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Study on transition from photonic-crystal laser to random laser

OPTICS EXPRESS 2012年第7期20卷 7300-7315页

作者： Fujii, Garuda Matsumoto, Toshiro Takahashi, Toru Ueta, Tsuyoshi Nagoya Univ Dept Mech Sci & Engn Chikusa Ku Nagoya Aichi Japan Jikei Univ Sch Med Phys Lab Tokyo Japan

The dependence of the lasing threshold on the amount of positional disorder in photonic crystal structures is newly studied by means of the finite element method, not of the finite difference time domain method usually used. A two-dimensional model of a photonic crystal consisting of dielectric cylinders arranged on a triangular lattice within a circular region is considered. The cylinders are assumed to be homogeneous and infinitely long. Positional disorder of the cylinders is introduced to the photonic crystals. Optically active medium is introduced to the interspace among the cylinders. The population inversion density of the optically active medium is modeled by the negative imaginary part of dielectric constant. The ratio between radiative power of electromagnetic field without amplification and that with amplification is computed as a function of the frequency and the imaginary part of the dielectric constant, and the threshold of the imaginary part, namely population inversion density for laser action is obtained. These analyses are carried out for various amounts of disorder. The variation of the lasing threshold from photonic-crystal laser to random laser is revealed by systematic computations with numerical method of reliable accuracy for the first time. Moreover, a novel phenomenon, that the lasing threshold have a minimum against the amount of disorder, is found. In order to investigate the properties of the lasing states within the circular system, the distributions of the electric field amplitudes of the states are also calculated. (C) 2012 Optical Society of America

关键词： computation methods Finite difference time domain Laser modes Photonic crystal lasers Photonic crystals Random lasers

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Faster generation of holographic video of 3-D scenes with a Fourier spectrum-based NLUT method

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OPTICS EXPRESS 2021年第24期29卷 39738-39754页

作者： Cao, Hongkun Jin, Xin Ai, Lingyu Kim, Eun-Soo Tsinghua Univ Shenzhen Int Grad Sch Shenzhen 518055 Peoples R China Jiangnan Univ Engn Res Ctr IoT Technol Applicat Dept Elect Engn Minist Educ Wuxi 214122 Jiangsu Peoples R China Kwangwoon Univ Holodigilog Human Media Res Ctr Nano Device Applicat Ctr 447-1 Wolge Dong Seoul 139701 South Korea

In this article, a new type of Fourier spectrum-based novel look-up table (FS-NLUT) method is proposed for the faster generation of holographic video of three-dimensional (3-D) scenes. This proposed FS-NLUT method consists of principal frequency spectrums (PFSs) which are much smaller in size than the principal fringe patterns (PFPs) found in the conventional NLUT-based methods. This difference in size allows for the number of basic algebraic operations in the hologram generation process to be reduced significantly. In addition, the fully one-dimensional (1-D) calculation framework of the proposed method also allows for a significant reduction of overall hologram calculation time. In the experiments, the total number of basic algebraic operations needed for the proposed FS-NLUT method were found to be reduced by 81.23% when compared with that of the conventional 1-D NLUT method. In addition, the hologram calculation times of the proposed method, when implemented in the CPU and the GPU, were also found to be 60% and 66% faster than that of the conventional 1-D NLUT method, respectively. It was also confirmed that the proposed method implemented with two GPUs can generate a holographic video of a test 3-D scene in real-time (>24f/s). (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： computation methods Fresnel equations Holographic displays Image quality Motion estimation Real time holography

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Iterative reconstruction method for the accurate measurement of optical transfer function

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APPLIED OPTICS 2021年第26期60卷 8164-8173页

作者： Pu, Dong Pan, Xingchen Tao, Hua Liu, Cheng Zhu, Jianqiang Chinese Acad Sci Shanghai Inst Opt & Fine Mech Key Lab High Power Laser & Phys Shanghai 201800 Peoples R China Chinese Acad Sci China Acad Engn Phys Natl Lab High Power Laser & Phys Shanghai 201800 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China

An iterative computation method was proposed to accurately reconstruct the optical transfer function (OTF) of an imaging lens from a series of recorded images of different patterns displayed on a digital micromirror device (DMD). Since several tens of recorded images are adopted in combination, the measurement noise is remarkably reduced in comparison with the conventional measurement method using a point object, and quite high measurement accuracy is reached by taking the known shape of each tiny mirror of the DMD into computation. While theoretical analysis is demonstrated, the validity of this proposed method is verified both numerically and experimentally. (C) 2021 Optical Society of America

关键词： computation methods Digital micromirror devices Image quality Image reconstruction Imaging systems Optical measurement

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Optical performance of symmetrical and asymmetrical Y-branch couplers for plastic optical fibers

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APPLIED OPTICS 2012年第19期51卷 4448-4456页

作者： Kuang, Jao-Hwa Chen, Pao-Chuan Chen, Yung-Chuan Natl Pingtung Univ Sci & Technol Dept Vehicle Engn Pingtung 91201 Taiwan Natl Sun Yat Sen Univ Dept Mech & Electromech Engn Kaohsiung 80424 Taiwan

The excess loss and output optical power ratio of symmetrical and asymmetrical Y-branch couplers for plastic optical fibers (POFs) are studied in this work. A ray-tracing model for the Y-branch coupler is derived to investigate the effect of coupling parameters on its optical performance. The coupling parameters, namely coupling angle, axial displacement, and refractive index of filling medium between the emitting-end and receiving-end POFs, are studied. The simulated and measured results indicate that the coupling efficiency is sensitive to all these coupling parameters. A minimum excess loss of approximately 0.83 dB is observed for the symmetrical Y-branch coupler. It is found that both the excess loss and the output power ratio are increased with the increase of the refractive index of the filling medium and the total coupling angle (alpha + beta) for the asymmetrical Y-branch coupler. The experimental results indicate that the maximum output power ratio P-1:P-2 is found to be 3.8:1 for excess loss of less than 2.8 dB for the asymmetrical Y-branch coupler. (C) 2012 Optical Society of America

关键词： Fiber optics and optical communications Buffers couplers routers switches and multiplexers Geometric optics computation methods

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Research on the computational method of creeping waves diffraction of arbitrary complex target based on the planar mesh model

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OPTICS EXPRESS 2023年第4期31卷 6426-6452页

作者： Huang, Qi He, Siyuan Zhang, Yunhua Zhu, Guoqiang Chen, Haitao Wuhan Univ Elect Informat Sch Wuhan 430072 Peoples R China China Shipbuilding Ind Corp Res Inst 722 Wuhan 430000 Peoples R China

For a long time, due to the difficulty of obtaining accurate propagation trajectories, the research on creeping waves is limited to canonical geometries or simple targets, which leads to the situation that it is relatively mature in theoretical research on creeping waves, while the practical application scope of creeping waves for complex targets is narrow. In this paper, a thorough electromagnetic computation method for creeping waves on complex planar mesh model is systematically proposed. This approach broadens the field of creeping waves applications due to the generality of planar mesh models in electromagnetic engineering. The contents consist of the tracing of creeping waves, the calculation of the diffraction field, and the coupling effect with other scattering mechanisms. Aiming at the trajectory of creeping waves, we propose a set of tracing algorithms that enable rapid, real-time tracing based on analytical geometry and related computer graphics algorithms. Utilizing information such as vertices, triangles, and topological relations in the mesh model, one can recover the mathematical properties of the surfaces of the model and then, the corresponding parameters can be obtained. Therefore, the uniform geometrical theory of diffraction (UTD) can be used to accurately calculate the diffraction field. Moreover, for complex targets, the multiple coupling effect caused by creeping waves is the main source of radar echoes in many cases, which is not unimportant. Hence based on the electromagnetic accurate modeling, the coupling mechanism of creeping waves and various scattering mechanisms are studied. The research content is expected to have high application values in target recognition and characteristics.

关键词： computation methods Diffraction theory Forward scattering In field scattering Surface waves Synthetic aperture radar

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Light transport in homogeneous tissue with m-dependent anisotropic scattering II: Fourier transform solution and consistent relations

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BIOMEDICAL OPTICS EXPRESS 2018年第9期9卷 4031-4053页

作者： Wang, Lin Rong, Meng Li, Kaiyang Wuhan Univ Sch Phys & Technol Dept Elect Sci & Technol 299 Bayi Rd Wuhan 430072 Hubei Peoples R China

This paper is the second of two focusing on the analytical solutions for light transport in infinite homogeneous tissue with an azimuth-dependent (m-dependent) anisotropic scattering kernel by two approaches, Case's singular eigenfuncions (CSEs) expansion and Fourier transform, and proving the consistence of the two solutions theoretically. In this paper, the analytical solution for the m-dependent truncated scattering kernel was derived via the Fourier transform and inversion, and expanded with the m-dependent generalized singular eigenfuncions (GSEs). Two kinds of GSEs that are defined by Ganapol in the case m = 0 are extended to arbitrary azimuthal orders and proven to be consistent with CSEs both in expression forms and in intrinsic behaviors. By applying the Fourier transform inversion on the solution for the three-term recurrences, the Green's function of radiance distributions is obtained successfully, and it conforms perfectly to the CSEs solution in the limit, which has already been discussed in our first accompanying paper. Meanwhile, as a byproduct, a series of identities about the m-dependent Chandrasekhar orthogonal polynomials were presented and will be greatly helpful for further studies. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Absorption coefficient Attenuation coefficient computation methods Fourier transforms Scattering Tissue

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Refraction correction for deep-water three-dimensional visual measurement based on multi-objective optimization

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OPTICS EXPRESS 2023年第19期31卷 31383-31396页

作者： Gu, Liuning Chen, Wenwu Hu, Xiaohan Tong, Zixiang Shao, Xinxing Southeast Univ Sch Civil Engn Dept Engn Mech Nanjing 210096 Peoples R China China Ship Sci Res Ctr Nanjing 210096 Peoples R China

Refraction-induced errors affect the accuracy of three-dimensional visual measurements in deepwater environments. In this study, a binocular camera refractive imaging model was established, and a calibration method for the refraction parameters was proposed for high-accuracy shape and deformation measurements in deep-water environments. First, an initial estimate of the refractive axis was obtained using a three-dimensional calibration target. Then, the errors in the distance between the spatial point pairs and the reprojection errors are taken as the dual optimization objectives, and the Non-dominated Sorting Genetic Algorithm II is applied to optimize the refraction parameters. To efficiently calculate the reprojection error, an improved numerical computation method is proposed to accelerate the calculation of the analytical forward projection. Underwater experiments were conducted to verify the method's effectiveness. The results showed that the average error of the absolute position of the reconstructed points was less than 1.1 mm and the average error of the displacement was less than 0.04 mm. This study provides a sound solution for accurate three-dimensional visual measurement in deep-water environments.

关键词： Camera calibration computation methods Genetic algorithms Refractive index Three dimensional measurement Underwater imaging

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Performance analysis of the retractable dome for the Chinese Large Telescope

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OPTICS EXPRESS 2015年第20期23卷 25376-25405页

作者： Nian, Pan Wen-Li, Ma Chinese Acad Sci Inst Opt & Elect Chengdu 610209 Sichuan Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China

In order to quantitatively assess the influence of the retractable dome on the observational performance of the 4-m Chinese Large Telescope (CLT), an integrated analysis method based on computational fluid dynamics (CFD) and sub-harmonic phase screen is proposed in this paper. The pressure, the temperature, and the speed of air surrounding the retractable dome are attained by CFD simulations, and then the fluctuation of refractive index of air is calculated. Based on sub-harmonic phase screen algorithm, three kinds of performance evaluation parameters are presented: irradiance, phase of the target, and Full Width Half Maximum (FWHM). The wind tunnel tests (WT) with a 1: 120 scaled model of the retractable dome for the CLT are conducted to verify the calculated precision of the CFD. The results show that the fluctuation of air refractive index surrounding the CLT is mainly caused by the inhomogeneous distribution of temperature and speed, and with the help of pier's height the impact of inhomogeneous air temperature from the ground layer on the fluctuation of air refractive index can be effectively decreased. Furthermore, the lower of the air speed is, the better performance of the retractable dome will be, and when the speed of air is less than 5m/s, the dome seeing induced by the retractable dome on the observational wave front is less than 0.13 arcsec. (C) 2015 Optical Society of America

关键词： computation methods Large telescopes Optical telescopes Power spectral density Refractive index Wavefronts

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Extending capture range for piston retrieval in segmented systems

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APPLIED OPTICS 2017年第33期56卷 9186-9192页

作者： Paine, Scott W. Fienup, James R. Univ Rochester Inst Opt Rochester NY 14627 USA

Image-based wavefront sensing is a powerful technique for measuring the aberrations of optical systems and surfaces. It often fails for segmented systems with large piston errors per segment. We propose a method for finding these errors using broadband light and a specialized grid search as part of a more global search. We show that this method has a high rate of success for a case where nonlinear optimization gets stuck in local minima. We also explore points of failure. (C) 2017 Optical Society of America

关键词： computation methods Optical aberrations Optical surfaces Phase retrieval Space telescopes Wave front sensing

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Effective memory reduction of the novel look-up table with one-dimensional sub-principle fringe patterns in computer-generated holograms

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OPTICS EXPRESS 2012年第11期20卷 12021-12034页

作者： Kim, Seung-Cheol Kim, Jae-Man Kim, Eun-Soo Kwangwoon Univ HoloDigilog Human Media Res Ctr HoloDigilog Display Res Ctr 3D Seoul 139701 South Korea

We propose a novel approach to massively reduce the memory of the novel look-up table (N-LUT) for computer-generated holograms by employing one-dimensional (1-D) sub-principle fringe patterns (sub-PFPs). Two-dimensional (2-D) PFPs used in the conventional N-LUT method are decomposed into a pair of 1-D sub-PFPs through a trigonometric relation. Then, these 1-D sub-PFPs are pre-calculated and stored in the proposed method, which results in a remarkable reduction of the memory of the N-LUT. Experimental results reveal that the memory capacity of the LUT, N-LUT and proposed methods have been calculated to be 149.01 TB, 2.29 GB and 1.51 MB, respectively for the 3-D object having image points of 500 x 500 x 256, which means the memory of the proposed method could be reduced by 103 x 10(6) fold and 1.55 x 10(3) fold compared to those of the conventional LUT and N-LUT methods, respectively. (c) 2012 Optical Society of America

关键词： computation methods Computer generated holograms Holography Light wavelength Ptychography Three dimensional imaging

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