Research On Electro-Optic Nutation Coupling Technology In Space Laser Communication

In recent years,free space laser communication has gradually received extensive attention due to its advantages of large information capacity,high communication rate,small beam divergence angle,small system size,light weight and low power consumption.It is one of the most important problems to be solved in the space laser communication system to realize the stable and high coupling efficiency of the space laser to single-mode fiber.This paper carry out research to solve the above problems,and the main work includes:First,this paper mainly carry out the theoretical research on the coupling of space light to single-mode fiber,and study the effects of static offsets such as radial offsets,axial defocus and angular offsets on the coupling efficiency.The influence of random jitter caused by satellite platform vibration and atmospheric turbulence on the coupling efficiency are also analyzed.Second,with the needs of the laser communication system,the overall scheme design of laser communication electro-optic nutation coupling has been completed.Accroding to the scheme,this paper carry out research on the beam deflection technology of electro-optic crystals.The influences of electro-optic effects of crystals,the effects of different electro-optic crystal materials and structure types on the electro-optic effects are analyzed.The finite element method is used to study the electric field of electro-optic crystals with different electrode structures.A new quadrupole octagonal electro-optic deflection device with lithium niobate（Li Nb O₃）material is designed,and experiments are carried out to verify the device's deflection performance.It is found that the performance is agreed with the design,and meets the needs of electro-optic nutation deflection.Then,this paper simulates the nutation algorithm and stochastic parallel gradient descent（SPGD）algorithm in the space laser to single-mode fiber coupling,and study the influence of the key parameters in two algorithms on the coupling efficiency improvement and algorithm stability.In addition,the simulations study the effects of atmospheric turbulence on the coupling efficiency with method of generating the phase screen by FFT method.Finally,this paper builds an experiment of space laser coupling to single-mode fiber and tests the influence of static offsets and atmospheric turbulence on the optical power in the fiber.The experiment results show that the laser nutation scheme under static offsets is basically consistent with simulation.In this paper,with studying the coupling technology of electro-optic nutation in the space laser communication system,a new electro-optic deflection device for nutation is designed.The influence of the nutation algorithm to compensate the random jitter on the coupling efficiency is simulated comparied with the SPGD algorithm.Effectiveness of new electro-optic deflectors and nutation algorithms to improve the coupling efficiency of space laser to single-mode fiber is verified by experiments.It provides technical support for designing the electro-optic nutation coupling model in space laser communications in future.