Research On The Dynamic Characteristics Of 90° Space Optical Hybrid

Compare with the traditional direct detection optical communication system,the spatial coherent optical communication system has become a research hotspot in the field of free space optical communication(FSOC),because of its advantages of high sensitivity,long transmission distance,and large transmission capacity.The space optical hybrid is one of the important devices of the space coherent optical communication receiving system.It provides energy gain for the signal light by interfering the wave front of the signal laser and the local laser,and at the same time converts the phase information into the intensity information.In practical space laser communication applications,homodyne coherent receiving systems need to ensure that the local laser and signal laser are completely identical in frequency and phase.A dynamic process of tracking acquisition-frequency locked phase locked-communication is worked.Due to the existence of atmospheric turbulence in the space channel,the space optical hybrid is always in a dynamic working environment.So it is very meaningful to study the dynamic characteristics of the 90 ° space optical hybrid.This paper focuses on the dynamic characteristics of the 90 ° space optical hybrid.The main work are as follows:1.The advantages of free-space optical communication and its research significance are summarized.The research on the 90 ° space optical hybrid,the core device of the free-space coherent optical communication receiver,is of great significance and has become a research hotspot in the field of coherent communication.The article summarizes the development of space optical communications and the current research trends of 90 ° space optical hybrid at home and abroad.2.The principle,system composition and common coherent optical communication modulation formats of space coherent laser communication are introduced.The core components in space coherent optical communication system: optical hybrid,optical phase-locked loop and balanced detector are introduced in detail,and their respective advantages and disadvantages as well as applicable conditions are compared.3.Aiming at the dynamic working process of the 90 ° space optical hybrid,a mathematical model is established to analyze the influence of the signal optical splitting ratio on the phase-lock time,phase-lock range,phase-lock residual error,and loop stability.According to the phase-locked loop,The residual error threshold determines the control range of the spectral ratio.Aiming at the dynamic working conditions of the 90 ° space optical hybrid,a mathematical model was established to analyze the five primary aberrations of tilt,defocus,astigmatism,field curvature,spherical aberration and turbulence intensities on the homodyne efficiency of the 90 ° space optical hybrid.Affect the law.The performance of the space output type with single-mode fiber output type when the signal laser has wave front distortion.4.Based on Chapter 3,a 90 ° space optical hybrid with adaptively adjustable splitting ratio is proposed,which can complete the optimization of the splitting ratio under different working processes according to requirements.The optical communication simulation software Optisystem and the mathematical simulation software Simulink were used to establish a 90 ° space optical hybrid with a variable optical splitting ratio.The effect of the optical splitting ratio on the performance of the 90 ° space optical hybrid and the feasibility of the adaptive system were verified.5.First,the basic performances of the spatial output type 90 ° space optical hybrid and the single-mode output type 90 ° space optical hybrid are measured.Subsequently,a variable splitting ratio experimental platform was established to verify the adjustment rule of the splitting ratio,and experimentally studied the bit error rate of the homodyne receiver with different splitting ratios.In addition,a primary aberration simulation experiment platform based on a 140-unit anamorphic mirror based on MEMS was built to achieve the simulation of five primary aberrations.The homodyne efficiency of a 90 ° space optical hybrid under the conditions of five aberrations was experimentally studied.The influence of aberration on the homodyne efficiency is verified.Finally,a random phase plate was produced for the simulation of atmospheric turbulence,and two types of turbulence with different intensities were simulated.The peak signal of the 90 ° spatial optical hybrid under turbulence was experimentally measured,and the theoretical results were verifiedThis paper's work improves the existing influence law of 90 ° space optical hybrid's dynamic performance,and improves the adaptability of 90 ° space optical hybrid in practical applications.It also provides theoretical and experimental basis for wave front aberration correction under turbulent conditions of FSO system adaptive optical system.