Application Of SPGD Algorithm Based On Phase Locking Technology In Fiber Laser Phased Array System

Fiber laser phased array system is an optical phased array system based on fiber laser,which can carry out fast and accurate beam control,and has a broad application prospect in the fields of lidar,photoelectric countermeasures and laser communication.The research of phase-locked technology based on fiber laser phased array avoids the difficulty of compensation of wavefront measurement error when the wavefront distortion of adaptive optics based on wavefront sensing is serious,and is beneficial to precise control of fiber laser phased array,and has the advantages of simple implementation and compact structure.Therefore,it is an important development direction to use phase-locked method to compensate the phase of each unit beam to improve the comprehensive effect of phased array system.In this paper,a fiber laser phase control array based on stochastic parallel gradient descent(SPGD)algorithm is studied.In order to improve the convergence speed of the algorithm,combined with the optimization algorithm of deep learning to improve the algorithm,thus proposed Adel Adel SPGD algorithm,and through simulation and experiments to verify the feasibility of the improved algorithm.This provides a theoretical guidance for the algorithm selection of the actual fiber laser phase control system.Designed and constructed based on one-dimensional and two-dimensional optical fiber laser phased array scanning phase locking system,puts forward the two-dimensional scans of "Z + N" mode,implement the "lock-scan-unlock-locking-then scan" way of scanning combination lock,by changing the scan voltage gain according to the demand change the scanning speed,through many children joining together to expand the range scan.The multi-channel laser communication method is introduced into the laser phased array system,and the experimental system is built.The experiment proves that the multi-channel communication reduces the spot contrast and the main lobe energy concentration,and the AdaDel SPGD algorithm can be effectively improved.At the same time,the phase locking algorithm also reduces the bit error rate of multichannel communication,which verifies the feasibility of fiber laser phased array multichannel communication system.The main research contents of this paper are as follows:(1)Introduced phased array system and phase-locked technology,and analyzed the traditional gradient descent algorithm: Introduction optical fiber laser phase control system,of several phase locking technology are analyzed in detail,Outlines a few examples,the passive phase locking compared the several methods of active phase control,finally choose the stochastic gradient descent algorithm algorithm in the optimization algorithm as the main research direction,this paper expounds the research direction and development trend at home and abroad of the algorithm.This paper introduces the traditional gradient and analyzes the convergence of SPGD algorithm,proves that the algorithm converges after enough iterations,and explains the flow of SPGD algorithm.(2)Proposed an optimized AdaDel SPGD algorithm: in the optimization of SPGD algorithm,firstly adopted the unilateral perturbation into multilateral perturbation to improve the convergence speed.Secondly,the SPGD algorithm is optimized by changing the gain coefficient,and the simulation results show that the variable gain coefficient can improve the convergence speed of the algorithm.Finally,combined with AdaDelta algorithm in deep learning,an improved SPGD algorithm is proposed.In order to lead out this algorithm,the idea of optimization algorithm in deep learning is first introduced.In order to demand optimal solution,SGD algorithm and momentum SGD algorithm are studied,and Ada Grad algorithm and more optimized AdaDelta algorithm are further compared.Finally,I combine SPGD algorithm with AdaDelta algorithm and propose AdaDel SPGD algorithm.Simulation results show that the algorithm can significantly improve the convergence speed of SPGD algorithm.And the more ways,the more obvious the improvement effect.(3)The scanning phase locking system based on one-dimensional and two-dimensional fiber laser phased array is designed and constructed: firstly,the principle of one-dimensional phased array scanning is explored,and the phase locking technology is proposed to improve the stability of interference fringe.According to the requirements of the index,a one-dimensional scanning phase-locked system was built,in which SPGD algorithm was used to phase lock,which improved the contrast of interference fringes and the energy concentration of the main lobe.At the same time,AdaDel SPGD algorithm was added to further optimize the contrast of interference fringes and the energy concentration of the main lobe.Finally,a scanning program was added to meet the requirements of the index.In the study of 2-D fiber laser phased array scanning phase locking system,the principle of 2-D scanning is introduced firstly,and the scanning mode of 2-D "Z+N" is proposed,and the combination mode of "lock-scanning-look-re-lock-re-scan" is realized.According to the requirements of the index,a two-dimensional fiber laser phased array scanning phase locking system is built.The simulation and experimental verification of two dimensional fiber laser phased array system are carried out.AdaDel SPGD algorithm is used to improve the contrast of interference fringes and the energy concentration of the main lobe.Finally,the transverse scanning experiment of two-dimensional system is carried out.After two subarrays are spliced,the experimental basis is provided for increasing scanning Angle by multi-path subarray splicing.(4)Designed and constructed a fiber laser phased array multi-channel communication system to improve spot quality and bit error rate through phase locking technology: First this paper introduces the principle of optical fiber laser phased array communication,set the fiber laser phased array phase locking and multiplex communication integration system architecture,by comparing different communication frequency interference fringe contrast and motherboard energy concentration,proof that join communication modulation will reduce the beam quality,and the higher the frequency,beam quality is poor.Therefore,SPGD algorithm of bilateral perturbation and AdaDel SPGD algorithm are used to phase lock the interference fringes,which have achieved good results,especially AdaDel SPGD algorithm,for each laser after communication modulation interference fringes,beam quality has been improved.Finally,the bit error rate of multiplex communication is tested and the feasibility of fiber laser phased array multiplex communication system is verified.