Research On The Crosstalk Mitigation In Orbitalangular Momentum Multiplexing System Based On Mimo Equalization

In recent years,orbital angular momentum(OAM)multiplexing technology has come into people's view as a new multiplexing technology.Taking advantage of the orthogonality of OAM beams with different topological charges,researchers apply OAM beams as a kind of information carrier in multiplexing technology to realize the information transmission effectively,channel capacity and spectral efficiency are greatly improved.However,the existence of interference in the transmission channel affects the orthogonality between the OAM modes with different topological charges,and energy will spread to the OAM modes with neighboring topological charges,which results in inter-mode crosstalk and affects the performance of the system.Therefore,how to mitigate inter-mode crosstalk in OAM multiplexing system has become an important issue in optical communication.To solve this problem,first of all,we analyse inter-mode crosstalk in OAM multiplexing system.Then,multi-input multiple-output(MIMO)equalization algorithm is used to mitigate inter-mode crosstalk.Finally,According to the simulation results,we analyze the performance of crosstalk mitigation with MIMO equalization,and compare the performance of system before and after equalization.The main works are as follows:(1)The concept of OAM multiplexing system is introduced,and OAM multiplexing system in free space and optical fiber is built with Optisystem and MATLAB.Theoretical analysis and simulation of inter-mode crosstalk in two kinds of OAM multiplexing systems are given in the dissertation.(2)Independent component analysis(ICA)algorithm for crosstalk mitigation in OAM multiplexing systems is proposed and implemented.ICA is one of the MIMO equalization algorithms,which can realize the separation of signals effectively.In this dissertation,objective function is built according to the non-Gauss maximization,and the gradient descent method is used as the optimization algorithm.ICA is implemented by MATLAB,and crosstalk mitigation in free space OAM multiplexing system and optical fiber OAM multiplexing system is simulated with co-simulation of Optisystem and MATLAB,respectively.The simulation results indicate that the ICA algorithm can mitigate inter-modecrosstalk effectively.(3)To solve the problem of fixed iterative step size in traditional ICA algorithm,CSO-ICA is proposed and implemented.By using CSO as the optimization algorithm of ICA,the problem of fixed iterative step size in traditional ICA algorithm is improved.Through the co-simulation of Optisystem and MATLAB,the simulations of crosstalk mitigation in OAM multiplexing system in free space and optical fiber with CSO-ICA are realized,and results indicate that the iterative speed of CSO-ICA is improved by one order of magnitude compared with traditional ICA algorithm,and the performance of the two algorithms is similar in the mitigation of inter-mode crosstalk.