针对相干光通信中载波频率漂移的问题,根据实际相干光通信系统,分别采用二进制相移键控(BPSK)和四相相移键控(QPSK)的调制方式,仿真分析了频率漂移引起的星座图周向旋转和误码率的升高。依据激光器频率调节和控制的原理,采用在信号输出端外接鉴相器、单片机和压电陶瓷驱动放大器的方法,设计了一种基于反馈判决控制回路的电路,实现本振激光器的频率对信号激光器的频率的跟踪,稳定载波频率。实验结果表明:当中频载波以100 MHz为基准时,反馈判决电路可将频率漂移稳定在±2 MHz的范围内,频率漂移补偿范围可达到吉赫兹量级,利于后续信号解调。该方案简单切实可行,适用于实际相干光通信系统。

For the problem of carrier frequency drift in coherent optical communications, according to the actual coherent optical communication system, we adopt the binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) modulation modes respectively, and simulate the frequency shift to cause the rotation of the constellation map and the increase of the bit error rate. Based on laser frequency adjustment and control principle, adopting the method of external phase detector, single-chip computer(STM32) and piezo-electricity (PZT) driver amplifier at the signal output end, we design a circuit based on feedback decision control loop, which is used for tracking the frequency of the local oscillator laser to the frequency of the signal laser so as to stabilize the carrier frequency. The experimental results show that the feedback decision circuit can stabilize the frequency drift within the range of ±2 MHz when the intermediate frequency carrier is considered as the reference 100 MHz, which is beneficial to the processing of the demodulated signal, and the frequency drift compensation range can reach GHz magnitude. This scheme is simple and practical, which is suitable for coherent optical communication system.