Research And Implementation Of Active Coherent Beam Combining Technology Of Multi-Channel Laser Using SPGD Algorithm

High-energy lasers have been widely used in national defense,industry and other fields.However,the output power of single beam laser is limited by some factors.And laser beams combining can achieve high-power laser output.Among them,laser active coherent beam combining system has the advantages of expansibility intensity and high combination efficiency.The control of laser phase is the key to the active coherent beam combination.Based on the phase control technology,this thesis carried out the research on multi-channel laser active coherent combination technology,the main contents are as follows:Firstly,the basic theory of coherent beam combination is summarized in this thesis.A theoretical analysis of the SPGD algorithm is carried out,and found the fixed gain coefficient and disturbance amplitude in the algorithm leads to a contradiction between convergent rate and convergence effect,which limiting the convergent effect and convergent rate of the coherent combining system.Therefore,from the aspect of gain coefficient,combined with Nadam algorithm,the adaptive gain SPGD(Nadam-SPGD)algorithm is proposed;from the aspect of disturbance amplitude,combined with the idea of segmental disturbance,the variable disturbance amplitude SPGD algorithm is proposed.Under the input limitation of the thesis research,the scheme design of multichannel laser active coherent combining based on SPGD algorithm and its improved algorithm is completed.Then,the thesis uses the means of simulation analysis to verify the feasibility and effectiveness of the multi-channel laser beams coherent combination scheme based on SPGD algorithm and its improved algorithm.Output demonstrate that SPGD algorithm and its optimization algorithm can effectively compensate the phase difference between beams and complete the coherent combination of multiple beams.And,the convergence speed and effect of coherent combination based on Nadam-SPGD algorithm and variable disturbance amplitude SPGD algorithm are better than that of SPGD algorithm.Finally,this thesis builds a 32-channel laser beams coherent combination experimental platform to verify the feasibility and effectiveness of the multi-channel laser beams coherent combination scheme based on SPGD algorithm and its improved algorithm.The experimental results are as follows: SPGD algorithm,variable disturbance amplitude SPGD algorithm and adaptive gain SPGD algorithm all can achieve 32-channel laser beams coherent combination,the control bandwidth of corresponding system are506 Hz,737Hz and 1327 Hz respectively,the performance evaluation function(voltage value)of the closed-loop system are 4.047,4.676 and 4.837 times of that of the open-loop system.By profiling the performance of system,it is found that the convergence speed(control bandwidth)and convergence effect of coherent beams combination based on the improved SPGD algorithm is higher than that of SPGD algorithm,and the performance indicators of the system are in line with the expected requirements.Through theoretical analysis,simulation and experimental verification,it is known that the 32-channel laser beams coherent combining scheme based on SPGD algorithm designed in the thesis is feasible;and the improved SPGD algorithm——adaptive gain SPGD(Nadam-SPGD)algorithm and variable disturbance amplitude SPGD algorithm which are proposed in this paper can effectively control the beam phase and complete the coherent combination of 32 beams,and the convergence speed and convergence effect of system are improved to a certain extent.