光学锁相环(OPLL)是相干激光通信系统中的重要组成部分。设计了科斯塔斯数字光学锁相系统，用于星间相干通信中零差接收和多普勒频移跟踪。锁相系统采用可编程逻辑门阵列(FPGA)作为主控单元，本振激光器(LO)采用调制边带注入锁定的可调谐激光器，中心波长为1550 nm，具有窄线宽和快速调谐的优点。与传统锁相环相比，系统具有更快的频率捕获速度，具有更高的稳定性。实验中，能够实现140 MHz 频差范围内的快速锁定，保持锁定时间大于1 h，并能够对20 MHz/s多普勒频移跟踪，为后续星间相干通信实验提供支持。

Optical phase lock loop (OPLL) is an important part in the coherent laser communication system. A castas digital optical phase lock loop system is designed, which is used in the inter- orbit coherent laser communication and Doppler frequency shift tracking. The system uses field programmable gate array (FPGA) as the central processor. The local laser (LO) is 1550 nm central wavelength sideband modulation injection locking laser, which has high tuning speed and narrow linewidth. Compared with the traditional OPLL, the proposed system provides more stability and frequency acquisition speed. It can achieve phase lock in frequency deviation range of 140 MHz and the phase locked time is longer than 1 h in the experiment. It can also achieve 20 MHz/s Doppler frequency shift tracking and provide the experimental supports for followed- up inter- orbit coherent laser communications.