Research On The Influence Of Non-Kolmogorov Turbulence On Single-mode Fiber Coupling Efficiency In Space Laser Communication System

As the next generation communication technology,space laser communication technology has attracted worldwide attention in recent years,and fierce competition has begun in this field of research.At present,satellite experiments have been performed by America,Europe and Japan,which take the superior position.Other countries in the world are also vigorously developing space laser communication.Using mature ground optical fiber communication technology to improve the performance of space laser communication system has become one of the mainstream options,optical amplifier and wavelength division multiplexing technology can effectively improve the space laser communication system detection sensitivity and communication data rate.Therefore,the coupling efficiency of spatial light to a single-mode fiber will directly influence the energy efficiency of system.In consideration of the power consumption and volume limitation of the satellite platform payload,improving the coupling efficiency is crucial,which has become a hotspot in recent years.In the space laser communication link,on account of the random fluctuations of refractive index caused by atmospheric turbulence,the signal light will generate wavefront phase distortion during the transmission process,and the spatial coherence is destroyed.This can reduce the matching degree of received signal light field and the single-mode fiber field.Thus,coupling loss is introduced,and the coupling efficiency of spatial light to a single-mode fiber reduces.To date,most studies on the influence of atmospheric turbulence on space laser communication system are concerned with the Kolmogorov turbulence.However,more and more theoretical and experimental results have shown that Non-Kolmogorov turbulence is closer to the actual situation of atmospheric turbulence,which adds an important parameter of spectrum power law ?.For the space laser communication system in which fiber coupling technology is used,the pivotal problems that should be researched are as follows:(1)The variation of spectrum power law ? will influence the state of atmospheric turbulence,make the received signal light field change,and then influence the single-mode fiber coupling efficiency,bring down the performance of space laser communication system.Therefore,the theoretical model of average single-mode fiber coupling efficiency based on Non-Kolmogorov turbulence is needed.(2)Since the spectrum power law ? is a real-time dynamic random variable,the theoretical model of temporal power spectrum of irradiance fluctuations based on Non-Kolmogorov turbulence is needed.(3)For the space laser communication system in which fiber coupling technology is used,the system error rate is usually not a linear relationship with the fiber coupling efficiency,and phase compensation is necessary for the received signal light field.Therefore,the fiber coupling efficiency probability distribution after phase compensation is crucial for analyzing the performance of space laser communication system.The theoretical model of single-mode fiber coupling efficiency probability distribution after phase compensation based on NonKolmogorov turbulence is needed.In allusion to the above problems,based on the actual situation of atmospheric turbulence(Non-Kolmogorov turbulence),the research works that have been completed in this thesis are as follows:1.The theoretical model of average single-mode fiber coupling efficiency based on Non-Kolmogorov turbulence is established,the restriction relation between the spectrum power law ? and the average single-mode fiber coupling efficiency is obtained.2.The theoretical model of temporal power spectrum of irradiance fluctuations based on Non-Kolmogorov turbulence is established,the restriction relation between the temporal power spectrum of irradiance fluctuations for a Gaussian-beam wave and the transmitter parameters is given,which provides the theoretical basis for the experimental measurement of spectrum power law ?.3.The theoretical model of single-mode fiber coupling efficiency probability distribution after phase compensation based on Non-Kolmogorov turbulence is established,the influences of transmitter parameters and spectrum power law ? on the single-mode fiber coupling efficiency probability distribution after phase compensation for a Gaussian-beam wave are analyzed.4.For the experimental verification of the established theoretical models,an experiment about the influence of atmospheric turbulence on single-mode fiber coupling efficiency is done in a 11.16 km urban horizontal link.This thesis is a fundamental research about Non-Kolmogorov turbulence and its effects on the coupling efficiency of spatial light to a single-mode fiber.In this thesis,we analyzed the effects of spectrum power law ? on the coupling of spatial light to a single-mode fiber,which is an important scientific problem in space laser communication system.The works in this thesis will expand the coupling theory of spatial light to a single-mode fiber,and establish the theoretical foundation for the design and parameters optimization of space laser communication system based on fiber coupling.