High Efficiency Space Mixer Design For Spatially Coherent Laser Communication System

Laser communication can be divided into the direct detection and coherent detection. The direct detection is susceptible to the influence of itself thermal noise and background light, reducing the sensitivity of the receiver. Coherent detection can inhibit channel noise significantly, thereby improving the receiver’s signal-to-noise ratio, improving the reception sensitivity greatly,10～25dB advantage for direct detection.With further research, how to improve the sensitivity of the receiver is becoming the core of coherent optical communication systems research, in order to make full use of the advantages of the coherent optical communication. In a variety of receivers, homodyne receiver’s sensitivity is the highest, its theoretical value is up to9photons/bit. However, homodyne receiver’s realization is facing the phase synchronization problem between signal light and local light.This paper based on use homodyne BPSK optical communication system, using COSTAS phase-locked loop to achieve OPLL subsystem. After a full analysis of the spatial light mixer, this paper identified several factors that affect the mixing efficiency, and propose several effective methods to improve the mixing efficiency. This laid the foundation for the realization of coherent communication system of high efficiency space laser communication link.