Research On The Transmission Mechanism Of Polarized Beam In Single Beam Coherent Optical Communication

The preparation of light beam and the transmission characteristics of light beam in atmospheric turbulence have been the hot topics in the coherent optical communication at home and abroad.This paper proposes two special light beams preparation systems,for the partially coherent flat-topped beam preparation system,the transmission characteristics of the radial Gaussian Shell-Model array beam(RGSMA)in this system and the partially coherent flat-topped beam(PCFT)obtained by beam shaping and other methods under non-Kolmogorov atmospheric turbulence conditions are studied.The paper includes the following research aspects:Firstly,a light beam preparation system based on corner cube cavity to preparation flat-topped beam is proposed.This system makes use of the self-coupling of the array beam to combine a flat-topped beam and the mutual injection phase-locked of the system can improve the efficiency of the beam synthesis.In addition,the influence of system parameters on combined light is discussed.Combined light quality evaluation standard,the genetic algorithm(GA)is used to optimize the system parameters.When the filling factor of the array beam is 0.82 and the beam waist radius is 2mm,high quality flat-topped beam is gotten.Then a micro-structure of a vortex controllable vortex beam generator based on a ring resonator and an optical switch is proposed.Furthermore,the composition of the entire micro-structure is described in detail,and the role of each module is analyzed theoretically.Secondly,a fiber-coupled beam splitting experiment platform is set up to acquire the radial array beam,and the CCD is used to detect the beam spot change process during the propagation.The experimental results show that one beam is synthesized from the six independent beams during the propagation process.Experiments demonstrate the feasibility of the self-coupling characteristics of the radial array beam for preparation flat-topped beam.Finally,the basic theory of atmospheric turbulence is introduced,and several power spectrum models commonly used in atmospheric turbulence analysis are listed.The effects of atmospheric turbulence on the polarization characteristics of polarized beam,the scintillation effect and drift characteristic brought by the propagation are briefly described.Additionally,the cross-spectral density matrix of the radial Gaussian Shell-Model array beam and the partially coherent flat-topped beam under non-Kolmogorov atmospheric turbulence are deduced,combined with the polarization-coherence unity theory,numerical methods are used to analyze their polarization characteristics under atmospheric turbulence conditions,and the effects of turbulence intensity,scale and light source parameters on the degree of polarization and the polarization state of the radial Gaussian Shell-Model array beam are studied.Then the atmospheric turbulence low-frequency compensation phase screen is constructed,and the scintillation effect and drift characteristic of the radial Gaussian Shell-Model array beam and the partially coherent flat-topped beam are studied by the method of phase screen numerical simulation.The studies have shown that the radial Gaussian Shell-Model array beam have a strong ability to resist depolarization in the propagation process,and almost the same scintillation characteristics as the partially coherent flat-topped beam,but in the drift characteristic the radial Gaussian Shell-Model array beam has a better ability to resistant interference than the partially coherent flat-topped beam.The preparation system of partially coherent flat-topped beam proposed in this paper is more suitable for the single-beam coherent optical communication system than the partially coherent flat-topped beam by beam shaping and other methods.