超长距离高精度光纤双向时间传递

 采用双向时分复用同纤同波传输（BTDM-SFSW）方案进行了超长距离高精度双向时间传递实验，设计了改进的IRIG-B时间码和相应的低抖动、自对准时间编/解码器。在2000 km的光纤环路上，实现了稳定度优于89 ps/s和23 ps/10⁵ s时间传递。针对现有单纤双向光放大器受后向散射噪声影响，以及无法有效利用现有光网络资源的问题，结合BTDM-SFSW的特点，提出了一种单向放大单纤双向传输的方法；在6000 km的光纤环路上，实现了稳定度优于190 ps/s和61 ps/10⁵ s时间传递。计算的时间传递不确定度小于70 ps，并进行了实验验证。

Ultra-long haul high-precison fiber-optic two way time transfer

Ultra-long haul high-precision fiber-optic two-way time transfer is demonstrated by adopting the proposed scheme called bidirectional time division multiplexing transmission over single fiber with the same wavelength (BTDM-SFSW), which can effectively eliminate the impact of Rayleigh backscattering and reach the maximum bidirectional symmetry at the same time. The inter-range instrumentation group (IRIG-B) time code is modified by increasing bit rate and defining new fields for the proposed BTDM-SFSW time transfer scheme. A dedicated codec (encoder and decoder) with low delay fluctuation and self-synchronization is developed by using a mask technique and combinational logic circuit. A BTDM-SFSW based time transfer testbed is built with the employment of loop configuration in laboratory to evaluate the performance of fiber-optic time transfer over thousands of kilometers. Stabilities of less than 89 ps/s and 23 ps/10⁵ s are achieved for the time transfer over a 2000 km fiber link with single fiber bidirectional amplifiers (SFBA). In order to overcome the issues of using the SFBA including the impact of Rayleigh backscattering and incompatibility with commercial fiber links, a novel time transfer scheme of single-fiber bidirectional-transmission with unidirectional optical amplifiers (SFBT-UOA) is proposed. Transmission over 6000 km is experimentally demonstrated with the time deviations of 190 ps/s and 61 ps/10⁵ s, respectively. A full uncertainty budget for the BTDM-SFSW based time transfer is provided, which considers the contributions of different factors, including the precision and stability of transmitted wavelengths, power dependence of transceivers'receiving delays, Sagnac effect, etc. The calculated theoretic combined uncertainty is not beyond 70 ps without the requirement of fiber link calibration, which well agrees with the experimental verification over different lengths of non-calibrated fiber link.