Дифракционная оптика, оптические технологии. Рубрика в журнале - Компьютерная оптика
"Бездифракционные пучки" и их каустики
Статья научная
В настоящей работе обсуждается возможность формирования фокальных областей в различных зонах дифракции и доказывается, что термин "бездифракционные пучки" применяется для обозначения ограниченной в пространстве части тороидальной световой волны. Световая линия, или осевая каустика, является результатом интерференции пересекающихся областей этой волны. Показано, что "бездифракционные пучки" формируются такими оптическими элементами, фазовая функция пропускания которых содержит линейные по радиальной координате слагаемые. Выполнено сравнение оптических характеристик каустик в ближней и в дальней зонах дифракции. Сообщается о синтезе нового дифракционного модулированного аксикона, который формирует две фокальных области различного типа. Приводятся результаты экспериментального исследования его оптических характеристик.
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3D measurement using fringe projection profilometry
Статья научная
This work is devoted to measuring the depth of the 3D object using the structured light method, in particular, phase shift profilometry. Theoretical studies on the methods of three-dimensional measurement systems and fringe projection profilometry are presented. The phase shift profilometry method with an improved calculation of the frequency of sinusoidal patterns is applied. In practical implementation in the environment (20 cm × 30 cm), the algorithm is tested on a stepped object consisting of eight steps with a difference of 150 mm between two successive steps. In this case, the achievable error for measuring such an object is 20 mm. Our method has great potential in industrial applications where the measurement of the smoothing of the surface of the object is needed to find the defect in the surface with high accuracy without contacting the object.
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3D-визуализация многократно рассеивающих сред
Статья научная
Настоящая работа посвящена теоретическим исследованиям распространения низкоинтенсивного лазерного излучения оптического диапазона в многократно рассеивающих средах и направлена на создание универсальной оптической схемы их визуализации. При анализе внутренней структуры объекта и протекающих в нем процессов в большинстве случае необходимо учитывать не абсолютные значения оптических параметров, а их пространственно-временные флуктуации. В связи с этим в качестве базового метода исследования выбран дифференциальный алгоритм метода обратного рассеяния. Построена 3D-модель многократного рассеяния в программной среде TracePro с применением статистического метода Монте-Карло. Проведены численные эксперименты по математическому моделированию взаимодействия лазерного излучения с объектом и визуализации его строения. Определены зависимости дифференциальных характеристик рассеянного излучения от топологии и оптических параметров среды. На основании полученных данных сделан вывод о возможности применения созданной объемной модели для решения задач диагностики многократно рассеивающих объектов, в частности, биообъектов.
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Статья научная
In this paper, a compact design of a balanced 1×4 optical power splitter based on coupled mode theory (CMT) is presented. The design consists of seven vertically slotted waveguides based on the silicon-on-insulator platform. The 1×4 OPS is modelled using commercial finite element method (FEM) simulation tool COMSOL Multiphysics 5.1. The optimized OPS is capable of working across the whole C-band with maximum ~39 % of power decay in the wavelength range 1530 - 1565 nm.
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Ab initio modeling of Raman and infrared spectra of calcite
Статья научная
Calcite is the most thermodynamically stable polymorphic phase of the CaCO3 crystal. It is widely used in modern optical instruments operating in the infrared and visible wavelengths of electromagnetic radiation. In particular, due to its anisotropic properties, calcite is used in polarization optics devices. Ab initio quantum mechanical modeling of the Raman and infrared spectra of calcite makes it possible to better understand the structure and nature of the chemical bonds of the compound, and find the optimal conditions for the effective use of unique properties of calcite in photonics tools. The calculations are performed within the framework of the density functional theory in the CRYSTAL program, using the “hybrid” B3LYP functional and the all-electronic bases of the STO-6G, PO-TZVP and BSD atomic orbitals of the Gaussian type. The obtained results for the elastic constants, Raman and infrared spectra of calcite agree satisfactorily with the available experimental data for the basic sets of POB-TZVP and BSD.
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Accelerated algorithm for calculating spectra of aperiodic gratings
Статья научная
To compute the spectrum of aperiodic Bragg gratings, we address a direct scattering problem for the Helmholtz equation. Numerically, this problem necessitates the calculation of transfer matrix products, which involves multiple multiplications of matrix elements – polynomials that depend on the spectral parameter of the problem. We propose an accelerated algorithm to solve the scattering problem with second-order accuracy. This algorithm leverages the integral approach for discretization, a duplication strategy, the convolution theorem, and the fast Fourier transform. The computational complexity of this approach is asymptotically O(N log2N) arithmetic operations (multiplications) for a discrete grid of size N. Numerical simulations corroborate the algorithm’s second-order accuracy and its high computational speed, in accordance with the estimates obtained.
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Amplification of UV radiation and gain mechanisms in ZnO films with loose-packed structure
Статья научная
The modern demands for miniaturization of optoelectronic devices, in particular, for the UV range, are inextricably linked with the improvement of fabrication technologies for the corresponding photonic nano/micro objects and the study of their radiative properties. In this work, the method of pyrolytic carbothermal synthesis, which is a modification of the thermal evaporation method, was used to fabricate microcrystalline ZnO films with laser properties. The influence of the size and packing type of ZnO microcrystallites in the films on their emissive properties were revealed. The films with relatively large microcrystallites (10–15 µm in size on average) were found to exhibit UV amplified spontaneous emission at room temperature. The possibility of additional enhancement of this emission and its two-threshold behavior in loose-packed regions of such films were found for the first time. It was shown that the observed phenomenon is due to the competition between two gain mechanisms, which are assumed to arise predominantly in different regions of microcrystallites as a result of exciton-phonon and exciton-electron interaction processes. As the temperature decreases, the dominant gain mechanism gradually changes to exciton-exciton scattering, regardless of the type of film structure. The results obtained open up the possibilities of the thermal evaporation synthesis to a wider extent and can be useful in interpreting the optical gain mechanisms in ZnO micro- and nanostructures.
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Automatic 4-mirrors system for alignment of high-power laser radiation
Статья научная
This paper presents the automated system for minimizing the deviation of the path of passage and the divergence of a secondary radiation source with parameters similar to ones of the main beam of a high-power Ti:Sa laser using mirrors in kinematic mounts on the motorized stages. As an alignment laser, the diode laser with a fiber output was used with radiation characteristics coinciding with the parameters of the main beam (wavelength, beam diameter). The successive approximation algorithm was used to minimize the beam deflection. The positioning accuracy and beam size matching were analyzed on the near-field camera and were equaled to 28.6 µm along the X-axis and 26.4 µm along the Y-axis. Beam size mismatch was equaled to 0.151 mm. The pointing accuracy was analyzed on the far-field sensor and equaled 15.34 µrad along the X axis and 12.03 µrad along the Y axis. The curvature of the wavefront was 0.06 µm.
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Bragg-fresnel optics and supermirrors
Статья научная
The main principles and some applications of Bragg-Fresnel multilayer optics and X-ray supermirrors are described. An elliptical Bragg-Fresnel multilayer lens (BFML), designed and fabricated in the IMT RAS has been used for 2-dimensional focusing of the white X-ray synchrotron beam. For the beam energy of about 12 KeV the spot size checked with the knife edge method was about 1 mm. Applications of BFML and supermirrors in x-ray imaging are discussed.
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Статья научная
Photonic crystal fiber as a new type of optical fiber has been extensively applied because of its unique properties. The effective mode area of optical fiber is an important parameter, which has a great influence on the performance of optical fiber. In this study, digital image processing algo-rithm was used for preprocessing to improve the accuracy of calculation of mode field area. Then the effective mode field area of optical fiber was calculated using Matlab based Gauss fitting method. Take single-mode fiber G.652 as an example, the effective mode field area was calculated using the traditional algorithm and digital image processing algorithm respectively. It was found that the results obtained using digital image processing algorithm were within the allowed error range, suggesting the effectiveness of the algorithm. Then the calculation of the effective mode area of the triangular lattice photonic crystal fiber further verified the reliability of the algorithm.
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Статья научная
In this study, an algorithm based on convolutional neural networks is employed as an interrogation method for a fiber specklegram sensor. This algorithm is compared with conventional interrogation methods, including correlation between images, measurement of optical power, and radial moments. Fiber specklegram sensors have room for improvement as conventional methods only consider a single characteristic of the specklegram for variable prediction, thus failing to leverage the full spectrum of information within the specklegram. Consequently, the approach put forth here introduces a convolutional neural network for the extraction of specklegram features, accompanied by an artificial neural network for variable regression. The specklegrams used in this investigation are obtained through simulating temperature disturbances in a multimode fiber using the Finite Elements Method. The results reveal prediction RMSE errors ranging from 10.26°C for the first radial moment to 1.42°C for the proposed algorithm. These findings underscore the effectiveness of the proposed strategy in enhancing sensor performance and robustness, all while upholding their cost-efficiency.
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Computational and experimental studies on SnO2 thin films at various temperatures
Статья научная
Tin oxide (SnO2) thin films was prepared by dip-coating technique at various bath temperatures (313, 333, 353 and 373 K) and annealed at 673 K in this study. And the obtained results were studied and correlated with the computational method. Scanning electron microscopy (SEM) investigation demonstrated that the prepared samples are spherical with agglomeration. The elemental analysis (EDAX) confirms the presence of Sn and O. Further, the SnO2 thin films microstructures are simulated, their thermodynamic and surface properties have been calculated. Micro-Raman spectra were recorded for the prepared samples. Micro-Raman results exhibit the first-order Raman mode E1g (475 cm-1) indicating that the grown SnO2 belongs to the rutile structure. In addition, the envelope method used for studying optical characteristics of the thin films from the transmittance spectra. The semiconducting nature of the films has been noticed from linear I-V characteristics. Furthermore, the electrical conductivity studies suggest that the highest conductivity samples acquire the lowest activation energy and their values are also in the semiconducting range.
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Статья научная
Nowadays, various materials are extensively utilized in various fields. These materials often cause invisible damage with the long-term service of machines. A health monitoring system for materials was presented to eliminate safety hazards as much as possible. This study proposed a fiber optic stress wave sensing system in view of Lamb wave damage imaging to address the limitations in the use of materials in some flaw detection systems. Meanwhile, Lamb waves with small propagation attenuation and long distance in the material were selected as the detection method. Then the fiber optic stress wave sensing system was used to carry out damage imaging. The imaging principle of wavelet packet decomposition was selected to avoid losing low-frequency information. The experiment demonstrated that compared to the original method in view of time correlation coefficient, the method used in this study improved the signal-to-noise ratio of damaged images by 1.0112 dB, higher accuracy, better imaging quality, and more pronounced output images. This research offers a theoretical foundation for the application of fiber optic stress wave sensing systems in the flaw detection, provides practical value for the practical application of Lamb waves, and has positive significance for the application of flaw detection in industry.
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Статья научная
The work is devoted to an overview of the current state of optoacoustic fiber-optic ultrasonic transducers based on thermoelastic effect and fiber-optic interference receivers, its scope, technologies and materials used, the advantages and disadvantages of different methods and the prospects for the development of the industry.
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Cравнение разных подходов к формированию «идеального» оптического вихря
Статья научная
Получены точные аналитические выражения, описывающие комплексную амплитуду идеального оптического вихря, сформированного тремя разными оптическими элементами: амплитудно-фазовым с пропусканием, пропорциональным функции Бесселя, оптимальным фазовым с пропусканием, равным знаковой функции от функции Бесселя, и вихревым аксиконом. Показано, что интенсивность света на кольце больше для оптимального фазового элемента. Ширина светового кольца, сформированного вихревым аксиконом, примерно в два раза больше, чем ширина двух других колец. Таким образом, оптимальный элемент является наилучшим кандидатом для формирования идеального оптического вихря. Результаты моделирования подтверждают теоретические выводы, а результаты эксперимента согласуются с теорией и результатами моделирования.
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Cуперпозиция оптического вихря и плоской волны с линейными поляризациями в остром фокусе
Статья научная
Рассмотрена острая фокусировка суперпозиции вихревого лазерного пучка с топологическим зарядом n с линейной поляризацией и плоской волны с такой же линейной поляризацией, направленной вдоль горизонтальной оси. В формализме Ричардса–Вольфа получены аналитические выражения для распределения интенсивности и продольной проекции спинового углового момента в плоскости фокуса. Показано, что для четных и нечетных номеров n интенсивность и спиновый угловой момент обладают разной симметрией: при четном n они симметричны относительно обеих декартовых осей, а при нечетном n они симметричны только относительно вертикальной оси. Распределение интенсивности имеет 2n локальных максимумов в фокусе, и на оптической оси интенсивность при любом n отлична от нуля. Распределение продольной проекции спинового углового момента (плотность спина) в плоскости фокуса имеет (n+2) субволновых областей с положительным спиновым угловым моментом и (n+2) областей с отрицательным спиновым угловым моментом, центры которых, чередуясь, лежат на окружности некоторого радиуса с центром на оптической оси. Такое распределение спина с разным знаком демонстрирует продольный спиновый эффект Холла в фокусе. Суммарно в фокусе отрицательный и положительный спин взаимно компенсируется и равен нулю.
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Статья научная
We propose and numerically verify a design of the photonic integrated circuit for in-plane generation of a 1st azimuthal order vortex mode in dielectric rectangular waveguides. Radiation is introduced into the proposed structure in a standard way through two grating couplers. Applying a mode coupling and specific phase shift, a field with the required amplitude-phase distribution is formed directly in the output waveguide. The geometric dimensions of the device are simulated and optimized to fit the technological parameters of the silicon-on-insulator platform.
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Design and optimization of high-contrast gratings for multispectral VCSEL-SOI laser sources
Статья научная
In the scope of a computational experiment, high-contrast gratings (HCG) formed on a silicon-on-insulator (SOI) platform within vertical-cavity surface-emitting lasers (VCSELs) were studied for multispectral laser sources. A simulation model for spectral characteristics calculation is proposed, which includes two heterogeneously integrated parts of the VCSEL: 1) the lower output mirror based on a HCG grating in the silicon layer of the SOI surrounded by air cavities to enhance the contrast of the HCG; 2) the semiconductor VCSEL structure with an air aperture for current and optical confinement. Comparative analysis results of the spectral characteristics of VCSEL-SOI structures for zeroth, first, and second-order modes, which can be excited in the air aperture of the VCSEL, are presented. It is demonstrated that the HCG, acting as one of the cavity mirrors, effectively discriminates the VCSEL higher-order modes. An algorithm for calculating HCG parameters that ensure the maximum reflectivity at a fixed thickness of the silicon layer of the SOI is developed.
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Статья научная
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.
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Designing multilayer dielectric filter based on TiO2/SiO2 for fluorescence microscopy applications
Статья научная
This study presents a new construction design of a distributed Bragg reflector (DBR) filter and a Fabry-Pérot (FP) filter by using needle technique as a synthesis method. The optimized DBR and FP filters having a proper number of layers with controlling thickness TiO2/SiO2 are utilized to transmit only a certain narrow band of wavelengths while blocking the others. As a proof of concept, the filters are designed to selectively transmit only a very narrow band of wavelength at 780 nm which is the near infrared (NIR) fluorescent emission from Alexa Fluor 750 dye. The obtained results show that the optimized filters represent advanced spectral performance which can be used to improve the sensitivity and the imaging contrast in fluorescence microscopy.
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