The Study On The Novel Beams Propagation Through Atmospheric Turbulence

With the progress of science and technology,in particular,the development of space technology,more exploitation and utilization of space is being made.The amount of information acquired from space is increasing and the bandwidth needed to transmit the information is also rising up.The free space optical(FSO)communication has great application prospect in the communication between satellites and ground because of its high bandwidth.However,when the beam propagates in the atmospheric turbulence,the effects induced by atmospheric turbulence including beam spreading,beam wander and intensity fluctuations(scintillations)can severely damage the link performance of free space optical communications.The propagation characteristics of different beams in atmospheric turbulence are different,so they have different characteristic to resist the complicated effects caused by the atmospheric turbulence.In this thesis,the abilities to overcome the complex effects of atmospheric turbulence of Bessel beam,flat topped vortex hollow beam and sinh-gaussian vortex beam are systematically investigated based on the propagation characteristics in turbulent atmosphere.Their performances as communication links are also studied.These work can help to explore the novel beam which can resist the complex effects of atmospheric turbulence,provide the basis for optimizing the parameters of the beam as the optical communication link and improve the link performance of the space optical communication.The research in this thesis focuses on the aperture averaged scintillation of the beams.It is of important practical significance to investigate the aperture averaged scintillation,because it determines the mean signal-to-noise ratio and average bit error rate of the communication system.It is very hard to study the aperture averaged scintillation of the novel beam effectively by using analytic method.To solve this problem,the calculation of the aperture averaged scintillation of coherent beams and partially coherent beams is accomplished by using of modeling and simulation in this thesis.The simulation platform includes the modeling of the transmission algorithm,atmospheric turbulence and the phase screen which is used for the formation of the partially coherent beams.The simulation platform can be used to investigate the aperture averaged scintillation and obtain the direct and clear relationship between aperture averaged scintillation and the parameters of the beams.This work further provides support for predicting the performance of beam as communication link for long distance free space optical communication system.The aperture averaged scintillations for the Bessel beam,flat topped vortex hollow beam and sinh-gaussian vortex beam propagation in the atmospheric turbulence have been investigated in this thesis.The systematic analysis about the effects of the beam order,beam shape,beam size,the refractive-index structure constant and inner or outer scale of the turbulence,propagation distance and the size of the receiver aperture on the aperture averaged scintillation is accomplished.With the help of the probability density distribution function of intensity fluctuation,the mean SNR and average BER of the Bessel beam,flat topped vortex hollow beam and sinh-gaussian vortex beam as optical communication link in the turbulence are calculated.Also,the effects of the different parameters of the beam,propagation distance and the radius of the receiver aperture on the mean SNR and average BER are analyzed.Here,the comparative study between the Bessel beam and the flat-topped vortex hollow beam is made under the same conditions.Also,the aperture averaged scintillations of the partially coherent Bessel beam,partially coherent flat-topped vortex hollow beam and partially coherent sinh-gaussian vortex beam are calculated.The influence of coherence length,beam order,topological charge,propagation distance and the radius of the receiver aperture on the aperture averaged scintillation is also studied systematically.The mean SNR and average BER for these three partially coherent beams as optical communication link are also investigated.Similarly,the effects of the different parameters of the beam,propagation distance and the radius of the receiver aperture on the mean SNR and average BER are also studied.Similarly,the comparative study between the partially coherent Bessel beam and the partially coherent flat-topped vortex hollow beam is made under the same conditions.