The bidirectional recirculating loop system for 10000 km fiber-optic time transfer

Two-way fiber-optic time transfer eliminates the transmission delay between two stations by bidirectional comparison over a long transmission distance. Considering the high cost of ultra-long haul fiber-optic transmission in laboratory, recirculating loop systems can be used for the emulation of straight-line pattern. Compared with the conventional one-way loop system, a simple bidirectional recirculating loop system is designed for the two-way time transfer in this paper. Since the stability of transmission is vital for the precise time transfer, an experimental platform for bidirectional time transfer in loop system is established and the result shows the time root mean square (RMS) is roughly proportional to the number of the loops. That means the loop system won't bring extra jitter to the transmission link. In the experiment, the bidirectional time signal can be transmitted as long as 10000 km in loop system.