Atmospheric Timing Transfer Using a Femtosecond Frequency Comb

We have experimentally demonstrated atmospheric transfer of microwave timing references using a femtosecond frequency comb. The excess timing jitter induced by the atmospheric propagation has been characterized, and evidence is provided to show that such characterization is not compromised by the parasitic effect of power-to-phase coupling in the photodetector. The fractional frequency stability for a 60-m total transmission distance is on the order of 10^-12 with a 1-s averaging time. The Allan deviation shows a τ^-1 dependence up to 500 s. Scale estimate confirms that the measured excess timing noise is caused by clear-air turbulence. Comparisons with previous works show that our results offer a more precise characterization of atmospheric timing transfer. The work may potentially help the development of high-fidelity synchronization for future free-space optical communications.