Research Of Orbital Angular Momentum Light Field Modulation In Space Optical Communication Based On Scattering Diffuser

With the booming development of mobile Internet,Internet of Things,big data and other technologies,people’s demand for communication speed and capacity is steadily on the increase.A beam carrying orbital angular momentum(OAM)has a unique helical phase distribution.It has shown great potential in improving the speed and capacity of free-space optical communication(FSOC),which has attracted extensive attention of researchers.However,the OAM beam carries information through the special phase distribution,and the existing detection technology based on light intensity can not obtain the information of the whole field.In addition,turbulence and other factors in the transmission process could cause crosstalk between OAM modes.These are the problems faced by the implementation of OAM-FSOC systems.Recently,with the development of computational optics technology,the light field regulation technology based on scattering diffuser has gradually shown great application value in the field of scattering imaging and focusing,providing new ideas for OAM light field detection and demultiplexing.Therefore,this paper studies the light field regulation technology of scattering medium diffuser in OAM-FSOC,and explores its system performance and optimization scheme in OAM light field detection and demultiplexing.The main work contents and research results are as follows:1.Based on the structure characteristics of the scattering medium diffuser and the statistical distribution of beams transmission through a diffuser,the optical propagation matrix simulation model of the diffuser is established.The energy transmittance of the model is constrained from the perspective of energy conservation,and the modified transmission matrix is verified to conform to the theory from the singular value distribution.The speckle pattern of light beam passing through a diffuser and the relationship between the number of output channels of the diffuser’s transmission matrix and the average speckle size are analyzed by simulation.2.The OAM light field inversion system based on diffuser is established to realize the single intensity detection OAM light field inversion without reference information.A generalized hybrid input-output algorithm(GHIOA)is proposed for iterative optimization of the inverted OAM light field,and the optimization effect is analyzed by simulation.The results illustrate that GHIOA can effectively improve the inversion correlation of OAM inversion light field,and can avoid falling into the local optimal situation,and achieve rapid iterative convergence.3.Based on the wavefront feedback control technology,combining the focusing speed advantage of the sequential algorithm and the noise immunity advantage of the genetic algorithm,a fast focusing global optimization scheme with good anti-noise performance is proposed.Then a scheme of multiplexing OAM beam demultiplexing system based on diffuser is designed,the average detection probability and anti-noise performance of the system are analyzed by simulation,as well as the performance of the scheme in ocean turbulent channel.The simulation results show that the scheme can effectively realize the demultiplexing of OAM beams and alleviate the ocean turbulence to some extent.