| Free space optical communication has become an important component of modern communication due to its advantages such as large communication capacity,high speed,and fast deployment.Free space optical communication is a communication method that uses laser as a carrier to transmit in space links.However,due to the presence of atmospheric turbulence,it often causes problems such as beam wavefront distortion,light intensity flicker,and beam drift.Moreover,the receiving end requires the use of optical fibers for energy coupling,and the extremely small end face of the optical fiber greatly affects the coupling efficiency of the beam,resulting in a decrease in communication quality.So how to combat the impact of atmospheric turbulence,compensate for the phase of turbulent light spots,and improve coupling efficiency is a problem that needs to be solved in space optical communication.This article mainly studies the relevant technologies of turbulence compensation in space optical communication,and the main research content and work are as follows:1.Investigated and analyzed the current research status of free space optical communication both domestically and internationally,the impact of atmospheric turbulence,and mainstream turbulence compensation technologies.Studied the theory of free space light transmission,achieved laser transmission simulation in the atmosphere based on dynamic phase screen method,introduced lens coupling based on Fourier transform and 4F system simulation method.2.The numerical simulation model of dynamic turbulence of multiphase screen in horizontal link is established,and two kinds of adaptive optics simulation are realized:adaptive optics without wavefront sensing based on SPGD algorithm and traditional adaptive optics with wavefront sensing.The coupling efficiency of the two receiving through single-mode fiber is compared under different turbulence conditions.According to the results,it is concluded that wavefront sensing free adaptive optics is suitable for weak turbulence compensation,and wavefront sensing adaptive optics is more suitable for strong turbulence compensation.3.A numerical simulation model of dynamic turbulence of multi-phase screen in satellite ground link is established,and the performance of wavefront sensing adaptive optics is analyzed.The atmospheric turbulence suppression performance of the satellite ground link based on mode diversity technology and adaptive optics combined with mode diversity technology is studied through numerical simulation.The simulation results show that the coupling efficiency of mode diversity reception can be increased by 11.79dB compared with that of single mode fiber reception,14.98dB compared with that of adaptive optics,and 16.61dB compared with that without adaptive optics.4.We have designed and prepared a key device for mode diversity technology-multimode mode mismatch photon lanterns.Simulation analysis was conducted on the coupling characteristics of multimode mode mismatched photon lanterns on random mode field light spots inside the fiber.The results showed that after the turbulence like random light spots were inserted,the average insertion loss of the seven ports was-3.21dB,with a minimum of-2.37dB and a maximum of-4.62dB.The test results of the photon lanterns with mismatched modes showed that the average loss of the seven ports was less than 12.58dB. |
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