Research On Wavefront Disrortion Control And Experiment Of Adaptive Optics

Free-space coherent optical communication has gradually become one of the research hotspots in the field of wireless communication due to its advantages such as high transmission speed and strong resistance to electromagnetic interference.Owing to the random disturbance of atmospheric turbulence,the optical signal will produce beam drift,phase fluctuations and other phenomena,which will seriously reduce the quality of optical communication.Therefore,adaptive optics technology is introduced as the most effective method to suppress the effects of atmospheric turbulence.In adaptive optics technology,the control algorithm is the core and its performance directly determines the correction effect of the system wavefront distortion.In this thesis,the correction characteristics of the proportional integral(PI)algorithm and iterative algorithms in the adaptive optical system are studied.Concurrently,the PI algorithm is optimized.The main work contents are as follows:1.Zernike polynomials are used to simulate wavefront with phase distortion due to random disturbances in atmospheric turbulence.Then the Gauss-Seidel iterative algorithm,Iterative Learning Control iterative algorithm and PI control algorithm based on direct wavefront gradient algorithm are used in turn to correct the simulated distortion wavefront in order to analyze the influence of parameters.At the same time,the computation of the above three algorithms is analyzed to discuss the correction characteristics of the two iterative algorithms and the PI algorithm.2.On the basis of PI algorithm,the dual fuzzy adaptive Proportional Integral Differential(PID)control algorithm is formed.By introducing the weight factor and threshold judgment module,the dual fuzzy adaptive PID control algorithm can flexibly adjust the algorithm calculation and complete the control parameter self-tuning,which can improve the performance of the algorithm.Meanwhile,the effects of various parameters in fuzzy adaptive PID control algorithm are analyzed through simulation.3.An experimental platform is built for wavefront correction.Using wavefront Peak-Valley(PV)value and Root Mean Square(RMS)value as evaluation indexes,the effectiveness of iterative algorithms and PID-type algorithms based on the direct wavefront gradient algorithm are verified through a lot of experiments,and the influence of each parameter in all algorithms is analyzed and discussed.At the same time,a field experiment platform is built for the dual fuzzy adaptive PID algorithm to verify the influence of parameters and the correction ability of wavefront distortion.This thesis verifies that iterative algorithms and PID-type algorithms can effectively correct wavefront distortion by the experiments,but their correction characteristics are different.Due to the diversity of the iterative formula construction principles,iterative algorithms can provide more correction ideas for the adaptive optical system to correct the distorted wavefront.However,such algorithms have lots of problems such as convergence,convergence speed,and parameter tuning.In contrast,PI algorithm is more suitable for wavefront correction due to its simple principle and excellent correction effect.The dual fuzzy adaptive PID algorithm optimized on the basis of the PI algorithm improves its performance by adding fuzzy control,weight factor,threshold judgment and so on.Experimental results show that compared with PI algorithm,this algorithm can increase the adaptive force to the external environment while ensuring the system correction effect.In the meantime,its calculation amount can be adjusted according to actual needs.