High-precision dual-wavelength time transfer via1085-km telecommunication fiber link

Abstract

To reduce the influence of fiber dispersion on accuracy of fiber-based time synchronization, a method of dispersion-error corrected dual-wavelength time synchronization is proposed in this paper. Specificlly, the method is to measure the dispersion coefficient of the fiber link, and then input it to each remote terminal, the time delay error caused by the fiber dispersion is eliminated through the delay phase controller. With the self-developed engineering prototypes, the experimental verifications are subsequently made both in laboratory and real field. Before the test, 16 devices of time synchronization are connected in series for calibration. The time synchronization system is able to keep delay difference within ± 15 ps after being calibrated. In the laboratory, the experimental setup is built by cascading 16 rolls of 50km-long fiber coils, and the total length of the fiber link is 800 km. The experimental results show that the dispersion coefficient of 800 km fiber link is 13.36 ps/(km·nm), and the delay error caused by dispersion is maintained within 10 ps after correction. The stability of the time transfer is 5.7 ps in standard deviation and the time deviation is 1.12 ps at an averaging time of 100000 s. In the real field test, a 1085-km-long field fiber link is utilized, along which 16 self-developed time-frequency transceiversare set at the cascaded fiber-optic stations. After being corrected with a dispersion coefficient of 16.67 ps/(km·nm) for 1085 km urban fiber link, the time transfer is demonstrated to have a dispersion-caused delay error of 60 ps. The experimental results show that the time standard deviation is 18 ps and the time transfer instability is 9.2 ps at an averaging time of 1 s and 5.4 ps at an averaging time of 40000 s. Finally, the time uncertainty of 800-km-long laboratory optical fiber link and 1085-km-long urban optical fiber link are evaluated, and the time uncertainty is 18.4 ps and 63.5 ps, respectively. This work paves the way for constructing the time synchronization fiber network in China. To further reduce the delay error caused by dispersion in a long-distance time transfer link, the more accurate thermal control of the lasers should be adopted to reduce the shifts of forward and backward wavelengths.