Atmospheric Two-Way Time Transfer over Kilometers Free-Space Link with Dual Optical Frequency Comb

In this paper, we report an outdoor free space optical two-way time transfer technique with dual optical frequency comb (OFC). Using the transfer method, we transmitted the pulse time signal on the kilometer-level free space link. In the time transfer experiment, the time drift and time deviation of 1 km and 20 km links are measured and simulated respectively. The experimental results show that the total root mean square (RMS) time drift of 1-km link is about 2.2 ps within 5000 seconds, the time deviation is 2 ps when the average time is 1 second, and the time deviation is 0.32 ps when the average time is 100 s. The emulation estimates that the RMS time drift of a 20 km link is about 232 ps within 5000 seconds, the time deviation is 115 ps when the average time is 1 second, and the time deviation is 36 ps when the average time above 100 s.