13,134-km fiber-optic time synchronization

In this paper, we experimentally demonstrate an ultra-long haul and multi-access fiber-optic time synchronization system over the equivalent 13,134 km fiber link based on the bidirectional time division multiplexing transmission over a single fiber with the same wavelength (BTDM-SFSW) scheme. The 13,134 km fiber link is simulated by re-circulating the time signals 33 laps in the 398 km fiber loop. Intermediate stations are employed to implement a high-symmetry low-noise bidirectional amplification for extending transmission distance, and extract the time signals for multi-access time synchronization applications at the same time. The results illustrate that time signals aligned with the master station can be available at the slaver station and arbitrary intermediate station without requiring link calibrations. Time synchronization stability in terms of time deviation (TDEV) of less than 32 ps and the expanded uncertainty of less than 87 ps are achieved for the 13,134 km main fiber link. The intermediate stations also have the similar performance with the main fiber link. The simple, robust and precise ultra-long haul fiber-optic time synchronization technique demonstrated here represents a new class of high-precision time synchronization that could be used for national/intercontinental atomic clock comparison campaigns and opens up a possibility to providing synchronized time signals to multiple users over the large-scale fiber-optic networks.