High precision time transfer based on laser wavelength tracking

Abstract

In a high-precision optical fiber time transfer system, in order to solve the scientific problem of time transfer dispersion deviation caused by the inconsistency of the two-way laser wavelengths, a high-precision time transfer method based on laser wavelength tracking is proposed in this paper. In the two-way time comparison, the laser emitted by the local site is used as a reference, and other lasers in the system track the reference, and the difference between the two-way laser wavelengths is small enough and stable for a long time, thereby greatly reducing the time transfer deviation caused by the inconsistency of the two-way laser wavelengths. In order to verify the performance of laser wavelength tracking, a double-layer temperature controlled externally modulated laser is designed, an experimental device for automatic laser wavelength tracking is designed, and laser wavelength tracking experimental modules are developed. The results show that the standard deviation of wavelength jitter is 55 fm, and the long-term relative stability of laser wavelength tracking is better than 5 fm@1×10<sup>4</sup> s, which ensures that the two laser wavelengths can remain relatively stable for a long time. In the case of long-distance fiber time transfer, by optimizing the setting value of the wavelength difference between each laser and the reference light on the link, the dispersion deviation of time transfer can be further reduced. In order to verify the feasibility of the high-precision optical fiber time transfer method based on laser wavelength tracking, a long-distance multi-station optical fiber time transfer experimental setup is built in our laboratory. The experiment is carried out in the laboratory by using 0.005, 250, 500, 750 km optical fiber links. The experimental results obtained on 750 km link show that the time transfer deviation is better than 5 ps, the stability is 4.7 ps@1 s, 0.4 ps@4×10<sup>4</sup> s, and the uncertainty is 8.4 ps. In the engineering application of optical fiber time transfer, by optimizing the working sequence of the system, the holding time length of the remote site clock can be reduced, and the accuracy of optical fiber time transfer can be further improved, which lays a foundation for realizing high-precision long-haul optical fiber time transfer.