Parallel transfer of optical reference frequency, radio frequency, and 1 PPS signal with timestamp over a 120-km single fiber channel in an urban area

Accurate and stable long-haul time and frequency distribution plays an important role in advanced scientific and industrial application fields, for instance, large-scale optical clock networks, advanced satellite navigation, very long baseline interferometry, clock-based geodesy, and fundamental physics. Here, we present a parallel transfer of optical reference frequency, radio frequency, and a one pulse per second (1 PPS) signal with timestamp over a single optical carrier by merging optical phase-locking with pseudo-code spread spectrum modulation. The method effectively reduces the crosstalk and non-reciprocity in dense wavelength division multiplexing (DWDM)-based fiber links. Measurement campaign has been conducted over a 120-km fiber link for half a month. Experimental results show that the fractional frequency instability of optical reference frequency transfer reached 7.3 × 10^-16 and 4.6 × 10^-19 at 1-s and 10⁵-s averaging times, respectively, while the fractional frequency instability of radio frequency transfer reached 7.9 × 10^-13 and 2.9 × 10^-19 at 1-s and 10⁵-s averaging times, respectively. The time deviation of 1 PPS signal transfer reached 0.02 ps at an average time of 10⁵-s. This approach also shows a potential in free-space simultaneous time and frequency transfer to establish satellite-to-ground and inter-satellite optical time and frequency transfer networks.