Phase-Stabilized Side-Branch RoF Link for Extensible Frequency Dissemination in Distributed Systems

Synchronization is a long-standing challenge in modern large-scale distributed systems, and newly deployed systems such as 5G and modern netted radars require more extensive synchronization. As the number of distributed stations increasing, new synchronization solution with much effort on extensibility is highly expected. In this paper we first analyze the requirements on extensibility of fiber-based sync systems, and then propose a phase-stabilized side-branch radio-over-fiber (RoF) link, which fully satisfies the extensibility requirements. The extensible side-branch link can be constructed at any intermediate point along the main link, without any reconfiguration at the central station, which is especially feasible when adding extra stations in system capacity expansion. The main link phase shift is first stabilized by tuning the optical carrier wavelength, while another phase-locked-loop constructed at the starting point of the branch link stabilizes the phase shift from the central station to the end of branch link, by phase locking two phase-varying signals. Moreover, the phase-stable side branch is inherently extensible to multiple frequency signals, which can be used in receivers requiring multiple local oscillators (LOs). Two frequency signals are simultaneously disseminated to the end of branch link in the experiment, with frequency stability optimization of two orders of magnitude on both LOs achieved. The proposed stable side-branch RoF link shows the potential of constructing a highly-extensible frequency dissemination network for the synchronization in modern distributed systems.