Research On Estimation Of Atmospheric Turbulence Intensity And Wavefront Distortion Correction Method Of Vortex Beams Based On Adaptive Optics

Compared with free-space optical communication,vortex beam carrying orbital angular momentum can greatly increase the channel capacity of free-space optical communication systems,so it has attracted widespread attention.However,when propagating in the atmosphere,it will be affected by various factors,which will reduce the performance of the communication system,including atmospheric attenuation,atmospheric scattering,atmospheric turbulence,etc.Among them,the wavefront distortion caused by atmospheric turbulence is one of the most important factors affecting the performance of the vortex optical communication system.Based on the study of atmospheric turbulence characteristics,adaptive optics technology is used to correct wavefront distortion this paper.The specific research content is as follows:1.Estimation of the intensity of atmospheric turbulence.The influence of atmospheric turbulence on the vortex optical communication system is mainly related to the intensity of turbulence.Estimation of turbulence intensity is an important basis for analyzing the properties of atmospheric turbulence and suppressing the influence of turbulence.In this paper,the commonly used atmospheric turbulence intensity estimation methods are analyzed,and a method that uses convolutional neural networks to analyze the characteristics of the distorted spot image at the receiving end and extract the turbulence intensity characteristics is proposed.The simulation results show that the correlation coefficient between the estimated value and the actual value reaches99.80%.2.Improving the SPGD algorithm of the wavefront sensorless adaptive optics system.The correction performance of the SPGD algorithm is mainly related to the random disturbance voltage and the correlation coefficient.An improved SPGD algorithm that adjusts the iterative method of random disturbance voltage and gain coefficient is proposed in this paper.The optimization process of the algorithm is optimized,and the correction performance of the improved algorithm is analyzed under different turbulence intensities.The simulation results show that the improved SPGD algorithm can effectively accelerate the convergence speed of the algorithm,and the correction effect is also improved to a certain extent.3.In order to further improve the correction performance of the wavefront sensorless adaptive optics system.In this paper,the iterative method of particle position and velocity in the PSO algorithm is adjusted to avoid local convergence during the correction process.The correction performance of the improved algorithm is analyzed under different turbulence intensities.The simulation results show that the improved algorithm can effectively accelerate the convergence speed of the algorithm,and the fastest can increase by 81.25%.4.Under strong turbulence conditions,an adaptive optical system with a wavefront sensor is used to correct wavefront distortion.A reconstruction method of wavefront distortion based on wavelet fractal interpolation is proposed in this paper.Compared with the traditional MVE algorithm,the reconstruction accuracy is improved.The average gray gradient is increased from 0.065 to 0.7654,and the root mean square error of the wavefront reconstruction is also reduced from 3.2492 to 0.6346.The simulation result proves that the method improves the reconstruction accuracy and reduces the reconstruction error at the same time.In addition,compared with the adaptive optical system without a wavefront sensor,the light intensity correlation coefficient under strong turbulence is also increased from 76% to 99.3%,which improved the wavefront distortion correction performance of the adaptive optical system under strong turbulence conditions.