential for increased efficiency and size reduction.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, University of Southampton, United Kingdom
Contributors: Gray, A. C., Woods, J. R., Carpenter, L. G., Kahle, H., Berry, S. A., Tropper, A. C., Guina, M., Apostolopoulos, V., Smith, P. G., Gawith, C. B.
Number of pages: 6
Pages: 4921-4926
Publication date: 1 Jun 2020
Peer-reviewed: Yes

Publication information

Journal: Applied Optics
Volume: 59
Issue number: 16
ISSN (Print): 1559-128X
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Electrical and Electronic Engineering
Source: Scopus
Source ID: 85085950920

Research output: Contribution to journalArticleScientificpeer-review

Lensless hyperspectral phase imaging in a self-reference setup based on Fourier transform spectroscopy and noise suppression

A novel phase retrieval algorithm for broadband hyperspectral phase imaging from noisy intensity observations is proposed. It utilizes advantages of the Fourier transform spectroscopy in the self-referencing optical setup and provides additional, beyond spectral intensity distribution, reconstruction of the investigated object's phase. The noise amplification Fellgett's disadvantage is relaxed by the application of a sparse wavefront noise filtering embedded in the proposed algorithm. The algorithm reliability is proved by simulation tests and by results of physical experiments for transparent objects. These tests demonstrate precise phase imaging and object depth (profile) reconstruction.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences
Contributors: Shevkunov, I., Katkovnik, V., Egiazarian, K.
Number of pages: 13
Pages: 17944-17956
Publication date: Jun 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 28
Issue number: 12
ISSN (Print): 1094-4087
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85086505435

Research output: Contribution to journalArticleScientificpeer-review

Hyperspectral phase imaging based on denoising in complex-valued eigensubspace

A novel algorithm for reconstruction of hyperspectral 3D complex domain images (phase/amplitude) from noisy complex domain observations has been developed and studied. This algorithm starts from the SVD (singular value decomposition) analysis of the observed complex-valued data and looks for the optimal low dimension eigenspace. These eigenspace images are processed based on special non-local block-matching complex domain filters. The accuracy and quantitative advantage of the new algorithm for phase and amplitude imaging are demonstrated in simulation tests and in processing of the experimental data. It is shown that the algorithm is effective and provides reliable results even for highly noisy data.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Computational Imaging-CI, ITMO University, University of Ulm Medical Center, University of Stuttgart
Contributors: Shevkunov, I., Katkovnik, V., Claus, D., Pedrini, G., Petrov, N. V., Egiazarian, K.
Number of pages: 10
Publication date: 1 Apr 2020
Peer-reviewed: Yes
Early online date: 6 Dec 2019

Publication information

Journal: Optics and Lasers in Engineering
Volume: 127
Article number: 105973
ISSN (Print): 0143-8166
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Mechanical Engineering, Electrical and Electronic Engineering
Keywords: Hyperspectral imaging, Noise filtering, Noise in imaging systems, Phase imaging, Singular value decomposition, Sparse representation
Electronic versions: 
Source: Scopus
Source ID: 85076060273

Research output: Contribution to journalArticleScientificpeer-review

Temporal ghost imaging with random fiber lasers

Ghost imaging in the time domain has opened up new possibilities to retrieve ultrafast waveforms. A pre-requisite to ghost imaging in the time domain is a light source with random temporal intensity fluctuations that are fully uncorrelated over the duration of the temporal waveform being imaged. Here, we show that random fiber lasers are excellent candidates for ghost imaging in the time domain. We study the temporal correlations of the intensity fluctuations of a random fiber laser in different operating regimes and compare its performance in temporal ghost imaging configurations with that of a conventional multi-mode cavity-based fiber laser. Our results demonstrate that random fiber lasers can achieve superior performance for ghost imaging as compared to cavity-based fiber lasers where strong correlations at the cavity round-trip time can yield artefacts for waveforms of long duration.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Ultrafast Optics, Sichuan University, University of Electronic Science and Technology of China
Contributors: Wu, H., Han, B., Wang, Z., Genty, G., Feng, G., Liang, H.
Number of pages: 8
Pages: 9957-9964
Publication date: 30 Mar 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 28
Issue number: 7
ISSN (Print): 1094-4087
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85082635141

Research output: Contribution to journalArticleScientificpeer-review

Instabilities in a dissipative soliton-similariton laser using a scalar iterative map

Numerical simulations of a dissipative soliton-similariton laser are shown to reproduce a range of instabilities seen in recent experiments. The model uses a scalar nonlinear Schrödinger equation map, and regions of stability and instability are readily identified as a function of gain and saturable absorber parameters. Studying evolution over multiple round trips reveals spectral instabilities linked with soliton molecule internal motion, soliton explosions, chaos, and intermittence. For the case of soliton molecules, the relative phase variation in the spectrum is shown to be due to differences in nonlinear phase evolution between the molecule components over multiple round trips.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, UMR 6174
Contributors: Meng, F., Lapre, C., Billet, C., Genty, G., Dudley, J. M.
Number of pages: 4
Pages: 1232-1235
Publication date: 1 Mar 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 45
Issue number: 5
ISSN (Print): 0146-9592
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85080943075

Research output: Contribution to journalArticleScientificpeer-review

High-dimensional quantum gates using full-field spatial modes of photons

Unitary transformations are the fundamental building blocks of gates and operations in quantum information processing, allowing the complete manipulation of quantum systems in a coherent manner. In the case of photons, optical elements that can perform unitary transformations are readily available only for some degrees of freedom, e.g., wave plates for polarization. However, for high-dimensional states encoded in the transverse spatial modes of light, performing arbitrary unitary transformations remains a challenging task for both theoretical proposals and actual implementations. Following the idea of multi-plane light conversion, we show that it is possible to perform a broad variety of unitary operations at high quality by using only a few phase modulation planes. More importantly, we experimentally implement several high-dimensional quantum gates for up to five-dimensional states encoded in the full-field mode structure of photons. In particular, we realize cyclic and quantum Fourier transformations, known as Pauli X -gates and Hadamard Ĥ-gates, respectively, with an average visibility of more than 90%. In addition, we demonstrate near-perfect “unitarity” by means of quantum process tomography, unveiling a process purity of 99%. Last, we demonstrate the benefit of the two independent spatial degrees of freedom, i.e., azimuthal and radial, and implement a two-qubit controlled-NOT quantum operation on a single photon. Thus, our demonstrations open up new paths to implement high-dimensional quantum operations, which can be applied to various tasks in quantum communication, computation, and sensing schemes.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Austrian Academy of Sciences, University of Ottawa, Canada
Contributors: Brandt, F., Hiekkamäki, M., Bouchard, F., Huber, M., Fickler, R.
Number of pages: 10
Pages: 98-107
Publication date: 20 Feb 2020
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 7
Issue number: 2
ISSN (Print): 2334-2536
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85079614867

Research output: Contribution to journalArticleScientificpeer-review

Single exposure lensless subpixel phase imaging: Optical system design, modelling, and experimental study

Design and optimization of lensless phase-retrieval optical system with phase modulation of free-space propagation wavefront is proposed for subpixel imaging to achieve super-resolution reconstruction. Contrary to the traditional super-resolution phase-retrieval, the method in this paper requires a single observation only and uses the advanced Super-Resolution Sparse Phase Amplitude Retrieval (SR-SPAR) iterative technique which contains optimized sparsity based filters and multi-scale filters. The successful object imaging relies on modulation of the object wavefront with a random phase-mask, which generates coded diffracted intensity pattern, allowing us to extract subpixel information. The system’s noise-robustness was investigated and verified. The super-resolution phase-imaging is demonstrated by simulations and physical experiments. The simulations included high quality reconstructions with super-resolution factor of 5, and acceptable at factor up to 9. By physical experiments 3 µm details were resolved, which are 2.3 times smaller than the resolution following from the Nyquist-Shannon sampling theorem.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Computational Imaging-CI
Contributors: Kocsis, P., Shevkunov, I., Katkovnik, V., Egiazarian, K.
Number of pages: 13
Pages: 4625-4637
Publication date: 17 Feb 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 28
Issue number: 4
ISSN (Print): 1094-4087
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85079348632

Research output: Contribution to journalArticleScientificpeer-review

Precise length definition of active GaAs-based optoelectronic devices for low-loss silicon photonics integration

The length variation associated with standard cleaving of III–V optoelectronic chips is a major source of loss in the integration with the micron-scale silicon-on-insulator waveguides. To this end, a new, to the best of our knowledge, approach for precise definition of the III–V chip length is reported. The method employs lithography and wet etching of cleave marks outside the active III–V waveguides. The marks follow a specific crystallographic orientation and are used to initiate and guide the cleaving process. Besides minimizing the air gap between the butt-coupled III–V and Si waveguides and hence minimizing the coupling losses, the use of precisely defined length significantly improves the integration yield owing to the increased length uniformity. We apply this technique to defining the lengths of GaAs-based semiconductor optical amplifiers and demonstrate length control with an accuracy better than 250 nm per facet. This variation is more than 1 order of magnitude smaller than with the traditional cleaving methods, resulting in improvement of coupling by several dBs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, VTT Technical Research Centre of Finland
Contributors: Tuorila, H., Viheriälä, J., Zia, N., Cherchi, M., Harjanne, M., Isoaho, R., Aalto, T., Guina, M.
Number of pages: 4
Pages: 943-946
Publication date: 15 Feb 2020
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 45
Issue number: 4
ISSN (Print): 0146-9592
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85079361695

Research output: Contribution to journalArticleScientificpeer-review

Comparative Analysis of Injection Microdisk Lasers Based on InGaAsN Quantum Wells and InAs/InGaAs Quantum Dots

Abstract: The results of comparative analysis of the spectral and threshold characteristics of room-temperature injection microdisk lasers of the spectral range 1.2×× μm with different active regions, notably, InGaAsN/GaAs quantum wells or InAs/InGaAs/GaAs quantum dots are presented. It is found that microlasers of a comparable size with quantum wells possess a larger laser generation threshold when compared with microlasers with quantum dots. At the same time, the latter are characterized by a noticeably smaller fraction of emitted power corresponding to laser modes. The jump to lasing via an excited-state optical transition is also characteristic for them. Microdisk lasers based on InGaAsN alloy do not have these disadvantages.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Russian Academy of Science, St. Petersburg State Polytechnical University, Ioffe Physico-Technical Institute
Contributors: Moiseev, E. I., Maximov, M. V., Kryzhanovskaya, N. V., Simchuk, O. I., Kulagina, M. M., Kadinskaya, S. A., Guina, M., Zhukov, A. E.
Number of pages: 5
Pages: 263-267
Publication date: 1 Feb 2020
Peer-reviewed: Yes

Publication information

Journal: Semiconductors
Volume: 54
Issue number: 2
ISSN (Print): 1063-7826
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics
Keywords: microlaser, nitrogen-containing semiconductors, quantum dots, quantum wells
Source: Scopus
Source ID: 85081636724

Research output: Contribution to journalArticleScientificpeer-review

Goos-Hänchen and Imbert-Fedorov shifts for epsilon-near-zero materials

We investigate the reflection of a Gaussian beam impinging upon the surface of an epsilon-near-zero (ENZ) medium. In particular, we discuss the occurrence of Goos-Hänchen and Imbert-Fedorov shifts. Our calculations reveal that spatial shifts are significantly enhanced owing to the ENZ nature of the medium, and that their value and angular position can be tuned by tuning the plasma frequency of the medium.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Università dell'Aquila
Contributors: Nieminen, A., Marini, A., Ornigotti, M.
Publication date: 28 Jan 2020
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 22
Issue number: 3
Article number: 035601
ISSN (Print): 2040-8978
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: beam shifts, Epsilon-near-zero, physical reflection
Source: Scopus
Source ID: 85080149323

Research output: Contribution to journalArticleScientificpeer-review

Sequential Collinear Photofragmentation and Atomic Absorption Spectroscopy for Online Laser Monitoring of Triatomic Metal Species

Industrial chemical processes are struggling with adverse effects, such as corrosion and deposition, caused by gaseous alkali and heavy metal species. Mitigation of these problems requires novel monitoring concepts that provide information on gas-phase chemistry. However, selective optical online monitoring of the most problematic diatomic and triatomic species is challenging due to overlapping spectral features. In this work, a selective, all-optical, in situ gas-phase monitoring technique for triatomic molecules containing metallic atoms was developed and demonstrated with detection of PbCl2. Sequential collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) enables determination of the triatomic PbCl2 concentration through detection of released Pb atoms after two consecutive photofragmentation processes. Absorption cross-sections of PbCl2, PbCl, and Pb were determined experimentally in a laboratory-scale reactor to enable calibration-free quantitative determination of the precursor molecule concentration in an arbitrary environment. Limit of detection for PbCl2 in the laboratory reactor was determined to be 0.25 ppm. Furthermore, the method was introduced for in situ monitoring of PbCl2 concentration in a 120 MWth power plant using demolition wood as its main fuel. In addition to industrial applications, the method can provide information on chemical reaction kinetics of the intermediate species that can be utilized in reaction simulations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Applied Optics, Tampere University, University Central Hospital Kuopio, Valmet Automation Oy, Universidad Nacional Autónoma de México
Contributors: Viljanen, J., Kalmankoski, K., Contreras, V., Sarin, J. K., Sorvajärvi, T., Kinnunen, H., Enestam, S., Toivonen, J.
Number of pages: 14
Publication date: 18 Jan 2020
Peer-reviewed: Yes

Publication information

Journal: Sensors (Basel, Switzerland)
Volume: 20
Issue number: 2
Article number: 533
ISSN (Print): 1424-8220
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Biochemistry, Atomic and Molecular Physics, and Optics, Instrumentation, Electrical and Electronic Engineering
Keywords: absorption, combustion, kinetics, lead, photofragmentation

Bibliographical note

INT=phys,"Kalmankoski, Kim"
INT=phys,"Sarin, Jaakko K."

Source: Scopus
Source ID: 85078213348

Research output: Contribution to journalArticleScientificpeer-review

Backscattering-based wireless communication and power transfer to small biomedical implants

In this paper and presentation, we will focus on different aspects of backscattering-based wireless communication and power transfer to small biomedical implants. We will present three different antenna topologies for data and power transfer through tissue, in vitro and in vivo studies on implantable intracranial pressure (ICP) sensors and give insight and analysis on wireless link reliability in tissue environment. We will also present radio frequency identification (RFID)-based implant platform and communication method. Moreover, we will focus on differences and challenges of in vivo environment compared to laboratory phantoms and tissue models. In our studies, different types of implantable antennas have been tested to investigate reliability, accuracy and sensitivity of the brain implants: A hybrid near field-far field system with a piezoresistive sensor for ICP monitoring [2], [4], a UHF band spilt-ring resonator system [3] and LC tank based miniature implantable antenna [5]. This paper will present these implant antennas and wireless power transfer in tissue environment present in human head.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech, Research group: Wireless Identification and Sensing Systems Research Group
Contributors: Ukkonen, L., Sydänheimo, L., Ma, S., Björninen, T.
Publication date: 2020

Host publication information

Title of host publication: Microfluidics, BioMEMS, and Medical Microsystems XVIII
Publisher: SPIE
Editors: Gray, B. L., Becker, H.
Article number: 112350A
ISBN (Print): 9781510632332
ISBN (Electronic): 9781510632349

Publication series

Name: Progress in Biomedical Optics and Imaging - Proceedings of SPIE
Volume: 11235
ISSN (Print): 1605-7422
ISSN (Electronic): 2410-9045
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Atomic and Molecular Physics, and Optics, Radiology Nuclear Medicine and imaging
Keywords: implant antennas, Wireless biomedical implants, wireless power transfer

Bibliographical note

jufoid=65546

Source: Scopus
Source ID: 85082726318

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Controlling the plasmon resonance via epsilon-near-zero multilayer metamaterials

Localized plasmon resonance of a metal nanoantenna is determined by its size, shape and environment. Here, we diminish the size dependence by using multilayer metamaterials as epsilon-near-zero (ENZ) substrates. By means of the vanishing index of the substrate, we show that the spectral position of the plasmonic resonance becomes less sensitive to the characteristics of the plasmonic nanostructure and is controlled mostly by the substrate, and hence, it is pinned at a fixed narrow spectral range near the ENZ wavelength. Moreover, this plasmon wavelength can be adjusted by tuning the ENZ region of the substrate, for the same size nanodisk (ND) array. We also show that the difference in the phase of the scattered field by different size NDs at a certain distance is reduced when the substrate is changed to ENZ metamaterial. This provides effective control of the phase contribution of each nanostructure. Our results could be utilized to manipulate the resonance for advanced metasurfaces and plasmonic applications, especially when precise control of the plasmon resonance is required in flat optics designs. In addition, the pinning wavelength can be tuned optically, electrically and thermally by introducing active layers inside the hyperbolic metamaterial.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Metaplasmonics
Contributors: Habib, M., Briukhanova, D., Das, N., Yildiz, B. C., Caglayan, H.
Number of pages: 8
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Nanophotonics
Volume: 9
Issue number: 11
Article number: 20200245
ISSN (Print): 2192-8614
Original language: English
ASJC Scopus subject areas: Biotechnology, Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: epsilon near zero, hyperbolic metamaterial, localized surface plasmon, pinning effect

Bibliographical note

INT=phys,"Briukhanova, Daria"
INT=phys,"Das, Nekhel"
INT=phys,"Yildiz, Bilge Can"

Source: Scopus
Source ID: 85089689543

Research output: Contribution to journalArticleScientificpeer-review

Features of correlation measurements of the parameters of pulsed hyperspectral optical fields using an asymmetric interferometer

Differences in correlation measurements of the parameters of pulsed hyperspectral optical fields using symmetric and asymmetric interferometers are considered. It is shown analytically that the resulting cross-correlation function is sensitive to phase perturbations in the original wave field. The considered setup, which contains a telescopic reflective 4f system of parabolic mirrors in one arm, demonstrates that in the case of an asymmetric interferometer, the presence of aberrations leads to degradation of the reconstructed image, whereas in the case of symmetric interferometers these aberrations do not affect the result.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Computational Imaging-CI, ITMO University
Contributors: Kulya, M. S., Katkovnik, V. Y., Egiazarian, K., Petrov, N. V.
Number of pages: 4
Pages: 679-682
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Quantum Electronics
Volume: 50
Issue number: 7
ISSN (Print): 1063-7818
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Statistical and Nonlinear Physics, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: correlation measurements, hyperspectral fields, symmetric and asymmetric interferometers
Source: Scopus
Source ID: 85090382756

Research output: Contribution to journalArticleScientificpeer-review

Full-field mode sorter using two optimized phase transformations for high-dimensional quantum cryptography

High-dimensional encoding schemes have emerged as a novel way to perform quantum information tasks. For high dimensionality, temporal and transverse spatial modes of photons are the two paradigmatic degrees of freedom commonly used in such experiments. Nevertheless, general devices for multi-outcome measurements are still needed to take full advantage of the high-dimensional nature of encoding schemes. We propose a general full-field mode sorting scheme consisting of only up to two optimized phase elements based on evolutionary algorithms that allows for joint sorting of azimuthal and radial modes. We further study the performance of our scheme through simulations in the context of high-dimensional quantum cryptography, where sorting in different mutually unbiased bases and high-fidelity measurement schemes are crucial.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Austrian Academy of Sciences, University of Ottawa, Canada, University of Ulm Medical Center, Centro S3, Max Planck Institute for the Science of Light, Friedrich-Alexander-Universität Erlangen-Nürnberg
Contributors: Fickler, R., Bouchard, F., Giese, E., Grillo, V., Leuchs, G., Karimi, E.
Number of pages: 7
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics (United Kingdom)
Volume: 22
Issue number: 2
Article number: 024001
ISSN (Print): 2040-8978
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: mode demultiplexing high-dimensional quantum information, quantum cryptography, transverse spatial modes
Electronic versions: 
Source: Scopus
Source ID: 85079689477

Research output: Contribution to journalArticleScientificpeer-review

Harmonic mode-locking fiber ring laser with a pulse repetition rate up to 12 GHz

We experimentally demonstrate a harmonically mode-locked Er-doped fiber laser. The distinctive feature of the laser is highly stable pulse trains generated via self-starting hybrid mode-locking triggered by frequency-shifting and nonlinear polarization evolution. A intra-cavity tunable bandpass filter allows getting a pulse repetition rate up to 12 GHz with local adjustment of the wavelength.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Nanophotonics, Ulyanovsk State University, St. Petersburg State Polytechnical University, ITMO University
Contributors: Korobko, D. A., Stoliarov, D. A., Itrin, P. A., Odnoblyudov, M. A., Petrov, A. B., Gumenyuk, R. V.
Number of pages: 6
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Optics and laser technology
Volume: 133
Article number: 106526
ISSN (Print): 0030-3992
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Fiber lasers, Harmonic mode-locking, High-repetition pulse trains
Source: Scopus
Source ID: 85089483506

Research output: Contribution to journalArticleScientificpeer-review

Multiphoton microscopy of the dermoepidermal junction and automated identification of dysplastic tissues with deep learning

Histopathological image analysis performed by a trained expert is currently regarded as the gold-standard for the diagnostics of many pathologies, including cancers. However, such approaches are laborious, time consuming and contain a risk for bias or human error. There is thus a clear need for faster, less intrusive and more accurate diagnostic solutions, requiring also minimal human intervention. Multiphoton microscopy (MPM) can alleviate some of the drawbacks specific to traditional histopathology by exploiting various endogenous optical signals to provide virtual biopsies that reflect the architecture and composition of tissues, both in-vivo or ex-vivo. Here we show that MPM imaging of the dermoepidermal junction (DEJ) in unstained fixed tissues provides useful cues for a histopathologist to identify the onset of non-melanoma skin cancers. Furthermore, we show that MPM images collected on the DEJ, besides being easy to interpret by a trained specialist, can be automatically classified into healthy and dysplastic classes with high precision using a Deep Learning method and existing pre-trained convolutional neural networks. Our results suggest that deep learning enhanced MPM for in-vivo skin cancer screening could facilitate timely diagnosis and intervention, enabling thus more optimal therapeutic approaches.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Nonlinear Optics, University Politehnica of Bucharest, Carol Davila University of Medicine and Pharmacy
Contributors: Huttunen, M. J., Hristu, R., Dumitru, A., Floroiu, I., Costache, M., Stanciu, S. G.
Number of pages: 14
Pages: 186-199
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Biomedical Optics Express
Volume: 11
Issue number: 1
ISSN (Print): 2156-7085
Original language: English
ASJC Scopus subject areas: Biotechnology, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85078941474

Research output: Contribution to journalArticleScientificpeer-review

Neuromorphic Photonics with Coherent Linear Neurons Using Dual-IQ Modulation Cells

Neuromorphic photonics aims to transfer the high-bandwidth and low-energy credentials of optics into neuromorphic computing architectures. In this effort, photonic neurons are trying to combine the optical interconnect segments with optics that can realize all critical constituent neuromorphic functions, including the linear neuron stage and the activation function. However, aligning this new platform with well-established neural network training models in order to allow for the synergy of the photonic hardware with the best-in-class training algorithms, the following requirements should apply: i) the linear photonic neuron has to be able to handle both positive and negative weight values, ii) the activation function has to closely follow the widely used mathematical activation functions that have already shown an enormous performance in demonstrated neural networks so far. Herein, we demonstrate a coherent linear neuron architecture that relies on a dual-IQ modulation cell as its basic neuron element, introducing distinct optical elements for weight amplitude and weight sign representation and exploiting binary optical carrier phase-encoding for positive/negative number representation. We present experimental results of a typical IQ modulator performing as an elementary two-input linear neuron cell and successfully implementing all-optical linear algebraic operations with 104-ps long optical pulses. We also provide the theoretical proof and formulation of how to extend a dual-IQ modulation cell into a complete N-input coherent linear neuron stage that requires only a single-wavelength optical input and avoids the resource-consuming Wavelength Division Multiplexing (WDM) weighting schemes. An 8-input coherent linear neuron is then combined with an experimentally validated optical sigmoid activation function into a physical layer simulation environment, with respective training and physical layer simulation results for the MNIST dataset revealing an average accuracy of 97.24% and 94.37%, respectively.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Aristotle University of Thessaloniki
Contributors: Mourgias-Alexandris, G., Totovic, A., Tsakyridis, A., Passalis, N., Vyrsokinos, K., Tefas, A., Pleros, N.
Number of pages: 9
Pages: 811-819
Publication date: 2020
Peer-reviewed: Yes
Early online date: 2019

Publication information

Journal: Journal of Lightwave Technology
Volume: 38
Issue number: 4
ISSN (Print): 0733-8724
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: All-optical signal processing, neural networks, neuromorphic computing, neuromorphic photonics, optical neural network accelerators

Bibliographical note

EXT="Tefas, Anastasios"

Source: Scopus
Source ID: 85079482912

Research output: Contribution to journalArticleScientificpeer-review

Spectral invariance and scaling law for nonstationary optical fields

We develop a scaling law for a class of statistically nonstationary scalar optical fields, which ensures spectral invariance on their propagation into the far zone of a planar source. The invariance involves the constraint that the normalized far-zone spectrum must be the same in every direction of observation, as well as equal to the normalized area-averaged source spectrum. Thus, it additionally represents an extension of the earlier work by Wolf on stationary fields [Phys. Rev. Lett. 56, 1370 (1986)PRLTAO0031-900710.1103/PhysRevLett.56.1370] that assumed the normalized source spectrum as independent of position. We present examples of both nonstationary and stationary fields that satisfy the scaling law and extended spectral invariance.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Luoyang Normal University, University of Eastern Finland
Contributors: Ding, C., Koivurova, M., Setälä, T., Turunen, J., Friberg, A. T.
Number of pages: 7
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 101
Issue number: 3
Article number: 033808
ISSN (Print): 2469-9926
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85082680273

Research output: Contribution to journalArticleScientificpeer-review

Stabilization of passive harmonic mode locking in a fiber ring laser

We propose the model of a harmonically mode-locked soliton fiber ring laser based on the nonlinear polarization rotation taking into account the gain depletion and recovery effects. It is shown that a specific timing jitter could arise in such lasers, since the pulses in the cavity are not strongly identical. To suppress the jitter and stabilize the harmonic mode-locking operation, a method using a small frequency shift followed by the laser radiation filtering is described. The performed numerical simulation shows that the proposed method is able to provide extremely stable harmonic mode locking in a soliton fiber ring laser.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Ulyanovsk State University
Contributors: Gumenyuk, R. V., Korobko, D. A., Zolotovskii, I. O.
Number of pages: 4
Pages: 184-187
Publication date: 23 Dec 2019
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 45
Issue number: 1
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2019): CiteScore 7.2 SJR 1.788 SNIP 1.613
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85077516756

Research output: Contribution to journalArticleScientificpeer-review

Environmental monitoring with distributed mesh networks: An overview and practical implementation perspective for urban scenario

Almost inevitable climate change and increasing pollution levels around the world are the most significant drivers for the environmental monitoring evolution. Recent activities in the field of wireless sensor networks have made tremendous progress concerning conventional centralized sensor networks known for decades. However, most systems developed today still face challenges while estimating the trade-off between their flexibility and security. In this work, we provide an overview of the environmental monitoring strategies and applications. We conclude that wireless sensor networks of tomorrow would mostly have a distributed nature. Furthermore, we present the results of the developed secure distributed monitoring framework from both hardware and software perspectives. The developed mechanisms provide an ability for sensors to communicate in both infrastructure and mesh modes. The system allows each sensor node to act as a relay, which increases the system failure resistance and improves the scalability. Moreover, we employ an authentication mechanism to ensure the transparent migration of the nodes between different network segments while maintaining a high level of system security. Finally, we report on the real-life deployment results.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Research group: Emerging Technologies for Nano-Bio-Info-Cogno, St. Petersburg State University of Aerospace Instrumentation, ITMO University, Brno University of Technology, National Research University Higher School of Economics
Contributors: Ometov, A., Bezzateev, S., Voloshina, N., Masek, P., Komarov, M.
Number of pages: 19
Publication date: 2 Dec 2019
Peer-reviewed: Yes

Publication information

Journal: Sensors (Switzerland)
Volume: 19
Issue number: 24
Article number: 5548
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2019): CiteScore 5 SJR 0.653 SNIP 1.586
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Biochemistry, Atomic and Molecular Physics, and Optics, Instrumentation, Electrical and Electronic Engineering
Keywords: Authentication mechanism, Distributed systems, Environmental monitoring, Security, Wireless sensor network
Electronic versions: 

Bibliographical note

EXT="Komarov, Mikhail"

Source: Scopus
Source ID: 85076920114

Research output: Contribution to journalArticleScientificpeer-review

Eco-friendly flexible wireless platforms by 3D printing pen

We present a new type of 3D printing pen fabrication of flexible passive UHF (ultra-high frequency) RFID (radio frequency identification) platforms. The used 3D printing material is cost-effective and fully biodegradable. The tag antenna is fabricated from conductive thread. This antenna and antenna-IC interconnections are fixed inside the 3D-printed platforms with 3D-printed fasteners. Thus, our solution requires no additional process steps or chemicals. For wireless evaluation, the platforms are firstly bended around different size cylinders, with and without a 3D-printed top layer. Further, the reliability of the platforms in high moisture is also tested, by keeping the platforms in water for 1 minute. Based on these preliminary tests, our manufacturing method enables establishment of highly reliable eco-friendly platforms with excellent wireless performance. The developed solutions have versatile future applications, especially in the field of wearable electronics, where lightweight, cost-effective, flexible, and waterproof platforms are needed.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech
Contributors: Mehmood, A., Chen, X., He, H., Ukkonen, L., Virkki, J.
Number of pages: 4
Pages: 2422-2425
Publication date: 1 Dec 2019

Host publication information

Title of host publication: 2019 Photonics and Electromagnetics Research Symposium - Fall, PIERS - Fall 2019 - Proceedings
Publisher: IEEE
Article number: 9021887
ISBN (Electronic): 9781728153049

Publication series

Name: 2019 Photonics and Electromagnetics Research Symposium - Fall, PIERS - Fall 2019 - Proceedings
ASJC Scopus subject areas: Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Mathematical Physics

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Embroidered and e-textile conductors embedded inside 3D-printed structures

This paper discusses the fabrication and wireless performance evaluation of textile-integrated passive ultra-high frequency (UHF) radiofrequency identification (RFID) tags, which are embedded inside flexible additively manufactured wireless platforms. Two different methods are utilized to fabricate the tag antenna, including embroidery with conductive thread and conductive e-textiles. After antenna fabrication, RFID ICs (integrated circuits) are attached to the antenna patterns, to achieve fully functional RFID tags. These two types of tags are embedded inside flexible 3D-printed platforms, which can protect the tags from mechanical stresses and moisture. Our preliminary results show that the peak read ranges of both types of platforms are higher than 6 meters, which are suitable for versatile wireless applications.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech
Contributors: Khan, Z., He, H., Chen, X., Ukkonen, L., Virkki, J.
Number of pages: 6
Pages: 1675-1680
Publication date: 1 Dec 2019

Host publication information

Title of host publication: 2019 Photonics and Electromagnetics Research Symposium - Fall, PIERS - Fall 2019 - Proceedings
Publisher: IEEE
Article number: 9021681
ISBN (Electronic): 9781728153049
ASJC Scopus subject areas: Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Mathematical Physics

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Maintenance-free moisture sensor on dishcloth substrate

In this study, a passive UHF RFID-based moisture sensor is fabricated and evaluated. The sensor tag can sense the high humidity of the environment and indicate it with a permanent change in its backscattered signal. The sensor tag antenna and antenna-IC interconnections are fabricated on a biodegradable dishcloth material using conductive thread. The sensors are tested in an anechoic chamber and in normal office conditions, when initially dry, after dipped into water for 1 minute, and again after 24 hours of drying in air. These sensor tags initially show read ranges of 6-9 meters throughout the global UHF RFID frequency band. When wet, the read range decreases to 5 meters, while after 24 hours of drying, the read ranges of the tags permanently decrease to around 2-4 meters. The dishcloth material comes thicker when wet, also causing a change to the embroidered antenna structure, finally causing the permanent change in the backscattered signal. In normal office conditions, moisture causes the average backscattered signal an obvious change from around -66 dBm to -69 dBm.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech, City University of Hong Kong
Contributors: Chen, X., He, H., Yang, Y., Gou, M., Sydanheimo, L., Ukkonen, L., Virkki, J.
Number of pages: 4
Pages: 2418-2421
Publication date: 1 Dec 2019

Host publication information

Title of host publication: 2019 Photonics and Electromagnetics Research Symposium - Fall, PIERS - Fall 2019 - Proceedings
Publisher: IEEE
Article number: 9021487
ISBN (Electronic): 9781728153049
ASJC Scopus subject areas: Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Mathematical Physics

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Passive UHF RFID-based user interface on a wooden surface

We present a passive ultra-high frequency (UHF) radio frequency identification (RFID)-based human-technology interface platform. The platform comprises of two dipole antennas and three integrated circuits (IC), each with a unique ID. The platform, which is fixed on a wooden table by cutting the antennas and antenna-IC interconnections from copper tape, can be used for push button and swipe controlling. Each IC can be activated, i.e., connected to the antennas, by touching with finger. As the RFID reader can be connected to any application through WIFI, these ICs can act as wireless input points integrated into furniture, items, and textiles, where they can be used as inputs to desired digital actions. The platform allows all connected devices to be controlled accurately and effortlessly, which will take the convenience of implementation and utilization of these systems to a new level. As a preliminary trial, the platform was tested by two people giving 200 random inputs and 98% and 99% success rates were achieved. Based on these results, this type of passive RFID-based solutions could be used for administrating interfaces that would administer wide variety of interaction modalities, such as touch or tangible interaction on flat surfaces (e.g., tabletop surfaces, walls, doors).

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech, Computing Sciences, Tampere University
Contributors: Mehmood, A., Vianto, V., He, H., Chen, X., Buruk, O. O., Ukkonen, L., Virkki, J.
Number of pages: 4
Pages: 1760-1763
Publication date: 1 Dec 2019

Host publication information

Title of host publication: 2019 Photonics and Electromagnetics Research Symposium - Fall, PIERS - Fall 2019 - Proceedings
Publisher: IEEE
Article number: 9021441
ISBN (Electronic): 9781728153049
ASJC Scopus subject areas: Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Mathematical Physics

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Resolution and contrast in terahertz pulse time-domain holographic reconstruction

Here, we present a comprehensive study of the reconstruction quality in terahertz (THz) pulse time-domain holography. We look into single wavelength reconstructions, as well as broadband recovery enabled by the ultrabroadband nature of radiation and coherent detection enabled by electro-optic or photoconductive sensing. We demonstrate the transverse resolution dependence for amplitude and phase objects on the solid angle of the inline recorded time-domain THz hologram, and then turn to the contrast of reconstructed binary amplitude objects, and further to longitudinal resolution of phase objects. We show that transverse resolution can reach values comparable to the wavelength of the radiation used, and longitudinally, phase objects can be resolved with even greater precision. We compare the obtained resolution with theoretical estimates and show that THz pulse time-domain holography is a powerful non-contact imaging tool.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, ITMO University, University of Birmingham
Contributors: Turov, A. T., Kulya, M. S., Petrov, N. V., Gorodetsky, A.
Pages: G231-G240
Publication date: 1 Dec 2019
Peer-reviewed: Yes

Publication information

Journal: Applied Optics
Volume: 58
Issue number: 34
ISSN (Print): 1559-128X
Ratings: 
  • Scopus rating (2019): CiteScore 3.8 SJR 0.762 SNIP 1.166
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Electrical and Electronic Engineering
Source: Scopus
Source ID: 85075600417

Research output: Contribution to journalArticleScientificpeer-review

Terahertz pulse time-domain holography with balance detection: Complex-domain sparse imaging

We investigated the peculiarities of the terahertz pulse time-domain holography principle in the case of raster scanning with the balance detection system. The noise in this system represents a Skellam distribution model, which differentiates it from systems based on a photoconductive antenna. We analyzed this Skellam model and provided both numerical and experimental investigations. We found that the variance of the noise in the balance detection system does not depend on the true signal. Complex-domain images obtained in this model are filtered by block-matching algorithms adapted for spatio-temporal and spatiospectral volumetric data. We presented a new cube complex-domain filter algorithm that uses block matching in all 3D data sets simultaneously in spatial and frequency coordinates. A combination of temporal and complex-domain filters allows us to expand the dynamic range of terahertz frequencies for which we can obtain amplitude/phase information. Experimental data demonstrate an improvement in the quality of the resultant images both in the time domain and complex-spectral domain. The simulation and experimental results are in good agreement.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Computational Imaging-CI, ITMO University
Contributors: Kulya, M., Petrov, N. V., Katkovnik, V., Egiazarian, K.
Pages: G61-G70
Publication date: 1 Dec 2019
Peer-reviewed: Yes

Publication information

Journal: Applied Optics
Volume: 58
Issue number: 34
ISSN (Print): 1559-128X
Ratings: 
  • Scopus rating (2019): CiteScore 3.8 SJR 0.762 SNIP 1.166
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Electrical and Electronic Engineering
Source: Scopus
Source ID: 85075613421

Research output: Contribution to journalArticleScientificpeer-review

Spectral object recognition in hyperspectral holography with complex-domain denoising

In this paper, we have applied a recently developed complex-domain hyperspectral denoiser for the object recognition task, which is performed by the correlation analysis of investigated objects’ spectra with the fingerprint spectra from the same object. Extensive experiments carried out on noisy data from digital hyperspectral holography demonstrate a significant enhancement of the recognition accuracy of signals masked by noise, when the advanced noise suppression is applied.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Computational Imaging-CI, ITMO University, University of Ulm Medical Center, University of Stuttgart
Contributors: Shevkunov, I., Katkovnik, V., Claus, D., Pedrini, G., Petrov, N. V., Egiazarian, K.
Number of pages: 10
Publication date: 26 Nov 2019
Peer-reviewed: Yes

Publication information

Journal: Sensors (Switzerland)
Volume: 19
Issue number: 23
Article number: 5188
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2019): CiteScore 5 SJR 0.653 SNIP 1.586
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Biochemistry, Atomic and Molecular Physics, and Optics, Instrumentation, Electrical and Electronic Engineering
Keywords: Hyperspectral imaging, Noise filtering, Noise in imaging systems, Singular value decomposition, Sparse representation
Electronic versions: 
Source: Scopus
Source ID: 85075511855

Research output: Contribution to journalArticleScientificpeer-review

Path-integral description of quantum nonlinear optics in arbitrary media

We present a method, based on Feynman path integrals, to describe the propagation and properties of the quantized electromagnetic field in an arbitrary, nonlinear medium. We provide a general theory, valid for any order of optical nonlinearity, and we then specialize the case of second-order nonlinear processes. In particular, we show that second-order nonlinear processes in arbitrary media, under the undepleted pump approximation, can be described by an effective free electromagnetic field, propagating in a vacuum, dressed by the medium itself. Moreover, we show that the probability of such processes to occur is related to the biphoton propagator, which contains information about the structure of the medium, its nonlinear properties, and the structure of the pump beam.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, El Oued University, Universität Rostock, Universität Rostock, Albert
Contributors: Difallah, M., Szameit, A., Ornigotti, M.
Publication date: 20 Nov 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 100
Issue number: 5
Article number: 053845
ISSN (Print): 2469-9926
Ratings: 
  • Scopus rating (2019): SJR 1.416 SNIP 0.939
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85075715771

Research output: Contribution to journalArticleScientificpeer-review

Statistical evaluation of barkhausen noise testing (BNT) for ground samples

Barkhausen noise testing (BNT) is a nondestructive method for investigating many properties of ferromagnetic materials. The most common application is the monitoring of grinding burns caused by introducing locally high temperatures while grinding. Other features, such as microstructure, residual stress changes, hardening depth, and so forth, can be monitored as well. Nevertheless, because BNT is a method based on a complex magnetoelectric phenomenon, it is not yet standardized. Therefore, there is a need to study the traceability and stability of the measurement method. This study aimed to carry out a statistical analysis of ferromagnetic samples after grinding processes by the use of BNT. The first part of the experiment was to grind samples in different facilities (Sweden and Finland) with similar grinding parameters, different grinding wheels, and different hardness values. The second part was to evaluate measured BNT parameters to determine significant factors affecting BNT signal value. The measurement data from the samples were divided into two different batches according to where they were manufactured. Both grinding batches contained measurement data from three different participants. The main feature for calculation was the root-mean-square (RMS) value. The first processing step was to normalize the RMS values for all the measurements. A standard analysis of variance (ANOVA) was applied for the normalized dataset. The ANOVA showed that the grinding parameters had a significant impact on the BNT signal value, while the other investigated factors (e.g., participant) were negligible. The reasons for this are discussed at the end of the paper.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Univ of Oulu, Schlumpf Scandinavia AB, Kungliga Tekniska Högskolan KTH
Contributors: Tomkowski, R., Sorsa, A., Santa-Aho, S., Lundin, P., Vippola, M.
Publication date: 1 Nov 2019
Peer-reviewed: Yes

Publication information

Journal: Sensors (Switzerland)
Volume: 19
Issue number: 21
Article number: 4716
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2019): CiteScore 5 SJR 0.653 SNIP 1.586
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Biochemistry, Atomic and Molecular Physics, and Optics, Instrumentation, Electrical and Electronic Engineering
Keywords: ANOVA, Barkhausen noise testing (BNT), Proficiency test, Uncertainty
Electronic versions: 
Source: Scopus
Source ID: 85074321480

Research output: Contribution to journalArticleScientificpeer-review

Near-perfect measuring of full-field transverse-spatial modes of light

Along with the growing interest in using the transverse-spatial modes of light in quantum and classical optics applications, developing an accurate and efficient measurement method has gained importance. Here, we present a technique relying on a unitary mode conversion for measuring any full-field transverse-spatial mode. Our method only requires three consecutive phase modulations followed by a single mode fiber and is, in principle, error-free and lossless. We experimentally test the technique using a single spatial light modulator and achieve an average error of 4.2 % for a set of 9 different full-field Laguerre-Gauss and Hermite-Gauss modes with an efficiency of up to 70%. Moreover, as the method can also be used to measure any complex superposition state, we demonstrate its potential for quantum cryptography applications and in high-dimensional quantum state tomography.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Tampere University, Tampere University
Contributors: Hiekkamäki, M., Prabhakar, S., Fickler, R.
Number of pages: 9
Pages: 31456-31464
Publication date: 28 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 27
Issue number: 22
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2019): CiteScore 6.7 SJR 1.533 SNIP 1.651
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

INT=PHYS,"Hiekkamäki, Markus"
INT=PHYS,"Prabhakar, Shashi"

Source: Scopus
Source ID: 85074434779

Research output: Contribution to journalArticleScientificpeer-review

High Power 1.5um Pulsed Laser Diode with Asymmetric Waveguide and Active Layer Near p-cladding

We report first experimental results on a high-power pulsed semiconductor laser operating in the eye-safe spectral range (wavelength around 1.5 lm) with an asymmetric waveguide structure. The laser has a bulk active layer positioned very close to the p-cladding in order to eliminate current-induced nonuniform carrier accumulation in the p-side of the waveguide and the associated carrier losses. Moderate doping of the n-side of the waveguide is used to strongly suppress nonuniform carrier accumulation within this part of the waveguide. Highly p-doped InP p-cladding facilitates low series resistance. An as-cleaved sample with a stripe width of 90 lm exhibits an output power of about 18 W at a pumping current amplitude of 80 A. Theoretical calculations, validated by comparison to experiment, suggest that the performance of lasers of this type can be improved further by optimization of the waveguide thickness and doping as well as improvement of injection efficiency.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, University of Oulu, Ioffe Physico-Technical Institute, University of York
Contributors: Hallman, L. W., Ryvkin, B. S., Avrutin, E. A., Aho, A. T., Viheriälä, J., Guina, M., Kostamovaara, J. T.
Pages: 1635-1638
Publication date: 15 Oct 2019
Peer-reviewed: Yes
Early online date: 10 Sep 2019

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 31
Issue number: 20
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2019): CiteScore 5.5 SJR 0.945 SNIP 1.212
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Radiation, Electrical and Electronic Engineering

Research output: Contribution to journalArticleScientificpeer-review

Double-asymmetric-structure 1.5 μ m high power laser diodes

Design considerations for high pulsed power and brightness 1.5 μm laser emitters for laser radar applications, based on comprehensive semi-analytical theory, are presented. A strongly asymmetric waveguide design with a bulk active layer positioned very near the p-emitter interface is chosen to minimize the current-induced losses at high power while maintaining a single, broad transverse mode. Moderate to high doping of the n-side of the Optical Confinement Layer and high p-doping of the p-cladding layer are used to reduce the residual current-induced losses and the electric resistance of the structure. For pulsed room-temperature operation, short laser resonators are found to be advantageous. First experimental results are presented. An as-cleaved sample with a stripe width of90 μm and a resonator2 mm long exhibits an output power of about 18 W at a pumping current amplitude of 80 A, with 1 mm long resonators showing higher power output. Further improvements are predicted by structure optimization as well as increase in internal quantum efficiency and thermal performance.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, University of Oulu, Ioffe Physico-Technical Institute, University of York
Contributors: Hallman, L., Ryvkin, B. S., Avrutin, E. A., Aho, A. T., Viheriälä, J., Guina, M., Kostamovaara, J. T.
Number of pages: 2
Pages: 19-20
Publication date: 1 Oct 2019

Host publication information

Title of host publication: Proceedings of the 2019 IEEE High Power Diode Lasers and Systems Conference, HPD 2019 - Co-located with Photonex 2019
Publisher: IEEE
ISBN (Electronic): 9781728130972
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: efficiency, high power lasers, laser diodes, modelling

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Realization of Free-Space Long-Distance Self-Healing Bessel Beams

A new approach for generating long-distance self-healing Bessel beams, which is based on a ring-shaped (annular) lens and a spherical lens in 4f-configuration, is reported. With this, diffraction-free light evolution of a zeroth order Bessel beam over several meters is shown and available scaling opportunities that surpass current technologies by far are discussed. Furthermore, it is demonstrated how this setup can be adapted to create Bessel beam superpositions, realizing the longest ever reported optical conveyor beam and helicon beam, respectively. Last, the self-healing capabilities of the beams are tested against strong opaque and non-opaque scatterers, which again emphasizes the great potential of this new method.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Friedrich-Schiller-University Jena, UMR 6174, Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Vacom GmbH, Institute of Applied Physics, Institut für Physik, Universität Rostock, Albert
Contributors: Vetter, C., Steinkopf, R., Bergner, K., Ornigotti, M., Nolte, S., Gross, H., Szameit, A.
Publication date: 1 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Laser and Photonics Reviews
Volume: 13
Issue number: 10
Article number: 1900103
ISSN (Print): 1863-8880
Ratings: 
  • Scopus rating (2019): CiteScore 16.9 SJR 4.014 SNIP 2.903
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics
Keywords: beam-shaping, Bessel-beams, laser-technology, self-healing, telecommunication
Source: Scopus
Source ID: 85073597306

Research output: Contribution to journalArticleScientificpeer-review

Observation of PT-symmetric quantum interference

A common wisdom in quantum mechanics is that the Hamiltonian has to be Hermitian in order to ensure a real eigenvalue spectrum. Yet, parity–time (PT)-symmetric Hamiltonians are sufficient for real eigenvalues and therefore constitute a complex extension of quantum mechanics beyond the constraints of Hermiticity. However, as only single-particle or classical wave physics has been exploited so far, an experimental demonstration of the true quantum nature of PT symmetry has been elusive. In our work, we demonstrate two-particle quantum interference in a PT-symmetric system. We employ integrated photonic waveguides to reveal that the quantum dynamics of indistinguishable photons shows strongly counterintuitive features. To substantiate our experimental data, we analytically solve the quantum master equation using Lie algebra methods. The ideas and results presented here pave the way for non-local PT-symmetric quantum mechanics as a novel building block for future quantum devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Universität Rostock, Albert
Contributors: Klauck, F., Teuber, L., Ornigotti, M., Heinrich, M., Scheel, S., Szameit, A.
Publication date: 16 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Nature Photonics
ISSN (Print): 1749-4885
Ratings: 
  • Scopus rating (2019): CiteScore 58.3 SJR 13.614 SNIP 7.931
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85073826086

Research output: Contribution to journalArticleScientificpeer-review

Short-range supercontinuum-based lidar for temperature profiling

We developed a short-range light detection and ranging system using a supercontinuum (SC) source spectrally tailored to cover the ro-vibrational transition energies of desired components of a flue gas. The system enables remote measurements of the gas parameters, including temperature and concentration which play a key role in the performance of combustion power plants. The technique requires only one inspection window and, thus, can be used in combustion units with limited access. It exploits differential absorption between specific wavelength bands of the gas absorption spectrum. The transmittance of an individual wavelength band is derived from the detected backscattered temporal intensity of the SC pulses. We demonstrate water vapor temperature measurement in the range of 400°C–900°C in a laboratory furnace with the use of only two wavelength bands. Using more than two wavelength bands, the technique can be further extended to simultaneously measure temperature and concentration. By varying the direction of the incident beam in a non-parallel plane, a full 3D profile is also obtainable.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Valmet Automation Oy
Contributors: Saleh, A., Aalto, A., Ryczkowski, P., Genty, G., Toivonen, J.
Number of pages: 4
Pages: 4223-4226
Publication date: 1 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 44
Issue number: 17
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2019): CiteScore 7.2 SJR 1.788 SNIP 1.613
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85071398770

Research output: Contribution to journalArticleScientificpeer-review

High power GaInNAs superluminescent diodes emitting over 400 mW in the 1.2 μm wavelength range

A high-power superluminescent diode emitting over 400 mW in the 1.2 μm range is reported. The active region is based on a single GaInNAs/GaAs quantum well positioned within a low-confinement vertical waveguide and a lateral ridge waveguide geometry, ensuring single transverse mode operation. The peak wall-plug efficiency and the differential efficiency in the linear region were 22.8% and 0.38 W/A, respectively. The full width at half-maximum spectral width for the maximum output power was 22 nm, corresponding to a spectral power density of 19 mW/nm, a threefold increase compared to continuous wave superluminescent diodes based on a quantum dot active region operating in the same wavelength range. Besides exhibiting excellent optical and electrical properties, the GaInNAs active region enhances operation at elevated temperatures. In this respect, an output power of about 210 mW is demonstrated at operation temperatures as high as 60 °C, while 150 mW is still emitted at 70 °C. The unique combination of parameters demonstrated makes these GaInNAs QW-based superluminescent diodes particularly attractive for hybrid integration with silicon photonic circuitry, enabling the demonstration of compact solutions for sensing, optical coherence tomography, and other emerging concepts exploiting photonic integration technology and requiring single transversal mode operation, good efficiency, broadband high spectral power density, and uncooled operation at elevated temperatures.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC
Contributors: Aho, A., Viheriälä, J., Virtanen, H., Zia, N., Isoaho, R., Guina, M.
Number of pages: 4
Publication date: 22 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Applied Physics Letters
Volume: 115
Issue number: 8
Article number: 081104
ISSN (Print): 0003-6951
Ratings: 
  • Scopus rating (2019): CiteScore 7 SJR 1.343 SNIP 1.252
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Radiation
Keywords: Superluminescent diodes, High power, OCT

Research output: Contribution to journalArticleScientificpeer-review

AlGaAs/AlGaInP VECSELs with Direct Emission at 740-770 nm

An optically-pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) with 3.25-W output power emitting around 750 nm is demonstrated. The gain structure incorporates AlGaAs quantum wells (QWs) and barriers, and AlGaInP claddings. The emission wavelength could be tuned from 740 to 770 nm. The development addresses the need for high brightness lasers at a wavelength range that has proven difficult to reach. The demonstrated structure exhibits polarization-related peculiarities, which cause polarization switching under increased pump power due to mode competition. The presence of birefringence inside the active region is attributed to known long-range ordering within the AlGaInP claddings which causes distorted beam profiles. This influence on laser features has not been reported in VECSELs so far.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics
Contributors: Nechay, K., Kahle, H., Penttinen, J., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Number of pages: 4
Pages: 1245-1248
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 31
Issue number: 15
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2019): CiteScore 5.5 SJR 0.945 SNIP 1.212
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: AlGaAs, AlGaInP, quantum well lasers, semiconductor disk lasers, semiconductor growth, semiconductor laser, vertical-external-cavity surface-emitting lasers (VECSELs)

Bibliographical note

INT=phys,"Rajala, Patrik"

Source: Scopus
Source ID: 85069529749

Research output: Contribution to journalArticleScientificpeer-review

Bayesian inversion of a forest reflectance model using Sentinel-2 and Landsat 8 satellite images

The inversion of reflectance models is a generalizable tool to obtain estimates on forest biophysical parameters, such as leaf area index, with theoretically little information need from a study area, instead relying on the knowledge about physical processes in the forest radiation regime. The use of prior information can greatly improve the reflectance model inversion, however, the literature does not yet provide much information on the selection of priors and their influence on the inversion results. In this study, we used a Bayesian approach to invert the PARAS forest reflectance model and retrieve leaf area index from Sentinel-2 MSI and Landsat 8 OLI multispectral satellite images. The PARAS model is based on the theory of spectral invariants, which describes the influence of wavelength-independent parameters on forest radiative transfer. The Bayesian inversion approach is highly flexible, provides uncertainty quantification, and enables the explicit incorporation of prior knowledge into the inversion process. We found that the choice of prior information is crucial in inverting a forest reflectance model to predict leaf area index. Regularizing and informative priors for leaf area index strongly improved the predictions, relative to an uninformative prior, in that they counteracted the saturation effect of the optical signal occuring at high values for leaf area index. The predictions of leaf area index were more accurate for Landsat 8 than for Sentinel-2, due to potential inconsistencies in the visible bands of Sentinel-2 in our data, and the higher spectral resolution.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Aalto University, University of Eastern Finland
Contributors: Schraik, D., Varvia, P., Korhonen, L., Rautiainen, M.
Number of pages: 12
Pages: 1-12
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: JOURNAL OF QUANTITATIVE SPECTROSCOPY AND RADIATIVE TRANSFER
Volume: 233
ISSN (Print): 0022-4073
Ratings: 
  • Scopus rating (2019): CiteScore 5.2 SJR 0.888 SNIP 1.335
Original language: English
ASJC Scopus subject areas: Radiation, Atomic and Molecular Physics, and Optics, Spectroscopy
Keywords: Bayesian inversion, Clumping, Forest reflectance, Landsat 8, Leaf area index, PARAS, Recollision probability, Sentinel-2, Spectral invariants
Electronic versions: 
Source: Scopus
Source ID: 85065605532

Research output: Contribution to journalArticleScientificpeer-review

Influence of pump coherence on the generation of position-momentum entanglement in optical parametric down-conversion

We examine experimentally how the degree of position-momentum entanglement of photon pairs depends on the transverse coherence of the pump beam that excites them in a process of spontaneous parametric down-conversion. Using spatially incoherent light from a light-emitting diode, we obtain strong position correlation of the photons, but we find that transverse momentum correlation, and thus entanglement, is entirely absent. When we continuously vary the degree of spatial coherence on the pump beam, we observe the emergence of stronger momentum correlations and entanglement. We present theoretical arguments that explain our experimental results. Our results shed light on entanglement generation and can be applied to control entanglement for quantum information applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Xiamen University, University of Ottawa, Canada, University of Ulm Medical Center, University of Rochester Institute of Optics
Contributors: Zhang, W., Fickler, R., Giese, E., Chen, L., Boyd, R. W.
Number of pages: 9
Pages: 20745-20753
Publication date: 22 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 27
Issue number: 15
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2019): CiteScore 6.7 SJR 1.533 SNIP 1.651
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85069963559

Research output: Contribution to journalArticleScientificpeer-review

Temporal ghost imaging using wavelength conversion and two-color detection

Ghost imaging constructs an image by correlating two signals: one that interacts with an object but possesses no spatial information, and the other that contains spatial information but does not interact with the object. Ghost imaging can be extended into the time domain by using laser intensity fluctuations to reconstruct an unknown time-varying pattern, but this requires the measurement of laser fluctuations on ultrafast timescales, a significant limitation at wavelengths where ultrafast detectors are not available.We overcome this by using wavelength conversion to shift the probe laser into a spectral region where ultrafast detectors are available, and we apply this technique to image a temporal object at 2 μm. Our results demonstrate that temporal correlation information can be transferred to an arbitrary spectral region, opening possibilities for ultrafast ghost imaging at new wavelengths.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Electronic Science and Technology of China, UMR 6174, Ita-Suomen yliopisto
Contributors: Wu, H., Ryczkowski, P., Friberg, A. T., Dudley, J. M., Genty, G.
Number of pages: 5
Pages: 902-906
Publication date: 20 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 6
Issue number: 7
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2019): CiteScore 18.1 SJR 5.6 SNIP 3.375
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Wu, Han"

Source: Scopus
Source ID: 85071154886

Research output: Contribution to journalArticleScientificpeer-review

Methods for simultaneous robot-world-hand–eye calibration: A comparative study

In this paper, we propose two novel methods for robot-world-hand-eye calibration and provide a comparative analysis against six state-of-the-art methods. We examine the calibration problem from two alternative geometrical interpretations, called 'hand-eye' and 'robot-world-hand-eye', respectively. The study analyses the effects of specifying the objective function as pose error or reprojection error minimization problem. We provide three real and three simulated datasets with rendered images as part of the study. In addition, we propose a robotic arm error modeling approach to be used along with the simulated datasets for generating a realistic response. The tests on simulated data are performed in both ideal cases and with pseudo-realistic robotic arm pose and visual noise. Our methods show significant improvement and robustness on many metrics in various scenarios compared to state-of-the-art methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Remote Handling Project Team
Contributors: Ali, I., Suominen, O., Gotchev, A., Morales, E. R.
Publication date: 2 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Sensors (Switzerland)
Volume: 19
Issue number: 12
Article number: 2837
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2019): CiteScore 5 SJR 0.653 SNIP 1.586
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: Hand-eye calibration, Optimization, Robot-world-hand-eye calibration
Electronic versions: 
Source: Scopus
Source ID: 85068904338

Research output: Contribution to journalArticleScientificpeer-review

Bioimpedance Sensor Array for Long-Term Monitoring of Wound Healing from Beneath the Primary Dressings and Controlled Formation of H2O2 Using Low-Intensity Direct Current

Chronic wounds impose a significant financial burden for the healthcare system. Currently, assessment and monitoring of hard-to-heal wounds are often based on visual means and measuring the size of the wound. The primary wound dressings must be removed before assessment can be done. We have developed a quasi-monopolar bioimpedance-measurement-based method and a measurement system to determine the status of wound healing. The objective of this study was to demonstrate that with an appropriate setup, long-term monitoring of wound healing from beneath the primary dressings is feasible. The developed multielectrode sensor array was applied on the wound area and left under the primary dressings for 142 h. The impedance of the wounds and the surrounding intact skin area was measured regularly during the study at 150 Hz, 300 Hz, 1 kHz, and 5 kHz frequencies. At the end of the follow-up period, the wound impedance had reached the impedance of the intact skin at the higher frequencies and increased significantly at the lowest frequencies. The measurement frequency affected the measurement sensitivity in wound monitoring. The skin impedance remained stable over the measurement period. The sensor array also enabled the administration of periodical low-intensity direct current (LIDC) stimulation in order to create an antimicrobial environment across the wound area via the controlled formation of hydrogen peroxide (H2O2).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Turku University Hospital, Kaarinantie 700, Åbo Akademi University
Contributors: Kekonen, A., Bergelin, M., Johansson, M., Kumar Joon, N., Bobacka, J., Viik, J.
Publication date: 31 May 2019
Peer-reviewed: Yes

Publication information

Journal: Sensors
Volume: 19
Issue number: 11
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2019): CiteScore 5 SJR 0.653 SNIP 1.586
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: beneath the dressings, bioimpedance, hydrogen peroxide, long-term monitoring, low-intensity direct current, multielectrode, quasi-monopolar, sensor array, wound dressing, wound monitoring, wound stimulation
Electronic versions: 
Source: Scopus
Source ID: 85067176313

Research output: Contribution to journalArticleScientificpeer-review

Double-side pumped membrane external-cavity surface-emitting laser (MECSEL) with increased efficiency emitting > 3 W in the 780 nm region

We demonstrate a double-side pumped MECSEL emitting more than 3 W of output power in the 780 nm wavelength region. The laser exhibits an efficiency as high as 34.4 %.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics
Contributors: Kahle, H., Phung, H., Penttinen, J., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Rajala, Patrik"

Source: Scopus
Source ID: 85069191246

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Frequency Comb Generation in a Continuous-Wave Pumped Second-Order Nonlinear Waveguide Resonator

Optical frequency comb generation has been experimentally studied using an integrated system based on a lithium niobate waveguide resonator featuring a strong quadratic nonlinearity. Our theoretical model shows good agreement with the experimental results.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Paderborn University, University of Helsinki, VTT Technical Research Centre of Finland
Contributors: Abdallah, Z., Stefszky, M., Ulvila, V., Silberhorn, C., Vainio, M.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85069196416

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

GaInAsSb/AlGa(In)AsSb type I quantum wells emitting in 3 μm range for application in superluminescent diodes

In this paper, we present results of Fourier-transformed photoluminescence measurements of quaternary GaInAsSb quantum wells with quinary AlGaInAsSb barriers grown on GaSb substrate, designed for spectral range of mid-infrared. Here, we show an emission shift towards longer wavelength as a result of incorporation of indium into the quantum wells reaching up to 3 μm at room temperature (RT). Additionally, we have observed an additional low-energy photoluminescence signal with maximum wavelength of 3.5 μm at RT, which we have attributed as states localised on the layer interfaces. The activation energy of carriers trapped in those states is estimated to be 35 meV.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: ORC, Physics, Wrocław University of Technology
Contributors: Kurka, M., Dyksik, M., Suomalainen, S., Koivusalo, E., Guina, M., Motyka, M.
Number of pages: 5
Pages: 274-278
Publication date: 1 May 2019
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 91
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2019): CiteScore 4.4 SJR 0.594 SNIP 1.068
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Fourier-transformed spectroscopy, MBE, Optical gas sensing, Photoluminescence, Superluminescent diodes
Source: Scopus
Source ID: 85063381328

Research output: Contribution to journalArticleScientificpeer-review

High-Q resonance train in a plasmonic metasurface

We experimentally demonstrate a plasmonic surface that supports a series of high-quality-factor (Q ≈ 100) surface lattice resonances. These resonances are enabled by tuning the thickness of the top-cladding layer to confine higher order diffraction-orders.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, University of Ottawa, Canada, Iridian Spectral Technologies, University of Rochester Institute of Optics
Contributors: Saad-Bin-Alam, M., Reshef, O., Huttunen, M. J., Carlow, G., Sullivan, B., Menard, J. M., Dolgaleva, K., Boyd, R. W.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85069156893

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Optical Frequency Comb Photoacoustic Spectroscopy

We combine for the first time a mid-infrared optical frequency comb Fourier transform spectrometer with cantilever-enhanced photoacoustic detection and measure high-resolution broadband spectra of the fundamental band of methane in a few milliliter sample volume.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Energy Technology and Thermal Process Chemistry, University of Helsinki
Contributors: Sadiek, I., Mikkonen, T., Vainio, M., Toivonen, J., Foltynowicz, A.
Publication date: 1 May 2019

Host publication information

Title of host publication: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781943580576
ASJC Scopus subject areas: Spectroscopy, Industrial and Manufacturing Engineering, Safety, Risk, Reliability and Quality, Management, Monitoring, Policy and Law, Electronic, Optical and Magnetic Materials, Radiology Nuclear Medicine and imaging, Instrumentation, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85069190764

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Alpha radiation-induced luminescence by am-241 in aqueous nitric acid solution

When exposed to air, alpha particles cause the production of light by exciting the molecules surrounding them. This light, the radioluminescence, is indicative of the presence of alpha radiation, thus allowing for the optical sensing of alpha radiation from distances larger than the few centimeters an alpha particle can travel in air. While the mechanics of radioluminescence in air and other gas compositions is relatively well understood, the same cannot be said about the radioluminescence properties of liquids. Better understanding of the radioluminescence properties of liquids is essential to design methods for the detection of radioactively contaminated liquids by optical means. In this article, we provide radioluminescence images of Am-241 dissolved in aqueous nitric acid (HNO 3 ) solution and present the recorded radioluminescence spectrum with a maximum between and, and a steep decrease at the short wavelength side of the maximum. The shape of the spectrum resembles a luminescence process rather than Cerenkov light, bremsstrahlung, or other mechanisms with broadband emission. We show that the amount of light produced is about 150 times smaller compared to that of the same amount of Am-241 in air. The light production in the liquid is evenly distributed throughout the sample volume with a slight increase on the surface of the liquid. The radioluminescence intensity is shown to scale linearly with the Am-241 concentration and not be affected by the HNO 3 concentration.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Helsinki, European Commission Joint Research Centre
Contributors: Kerst, T., Malmbeck, R., lal Banik, N. L., Toivonen, J.
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Sensors (Switzerland)
Volume: 19
Issue number: 7
Article number: 1602
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2019): CiteScore 5 SJR 0.653 SNIP 1.586
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: Alpha radiation, Americium, Liquid phase luminescence, Radioluminescence
Electronic versions: 
Source: Scopus
Source ID: 85064822061

Research output: Contribution to journalArticleScientificpeer-review

Positioning information privacy in intelligent transportation systems: An overview and future perspective

Today, the Intelligent Transportation Systems (ITS) are already in deep integration phase all over the world. One of the most significant enablers for ITS are vehicle positioning and tracking techniques. Worldwide integration of ITS employing Dedicated Short Range Communications (DSRC) and European standard for vehicular communication, known as ETSI ITS-G5, brings a variety of options to improve the positioning in areas where GPS connectivity is lacking precision. Utilization of the ready infrastructure, next-generation cellular 5G networks, and surrounding electronic devices together with conventional positioning techniques could become the solution to improve the overall ITS operation in vehicle-to-everything (V2X) communication scenario. Nonetheless, effective and secure communication protocols between the vehicle and roadside units should be both analyzed and improved in terms of potential attacks on the transmitted positioning-related data. In particular, said information might be misused or stolen at the infrastructure side conventionally assumed to be trusted. In this paper, we first survey different methods of vehicle positioning, which is followed by an overview of potential attacks on ITS systems. Next, we propose potential improvements allowing mutual authentication between the vehicle and infrastructure aiming at improving positioning data privacy. Finally, we propose a vision on the development and standardization aspects of such systems.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, St. Petersburg State University of Aerospace Instrumentation, ITMO University, Brno University of Technology
Contributors: Ometov, A., Bezzateev, S., Davydov, V., Shchesniak, A., Masek, P., Lohan, E. S., Koucheryavy, Y.
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Sensors
Volume: 19
Issue number: 7
Article number: 1603
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2019): CiteScore 5 SJR 0.653 SNIP 1.586
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: Authentication, Data privacy, GDPR, Intelligent transportation systems, Positioning
Electronic versions: 
Source: Scopus
Source ID: 85064829981

Research output: Contribution to journalArticleScientificpeer-review

Noise measurements from reconstructed digital breast tomosynthesis

In this work, we investigated and measured the noise in Digital Breast Tomosynthesis (DBT) slices considering the back-projection (BP) algorithm for image reconstruction. First, we presented our open-source DBT reconstruction toolbox and validated with a freely available virtual clinical trials (VCT) software, comparing our results with the reconstruction toolbox available at the Food and Drug Administration's (FDA) repository. A virtual anthropomorphic breast phantom was generated in the VCT environment and noise-free DBT projections were simulated. Slices were reconstructed by both toolboxes and objective metrics were measured to evaluate the performance of our in-house reconstruction software. For the noise analysis, commercial DBT systems from two vendors were used to obtain x-ray projections of a uniform polymethyl methacrylate (PMMA) physical phantom. One system featured an indirect thallium activated cesium iodide (CsI(TI)) scintillator detector and the other a direct amorphous selenium (a-Se) detector. Our in-house software was used to reconstruct raw projections into tomographic slices, and the mean pixel value, noise variance, signal-to-noise ratio (SNR) and the normalized noise power spectrum (NNPS) were measured. In addition, we investigated the adequacy of a heteroskedastic Gaussian model, with an affine variance function, to describe the noise in the reconstruction domain. The measurements show that the variance and SNR from reconstructed slices report similar spatial and signal dependency from previously reported in the projection domain. NNPS showed that the reconstruction process correlates the noise of the DBT slices in the case of projections degraded with almost uncorrelated noise.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences, University of São Paulo, Pio XII Foundation, University of Pennsylvania
Contributors: Vimieiro, R. B., Borges, L. R., Caron, R. F., Barufaldi, B., Bakic, P. R., Maidment, A. D., Vieira, M. A.
Publication date: 1 Mar 2019

Host publication information

Title of host publication: Medical Imaging 2019 : Physics of Medical Imaging
Publisher: SPIE, IEEE
Editors: Schmidt, T. G., Chen, G., Bosmans, H.
Article number: 109480C
ISBN (Electronic): 9781510625433

Publication series

Name: Progress in Biomedical Optics and Imaging - Proceedings of SPIE
Volume: 10948
ISSN (Print): 1605-7422
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Atomic and Molecular Physics, and Optics, Radiology Nuclear Medicine and imaging
Keywords: Back-projection, Digital breast tomosynthesis, Image reconstruction, Noise measurements, Virtual clinical trials
Source: Scopus
Source ID: 85068400087

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Layered approach for improving the quality of free-viewpoint depth-image-based rendering images

In free-viewpoint rendering systems, one of the most challenging goals is the creation of virtual views based on available color texture (RGB) and depth data. Conventional depth-image-based rendering (DIBR) approaches have assumed that the virtual camera can only be displaced horizontally, thus leading to fairly simple disocclusion artifacts. However, in free-viewpoint DIBR, the virtual camera can be positioned in an arbitrary way and the respective disocclusion artifacts can exhibit complicated anisotropic appearances. Consequently, conventional approaches for compensating disocclusion holes usually fail in such arbitrary camera motion. We present a disocclusion compensation technique based on texture inpainting. We propose a layered representation of both the color and depth images in local foreground, background, and undefined segments (a trimap). This representation allows for employing an efficient alpha-matting approach for reconstructing the underlying opacity layer followed by a background compensation and layered rendering. The performance of the proposed method is evaluated with respect to the state-of-the-art through objective and subjective tests. The achieved results, especially for large camera displacements, outperform the state-of-the-art. Those results assess the effectiveness of the proposed method and highlight the need for new quality metrics able to address the impairments of this type of content.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: 3D MEDIA, University “Roma Tre”
Contributors: Smirnov, S., Battisti, F., Gotchev, A.
Publication date: 27 Feb 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Electronic Imaging
Volume: 28
Issue number: 1
Article number: 013049
ISSN (Print): 1017-9909
Ratings: 
  • Scopus rating (2019): CiteScore 2 SJR 0.264 SNIP 0.566
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Computer Science Applications, Electrical and Electronic Engineering
Keywords: depth-image-based rendering, inpainting, multiview, quality, RGB+D

Bibliographical note

EXT="Battisti, Federica"

Source: Scopus
Source ID: 85062623919

Research output: Contribution to journalArticleScientificpeer-review

Experimental realization of wave-packet dynamics in cyclic quantum walks

Quantum walks present novel tools for redesigning quantum algorithms, universal quantum computations, and quantum simulators. Hitherto, one- and two-dimensional quantum systems (lattices) have been simulated and studied with photonic systems. Here, we report the photonic simulation of cyclic quantum systems, such as hexagonal structures. We experimentally explore the wavefunction dynamics and probability distribution of a quantum particle located on a six-site system, along with three- and four-site systems while under different initial conditions. Various quantum walk systems employing Hadamard, C-NOT, and Pauli-Z gates are experimentally simulated, where we find configurations capable of simulating particle transport and probability density localization. Our technique can potentially be integrated into small-scale structures using microfabrication, and thus would open a venue towards simulating more complicated quantum systems comprised of cyclic structures.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: University of Ottawa, Canada, Austrian Academy of Sciences
Contributors: Nejadsattari, F., Zhang, Y., Bouchard, F., Larocque, H., Sit, A., Cohen, E., Fickler, R., Karimi, E.
Number of pages: 7
Pages: 174-180
Publication date: 20 Feb 2019
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 6
Issue number: 2
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2019): CiteScore 18.1 SJR 5.6 SNIP 3.375
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85063372591

Research output: Contribution to journalArticleScientificpeer-review

Supercontinuum generation: Introduction

The article collection in this feature issue presents the most recent experimental and numerical studies of supercontinuum generation in bulk nonlinear media, photonic crystal fibers, and waveguides. It also introduces new results of design and fabrication of these structures with engineered dispersion, development of new diagnostic tools, as well as applications of spectral broadening and supercontinuum generation for pulse compression, imaging, and sensing.

General information

Publication status: Published
MoE publication type: B1 Article in a scientific magazine
Organisations: Physics, Research group: Ultrafast Optics, Vilnius University, Université Paris-Saclay
Contributors: Dubietis, A., Couairon, A., Genty, G.
Pages: SG1-SG3
Publication date: 1 Feb 2019
Peer-reviewed: No

Publication information

Journal: Journal of the Optical Society of America B: Optical Physics
Volume: 36
Issue number: 2
ISSN (Print): 0740-3224
Ratings: 
  • Scopus rating (2019): CiteScore 3.9 SJR 0.851 SNIP 0.964
Original language: English
ASJC Scopus subject areas: Statistical and Nonlinear Physics, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85060854199

Research output: Contribution to journalEditorialScientific

Additional lossless compression of JPEG images based on BPG

The task of additional lossless compression of JPEG images is considered. We propose to decode JPEG image and recompress it using lossy BPG (Better Portable Graphics) codec based on a subset of the HEVC open video compression standard. Then the decompressed and smoothed BPG image is used for calculation and quantization of DCT coefficients in 8x8 image blocks using quantization tables of the source JPEG image. A difference between obtained quantized DCT coefficients and quantized DCT coefficients of the source JPEG image (prediction error) is calculated. The difference is lossless compressed by a proposed context modeling and arithmetical coding. In this way the source JPEG image is replaced by two files: compressed BPG image and the compressed difference which needed for lossless restoration of the source JPEG image. It is shown that the proposed approach provides compression ratios comparable with state of the art PAQ8, WinZip and STUFFIT file archivers. At the same time BPG images may be used for fast preview of compressed JPEG images.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences, Kharkiv National Aerospace University
Contributors: Ponomarenko, M., Miroshnichenko, O., Lukin, V., Egiazarian, K.
Publication date: 13 Jan 2019

Host publication information

Title of host publication: Image Processing: Algorithms and Systems XVII

Publication series

Name: IS and T International Symposium on Electronic Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Context modelling, Discrete cosine transform, JPEG, JPEG additional compression
Source: Scopus
Source ID: 85080092000

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Combined no-reference IQA metric and its performance analysis

The problem of increasing efficiency of blind image quality assessment is considered. No-reference image quality metrics both independently and as components of complex image processing systems are employed in various application areas where images are the main carriers of information. Meanwhile, existing no-reference metrics have a significant drawback characterized by a low adequacy to image perception by human visual system (HVS). Many well-known no-reference metrics are analyzed in our paper for several image databases. A method of combining several no-reference metrics based on artificial neural networks is proposed based on multi-database verification approach. The effectiveness of the proposed approach is confirmed by extensive experiments.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences, Kharkiv National Aerospace University
Contributors: Ieremeiev, O., Lukin, V., Ponomarenko, N., Egiazarian, K.
Publication date: 13 Jan 2019

Host publication information

Title of host publication: Image Processing: Algorithms and Systems XVII

Publication series

Name: IS and T International Symposium on Electronic Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Combined metrics, Full-reference metrics, Image visual quality assessment, Robust metrics
Source: Scopus
Source ID: 85080028392

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Phase masks optimization for broadband diffractive imaging

The task of optimization of phase masks for broadband diffractive imaging to minimize chromatic aberrations and to provide given value of Depth of Focus (DoF) is considered. Different schemes of multilevel phase mask (MPM) forming by combining pixels of two Fresnel lenses are analyzed. The Fresnel lenses are calculated for the same focal distance but for very different wavelengths. A possibility of adding to the optimized mask a cubic component is taking into account as well as usage of discrete phase masks with optimized number of levels. It is shown that the proposed approach in the combination with inverse imaging allows to significantly increase image quality for a focus distance in comparison to refractive lens-based optical systems. Moreover, it is shown that by changing of aforementioned parameters it is possible to increase or decrease DoF value depending from a given goal of optimization. It is demonstrated by numerical analysis that the proposed approach significantly increases robustness of designed MPM to Gaussian additive noise in MPM introduced due to fabrication errors.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences, Research group: Computational Imaging-CI
Contributors: Ponomarenko, M., Katkovnik, V., Egiazarian, K.
Publication date: 13 Jan 2019

Host publication information

Title of host publication: Image Processing: Algorithms and Systems XVII

Publication series

Name: IS and T International Symposium on Electronic Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Diffractive optical elements, Inverse imaging, Lensless imaging, Multilevel phase mask design
Source: Scopus
Source ID: 85080039777

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Thin form-factor super multiview head-up display system

We propose a virtual-image head-up display (HUD) based on the super multiview (SMV) display technology. Implementation-wise, the HUD provides a compact solution, consisting of a thin form-factor SMV display and a combiner placed on the windshield of the vehicle. Since the utilized display is at most few centimeters thick, it does not need extra installation space that is usually required by most of the existing virtual image HUDs. We analyze the capabilities of the proposed system in terms of several HUD related quality factors such as resolution, eyebox width, and target image depth. Subsequently, we verify the analysis results through experiments carried out using our SMV-HUD demonstrator. We show that the proposed system is capable of visualizing images at the typical virtual image HUD depths of 2 − 3m, in a reasonably large eyebox, which is slightly over 30cm in our demonstrator. For an image at the target virtual image depth of 2.5m, the field of view of the developed system is 11x16 and the spatial resolution is around 240x60 pixels in vertical and horizontal directions, respectively. There is, however, plenty of room for improvement regarding the resolution, as we actually utilize an LCD at moderate resolution (216 ppi) and off-the-shelf lenticular sheet in our demonstrator.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Computing Sciences
Contributors: Akpinar, U., Sahin, E., Suominen, O., Gotchev, A.
Publication date: 13 Jan 2019

Host publication information

Title of host publication: Stereoscopic Displays and Applications XXX

Publication series

Name:  IS&T International Symposium on Electronic Imaging
ISSN (Electronic): 2470-1173
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics

Bibliographical note

jufoid=84313

Source: Scopus
Source ID: 85081086336

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Phosphate glasses with blue persistent luminescence prepared using the direct doping method

Phosphate glasses with the composition (90NaPO3-(10-x)Na2O-xNaF) (mol%) with x = 0 and 10 were prepared with blue persistent luminescence (PeL) using direct particles doping method. Commercial CaAl2O4:Eu2+,Nd3+ microparticles (MPs) with blue PeL were added in the glass melt at a lower temperature than the melting temperature. The PeL properties of the glasses were related to the diffusion of Al from the MPs to the glass occurring during the glass preparation, which was found to depend on the temperature at which the MPs are added in the melt and also on the time before casting the melt after adding the MPs. The glass with x = 0 can be prepared with homogeneous PeL if the MPs are added at 575 °C. This Tdoping temperature can be reduced to 550 °C by replacing Na2O by NaF in the glass.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Turun Yliopisto/Turun Biomateriaalikeskus
Contributors: Ojha, N., Tuomisto, M., Lastusaari, M., Petit, L.
Pages: 151-156
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Optical Materials
Volume: 87
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2019): CiteScore 4.4 SJR 0.594 SNIP 1.068
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: CaAlO:Eu,Nd microparticles, Corrosion, Fluorophosphate glass, Persistent luminescence
Source: Scopus
Source ID: 85044951460

Research output: Contribution to journalArticleScientificpeer-review

Comparison of single-side and double-side pumping of membrane external-cavity surface-emitting lasers

We studied and compared single-side pumping (SSP) and double-side pumping (DSP) of a semiconductor membrane external-cavity surface-emitting laser (MECSEL). The MECSEL-active region was based on an AlGaAs quantum well structure embedded between two silicon carbide (SiC) wafer pieces that were used as transparent intra-cavity (IC) heat spreaders creating a symmetrical cooling environment. The gain structure targeted emission at 780 nm, a wavelength region that is important for many applications, and where the development of high-brightness high-power laser sources is gaining more momentum. By DSP at 20°C heat sink temperature, we could reduce the laser threshold from 0.79 to 0.69 W of absorbed pump power, while the maximum output power was increased from 3.13 to 3.22 W. The differential efficiency was improved from 31.9% to 34.4%, which represents a record value for SiC-cooled vertically emitting semiconductor lasers. The improvements are enabled by a reduced thermal resistance of the gain element by 9% compared to SSP. The beam quality was measured to be M 2 < 1.09. Finally, we demonstrate a maximum tuning range from 767 to 811 nm. This wavelength range was not addressed by any MECSEL or vertical external-cavity surface-emitting laser device before and extends the available wavelengths for semiconductor based high-quality beam and high-power laser sources to a wavelength window relevant for quantum technology, spectroscopy, or medicine.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, Department of Chemistry and Bioengineering
Contributors: Kahle, H., Penttinen, J. P., Phung, H. M., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Number of pages: 4
Pages: 1146-1149
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 44
Issue number: 5
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2019): CiteScore 7.2 SJR 1.788 SNIP 1.613
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Rajala, Patrik"

Source: Scopus
Source ID: 85062214909

Research output: Contribution to journalArticleScientificpeer-review

Efficient nonlinear metasurfaces by using multiresonant high-Q plasmonic arrays

We numerically investigate second-harmonic generation from multiresonant plasmonic metasurfaces by designing an array consisting of L-shaped aluminum nanoparticles that simultaneously supports two surface lattice resonances with relatively high quality factors (>100). Using an approach based on the nonlinear discrete-dipole approximation, we predict an over million-fold enhancement of the emitted second-harmonic intensity from a particle at the center of the metasurface compared to an individual particle and estimate that conversion efficiencies of around 10-5 could be achievable from the surface. Our results are an important step towards making nonlinear metasurfaces practical for nonlinear applications, such as for frequency conversion.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Ottawa, Canada, Tampere University, University of Rochester Institute of Optics
Contributors: Huttunen, M. J., Reshef, O., Stolt, T., Dolgaleva, K., Boyd, R. W., Kauranen, M.
Pages: E30-E35
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America B: Optical Physics
Volume: 36
Issue number: 7
ISSN (Print): 0740-3224
Ratings: 
  • Scopus rating (2019): CiteScore 3.9 SJR 0.851 SNIP 0.964
Original language: English
ASJC Scopus subject areas: Statistical and Nonlinear Physics, Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Stolt, Timo"

Source: Scopus
Source ID: 85069551856

Research output: Contribution to journalArticleScientificpeer-review

Flip-chip Wafer-fused OP-VECSELs emitting 3.65 W at the 1.55-&#x03BC;m waveband

Optically-pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55-&#x03BC;m wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors fixed on a diamond heat-sink substrate in a flip-chip geometry, incorporated in a V-cavity configuration. A maximum output power of 3.65 W was achieved for a heat sink temperature of 11&#x00B0;C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. This demonstration represents more than 5-fold increase of the output power compared to state-of-the-art flip-chip VECSELs previously reported at the 1.55 &#x03BC;m wavelength range. It opens new perspectives for developing practical VECSEL-based laser systems operating at a wavelength range widely used in many applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, CRPP, LakeDiamond SA
Contributors: Mereuta, A., Nechay, K., Caliman, A., Suruceanu, G., Rudra, A., Gallo, P., Guina, M., Kapon, E.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Journal of Selected Topics in Quantum Electronics
Volume: 25
Issue number: 6
ISSN (Print): 0792-1233
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Atomic and Molecular Physics, and Optics, Materials Chemistry, Electrical and Electronic Engineering
Keywords: diode pumped, Flip-chip devices, Heating systems, Lasers, Mirrors, Optical pumping, Power generation, Semiconductor lasers, Temperature measurement, Vertical cavity surface emitting lasers, Vertical emitting lasers
Source: Scopus
Source ID: 85067801249

Research output: Contribution to journalArticleScientificpeer-review

Hyperspectral data denoising for terahertz pulse time-domain holography

We investigated data denoising in hyperspectral terahertz pulse time-domain holography. Using the block-matching algorithms adapted for spatio-temporal and spatio-spectral volumetric data we studied and optimized parameters of these algorithms to improve phase image reconstruction quality. We propose a sequential application of the two algorithms oriented on work in temporal and spectral domains. Experimental data demonstrate the improvement in the quality of the resultant time-domain images as well as phase images and object’s relief. The simulation results are proved by comparison with the experimental ones.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Digital and Display Holography Laboratory, ITMO University
Contributors: Kulya, M., Petrov, N. V., Tsypkin, A., Egiazarian, K., Katkovnik, V.
Number of pages: 21
Pages: 18456-18476
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 27
Issue number: 13
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2019): CiteScore 6.7 SJR 1.533 SNIP 1.651
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85068035148

Research output: Contribution to journalArticleScientificpeer-review

Interferometric autocorrelation measurements of supercontinuum based on two-photon absorption

We report on interferometric autocorrelation measurements of broadband supercontinuum light in the anomalous dispersion regime using two-photon absorption in a GaP photodetector. The method is simple and low-cost and provides a direct measure of second-order coherence properties, including quantitative information on coherence time and average duration of the supercontinuum pulses as well as on the presence of temporally coherent sub-structures. We report measurements in regimes where the supercontinuum is coherent and incoherent. In the former case, the interferometric measurements are similar to what is observed for mode-locked laser pulses, while in the latter case, the interferometric measurements and coherence properties are shown to have characteristics similar to those of a stationary chaotic light source.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, UMR 6174
Contributors: Toenger, S., Mäkitalo, R., Ahvenjärvi, J., Ryczkowski, P., Närhi, M., Dudley, J. M., Genty, G.
Number of pages: 7
Pages: 1320-1326
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America B: Optical Physics
Volume: 36
Issue number: 5
ISSN (Print): 0740-3224
Ratings: 
  • Scopus rating (2019): CiteScore 3.9 SJR 0.851 SNIP 0.964
Original language: English
ASJC Scopus subject areas: Statistical and Nonlinear Physics, Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Mäkitalo, Roosa"
INT=phys,"Ahvenjärvi, Jani"

Source: Scopus
Source ID: 85069553087

Research output: Contribution to journalArticleScientificpeer-review

Large-scale efficient water harvesting using bioinspired micro-patterned copper oxide nanoneedle surfaces and guided droplet transport

As the Earth's atmosphere contains an abundant amount of water as vapors, a device which can capture a fraction of this water could be a cost-effective and practical way of solving the water crisis. There are many biological surfaces found in nature which display unique wettability due to the presence of hierarchical micro-nanostructures and play a major role in water deposition. Inspired by these biological microstructures, we present a large scale, facile and cost-effective method to fabricate water-harvesting functional surfaces consisting of high-density copper oxide nanoneedles. A controlled chemical oxidation approach on copper surfaces was employed to fabricate nanoneedles with controlled morphology, assisted by bisulfate ion adsorption on the surface. The fabricated surfaces with nanoneedles displayed high wettability and excellent fog harvesting capability. Furthermore, when the fabricated nanoneedles were subjected to hydrophobic coating, these were able to rapidly generate and shed coalesced droplets leading to further increase in fog harvesting efficiency. Overall, ∼99% and ∼150% increase in fog harvesting efficiency was achieved with non-coated and hydrophobic layer coated copper oxide nanoneedle surfaces respectively when compared to the control surfaces. As the transport of the harvested water is very important in any fog collection system, hydrophilic channels inspired by leaf veins were made on the surfaces via a milling technique which allowed an effective and sustainable way to transport the captured water and further enhanced the water collection efficiency by ∼9%. The system presented in this study can provide valuable insights towards the design and fabrication of fog harvesting systems, adaptable to arid or semi-arid environmental conditions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Research group: Surface Science, Physics, Research group: Bioinspired Materials and Robotics (BMR)
Contributors: Sharma, V., Yiannacou, K., Karjalainen, M., Lahtonen, K., Valden, M., Sariola, V.
Number of pages: 16
Pages: 4025-4040
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Nanoscale Advances
Volume: 1
Issue number: 10
ISSN (Print): 2516-0230
Ratings: 
  • Scopus rating (2019): CiteScore 1
Original language: English
ASJC Scopus subject areas: Engineering(all), Bioengineering, Atomic and Molecular Physics, and Optics, Materials Science(all), Chemistry(all)
Source: Scopus
Source ID: 85073635162

Research output: Contribution to journalArticleScientificpeer-review

Measuring stem diameters with TLS in boreal forests by complementary fitting procedure

Point clouds generated by terrestrial laser scanners (TLS) have enabled new ways to measure stem diameters. A common method for diameter calculation is to fit cylindrical or circular shapes into the TLS point cloud, which can be based either on a single scan or a co-registered combination of several scans. However, as various defects in the point cloud may affect the final diameter results, we propose an automatized processing chain which takes advantage of complementing steps. Processing consists of two fitting phases and an additional taper curve calculation to define the final diameter measurements. First, stems are detected from co-registered data of several scans using surface normals and cylinder fitting. This provides a robust framework for localizing the stems and estimating diameters at various heights. Then, guided by the cylinders and their indicative diameters, another fitting round is performed by cutting the stems into thin horizontal slices and reassessing their diameters by circular shape. For each slice, the quality of the cylinder-modelled diameter is evaluated first with co-registered data and if it is found to be deficient, potentially due to modelling defects or co-registration errors, diameter is detected through single scans. Finally, slice diameters are applied to construct a spline-based taper curve model for each tree, which is used to calculate the final stem dimensions. This methodology was tested in southern Finland using a set of 505 trees. At the breast height level (1.3 m), the results indicate 5.2 mm mean difference (3.2%), −0.4 mm bias (-0.3%) and 7.3 mm root mean squared error (4.4%) to reference measurements, and at the height of 6.0 m, respective values are 6.5 mm (3.6%), +1.6 mm (0.9%) and 8.4 mm (4.8%). These values are smaller compared to most of the corresponding contemporary studies, and outperform the initial cylinder models. This indicates that the applied processing chain is capable of producing relatively accurate diameter measurements, which can, at the cost of computational heaviness, remove various defects and improve the modelling results.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mathematics, Natural Resources Institute Finland (Luke)
Contributors: Pitkänen, T. P., Raumonen, P., Kangas, A.
Number of pages: 13
Pages: 294-306
Publication date: 2019
Peer-reviewed: Yes
Early online date: 8 Dec 2018

Publication information

Journal: ISPRS Journal of Photogrammetry and Remote Sensing
Volume: 147
ISSN (Print): 0924-2716
Ratings: 
  • Scopus rating (2019): CiteScore 11.7 SJR 3.122 SNIP 2.881
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Computer Science Applications, Computers in Earth Sciences
Keywords: Circle fitting, Cylinder fitting, Stem extraction, Taper curve, Terrestrial laser scanning
Electronic versions: 
Source: Scopus
Source ID: 85057752987

Research output: Contribution to journalArticleScientificpeer-review

Optical wireless cochlear implants

In the present contribution, we introduce a wireless optical communication-based system architecture which is shown to significantly improve the reliability and the spectral and power efficiency of the transcutaneous link in cochlear implants (CIs). We refer to the proposed system as optical wireless cochlear implant (OWCI). In order to provide a quantified understanding of its design parameters, we establish a theoretical framework that takes into account the channel particularities, the integration area of the internal unit, the transceivers misalignment, and the characteristics of the optical units. To this end, we derive explicit expressions for the corresponding average signal-to-noise-ratio, outage probability, ergodic spectral efficiency and capacity of the transcutaneous optical link (TOL). These expressions are subsequently used to assess the dependence of the TOL’s communication quality on the transceivers design parameters and the corresponding channels characteristics. The offered analytic results are corroborated with respective results from Monte Carlo simulations. Our findings reveal that OWCI is a particularly promising architecture that drastically increases the reliability and effectiveness of the CI TOL, whilst it requires considerably lower transmit power compared to the corresponding widely-used radio frequency (RF) solution.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Wireless Communications and Positioning, Electrical Engineering, Aristotle University of Thessaloniki, Khalifa University, University of Piraeus, Department of Electrical and Computer Engineering
Contributors: Trevlakis, S. E., Boulogeorgos, A. A. A., Sofotasios, P. C., Muhaidat, S., Karagiannidis, G. K.
Number of pages: 24
Pages: 707-730
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Biomedical Optics Express
Volume: 10
Issue number: 2
ISSN (Print): 2156-7085
Ratings: 
  • Scopus rating (2019): CiteScore 6.7 SJR 1.591 SNIP 1.796
Original language: English
ASJC Scopus subject areas: Biotechnology, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85061526751

Research output: Contribution to journalArticleScientificpeer-review

Random lasing control with optical spatial solitons in nematic liquid crystals

We discuss the synergy of reorientational self-focusing and random lasing in a dye- doped nematic liquid crystalline material. The laser emission resulting from amplification and multiple scattering inside the medium can be either modulated or triggered depending on the energy of the visible pump beam and the power of the near-infrared spatial soliton, respectively exciting the two nonlinear responses. Moreover, the presence of the self-induced waveguide improves the properties of the emitted beam, i. e., directionality and profile. Finally, the laser light can be re-directed by steering the spatial soliton with the aid of an external low-frequency electric field.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Research group: Nonlinear Optics, University “Roma Tre”, Case Western Reserve University, Univ Roma Tre, Roma Tre University, Dept Elect Engn, NooEL
Contributors: Piccardi, A., Perumbilavil, S., Kauranen, M., Strangi, G., Assanto, G.
Number of pages: 5
Pages: 289-293
Publication date: 2019

Host publication information

Title of host publication: PHOTOPTICS 2019 - Proceedings of the 7th International Conference on Photonics, Optics and Laser Technology
Publisher: SCITEPRESS
Editors: Ribeiro, P., Raposo, M., Andrews, D.
ISBN (Electronic): 9789897583643
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: Nematic Liquid Crystals, Optical Spatial Solitons, Random Laser

Bibliographical note

EXT="Assanto, Gaetano"

Source: Scopus
Source ID: 85064602881

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Spatiospectral features of a soliton-assisted random laser in liquid crystals

We report on novel features of random lasers assisted by near-infrared spatial solitons in nematic liquid crystals. Specifically, we study the role of light-induced reorientational waveguides (nematicons) on the spatial and spectral distributions of the laser modes. We show that the spatially spiky character of the laser emission propagating backwards with respect to the pump tends to disappear in the forward direction, due to the soliton confinement of the generated light. Moreover, the spectral features associated with various random laser resonances appear to merge upon guided-wave propagation along the nematicon, making the nematicon-aided random laser a bidirectional device with distinct emission properties at the two opposite outputs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Nonlinear Optics, University “Roma Tre”
Contributors: Perumbilavil, S., Kauranen, M., Assanto, G.
Number of pages: 4
Pages: 3574-3577
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 44
Issue number: 14
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2019): CiteScore 7.2 SJR 1.788 SNIP 1.613
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

EXT="Assanto, Gaetano"

Source: Scopus
Source ID: 85069547888

Research output: Contribution to journalArticleScientificpeer-review

Tuning plasmon induced reflectance with hybrid metasurfaces

Electrically tunable metasurfaces with graphene offer design flexibility to efficiently manipulate and control light. These metasurfaces can be used to generate plasmon-induced reflectance (PIR), which can be tuned by electrostatic doping of the graphene layer. We numerically investigated two designs for tunable PIR devices using the finite difference time-domain (FDTD) method. The first design is based on two rectangular antennas of the same size and a disk; in the second design, two parallel rectangular antennas with different dimensions are used. The PIR-effect was achieved by weak hybridization of two bright modes in both devices and tuned by changing the Fermi level of graphene. A total shift of 362 nm was observed in the design with the modulation depth of 53% and a spectral contrast ratio of 76%. These tunable PIR devices can be used for tunable enhanced biosensing and switchable systems.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Photonics Laboratory, Balochistan University of Information Technology, Bilkent University
Contributors: Habib, M., Ozbay, E., Caglayan, H.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Photonics
Volume: 6
Issue number: 1
Article number: 29
ISSN (Print): 2304-6732
Ratings: 
  • Scopus rating (2019): CiteScore 2.9 SJR 0.646 SNIP 1.182
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Instrumentation, Radiology Nuclear Medicine and imaging
Keywords: Plasmonics, Surface plasmon, Tunable metasurfaces
Electronic versions: 
Source: Scopus
Source ID: 85063129342

Research output: Contribution to journalArticleScientificpeer-review

Intense radioluminescence of NO/N2-mixture in solar blind spectral region

Luminescence in air induced by alpha particle emitters can be used to optically detect radioactive contamination from distances that surpass the range of the alpha radiation itself. Alpha particles excite nitrogen molecules in air and the relaxation creates a faint light emission. When the composition of the gases surrounding the alpha particle emitter is altered then the luminescence spectrum changes. In this work, we report the creation of an intense light emission in the wavelength regime below 300 nm originating from alpha particle excited nitric oxide (NO). The light yield has been investigated as a function of the NO concentration in an N2 atmosphere. Unlike the emission from molecular nitrogen, NO emits at wavelengths shorter than 300 nm, where solar background and artificial lighting are negligible, thus enabling optical detection of alpha radiation even under bright lighting conditions. We show that the radioactively induced NO emission reaches its maximum intensity at a concentration of 50 ppm of NO diluted in N2. At this concentration, the strongest emission line of NO is about 25 times more intense than the most intense line of N2 radioluminescence. Lastly, we discuss potential applications and limitations of the technique.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Helsinki
Contributors: Kerst, T., Toivonen, J.
Number of pages: 8
Pages: 33764-33771
Publication date: 24 Dec 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 26
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85059213995

Research output: Contribution to journalArticleScientificpeer-review

Towards optical-frequency-comb generation in continuous-wave-pumped titanium-indiffused lithium-niobate waveguide resonators

Much progress, both experimentally and theoretically, has recently been made towards optical-frequency-comb generation from continuously pumped second-order nonlinear systems. Here, we present observations towards finding an integrated solution for such a system, using a titanium-indiffused lithium-niobate waveguide resonator. These results are compared to the recently developed theory for equivalent systems. The system is seen to exhibit strong instabilities, which require further investigation in order to fully determine the suitability of this platform for stable optical-frequency-comb generation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Paderborn University, VTT Technical Research Centre of Finland, Laboratory of Photonics, Molecular Science
Contributors: Stefszky, M., Ulvila, V., Abdallah, Z., Silberhorn, C., Vainio, M.
Publication date: 27 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 98
Issue number: 5
Article number: 053850
ISSN (Print): 2469-9926
Ratings: 
  • Scopus rating (2018): CiteScore 2.84 SJR 1.268 SNIP 0.987
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85057526410

Research output: Contribution to journalArticleScientificpeer-review

Cascaded crystalline raman lasers for extended wavelength coverage: Continuous-wave, third-stokes operation

The development of high-power laser sources with narrow emission, tunable within the water transmission window around 1.7 μm, is of interest for applications as diverse as medical imaging and atmospheric sensing. Where suitable laser gain media are not available, operation in this spectral region is often achieved via nonlinear frequency conversion, and optical parametric oscillators (OPOs) are a common solution. A practical alternative to OPOs, to avoid birefringent-or quasi-phase-matching requirements, is the use of stimulated Raman scattering within a suitable material to convert a pump source to longer wavelengths via one or more Stokes shifts; however, as this is a χ3 nonlinear process, such frequency conversion is usually the preserve of high-energy pulsed lasers. Semiconductor disk lasers (SDLs), on the other hand, have very high-finesse external resonators, suitable for efficient intracavity nonlinear conversion even in continuous-wave (CW) operation. Here we report, to the best of our knowledge, the first continuous-wave third-Stokes crystalline Raman laser and the longest emission wavelength from an SDL-pumped Raman laser, achieving high power, CW output, and broad wavelength tuning around 1.73 μm. The KGd WO4 2 (KGW) Raman laser, which was intracavity-pumped by a 1.18 μm InGaAs-based SDL, demonstrated cascaded CW Stokes oscillation at 1.32 μm, 1.50 μm, and 1.73 μm with watt-level output achievable at each wavelength. The 1.73 μm Stokes emission was diffraction limited (M2 < 1.01) and narrow linewidth (<46 pm FWHM; measurement limited). By rotation of a birefringent filter placed within the fundamental resonator, we attained three tunable emission wavelength bands, one centred at each Stokes component, and achieved up to 65 nm tuning for the third-Stokes Raman laser from 1696 nm to 1761 nm. We have thus demonstrated a platform laser technology that takes well-developed InGaAs-based SDLs and provides spectral coverage and high performance in the near-infrared water transmission windows using commercially available components.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Strathclyde
Contributors: Casula, R., Penttinen, J., Guina, M., Kemp, A. J., Hastie, J. E.
Number of pages: 8
Pages: 1406-1413
Publication date: 20 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 5
Issue number: 11
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2018): CiteScore 15.6 SJR 4.914 SNIP 3.162
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85059018872

Research output: Contribution to journalArticleScientificpeer-review

M2M Communication Assessment in Energy-Harvesting and Wake-Up Radio Assisted Scenarios Using Practical Components

Techniques for wireless energy harvesting (WEH) are emerging as a fascinating set of solutions to extend the lifetime of energy-constrained wireless networks, and are commonly regarded as a key functional technique for almost perpetual communications. For example, with WEH technology, wireless devices are able to harvest energy from different light sources or Radio Frequency (RF) signals broadcast by ambient or dedicated wireless transmitters to support their operation and communications capabilities. WEH technology will have increasingly wider range of use in upcoming applications such as wireless sensor networks, Machine-to-Machine (M2M) communications, and the Internet of Things. In this paper, the usability and fundamental limits of joint RF and solar cell or photovoltaic harvesting based M2M communication systems are studied and presented. The derived theoretical bounds are in essence based on the Shannon capacity theorem, combined with selected propagation loss models, assumed additional link nonidealities, diversity processing, as well as the given energy harvesting and storage capabilities. Fundamental performance limits and available capacity of the communicating link are derived and analyzed, together with extensive numerical results evaluated in different practical scenarios, including realistic implementation losses and state-of-the-art printed supercapacitor performance figures with voltage doubler-based voltage regulator. In particular, low power sensor type communication applications using passive and semi-passive wake-up radio (WuR) are addressed in the study. The presented analysis principles and results establish clear feasibility regions and performance bounds for wireless energy harvesting based low rate M2M communications in the future IoT networks.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Nano Communication Centre, Department of Electrical and Computer Engineering, Ohio State University
Contributors: Rinne, J., Keskinen, J., Berger, P. R., Lupo, D., Valkama, M.
Publication date: 16 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Sensors (Basel, Switzerland)
Volume: 18
Issue number: 11
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2018): CiteScore 4.3 SJR 0.592 SNIP 1.642
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: diversity system, M2M communications, perpetual communications, propagation loss, Shannon limit, supercapacitor, wake-up radio, wireless energy harvesting
Electronic versions: 
Source: Scopus
Source ID: 85056711381

Research output: Contribution to journalArticleScientificpeer-review

Control of Rydberg-state population with realistic femtosecond laser pulses

We investigate computationally a method for ultrafast preparation of alkali-metal atoms in their Rydberg states using a three-dimensional model potential in the single active electron approximation. By optimizing laser pulse shapes that can be generated with modern waveform synthesizers, we propose pulses for controlling the population transfer from the ground state to a preselected set of Rydberg states. Dynamical processes under the optimized pulses are shown to be much more complicated than in the traditional optical two-photon preparation of Rydberg states.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics
Contributors: Solanpää, J., Räsänen, E.
Publication date: 15 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 98
Issue number: 5
Article number: 053422
ISSN (Print): 2469-9926
Ratings: 
  • Scopus rating (2018): CiteScore 2.84 SJR 1.268 SNIP 0.987
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85057035731

Research output: Contribution to journalArticleScientificpeer-review

Tunable Reflection Type Plasmon Induced Transparency with Graphene

Plasmon induced transparency (PIT) has always been investigated in transmission mode, which makes the design dependent upon the type of substrate. In this work, we propose a first tunable reflection type PIT (RPIT) device based on simple design of two parallel gold strips on graphene. We have numerically investigated the design by using Finite Difference Time-Domain (FDTD) method. This response is tunable by changing the Fermi level (Ef) of graphene. High tunability of 215 nm shift was observed by changing the Ef of graphene from 0 to 0.8 eV. The spectral contrast ratio of our device is 99.2%.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Department of Electrical and Electronics Engineering, Bilkent University, Nanotechnology Research Center
Contributors: Habib, M., Ozbay, E., Caglayan, H.
Number of pages: 3
Pages: 170-172
Publication date: 13 Nov 2018

Host publication information

Title of host publication: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018
Publisher: IEEE
ISBN (Electronic): 9781538647028
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Acoustics and Ultrasonics, Atomic and Molecular Physics, and Optics, Radiation

Bibliographical note

EXT="Habib, M."

Source: Scopus
Source ID: 85058538366

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Super-resolution microscopy for biological specimens: Lensless phase retrieval in noisy conditions

The paper is devoted to a computational super-resolution microscopy. A complex-valued wavefront of a transparent biological cellular specimen is restored from multiple intensity diffraction patterns registered with noise. For this problem, the recently developed lensless super-resolution phase retrieval algorithm [Optica, 4(7), 786 (2017)] is modified and tuned. This algorithm is based on a random phase coding of the wavefront and on a sparse complex-domain approximation of the specimen. It is demonstrated in experiments, that the reliable phase and amplitude imaging of the specimen is achieved for the low signal-to-noise ratio provided a low dynamic range of observations. The filterings in the observation domain and specimen variables are specific features of the applied algorithm. If these filterings are omitted the algorithm becomes a super-resolution version of the standard iterative phase retrieval algorithms. In comparison with this simplified algorithm with no filterings, our algorithm shows a valuable improvement in imaging with much smaller number of observations and shorter exposure time. In this way, presented algorithm demonstrates ability to work in a low radiation photon-limited mode.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI, ITMO University
Contributors: Shevkunov, I., Katkovnik, V., Petrov, N. V., Egiazarian, K.
Number of pages: 13
Pages: 5511-5523
Publication date: 1 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Biomedical Optics Express
Volume: 9
Issue number: 11
Article number: #340805
ISSN (Print): 2156-7085
Ratings: 
  • Scopus rating (2018): CiteScore 6.5 SJR 1.516 SNIP 1.604
Original language: English
ASJC Scopus subject areas: Biotechnology, Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85056609807

Research output: Contribution to journalArticleScientificpeer-review

Metal/Polymer Back Reflectors with Diffraction Gratings for Light Trapping in III-V Solar Cells

We report on the fabrication, characterization and simulation of diffraction gratings for back contact reflectors in III-V solar cells. The gratings are designed for thin-film solar cells incorporating absorbers with bandgap slightly lower than GaAs, such as InAs/GaAs quantum dot or GaInNAs solar cells. Metal/polymer back reflectors with a blazed grating or a pyramid grating were fabricated by nanoimprint lithography. The gratings are compared in terms of diffraction ability, which is the feature responsible for increasing the absorption. The pyramid grating showed higher diffraction of light compared to the blazed grating. The diffraction efficiency measurements were in agreement with the numerical simulations. The model validation enables tailoring the properties of the reflectors for other type of solar cells by adjusting the optimal dimensions of the gratings for different wavelengths.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Research group: ORC, Research group: Nanophotonics, Politecnico di Torino, Dispelix Oy, University of Eastern Finland
Contributors: Aho, T., Guina, M., Elsehrawy, F., Cappelluti, F., Raappana, M., Tukiainen, A., Khairul Alam, A. B. M., Vartiainen, I., Kuittinen, M., Niemi, T.
Number of pages: 5
Pages: 2847-2851
Publication date: Nov 2018

Host publication information

Title of host publication: 2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) : A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC
Publisher: IEEE
ISBN (Electronic): 978-1-5386-8529-7

Publication series

Name: CONFERENCE RECORD OF THE IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE
Publisher: IEEE
ISSN (Print): 0160-8371
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Step-modulated decay cavity ring-down detection for double resonance spectroscopy

A method of measuring double resonant two-photon signal and background from a single cavity ring-down decay is introduced. This is achieved by modulating the double resonance loss via one of the light sources exciting the transition. The noise performance of the method is characterized theoretically and experimentally. The addition of a new parameter to the fitting function introduces a minor noise increase due to parameter correlation. However, the concurrent recording of the background can extend the stable measurement time. Alternatively, the method allows a faster measurement speed, while still recording the background, which is often advantageous in double resonance measurements. Finally, the method is insensitive to changes in the cavity decay rate at short timescales and can lead to improved performance if they have significant contribution to the final noise level compared to the detector noise.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Helsinki, University of Virginia
Contributors: Karhu, J., Lehmann, K., Vainio, M., Metsälä, M., Halonen, L.
Number of pages: 13
Pages: 29086-29098
Publication date: 29 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 22
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85055774623

Research output: Contribution to journalArticleScientificpeer-review

Demonstration of optical nonlinearity in InGaAsP/InP passive waveguides

We report on the study of the third-order nonlinear optical interactions in InxGa1-xAsyP1-y/InP strip-loaded waveguides. The material composition and waveguide structures were optimized for enhanced nonlinear optical interactions. We performed self-phase modulation, four-wave mixing and nonlinear absorption measurements at the pump wavelength 1568 nm in our waveguides. The nonlinear phase shift of up to 2.5π has been observed in self-phase modulation experiments. The measured value of the two-photon absorption coefficient α2 was 19 cm/GW. The four-wave mixing conversion range, representing the wavelength difference between maximally separated signal and idler spectral components, was observed to be 45 nm. Our results indicate that InGaAsP has a high potential as a material platform for nonlinear photonic devices, provided that the operation wavelength range outside the two-photon absorption window is selected.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Ottawa, Canada, Middle East Technical Univ.
Contributors: Saeidi, S., Rasekh, P., Awan, K. M., Tüğen, A., Huttunen, M. J., Dolgaleva, K.
Number of pages: 7
Pages: 524-530
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 84
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2018): CiteScore 3.9 SJR 0.59 SNIP 1.025
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Integrated optics, Nonlinear optics, Optical devices
Source: Scopus
Source ID: 85050358317

Research output: Contribution to journalArticleScientificpeer-review

Focus model for metric depth estimation in standard plenoptic cameras

In recent years, a lot of efforts have been devoted to the problem of depth estimation from lightfield images captured by standard plenoptic cameras. However, most of the metric depth estimation methods in the state-of-the-art leverage pixel disparity only. In this paper, we tackle the problem of focus-based metric depth estimation in standard plenoptic cameras. For this purpose we propose a closed-form model that relates the refocusing parameter with the focus distance of a plenoptic camera in order to allow for metric depth estimation. Based on the proposed model, we develop a calibration procedure that allows finding the parameters of the model. Using measurements of a time-of-flight sensor as ground-truth, experimental validation in a distance range of 0.2–1.6 m shows that focus-based depth estimation is feasible with a root-mean-squared error of less than 5 cm.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Universidad Industrial de Santander, Universidad Antonio Nariño
Contributors: Pertuz, S., Pulido-Herrera, E., Kämäräinen, J.
Number of pages: 10
Pages: 38-47
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: ISPRS Journal of Photogrammetry and Remote Sensing
Volume: 144
ISSN (Print): 0924-2716
Ratings: 
  • Scopus rating (2018): CiteScore 10.6 SJR 2.979 SNIP 3.205
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Computer Science Applications, Computers in Earth Sciences
Keywords: Calibration, Depth estimation, Focus, Lightfield, Plenoptic camera
Source: Scopus
Source ID: 85049523458

Research output: Contribution to journalArticleScientificpeer-review

Fluorescence bandwidth of 280nm from broadband Ce3+-doped silica fiber pumped with blue laser diode

Fluorescence properties of a Ce3+-doped silica fiber at different pump wavelengths between 405nm to 450 nm are investigated. With 405 nm pump wavelength and a fiber length of ∼130-140 cm broadband fluorescence of ∼280nm is achieved.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Research group: Nanophotonics, Aston University, Fiber Optics Research Center of the Russian Academy of Sciences, Russian Academy of Sciences
Contributors: Yadav, A., Chichkov, N. B., Gumenyuk, R., Zherebtsov, E., Melkumov, M. A., Yashkov, M. V., Dianov, E. M., Rafailov, E. U.
Number of pages: 1
Pages: 133-133
Publication date: 13 Aug 2018

Host publication information

Title of host publication: 2018 International Conference Laser Optics (ICLO)
Publisher: IEEE
Article number: 8435861
ISBN (Electronic): 9781538636121
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Broadband source, Ce-doped fiber, Ce ions, Fluorescence
Source: Scopus
Source ID: 85052525711

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Accelerated optical solitons in reorientational media with transverse invariance and longitudinally modulated birefringence

We demonstrate that reorientational spatial solitons can curve when propagating in a medium with engineered walk-off along the direction of propagation. In this regard, we employ nematic liquid crystals with molecular anchoring defined by electron-beam lithography and optic axis distribution modulated in the longitudinal direction only, keeping the transverse orientation constant. The experimental results are in remarkably good agreement with a simple modulation theory based on momentum conservation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Politechnika Warszawska, University of Edinburgh, University “Roma Tre”
Contributors: Laudyn, U. A., Kwaśny, M., Karpierz, M. A., Smyth, N. F., Assanto, G.
Publication date: 7 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 98
Issue number: 2
Article number: 023810
ISSN (Print): 2469-9926
Ratings: 
  • Scopus rating (2018): CiteScore 2.84 SJR 1.268 SNIP 0.987
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85051223073

Research output: Contribution to journalArticleScientificpeer-review

Multiwavelength surface contouring from phase-coded noisy diffraction patterns: Wavelength-division optical setup

We propose an algorithm for absolute phase retrieval from multiwavelength noisy phase coded diffraction patterns. A lensless optical system is considered with a set of successive single wavelength experiments (wavelength-division setup). The phase masks are applied for modulation of the multiwavelength object wavefronts. The algorithm uses the forward/backward propagation for coherent light beams and sparsely encoding wavefronts, which leads to the complex-domain block-matching three-dimensional filtering. The key-element of the algorithm is an original aggregation of the multiwavelength object wavefronts for high-dynamic-range absolute phase reconstruction. Simulation tests demonstrate that the developed approach leads to the effective solutions explicitly using the sparsity for noise suppression and high-accuracy object absolute phase reconstruction from noisy data.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI, ITMO University
Contributors: Katkovnik, V., Shevkunov, I., Petrov, N. V., Egiazarian, K.
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Optical Engineering
Volume: 57
Issue number: 8
Article number: 085105
ISSN (Print): 0091-3286
Ratings: 
  • Scopus rating (2018): CiteScore 2 SJR 0.403 SNIP 0.79
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering(all)
Keywords: absolute phase retrieval, discrete optical signal processing, multiwavelength phase retrieval, phase imaging, surface contouring
Source: Scopus
Source ID: 85052936635

Research output: Contribution to journalArticleScientificpeer-review

Temporal dynamics of light-written waveguides in unbiased liquid crystals

The control of light by light is one of the main aims in modern photonics. In this context, a fundamental cornerstone is the realization of light-written waveguides in real time, resulting in all-optical reconfigurability of communication networks. Light-written waveguides are often associated with spatial solitons, that is, non-diffracting waves due to a nonlinear self-focusing effect in the harmonic regime. From an applicative point of view, it is important to establish the temporal dynamics for the formation of such light-written guides. Here, we investigate theoretically the temporal dynamics in nematic liquid crystals, a material where spatial solitons can be induced using continuous wave lasers with a few milliwatts of power. We fully address the role of the spatial walk-off and the longitudinal nonlocality in the waveguide formation. We show that for powers large enough to induce light self-steering the beam undergoes several fluctuations before reaching the stationary regime, in turn leading to a much longer formation time for the light-written waveguide.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Friedrich-Schiller-University Jena, ENEA/CREATE/Università Degli Studi Napoli Federico II, Universidade do Porto, Fraunhofer Institute for Applied Optics and Precision Engineering IOF
Contributors: Alberucci, A., Barboza, R., Jisha, C. P., Nolte, S.
Number of pages: 10
Pages: 1878-1887
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America B: Optical Physics
Volume: 35
Issue number: 8
ISSN (Print): 0740-3224
Ratings: 
  • Scopus rating (2018): CiteScore 3.9 SJR 0.875 SNIP 0.971
Original language: English
ASJC Scopus subject areas: Statistical and Nonlinear Physics, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85057822710

Research output: Contribution to journalArticleScientificpeer-review

1.34 μm VECSEL mode-locked with a GaSb-based SESAM

Mode locking of a 1.34 μm vertical external cavity surface emitting laser is demonstrated using a GaSb-based semiconductor saturable absorber mirror (SESAM). The SESAM includes six AlGaSb quantum wells (QWs) with an absorption edge at ∼1.37 μm. The proposed approach has two key benefits: the QWs can be grown lattice matched, and only a small number of Bragg reflector layers is required to provide high reflectivity. Pump–probe measurements also reveal that the AlGaSb/GaSb structure exhibits an intrinsically fast absorption recovery on a picosecond timescale. The mode-locked laser pulse train had a fundamental repetition rate of 1.03 GHz, a pulse duration of ∼5 ps, and a peak power of ∼1.67 W. The demonstration paves the way for exploiting GaSb-based SESAMs for mode locking in the 1.3–2 μm wavelength range, which is not sufficiently addressed by GaAs and InP material systems.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Max Born Institute
Contributors: Härkönen, A., Suomalainen, S., Rantamäki, A., Nikkinen, J., Wang, Y., Griebner, U., Steinmeyer, G., Guina, M.
Number of pages: 4
Pages: 3353-3356
Publication date: 15 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 43
Issue number: 14
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2018): CiteScore 7.1 SJR 1.707 SNIP 1.602
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

EXT="Steinmeyer, Günter"

Source: Scopus
Source ID: 85049846710

Research output: Contribution to journalArticleScientificpeer-review

Evaluation of screen printed silver trace performance and long-term reliability against environmental stress on a low surface energy substrate

Otherwise attractive substrate materials for printed electronics may have such surface characteristics that make patterning challenging. This article focuses on the printability and performance characterization of conductive patterns on a low surface energy substrate. Surface characteristics of a hydrophobic polyphenylene ether (PPE) substrate and the effects of surface modification using chemical and physical pre-treatments were studied. In addition, silver ink performance and its reliability on this substrate were evaluated. The surface was characterized by surface energy measurements and surface profile analysis. Screen-printed test patterns were characterized to evaluate print quality and electrical and mechanical performance. A further inspection of substrate-ink interactions was conducted using environmental reliability tests. It was observed that ink adhesion could be significantly promoted by choosing a suitable surface pre-treatment method. Low sheet resistances were obtained, and thus, suitable inks for further characterization were found. In addition, it was observed that environmental stress has a significant impact on ink-substrate interactions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Nano Communication Centre
Contributors: Mikkonen, R., Mäntysalo, M.
Number of pages: 12
Pages: 54-65
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Microelectronics Reliability
Volume: 86
ISSN (Print): 0026-2714
Ratings: 
  • Scopus rating (2018): CiteScore 2.6 SJR 0.376 SNIP 1.017
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Safety, Risk, Reliability and Quality, Surfaces, Coatings and Films, Electrical and Electronic Engineering
Keywords: Adhesion, Environmental stress, PPE, Printed electronics, Reliability, Surface modification
Electronic versions: 
URLs: 
Source: Scopus
Source ID: 85047240351

Research output: Contribution to journalArticleScientificpeer-review

Segmentation of vessel structures from photoacoustic images with reliability assessment

Photoacoustic imaging enables the imaging of soft biological tissue with combined optical contrast and ultrasound resolution. One of the targets of interest is tissue vasculature. However, the photoacoustic images may not directly provide the information on, for example, vasculature structure. Therefore, the images are improved by reducing noise and artefacts, and processed for better visualisation of the target of interest. In this work, we present a new segmentation method of photoacoustic images that also straightforwardly produces assessments of its reliability. The segmentation depends on parameters which have a natural tendency to increase the reliability as the parameter values monotonically change. The reliability is assessed by counting classifications of image voxels with different parameter values. The resulting segmentation with reliability offers new ways and tools to analyse photoacoustic images and new possibilities for utilising them as anatomical priors in further computations. Our MATLAB implementation of the method is available as an open-source software package [P. Raumonen, Matlab, 2018].

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mathematics, University of Eastern Finland, University College London
Contributors: Raumonen, P., Tarvainen, T.
Number of pages: 18
Pages: 2887-2904
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Biomedical Optics Express
Volume: 9
Issue number: 7
ISSN (Print): 2156-7085
Ratings: 
  • Scopus rating (2018): CiteScore 6.5 SJR 1.516 SNIP 1.604
Original language: English
ASJC Scopus subject areas: Biotechnology, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85049377889

Research output: Contribution to journalArticleScientificpeer-review

Acquiring respiration rate from photoplethysmographic signal by recursive bayesian tracking of intrinsic modes in time-frequency spectra

Respiration rate (RR) provides useful information for assessing the status of a patient. We propose RR estimation based on photoplethysmography (PPG) because the blood perfusion dynamics are known to carry information on breathing, as respiration-induced modulations in the PPG signal. We studied the use of amplitude variability of transmittance mode finger PPG signal in RR estimation by comparing four time-frequency (TF) representation methods of the signal cascaded with a particle filter. The TF methods compared were short-time Fourier transform (STFT) and three types of synchrosqueezing methods. The public VORTAL database was used in this study. The results indicate that the advanced frequency reallocation methods based on synchrosqueezing approach may present improvement over linear methods, such as STFT. The best results were achieved using wavelet synchrosqueezing transform, having a mean absolute error and median error of 2.33 and 1.15 breaths per minute, respectively. Synchrosqueezing methods were generally more accurate than STFT on most of the subjects when particle filtering was applied. While TF analysis combined with particle filtering is a promising alternative for real-time estimation of RR, artefacts and non-respiration-related frequency components remain problematic and impose requirements for further studies in the areas of signal processing algorithms an PPG instrumentation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Sensor Technology and Biomeasurements (STB)
Contributors: Pirhonen, M., Peltokangas, M., Vehkaoja, A.
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Sensors
Volume: 18
Issue number: 6
Article number: 1693
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2018): CiteScore 4.3 SJR 0.592 SNIP 1.642
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: Particle filters, Photoplethysmography, Respiration, Synchrosqueezing, Time-frequency analysis
Electronic versions: 

Bibliographical note

int=TUT-BMT,"Pirhonen, Mikko"

Source: Scopus
Source ID: 85047608517

Research output: Contribution to journalArticleScientificpeer-review

Evaluation of dry electrodes in canine heart rate monitoring

The functionality of three dry electrocardiogram electrode constructions was evaluated by measuring canine heart rate during four different behaviors: Standing, sitting, lying and walking. The testing was repeated (n = 9) in each of the 36 scenarios with three dogs. Two of the electrodes were constructed with spring-loaded test pins while the third electrode was a molded polymer electrode with Ag/AgCl coating. During the measurement, a specifically designed harness was used to attach the electrodes to the dogs. The performance of the electrodes was evaluated and compared in terms of heartbeat detection coverage. The effect on the respective heart rate coverage was studied by computing the heart rate coverage from the measured electrocardiogram signal using a pattern-matching algorithm to extract the R-peaks and further the beat-to-beat heart rate. The results show that the overall coverage ratios regarding the electrodes varied between 45-95% in four different activity modes. The lowest coverage was for lying and walking and the highest was for standing and sitting.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Pervasive Computing, Research group: Sensor Technology and Biomeasurements (STB), University of Helsinki, Institute of Biomedical Engineering and Informatics, University of Tampere (UTA), Research Group for Emotions
Contributors: Virtanen, J., Somppi, S., Törnqvist, H., Jeyhani, V., Fiedler, P., Gizatdinova, Y., Majaranta, P., Väätäjä, H., Cardó, A. V., Lekkala, J., Tuukkanen, S., Surakka, V., Vainio, O., Vehkaoja, A.
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Sensors
Volume: 18
Issue number: 6
Article number: 1757
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2018): CiteScore 4.3 SJR 0.592 SNIP 1.642
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: Dry electrode, Heart rate canine
Electronic versions: 
Source: Scopus
Source ID: 85047961818

Research output: Contribution to journalArticleScientificpeer-review

Morphology evolution of PS-b-PDMS block copolymer and its hierarchical directed self-assembly on block copolymer templates

Cylinder-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS, 27.2k-b-11.7k, SD39) block copolymer having a total molecular weight of 39 kg mol−1 was exploited to achieve in-plane morphologies of lines, dots and antidots. Brush-free self-assembly of the SD39 on silicon substrates was investigated using solvents that were PS or PDMS selective, neutral and non-solvents based on their Hansen solubility parameters. The different morphologies were achieved with annealing times ranging from 10 min to 1 h at room temperature. The SD39 patterns were used as an etch mask for transferring the pattern into the underlying substrate. Directed self-assembly and hierarchical directed self-assembly on block copolymer templates for confinement of dots was successfully demonstrated. The strategy for achieving multiple morphologies using one BCP by mere choice of the annealing solvents on unmodified substrates provides a simplified method for surface nanopatterning, templated growth of nanomaterials and nanofabrication.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Danmarks Tekniske Universitet, DTU Informatik, Trinity College Dublin, Laboratory of Photonics
Contributors: Rasappa, S., Schulte, L., Borah, D., Hulkkonen, H., Ndoni, S., Salminen, T., Senthamaraikanan, R., Morris, M. A., Niemi, T.
Number of pages: 7
Pages: 1-7
Publication date: 15 May 2018
Peer-reviewed: Yes

Publication information

Journal: Microelectronic Engineering
Volume: 192
ISSN (Print): 0167-9317
Ratings: 
  • Scopus rating (2018): CiteScore 4.2 SJR 0.561 SNIP 0.958
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Surfaces, Coatings and Films, Electrical and Electronic Engineering
Keywords: Block copolymer, Hansen solubility, Hierarchical self-assembly, Selective solvent
Source: Scopus
Source ID: 85041706803

Research output: Contribution to journalArticleScientificpeer-review

Thermo-optic soliton routing in nematic liquid crystals

We demonstrate thermo-optic control on the propagation of optical spatial solitons in nematic liquid crystals. By varying the sample temperature, both linear and nonlinear optical properties of the reorientational material are modulated by acting on the refractive indices, the birefringence, and the elastic response. As a result, both the trajectory and transverse confinement of spatial solitons can be adjusted, demonstrating an effective means to tune and readdress self-induced optical waveguides.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Politechnika Warszawska, University “Roma Tre”, NooEL–Nonlinear Optics and OptoElectronics Lab
Contributors: Laudyn, U. A., Piccardi, A., Kwasny, M., Karpierz, M. A., Assanto, G.
Number of pages: 4
Pages: 2296-2299
Publication date: 15 May 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 43
Issue number: 10
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2018): CiteScore 7.1 SJR 1.707 SNIP 1.602
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85047265805

Research output: Contribution to journalArticleScientificpeer-review

Sub-10 optical-cycle passively mode-locked Tm:(Lu2/3Sc1/3)2O3 ceramic laser at 2 µm

A Tm-doped mixed sesquioxide ceramic laser is mode-locked near 2 µm using InGaAsSb quantum-well semiconductor saturable absorber and chirped mirrors for dispersion compensation. Maximum average output power of 175 mW is achieved for a pulse duration of 230 fs at a repetition rate of 78.9 MHz with a 3% output coupler. Applying a 0.2% output coupler pulses as short as 63 fs are generated at 2.057 µm.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Max Born Institute, China Academy of Engineering Physics, ITMO University, Jiangsu Normal University, Universitat Rovira i Virgili
Contributors: Wang, Y., Jing, W., Loiko, P., Zhao, Y., Huang, H., Mateos, X., Suomalainen, S., Härkönen, A., Guina, M., Griebner, U., Petrov, V.
Number of pages: 6
Pages: 10299-10304
Publication date: 16 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 8
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85045566318

Research output: Contribution to journalArticleScientificpeer-review

Ho:KY(WO4)2 thin-disk laser passively Qswitched by a GaSb-based SESAM

A Holmium thin-disk laser based on a 3 at.% Ho:KY(WO4)2 /KY(WO4)2 epitaxy and single-bounce pumping by a 1960 nm Tm-fiber laser is passively Q-switched with a GaSb-based quantum-well semiconductor saturable absorber mirror. It generates an average output power of 551 mW at 2056 nm with a slope efficiency of 44% (with respect to the absorbed pump power). The best pulse characteristics (energy and duration) are 4.1 μJ /201 ns at a repetition rate of 135 kHz and the conversion efficiency with respect to the continuous-wave regime is as high as 93%.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Max Born Institute, Universitat Rovira i Virgili, LISA Laser Products OHG, ITMO University, Institute of Laser Physics of the Siberian Branch of the RAS
Contributors: Mateos, X., Loiko, P., Lamrini, S., Scholle, K., Fuhrberg, P., Suomalainen, S., Härkönen, A., Guina, M., Vatnik, S., Vedin, I., Aguiló, M., Díaz, F., Wang, Y., Griebner, U., Petrov, V.
Number of pages: 6
Pages: 9011-9016
Publication date: 2 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 7
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85044766941

Research output: Contribution to journalArticleScientificpeer-review

AlGaAs-based vertical-external-cavity surface-emitting laser exceeding 4 W of direct emission power in the 740–790 nm spectral range

An optically pumped vertical-external-cavity surface-emitting laser (VECSEL) for direct emission in the 740–790 nm wavelength region is reported. The gain structure is based on 12 AlGaAs quantum wells. We demonstrate wavelength tuning between 747 nm and 788 nm and free-running operation with a maximum power of 4.24 W (pump power limited) for a heat sink temperature of 14°C. This laser system addresses a spectral gap not currently covered by VECSEL technology and represents the most powerful VECSEL reported within the 7XX-nm wavelength region.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC
Contributors: Kahle, H., Nechay, K., Penttinen, J., Tukiainen, A., Ranta, S., Guina, M.
Number of pages: 4
Pages: 1578-1581
Publication date: 1 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 43
Issue number: 7
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2018): CiteScore 7.1 SJR 1.707 SNIP 1.602
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85044838897

Research output: Contribution to journalArticleScientificpeer-review

Comparison of metal/polymer back reflectors with half-sphere, blazed, and pyramid gratings for light trapping in III-V solar cells

We report on the fabrication of diffraction gratings for application as back contact reflectors. The gratings are designed for thin-film solar cells incorporating absorbers with bandgap slightly lower than GaAs, i.e. InAs quantum dot or GaInNAs solar cells. Light trapping in the solar cells enables the increase of the absorption leading to higher short circuit current densities and higher efficiencies. We study metal/polymer back reflectors with half-sphere, blazed, and pyramid gratings, which were fabricated either by photolithography or by nanoimprint lithography. The gratings are compared in terms of the total and the specular reflectance, which determine their diffraction capabilities, i.e.The feature responsible for increasing the absorption. The pyramid grating showed the highest diffuse reflection of light compared to the half-sphere structure and the blazed grating. The diffraction efficiency measurements were in agreement with the numerical simulations. The validated model enables designing such metal/polymer back reflectors for other type of solar cells by refining the optimal dimensions of the gratings for different wavelength ranges.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Faculty of Natural Sciences, Politecnico di Torino, Ita-Suomen yliopisto, Dispelix Oy
Contributors: Aho, T., Guina, M., Elsehrawy, F., Cappelluti, F., Raappana, M., Tukiainen, A., Khairul Alam, A. B., Vartiainen, I., Kuittinen, M., Niemi, T.
Pages: A331-A340
Publication date: 19 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 6
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85044133519

Research output: Contribution to journalArticleScientificpeer-review

Guided-mode resonance gratings for enhanced mid-infrared absorption in quantum dot intermediate-band solar cells

Achieving strong absorption of low-energy photons is one of the key issues to demonstrate quantum dot solar cells working in the intermediate band regime at practical concentration factors and operating temperatures. Guided-mode resonance effects may enable large enhancement of quantum dot intraband optical transitions. We propose quantum dot thin-film cells designed to have significant field waveguiding in the quantum dot stack region and patterned at the rear-side with a sub-wavelength diffraction grating. Remarkable increase of the optical path length at mid-infrared wavelengths is shown owing to guided-mode resonances. Design guidelines are presented for energy and strength of the second-photon absorption for III-V quantum dots, such as InAs/GaAs and GaSb/GaAs, whose intraband and intersubband transitions roughly extends over the 2-8 μm range. The proposed design can also be applied to quantum dot infrared detectors. Angle-selectivity is discussed in view of applications in concentrator photovoltaic systems and infrared imaging systems.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Politecnico di Torino
Contributors: Elsehrawy, F., Niemi, T., Cappelluti, F.
Pages: A352-A359
Publication date: 19 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 6
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85044122507

Research output: Contribution to journalArticleScientificpeer-review

Ultra-large core birefringent Yb-doped tapered double clad fiber for high power amplifiers

We present a birefringent Yb-doped tapered double-clad fiber with a record core diameter of 96 μm. An impressive gain of over 38 dB was demonstrated for linearly polarized CW and pulsed sources at a wavelength of 1040 nm. For the CW regime the output power was70 W. For a mode-locked fiber laser a pulse energy of 28 μJ with 292 kW peak power was reached at an average output power of 28 W for a 1 MHz repetition rate. The tapered double-clad fiber has a high value of polarization extinction ratio at 30 dB and is capable of delivering the linearly polarized diffraction-limited beam (M2 = 1.09).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Nanophotonics, Ampliconyx Ltd, Institute of Radio Engineering and Electronics of the Russian Academy of Sciences, Moscow Institute of Physics and Technology, St. Petersburg State Polytechnical University
Contributors: Fedotov, A., Noronen, T., Gumenyuk, R., Ustimchik, V., Chamorovskii, Y., Golant, K., Odnoblyudov, M., Rissanen, J., Niemi, T., Filippov, V.
Number of pages: 12
Pages: 6581-6592
Publication date: 19 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 6
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 

Bibliographical note

EXT=”Noronen,Teppo”
INT=fot, "Rissanen, Joona"
EXT="Filippov, Valery"

Source: Scopus
Source ID: 85044203104

Research output: Contribution to journalArticleScientificpeer-review

Speckle reduction method for image-based coherent stereogram generation

We propose a speckle noise reduction method for generation of coherent holographic stereograms. The method employs densely sampled light field (DSLF) of the scene together with depth information acquired for each ray in the captured DSLF. Speckle reduction is achieved based on the ray separation technique where the scene is first described as a superposition of sparse sets of point sources corresponding to separated sets of rays and then the holographic reconstructions corresponding to these sparse sets of point sources are added incoherently (intensity-wise) to obtain the final reconstruction. The proposed method handles the light propagation between the sparse scene points and hologram elements accurately by utilizing ray resampling based on the notion of DSLF. As a result, as demonstrated via numerical simulations, significant speckle suppression is achieved at no cost of sampling related reconstruction artifacts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: 3D MEDIA
Contributors: Kinen, J. M., Sahin, E., Gotchev, A.
Number of pages: 14
Pages: 5381-5394
Publication date: 5 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 26
Issue number: 5
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2018): CiteScore 6.8 SJR 1.473 SNIP 1.631
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85042784476

Research output: Contribution to journalArticleScientificpeer-review

Noise minimized high resolution digital holographic microscopy applied to surface topography

The topography of surface relief gratings was studied by digital holographic microscopy. The applicability of the method for quantitative measurements of surface microstructure at nanoscale was demonstrated. The method for wavefront reconstruction of surface relief from a digital hologram recorded in off-axis configuration was also applied. The main feature is noise filtration due to the presence of noise in the recorded intensity distribution and the use of all orders of the hologram. Reconstruction results proved a better effectiveness of our approach for topography studying of relief grating patterned on a ChG As2S3 - Se nanomultilayers in comparison with standard Fourier Transform and Atom Force Microscope methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI, Institute of Applied Physics Academy of Sciences of Moldava, University of Stuttgart, St. Petersburg State University, Department of Signal Processing
Contributors: Achimova, E., Abaskin, V., Claus, D., Pedrini, G., Shevkunov, I., Katkovnik, V.
Number of pages: 6
Pages: 267-272
Publication date: 1 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Computer Optics
Volume: 42
Issue number: 2
ISSN (Print): 0134-2452
Ratings: 
  • Scopus rating (2018): CiteScore 3.3 SJR 0.535 SNIP 2.365
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Computer Science Applications, Electrical and Electronic Engineering
Keywords: Diffraction gratings, Digital holography, Digital image processing
Source: Scopus
Source ID: 85046122008

Research output: Contribution to journalArticleScientificpeer-review

An activity recognition framework deploying the random forest classifier and a single optical heart rate monitoring and triaxial accelerometer wrist-band

Wrist-worn sensors have better compliance for activity monitoring compared to hip, waist, ankle or chest positions. However, wrist-worn activity monitoring is challenging due to the wide degree of freedom for the hand movements, as well as similarity of hand movements in different activities such as varying intensities of cycling. To strengthen the ability of wrist-worn sensors in detecting human activities more accurately, motion signals can be complemented by physiological signals such as optical heart rate (HR) based on photoplethysmography. In this paper, an activity monitoring framework using an optical HR sensor and a triaxial wrist-worn accelerometer is presented. We investigated a range of daily life activities including sitting, standing, household activities and stationary cycling with two intensities. A random forest (RF) classifier was exploited to detect these activities based on the wrist motions and optical HR. The highest overall accuracy of 89.6 ± 3.9% was achieved with a forest of a size of 64 trees and 13-s signal segments with 90% overlap. Removing the HR-derived features decreased the classification accuracy of high-intensity cycling by almost 7%, but did not affect the classification accuracies of other activities. A feature reduction utilizing the feature importance scores of RF was also carried out and resulted in a shrunken feature set of only 21 features. The overall accuracy of the classification utilizing the shrunken feature set was 89.4 ± 4.2%, which is almost equivalent to the above-mentioned peak overall accuracy.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Faculty of Biomedical Sciences and Engineering, Research group: Personal Health Informatics-PHI, Department of Future Technologies
Contributors: Mehrang, S., Pietilä, J., Korhonen, I.
Publication date: 22 Feb 2018
Peer-reviewed: Yes

Publication information

Journal: Sensors
Volume: 18
Issue number: 2
Article number: 613
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2018): CiteScore 4.3 SJR 0.592 SNIP 1.642
Original language: English
ASJC Scopus subject areas: Analytical Chemistry, Atomic and Molecular Physics, and Optics, Biochemistry, Instrumentation, Electrical and Electronic Engineering
Keywords: Accelerometer, Activity recognition, Context awareness, Machine learning, Photoplethysmography, Random forest, Wrist-worn sensors
Electronic versions: 
Source: Scopus
Source ID: 85042489750

Research output: Contribution to journalArticleScientificpeer-review

87 fs mode-locked Tm,Ho:CaYAlO4 laser at ~2043 nm

We report on, to the best of our knowledge, the first sub-100 fs mode-locked Ho3+-laser in the 2 μm spectral range employing a disordered co-doped Tm;Ho:CaYAlO4 (Tm, Ho:CALYO) crystal as a gain medium. Pulses as short as 87 fs are produced with an average output power of 27 mW at 80.45 MHz repetition rate. An output power of 96 mW is reached for a pulse duration of 98 fs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Max Born Institute, Jiangsu Normal University, Universitat Rovira i Virgili, China Academy of Engineering Physics, ITMO University, Tongji University
Contributors: Zhao, Y., Wang, Y., Zhang, X., Mateos, X., Pan, Z., Loiko, P., Zhou, W., Xu, X., Xu, J., Shen, D., Suomalainen, S., Härkönen, A., Guina, M., Griebner, U., Petrov, V.
Number of pages: 4
Pages: 915-918
Publication date: 1 Feb 2018
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 43
Issue number: 4
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2018): CiteScore 7.1 SJR 1.707 SNIP 1.602
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85042032809

Research output: Contribution to journalArticleScientificpeer-review

Surface relief and refractive index gratings patterned in chalcogenide glasses and studied by off-axis digital holography

Surface relief gratings and refractive index gratings are formed by direct holographic recording in amorphous chalcogenide nanomultilayer structures As2S3−Se and thin films As2S3. The evolution of the grating parameters, such as the modulation of refractive index and relief depth in dependence of the holographic exposure, is investigated. Off-axis digital holographic microscopy is applied for the measurement of the photoinduced phase gratings. For the high-accuracy reconstruction of the wavefront (amplitude and phase) transmitted by the fabricated gratings, we used a computational technique based on the sparse modeling of phase and amplitude. Both topography and refractive index maps of recorded gratings are revealed. Their separated contribution in diffraction efficiency is estimated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI, Institute of Applied Physics of Academy of Sciences of Moldova, University of Stuttgart
Contributors: Cazac, V., Meshalkin, A., Achimova, E., Abashkin, V., Katkovnik, V., Shevkunov, I., Claus, D., Pedrini, G.
Number of pages: 7
Pages: 507-513
Publication date: 20 Jan 2018
Peer-reviewed: Yes

Publication information

Journal: Applied Optics
Volume: 57
Issue number: 3
ISSN (Print): 1559-128X
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.749 SNIP 1.263
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85040793865

Research output: Contribution to journalArticleScientificpeer-review

Blind estimation of white Gaussian noise variance in highly textured images

In the paper, a new method of blind estimation of noise variance in a single highly textured image is proposed. An input image is divided into 8x8 blocks and discrete cosine transform (DCT) is performed for each block. A part of 64 DCT coefficients with lowest energy calculated through all blocks is selected for further analysis. For the DCT coefficients, a robust estimate of noise variance is calculated. Corresponding to the obtained estimate, a part of blocks having very large values of local variance calculated only for the selected DCT coefficients are excluded from the further analysis. These two steps (estimation of noise variance and exclusion of blocks) are iteratively repeated three times. For the verification of the proposed method, a new noise-free test image database TAMPERE17 consisting of many highly textured images is designed. It is shown for this database and different values of noise variance from the set {25, 49, 100, 225}, that the proposed method provides approximately two times lower estimation root mean square error than other methods.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Don State Technical University
Contributors: Ponomarenko, M., Gapon, N., Voronin, V., Egiazarian, K.
Publication date: 2018

Host publication information

Title of host publication: Electronic Imaging : Image Processing: Algorithms and Systems XVI
Publisher: Society for Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Blind estimation of noise characteristics, Discrete cosine transform (DCT), Noise free test image database

Bibliographical note

jufoid=84313

Source: Scopus
Source ID: 85052856410

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Combined local and global image enhancement algorithm

We present a new image enhancement algorithm based on combined local and global image processing. The basic idea is to apply α-rooting image enhancement approach for different image blocks. For this purpose, we split image in moving windows on disjoint blocks with different size (8 by 8, 16 by 16, 32 by 32 and, i.e.). The parameter alfa for every block driven through optimization of measure of enhancement (EME). The resulting image is a weighted mean of all processing blocks. This strategy for image enhancement allows getting more contrast image with the following properties: irregular lighting and brightness gradient. Some experimental results are presented to illustrate the performance of the proposed algorithm.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Don State Technical University, College of Staten Island
Contributors: Voronin, V., Semenishchev, E., Ponomarenko, M., Agaian, S.
Publication date: 2018

Host publication information

Title of host publication: Electronic Imaging : Image Processing: Algorithms and Systems XVI
Publisher: Society for Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics

Bibliographical note

jufoid=84313

Source: Scopus
Source ID: 85052861928

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Compression of signs of DCT coefficients for additional lossless compression of JPEG images

One of the main approaches to additional lossless compression of JPEG images is decoding of quantized values of discrete cosine transform (DCT) coefficients and further more effective recompression of the coefficients. Values of amplitudes of DCT coefficients are highly correlated and it is possible to effectively compress them. At the same time, signs of DCT coefficients, which occupy up to 20% of compressed image, are often considered unpredictable. In the paper, a new and effective method for compression of signs of quantized DCT coefficients is proposed. The proposed method takes into account both correlation between DCT coefficients of the same block and correlation between DCT coefficients of neighbor blocks. For each of 64 DCT coefficients, positions of 3 reference coefficients inside the block are determined and stored in the compressed file. Four reference coefficients with fixed positions are used from the neighbor blocks. For all reference coefficients, 15 frequency models to predict signs of a given coefficient are used. All 7 probabilities (that the sign is negative) are mixed by logistic mixing. For test set of JPEG images, we show that the proposed method allows compressing signs of DCT coefficients by 1.1 ⋯ 1.3 times, significantly outperforming nearest analogues.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Kharkiv National Aerospace University
Contributors: Miroshnichenko, O., Ponomarenko, M., Lukin, V., Egiazarian, K.
Publication date: 2018

Host publication information

Title of host publication: Electronic Imaging : Image Processing: Algorithms and Systems XVI
Publisher: Society for Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Discrete cosine transform, JPEG, JPEG additional compression, Sign compression

Bibliographical note

jufoid=84313
EXT="Lukin, Vladimir"

Source: Scopus
Source ID: 85052859716

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Conversion of sparsely-captured light field into alias-free fullparallax multiview content

We propose shearlet decomposition based light field (LF) reconstruction and filtering techniques for mitigating artifacts in the visualized contents of 3D multiview displays. Using the LF reconstruction capability, we first obtain the densely sampled light field (DSLF) of the scene from a sparse set of view images. We design the filter via tiling the Fourier domain of epipolar image by shearlet atoms that are directionally and spatially localized versions of the desired display passband. In this way, it becomes possible to process the DSLF in a depth-dependent manner. That is, the problematic areas in the 3D scene that are outside of the display depth of field (DoF) can be selectively filtered without sacrificing high details in the areas near the display, i.e. inside the DoF. The proposed approach is tested on a synthetic scene and the improvements achieved by means of the quality of the visualized content are verified, where the visualization process is simulated using a geometrical optics model of the human eye.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Electronics and Telecommunication Research Institute (ETRI)
Contributors: Sahin, E., Vagharshakyan, S., Bregovic, R., Lee, G., Gotchev, A.
Number of pages: 5
Pages: 1441-1445
Publication date: 2018

Host publication information

Title of host publication: Electronic Imaging : Stereoscopic Displays and Applications XXIX
Publisher: Society for Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics

Bibliographical note

jufoid=84313

Source: Scopus
Source ID: 85052854954

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Deep p-Fibonacci scattering networks

Recently, the use of neural networks for image classification has become widely spread. Thanks to the availability of increased computational power, better performing architectures have been designed, such as the Deep Neural networks. In this work, we propose a novel image representation framework exploiting the Deep p- Fibonacci scattering network. The architecture is based on the structured p-Fibonacci scattering over graph data. This approach allows to provide good accuracy in classification while reducing the computational complexity. Experimental results demonstrate that the performance of the proposed method is comparable to state-of-the-art unsupervised methods while being computationally more efficient.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, University “Roma Tre”
Contributors: Battisti, F., Carli, M., De Paola, E., Egiazarian, K.
Publication date: 2018

Host publication information

Title of host publication: Electronic Imaging : Image Processing: Algorithms and Systems XVI
Publisher: Society for Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics

Bibliographical note

jufoid=84313
EXT="Battisti, F."
EXT="Carli, M."

Source: Scopus
Source ID: 85052873638

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Lensless broadband diffractive imaging with improved depth of focus: wavefront modulation by multilevel phase masks

This paper introduces a novel lensless full colour diffractive computational imaging system with a planar Multilevel Phase Mask (MPM) as a diffractive optical element (DOE). The novelty concerns: a methodology of MPM design for improved depth of focus (DoF); design of PSFs for RGB imaging and an inverse imaging algorithm with sparse colour image modelling simultaneous for all RGB channels. MPMs are step-wise invariant. The cubic wavefront coding (WFC) is incorporated in MPMs with optimization of number of levels and width of invariant steps. This design of MPM makes the system robust with respect to defocus (improves DoF) and diminish chromatic aberrations typical for DOEs. Broadband multichannel test-images are exploited for design and testing of the lensless system. We consider two alternative optical setups: Wavelength Multiplexing (WM) and Wavelength Division (WD). In WM, the light beam is broadband multichannel with light sources radiating all wavelengths simultaneously and a CMOS sensor is equipped with a Bayer colour filter array (CFA) for registration of spectral measurements. In this setup, a single MPM is designed for the broadband multichannel light beams. In WD, separate exposures of RGB channels are registered by a broadband grey-scale CCD sensor. Different MPMs are designed for each of the RGB channels. Simulation experiments demonstrate the essentially extended DoF of the designed lensless systems and the advanced accuracy and quality of imaging with respect to the corresponding WM and WD systems with refractive lenses. Due to robustness of the designed lensless system to chromatic aberrations, this advantage has a place even with respect to the lens-system.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI
Contributors: Katkovnik, V., Ponomarenko, M., Egiazarian, K.
Publication date: 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Modern Optics
ISSN (Print): 0950-0340
Ratings: 
  • Scopus rating (2018): CiteScore 2.7 SJR 0.436 SNIP 0.694
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: chromatic aberrations, computational imaging, extended depth of focus, inverse imaging, Multilevel diffractive optical elements, multilevel phase mask design, wavefront coding
Source: Scopus
Source ID: 85054570905

Research output: Contribution to journalArticleScientificpeer-review

Light propagation analysis in nervous tissue for wireless optogenetic nanonetworks

In recent years, numerous methods have been sought for developing novel solutions to counter neurodegenerative diseases. An objective that is being investigated by researchers is to develop cortical implants that are able to wirelessly stimulate neurons at the single cell level. This is a major development compared to current solutions that use electrodes, which are only able to target a population of neurons, or optogenetics, which requires optical fiber-leads to be embedded deep into the brain. In this direction, the concept of wireless optogenetic nanonetworks has been recently introduced. In such architecture, miniature devices are implanted in the cortex for neuronal stimulation through optogenetics. One of the aspects that will determine the topology and performance of wireless optogenetic nanonetworks is related to light propagation in genetically-engineered neurons. In this paper, a channel model that captures the peculiarities of light propagation in neurons is developed. First, the light propagation behavior using the modified Beer-Lambert law is analyzed based on the photon transport through the nervous tissue. This includes analyzing the scattering light diffraction and diffusive reflection that results from the absorption of neural cell chromophores, as well as validating the results by means of extensive multiphysics simulations. Then, analysis is conducted on the path loss through cells at different layers of the cortex by taking into account the multi-path phenomenon. Results show that there is a light focusing effect in the soma of neurons that can potentially help the to stimulate the target cells.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Electronics and Communications Engineering, State University of New York
Contributors: Wirdatmadja, S., Johari, P., Balasubramaniam, S., Bae, Y., Stachowiak, M. K., Jornet, J. M.
Publication date: 2018

Host publication information

Title of host publication: Optogenetics and Optical Manipulation 2018
Publisher: SPIE
Article number: 104820R
ISBN (Electronic): 9781510614499
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Atomic and Molecular Physics, and Optics, Radiology Nuclear Medicine and imaging
Keywords: Light propagation, Optogenetics, Single-neuron stimulation, Wireless nanonetworks

Bibliographical note

jufoid=65546

Source: Scopus
Source ID: 85047010302

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Methods and tools for denoising of complex-valued images based on block-matching and high order singular value decomposition

Noise suppression in complex-valued data is an important task for a wide class of applications, in particular concerning the phase retrieval in coherent imaging. The approaches based on BM3D techniques are ones of the most successful in the field. In this paper, we propose and develop a new class of BM3Dstyle algorithms, which use high order (3D and 4D) singular value decomposition (HOSVD) for transform design in complex domain. This set of the novel algorithms is implemented as a toolbox In Matlab. This development is produced for various types of the complex-domain sparsity: directly in complex domain, real/imaginary and phase/ amplitude parts of complexvalued variables. The group-wise transform design is combined with the different kinds of thresholding including multivariable Wiener filtering. The toolbox includes iterative and non-iterative novel complex-domain algorithms (filters). The efficiency of the developed algorithms is demonstrated on denoising problems with an additive Gaussian complex-valued noise. A special set of the complex-valued test-images was developed with spatially varying correlated phase and amplitudes imitating data typical for optical interferometry and holography. It is shown that for this class of the test-images the developed algorithms demonstrate the stateof- the-art performance.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing
Contributors: Ponomarenko, M., Katkovnik, V., Egiazarian, K.
Publication date: 2018

Host publication information

Title of host publication: Electronic Imaging : Image Processing: Algorithms and Systems XVI
Publisher: Society for Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Block matching, Complex domain, Higher-order singular value decomposition, Image denoising, Phase imaging, Sparsity

Bibliographical note

jufoid=84313

Source: Scopus
Source ID: 85052877244

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Narrow-linewidth 780 nm DFB lasers fabricated using nanoimprint lithography

The paper presents narrow-linewidth 780 nm edgeemitting semiconductor DFB lasers fabricated without regrowth using UV-nanoimprinted surface gratings. The thirdorder laterally-coupled ridge-waveguide surface gratings enable single mode operation, excellent spectral purity (40-55 dB side mode suppression ratio and 10 kHz linewidth) and good lightcurrent- voltage characteristics in continuous wave operation (~112 mA threshold current, ~1.55 V opening voltage and 28.9 mW output power from one facet at 300 mA current for 2.4 mm long devices), which are vital in various applications, such as rubidium spectroscopy and atomic clock pumping. The low fabrication costs, high throughput, structural flexibility and high device yield make the fabrication method fully compatible with large scale mass production, enabling the fabrication of low-cost miniaturized modules.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics
Contributors: Virtanen, H., Uusitalo, T., Karjalainen, M., Ranta, S., Viheriala, J., Dumitrescu, M.
Pages: 51-54
Publication date: 2018
Peer-reviewed: Yes
Early online date: 9 Nov 2017

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 30
Issue number: 1
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2018): CiteScore 5.4 SJR 0.991 SNIP 1.272
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: DFB laser, Gratings, Laser modes, Measurement by laser beam, narrow linewidth, Optical device fabrication, Optical interferometry, Surface emitting lasers, surface gratings, UV-nanoimprint lithography
Source: Scopus
Source ID: 85034223754

Research output: Contribution to journalArticleScientificpeer-review

Programming Photoresponse in Liquid Crystal Polymer Actuators with Laser Projector

A versatile, laser-projector-based method is demonstrated for programming alignment patterns into monolithic films of liquid crystal polymer networks. Complex images can be photopatterned into the polymer films with sub-100 μm resolution, using relatively short exposure times. The method is further used to devise both photochemically and photothermally driven actuators that can undergo distinct light-induced shape changes, dictated by the programmed alignment patterns. Deformation modes such as buckling and coiling, as well as miniature robotic devices such as a gripper and a light-responsive octopod, are demonstrated. The reported technique enables easy and cost-effective programmable actuation with relatively high throughput, thus significantly facilitating the design and realization of functional soft robotic actuators.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, University of Warsaw
Contributors: Wani, O. M., Zeng, H., Wasylczyk, P., Priimagi, A.
Publication date: 2018
Peer-reviewed: Yes
Early online date: 2017

Publication information

Journal: Advanced Optical Materials
Volume: 6
Issue number: 1
Article number: 1700949
ISSN (Print): 2195-1071
Ratings: 
  • Scopus rating (2018): CiteScore 10.2 SJR 2.711 SNIP 1.6
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Azobenzene, Laser projectors, Liquid crystal, Patterning, Photoactuation, Photoalignment
Electronic versions: 
Source: Scopus
Source ID: 85037631675

Research output: Contribution to journalArticleScientificpeer-review

Real-time full-field characterization of transient dissipative soliton dynamics in a mode-locked laser

Dissipative solitons are remarkably localized states of a physical system that arise from the dynamical balance between nonlinearity, dispersion and environmental energy exchange. They are the most universal form of soliton that can exist, and are seen in far-from-equilibrium systems in many fields, including chemistry, biology and physics. There has been particular interest in studying their properties in mode-locked lasers, but experiments have been limited by the inability to track the dynamical soliton evolution in real time. Here, we use simultaneous dispersive Fourier transform and time-lens measurements to completely characterize the spectral and temporal evolution of ultrashort dissipative solitons as their dynamics pass through a transient unstable regime with complex break-up and collisions before stabilization. Further insight is obtained from reconstruction of the soliton amplitude and phase and calculation of the corresponding complex-valued eigenvalue spectrum. These findings show how real-time measurements provide new insights into ultrafast transient dynamics in optics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, UMR 6174
Contributors: Ryczkowski, P., Närhi, M., Billet, C., Merolla, J. M., Genty, G., Dudley, J. M.
Number of pages: 7
Pages: 221–227
Publication date: 2018
Peer-reviewed: Yes
Early online date: 5 Mar 2018

Publication information

Journal: Nature Photonics
Volume: 12
ISSN (Print): 1749-4885
Ratings: 
  • Scopus rating (2018): CiteScore 59.9 SJR 13.456 SNIP 8.761
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85042848951

Research output: Contribution to journalArticleScientificpeer-review

Robust linearized combined metrics of image visual quality

Existing full-reference metrics still do not provide a desirable degree of adequacy to a human visual perception, for evaluation of images with different types and levels of distortions. One reason for this is that it is difficult to incorporate the peculiarities of human visual system in the metrics design. In this paper, a robust approach to full-reference metrics' design is proposed, based on a combination of several existing full-reference metrics. A preliminary linearization (fitting) of the dependence of MOS with respect to the components metrics is performed in order to compensate shortcomings of each component. The proposed method is tested on several known databases, and demonstrate better performance than existing metrics.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Kharkiv National Aerospace University
Contributors: Ieremeiev, O., Lukin, V., Ponomarenko, N., Egiazarian, K.
Publication date: 2018

Host publication information

Title of host publication: Electronic Imaging : Image Processing: Algorithms and Systems XVI
Publisher: Society for Imaging Science and Technology
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Combined metrics, Full-reference metrics, Image visual quality assessment, Robust metrics

Bibliographical note

jufoid=84313
EXT="Ponomarenko, Nikolay"
EXT="Lukin, Vladimir"

Source: Scopus
Source ID: 85052901571

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Standoff alpha radiation detection for hot cell imaging and crime scene investigation

This paper presents the remote detection of alpha contamination in a nuclear facility. Alpha-active material in a shielded nuclear radiation containment chamber has been localized by optical means. Furthermore, sources of radiation danger have been identified in a staged crime scene setting. For this purpose, an electron-multiplying charge-coupled device camera was used to capture photons generated by alpha-induced air scintillation (radioluminescence). The detected radioluminescence was superimposed with a regular photograph to reveal the origin of the light and thereby the alpha radioactive material. The experimental results show that standoff detection of alpha contamination is a viable tool in radiation threat detection. Furthermore, the radioluminescence spectrum in the air is spectrally analyzed. Possibilities of camera-based alpha threat detection under various background lighting conditions are discussed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Helsinki Institute of Physics, STUK - Radiation and Nuclear Safety Authority, European Commission Joint Research Centre, Institute for Transuranium Elements Karlsruhe
Contributors: Kerst, T., Sand, J., Ihantola, S., Peräjärvi, K., Nicholl, A., Hrnecek, E., Toivonen, H., Toivonen, J.
Pages: 429–436
Publication date: 2018
Peer-reviewed: Yes
Early online date: 13 Feb 2018

Publication information

Journal: Optical Review
Volume: 25
Issue number: 3
ISSN (Print): 1340-6000
Ratings: 
  • Scopus rating (2018): CiteScore 1.7 SJR 0.312 SNIP 0.56
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: Alpha radiation, Radioluminescence, Remote detection, Solar blind
Source: Scopus
Source ID: 85041913306

Research output: Contribution to journalArticleScientificpeer-review

Sub-100 ps monolithic diamond Raman laser emitting at 573 nm

We report a compact and efficient picosecond diamond Raman laser at 573 nm wavelength. The laser consists of a 0.5 mm thick single-crystal synthetic diamond coated to form a plane&#x2013;plane laser resonator, and pumped at 532 nm by a frequency-doubled Q-switched microchip laser system. The pump delivers 85 ps pulses at 100 kHz repetition rate at a maximum average power of &#x007E;500 mW. We demonstrate 1st Stokes emission from the diamond Raman laser with maximum power of 175 mW, corresponding to a conversion efficiency of 47&#x0025; and a pulse duration of 71 ps. Substantial pulse shortening is obtained by proper adjustment of the pump spot diameter on the diamond sample. A minimum pulse duration of 39 ps is reported for a conversion efficiency of 36&#x0025; and 150 mW output power. The simplicity of the architecture makes the system highly appealing as a yellow picosecond laser source.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, University of Strathclyde
Contributors: Nikkinen, J., Savitski, V., Reilly, S., Dziechciarczyk, L., Härkönen, A., Kemp, A., Guina, M.
Pages: 981-984
Publication date: 2018
Peer-reviewed: Yes
Early online date: 13 Feb 2018

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 30
Issue number: 11
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2018): CiteScore 5.4 SJR 0.991 SNIP 1.272
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Diamond, Diamond Raman lasers, Laser excitation, Lenses, Microchip lasers, Power generation, Pulsed lasers, Pump lasers, Q-switched lasers, Raman lasers, Stimulated emission, Visible lasers
Source: Scopus
Source ID: 85042062344

Research output: Contribution to journalArticleScientificpeer-review

1.4 µm continuous-wave diamond Raman laser

The longest wavelength (~1.4 µm) emitted by a diamond Raman laser pumped by a semiconductor disk laser (SDL) is reported. The output power of the intracavity-pumped Raman laser reached a maximum of 2.3 W with an optical conversion efficiency of 3.4% with respect to the absorbed diode pump power. Narrow Stokes emission (FWHM <0.1 nm) was attained using etalons to limit the fundamental spectrum to a single etalon peak. Tuning of the Raman laser over >40 nm was achieved via rotation of an intracavity birefringent filter that tuned the SDL oscillation wavelength.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, University of Strathclyde
Contributors: Casula, R., Penttinen, J., Kemp, A. J., Guina, M., Hastie, J. E.
Number of pages: 7
Pages: 31377-31383
Publication date: 11 Dec 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 25
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: VECSEL
Electronic versions: 

Research output: Contribution to journalArticleScientificpeer-review

Bright off-axis directional emission with plasmonic corrugations

In this work, a new plasmonic bulls-eye structure is introduced to efficiently harvest the emitted light from diamond nitrogen vacancy (NV) centers. We show that the presence of a simple metal sub-layer underneath of a conventional bulls-eye antenna, separated by a dielectric layer, results in the spontaneous emission enhancement and increment in out-coupled light intensity. High Purcell factor is accessible in such a structure, which consequently boosts efficiency of the radiated light intensity from the structure. The structure shows considerable enhancement in far-field intensity, about three times higher than that of a one-side corrugated (conventional) optimized structure. In addition, we study for the first time asymmetric structures to steer emitted beams in two-axis. Our results show that spatial off-axial steering over a cone is approachable by introducing optimal asymmetries to grooves and ridges of the structure. The steered light retains a level of intensity even higher than conventional symmetric structures. A high value of directivity of 16 for off-axis steering is reported.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, CRPP, Bilkent University, Nanotechnology Research Center
Contributors: Sattari, H., Rashed, A. R., Ozbay, E., Caglayan, H.
Number of pages: 16
Pages: 30827-30842
Publication date: 11 Dec 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 25
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85038213896

Research output: Contribution to journalArticleScientificpeer-review

Bending reorientational solitons with modulated alignment

While curved waveguides are fundamental elements in photonics, those induced all optically in nonlinear uniform dielectrics tend to be straight. In uniaxial soft matter with a reorientational response, such as nematic liquid crystals (NLCs), light beams in the extraordinary polarization undergo self-focusing via an increase in refractive index and eventually form spatial solitons, i.e., self-induced waveguides. Hereby we investigate the bending of such waveguides by analyzing the trajectory of solitons in NLCs—nematicons—in the presence of a linearly varying transverse orientation of the optic axis. To this extent, we use and compare two approaches: i) a slowly varying (adiabatic) approximation based on momentum conservation of the nematicon in a Hamiltonian sense; and ii) the Frank–Oseen elastic theory coupled with a fully vectorial and nonlinear beam propagation method. The models provide comparable results in such a non-homogeneously oriented uniaxial medium and predict bent soliton paths with either monotonic or non-monotonic curvatures, enabling the design of curved channel waveguides induced by light beams.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Politechnika Warszawska, University of Edinburgh, Department of Electrical Engineering, University of Rome Roma Tre, University “Roma Tre”, Laboratory of Photonics
Contributors: Sala, F. A., Smyth, N. F., Laudyn, U. A., Karpierz, M. A., Minzoni, A. A., Assanto, G.
Number of pages: 8
Pages: 2459-2466
Publication date: 1 Dec 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America B: Optical Physics
Volume: 34
Issue number: 12
ISSN (Print): 0740-3224
Ratings: 
  • Scopus rating (2017): CiteScore 3.8 SJR 0.859 SNIP 0.834
Original language: English
ASJC Scopus subject areas: Statistical and Nonlinear Physics, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85037529512

Research output: Contribution to journalArticleScientificpeer-review

High-Power 1180-nm GaInNAs DBR Laser Diodes

We report high-power 1180-nm GaInNAs distributed Bragg reflector laser diodes with and without a tapered amplifying section. The untapered and tapered components reached room temperature output powers of 655 mW and 4.04 W, respectively. The diodes exhibited narrow linewidth emission with side-mode suppression ratios in the range of 50 dB for a broad range of operating current, extending up to 2 A for the untapered component and 10 A for the tapered component. The high output power is rendered possible by the use of a high quality GaInNAs-based quantum well gain region, which allows for lower strain and better carrier confinement compared with traditional GaInAs quantum wells. The development opens new opportunities for the power scaling of frequency-doubled lasers with emission at yellow–orange wavelengths.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Research group: Surface Science, Okmetic Oyj, Norlase ApS, Denmark Technical University DTU, Optoelectronics Research Centre, Tampere University of Technology
Contributors: Aho, A. T., Viheriälä, J., Korpijärvi, V., Koskinen, M., Virtanen, H., Christensen, M., Uusitalo, T., Lahtonen, K., Valden, M., Guina, M.
Number of pages: 4
Pages: 2023-2026
Publication date: 1 Dec 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 29
Issue number: 23
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2017): CiteScore 5.2 SJR 0.961 SNIP 1.267
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: High power, distributed Bragg reflector laser, frequency doubling, Coating(s)
Electronic versions: 

Bibliographical note

INT=FOT, "Koskinen, Mervi"

Research output: Contribution to journalArticleScientificpeer-review

Sub-50 ps pulses at 620 nm obtained from frequency doubled 1240 nm diamond Raman laser

We report a monolithic 1240 nm diamond Raman laser producing pulses with duration of 42–62 ps at 100 kHz repetition rate, and maximum average power of 246 mW. The Raman laser is formed by a 0.5-mm thick planar diamond, coated on both sides and pumped by ~100 ps pulses from a Q-switched 1064 nm laser. The maximum conversion efficiency from 1064 nm to 1240 nm was about 25%. The 1240 nm signal was frequency-doubled in single-pass configuration through a 10-mm long LBO crystal, enabling generation of pulses with a duration of 29–46 ps at 620 nm. The maximum average power at 620 nm was 128 mW, and the maximum conversion efficiency from 1240 nm to 620 nm was 50%. The Raman laser provides an efficient and flexible way to extend short pulse operation to wavelengths in spectral domains difficult to reach, such as 620 nm and in addition provides a simple pulse shortening mechanisms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics
Contributors: Nikkinen, J., Härkönen, A., Guina, M.
Number of pages: 6
Pages: 30365-30370
Publication date: 27 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 24
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85036471667

Research output: Contribution to journalArticleScientificpeer-review

Generation of Sub-100 ps Pulses at 532, 355, and 266 nm Using a SESAM Q-Switched Microchip Laser

We report a single-frequency semiconductor saturable absorber mirror Q-switched microchip laser system generating sub-100 ps pulses at 532, 355, and 266 nm. The system consists of a 1064 nm Nd:YVO4 master oscillator, Nd:YVO4 power amplifier, and one or two nonlinear crystals for single-pass frequency-conversion to visible and UV. The average output power is about 720 mW at 532 nm, 150 mW at 355 nm and 83 mW at 266 nm for a pulse repetition rate of 100 kHz. At 532 nm the peak power is nearly 80 kW with pulse energy of about 7.2 μJ and spectral width of about 0.026 nm. The optical-to-optical conversion efficiency from 808 to 532 nm is about 8.3%. In comparison with mode-locked picosecond systems, the proposed laser has intrinsically low repetition rate, which is desirable in certain applications. The laser has also inherently narrow spectral width, and high peak power and pulse energy. This unique combination of output parameters could make the system useful in several applications including fluorescence lifetime imaging microscopy, high-accuracy submarine LIDAR, STED microscopy, time-gated Raman spectroscopy two-photon polymerization, diamond Raman laser pumping, photo-acoustic imaging, and micro-machining/marking.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics
Contributors: Nikkinen, J., Härkönen, A., Leino, I., Guina, M.
Number of pages: 4
Pages: 1816-1819
Publication date: 1 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 29
Issue number: 21
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2017): CiteScore 5.2 SJR 0.961 SNIP 1.267
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Microchip lasers, pulsed lasers, Q-switched lasers, UV lasers, visible lasers
Source: Scopus
Source ID: 85030256814

Research output: Contribution to journalArticleScientificpeer-review

Investigating solvent effects on aggregation behaviour, linear and nonlinear optical properties of silver nanoclusters

We herein report the solvent effects on the aggregation, linear and nonlinear optical properties of silver nanoclusters synthesised using three solvents namely; ethanol, acetone and isopropanol. The Ag clusters were characterized using UV–Visible (UV–vis) and photoluminescence (PL) spectroscopy, Fourier transform-infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and open aperture Z-Scan measurements. Density functional theory (DFT) calculations at the B3PW91 level of theory, were done to compute the electric dipole, quadrupole, octapole and hexadecapole moment of mercaptosuccinic acid and mercaptosuccinic acid-Ag9 cluster in three solvents. Linear optical properties show characteristic absorption profile with quantum confinement at different wavelengths for all the three clusters. The Open aperture Z-scan measurement in Ag clusters establishes the optical limiting properties which arise mostly from excited state absorption (ESA) and relatively weak saturable absorption (SA). The nonlinear optical behaviour varies within the three clusters with maximum optical limiting value obtained for the clusters synthesised using acetone. The theoretically computed hyperpolarizabilities together with z-scan measurements establish the solvent effect on the clusters and their potential applications in optical limiting devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, St Teresas’s College, Mahatma Gandhi University, Kolkata Centre, Birla Institute of Technology & Science, Swinburne University of Technology, University of Johannesburg
Contributors: Bhavitha, K. B., Nair, A. K., Perumbilavil, S., Joseph, S., Kala, M. S., Saha, A., Narayanan, R. A., Hameed, N., Thomas, S., Oluwafemi, O. S., Kalarikkal, N.
Number of pages: 11
Pages: 695-705
Publication date: 1 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 73
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2017): CiteScore 3.7 SJR 0.592 SNIP 1.054
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Aggregation behaviour, DFT, Linear optical properties, Non linear optical properties, Silver nanoclusters, Solvent effects
Source: Scopus
Source ID: 85030173026

Research output: Contribution to journalArticleScientificpeer-review

Paraxial light beams in structured anisotropic media

We discuss the paraxial approximation for optical waves propagating in a uniaxial anisotropic medium inhomogeneously twisted on the plane normal to the wave vector, with the latter being parallel to one of the two principal axes normal to the optic axis. Such geometry implies a continuous power transfer between the ordinary and extraordinary components, regardless of the input beam polarization. We pinpoint that this peculiar feature, generalizable to any inhomogeneous linear birefringent material, strongly affects the application of the paraxial approximation due to the simultaneous presence of two different phase velocities. We eventually show that a local coordinate transformation permits a correct application of the paraxial approximation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Nonlinear Optics, Univ Porto, Universidade do Porto, Fac Med, Dept Med Imaging
Contributors: Jisha, C. P., Alberucci, A.
Number of pages: 6
Pages: 2019-2024
Publication date: 1 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America A: Optics and Image Science, and Vision
Volume: 34
Issue number: 11
ISSN (Print): 1084-7529
Ratings: 
  • Scopus rating (2017): CiteScore 3.5 SJR 0.687 SNIP 1.098
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Computer Vision and Pattern Recognition
Source: Scopus
Source ID: 85033368214

Research output: Contribution to journalArticleScientificpeer-review

Diode-pumped Tm: KY(WO4)2 laser passively modelocked with a GaSb-SESAM

We present the first diode-pumped modelocked thulium (Tm3+) laser based on a double-tungstate crystalline gain material. The solid-state laser consists of a Tm:KY(WO4)2 crystal as gain medium and a GaInSb/GaSb quantum well saturable absorber for self-starting passive mode locking. The laser is pumped by a multi-mode fiber-coupled laser diode at a wavelength of 793 nm. An average output power of 202 mW is achieved at a center wavelength of 2032 nm. Pulses with duration of 3 ps are generated at a repetition rate of 139.6 MHz. We also report on the first noise evaluation of a modelocked solid-state laser operating in the 2-µm wavelength range. We measured a timing jitter of sub-100 fs and a relative intensity noise of only 0.04% (frequency range from 500 Hz to 1 MHz).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Université de Neuchâtel, Belarusian National Technical University, RefleKron Ltd
Contributors: Gaponenko, M., Wittwer, V. J., Härkönen, A., Suomalainen, S., Kuleshov, N., Guina, M., Südmeyer, T.
Number of pages: 7
Pages: 25760-25766
Publication date: 16 Oct 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 21
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85031940564

Research output: Contribution to journalArticleScientificpeer-review

High power VECSEL prototype emitting at 625 nm

We demonstrate an OP-VECSEL prototype emitting more than 6W of CW output power at 625 nm. We employ dilute nitride (GaInNAs) quantum wells emitting fundamentally at 1250 nm together with intracavity frequency doubling.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics
Contributors: Penttinen, J., Leinonen, T., Rantamäki, A., Korpijärvi, V., Kantola, E., Guina, M.
Number of pages: 3
Publication date: Oct 2017

Host publication information

Title of host publication: Advanced Solid State Lasers 2017 : Nagoya, Aichi Japan 1–5 October 2017
Publisher: Optical Society of America
Article number: ATu1A.8
ISBN (Electronic): 978-0-9600380-7-7
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: VECSEL
Electronic versions: 
URLs: 

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Sparse superresolution phase retrieval from phase-coded noisy intensity patterns

We consider a computational superresolution inverse diffraction problem for phase retrieval from phase-coded intensity observations. The optical setup includes a thin lens and a spatial light modulator for phase coding. The designed algorithm is targeted on an optimal solution for Poissonian noisy observations. One of the essential instruments of this design is a complex-domain sparsity applied for complex-valued object (phase and amplitude) to be reconstructed. Simulation experiments demonstrate that good quality imaging can be achieved for high-level of the superresolution with a factor of 32, which means that the pixel of the reconstructed object is 32 times smaller than the sensor's pixel. This superresolution corresponds to the object pixel as small as a quarter of the wavelength.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI
Contributors: Katkovnik, V., Egiazarian, K.
Publication date: 1 Sep 2017
Peer-reviewed: Yes

Publication information

Journal: Optical Engineering
Volume: 56
Issue number: 9
Article number: 094103
ISSN (Print): 0091-3286
Ratings: 
  • Scopus rating (2017): CiteScore 2.2 SJR 0.424 SNIP 0.81
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Engineering(all)
Keywords: complex-domain sparsity, discrete optical signal processing, phase imaging, phase retrieval, superresolution
Electronic versions: 
Source: Scopus
Source ID: 85029753126

Research output: Contribution to journalArticleScientificpeer-review

Tunable narrow-linewidth VECSELs for atomic and molecular physics

General information

Publication status: Published
Organisations: Photonics, National Institute of Standards and Technology, Time and Frequency Division, Boulder, Colorado
Contributors: Penttinen, J., Leinonen, T., Burd, S., Guina, M.
Publication date: 23 Aug 2017
Peer-reviewed: Unknown
Event: Paper presented at The 25th Colloquium on High-Resolution Molecular Spectroscopy, Helsinki, Finland.
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: VECSEL
Electronic versions: 

Research output: Other conference contributionPaper, poster or abstractScientific

VECSEL: a versatile laser tool for ion trappers

General information

Publication status: Published
Organisations: Photonics, National Institute of Standards and Technology, Time and Frequency Division, Boulder, Colorado
Contributors: Penttinen, J., Leinonen, T., Burd, S. C., Allcock, D. T., Leibfried , D., Guina, M.
Publication date: 16 Aug 2017
Peer-reviewed: Unknown
Event: Paper presented at 1st North American Conference on Trapped Ions, Boulder, United States.
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: VECSEL
Electronic versions: 

Research output: Other conference contributionPaper, poster or abstractScientific

Computational super-resolution phase retrieval from multiple phase-coded diffraction patterns: Simulation study and experiments

In this paper, we consider computational super-resolution inverse diffraction phase retrieval. The optical setup is lensless, with a spatial light modulator for aperture phase coding. The paper is focused on experimental tests of the super-resolution sparse phase amplitude retrieval algorithm. We start from simulations and proceed to physical experiments. Both simulation tests and experiments demonstrate good-quality imaging for super-resolution with a factor of 4 and a serious advantage over diffraction-limited resolution as defined by Abbe’s criterion.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI, Department of Photonics and Optical Information Technology, ITMO University
Contributors: Katkovnik, V., Shevkunov, I., Petrov, N. V., Egiazarian, K.
Number of pages: 9
Pages: 786-794
Publication date: 20 Jul 2017
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 4
Issue number: 7
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2017): CiteScore 11.9 SJR 4.602 SNIP 2.811
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Discrete optical signal processing, Image processing, Noise in imaging systems, Phase retrieval, Superresolution
Source: Scopus
Source ID: 85025162894

Research output: Contribution to journalArticleScientificpeer-review

Chiral near-field manipulation in Au-GaAs hybrid hexagonal nanowires

We demonstrate the control of enhanced chiral field distribution at the surface of hybrid metallo-dielectric nanostructures composed of self-assembled vertical hexagonal GaAs-based nanowires having three of the six sidewalls covered with Au. We show that weakly-guided modes of vertical GaAs nanowires can generate regions of high optical chirality that are further enhanced by the break of the symmetry introduced by the gold layer. Changing the angle of incidence of a linearly polarized plane wave it is possible to tailor and optimize the maps of the optical chirality in proximity of the gold plated walls. The low cost feasibility of the sample combined to the simple control by using linearly polarized light and the easy positioning of chiral molecules by functionalization of the gold plates make our proposed scheme very promising for enhanced enantioselective spectroscopy applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Sapienza University
Contributors: Petronijevic, E., Centini, M., Belardini, A., Leahu, G., Hakkarainen, T., Sibilia, C.
Number of pages: 10
Pages: 14148-14157
Publication date: 26 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 13
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85021225855

Research output: Contribution to journalArticleScientificpeer-review

Dynamic speckle analysis with smoothed intensity-based activity maps

Pointwise intensity-based algorithms are the most popular algorithms in dynamic laser speckle measurement of physical or biological activity. The output of this measurement is a two-dimensional map which qualitatively separates regions of higher or lower activity. In the paper, we have proposed filtering of activity maps to enhance visualization and to enable quantitative determination of activity time scales. As a first step, we have proved that the severe spatial fluctuations within the map resemble a signal-dependent noise. As a second step, we have illustrated implementation of the proposed idea by applying filters to non-normalized and normalized activity estimates derived from synthetic and experimental data. Statistical behavior of the estimates has been analyzed to choose the filter parameters, and substantial narrowing of the probability density functions of the estimates has been achieved after the filtering. The filtered maps exhibit an improved contrast and allowed for quantitative description of activity.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: 3D MEDIA, Bulgarian Academy of Sciences, Korea Electronics Technology Institute
Contributors: Stoykova, E., Berberova, N., Kim, Y., Nazarova, D., Ivanov, B., Gotchev, A., Hong, J., Kang, H.
Number of pages: 11
Pages: 55-65
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: Optics and Lasers in Engineering
Volume: 93
ISSN (Print): 0143-8166
Ratings: 
  • Scopus rating (2017): CiteScore 6.2 SJR 1.018 SNIP 1.919
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Mechanical Engineering, Electrical and Electronic Engineering
Keywords: Digital image processing, Dynamic speckle, Speckle, Speckle metrology
Source: Scopus
Source ID: 85010222438

Research output: Contribution to journalArticleScientificpeer-review

Enhanced self-mixing interferometry based on volume Bragg gratings and laser diodes emitting at 405-nm wavelengths

Self-mixing interferometry (SMI) represents a robust, self-aligned technique for metrology applications. Recently, it has been shown that the detection of the frequency-modulated (FM) signal enhances the conventional SMI signal based on the amplitude modulation. Here, an all-optical, simple and effective alternative approach to detect the FM self-mixing signal is presented. We demonstrate the enhanced self-mixing approach using a laser diode emitting at 405 nm and a volume Bragg grating (VBG) to map frequency to intensity modulations for further optical detection. Our approach overcomes the spectral range limitation of the edge filtering approach based on molecular absorption filters, since the VBGs can be fabricated at any spectral range.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Applied Optics, Department of Electrical Engineering
Contributors: Contreras, V., Toivonen, J., Martinez, H.
Number of pages: 3
Pages: 2221-2223
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 42
Issue number: 11
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2017): CiteScore 7.3 SJR 1.79 SNIP 1.572
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85020460315

Research output: Contribution to journalArticleScientificpeer-review

Broadband Anti-reflective Coatings for Multi-junction Solar Cells

General information

Publication status: Published
Organisations: Facilities and Infrastructure, Photonics, Research group: ORC
Contributors: Reuna, J., Polojärvi, V. (ed.), Aho, T. (ed.), Aho, A. (ed.), Isoaho, R. (ed.), Tukiainen, A. (ed.), Guina, M. (ed.)
Number of pages: 1
Pages: 1
Publication date: 29 May 2017
Peer-reviewed: Unknown
Event: Paper presented at Optics and Photonics days 2017, Oulu, Finland.
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: anti-reflective coating, thin films, multi-junction solar cell, material characterization

Bibliographical note

Poster and an abstract for Optics and Photonics days 2017.

Research output: Other conference contributionPaper, poster or abstractScientific

Reply to "comment on 'Spatial optical solitons in highly nonlocal media"'

In their Comment, Petrović et al. claim that some of the results previously published by us on the use of the "accessible soliton" model of Snyder et al. are incorrect, and they claim that the correct results were published elsewhere. In order to give our perspective on the problem, we discuss and clarify some of the existing literature and our own work on the subject, underlining the importance of the accessible soliton approximation and its recent improvements towards enabling a general understanding of light self-confinement in highly nonlocal media, both quantitatively and qualitatively.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Univ Porto, Universidade do Porto, Fac Med, Dept Med Imaging, University of Edinburgh, University “Roma Tre”, CNR-ISC, Institute for Complex Systems
Contributors: Alberucci, A., Jisha, C. P., Smyth, N. F., Assanto, G.
Publication date: 25 May 2017
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 95
Issue number: 5
Article number: 057802
ISSN (Print): 2469-9926
Ratings: 
  • Scopus rating (2017): CiteScore 8.1 SJR 1.288 SNIP 1.014
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85026922362

Research output: Contribution to journalArticleScientificpeer-review

Anisotropic tapered polarization-maintaining large mode area optical fibers

We demonstrate a novel type of tapered large mode area polarization-maintaining fiber. These birefringent fibers have an elliptical inner cladding and a core diameter that increases adiabatically from 8 μm to 70 μm. The polarization maintaining ability of the fiber samples was investigated by measuring the spatial distribution of polarization beat length by using optical frequency-domain reflectometry. The measurements show a clear correlation between the birefringence and the fiber core size, resulting in a modest 10-15% variation in polarization beat length along the fiber. There is no significant coupling of polarization modes or transverse modes in the tested fibers and, therefore, the linear polarization state of propagating light is preserved.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Russian Quantum Center, Institute of Radio Engineering and Electronics of the Russian Academy of Sciences, Moscow Institute of Physics and Technology
Contributors: Ustimchik, V. E., Rissanen, J., Popov, S. M., Chamorovskii, Y. K., Nikitov, S. A.
Number of pages: 11
Pages: 10693-10703
Publication date: 1 May 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 9
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 

Bibliographical note

INT=fot,"Rissanen, J."

Source: Scopus
Source ID: 85018264751

Research output: Contribution to journalArticleScientificpeer-review

Nonlinear imaging of nanostructures using beams with binary phase modulation

We demonstrate nonlinear microscopy of oriented nanowires using excitation beams with binary phase modulation. A simple and intuitive optical scheme comprising a spatial light modulator gives us the possibility to control the phase across an incident Hermite-Gaussian beam of order (1,0) (HG10 mode). This technique allows us to gradually vary the spatial distribution of the longitudinal electric fields in the focal volume, as demonstrated by second-harmonic generation from vertically-aligned GaAs nanowires. These results open new opportunities for the full control of polarization in the focal volume to enhance light interaction with nanostructured materials.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research area: Optics, Research group: Nonlinear Optics, Research group: Nonlinear Optics, Aalto University
Contributors: Turquet, L., Kakko, J. P., Jiang, H., Isotalo, T. J., Huhtio, T., Niemi, T., Kauppinen, E., Lipsanen, H., Kauranen, M., Bautista, G.
Number of pages: 8
Pages: 10441-10448
Publication date: 1 May 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 9
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85018298162

Research output: Contribution to journalArticleScientificpeer-review

Universal scaling relations for the energies of many-electron Hooke atoms

A three-dimensional harmonic oscillator consisting of N≥2 Coulomb-interacting charged particles, often called a (many-electron) Hooke atom, is a popular model in computational physics for, e.g., semiconductor quantum dots and ultracold ions. Starting from Thomas-Fermi theory, we show that the ground-state energy of such a system satisfies a nontrivial relation: Egs=ωN4/3fgs(βN1/2), where ω is the oscillator strength, β is the ratio between Coulomb and oscillator characteristic energies, and fgs is a universal function. We perform extensive numerical calculations to verify the applicability of the relation. In addition, we show that the chemical potentials and addition energies also satisfy approximate scaling relations. In all cases, analytic expressions for the universal functions are provided. The results have predictive power in estimating the key ground-state properties of the system in the large-N limit, and can be used in the development of approximative methods in electronic structure theory.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Quantum Control and Dynamics, Research area: Computational Physics, ICIMAF
Contributors: Odriazola, A., Solanpää, J., Kylänpää, I., González, A., Räsänen, E.
Publication date: 19 Apr 2017
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 95
Issue number: 4
Article number: 042511
ISSN (Print): 2469-9926
Ratings: 
  • Scopus rating (2017): CiteScore 8.1 SJR 1.288 SNIP 1.014
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

INT=fys,"Ordiazola, A."

Source: Scopus
Source ID: 85017581330

Research output: Contribution to journalArticleScientificpeer-review

Halogen bonding stabilizes a cis-azobenzene derivative in the solid state: A crystallographic study

Crystals of trans- and cis-isomers of a fluorinated azobenzene derivative have been prepared and characterized by single-crystal X-ray diffraction. The presence of F atoms on the aromatic core of the azobenzene increases the lifetime of the metastable cis-isomer, allowing single crystals of the cis-azobenzene to be grown. Structural analysis on the cis-azobenzene, complemented with density functional theory calculations, highlights the active role of the halogen-bond contact (N...I synthon) in promoting the stabilization of the cis-isomer. The presence of a long aliphatic chain on the azobenzene unit induces a phase segregation that stabilizes the molecular arrangement for both the trans- and cis-isomers. Due to the rarity of cis-azobenzene crystal structures in the literature, our paper makes a step towards understanding the role of non-covalent interactions in driving the packing of metastable azobenzene isomers. This is expected to be important in the future rational design of solid-state, photoresponsive materials based on halogen bonding. We show by single-crystal X-ray diffraction studies and computational analysis that halogen bonding can stabilize a metastable cis-azobenzene derivative in the solid state.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Supramolecular photochemistry, Research group: Chemistry & Advanced Materials, Politecnico di Milano, Aalto University
Contributors: Saccone, M., Siiskonen, A., Fernandez-Palacio, F., Priimägi, A., Terraneo, G., Resnati, G., Metrangolo, P.
Number of pages: 7
Pages: 227-233
Publication date: 1 Apr 2017
Peer-reviewed: Yes

Publication information

Journal: ACTA CRYSTALLOGRAPHICA SECTION B : STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS
Volume: 73
Issue number: 2
ISSN (Print): 2052-5192
Ratings: 
  • Scopus rating (2017): CiteScore 6.1 SJR 1.654 SNIP 1.602
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Metals and Alloys, Materials Chemistry
Keywords: azobenzene, halogen bonding, isomerization
Source: Scopus
Source ID: 85017113549

Research output: Contribution to journalArticleScientificpeer-review

Simulation studies of DFB laser longitudinal structures for narrow linewidth emission

The paper presents simulation studies targeting high-power narrow-linewidth emission from semiconductor distributed feedback (DFB) lasers. The studies contain analytic and numerical calculations of emission linewidth, side mode suppression ratio and output power for DFB lasers without phase shifts and with 1 × λ/ 4 and 2 × λ/ 8 phase shifts, taking into account the grating and facets reflectivities, the randomness of the spontaneous emission and the longitudinal photon and carrier density distributions in the laser cavity. Single device structural parameter optimization is generally associated with a trade-off between achieving a narrow linewidth and a high output power. Correlated optimization of multiple structural parameters enables the evaluation of achievable ranges of narrow linewidth and high power combinations. Devices with long cavities and low grating coupling coefficients, κ (keeping κL values below the levels that promote re-broadening), with AR-coated facets and with a distributed phase-shift have the flattest longitudinal photon and carrier density distributions. This flatness enables stable single-longitudinal-mode operation with high side-mode-suppression ratio up to high injection current densities, which facilitates narrow linewidths and high output powers. The results reported in the paper indicate that Master-Oscillator Power-Amplifier laser structures are needed for achieving W-level high-powers with sub-MHz linewidths because most single-cavity DFB laser structural variations that reduce the linewidth also limit the achievable output power in single-mode operation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Semiconductor Technology and Applications
Contributors: Virtanen, H., Uusitalo, T., Dumitrescu, M.
Number of pages: 13
Publication date: 23 Mar 2017
Peer-reviewed: Yes

Publication information

Journal: Optical and Quantum Electronics
Volume: 49
Issue number: 4
Article number: 160
ISSN (Print): 0306-8919
Ratings: 
  • Scopus rating (2017): CiteScore 1.8 SJR 0.353 SNIP 0.631
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Distributed feedback laser, High power, Narrow linewidth
Electronic versions: 
URLs: 
Source: Scopus
Source ID: 85016097411

Research output: Contribution to journalArticleScientificpeer-review

33 W continuous output power semiconductor disk laser emitting at 1275 nm

We demonstrate a semiconductor disk laser emitting at 1275nm, employing a wafer fused AlInGaAs/InP-AlAs/GaAs gain mirror. A built-in Au-reflector was used to reflect the pump light not absorbed in a single pass through the gain chip active region. The laser exhibited an output power of 33 W for a pump spot with a diameter of 0.86 mm, an output coupler of 2.5%, and a heat-sink temperature of -5°C. When the temperature of the heat-sink was increased to 15°C, the maximum output power reached a value of ∼24 W. The study reveals that the wafer fused gain mirrors have a high optical quality and good uniformity enabling scaling of the maximum emitted power with the diameter of the pump spot, i.e. at least up to the 1 mm diameter.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Semiconductor Technology and Applications, II-VI Laser Enterprise GmbH, RTI-Research S.A., CRPP
Contributors: Leinonen, T., Iakovlev, V., Sirbu, A., Kapon, E., Guina, M.
Number of pages: 6
Pages: 7008-7013
Publication date: 20 Mar 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 6
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85015888267

Research output: Contribution to journalArticleScientificpeer-review

Diode-pumped mode-locked Tm: LuAG laser at 2 μm based on GaSb-SESAM

Mode-locking of a directly diode-pumped Tm:LuAG laser is demonstrated using GaSb-based semiconductor saturable absorber mirrors (SESAMs). Stable and self-starting mode-locked operation was realized, generating pulses as short as 13.6 ps at 2024 nm with a maximum output power of 98 mW. Two GaInAs-based SESAMs were used for comparison with the operation based upon the use of the GaSb SESAM; in this case, longer pulses with durations of 27 ps and 34 ps were obtained under the same experimental conditions. Our work sets a new record in pulse duration for mode-locked Tm:LuAG lasers and confirms that lattice-matched GaSb-based SESAMs are beneficial for mode-locked solid-state lasers in the 2 μm range.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Semiconductor Technology and Applications, Qingdao Univ, Qingdao University, Shandong University, Shandong Univ, Key Lab Photon Mat & Technol, School of Information Science and Engineering, State Key Laboratory of Crystal Material, Shandong Jianzhu University, German Aerospace Center, Shanghai Institute of Ceramics Chinese Academy of Sciences
Contributors: Luan, C., Yang, K., Zhao, J., Zhao, S., Li, T., Zhang, H., He, J., Song, L., Dekorsy, T., Guina, M., Zheng, L.
Number of pages: 4
Pages: 839-842
Publication date: 15 Feb 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 42
Issue number: 4
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2017): CiteScore 7.3 SJR 1.79 SNIP 1.572
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85013403108

Research output: Contribution to journalArticleScientificpeer-review

Spin-orbit interactions in optically active materials

We investigate the inherent influence of light polarization on the intensity distribution in anisotropic media undergoing a local inhomogeneous rotation of the principal axes. Whereas, in general, such a configuration implies a complicated interaction between the geometric and the dynamic phase, we show that, in a medium showing an inhomogeneous circular birefringence, the geometric phase vanishes. Due to the spin-orbit interaction, the two circular polarizations perceive reversed spatial distribution of the dynamic phase. Based on this effect, polarization-selective lenses, waveguides, and beam deflectors are proposed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Nonlinear Optics, Univ Porto, Universidade do Porto, Fac Med, Dept Med Imaging
Contributors: Jisha, C. P., Alberucci, A.
Number of pages: 4
Pages: 419-422
Publication date: 1 Feb 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 42
Issue number: 3
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2017): CiteScore 7.3 SJR 1.79 SNIP 1.572
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85011650203

Research output: Contribution to journalArticleScientificpeer-review

Very high dose electron irradiation effects on photoluminescence from GaInNAs/GaAs quantum wells grown by molecular beam epitaxy

The effects of 7 MeV electron irradiation at very high doses of 2×1017 and 1.5×1018electrons/cm2 and subsequent rapid thermal annealing on photoluminescence from a strain-compensated GaInAsN/GaAsN/GaAs quantum well structure are investigated. A large additional blueshift of photoluminescence has been observed from the lower-dose irradiated sample as compared to the non-irradiated one when annealed after the irradiation. This additional blueshift will become considerably reduced by an ageing effect, which occurs already at room temperature. The mechanism causing the additional blueshift of photoluminescence and its reduction is qualitatively assigned to metastable complex defects promoted by electron irradiation in the nitrogen containing layers. No such additional blueshift of photoluminescence under the thermal treatment has been observed in the higher-dose irradiated sample.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, National Institute for Research and Development in Microtechnologies Romania, Faculty of Exact Sciences and Engineering, Hyperion University
Contributors: Pavelescu, E. M., Bălţăţeanu, N., Spânulescu, S. I., Arola, E.
Number of pages: 5
Pages: 361-365
Publication date: 1 Feb 2017
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 64
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2017): CiteScore 3.7 SJR 0.592 SNIP 1.054
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Dilute nitrides, Electron irradiation, Photoluminescence

Bibliographical note

EXT="Pavelescu, E. M."

Source: Scopus
Source ID: 85008334984

Research output: Contribution to journalArticleScientificpeer-review

Polarization resolved photoluminescence in GaAs1−xBix/GaAs quantum wells

We have investigated polarization resolved photoluminescence (PL) of GaAs1−xBix/GaAs quantum wells (QWs) with different Bi concentrations in the dilute range (x1−xBix/GaAs QWs increase with the increase of Bi concentration. Excitonic gex-factors of 4 and 10 were obtained at 15 T for as-grown GaAs1−xBix/GaAs QWs with 1.2% and 1.9% Bi concentration, respectively. These values evidence an important increase of electron and hole g-factors with the introduction of Bi in GaAs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, Universid ade Federal de São Carlos, University of Nottingham, Universidade Federal de São Carlos
Contributors: Balanta, M. A. G., Orsi Gordo, V., Carvalho, A. R. H., Puustinen, J., Alghamdi, H. M., Henini, M., Galeti, H. V. A., Guina, M., Galvão Gobato, Y.
Number of pages: 4
Pages: 49-52
Publication date: Feb 2017
Peer-reviewed: Yes
Early online date: 13 Oct 2016

Publication information

Journal: Journal of Luminescence
Volume: 182
ISSN (Print): 0022-2313
Ratings: 
  • Scopus rating (2017): CiteScore 5 SJR 0.694 SNIP 1.074
Original language: English
ASJC Scopus subject areas: Biophysics, Chemistry(all), Atomic and Molecular Physics, and Optics, Biochemistry, Condensed Matter Physics
Source: Scopus
Source ID: 84992707527

Research output: Contribution to journalArticleScientificpeer-review

Architectures and codecs for real-time light field streaming

Light field 3D displays represent a major step forward in visual realism, providing glasses-free spatial vision of real or virtual scenes. Applications that capture and process live imagery have to process data captured by potentially tens to hundreds of cameras and control tens to hundreds of projection engines making up the human perceivable 3D light field using a distributed processing system. The associated massive data processing is difficult to scale beyond a specific number and resolution of images, limited by the capabilities of the individual computing nodes. The authors therefore analyze the bottlenecks and data flow of the light field conversion process and identify possibilities to introduce better scalability. Based on this analysis they propose two different architectures for distributed light field processing. To avoid using uncompressed video data all along the processing chain, the authors also analyze how the operation of the proposed architectures can be supported by existing image/video codecs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: 3D MEDIA, Holografika, Nokia
Contributors: Kovács, P. T., Zare, A., Balogh, T., Bregovic, R., Gotchev, A.
Publication date: 1 Jan 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Imaging Science and Technology
Volume: 61
Issue number: 1
Article number: 010403
ISSN (Print): 1062-3701
Ratings: 
  • Scopus rating (2017): CiteScore 0.9 SJR 0.237 SNIP 0.718
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Chemistry(all), Atomic and Molecular Physics, and Optics, Computer Science Applications
Source: Scopus
Source ID: 85016298177

Research output: Contribution to journalArticleScientificpeer-review

All-optical guided-wave random laser in nematic liquid crystals

Spatial solitons can affect and enhance random lasing in optically-pumped dye-doped nematic liquid crystals. Upon launching two collinear beams in the sample, the first to pump the fluorescent guest molecules and the second to induce a reorientational soliton, strikingly the second beam not only guides the emitted photons in the soliton waveguide, but also enhances the lasing efficiency and modulates its spectral width. By altering the scattering paths of the emitted photons, the soliton also contributes to the selection of the lasing modes, as further confirmed by the observed kinks in the input/output characteristics. These experimental results demonstrate that random lasing can be efficiently controlled by a light beam which does not interact with the gain molecules, opening a route towards light-controlled random lasers.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University “Roma Tre”, University of Southampton, United Kingdom, Case Western Reserve University, Nonlinear Optics and OptoElectronics Lab
Contributors: Perumbilavil, S., Piccardi, A., Buchnev, O., Kauranen, M., Strangi, G., Assanto, G.
Number of pages: 8
Pages: 4672-4679
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 25
Issue number: 5
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2017): CiteScore 6.7 SJR 1.519 SNIP 1.562
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic versions: 
Source: Scopus
Source ID: 85014546572

Research output: Contribution to journalArticleScientificpeer-review

BM3D-HVS: Content-Adaptive denoising for improved visual quality

We introduce a content-Adaptive approach to image denoising where the filter design is based on mean opinion scores (MOSs) from preliminary experiments with volunteers who evaluated the quality of denoised image fragments. This allows to tune the filter parameters so to improve the perceptual quality of the output image, implicitly accounting for the peculiarities of the human visual system (HVS). A modification of the BM3D image denoising filter (Dabov et al., IEEE TIP, 2007), namely BM3DHVS, is proposed based on this framework. We show that it yields a higher visual quality than the conventional BM3D. Further, we have also analyzed the MOSs against popular full-reference visual quality metrics such as SSIM (Wang et al., IEEE TIP, 2004), its extension FSIM (Zhang et al., IEEE TIP, 2011), and the noreference IL-NIQE (Zhang et al., IEEE TIP, 2015) over each image fragment. Both the Spearman and the Kendall rank order correlation show that these metrics do not correspond well to the human perception. This calls for new visual quality metrics tailored for the benchmarking and optimization of image denoising methods.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Kharkiv National Aerospace University, Noiseless Imaging Ltd
Contributors: Egiazarian, K., Danielyan, A., Ponomarenkoa, N., Foia, A., Ieremeiev, O., Lukin, V.
Number of pages: 8
Pages: 48-55
Publication date: 2017

Host publication information

Title of host publication: Image Processing: Algorithms and Systems XV

Publication series

Name: Electronic Imaging
ISSN (Print): 2470-1173
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics

Bibliographical note

EXT="Danielyan, Aram"
EXT="Lukin, Vladimir"
jufoid=84313

Source: Scopus
Source ID: 85040604686

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Design of a 25 MWe Solar Thermal Power Plant in Iran with Using Parabolic Trough Collectors and a Two-Tank Molten Salt Storage System

Nowadays, parabolic trough solar thermal plants are prevalent around the world. In different areas concerning the amount of solar radiation, their standard size is approximately between 20 and 100 MWe. Certainly, the right size of the solar field is the first selection with regard to nominal electrical power. A vast area will be economically unreasonable whereas a small area will mainly cause the power plant to operate at the part-load condition. This paper presents an economic modeling of a solar parabolic trough plant, operating at 25 MWe in Yazd, Iran. The varying types of collector dimensions have been investigated; then, by selecting autumnal equinox (22 September) at 12:00 PM as the design point, thermal performance of the solar power plant has been featured annually, in all conditions. The total operating time of the power plant is about 1726 hours (1248 hours in full-load condition). In the end, the effect of thermal storage tanks has been analyzed to save extra solar heat and use it at nights in hot months. By implementing a storage system, the total operating time will be increased to 3169 hours (2785 in full-load condition). Moreover, 7974 GJ useful thermal energy can be obtained from the solar field and storage system.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Automation and Hydraulic Engineering, University of Guilan
Contributors: Kordmahaleh, A. A., Naghashzadegan, M., Javaherdeh, K., Khoshgoftar, M.
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: International Journal of Photoenergy
Volume: 2017
Article number: 4210184
ISSN (Print): 1110-662X
Ratings: 
  • Scopus rating (2017): CiteScore 2.8 SJR 0.341 SNIP 0.605
Original language: English
ASJC Scopus subject areas: Chemistry(all), Atomic and Molecular Physics, and Optics, Renewable Energy, Sustainability and the Environment, Materials Science(all)
Electronic versions: 

Bibliographical note

INT=aut,"Kordmahaleh, Aidin Alinezhad"

Source: Scopus
Source ID: 85038904387

Research output: Contribution to journalArticleScientificpeer-review

Evaluation of long-term post process inactivation of bioleaching microorganisms

The H2020 BioMOre project (www.biomore.info, Grant Agreement #642456) tests the feasibility of in-situ bioleaching of copper in deep subsurface deposits in the Rudna Mine, Poland. Copper is leached using biologically produced ferric iron solution, which is recycled back to the in-situ reactor after re-oxidation by iron-oxidizing bacteria (IOB). From a post operational point of view, it is important that the biological processes applied during the operation can be controlled and terminated. Our goal was to determine the possibility to use natural saline mine water for the inactivation of introduced IOB remaining in the in-situ reactor after completion of the leaching process of the Kupferschiefer ore. Aerobic and anaerobic microcosms containing acid-leached (pH 2) sandstone or black shale from the Kupferschiefer in the Rudna mine were further leached with the effluent from an iron-oxidizing bioreactor, at a temperature of 30°C, for 10 days, to simulate in-situ leaching. After the removal of the iron solution, residing IOB were inactivated by filling the microcosms with saline water (65 g L-1 Cl-) originating from the mine. The saline water completely inactivated the IOB and the naturally occurring saline water of the mine can be used for long-term post process inactivation of bioleaching microorganisms.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Chemistry and Bioengineering, Research group: Bio- and Circular Economy, VTT Technical Research Centre of Finland
Contributors: Bomberg, M., Miettinen, H., Wahlström, M., Kaartinen, T., Ahoranta, S., Lakaniemi, A., Kinnunen, P.
Number of pages: 4
Pages: 57-60
Publication date: 2017

Host publication information

Title of host publication: 22nd International Biohydrometallurgy Symposium
Publisher: Trans Tech Publications Ltd
ISBN (Print): 9783035711806

Publication series

Name: Solid State Phenomena
Volume: 262 SSP
ISSN (Electronic): 1662-9779
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Materials Science(all), Condensed Matter Physics
Keywords: In situ bioleaching, Inactivation, Iron-oxidizing bacteria

Bibliographical note

EXT="Kinnunen, Päivi"

Source: Scopus
Source ID: 85028980141

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Full-reference metrics multidistortional analysis

This paper is devoted to analysis and further improvement of full-reference metrics of image visual quality. The effectiveness of a metric is characterized by the rank correlation factors between the obtained array of mean opinion scores (MOS) and the corresponding array of given metric values. This allows to determine the correspondence of a considered metric to a human visual system (HVS). Results obtained on the database TID2013 show that Spearman correlation for the best existing metrics (PSNRHMA, FSIM, SFF, etc.) does not exceed 0.85. In this paper, extended verification tools that allow to detect the shortcomings of the metrics taking into account combined distortions is proposed. An example for further improvement of the PSNRHMA metric is presented.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Kharkiv National Aerospace University
Contributors: Ieremeiev, O., Lukin, V., Ponomarenko, N., Egiazarian, K.
Number of pages: 9
Pages: 27-35
Publication date: 2017

Host publication information

Title of host publication: Image Processing: Algorithms and Systems XV

Publication series

Name: Electronic Imaging
ISSN (Print): 2470-1173
ASJC Scopus subject areas: Computer Graphics and Computer-Aided Design, Computer Science Applications, Human-Computer Interaction, Software, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Full-reference metrics, Image visual quality assessment, Metrics analysis, Metrics verification, Multiple distortions

Bibliographical note

jufoid=84313
EXT="Ponomarenko, Nikolay"
EXT="Lukin, Vladimir"

Source: Scopus
Source ID: 85040625876

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

High-resolution coded-aperture design for compressive X-ray tomography using low resolution detectors

One of the main challenges in Computed Tomography (CT) is obtaining accurate reconstructions of the imaged object while keeping a low radiation dose in the acquisition process. In order to solve this problem, several researchers have proposed the use of compressed sensing for reducing the amount of measurements required to perform CT. This paper tackles the problem of designing high-resolution coded apertures for compressed sensing computed tomography. In contrast to previous approaches, we aim at designing apertures to be used with low-resolution detectors in order to achieve super-resolution. The proposed method iteratively improves random coded apertures using a gradient descent algorithm subject to constraints in the coherence and homogeneity of the compressive sensing matrix induced by the coded aperture. Experiments with different test sets show consistent results for different transmittances, number of shots and super-resolution factors.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing
Contributors: Mojica, E., Pertuz, S., Arguello, H.
Pages: 103-109
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Communications
Volume: 404
ISSN (Print): 0030-4018
Ratings: 
  • Scopus rating (2017): CiteScore 3.5 SJR 0.614 SNIP 0.933
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Physical and Theoretical Chemistry, Electrical and Electronic Engineering
Keywords: Coded apertures, Compressive sensing, Computed tomography, Super-resolution
Source: Scopus
Source ID: 85021667000

Research output: Contribution to journalArticleScientificpeer-review

Optimal control of photoelectron emission by realistic waveforms

Recent experimental techniques in multicolor waveform synthesis allow the temporal shaping of strong femtosecond laser pulses with applications in the control of quantum mechanical processes in atoms, molecules, and nanostructures. Prediction of the shapes of the optimal waveforms can be done computationally using quantum optimal control theory. In this work we demonstrate the control of above-threshold photoemission of one-dimensional hydrogen model with pulses feasible for experimental waveform synthesis. By mixing different spectral channels and thus lowering the intensity requirements for individual channels, the resulting optimal pulses can extend the cutoff energies by at least up to 50% and bring up the electron yield by several orders of magnitude. Insights into the electron dynamics for optimized photoelectron emission are obtained with a semiclassical two-step model.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Institute of Physics of the Academy of Sciences of the Czech Republic
Contributors: Solanpää, J., Ciappina, M. F., Räsänen, E.
Number of pages: 9
Pages: 1784-1792
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Modern Optics
Volume: 64
Issue number: 17
ISSN (Print): 0950-0340
Ratings: 
  • Scopus rating (2017): CiteScore 2.3 SJR 0.41 SNIP 0.62
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: Above-threshold ionization, optimal control, waveforms
Electronic versions: 
Source: Scopus
Source ID: 85018191164

Research output: Contribution to journalArticleScientificpeer-review

Optimization of convectively cooled heat sinks

Many factors of heat sink, such as its size and mass, component locations, number of fins, and fan power affect heat transfer. Owing to the opposite effects of these factors on heat sink maximum temperature, we have now a multi-objective optimization problem. A typical optimization case consists of hundreds of heat sink temperature field evaluations, which would be impractical to do with CFD. Instead, we propose to combine analytical results of convection and numerical solution of conduction to address these so-called conjugated heat transfer problems. We solve heat conduction in a solid numerically using the finite volume method and tackle convection with the analytical equation of forced convection in a parallel plate channel.This model is suitable for forced and natural convection heat sinks, and we have verified its validity by comparing its results to measured data and CFD calculations. We use the model to improve two industrial examples, using a multi-objective version of the particle swarm optimization (PSO) algorithm. The first example is a forced convection heat sink composed of nine heat generating components at the base plate, and the other is a natural convection case with two components. In both cases, mass is minimized; the other criterion is maximum temperature for the forced convection case and heat sink outer volume for the natural convection case. Our method is many orders of magnitude faster than CFD. Additionally, we provide some LES results of pin fins with natural convection for further use in similar optimizations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Bio- and Circular Economy, Mechanical Engineering and Industrial Systems
Contributors: Lampio, K., Karvinen, R.
Pages: 473-479
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Microelectronics Reliability
Volume: 79
ISSN (Print): 0026-2714
Ratings: 
  • Scopus rating (2017): CiteScore 2.6 SJR 0.388 SNIP 0.907
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Safety, Risk, Reliability and Quality, Surfaces, Coatings and Films, Electrical and Electronic Engineering
Keywords: Fin array, Forced convection, Heat sink, Multi-objective optimization, Natural convection, Pin fins
Source: Scopus
Source ID: 85020690970

Research output: Contribution to journalArticleScientificpeer-review

Pipeline for effective denoising of digital mammography and digital breast tomosynthesis

Denoising can be used as a tool to enhance image quality and enforce low radiation doses in X-ray medical imaging. The effectiveness of denoising techniques relies on the validity of the underlying noise model. In full-field digital mammography (FFDM) and digital breast tomosynthesis (DBT), calibration steps like the detector offset and flat-fielding can affect some assumptions made by most denoising techniques. Furthermore, quantum noise found in X-ray images is signal-dependent and can only be treated by specific filters. In this work we propose a pipeline for FFDM and DBT image denoising that considers the calibration steps and simplifies the modeling of the noise statistics through variance-stabilizing transformations (VST). The performance of a state-of-the-art denoising method was tested with and without the proposed pipeline. To evaluate the method, objective metrics such as the normalized root mean square error (N-RMSE), noise power spectrum, modulation transfer function (MTF) and the frequency signal-to-noise ratio (SNR) were analyzed. Preliminary tests show that the pipeline improves denoising. When the pipeline is not used, bright pixels of the denoised image are under-filtered and dark pixels are over-smoothed due to the assumption of a signal-independent Gaussian model. The pipeline improved denoising up to 20% in terms of spatial N-RMSE and up to 15% in terms of frequency SNR. Besides improving the denoising, the pipeline does not increase signal smoothing significantly, as shown by the MTF. Thus, the proposed pipeline can be used with state-of-the-art denoising techniques to improve the quality of DBT and FFDM images.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, University of São Paulo, University of Pennsylvania
Contributors: Borges, L. R., Bakic, P. R., Foi, A., Maidment, A. D., Vieira, M. A.
Publication date: 2017

Host publication information

Title of host publication: Medical Imaging 2017 : Physics of Medical Imaging
Publisher: SPIE
Article number: 1013206
ISBN (Electronic): 9781510607095

Publication series

Name: Progress in biomedical optics and imaging
ISSN (Electronic): 1605-7422
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Biomaterials, Radiology Nuclear Medicine and imaging
Keywords: Denoising, Digital breast tomosynthesis, Full field digital mammography, Variance stabilization
Electronic versions: 

Bibliographical note

jufoid=65546

Source: Scopus
Source ID: 85020415748

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Thermal Modification of ALD Grown Titanium Oxide Ultra Thin Film for Photoanode Applications

General information

Publication status: Published
Organisations: Optoelectronics Research Centre, Research group: Surface Science
Contributors: Hannula, M. K., Lahtonen, K. T., Isotalo, T. J., Saari, J. S., Valden, M. O.
Publication date: 15 Dec 2016
Peer-reviewed: Unknown
Event: Paper presented at Symposium on Future Prospects for Photonics, Tampere, Finland.
ASJC Scopus subject areas: Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films, Surfaces and Interfaces, Atomic and Molecular Physics, and Optics
Keywords: Titanium dioxide, titanium silicide, Atomic layer deposition (ALD), photoemission electron microscopy, PEEM, hydrogen energy

Research output: Other conference contributionPaper, poster or abstractScientific

Nonlinear guided waves: Preface

This special issue presents a collection of experimental and theoretical research in nonlinear waves, with emphasis on nonlinear optics, which were presented at the conference Nonlinear Guided Waves VIII held at the Hotel Victoria, Oaxaca, Mexico in April 2016. This preface provides a short history of the conference series Nonlinear Guided Waves and short introductions to the contributed papers which puts them in context.

General information

Publication status: Published
MoE publication type: B1 Article in a scientific magazine
Organisations: Photonics, Nonlinear Optics and OptoElectronics Lab, University “Roma Tre”, Optics Laboratory, Department of Physics, Tampere University of Technology, CNR-ISC, Institute for Complex Systems, University of Edinburgh
Contributors: Assanto, G., Smyth, N. F.
Publication date: 1 Dec 2016
Peer-reviewed: No

Publication information

Journal: Journal of Nonlinear Optical Physics and Materials
Volume: 25
Issue number: 4
Article number: 1650041
ISSN (Print): 0218-8635
Ratings: 
  • Scopus rating (2016): CiteScore 1.3 SJR 0.301 SNIP 0.493
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Physics and Astronomy (miscellaneous)
Keywords: discrete systems, Nonlinear optics, solitary waves, solitons
Source: Scopus
Source ID: 85011382866

Research output: Contribution to journalArticleScientific

Fabrication of Ion-Shaped Anisotropic Nanoparticles and their Orientational Imaging by Second-Harmonic Generation Microscopy

Ion beam shaping is a novel and powerful tool to engineer nanocomposites with effective threedimensional (3D) architectures. In particular, this technique offers the possibility to precisely control the size, shape and 3D orientation of metallic nanoparticles at the nanometer scale while keeping the particle volume constant. Here, we use swift heavy ions of xenon for irradiation in order to successfully
fabricate nanocomposites consisting of anisotropic gold nanoparticle that are oriented in 3D and embedded in silica matrix. Furthermore, we investigate individual nanorods using a nonlinear optical microscope based on second-harmonic generation (SHG). A tightly focused linearly or radially-polarized
laser beam is used to excite nanorods with different orientations. We demonstrate high sensitivity of the SHG response for these polarizations to the orientation of the nanorods. The SHG measurements are in excellent agreement with the results of numerical modeling based on the boundary element method.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research area: Optics, Research group: Nonlinear Optics, Optoelectronics Research Centre, Research group: Nanophotonics, Ecole Polytechnique, Laboratoire de Photonique et Nanostructures; CNRS, Marcoussis, France., 5Laboratoire de Physique des Solides CNRS/UMR8502, Bâtiment 510, University Paris-Sud, Orsay, 91405, France, 3Laboratoire des Solides Irradiés, Ecole Polytechnique, CEA/DRF/IRAMIS, CNRS, Université Paris-Saclay, Route de Saclay, 91128, Palaiseau, France., Université de Paris-Sud
Contributors: Slablab, A., Isotalo, T. J., Mäkitalo, J., Turquet, L., COULON, P., Niemi, T., Ulysse, C., Kociak, M., Mailly, D., Rizza, G., Kauranen, M.
Number of pages: 10
Publication date: 24 Nov 2016
Peer-reviewed: Yes

Publication information

Journal: Scientific Reports
Volume: 6
Issue number: 37469
Article number: 37469
ISSN (Print): 2045-2322
Ratings: 
  • Scopus rating (2016): CiteScore 4.2 SJR 1.692 SNIP 1.364
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: optics, plasmonics, Nonlinear microscopy, IRRADIATION
Electronic versions: 

Research output: Contribution to journalArticleScientificpeer-review

Frequency-doubled passively Q-switched microchip laser producing 225 ps pulses at 671 nm

We report a 671 nm laser source emitting 225 ps pulses with an average power of 55 mW and a repetition rate of 444 kHz. The system consists of a 1342 nm SESAM Q-switched Nd:YVO4 microchip master oscillator and a dual-stage Nd:YVO4 power amplifier. The 1342 nm signal was frequency-doubled to 671 nm using a periodically poled lithium niobate crystal. This laser source provides a practical alternative for applications requiring high energy picosecond pulses, such as time-gated Raman spectroscopy.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications
Contributors: Nikkinen, J., Korpijärvi, V., Leino, I., Härkönen, A., Guina, M.
Number of pages: 4
Pages: 5385-5388
Publication date: 15 Nov 2016
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 41
Issue number: 22
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2016): CiteScore 6.8 SJR 1.769 SNIP 1.511
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84995663953

Research output: Contribution to journalArticleScientificpeer-review

VECSEL systems for the generation and manipulation of trapped magnesium ions

Experiments in atomic, molecular, and optical (AMO) physics rely on lasers at many different wavelengths and with varying requirements on the spectral linewidth, power, and intensity stability. Vertical external-cavity surface-emitting lasers (VECSELs), when combined with nonlinear frequency conversion, can potentially replace many of the laser systems currently in use. Here, we present and characterize VECSEL systems that can perform all laser-based tasks for quantum information processing experiments with trapped magnesium ions. For the photoionization of neutral magnesium, 570.6 nm light is generated with an intracavity frequency-doubled VECSEL containing a lithium triborate crystal. External frequency doubling produces 285.3 nm light for a resonant interaction with the 1S0↔1P1 transition of neutral Mg. Using an externally frequency-quadrupled VECSEL, we implement Doppler cooling of Mg25+ on the 279.6 nm 2S1/2↔2P3/2 cycling transition, repumping on the 280.4 nm 2S1/2↔2P1/2 transition, coherent state manipulation, and resolved sideband cooling close to the motional ground state. Our systems serve as prototypes for applications in AMO requiring single-frequency, power-scalable laser sources at multiple wavelengths.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, National Institute of Standards and Technology, Time and Frequency Division, Boulder, Colorado
Contributors: Burd, S., Allcock, D., Leinonen, T., Penttinen, J., Slichter, D., Srinivas, R., Wilson, A., Jördens, R., Guina, M., Leibfried , D., Wineland, D.
Number of pages: 6
Pages: 1294-1299
Publication date: 8 Nov 2016
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 3
Issue number: 12
Article number: 268119
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2016): CiteScore 6.9 SJR 4.761 SNIP 3.34
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: Semiconductor lasers, Lasers, frequency doubled, Laser cooling, Quantum information and processing, Spectroscopy, high-resolution, Spectroscopy, trapped ion

Research output: Contribution to journalArticleScientificpeer-review

Adaptive multiresolution method for MAP reconstruction in electron tomography

3D image reconstruction with electron tomography holds problems due to the severely limited range of projection angles and low signal to noise ratio of the acquired projection images. The maximum a posteriori (MAP) reconstruction methods have been successful in compensating for the missing information and suppressing noise with their intrinsic regularization techniques. There are two major problems in MAP reconstruction methods: (1) selection of the regularization parameter that controls the balance between the data fidelity and the prior information, and (2) long computation time. One aim of this study is to provide an adaptive solution to the regularization parameter selection problem without having additional knowledge about the imaging environment and the sample. The other aim is to realize the reconstruction using sequences of resolution levels to shorten the computation time. The reconstructions were analyzed in terms of accuracy and computational efficiency using a simulated biological phantom and publically available experimental datasets of electron tomography. The numerical and visual evaluations of the experiments show that the adaptive multiresolution method can provide more accurate results than the weighted back projection (WBP), simultaneous iterative reconstruction technique (SIRT), and sequential MAP expectation maximization (sMAPEM) method. The method is superior to sMAPEM also in terms of computation time and usability since it can reconstruct 3D images significantly faster without requiring any parameter to be set by the user.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Signal Processing, BioMediTech
Contributors: Acar, E., Peltonen, S., Ruotsalainen, U.
Number of pages: 11
Pages: 24-34
Publication date: 1 Nov 2016
Peer-reviewed: Yes

Publication information

Journal: Ultramicroscopy
Volume: 170
ISSN (Print): 0304-3991
Ratings: 
  • Scopus rating (2016): CiteScore 5.5 SJR 1.896 SNIP 1.184
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Instrumentation
Keywords: Adaptive reconstruction, Electron tomography (ET), Maximum a posteriori (MAP) reconstruction, Missing wedge, Multiresolution reconstruction, Regularization parameter
Source: Scopus
Source ID: 84981309739

Research output: Contribution to journalArticleScientificpeer-review

UPS and DFT investigation of the electronic structure of gas-phase trimesic acid

Benzene-1,3,5-tricarboxylic acid (trimesic acid, TMA) molecules in gas-phase have been investigated by using valence band photoemission. The photoelectron spectrum in the binding energy region from 9 to 22 eV is interpreted based on the density functional theory calculations. The electronic configuration that makes contribution to each transition is demonstrated. Furthermore, electronic structure of TMA is compared with benzene and benzoic acid (BA) in order to demonstrate changes in molecular orbital energies induced by addition of carboxyl groups to benzene ring.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Surface Science, University of Tartu, MAX IV Laboratory, Lund University
Contributors: Reisberg, L., Pärna, R., Kikas, A., Kuusik, I., Kisand, V., Hirsimäki, M., Valden, M., Nõmmiste, E.
Number of pages: 6
Pages: 11-16
Publication date: Nov 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Electron Spectroscopy and Related Phenomena
Volume: 213
ISSN (Print): 0368-2048
Ratings: 
  • Scopus rating (2016): CiteScore 3.2 SJR 0.852 SNIP 0.731
Original language: English
ASJC Scopus subject areas: Organic Chemistry, Atomic and Molecular Physics, and Optics
Keywords: trimesic acid, molecules, electronic structure, synchrotron radiation, MAX IV Laboratory, UPS, DFT, organic acids, gas-phase, spectroscopy, photoemission
Electronic versions: 
URLs: 

Research output: Contribution to journalArticleScientificpeer-review

RF measurements to pinpoint defects in inkjet-printed, thermally and mechanically stressed coplanar waveguides

In this work 10-GHz-band RF measurement and microscopy characterizations were performed on thermally and mechanically long-term-stressed coplanar waveguides (CPW) to observe electrical and mechanical degradation in 1-mm-thick PPO/PPE polymer substrates with inkjet-printed Ag conductors. The structure contained two different CPW geometries in a total of 18 samples with 250/270 μm line widths/gaps and 670/180 μm line widths/gaps. A reliability test was carried out with three sets. In set #1 three 250 μm and three 670 μm lines were stored in room temperature conditions and used as a reference. In set #2 six samples were thermally cycled (TC) for 10,000 cycles, and in set #3 six samples were thermally cycled and bent with 6 mm and 8 mm bending diameters. Thermal stressing was done by cycling the samples in a thermal cycling test chamber operating at 0/100 °C with 15-minutes rise, fall, and dwell times, resulting in a one-hour cycle. The samples were analyzed during cycling breaks using a vector network analyzer (VNA). In addition to optical microscopy, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) imaging were used to mechanically characterize the structures. The results showed that the line width of 670 μm had better signal performance and better long-term reliability than the line width of 250 μm. In this study, the average limit for proper RF operation was 2500 thermal cycles with both line geometries. The wide CPW lines provided more stable characteristics than the narrow CPW lines for the whole 10,000-cycle duration of the test, combined with repeated bending with a maximum bending radius of 6 mm. A phenomenon of nanoparticle silver protruding from cracks in the print of the bent samples was observed, as well as fracturing of the silver print in the CPW lines.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Microelectronics Research, University of Oulu, Tampere University of Applied Sciences
Contributors: Myllymäki, S., Putaala, J., Hannu, J., Kunnari, E., Mäntysalo, M.
Number of pages: 9
Pages: 142-150
Publication date: 1 Oct 2016
Peer-reviewed: Yes

Publication information

Journal: Microelectronics Reliability
Volume: 65
ISSN (Print): 0026-2714
Ratings: 
  • Scopus rating (2016): CiteScore 2.6 SJR 0.447 SNIP 0.991
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Safety, Risk, Reliability and Quality, Surfaces, Coatings and Films, Electrical and Electronic Engineering

Bibliographical note

EXT="Kunnari, Esa"
EXT="Myllymäki, Sami"

Source: Scopus
Source ID: 84992618636

Research output: Contribution to journalArticleScientificpeer-review

General polarizability and hyperpolarizability estimators for the path-integral Monte Carlo method applied to small atoms, ions, and molecules at finite temperatures

The nonlinear optical properties of matter have a broad relevance and many methods have been invented to compute them from first principles. However, the effects of electronic correlation, finite temperature, and breakdown of the Born-Oppenheimer approximation have turned out to be challenging and tedious to model. Here we propose a straightforward approach and derive general field-free polarizability and hyperpolarizability estimators for the path-integral Monte Carlo method. The estimators are applied to small atoms, ions, and molecules with one or two electrons. With the adiabatic, i.e., Born-Oppenheimer, approximation we obtain accurate tensorial ground state polarizabilities, while the nonadiabatic simulation adds in considerable rovibrational effects and thermal coupling. In both cases, the 0 K, or ground-state, limit is in excellent agreement with the literature. Furthermore, we report here the internal dipole moment of PsH molecule, the temperature dependence of the polarizabilities of H-, and the average dipole polarizabilities and the ground-state hyperpolarizabilities of HeH+ and H3+.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research group: Semiconductor Technology and Applications, Research area: Computational Physics, Research group: Electronic Structure Theory
Contributors: Tiihonen, J., Kylänpää, I., Rantala, T. T.
Number of pages: 8
Publication date: 26 Sep 2016
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 94
Issue number: 3
Article number: 032515
ISSN (Print): 1050-2947
Ratings: 
  • Scopus rating (2016): CiteScore 6.7 SJR 1.482 SNIP 1.02
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Additional files: 
Source: Scopus
Source ID: 84989247221

Research output: Contribution to journalArticleScientificpeer-review

1.3 μm InAs quantum dot semiconductor disk laser

Vertical-external-cavity surface-emitting lasers (VECSEL), or semiconductor disk lasers (SDL), are attractive laser source for a wide range of applications owing to unique possibility to combine high output power with an excellent beam quality [1]. The intrinsic features of InAs quantum dots (QD) can offer low threshold, broad wavelength tunability, fast carrier dynamics and low temperature sensitivity. Recently, continuous wave (CW) operation of QD-based VECSEL emitting at 1.25 μm with output powers reaching multi-watt levels were achieved at room temperature [2]. However, extending the emission wavelength to 1.3 μm and beyond becomes more challenging. To date, QD-based VECSEL with optical power greater than 0.5 mW at 1305 nm has been demonstrated [3]. Here, we present a record-high power InAs/InGaAs QD-based VECSEL operating at the wavelength of 1.3 μm.

General information

Publication status: Published
Organisations: Optoelectronics Research Centre, Research group: Ultrafast and intense lasers, Ioffe Physico-Technical Institute, Peter the Great St. Petersburg Polytechnic University
Contributors: Blokhin, S. A., Bobrov, M. A., Blokhin, A. A., Kuzmenkov, A. G., Vasil'Ev, A. P., Maleev, N. A., Dudelev, V. V., Soboleva, K. K., Sokolovskii, G. S., Rantamäki, A., Okhotnikov, O., Ustinov, V. M.
Pages: R317
Publication date: 23 Aug 2016
Peer-reviewed: Unknown
Event: Paper presented at 2016 International Conference Laser Optics, LO 2016, St. Petersburg, Russian Federation.
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84987923895

Research output: Other conference contributionPaper, poster or abstractScientific

Advanced scheme of amplifier similariton laser

We propose an advanced scheme of amplifier similariton laser providing an output pulse spectrum much wider than the gain bandwidth. The proposed scheme demonstrates a drastic increase of the output pulse spectrum width, reduction of the pulse duration, and increase of the output pulse peak power after compression.

General information

Publication status: Published
Organisations: Optoelectronics Research Centre, Ulyanovsk State University, A. M. Prokhorov General Physics Institute, Russian Academy of Sciences
Contributors: Korobko, D. A., Okhotnikov, O. G., Sysoliatin, A. A., Zolotovskii, I. O.
Pages: R858
Publication date: 23 Aug 2016
Peer-reviewed: Unknown
Event: Paper presented at 2016 International Conference Laser Optics, LO 2016, St. Petersburg, Russian Federation.
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: amplifier similariton laser, generation of extra broad spectrum, parabolic pulses
Source: Scopus
Source ID: 84987901019

Research output: Other conference contributionPaper, poster or abstractScientific

State of polarization in anisotronic tapered fiber with extremely large core diameter

We produced numerical and experimental research of polarization maintaining properties of adiabatic anisotropic tapered optical fiber with extremely large output core diameter. Results show that polarization state of light coupling in the narrow end did not degrade dramatically through whole fiber length (while core diameter increasing adiabatically upto tens of wavelengths).

General information

Publication status: Published
Organisations: Optoelectronics Research Centre, Russian Quantum Center, Institute of Radio Engineering and Electronics of the Russian Academy of Sciences
Contributors: Ustimchik, V. E., Vyatkin, M. Y., Popov, S. M., Chamorovskii, Y. K., Filippov, V. N., Nikitov, S. A.
Pages: S123
Publication date: 23 Aug 2016
Peer-reviewed: Unknown
Event: Paper presented at 2016 International Conference Laser Optics, LO 2016, St. Petersburg, Russian Federation.
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: birefringence, large mode area fibers, polarization, taper fiber
Source: Scopus
Source ID: 84987880925

Research output: Other conference contributionPaper, poster or abstractScientific

Semiclassical two-step model for strong-field ionization

We present a semiclassical two-step model for strong-field ionization that accounts for path interferences of tunnel-ionized electrons in the ionic potential beyond perturbation theory. Within the framework of a classical trajectory Monte Carlo representation of the phase-space dynamics, the model employs the semiclassical approximation to the phase of the full quantum propagator in the exit channel. By comparison with the exact numerical solution of the time-dependent Schrödinger equation for strong-field ionization of hydrogen, we show that for suitable choices of the momentum distribution after the first tunneling step, the model yields good quantitative agreement with the full quantum simulation. The two-dimensional photoelectron momentum distributions, the energy spectra, and the angular distributions are found to be in good agreement with the corresponding quantum results. Specifically, the model quantitatively reproduces the fanlike interference patterns in the low-energy part of the two-dimensional momentum distributions, as well as the modulations in the photoelectron angular distributions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research group: Quantum Control and Dynamics, Research area: Computational Physics, Leibniz-Universität Hannover, Aarhus Universitet, TU Vienna, Hungarian Academy of Sciences, IAFE (UBA-Conicet), ELI-HU Nonprofit Ltd.
Contributors: Shvetsov-Shilovski, N. I., Lein, M., Madsen, L. B., Räsänen, E., Lemell, C., Burgdörfer, J., Arbó, D. G., Tokési, K.
Publication date: 19 Jul 2016
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 94
Issue number: 1
Article number: 013415
ISSN (Print): 1050-2947
Ratings: 
  • Scopus rating (2016): CiteScore 6.7 SJR 1.482 SNIP 1.02
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84978906019

Research output: Contribution to journalArticleScientificpeer-review

Nonlocal soliton scattering in random potentials

We experimentally investigate the transport behaviour of nonlocal spatial optical solitons when launched in and interacting with propagation-invariant random potentials. The solitons are generated in nematic liquid crystals; the randomness is created by suitably engineered illumination of planar voltage-biased cells equipped with a photosensitive wall. We find that the fluctuations follow a super-diffusive trend, with the mean square displacement lowering for decreasing spatial correlation of the noise.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, University “Roma Tre”, CNRS, Nonlinear Optics and OptoElectronics Lab, Optics Laboratory, Department of Physics, Tampere University of Technology
Contributors: Piccardi, A., Residori, S., Assanto, G.
Number of pages: 5
Publication date: 1 Jul 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 18
Issue number: 7
Article number: 07LT01
ISSN (Print): 2040-8978
Ratings: 
  • Scopus rating (2016): CiteScore 3.4 SJR 0.715 SNIP 0.829
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: liquid crystals, nematicons, random potential, scattering, spatial solitons
Source: Scopus
Source ID: 84978954030

Research output: Contribution to journalArticleScientificpeer-review

Electronically tunable thulium-holmium modelocked fiber laser for the 1700-1800 nm wavelength band

We demonstrate a widely tunable, mode-locked fiber laser capable of producing sub-picosecond pulses between 1705 and 1805 nm. The 100 nm tuning range is achieved by using intracavity acousto-optic tunable filter. The laser delivers highly stable pulses via self-starting hybrid mode-locking triggered by frequency-shifting and nonlinear polarization evolution.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Ultrafast and intense lasers
Contributors: Noronen, T., Okhotnikov, O., Gumenyuk, R.
Number of pages: 6
Pages: 14703-14708
Publication date: 27 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 24
Issue number: 13
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2016): CiteScore 6.7 SJR 1.532 SNIP 1.528
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84977638649

Research output: Contribution to journalArticleScientificpeer-review

Single-frequency 571nm VECSEL for photo-ionization of magnesium

We report the development of an intracavity-frequency-doubled vertical external-cavity surface-emitting laser (VECSEL) emitting at 571 nm for photoionization of magnesium. The laser employs a V-cavity geometry with a gain chip at the end of one cavity arm and a lithium triborate (LBO) crystal for second harmonic generation. The gain chip has a bottom-emitting design with ten GaInAs quantum wells of 7 nm thickness, which are strain compensated by GaAsP. The system is capable of producing up to 2.4 ± 0.1 W (total power in two separate output beams) in the visible. The free-running relative intensity noise was measured to be below −55 dBc/Hz over all frequencies from 1 Hz to 1 MHz. With acoustic isolation and temperature regulation of the laser breadboard, the mode-hop free operation time is typically over 5 hrs. To improve the long-term frequency stability, the laser can be locked to a Doppler-free transition of molecular iodine. To estimate the short-term linewidth, the laser was tuned to the resonance of a reference cavity. From analysis of the on-resonance Hänsch-Couillaud error signal we infer a linewidth of 50 ± 10 kHz. Light at 285 nm is generated with an external build-up cavity containing a β-barium borate (BBO) crystal. The UV light is used for loading 25Mg+ ions in a surface-electrode RF Paul trap. These results demonstrate the applicability and versatility of high-power, single-frequency VECSELs with intracavity harmonic generation for applications in atomic and molecular physics.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, National Institute of Standards and Technology, Time and Frequency Division, Boulder, Colorado
Contributors: Burd, S., Leinonen, T., Penttinen, J., Allcock, D., Slichter, D., Srinivas, R., Wilson, A., Guina, M., Leibfried , D., Wineland, D.
Number of pages: 8
Publication date: 2 Jun 2016

Host publication information

Title of host publication: Proceedings of SPIE : Vertical External Cavity Surface Emitting Lasers (VECSELs) VI
Volume: 9734
Place of publication: San Francisco
Publisher: SPIE
Article number: 973411
ISBN (Electronic): 9781628419696

Publication series

Name: SPIE Conference Proceedings
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: VECSEL, OPSL, SDL, frequency doubling, SHG, ion trapping, single-frequency, photoionization, doppler-free spectroscopy, magnesium

Bibliographical note

JUFOID=71479

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Roadmap on optical rogue waves and extreme events

The pioneering paper 'Optical rogue waves' by Solli et al (2007 Nature 450 1054) started the new subfield in optics. This work launched a great deal of activity on this novel subject. As a result, the initial concept has expanded and has been enriched by new ideas. Various approaches have been suggested since then. A fresh look at the older results and new discoveries has been undertaken, stimulated by the concept of 'optical rogue waves'. Presently, there may not by a unique view on how this new scientific term should be used and developed. There is nothing surprising when the opinion of the experts diverge in any new field of research. After all, rogue waves may appear for a multiplicity of reasons and not necessarily only in optical fibers and not only in the process of supercontinuum generation. We know by now that rogue waves may be generated by lasers, appear in wide aperture cavities, in plasmas and in a variety of other optical systems. Theorists, in turn, have suggested many other situations when rogue waves may be observed. The strict definition of a rogue wave is still an open question. For example, it has been suggested that it is defined as 'an optical pulse whose amplitude or intensity is much higher than that of the surrounding pulses'. This definition (as suggested by a peer reviewer) is clear at the intuitive level and can be easily extended to the case of spatial beams although additional clarifications are still needed. An extended definition has been presented earlier by N Akhmediev and E Pelinovsky (2010 Eur. Phys. J. Spec. Top. 185 1-4). Discussions along these lines are always useful and all new approaches stimulate research and encourage discoveries of new phenomena. Despite the potentially existing disagreements, the scientific terms 'optical rogue waves' and 'extreme events' do exist. Therefore coordination of our efforts in either unifying the concept or in introducing alternative definitions must be continued. From this point of view, a number of the scientists who work in this area of research have come together to present their research in a single review article that will greatly benefit all interested parties of this research direction. Whether the authors of this 'roadmap' have similar views or different from the original concept, the potential reader of the review will enrich their knowledge by encountering most of the existing views on the subject. Previously, a special issue on optical rogue waves (2013 J. Opt. 15 060201) was successful in achieving this goal but over two years have passed and more material has been published in this quickly emerging subject. Thus, it is time for a roadmap that may stimulate and encourage further research.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Australian National University, Université de Bourgogne Franche-Comté, Universita degli Studi di Brescia, Texas A and M University at Qatar, Shunde Polytechnic, Xi'an Jiaotong University, CSIC - Instituto de &amp;Oacute;ptica Daza de Vald&amp;eacute;s (IO), CRPP, Universidad Adolfo Ibánez, Université libre de Bruxelles (ULB), Vrije Universiteit Brussel, Université Lille 1, Université de Franche-Comté, Leibniz-Universität Hannover, Weierstrass-Institut für Angewandte Analysis und Stochastik, Max Born Institute, Universitat Politécnica de Catalunya, The University of Auckland, Dodd-Walls Centre for Photonic and Quantum Technologies, CNRS, CNR-INO
Contributors: Akhmediev, N., Kibler, B., Baronio, F., Belić, M., Zhong, W. P., Zhang, Y., Chang, W., Soto-Crespo, J. M., Vouzas, P., Grelu, P., Lecaplain, C., Hammani, K., Rica, S., Picozzi, A., Tlidi, M., Panajotov, K., Mussot, A., Bendahmane, A., Szriftgiser, P., Genty, G., Dudley, J., Kudlinski, A., Demircan, A., Morgner, U., Amiraranashvili, S., Bree, C., Steinmeyer, G., Masoller, C., Broderick, N. G. R., Runge, A. F. J., Erkintalo, M., Residori, S., Bortolozzo, U., Arecchi, F. T., Wabnitz, S., Tiofack, C. G., Coulibaly, S., Taki, M.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 18
Issue number: 6
Article number: 063001
ISSN (Print): 2040-8978
Ratings: 
  • Scopus rating (2016): CiteScore 3.4 SJR 0.715 SNIP 0.829
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: extreme events, nonlinear optics, rogue waves

Bibliographical note

EXT="Steinmeyer, Günter"
EXT="Erkintalo, Miro"

Source: Scopus
Source ID: 84975818584

Research output: Contribution to journalArticleScientificpeer-review

Robust statistical approaches for RSS-based floor detection in indoor localization

Floor detection for indoor 3D localization of mobile devices is currently an important challenge in the wireless world. Many approaches currently exist, but usually the robustness of such approaches is not addressed or investigated. The goal of this paper is to show how to robustify the floor estimation when probabilistic approaches with a low number of parameters are employed. Indeed, such an approach would allow a building-independent estimation and a lower computing power at the mobile side. Four robustified algorithms are to be presented: a robust weighted centroid localization method, a robust linear trilateration method, a robust nonlinear trilateration method, and a robust deconvolution method. The proposed approaches use the received signal strengths (RSS) measured by the Mobile Station (MS) from various heardWiFi access points (APs) and provide an estimate of the vertical position of the MS, which can be used for floor detection. We will show that robustification can indeed increase the performance of the RSS-based floor detection algorithms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Wireless Communications and Positioning
Contributors: Razavi, A., Valkama, M., Lohan, E. S.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: Sensors
Volume: 16
Issue number: 6
Article number: 793
ISSN (Print): 1424-8220
Ratings: 
  • Scopus rating (2016): CiteScore 4.1 SJR 0.623 SNIP 1.629
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Analytical Chemistry, Biochemistry
Keywords: Floor detection, Indoor localization, Robust regression, RSS-based localization, Trilateration, Weighted centroid localization
Electronic versions: 
Source: Scopus
Source ID: 84971596811

Research output: Contribution to journalArticleScientificpeer-review

Vortex stabilization by means of spatial solitons in nonlocal media

We investigate how optical vortices, which tend to be azimuthally unstable in local nonlinear materials, can be stabilized by a copropagating coaxial spatial solitary wave in nonlocal, nonlinear media. We focus on the formation of nonlinear vortex-soliton vector beams in reorientational soft matter, namely nematic liquid crystals, and report on experimental results, as well as numerical simulations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics
Contributors: Izdebskaya, Y., Krolikowski, W., Smyth, N. F., Assanto, G.
Publication date: 1 May 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 18
Issue number: 5
Article number: 054006
ISSN (Print): 2040-8978
Ratings: 
  • Scopus rating (2016): CiteScore 3.4 SJR 0.715 SNIP 0.829
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: liquid crystals, optical vortex, self-action effects, spatial solitons
Source: Scopus
Source ID: 84969245814

Research output: Contribution to journalArticleScientificpeer-review

Temporal coherence characterization of supercontinuum pulse trains using Michelson's interferometer

Temporal coherence properties of supercontinuum pulse trains generated in nonlinear fibers are analyzed within the framework of the second-order coherence theory of nonstationary light. Time-resolved Michelson's interference patterns are simulated, from which the full two-time mutual coherence function can (at least in principle) be determined experimentally. Standard time-integrated Michelson's interferograms are also simulated and shown to provide a rough estimate for the coherence time of the quasi-stationary contribution. A simple but illustrative analytical model representing supercontinuum pulse trains is presented, and numerically simulated realizations of such pulse trains are considered.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research group: Nonlinear Fiber Optics, Research area: Optics
Contributors: Dutta, R., Turunen, J., Genty, G., Friberg, A. T.
Pages: B72-B77
Publication date: 20 Apr 2016
Peer-reviewed: Yes

Publication information

Journal: Applied Optics
Volume: 55
Issue number: 12
ISSN (Print): 1559-128X
Ratings: 
  • Scopus rating (2016): CiteScore 3.1 SJR 0.695 SNIP 1.17
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84964414579

Research output: Contribution to journalArticleScientificpeer-review

Detection of single microparticles in airflows by edge-filter enhanced self-mixing interferometry

A laser Doppler velocimetry (LDV) sensor using the edge-filter enhanced self-mixing interferometry (ESMI) is presented based on speed measurements of single microparticles. The ESMI detection utilizes an acetylene edge-filter that maps the frequency modulation of a semiconductor laser into an intensity modulation as the laser wavelength is tuned to the steep edge of the absorption profile. In this work, the ESMI signal was analyzed for aerosol particles of different sizes from 1 μm to 10 μm at a distance of 2.5 m. At this operation range, the signal from single particles of all sizes was successfully acquired enabling particle velocity measurements through the Doppler shifted frequency along the beam axis. For the particular case of 10 μm particles, single aerosol particles were still detected at an unprecedented range of 10 m. A theoretical treatment describing the relation between Mie scattering theory and the self-mixing phenomenon on single-particle detection is presented supporting the experimental results. The results show that the edge-filter enhanced self-mixing technique opens new possibilities for self-mixing detection where longer ranges, lower backscattering laser powers and higher velocities are involved. For example, it can be used as a robust and inexpensive anemometer for LDV applications for airflows with low-number density of microparticles.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research area: Optics, Research group: Applied Optics, Vaisala Oyj
Contributors: Contreras, V., Lönnqvist, J., Toivonen, J.
Number of pages: 9
Pages: 8886-8894
Publication date: 18 Apr 2016
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 24
Issue number: 8
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2016): CiteScore 6.7 SJR 1.532 SNIP 1.528
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84964575559

Research output: Contribution to journalArticleScientificpeer-review

Microwave assisted laser-induced breakdown spectroscopy at ambient conditions

Signal enhancements in laser-induced breakdown spectroscopy (LIBS) using external microwave power are demonstrated in ambient air. Pulsed microwave at 2.45 GHz and of 1 millisecond duration was delivered via a simple near field applicator (NFA), with which an external electric field is generated and coupled into laser induced plasma. The external microwave power can significantly increase the signal lifetime from a few microseconds to hundreds of microseconds, resulting in a great enhancement on LIBS signals with the use of a long integration time. The dependence of signal enhancement on laser energy and microwave power is experimentally assessed. With the assistance of microwave source, a significant enhancement of ∼ 100 was achieved at relatively low laser energy that is only slightly above the ablation threshold. A limit of detection (LOD) of 8.1 ppm was estimated for copper detection in Cu/Al2O3 solid samples. This LOD corresponds to a 93-fold improvement compared with conventional single-pulse LIBS. Additionally, in the microwave assisted LIBS, the self-reversal effect was greatly reduced, which is beneficial in measuring elements of high concentration. Temporal measurements have been performed and the results revealed the evolution of the emission process in microwave-enhanced LIBS. The optimal position of the NFA related to the ablation point has also been investigated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research area: Optics, Research group: Applied Optics, Optics Laboratory, Department of Physics, Tampere University of Technology, University of Adelaide
Contributors: Viljanen, J., Sun, Z., Alwahabi, Z. T.
Number of pages: 8
Pages: 29-36
Publication date: 1 Apr 2016
Peer-reviewed: Yes

Publication information

Journal: Spectrochimica Acta Part B: Atomic Spectroscopy
Volume: 118
ISSN (Print): 0584-8547
Ratings: 
  • Scopus rating (2016): CiteScore 5.3 SJR 1.095 SNIP 1.351
Original language: English
ASJC Scopus subject areas: Instrumentation, Atomic and Molecular Physics, and Optics, Analytical Chemistry, Spectroscopy
Keywords: Copper Detection, Laser-induced breakdown spectroscopy, Microwave signal enhancement
Source: Scopus
Source ID: 84962861465

Research output: Contribution to journalArticleScientificpeer-review

Validity of power functionals for a homogeneous electron gas in reduced-density-matrix-functional theory

Physically valid and numerically efficient approximations for the exchange and correlation energy are critical for reduced-density-matrix-functional theory to become a widely used method in electronic structure calculations. Here we examine the physical limits of power functionals of the form f(n,n′)=(nn′)α for the scaling function in the exchange-correlation energy. To this end we obtain numerically the minimizing momentum distributions for the three- and two-dimensional homogeneous electron gas, respectively. In particular, we examine the limiting values for the power α to yield physically sound solutions that satisfy the Lieb-Oxford lower bound for the exchange-correlation energy and exclude pinned states with the condition n(k)

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, University of Missouri-Columbia, JENOPTIK Optical Systems GmbH, Nanoscience Center, University of Jyväskylä
Contributors: Putaja, A., Eich, F. G., Baldsiefen, T., Räsänen, E.
Publication date: 10 Mar 2016
Peer-reviewed: Yes

Publication information

Journal: Physical Review A
Volume: 93
Issue number: 3
Article number: 032503
ISSN (Print): 1050-2947
Ratings: 
  • Scopus rating (2016): CiteScore 6.7 SJR 1.482 SNIP 1.02
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

INT=fys,"Putaja, A."

Source: Scopus
Source ID: 84961714989

Research output: Contribution to journalArticleScientificpeer-review

Super-resolution in a defocused plenoptic camera: a wave-optics-based approach

Plenoptic cameras enable the capture of a light field with a single device. However, with traditional light field rendering procedures, they can provide only low-resolution two-dimensional images. Super-resolution is considered to overcome this drawback. In this study, we present a superresolution method for the defocused plenoptic camera (Plenoptic 1.0), where the imaging system is modeled using wave optics principles and utilizing low-resolution depth information of the scene. We are particularly interested in super-resolution of in-focus and near in-focus scene regions, which constitute the most challenging cases. The simulation results show that the employed wave-optics model makes super-resolution possible for such regions as long as sufficiently accurate depth information is available.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Signal Processing, Research group: 3D MEDIA
Contributors: Sahin, E., Katkovnik, V., Gotchev, A.
Number of pages: 4
Pages: 998-1001
Publication date: 1 Mar 2016
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 41
Issue number: 5
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2016): CiteScore 6.8 SJR 1.769 SNIP 1.511
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84961616493

Research output: Contribution to journalArticleScientificpeer-review

High-power temperature-stable GaInNAs distributed Bragg reflector laser emitting at 1180 nm

We report a single-mode 1180 nm distributed Bragg reflector (DBR) laser diode with a high output power of 340 mW. For the fabrication, we employed novel nanoimprint lithography that ensures cost-effective, large-area, conformal patterning and does not require regrowth. The output characteristics exhibited outstanding temperature insensitivity with a power drop of only 30% for an increase of the mount temperature from 20°C to 80°C. The high temperature stability was achieved by using GaInNAs/GaAs quantum wells (QWs), which exhibit improved carrier confinement compared to standard InGaAs/GaAs QWs. The corresponding characteristic temperatures were T0 = 110 K and T1 = 160 K. Moreover, we used a large detuning between the peak wavelength of the material gain at room temperature and the lasing wavelength determined by the DBR. In addition to good temperature characteristics, GaInNAs/GaAs QWs exhibit relatively low lattice strain with direct impact on improving the lifetime of laser diodes at this challenging wavelength range. The single-mode laser emission could be tuned by changing the mount temperature (0.1 nm/°C) or the drive current (0.5 pm/mA). The laser showed no degradation in a room-temperature lifetime test at 900 mA drive current. These compact and efficient 1180 nm laser diodes are instrumental for the development of compact frequency-doubled yellow - orange lasers, which have important applications in medicine and spectroscopy.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, Research group: Nanophotonics
Contributors: Korpijärvi, V., Viheriälä, J., Koskinen, M., Aho, A. T., Guina, M.
Number of pages: 4
Pages: 657-660
Publication date: 15 Feb 2016
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 41
Issue number: 4
ISSN (Print): 0146-9592
Ratings: 
  • Scopus rating (2016): CiteScore 6.8 SJR 1.769 SNIP 1.511
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics

Bibliographical note

INT=orc,"Koskinen, Mervi"
INT=orc,"Aho, Antti T."

Source: Scopus
Source ID: 84962091445

Research output: Contribution to journalArticleScientificpeer-review

Machine-to-machine communications over FiWi enhanced LTE networks: A power-saving framework and end-to-end performance

To cope with the unprecedented acceleration of machine-to-machine (M2M) services over cellular networks, this paper envisions a highly converged network architecture based on the integration of high-capacity and reliable Ethernet fiber-wireless (FiWi) access networks with flexible and cost-effective 4G long term evolution (LTE) technology to support M2M connectivity in an end-to-end fashion, i.e., from air interface to transport (backhaul) network. In such emerging architecture, energy efficiency must be addressed in a comprehensive way, in which both wireless front-end and optical backhaul segments are considered at the same time to maximize the battery life of battery-constrained M2M devices as well as reduce operational expenditures for network operators, while maintaining acceptable network performance. Toward this end, an end-to-end power-saving framework is introduced in this paper that devises a timeout driven discontinuous reception (DRX) mechanism for LTE-enabled M2M devices and a polling-based power-saving mechanism for optical network units (ONUs) to improve the overall energy efficiency. End-to-end performance in terms of energy saving and packet delay is analytically modeled based on a semi-Markov process for the front-end and an M/G/1 queue for the backhaul. The obtained results indicate that the device battery life is significantly prolonged by extending the DRX cycle, whereas the backhaul energy consumption is minimized by incorporating the ONU power-saving modes into the dynamic bandwidth allocation process of the optical backhaul.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Emerging Technologies for Nano-Bio-Info-Cogno, Surface and Corrosion Science, Institut National de la Recherche Scientifique, Ericsson Research
Contributors: Van, D. P., Rimal, B. P., Andreev, S., Tirronen, T., Maier, M.
Number of pages: 10
Pages: 1062-1071
Publication date: 15 Feb 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Lightwave Technology
Volume: 34
Issue number: 4
ISSN (Print): 0733-8724
Ratings: 
  • Scopus rating (2016): CiteScore 6.8 SJR 1.23 SNIP 1.818
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Keywords: Discontinuous reception (DRX), energy efficiency, Fiber-Wireless (FiWi), M2M communications, ONU sleep
Source: Scopus
Source ID: 84961918904

Research output: Contribution to journalArticleScientificpeer-review

Optimization of light field display-camera configuration based on display properties in spectral domain

The visualization capability of a light field display is uniquely determined by its angular and spatial resolution referred to as display passband. In this paper we use a multidimensional sampling model for describing the display-camera channel. Based on the model, for a given display passband, we propose a methodology for determining the optimal distribution of ray generators in a projection-based light field display. We also discuss the required camera setup that can provide data with the necessary amount of details for such display that maximizes the visual quality and minimizes the amount of data.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Signal Processing, Research group: 3D MEDIA, Holografika
Contributors: Bregovic, R., Kovács, P., Gotchev, A.
Number of pages: 22
Pages: 3067-3088
Publication date: 8 Feb 2016
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 24
Issue number: 3
ISSN (Print): 1094-4087
Ratings: 
  • Scopus rating (2016): CiteScore 6.7 SJR 1.532 SNIP 1.528
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84962300926

Research output: