Multiple access fiber-optic radio-frequency transfer, time, and phase synchronization using symmetric carrier...

In this Letter, we propose a multiple access fiber-optic radio-frequency transfer, time, and phase synchronization scheme using passive optical coupling and symmetric carrier configuration. In the proposed scheme, the RF signal is distributed to distant nodes via a symmetric carrier configuration, which inherently suppresses link length-dependent phase difference. Access nodes are connected to the fiber link via passive optical coupling. Time signals are generated at each node by leveraging transferred frequency signals and synchronized by time-division multiplexing transmission and active delay compensation. Experimentally, a 2 GHz RF signal is transferred to access and terminal nodes over 20-km and 60-km fiber links, respectively, and compensated separately. The measured frequency stability is better than 4×10^-14 and 2×10^-16 at averaging time of 1 s and 10⁴ s, respectively. For the synchronized link, the measured time stability is better than 7 ps at 1 s and 4 ps at 10⁴ s. The phase consistency of RF signals is better than 10 ps (2% of the entire signal cycle) when subjected to changes in link length and system restart.