Sub-Hundred-Femtosecond Atmospheric Radio-Frequency Transfer with Frequency Comb Using Fast Optical Phase Compensation.

We demonstrate an atmospheric radio frequency (RF) transmission using fast optical phase compensation based on frequency comb. Using this transmission technology, we transmitted a highly stable 2GHz RF signal for 5000 s over a 100m long free space link, and measured and discussed the timing jitter PSD (power spectral density), timing drift and instability. The experimental results show that the total RMS (root mean square) timing drift of RF signal after compensation is about 88 fs, and the fractional frequency instability is about $1.9\times 10^{-13}$ at 1 s, and the instability of fractional frequency is $2.4\times 10^{-18}$ at 1000s. The atmospheric frequency transmission method proposed in this paper has potential application prospects in outdoor environment because the instability of this scheme is less than the commercial off-the-shelf CS or H master clock.