Implementation Of SPGD Algorithm For Adaptive Optical System Based On 97-element MEMS DM

Influenced by the atmospheric turbulence,there will be different degrees of wavefront distortion,which will bring great obstacles to astronomical observation,when light travels through the atmosphere.It will be extremely difficult for high-definition imaging of astronomical targets.Adaptive optics(AO)technology will effectively reduce the wavefront distortion of light waves during atmospheric transmission,thereby improving the imaging quality of the optical system.The deformable mirror(DM)is the most important wavefront correction element of the adaptive optical system,as its performance directly determines the correction ability of the system.Micro electro mechanical system(MEMS)DM,which have developed rapidly over the past few years,is based on semiconductor manufacturing processes with the advantages of small size,low energy consumption,high accuracy,and mass production,and etc.It is one of the DMs with scientific research value in current wavefront correctors.In this paper,the wavefront correction capability of MEMS DM is taken as the research target.In the first place,the atmospheric turbulence transmission model of light wave is established.Then,based on the atmospheric transmission model,the fitting capabilities of 97-element MEMS DM to single-order and combined aberrations are analyzed separately.Finally,computer simulation and experimental platform were used to study the adaptive optical closed-loop correction capability of97-element MEMS DM.In the computer simulation,based on the actual measurement of the DM effect function,the fitting effect and closed-loop correction capability of the 97-element MEMS DM on low-single order and combined aberrations of Zernike Polynomial are analyzed.The Stochastic Parallel Gradient Descent(SPGD)was adopted in the analysis of closed-loop correction capability.It was proved that the DM can not only fully fit low-order aberrations of zernike,but also have the ability to fit high-order aberrations.Under the SPGD control algorithm,the aberrations could be basically corrected when the turbulence intensity is weak;apart from that,it also works when turbulence aberrations is relatively large.In the experiment section,a wavefront senseless AO system platform was set up,which is used to analyze and compare the correction convergence speed and diffraction limit of the system aberrations with D/r = 5,10,15,20.It shows that the convergent iterations of the algorithm at different turbulence intensities are 60,70,95,220,and 50 times and the diffraction limit of corrected light spots are 1.7,2.4,2.9,3.9,and 4.7 times.The experimental results have verified that the 97-element MEMS DM has a certain capability to correct system aberrations and different wavefront detection under wavefront senseless AO system platform.In summary,this paper researched the wavefront correction capabilities of97-element MEMS DM from different aspects.The simulation and experimental results of this paper will provide theoretical basis and data reference for researchers and engineering technicians in the field of AO system applications.Both the adjustment process of optimal parameter range and analysis of the corresponding correction results of the SPGD control algorithm under different turbulence intensities in the paper also provide theoretical basis and data reference for AO workers when they use this algorithm.