Research On Coherent Detection Technology Of Laser Communication

Free space homodyne coherent optical communication has a series of advantages, such as high sensitivity, high bit rate, narrow bandwidth, low power consumption, good secrecy,long communication distance, strong anti-interference ability, small volume and light weight.Homodyne coherent optical communication system uses optical phase-locked loop technology to realize phase synchronization of signal light and local oscillator light. Costas optical phase-locked loop is one of the most commonly used optical phase-locked loops, and has the outstanding advantages of low laser linewidth requirements.This paper studies the basic principle of optical phase-locked loop and establishs a mathematical model of Costas optical phase-locked loop. In this paper, the analysis of the noise in the loop and the requirements of the laser linewidth are presented, and a set of loop parameters is designed: ?1 = 29.7ms, ?2=22.5?s ,K = 115Mrad/ s, fn ? 10kHz , ? = 0.707 .According to the theoretical analysis results, static simulation of phase locking performance of homodyne BPSK communication system based on Costas optical phase-locked loop is carried out on the Optisystem optical simulation platform. The minimum signal power and the optimal transmission distance are obtained when the system meets the BER requirement.The simulation results show that the BER increases with the decrease of signal power, the increase of laser linewidth and the increase of transmission distance. The dynamic simulation of phase locked process of homodyne BPSK communication system based on Costas optical phase-locked loop is carried out in the Simulink mathematical simulation software. The locking time, locking and capturing range of the PLL are tested, and the noise characteristics of the loop are verificated. Finally, combined with theoretical analysis and simulation results, Costas optical phase locking, modulation and demodulation experiments are carried out.The experimental results verify the phase locking performance of the Costas loop.