Report on 3,143.6km Time and Frequency Transfer Fiber Link With Ps-level Stability

The letter describes the implementation of a high-precision time and frequency transmission system using a two-way and wavelength division multiplexing (WDM) scheme over 3,143.6 km of field fiber links, connecting 21 sites between Xi'an and Beijing, China. The scheme incorporates a link noise clean-up system (LNCUS), wherein the controlled very low-phase noise BVA oscillator acts as an internal frequency source at the relay site to effectively suppress the interference caused by fiber link noise. Additionally, high-stability pulse generation technology in LNCPS provides enough short-term stability to significantly improve the stability of the fiber time transfer. The results demonstrate that a time transfer stability in terms of time deviation (TDEV) of less than 2.07 ps@1s, 5.9 ps@100,000s, and the combined uncertainty of less than 49.29 ps can be obtained for the 3,143.6 km field fiber link. The obtained results represent a significant breakthrough in achieving high accuracy of time transfer and continuous operation over ultra-long span field optical fibers exceeding 3,000 km for the first time. This achievement enables the provision of time transfer and synchronization services over the longest international field optical fiber distance, thereby establishing the fundamental basis for constructing a nationwide high-precision time service through optical fiber networks.