Computer Optics

16-21

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

We analyze the propagation of hypergeometric beams with a parabolic initial wavefront in a homogeneous medium. While hypergeomentric beams have a central amplitude singularity in the initial plane and are of infinite energy, superposition of two such beams has no singularity and is of finite energy. A particular case of such a superposition we study in detail is a sinusoidal Gaussian beam with a unit topological charge. This beam belongs to the class of elegant laser beams since it is described by the same complex-argument function both in the initial plane and in the Fresnel diffraction zone. The diameter of the first light ring of the sinusoidal Gaussian beam is almost independent of the Gaussian beam waist radius.

30-38

Authors: N.A. Correa-Rojas, R.D. Gallego-Ruiz, M.I. Álvarez-Castaño

Linearly polarized modes were generated from the fundamental LP01 using Lee holograms displayed on a digital micromirror device. The phase in the holograms was optimized using simulated annealing algorithm and complex amplitude correlation to improve the quality of the converted modes. The correlation measurements, and comparisons between numerical and experimental results, show the fidelity of the obtained modes and the effectiveness of the optimization. Furthermore, the optimized holograms can be combined to generate multiple modes spatially addressed with individual control. The results, and the use of a digital micromirror device instead of the most common liquid crystal modulators, make this method suitable for Modal Division Multiplexing systems and compatible with other optical telecommunication techniques like Wavelength and Polarization Division multiplexing, and reconfigurable optical networks.

48-55

Authors: V.V. Ivakhnik, D.R. Kapizov, V.I. Nikonov

For a four-wave radiation converter in a two-dimensional multimode waveguide with thermal nonlinearity at a low reflection coefficient, we analyze the influence of the spatial structure of pump waves on the quality of wavefront reversal. It is shown that the half-width of modulus of the point spread function of a four-wave radiation converter decreases with decreasing radius of Gaussian pump waves on the waveguide edges, leading to an improvement in the quality of wavefront reversal. For a four-wave radiation converter in a two-dimensional waveguide with infinitely conducting surfaces, we show the presence of "generation" points, near which a sharp increase in the object wave amplitude is observed, with its form completely determined by one of the waveguide modes.

65-70

Authors: V.I. Guzhov, I.O. Marchenko, E.E. Trubilina

Reconstruction of the signal in the intervals between discrete values is of great importance in solving the problem of spatial superresolution in optical microscopy and digital holography. The article deals with the issue of restoring high-resolution image elements from a certain number of raster images displaced by a sub-pixel shift. The numerical values of the image samples are obtained by spatial integration over some finite area of regular rasters. The spatial resolution is increased using an analytical expression for the spectrum of discrete signals obtained using the apparatus of generalized functions. Unlike ideal sampling, the spectrum of the function is supplemented by a multiplier, whose form depends on the type of aperture. To obtain high-resolution image elements, it is necessary to divide the Fourier spectrum of the sampled image by a factor depending on the selected aperture. The spectrum of the aperture is usually used, therefore, if the spectrum of the image obtained by averaging over a certain aperture is known, then the spectrum of the original image can also be obtained. Apertures of various shapes are used, for example, elliptical, diamond-shaped, hexagonal, but most often rectangular apertures. The simulation results are presented for a rectangular aperture but in the case of its substitution with, for example, a set of regular apertures in the form of a circle, the expression will be true for regular circular rasters. The analytical expression for the spectrum of the image obtained by averaging over a certain aperture can be used to reconstruct the spectrum of the original image. Having received the inverse Fourier transform from it, it is possible to obtain the original image. With an increase in the spatial resolution it becomes possible to carry out studies by methods of digital holography of volumetric diffuse objects while retaining the quality of analog holography (when recording in photographic media) and create optical superresolution systems based on optical microscopes.

83-89

Authors: D.H. Nguyen, A.V. Bakholdin

The article presents an algorithm for the synthesis of cemented and air-spaced doublets. A description of the doublets design computer tool from materials of a user-defined catalog is presented. Features of doublets design automation are considered. An approach for ranking of the generated variants of the doublets according to the preliminary evaluation criterion determined with the main parameters within the framework of the theory of third-order aberrations is proposed. The developed computer tool will help an optical engineer to calculate quickly cemented and air-spaced doublets with the required characteristics.

97-102

Authors: S.M. Borzov, O.I. Potaturkin, S.B. Usilov

This work is devoted to the study of methods for detecting retroreflective objects, including optical and optoelectronic observation devices, based on the search for spatial anomalies in images formed in pulsed laser ranging systems. Algorithms, software and hardware for detecting retroreflective objects have been developed. At the same time, special attention is paid to various ways of forming difference frames with periodic illumination, including with the preliminary replacement of each pixel of the background images by the maximum value for the corresponding neighborhood. The effectiveness of the proposed methods for detecting retroreflective objects exposed to bright sunlight, despite the presence of (mirror and diffuse) reflecting surfaces in the field of view, is demonstrated.

113-120

Authors: D.S. Sidorchuk

This work considers the problem of quality assessment of multichannel image visualization methods. One approach to such an assessment, the Escore quality measure, is studied. This measure, initially proposed for decolorization methods evaluation, can be generalized for the assessment of hyperspectral image visualization methods. It is shown that Escore does not account for the loss of local contrast at the supra-pixel scale. The sensitivity to the latter in humans depends on the observation conditions, so we propose a modified wEscore measure which includes the parameters allowing for the adjustment of the local contrast scale based on the angular resolution of the images. We also describe the adjustment of wEscore parameters for the evaluation of known decolorization algorithms applied to the images from the COLOR250 and the Cadik datasets with given observational conditions. When ranking the results of these algorithms and comparing it to the ranking based on human perception, wEscore turned out to be more accurate than Escore.

130-138

Authors: S.V. Savvin, A.A. Sirota

The article describes algorithms for multi-frame image super-resolution, which recover high-resolution images from a sequence of low-resolution images of the same scene under applicative noise. Applicative noise generates local regions of outlying observations in each image and reduces the image resolution. So far, little attention has been paid to this problem. At the same time, the use of deep neural networks is considered to be a promising method of image processing, including multi-frame image super-resolution. The article considers the existing solutions to the problem and suggests a new approach based on using several pre-trained convolutional neural networks and directed acyclic graph neural networks trained by the authors. The developed approach and the algorithms based on this approach involve iterative processing of the input sequence of low-resolution images using different neural networks at different processing stages. The stages include registration of low-resolution images, their segmentation performed in order to determine regions damaged by applicative noise, and transformation performed in order to increase the resolution. The approach combines the strengths of the existing solutions while lacking their drawbacks resulting from the use of approximate mathematical data models required for the synthesis of the image processing algorithms within the statistical theory of solutions. The experimental studies demonstrated that the suggested algorithm is fully functional and allows more accurate recovery of high-resolution images than the existing analogues.

160-166

Authors: E.S. Noskova, I.E. Zakharov, Y.N. Shkandybin, S.G. Rykovanov

Nowadays, the problem of creating high-performance and energy-efficient hardware for Artificial Intelligence tasks is very acute. The most popular solution to this problem is the use of Deep Learning Accelerators, such as GPUs and Tensor Processing Units to run neural networks. Recently, NVIDIA has announced the NVDLA project, which allows one to design neural network accelerators based on an open-source code. This work describes a full cycle of creating a prototype NVDLA accelerator, as well as testing the resulting solution by running the resnet-50 neural network on it. Finally, an assessment of the performance and power efficiency of the prototype NVDLA accelerator when compared to the GPU and CPU is provided, the results of which show the superiority of NVDLA in many characteristics.