High-Precision Time Transfer Over 2000-km Fiber Link

The two-way fiber-optic time transfer based on bidirectional time-division multiplexing transmission over a single fiber with the same wavelength (BTDM-SFSW) is an effective way to eliminate the effect of Rayleigh backscattering and reach the maximum bidirectional symmetry at the same time. In this paper, a BTDM-SFSW-based time transfer testbed is built with the employment of loop configuration in the laboratory to evaluate the performance of fiber-optic time transfer over thousands of kilometers, which is confronted with worse signal-to-noise ratio (SNR), more serious fiber dispersion, and so on. The contributions of different factors, including the precision and stability of transmitted wavelengths, the power dependence of transceivers' receiving delays, Sagnac effect, etc., to the uncertainty of time transfer are investigated by theoretical analyses and experimental measurements. A full uncertainty budget for the BTDM-SFSW-based time transfer is provided. Experimental results show that the stabilities of less than 89 ps/s and 23 ps/10
⁵
s can be achieved for the time transfer over a 2000-km fiber link. The theoretical expanded uncertainty with the coverage factor
${k}=2$
can be less than 100 ps without the requirement of a fiber link calibration, which is validated by experimental results as well.