Coherent Optical Communication Link Heterodyne Receiver Technology Research

Coherent optical communication can solve the problems of the conventional optical communication IM/DD mode such as low receiver sensitivity and power constraints. To completely achieve coherent communication is very difficult, coherent optical communications heterodyne receiver technology can reduce the difficulty of realizing coherent reception system.This thesis focuses the technical research on the coherent optical detection, demodulation in coherent optical communication between stars and earth. Then, the appropriate coherent receiver mode is put forward, which is suitable for the atmospheric channel with the strong signal interference and serious attenuation. The main content of this thesis is following.Firstly, the recent domestic and foreign development of coherent communication is introduced. Then the basic principle of coherent optical communication is introduced in briefly and the coherent detection principle is introduced in detail. The receive system of homodyne and heterodyne coherent optical communication is built. Based on the simulation analysis, a phase modulation mode is put forward for coherent optical communication and the coherent heterodyne synchronous receiver system is established in the basis of the comparative analysis of coherent heterodyne receive system. The EPLL is selected for coherent heterodyne synchronization of receive system though the analysis and comparison of the different types of PLL.Secondly, a coherent heterodyne synchronous receiver system is established which is based on the feed-back PLL. The key factors affecting the system performance is analysised such as the noise bandwidth of phase-locked loop and the linear model of the decision feedback PLL is established. The phase noise and overall system performance of the PLL is analysised importantly. The laser line-width requirement of the coherent heterodyne synchronous receiver system is put forward after analysising the simulation results of system performance.Finally, the simulation model of the coherent heterodyne PSK synchronous receiving system is established. As a reference to the actual device parameters, the system performance is simulated under the conditions of different weather. Then a IM/DD simulation model is established and simulated under the conditions of different weather. The simulation result shows that the coherent heterodyne optical communication system has high sensitivity advantage to IM/DD system in atmospheric laser communication under the conditions of different weather.This thesis comes to the conclusion that the near-earth heterodyne coherent optical communication has a better performance to the IM/DD system. Under the demanding requirement on the optical phase lock loop and the laser in the homodyne coherent optical communications, heterodyne coherent optical communication is always a good choice.