Novel Polarization Control Approach to Long-Term Fiber-Optic Frequency TransferSupported by the National Key Research and Development Program of China (Grant No. 2016YFF0200200), the National Natural Science Foundation of China (Grant Nos. 91636101, 91836301 and 11803041), the West Light Foundation of the Chinese Academy of Sciences (Grant No. XAB2016B47), and the Strategic Priority Research Program of the Chinese Academy of Sciences

Abstract

We demonstrate a novel polarization control system based on a gradient descent algorithm, applied to a 450-km optical frequency transfer link. The power of the out-loop beat note is retrieved by controlling the polarization state of the transferred signal, with a recovery time of 24 ms, thereby ensuring the long-term evaluation of the fiber link. As a result, data utilization is enhanced from 70% to 99% over a continuous measurement period of ∼12 h. A fractional transfer instability of 7.2 × 10−20 is achieved at an integration time of 10000 s. This work lays the foundation for the comparison of a remote optical clock system via a long-haul optical fiber link.