The Research On Effects Of Atmospheric Turbulence On Coupling Efficiency Between The Free-Space Beam And Optical Fibers

For satellite-ground satellite communication,the traditional microwave communication mode has encountered a bottleneck due to the limitation of its capacity,while the free space optical communication(FSOC)has become the optimal choice for satellite-ground satellite communication due to its advantages such as high capacity,high confidentiality and reusable spectrum resources.In the FSOC system,the free-space beam generally needs to be coupled into the optical fiber and then use the mature optical fiber communication devices to improve the system performance.However,the wave-front phase distortion caused by atmospheric turbulence will affect the coupling efficiency of the free-space beam and optical fiber.Therefore,in the presence of atmospheric turbulence,improving the coupling efficiency of free-space beam and optical fiber is one of the most important issues in the FSOC system.In this paper,the effect of atmospheric turbulence on the coupling efficiency of optical fiber is studied as follows.Firstly,this thesis introduces the background,significance and current research status of the technology,and analyzes the advantages of using few-mode fiber as the coupling fiber.Secondly,the characteristics and effects of atmospheric turbulence are introduced.On this basis,a simulation model of the atmospheric turbulence based on the random phase screen is established,which power spectrum inversion and the subharmonic method are proposed to generate the random phase screen.After that,the simulation method of beam transmission in atmosphere is studied,and the split-step beam propagation method based on multi-layer random phase screen model and angular spectrum transmission method is established.On this model,the Fresnel scaling method is used to simulate the distortion phenomena of beam transmission caused by atmospheric turbulence,such as beam spreading,beam wander and scintillation index.Finally,the coupling efficiency of free-space beam with single mode fiber and few-mode fiber under different atmospheric turbulence conditions is calculated and compared.The results obtained have certain guiding significance for optimizing the design of coupling fiber in FSOC system.