Michelson interferometer-based coherent demodulation for joint time and frequency transfer

A high-precision joint time and radio frequency (RF) transfer scheme based on coherent demodulation is demonstrated. A one-pulse-per-second (1 PPS) time signal and an RF signal, transmitted at the same wavelength over a fiber link, are coherently demodulated at the receiver. Coherent demodulation is then achieved using a Michelson interferometer (MI), with balanced detection employed to enhance the signal-to-noise ratio (SNR) of the demodulated signals. An interferometer differential delay of 1042 ps is precisely designed through microwave phase discrimination techniques, enabling simultaneous demodulation of both time and RF signals. A joint time and frequency transfer experiment is then performed over a 560 km fiber link. The time stability (TDEV), measured as time deviation, of 1 PPS reached 31.1 ps at 1 s and 3.9 ps at 10,000 s. The frequency stability, in terms of Allan deviation (ADEV), for a 2.4 GHz signal reached 3.9 × 10^-14 at 1 s and 6.2 × 10^-17 at 10,000 s. This proposed technique could help to improve the integration of time and frequency synchronization networks using existing optical fibers.