Two-Way Fiber-Optic Time Synchronization System Based on Feedforward-Feedback Phase Compensation

Synchronizing remote frequency references is critical in two-way fiber-optic time synchronization systems. Without dedicated frequency transfer systems, it can be realized via frequency or phase compensation. However, these standalone compensation methods suffer from excessive parameter dependence or poor mitigation of time-varying frequency differences. Therefore, this letter proposes a feedforward-feedback phase compensation scheme integrating frequency compensation as a proactive method for clock difference drift suppression, overcoming single-method limitations while broadening applicability. The proposed method is validated on a laboratory 400 km two-way time synchronization system with a free-running remote oscillator, achieving 17.47 ps@1 s and 1.3 ps@1000 s, demonstrating its potential for precision time-frequency applications.