Computer Optics

845-855

Authors: A.I. Kashapov, L.L. Doskolovich, E.A. Bezus, N.V. Golovastikov, D.A. Bykov

We investigate the optical implementation of a second-order differentiation operation using a metal-dielectric layered structure in the oblique incidence geometry. It is shown that the transformation of the profile of a three-dimensional light beam occurring upon its reflection from a layered structure can be described using the theory of linear systems. The transfer function of the corresponding linear system is obtained, and it is shown that if a layered structure has a reflection zero of the second order with respect to the spatial frequency for one of the polarizations, the transformation performed by the structure corresponds to the weighted sum of the second derivatives of the incident beam profile with respect to the spatial coordinates. Using the presented theoretical description, layered metal-dielectric structures for computing the second derivative with respect to one of the spatial coordinates and for computing the Laplace operator of the profile of a three-dimensional linearly polarized light beam are calculated. The presented numerical simulation results demonstrate high-quality computation of these operators.

863-874

Authors: A.A. Kovalev, V.V. Kotlyar

We study a paraxial vector Gaussian beam with several polarization singularities located on a circle. Such a beam is superposition of a cylindrically polarized Laguerre-Gaussian beam and a linearly polarized Gaussian beam. It is found that although polarization in the initial plane is linear, alternating regions with the different-sign spin angular momentum density are generated upon free-space propagation, showing that a spin Hall effect arises. For an arbitrary transverse plane, it is shown that the spin angular momentum magnitude is maximal on a certain-radius circle. We obtain an approximate expression for the distance to the transverse plane where the spin angular momentum density is maximal. Besides, we derive an optimal radius of the singularity-containing circle in the initial plane for which the maximal spin angular momentum density can be achieved upon propagation. It is revealed that in this case, the energies of the Laguerre-Gaussian beam and the Gaussian beam are equal to each other. We also obtain an expression for the orbital angular momentum density and find it to be defined by the spin angular momentum density, multiplied by –m/2, with m being the upper index of the Laguerre-Gaussian beam, equal to the number of the polarization singularities. An analogy with plane waves reveals that the spin Hall effect arises due to different divergence rates of the linearly polarized Gaussian beam and the cylindrically polarized Laguerre-Gaussian beam.

884-894

Authors: A.G. Zakoyan, G.S. Voronkov, V.S. Lyubopytov, A.K. Sultanov, E.P. Grakhova, R.V. Kutluyarov

The paper proposes a new architecture for the photonic laboratory-on-a-chip sensing systems, where multiple sensors based on microring resonators (MRR) are fed by a MRR with low quality factor, working as a spectrum shaper. This architecture enables simultaneous intensity scanning of at least four MRR-based sensors on the silicon-on-insulator platform. We evaluated numerically the system’s sensitivity for various schemes of connecting the sensors and the spectrum shaper. The sensor’s sensitivity was 110 nm/RIU. The sensing system configuration largely determines its sensitivity, which reaches 1980 dB/RIU. The considered architecture may be useful for implementing fully integrated optical lab-on-a-chip structures, as well as distributed multichannel sensing systems.

901-912

Authors: E.G. Tsiplakova, A. Chopard, N.S. Balbekin, O.A. Smolyanskaya, J.-B. Perraud, J.-P. Guillet, P. Mounaix, N.V. Petrov

Iterative phase retrieval algorithms from multiple diffraction patterns in the terahertz (THz) frequency range are a promising tool of computational imaging capable of providing high spatial resolution of reconstructed phase images. One of the commonly used algorithms is SBMIR, which employs multiple intensity distributions of the diffraction object wavefield as input data. Compared with single-frame methods, the multi-plane approach allows for a faster convergence, but requires time-consuming data acquisition from a receiver positioned at a variety of distances from the object. Previously, we proposed a method for THz data acquisition in a single scan mode, which allows one to quickly obtain an exhaustive set of diffraction distributions. In this paper we evaluate an up-to-date phase retrieval algorithm based on the SBMIR/R-SBMIR method (which utilizes stochastic wavefront propagation) on the experimental data captured by a single-scan technique. Unlike a number of conventional phase retrieval algorithms, which may require a series of numerical experiments for determining optimal intensity distributions from a large dataset, disordered propagation of the estimation wavefront guarantees the high-contrast and high-resolution image reconstruction without pre-setting the parameters. It is shown that the package use of the single-scan technique with the subsequent data processing using the R-SBMIR algorithm has application potential for automation of the multi-plane phase retrieval in the THz range.

920-926

Authors: E.A. Yarunova, A.A. Krents, N.E. Molevich

The dynamics of a broad-area vertical-cavity semiconductor surface-emitting laser (VCSEL) is theoretically investigated with due regard for the Henry factor. A linear analysis of the stability of a spatially homogeneous lasing regime is performed and the modulation instability is shown to develop in such lasers. The minimum size of the aperture at which the instability of the optical field begins to develop is determined. The results are confirmed by the numerical solution of a system of differential equations. It is shown that the suppression of the modulation instability can be achieved by injecting into the resonator an external low-amplitude optical radiation.

938-947

Authors: D.A. Savelyev

Features of the near-field diffraction of Gaussian beams and Laguerre-Gauss modes by silicon subwavelength optical elements with varying relief height were studied in this paper using a finite-difference time-domain method. Diffractive axicons and subwavelength ring gratings were considered as the optical elements with varying relief height. It was shown that the height of individual rings of the ring grating relief can be selected in such a way that the focal spot size is reduced to 0.26λ, an extended intensity line of length up to 4.88λ is generated and optical traps are formed.

958-967

Authors: S.A. Korchagin, E.E. Zaychenkova, D.A. Sharapov, E.I. Ershov, Y.V. Butorin, Y.Y. Vengerov

This paper describes an in vitro medical express diagnostic system designed to determine the blood group by analyzing the agglutination reaction (gluing of erythrocytes). The medical staff only needs to take a blood sample, put it on a serological plate, placing it in a special scanner for the blood group to be automatically determined. Data digitizing and machine-assisted plate identification allows two critical tasks to be addressed at once: storing the analysis results and controlling the human factor. The proposed recognition algorithm allows the alveolus boundaries to be accurately determined and the agglutination degree to be evaluated using a lightweight convolutional neural network. A unique dataset was collected with the independent assessment of agglutination degree conducted by medical experts. The agglutination estimation accuracy on the collected dataset of 3231 alveole was comparable to the accuracy of an average medical expert and equal to 0.98.

972-979

Authors: O.O. Evsutin, A.S. Melman, D.I. Podbolotov, A.G. Stankevich

The use of screen-capture-resistant digital watermarks is a promising way to store information invisibly in a video stream for later retrieval by the user using a smartphone camera. However, the development of algorithms that implement this scenario is associated with the problem of balancing between the imperceptibility of embedding and robustness. A serious problem is the extraction of watermarks using a mobile device. Most people use the vertical positioning of the smartphone when shooting, which excludes the possibility of only marked video sequences entering the frame. The extraction algorithm first finds the screen area in the image and then extracts the watermark under various distortion conditions. This study proposes an approach to improve the efficiency of the algorithm for embedding digital watermarks into video data based on rectangular patterns, which provides resistance to screen shooting. The proposed approach to increasing the embedding imperceptibility provided an increase in the PSNR and SSIM values by 17.18 % and 7.90 %, respectively. The use of a neural network at the extraction stage reduced the BER value by 64.64 %.

991-1001

Authors: N.S. Davydov, V.V. Evdokimova, P.G. Serafimovich, V.I. Protsenko, A.G. Khramov, A.V. Nikonorov

Quality assessment and artifact detection in functional magnetic resonance imaging (fMRI) data is essential for clinical applications and brain research. Subject head motion remains the main source of artifacts - even the tiniest head movement can perturb the structural and functional data derived from the fMRI. In this paper, we propose an end-to-end neural network technology for detecting step anomalies with training on partially synthetic data with adaptation to a specific small set of real data. A procedure for generating a synthetic dataset for training and a module for automated labeling of real data is developed. A recurrent neural network model for detecting step anomalies is proposed. A method for the model adaptation to a small set of real data based on one-step meta-learning is developed. An experimental verification of the accuracy is carried out in the problem of detecting step anomalies using a sliding window of 10, 15, and 24 pixels. The experiments have shown the proposed technology to provide the detection of stepwise anomalies with an accuracy of 0.9546.

1011-1017

Authors: A.L. Reznik, A.A. Soloviev

An original approach to solving difficult time-consuming problems of registration and analysis of random point images is described. The approach is based on the development and application of high-performance specialized computer algebra systems. Three software packages have been created specifically for carrying out equivalent analytical transformations on a computer. The first software system is designed to calculate formulas describing the volumes of convex polyhedra with parametrically specified boundaries in n-dimensional space. The second system is based on the calculation of multidimensional integral expressions by the method of cyclic differentiation of the integral with respect to the parameter. The third system is based on the accelerated implementation of complex combinatorial-recursive transformations on a computer. Another distinctive feature of the work is the extension of the classical Catalan numbers to the multidimensional case (they were required to solve a number of intermediate probabilistic-combinatorial problems). The implementation of the above computer algebra software systems on a multi-core cluster of Novosibirsk State University, together with the direct use of the explicit form of generalized Catalan numbers, allowed the authors to obtain several new previously unknown probabilistic formulas and dependencies required for solving problems in the field of analysis of random point images.