The Research On Scattering Characteristics Of Orbital Angular Momentum Beams In Underwater Multi Particle Channels

In recent years,with the rapid growth of the demand for underwater information transmission,the vortex beam carrying Orbital Angular Momentum(OAM)has become a research hotspot in the field of Underwater Wireless Optical Communication(UWOC)because of its unique spiral phase structure,which can effectively improve the channel capacity and spectrum efficiency when transmitting information underwater.Due to the complexity and diversity of underwater environment,OAM beam will be affected by particle scattering when transmitting in underwater channel,resulting in beam energy attenuation,mode crosstalk,reduced detection probability and other problems,which affect the performance of uwoc system.This paper studies the scattering effects of typical OAM beams(Laguerre-Gaussian beam and Bessel-Gaussian beam)in underwater multi particle channel,and then provides a useful reference for the beam selection of OAM-UWOC system.The specific work and results are as follows:(1)Based on the Electric field Monte Carlo(EMC)method and Mie scattering theory,the propagation process of OAM beam in underwater scattering channel is simulated,and the influence degree of OAM beam by scattering is analyzed.The simulation results show that the beam with large OAM state has higher received light intensity and transmittance,but its detection probability is relatively small and the degree of mode crosstalk is large;The detection probability of Bessel-Gaussian beam is higher than that of Laguerre-Gaussian beam;When the particle size or refractive index of the medium increases,the attenuation of the beam increases and the received light intensity decreases.(2)Based on EMC Simulation Method and Transmission Matrix(TM)theory,TM of underwater scattering channel is simulated.Using the TM obtained,OAM beam propagation can be simulated.The simulation method improves the calculation efficiency and reduces the repeated calculation caused by the change of beam type and parameters.At the same time,based on TM,optical phase conjugation method is used to realize wavefront modulation,so as to restore the scattered light field,which can suppress the scattering effect to a certain extent.(3)Based on the theoretical analysis,according to the theoretical design scheme,an optical experimental platform for OAM beam transmission through underwater multi particle channel is built.The effects of different propagation distance,medium particle size and refractive index,beam topological charge on the received intensity and transmittance of OAM beams are studied.The experimental results show that it is consistent with the two simulation results,and prove the rationality of EMC theory and simulation method.