基于拍频法的激光器数字化频率跟踪

Lasers digital frequency tracking based on beat frequency method

为了在光纤双向时频传递系统往返链路中实现同波长传输,提出一种基于拍频法的激光器数字化频率跟踪技术,用于锁定系统中主、从两台分布式反馈激光器的频率。首先,采用光耦合器对两路激光信号进行合束,耦合后的合成光经拍频探测得到10 MHz的光学拍频信号;其次,将该信号和10 MHz正弦波信号进行混频并滤波后得到电学拍频信号,再对该电信号进行采样并由算法处理得到反馈电压值;最后以电流调谐的方式调节从激光器的波长,使其与主激光器的波长保持一致。实验结果表明:实验室50 km光纤时频传递系统连续运行60 h后时间同步百秒时差优于8 ps,相比未使用该技术的系统时间同步精度提高约36 ps。所提方案能够实现低成本激光器的频率跟踪,跟踪效果满足往返链路双向时延对称性要求。

In order to achieve the same wavelength transmission for round trip link in two-way time-frequency transfer system,a laser digital frequency tracking technology based on beat frequency method is proposed to lock the frequency of the main and secondary distributed feedback lasers in the system.Two laser signals are combined using an optical coupler,and the coupled synthetic light is detected by means of the beat frequency to obtain a 10 MHz optical beat frequency signal.The signal is mixed with a 10 MHz sine wave signal and filtered to obtain an electrical beat frequency signal.The electrical signal is then sampled and processed by means of the algorithm to obtain the feedback voltage value.The wavelength of the slave laser is adjusted to make it consistent with the wavelength of the main laser by means of the current tuning.The experimental results show that after continuously running for 60 h,the time synchronization 100 s time difference of the time-frequency transmission system connected by 50 km optical fiber used for laboratory is better than 8 ps.In comparison with systems without this technology,the time synchronization accuracy is improved by approximately 36 ps.The proposed scheme can achieve frequency tracking of low-cost lasers,and the tracking effect can meet the bidirectional delay symmetry requirements of the round-trip link.