Research On Coupling Efficiency Of Few Mode Fibers In Satellite Optical Communication

In recent years,satellite optical communication has developed rapidly and has become a hot research field.Satellite optical communication uses laser light to carry information,establishes a laser link in space,and finally receives it by the coupling system at the receiving end.Therefore,the coupling efficiency of the optical fiber is a very important index to measure the coupling process of space light to the optical fiber.Nowadays,single-mode and multi-mode optical fibers are widely used in satellite optical communications.The core diameter of a single-mode fiber is too small,which makes it sensitive to various disturbances,making the entire coupling process more difficult and low coupling efficiency;although the core diameter of a multi-mode fiber is large enough,it is due to inter-mode crosstalk and modal dispersion A series of problems,high-speed communication can not be achieved,and for satellite-to-earth links,amplifier compensation is very important,and the existing multi-mode fiber amplifiers are not suitable for satellite laser communication receiving end,which is a key but insoluble Problem: The few-mode fiber not only has a larger core diameter,which reduces the sensitivity to disturbances during the coupling process,but also has a few-mode fiber amplifier to compensate for the entire link.The use of few-mode fiber at the receiving end of satellite optical communication is a future research direction,so this article focuses on the coupling and interference factors of using few-mode fiber at the receiving end in the satellite-to-ground link.Since the disturbance has obvious influence on the entire coupling process,we mainly study the influence of various disturbances on the coupling efficiency.The coupling efficiency of the two-mode fiber under lateral offset,angular offset and defocus conditions is studied,and a mathematical model is established.For defocusing,the coupling efficiency is reduced,and the control system on the satellite optical communication terminal cannot compensate it well,and the two-mode fiber has a higher tolerance for defocusing,so the two-mode fiber is better than the single-mode fiber.Optical fiber is more suitable for the coupling process of space light to optical fiber in satellite optical communication.For turbulence,based on the Kolmogorov and Non-Kolmogorov turbulence spectra,the average coupling efficiency of the two-mode fiber in the two-mode fiber with different atmospheric refractive index constants is numerically simulated.At the same time,the effect of the α in the Non-Kolmogorov turbulence spectrum on the coupling efficiency is simulated.A space light-to-fiber coupling system was built,and the coupling experiments of single-mode and two-mode fibers were completed,which proved the correctness of the theoretical analysis and proved that the two-mode fiber has stronger anti-interference ability.Compared with single-mode fiber,when the lateral offset is 3.75μm(the angular offset is 5.356μrad),the coupling efficiency of the two-mode fiber is increased by 13%,and the lateral offset is 5.625μm(the angular offset 8.034μrad),the coupling efficiency of the two-mode fiber is increased by 10%;when the defocus distance is 60μm,the coupling efficiency of the two-mode fiber is increased by 4%,when the defocus distance is 100μm,the coupling efficiency of the two-mode fiber is increased by 11%.These experimental results well prove that the two-mode fiber has stronger anti-interference ability,and analyze the error source of experimental data and theoretical data,and prove the correctness of the mathematical model.