I. Introduction
Fiber-optic time transfer has attracted widespread research interest [1]–[7] because of its advantages of low loss, high reliability, wide bandwidth and high stability, and satellite-based time transfer is difficult to eliminate the effects of fluctuations and interferences induced by atmosphere [8]–[9]. Up to now, fiber-based time transfer mainly concentrates on two-way [1]–[2] and round-trip [3]–[7] dissemination using bidirectional wavelength division multiplexing (WDM) transmission that can suppress the impact of the Rayleigh backscattering by using WDM filter. The bidirectional WDM-based scheme, however, will cause bidirectional propagation delay mismatch induced by the chromatic dispersion, which will degrade the precision and accuracy of time transfer. Although some calibration methods can be used to measure the propagation delay mismatch, the uncertainty and difficulty to calibrate the mismatch will increase with the increase of fiber link length since the effect of the measurement errors of the dispersion coefficient and wavelength will increase linearly with the increase of fiber length.