Time Delay Measurement of Optical Fiber Link Using Time-Frequency Joint Transfer

A joint transfer scheme of frequency and one pulse-per-second time signals based on the same wavelength is proposed to meet the time delay measurement requirements of large-range and high-precision fiber-optic links. The scheme combines the coarse results of the one pulse-per-second time counting method and fine results of frequency signal phase-comparison method to achieve high-precision and large dynamic measurement of the true delay of the fiber link. We construct an experimental system to verify the consistency of the coarse and fine measurements and measure the absolute delay of the signal over 25 km of optic fibers under severe temperature change conditions. The experimental results demonstrate that the proposed method can effectively combine the large-range advantage of the one pulse-per-second counting method with the high-resolution advantage of the phase measurement method.