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Improved spgd algorithm to avoid local extremum for incoherent beam combining

OPTICS COMMUNICATIONS 2017年第0期382卷 547-555页

作者： Yang, Guoqing Liu, Lisheng Jiang, Zhenhua Wang, Tingfeng Guo, Jin Chinese Acad Sci State Key Lab Laser Interact Matter Changchun Inst Opt Fine Mech & Phys Changchun 130000 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China

The stochastic parallel gradient descent (spgd) algorithm and the fast steering mirrors (FSM) are applied for incoherent beam combining in this paper. An equation is derived to calculate the wavefront reflected from the FSM under certain control voltages and the relationship between the strength of random disturbances and the combing efficiency is discussed via simulations, indicating that the combining efficiency is inversely proportional to the square of the strength of disturbance. The maximum value of the acceptable disturbance can be determined though the fitting curve which presents an instructional way to reduce the disturbance in advance. Besides, the spgd algorithm is improved to overcome the weakness of tending to be trapped in the local extremum in incoherent beam combining. In the proposed algorithm, pattern recognition is used to check whether the algorithm is trapped and an "additional move" can be applied to get out of local extremum. The results of simulations show that the proposed algorithm can improve the performance of the incoherent beam combining. Comparative simulations are conducted where the value of evaluation function is increased about 60% compared to the conventional algorithm under the same conditions. The threshold of disturbance also increases about 15% when the accepted value of evaluation function set to 0.8 in the normalized form showing the feasibility of the method. Also, statistical data shows the proposed method depends less on the gain coefficient. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Laser beam combining spgd algorithm Pattern recognition

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Incoherent beam combining based on the momentum spgd algorithm

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OPTICS AND LASER TECHNOLOGY 2018年 101卷 372-378页

作者： Yang, Guoqing Liu, Lisheng Jiang, Zhenhua Guo, Jin Wang, Tingfeng Chinese Acad Sci Changchun Inst Opt Fine Mech & Phys State Key Lab Laser Interact Matter Changchun 130033 Jilin Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China

Incoherent beam combining (ICBC) technology is one of the most promising ways to achieve high-energy, near-diffraction laser output. In this paper, the momentum method is proposed as a modification of the stochastic parallel gradient descent (spgd) algorithm. The momentum method can improve the speed of convergence of the combining system efficiently. The analytical method is employed to interpret the principle of the momentum method. Furthermore, the proposed algorithm is testified through simulations as well as experiments. The results of the simulations and the experiments show that the proposed algorithm not only accelerates the speed of the iteration, but also keeps the stability of the combining process. Therefore the feasibility of the proposed algorithm in the beam combining system is testified. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Laser beam combining Momentum method spgd algorithm

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High-Precision Modal Decomposition of Laser Beams Based on Globally Optimized spgd algorithm

IEEE PHOTONICS JOURNAL

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IEEE PHOTONICS JOURNAL 2019年第5期11卷 1-10页

作者： Choi, Kyuhong Jun, Changsu Gwangju Inst Sci & Technol Adv Photon Res Inst Gwangju 61005 South Korea

We propose a globally optimized stochastic parallel gradient descent (spgd) algorithm to analyze the modal content of laser beams with high precision. Modal decomposition (MD) based on conventional spgd algorithms often falls to a local minimum when a laser beam consists of six or more fiber eigenmodes, which results in a false combination of modes. While keeping the simplicity and speed advantages of the spgd algorithm, we adopted several optimization techniques to discern the global minimum from local minima and achieve better accuracy. The enhanced spgd algorithm includes the annealing of the learning rates, identifying and escaping of local minima with large perturbations, and comparing of the transient error function with a reference value. We were able to exactly analyze the modal content of beams from six-mode optical fibers with high precision in seconds. Calculation of the modal weight and phase percentage errors, as well as simulations of far-field evolution images, confirmed the importance of finding the global minimum in improving the accuracy and real-time analysis of MD. The simple structure of the enhanced algorithm and its global optimization ability in multimode fibers will accelerate numerical MD in diverse laser applications.

关键词： Modal decomposition spgd algorithm fiber laser global minimum

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Experimental Demonstration of Efficient Coherent Combining of 19 Fiber Lasers By Adaptive Gain Coefficient spgd algorithm

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JOURNAL OF RUSSIAN LASER RESEARCH 2021年第5期42卷 609-617页

作者： Zuo, Jing Zou, Fan Geng, Chao Li, Feng Huang, Guan Liu, Jiaying Yang, Xu Jiang, Jiali Fan, Zhihua Ma, Xiaoyu Li, Xinyang Chinese Acad Sci Key Lab Adapt Opt Chengdu 610209 Sichuan Peoples R China Chinese Acad Sci Inst Opt & Elect Chengdu 610209 Sichuan Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China Sichuan Univ Arts & Sci Dazhou 635000 Sichuan Peoples R China

The fiber laser coherent combining system with tiled aperture structure is an effective method to obtain a high-brightness laser. To realize the high-efficiency combining effect, we develop a 19 fiber laser coherent combining system with a filling factor of 0.903. Then the adaptive gain coefficient is added to improve the spgd algorithm to speed up the convergence. When the phase controller and tilt controller are in closed loop, the power in the bucket (PIB) is as high as 0.48 with the residual phase error sigma(p)similar to lambda/21, and the contrast of the far-field intensity pattern is as high as 0.9851, which indicates the system achieving a superior coherent combining effect.

关键词： coherent combining phase noise tilt aberration spgd algorithm adaptive gain coefficient

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Phase optimization of a multimode fiber laser beam with spgd algorithm 4

Phase optimization of a multimode fiber laser beam with SPGD...

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4th International Symposium on Laser Interaction with Matter

作者： Zhang, Chi Liu, Wenguang Zhou, Qiong Natl Univ Def Technol Coll Optoelect Sci & Engn Changsha 410073 Hunan Peoples R China

ISBN: (数字)9781510608405

ISBN: (纸本)9781510608405

Compared with single-mode laser, multimode fiber laser can achieve higher output power. But with distorted phase distribution, the beam quality of multimode laser is poor. To improve the beam quality of multimode laser, phase optimization of multimode laser based on the stochastic parallel gradient descent (spgd) algorithm is presented in this paper. To realize the phase control of beam, a multiple pixels screen used as phase correction device is added in the output light path. In the spgd algorithm, the pixels of phase correction screen are regarded as the controlled variables, power in the bucket (PIB) of the far field is used as the evaluation function. By changing the phase modulation of each pixel, the optimal PIB is obtained by this algorithm, and the beam quality is improvemed. The optimazation of high-order mode beam and multimode beam are calculated respectively. The multimode beam includes two modes: TEM00 and TEM21 and the proportion of output power is 1:1. The results show that the PIB of the single high-order mode beam is improved from 0.02 to 0.70 after 30000 times iteration., the multimode laser is improved from 0.02 to 0.40 after 20000 times iteration. According to the result, parameters of the algorithm are adjusted to improve efficiency and practicability.

关键词： phase optimization multimode beam spgd algorithm

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Simulation and analysis of distortion correction of Super-Continuum wavefront based on spgd algorithm 5

Simulation and analysis of distortion correction of Super-Co...

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5th International Symposium on Laser Interaction with Matter (LIMIS)

作者： Ming, Zhang Dun, Li Yu, Ning Xin, Wang Xi, Fengjie Natl Univ Denfense Technol Coll Adv Interdisciplinary Studies Changsha 410073 Hunan Peoples R China State Key Lab Pulsed Power Laser Technol Changsha 410073 Hunan Peoples R China Hunan Prov Key Lab High Energy Laser Technol Changsha 410073 Hunan Peoples R China Army 92001 PLA Beijing Peoples R China Army 75841 PLA Beijing Peoples R China

ISBN: (数字)9781510627598

ISBN: (纸本)9781510627598

Supercontinuum laser, as a new type of laser source, compared with monochromatic or quasi-monochromatic light, has incandescent wide spectra and the brightness of the laser. However, the beam quality in high power is usually bad and greatly affected by atmospheric turbulence in the transmission process. Therefore, how to improve the beam quality to ensure the energy transmission and image quality has become a popular topic. According to the measurement results of the near field wavefront characteristics of the supercontinuum laser in different wavelength, we know that the wavefront phase of the light source is relatively stable and change slowly over time. The types of wavefront distortion at each wavelength are basically the same, mainly made up of defocus and astigmatism. In order to conform to the wavefront characteristics of supercontinuum laser, the input of simulation is low-order static distortion wavefront generated by using Zernike polynomia with defocus and astigmatism. Stochastic Parallel Gradient Descent (spgd) algorithm with the thorlabs DMP40 deformable mirror and CCD camera as the imaging sensor, is used to construct a simulation model for wavefront correction of low-order static distortion aberrations. Since B-spgd algorithm is superior to U-spgd in terms of convergence speed and correction effect, as well as adaptability to the near field wavefront distortion[1], we use B-spgd algorithm to construct the simulation program for wavefront correction simulation research. The ability and convergence of spgd algorithm to correct wavefront distortion are studied, mainly about the random disturbance amplitude and influence coefficient of the core parameters. In order to get close to the evaluation standard of laser in practical application, Strehl Ratio(SR) is selected as the performance evaluation function. According to the effective diameter of deformable mirror and the distance between electrodes, the influence function of deformable mirror is normalized

关键词： Supercontinuum wavefront characteristics spgd algorithm deformable mirror

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Star sensor calibration method based on the spgd algorithm

Star sensor calibration method based on the SPGD algorithm

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Annual Conference of Chinese-Society-of-Optical-Engineering (CSOE) - Space Optics, Telescopes, and Instrumentation (AOPC)

作者： Ma, Liheng Sun, Chunsheng Zhang, Xiaohui Hu, Qingping Naval Univ Engn Coll Weap Engn Wuhan 430032 Peoples R China

ISBN: (数字)9781510634558

ISBN: (纸本)9781510634558

Calibration of the intrinsic parameters of a star sensor before and after its launch is essential. The existing techniques have not taken the centroiding error into consideration thoroughly. Meanwhile, the calibration operation is complex. Based on the principle of the spgd algorithm, a calibration method fully considering the star image centroiding error is proposed in this work. Simulation result indicates that the intrinsic parameters are calibrated out and kept constantly after tens of iterations. The accuracy of principle point of the proposed spgd based method is 4 times as the IAICM. As for the focus length, the accuracy is improved by 6 times compared to the IAICM. Simultaneously, the calibration operation becomes extremely simple.

关键词： Star sensor calibration Centroiding error spgd algorithm Space instrument

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Beam analysis with improved precision using enhanced spgd algorithm for up-to-6-mode fiber laser 16

Beam analysis with improved precision using enhanced SPGD al...

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Conference on Fiber Lasers XVI - Technology and Systems

作者： Choi, Kyuhong Jun, Changsu GIST Adv Photon Res Inst Gwangju 61005 South Korea

ISBN: (纸本)9781510624375

Analyzing modal contents of arbitrary beams from optical fiber provides useful information for high-power fiber laser and mode-division-multiplexed optical communication. Numerical modal decomposition can be applied to diverse applications universally without complicated setup, but often leads to a false solution which is called as a local minimum We propose several ways to solve this issue and compare the results to find the best way for global optimization based on stochastic parallel gradient descent algorithm.

关键词： Numerical modal decomposition spgd algorithm large-mode-area fiber

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AS-spgd algorithm to improve convergence performance for fiber coupling in free space optical communication

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OPTICS COMMUNICATIONS 2022年 519卷

作者： Peng, Jinjin Qi, Bo Li, Hong Mao, Yao Chinese Acad Sci Key Lab Opt Engn Chengdu 610209 Peoples R China Chinese Acad Sci Inst Opt & Elect Chengdu 610209 Peoples R China Univ Chinese Acad Sci Beijing 100039 Peoples R China

In free space optical (FSO) communication, atmospheric turbulence will introduce aberration to the laser wavefront, which will reduce the coupling efficiency of space light to optical fiber. The system based on blind optimization principle can realize wavefront aberration compensation by using actuators such as fast steering mirror (FSM) and deformable mirror (DM), combined with blind optimization control algorithms. Stochastic parallel gradient descent (spgd) algorithm is widely used in this kind of system. The disadvantages of spgd algorithm are possibly local convergence and slow convergence. In order to improve the convergence performance of the spgd algorithm, we proposed improved spgd algorithms called Adagrad & Staged spgd algorithm (AS-spgd). Specifically, to accelerate spgd algorithm, the Adagrad spgd algorithm (A-spgd) integrated Adagrad's adaptive gain strategy is proposed firstly in wavefront tip-tilt aberration compensation using FSM. Then, we consider compensating the wavefront high-order aberration using DM. By adopting the strategy of using spgd algorithm with different settings in different stages, the Staged spgd algorithm (S-spgd) is proposed to improve the local convergence of the traditional spgd algorithm. The simulation results show that the Adagrad spgd algorithm converges faster than the traditional spgd algorithm in the compensation of tip-tilt aberrations of different amplitude;the Staged spgd algorithm has better global convergence ability than the traditional spgd algorithm in high-order aberration compensation.

关键词： Free space optical communication Fiber coupling spgd algorithm

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Multi-order hybrid vector mode decomposition in few-mode fibers with DL-based spgd algorithm

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OPTICS AND LASER TECHNOLOGY 2023年第1期167卷

作者： Xu, Mengjun Hou, Mengdie Luo, Xinhui Xu, Jiangtao Chen, Wei An, Yi Zeng, Xianglong Li, Jun Huang, Liangjin Shanghai Univ Inst Adv Commun & Data Sci Key Lab Specialty Fiber Opt & Opt Access Networks Joint Int Res Lab Specialty Fiber Opt & Adv Commun Shanghai 200444 Peoples R China Natl Univ Def Technol Coll Adv Interdisciplinary Studies Changsha 410073 Peoples R China Natl Univ Def Technol Nanhu Laser Lab Changsha 410073 Peoples R China

Multi-mode fibers (MMFs) guiding a serial of spatial transversal modes with unique intensity and polarization distribution have been widely employed in the emerging MMF imaging enabled by deep learning (DL) and mode division multiplexing (MDM) for scaling up the capability, and super-resolution microscopy. Compared with linearly polarized (LP) scalar modes and Laguerre-Gaussian modes, vector modes (VMs) are true eigenvector modes of a circular-core fiber, which can stably propagate in the MMF. However, how to efficiently and accurately measure the modal proportions of multi-order hybrid vector modes (HVMs) remains rarely investigated. Here we propose a DL-based stochastic parallel gradient descent (spgd) algorithm to precisely obtain the modal coefficients of the HVMs in the few-mode fibers (FMFs). Four typical convolutional neural network (CNN) models are exploited in the HVMs decomposition and the results present that Xception model can invariably provide excellent accuracy for vector modal prediction, keeping the average modal errors below 1.9% for modal weights and 3.5% for modal relative phases, and the average correlations exceeding 99% for the lowest three-order HVM cases. Moreover, the correlations can be greatly improved to reach over 99.999% based on the DL-based spgd algorithm. Finally, the hybrid zeroth- and first-order vector mode decomposition (MD) is experimentally implemented based on a mode selective coupler (MSC). Both simulation and experimental results quantitatively demonstrate that the proposed method can definitely acquire superb high-precision modal coefficients for multiorder HVM decomposition, which may open up a new perspective for intelligent MDM and MMF imaging enabled by DL-based algorithms.

关键词： Deep learning spgd algorithm Few-mode fibre Multi-order hybrid vector mode Mode decomposition

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