Highly accurate time-frequency synchronized self-reconfiguration network based on a two-fiber unidirectional path ring

We propose and demonstrate a self-reconfiguration network of high-precision time-frequency synchronization. The local oscillator (LO) signal and time reference signal generated by the central site are transmitted to the two-fiber unidirectional ring in opposite directions. The all-optical microwave phase conjugation and the time-frequency domain transform measurement are utilized to eliminate phase fluctuation and time delay introduced by optical fiber. The two-fiber unidirectional ring can automatically switch the working loop when the fiber link is broken and avoid manual intervention, which realizes the self-healing of the network. A 20 GHz frequency signal and 1 pulse per second time signal are transferred along a 7 km fiber ring. At 1000 s averaging time, the long-term frequency stability of the order of 10 to 16 and time stability of the order of ps can be achieved at remote sites. When the network is interrupted, the proposed system can automatically recover the time-frequency synchronization from the failure state within 37 ms.