Rasearch On Adaptive Optics Technology Of Vortex Beam In Atmospheric Turbulence Channel

The orthogonality of Orbital Angular Momentum(OAM)provides an additional dimension for Free Space Optical(FSO)communication.And it can expand communication capacity and spectral efficiency of FSO.Therefore,vortex beam with orbital angular momentum has been a hot research topic in the field of Optical communication in recent years.However,Atmospheric turbulence(AT)will lead to wavefront distortion and OAM crosstalk,and ultimately reduce the performance of the communication system.Therefore,it is necessary to research how to alleviate the effect of atmospheric turbulence on beam propagation.In this paper,we mainly study the adaptive optical technology of orbital angular momentum beam and Circular Airy beam.The main achievements of this research are as follows:Firstly,the hybrid input-output algorithm is used to realize adaptive phase retrieval in CAB.In order to achieve this goal,the basic theory of CAB is studied and its maximum light intensity and the changing trend of size under atmospheric turbulence are analyzed and deduced.The phase screen method is used to simulate CAB propagation in atmospheric turbulence channel.The effects of turbulence on the intensity,phase and spiral spectrum distribution of CAB were studied.Based on the theoretical derivation,the standard for guiding the optical beam expansion of probe beam was determined and applied in the phase retrieval algorithm based on the hybrid input-output algorithm.Secondly,the wavefront phase retrieval system based on phase diversity is studied.Under the guidance of beam propagation theory,the phase recovery system is simulated,and the phase function is simulated by using Zernike polynomial.Under the guidance of detection optimization function,the wavefront detection simulation is realized.In order to reduce the computation,principal component analysis(PCA)was introduced to reduce the dimensionality of the data.The effects of parameters such as defocus and polynomial order on the iterative restoration effect were simulated.Thirdly,in order to optimize the wavefront compensate system based on phase diversity,the GRNN is studied.Based on the study of its network layer and model structure,it is introduced into the wavefront detection system based on phase diversity,and the mapping between the intensity information of detection plane and the predicted coefficients of Zernike polynomial is established by using neural network.In combination with the advantages of high real-time performance of the system,an optimized scheme is proposed,which improves the compensate result of the system and provides more optional alternatives for practical application.To sum up,in order to alleviate the influence of atmospheric turbulence on optical communication,CAB,as the information carrier,and phase retrieval algorithm based on phase diversity technology are mainly studied in this paper,which will play a guiding role in the application of OAM optical communication in FSO field.