Research On Characteristics Of Bessel-gaussian Beam Carrying Orbital Angular Momentum And It's Application

Abstract:Orbital angular momentum?OAM?is a basic physical quantity of classical and quantum mechanics with unlimited topological charge value and orthogonality of different OAM modes,which bring a new degree of freedom for multiplexing.An important non-diffraction OAM mode-Gaussian Bessel beam is introduced in this thesis.This thesis firstly discusses the characteristics and applications of Gaussian Bessel,which has important theoretical significance and a certain value of application.The main work of the thesis are as follows.Firstly,traditional coding/decoding optical communications which uses single orbital angular momentum,and as a result,each topological charge can only carry a small amount of information,which is far from people's need.In this thesis,we propose superposition state of Gaussian Bessel beam carrying orbital angular momentum in coding/decoding optical communications,which can easily solve this problem.In this method,M kinds Gaussian Bessel beam with different topological charge l is contained in the superposition state,which can once code2^M bits information and each topological charge can carrylog₂Mbits information.,which can M times raise the information.The numerical simulation results show that the transmission rate is largely improved compared with traditional coding/decoding optical communications which uses single orbital angular momentum in the same condition.Secondly,considering the non-diffraction and self-reconstruction characteristics of Gaussian Bessel OAM mode can effectively overcome the interference of underwater turbulence on Gaussian Bessel beam,this thesis experimentally study the non-diffraction and self-reconstruction characteristics of Gaussian Bessel OAM mode in underwater environment.In the experiment,we simulate the underwater environment through the water tank equipped with pure water.By dissolving different amounts of salt in water tank to represent different salinity and changing the temperature of water through the heater.We experimentally discuss the non-diffraction characteristic of Gaussian Bessel OAM mode under different temperatures and salinity.Meanwhile,bar blocks are set to represent obstacles in beam propagation path for further study its self-reconstruction characteristic.The results show that,compared with the Laguerre Gaussian OAM mode,Gaussian Bessel OAM mode has better performance when face underwater turbulence in the same condition.And when the obstacle on the scale is small,the Gaussian Bessel OAM mode has self-reconstruction ability.