Free-space Synchronization with Sub-nanosecond Resolution Using Atmospheric Optical Time Transfer

A free space synchronization technique based on atmospheric optical time transfer is presented. A laser signal with a time code was transferred over a 120 m free space link. By adjusting the time delay between the transmitter and receiver, a sub-nanosecond synchronization between the two sites is achieved. The experimental results show the absolute synchronization accuracy is 300 ps, and the root mean square (RMS) time drift is less than 48 ps in the integral time of 1000 s. In addition, the time stability of the synchronization with delay correction is less than l0 ps after integral time of l0 s. The experiment proves that the effectiveness of this synchronization technique with sub-nanosecond precision over free space link.