Vortex Beam Transmission Characteristics In Atmospheric Turbulence Channels

Free-space optical communication(FSOC)is an important method for high-speed information transmission in spatial information networks.However,with the advancement of technology,it has some problems such as insufficient transmission capacity and channel congestion.Theoretically,these problems can be solved by using a vortex beam as a carrier of information.In addition,the axial field and the transverse field of the vortex beam exist at any time,and the linear momentum and the angular momentum exist in the propagation direction.The uncertainty of the angular position of the orbital angular momentum also increases the security of information transmission.However,in practical applications,vortex beams are affected by atmospheric turbulence.Wave front distortions in the optical wave induced by atmospheric turbulence result in orbital angular momentum dispersion(spiral spectrum dispersion),irradiance fluctuations,angle of arrival fluctuation,beam drift and beam spreading,among other effects.This reduces the signal-to-noise ratio of the communication system and increases the bit error rate.Therefore,itis of great significance to study the transmission characteristics of light beams with orbital angular momentum in atmospheric turbulence.Based on the theoretical derivation and a numerical simulation power spectrum inversion method,this paper establishes a simulation model of atmospheric turbulence channel and studies the transmission characteristics of vortex beams in atmospheric turbulence channels.The main work of this article is as follows:(1)Under the modified Rytov method,using the non-Kolmogorov power spectrum,applying the atmospheric turbulent inner scale and the outer scale which changes with altitude,obtained the expression of the spiral spectrum of the beam in slant atmospheric turbulence.The effects of various parameters of the vortex beam and the related parameters of the atmospheric turbulence on the transmission characteristics of the vortex beam are analyzed.(2)Using the power spectrum inversion method,the atmospheric turbulence phase screen was established,and the mathematical model for multi-phase screen beam transmission in the slant path was constructed.By using the multi-layer phase-screen method,the spiral spectrum dispersion characteristics of the LG beam in the slant path of the atmospheric channel are studied.(3)The multi-layer phase screen method is used to study the change trend of intensity and phase distribution of the vortex beam in slant atmospheric turbulence.And study the scintillation index of a vortex beam as it propagates in a slant atmosphere.