A femtosecond optical frequency comb for space-ground time and frequency comparison links

The space microgravity environment is conducive to enhancing the performance of atomic clock arrays and has the advantage of wide-area coverage, which can expand the application scope of high-precision time and frequency references. Therefore, developing high-precision atomic clock arrays in space has become an important research direction for international space frontier scientific exploration and the establishment of time and frequency systems. China's space station has also deployed active hydrogen maser clocks in space. In response to the demand for stable assessment of space optical frequency signals in complex space-ground environments, this paper introduces a femtosecond optical frequency comb (FOFC) for space-ground time and frequency comparison links. The constructed FOFC can achieve stable conversion of a 10 MHz hydrogen maser RF signal to a 200 MHz optical pulse signal. Ground test results show that the system can operate stably for more than 30 days, with the instability of fceo reaching 3.1×10^-17/τ ^1/2 and the instability of frep reaching 2.7×10^-13/τ ^1/2 . Using this system, the frequency deviation measurement result between two hydrogen masers in space and on the ground is 1.08 ps/s.