Research On DPSK Demodulation Technology In Coherent Optical Communication System

The coherent optical communication has the advantages of high sensitivity,large communication capacity,good confidentiality and various modulation At the same time,it can solve the problems of low receiving sensitivity and power limitation caused by traditio nal intensity modulation/direct detection(IM/DD),which is a potential in the future laser communication mode.This paper introduces the principle of coherent optical communication system,and focuses on the analysis of the demodulation scheme of the communication system.According to the principle of heterodyne detection,the system adopts a demodulation scheme of Costas pha se-lo cked loop with frequency estimation The demodulation scheme was verified by theoretical analysis and experimental simulation,and the demodulation platform of coherent optical communication system was built.The specific work is as follows:1.The coherent optical communication demodulation system based on heterodyne detection is designed.The main structure and function of each module in the demodulation system are introduced,and the hardware simulation of the frequency estimation module and carrier recovery module is carried out.The simulation results show that the frequency estimation module can correctly estimate the frequency of the IF sampled signal,and the carrier recovery module can perform correct phase recovery on the IF sampled signal,so as to correctly de modulate the symbol signal.2.FPGA is used to design the digital DPSK demodulator of the demodulation system.The real-time demodulation of the DPSK signal in the co herent optical communication system is realized by using the Costas phase-locked loop with frequency tracking.3.This article IF signal as an input signal generator generates a signal demodulation system,the system can verify the correct intermediate frequency signal phase recovery,and the 400 m and 1.3 km transmission experiment video outdoors.The experimental results show that the coherent optical communication demodulation system designed in this paper can realize real-time video transmission,and the co mmunication effect is good,and the bit error rate is less than 10-6.