Sub-hundred-femtosecond level atmospheric transfer of microwave signal at X-band with active optical phase correction

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We propose and demonstrate a scheme for atmospheric transfer of microwave signals at X-band with sub-hundred-femtosecond level precision using active optical phase correction. With the proposed scheme, we have transferred a microwave signal at 9.192 GHz over a 60-m atmospheric link. The timing fluctuations and Allan deviations are both measured and analyzed to assess the performance of our scheme. The root-mean-square timing drift of the transferred microwave signal with timing fluctuation suppression is 44 fs, and the Allan deviation is 9 × 10 − 14 at 1 s and 1 × 10 − 17 at 1000 s with optical phase correction. The transmission link achieved a lower instability than currently reported cesium fountain clocks, which means this proposed transfer scheme could be employed to transfer cesium atomic clock over the atmospheric transmission link.