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Space-frequency analysis with parallel computing in a phase-sensitive optical time-domain reflectometer distributed sensor

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APPLIED OPTICS 2014年第28期53卷 6586-6590页

作者： Hui, Xiaonan Ye, Taihang Zheng, Shilie Zhou, Jinhai Chi, Hao Jin, Xiaofeng Zhang, Xianmin Zhejiang Univ Dept Informat Sci & Elect Engn Hangzhou 310027 Zhejiang Peoples R China Zhejiang Univ Cyrus Tang Ctr Sensor Mat & Applicat Hangzhou 310027 Zhejiang Peoples R China

For a phase-sensitive optical time-domain reflectometer (phi-OTDR) distributed sensor system, space-frequency analysis can reduce the false alarm by analyzing the frequency distribution compared with the traditional difference value method. We propose a graphics processing unit (GPU)-based parallel computing method to perform multichannel fast Fourier transform (FFT) and realize the real-time space-frequency analysis. The experiment results show that the time taken by the multichannel FFT decreased considerably based on this GPU parallel computing. The method can be completed with a sensing fiber up to 16 km long and an entry-level GPU. Meanwhile, the GPU can reduce the computing load of the central processing unit from 70% down to less than 20%. We carried out an experiment on a two-point space-frequency analysis, and the results clearly and simultaneously show the vibration point locations and frequency components. The sensor system outputs the real-time space-frequency spectra continuously with a spatial resolution of 16.3 m and frequency resolution of 2.25 Hz. (C) 2014 Optical Society of America

关键词： computation methods Discrete Fourier transforms Erbium doped fiber amplifiers Fast Fourier transforms Spatial resolution Spectroscopy

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Fast non-line-of-sight imaging based on product-convolution expansions

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OPTICS LETTERS 2022年第18期47卷 4680-4683页

作者： Xu, W. E. I. H. A. O. Chen, S. O. N. G. M. A. O. Tian, Y. U. Y. U. A. N. Wang, D. I. N. G. J. I. E. Su, X. I. U. Q. I. N. Chinese Acad Sci Xian Inst Opt & Precis Mech Key Lab Space Precis Measurement Technol Xian 710119 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China Pilot Natl Lab Marine Sci & Technol Qingdao 266237 Peoples R China

Non-line-of-sight (NLoS) imaging reveals a hidden scene using indirect diffuse reflections. A common choice for ana-lyzing the time-of-flight (ToF) data from a non-confocal system is an ellipsoid model whose operator is high -dimensional, leading to a computationally arduous task. In this Letter, the product-convolution expansions method is utilized to formulate the operator and its adjoint based on the observation of a shift-variant point spread function (PSF) in the ToF data. The operator and its adjoint are locally approximated as a convolution, which allows the for-ward and backward procedure to be computed efficiently through fast Fourier transform (FFT). Moreover, the low -rank approximation of the operator is obtained by matrix decompositions, further improving the computational effi-ciency. The proposed method is validated using publicly accessible datasets. (c) 2022 Optica Publishing Group

关键词： computation methods Fast Fourier transforms Fourier transforms Point spread function Reflection Temporal resolution

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Discriminating the boundaries of half-tone images using the multiaperture gradient-estimate method

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JOURNAL OF OPTICAL TECHNOLOGY 2002年第1期69卷 32-35页

作者： Medennikov, PA All Russia Sci Ctr SI Vavilov State Opt Inst Sci Res Inst Comprehens Testing Optoelect Devices Sosnovyi Bor Leningrad Oblas Russia

This paper presents an algorithm for discriminating contours on half-tone images. An adaptive multiaperture system is proposed for calculating the boundary attribute for the image points, which makes it possible to fine-tune to the type of boundaries of the objects and to the noise level on the image. The contour is discriminated by tracing the local maxima of the boundary attribute. The results of the operation of the given algorithm are compared with the results of the operation of its nonadaptive analog, as well as with the results of the discrimination of boundaries by means of an algorithm based on Sobel's differential operator. (C) 2002 Optical Society of America.

关键词： Algorithms Brightness computation methods Image processing Imaging noise

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2-DIMENSIONAL IMAGE-RECONSTRUCTION FROM FOURIER COEFFICIENTS COMPUTED DIRECTLY FROM ZERO CROSSINGS

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APPLIED OPTICS 1993年第17期32卷 3092-3093页

作者： SALOMA, C HAEBERLI, P The authors are with the National Institute of Physics College of Science University of the Philippines Diliman Quezon City 1101 Philippines.

Two-dimensional image reconstruction using Fourier coefficients that are computed directly from the sampled representation of zero crossings is demonstrated. A two-dimensional image of dimensions N(x) x N(y) is interpreted as a set of N(y) independent x-space lines (in gray-scale format) that are arranged uniquely along they direction. Each line has N(x) elements. Reconstruction is achieved first by computing the entire set of N(y) one-dimensional Fourier transforms from the measured zero crossings using Newton's formula. Each N(y)th line spectra has N(x) Fourier coefficients. The inverse Fourier transform is then applied to each of the line spectra to obtain a set of N(y) reconstructed x-space lines. The reconstructed image is obtained by arranging the reconstructed lines properly along they direction.

关键词： CCD cameras computation methods Detectors Fast Fourier transforms Fourier transforms Image reconstruction

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DETERMINATION OF THICKNESS AND OPTICAL-CONSTANTS OF THIN-FILMS FROM PHOTOMETRIC AND ELLIPSOMETRIC MEASUREMENTS

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APPLIED OPTICS 1986年第24期25卷 4557-4561页

作者： ELIZALDE, E FRIGERIO, JM RIVORY, J UNIV PARIS 06 OPT SOLIDS LAB F-75230 PARIS 05 FRANCE

We describe a computational method of determining the optical constants n(λ),k(λ) and the film thickness d from photometric R(λ),T(λ) and ellipsometric Ψ(λ),Δ(λ) data. Combinations of three or four of the measured quantities are compared using Newton-Raphson and Simplex techniques. The method is applied to thin films of gold and amorphous metallic alloys. The results are discussed.

关键词： computation methods Optical constants Optical materials Optical measurement Phase shift Thin films

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Light-extraction efficiency control in AlGaN-based deep-ultraviolet flip-chip light-emitting diodes: a comparison to InGaN-based visible flip-chip light-emitting diodes

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OPTICS EXPRESS 2015年第16期23卷 20340-20349页

作者： Lee, Keon Hwa Park, Hyun Jung Kim, Seung Hwan Asadirad, Mojtaba Moon, Yong-Tae Kwak, Joon Seop Ryou, Jae-Hyun LG Innotek Co Dept LED Business Paju 413901 South Korea Univ Houston Dept Mech Engn Houston TX 77204 USA Sunchon Natl Univ Dept Printed Elect Engn Jeonnam 540742 South Korea Univ Houston Mat Sci & Engn Program Houston TX 77204 USA Univ Houston Texas Ctr Superconduct Houston TX 77204 USA

We study light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) using flip-chip (FC) devices with varied thickness in remaining sapphire substrate by experimental output power measurement and computational methods using 3-dimensional finite-difference time-domain (3D-FDTD) and Monte Carlo ray-tracing simulations. Light-output power of DUV-FCLEDs compared at a current of 20 mA increases with thicker sapphire, showing higher LEE for an LED with 250-mu m-thick sapphire by similar to 39% than that with 100-mu m-thick sapphire. In contrast, LEEs of visible FCLEDs show only marginal improvement with increasing sapphire thickness, that is, similar to 6% improvement for an LED with 250-mu m-thick sapphire. 3D-FDTD simulation reveals a mechanism of enhanced light extraction with various sidewall roughness and thickness in sapphire substrates. Ray tracing simulation examines the light propagation behavior of DUV-FCLED structures. The enhanced output power and higher LEE strongly depends on the sidewall roughness of the sapphire substrate rather than thickness itself. The thickness starts playing a role only when the sapphire sidewalls become rough. The roughened surface of sapphire sidewall during chip-separation process is critical for TM-polarized photons from AlGaN quantum wells to escape in lateral directions before they are absorbed by p-GaN and Au-metal. Furthermore, the ray tracing results show a reasonably good agreement with the experimental result of the LEE. (C) 2015 Optical Society of America

关键词： computation methods Light propagation Photonic crystals Quantum wells Ray tracing Spontaneous emission

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Achieving efficient inverse design of low-dimensional heterostructures based on a vigorous scalable multi-task learning network

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OPTICS EXPRESS 2021年第13期29卷 19727-19742页

作者： Du, Shiyin You, Jie Tang, Yuhua Ouyang, Hao Tao, Zilong Jiang, Tian Natl Univ Def Technol Coll Comp State Key Lab High Performance Comp Changsha 410073 Peoples R China Acad Mil Sci PLA China Def Innovat Inst Beijing 100071 Peoples R China Natl Univ Def Technol Coll Adv Interdisciplinary Studies Changsha 410073 Peoples R China Natl Univ Def Technol Beijing Inst Adv Study Beijing 100020 Peoples R China

A scalable multi-task learning (SMTL) model is proposed for the efficient inverse design of low-dimensional heterostructures and the prediction of their optical response. Specifically, several types of nanostructures, including single and periodic graphene-Si heterostructures consisting of nxn graphene squares (n=1 similar to 9), 1D periodic graphene ribbons, 2D arrays of graphene squares, pure Si cubes and their periodic array counterparts, are investigated using both traditional finite element method and SMTL network, with the former providing training data (optical absorption) for the latter. There are two important algorithms implemented in SMTL model: one is the normalization mechanism that makes different parameters of different structures on the same scale, ensuring that SMTL network can deal with tasks with different dataset impartially and without bias;the other one is used to capture the impact of nanostructures' dimensions on their optical absorption and thus improve the generalization ability of SMTL. Utilizing SMTL model, we first study the absorption property of the multiple shaped nanostructures and look deeper into the impacts of nxn graphene squares and Si cuboid on the optical absorption of their heterostructures. Equally important, the multi-structure inverse design functionality of SMTL is confirmed in this context, which not only owns high accuracy, fast computational speed, and excellent generalizable ability, but also can be applied to contrive new structures with desired optical response. This work adds to the rapidly expanding field of inverse design in nanophotonics and establishes a multi-task learning framework for heterostructures and more complicated nanoparticles. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： computation methods Light scattering Nonlinear optical devices Optical absorption Plasmon waveguides Surface plasmon polaritons

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Steerable photonic jet for super- resolution microscopy

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OPTICS EXPRESS 2022年第23期30卷 41757-41773页

作者： Karamehmedovic, Mirza Scheel, Kenneth Pedersen, Frederik Listov-Saabye Villegas, Arturo Hansen, Poul-Erik Tech Univ Denmark Dept Appl Math & Comp Sci DK-2800 Lyngby Denmark Barcelona Inst Sci & Technol ICFO Inst Ciencies Foton Castelldefels 08860 Barcelona Spain Danish Fundamental Metrol DK-2970 Horsholm Denmark

A promising technique in optical super-resolution microscopy is the illumination of the sample by a highly localized beam, a photonic jet (also called photonic nanojet). We propose a method of computation of incident field amplitude and phase profiles that produce photonic jets at desired locations in the near field after interaction with a fixed micro-scale dielectric lens. We also describe a practical way of obtaining the incident field profiles using spatial light modulators. We expect our photonic jet design method to work for a wide range of lens shapes, and we demonstrate its application numerically using two-dimensional micro-lenses of circular and square cross-sections. We furthermore offer a theoretical analysis of the resolution of photonic jet design, predicting among other that a larger lens can produce a narrower photonic jet. Finally, we give both theoretical and numerical evidence that the waist width of the achieved designed jets is increasing linearly and slowly over a large interval of radial distances. With uniform plane wave illumination, the circular two-dimensional micro-lens produces a similar-sized jet at a fixed radial distance, while the square lens does not form a jet at all. We expect our steerable optical photonic jet probe to enable highly localized adaptive real-time measurements and drive advances in super-resolution optical microscopy and scatterometry, as well as fluorescence and Raman microscopy. Our relatively weak peak jet intensity allows application in biology and health sciences, which require high resolution imaging without damaging the sample bio-molecules. (c) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Analytical techniques computation methods Direct write lithography Fluorescence microscopy Liquid crystal modulators Super resolution microscopy

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FAST ALGORITHM FOR THE computation OF THE ZERO-ORDER HANKEL TRANSFORM

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA 1983年第9期73卷 1130-1137页

作者： MURPHY, PK GALLAGHER, NC Purdue University West Lafayette Indiana 47907

The Hankel transform may be defined as the two-dimensional Fourier transform of a circularly symmetric function. A new Hankel-transform algorithm based on this definition is described. The proposed algorithm efficiently generates a rectangularly sampled two-dimensional output array by using the circular symmetry properties of the input array and two-dimensional vector radix fast-Fourier transform techniques. It accomplishes this by partitioning the input matrix into smaller and smaller processing blocks while removing redundant blocks from data manipulations. For applications that require the output data to be sampled on a two-dimensional rectangular raster, the convenience and the computational speed of the resulting algorithm offer advantages over the one-dimensional Hankel-transform algorithms currently available.

关键词： Algorithms computation methods Fast Fourier transforms Fourier transforms Interpolation Transforms

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Pose correction scheme for camera-scanning Fourier ptychography based on camera calibration and homography transform

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OPTICS EXPRESS 2022年第12期30卷 20697-20711页

作者： Cui, Baiqi Zhang, Shaohui Wang, Yechao Hu, Yao Hao, Qun Being Inst Technol Sch Opt & Photon Being 100081 Peoples R China Being Inst Technol Yangtze Delta Reg Acad Beijing Peoples R China Beijing Inst Space Mech & Elect Beijing 100094 Peoples R China

Fourier ptychography (FP), as a computational imaging method, is a powerful tool to improve imaging resolution. Camera-scanning Fourier ptychography extends the application of FP from micro to macro creatively. Due to the non-ideal scanning of the camera driven by the mechanical translation stage, the pose error of the camera occurs, greatly degrading the reconstruction quality, while a precise translation stage is expensive and not suitable for wide-range imaging. Here, to improve the imaging performance of camera-scanning Fourier ptychography, we propose a pose correction scheme based on camera calibration and homography transform approaches. The scheme realizes the accurate alignment of data set and location error correction in the frequency domain. Simulation and experimental results demonstrate this method can optimize the reconstruction results and realize high-quality imaging effectively. Combined with the feature recognition algorithm, the scheme provides the possibility for applying FP in remote sensing imaging and space imaging. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Camera calibration computation methods Image quality Optical systems Phase retrieval Three dimensional imaging

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