Coherent detection technology can improve the sensitivity of homodyne receiver effectively.In the system of space laser communication,homodyne receivers make the phases of a local oscillator (LO) signal and a signal wave synchronize,and the optical phase locked loop (OPLL) is the most efficacious technology.Firstly,by including the theoretical model of the optical phase locked loop,the corresponding transfer function is derived.Meanwhile the main parameters affecting the performance of the optical phase-locked loop are discussed,such as the loop noise bandwidth,the natural frequency,the damping factor of the loop.The basic structure and characteristic of each OPLL type are described including:balance OPLL,Costas OPLL,syncbit OPLL,dither OPLL and sub-carrier OPLL,and their properties are compared.Finally,the development and application of OPLLs are summarized,and the prospect of the OPLL technology is prospected.