基础科研、高技术工程应用、国防科技等领域对亚纳秒甚至皮秒量级的高精度授时提出迫切需求，为此我国启动构建分布式高精度光纤授时系统。本文研究分布式高精度光纤授时系统关键技术，包括光纤授时基础技术和光纤授时系统设计两部分，为我国分布式高精度光纤授时系统的建设提供技术支撑。本文的主要研究工作及贡献如下：

1.针对影响分布式高精度光纤授时系统授时精度、授时距离和覆盖范围等核心指标的关键技术问题，本文提出通过结合双向同波时分多址、双向波分时分多址、双向分时同波时分多址这三种光纤授时系统设计方案，组成城域、城际、省际三级授时网络的方法，首次在国内1085km实地通信光纤链路上实现稳定度为9.2ps@1s的分布式光纤授时，使授时精度、授时距离等指标达到国际先进水平。

2.针对光纤授时过程中链路时延及其漂移、链路噪声、链路损耗和分布式授时等影响授时指标的基础技术问题，本文提出了基于时间-电压转换的光纤链路时延精确测量技术、基于DDS的大范围高精度时延补偿技术、基于载波恢复时间再生的噪声抑制技术、双向光-电-光中继技术和基于载波恢复的时分多址授时技术。基于时间-电压转换的光纤链路时延精确测量技术的测量稳定度达到了2.5ps，优于主流仪器SR620的5ps稳定度的指标；基于DDS的大范围高精度时延补偿技术的时延补偿分辨率0.6ps，优于主流仪器DG645的5ps分辨率的指标，为分布式高精度光纤授时系统奠定技术基础。

3.针对城域分布式高精度光纤授时系统同时面临的多授时节点问题和双向波长不一致引入的色散偏差的问题，本文提出了基于载波恢复的双向同波时分多址光纤授时方案。采用载波恢复技术提高了各个节点的授时稳定度，而双向激光标称波长相同则减小了色散偏差。实现了1个本地端对11个远程端的授时，在550km实验室光纤和871.6km实地光纤链路上分别获得13.8ps@1s、2.5ps@40000s和15.1ps@1s、7.1ps@40000s的授时稳定度。双向同波时分多址光纤授时方案用于距离小于100km的链路，授时不确定度优于20ps，优于国际上报道的在73km链路上100ps授时不确定度的指标，故核心指标满足城域分布式高精度光纤授时系统的需求。

4.针对城际分布式高精度光纤授时系统存在的授时距离延长和信噪比恶化的问题，本文提出了基于色散偏差自动修正的双向波分时分多址光纤授时方案。双向采用密集波分复用（DWDM）系统两个相邻波道的激光，抑制了后向散射和端面反射光对信噪比的影响，色散偏差自动修正技术减小双向波长不一致引入的不确定度，从而延长了授时距离并提高了短期稳定度。经过实验测试，在800km实验室光纤和1085km实地光纤链路上分别获得了4.9ps@1s、0.8ps@40000s和9.2ps@1s、5.4ps@40000s的授时稳定度。双向波分时分多址光纤授时方案适用于距离小于500km的链路，授时不确定度可以达到60ps，优于国际上报道的在540km链路上250ps授时不确定度的指标，故核心指标满足城际分布式高精度光纤授时系统的需求。

5.针对省际分布式高精度光纤授时系统存在的授时距离进一步延长、信噪比进一步恶化和双向波长长期漂移引入色散偏差的问题，本文提出了基于波长跟踪的双向分时同波时分多址光纤授时方案。利用激光波长跟踪技术使双向波长差异足够小且保持长期稳定，解决了双向波长长期漂移引入色散偏差的问题；采用事件计时器模块测量时间间隔的方法，减小了链路时延测量的温度漂移和测量不确定度；采用分时双向时间比对的方法，保证链路上任意时刻只有上行或者下行一个方向的光在传播，避免了瑞利后向散射和接头端面反射的影响，进一步提高了信噪比，延长了单级传递的距离；利用基于数字锁相环的守时电路良好的相位保持能力，保证分时双向时间比对的稳定度。在实验室750km光纤链路上达到了4.7ps@1s、0.4ps@40000s的授时稳定度，8.4ps的不确定度。经过分析，该方案如果用在1000km光纤链路上，可以达到10.9ps的授时不确定度，优于国际上报道的在744km链路上112ps授时不确定度的指标，故核心指标满足城际分布式高精度光纤授时系统的需求。

本文研究的部分关键技术已在我国分布式高精度光纤授时系统的建设中得到应用。为了进一步提高光纤授时的精度，本文讨论了基于光纤微波频率传递的超高精度光纤授时技术，并通过实验进行了初期的验证；展望了基于光纤光频传递的超高精度光纤授时技术，以获得更高的光纤授时精度。

High accuracy time transfer in sub-nanosecond or even picosecond is urgently required in basic scientific research, high-tech engineering applications, national defense technology and other fields. Therefore, China started to build a distributed high-precision fiber-optic time transfer system. The key technologies of the distributed high-precision fiber-optic time transfer system are researched in this paper, including the basic technology of optical fiber time transfer and the design of optical fiber time transfer system, to provide technical support for the construction of the distributed high accuracy optical fiber time transfer system in China. The main research work and contributions of this dissertation are as follows:

1. Aiming at the key technical problems that affect the core indicators of the distributed high-precision fiber-optic time transfer system, such as timing accuracy, time transfer distance and range, a method to combine the three optical fiber time transfer schemes of the bidirectional same-wavelength time-division multi-access (BSW-TDMA), the bidirectional wavelength-division multiplexing time-division multi-access (BWDM-TDMA) and the bidirectional time-division multiplexing time-division multi-access (BTDM-TDMA) is proposed to constitute intra-city, inter-city and inter-provincial three-grade time transfer networks，and the time transfer with stability of 9.2ps@1s is realized on 1085km the commercial optical fiber link for the first time in China, which makes the time transfer range, accuracy and precision reach the international advanced level.

2. Aiming at the key technical problems affecting the time transfer index such as delay and its drift, noise, optical loss of fiber link and distributed time transfer, the accurate measurement technology of fiber link delay based on time-voltage conversion, large-scale high-precision time delay compensation technology based on DDS, noise suppression technology based on carrier recovery time regeneration, bidirectional optical-electrical-optical relay technology and time division multi-access timing technology based on carrier recovery are proposed, and the above problems are solved effectively to lay a technical foundation for the distributed high-precision fiber-optic time transfer system. The measurement stability of the fiber link delay based on time-voltage conversion has reached 2.5ps, which is better than the mainstream instrument SR620. In addition, the time delay compensation resolution of time delay compensation technology based on DDS is 0.6ps, which is better than the mainstream instrument DG645.

3. For the intra-city distributed high-precision fiber-optic time transfer system, the problem of multi-node and the dispersion deviation caused by bidirectional wavelength inconsistency need to be solved at the same time. The BSW-TDMA optical fiber time transfer scheme based on carrier recovery is proposed. The carrier recovery technology improves the time transfer stability of each node, while the same nominal wavelength of bidirectional laser reduces the dispersion deviation. In order to verify the scheme and explore its limit performance, a local site to 11 remote site timing is realized by experiments with self-developed equipment, 13.8ps@1s, 2.5ps@40000s and 15.1ps@1s, 7.1ps@40000s time transfer stability are obtained on 550 km laboratory fiber link and 871.6km field fiber link, respectively. The BSW-TDMA optical fiber time transfer scheme is used for links less than 100km, and the timing uncertainty is better than 20ps, which is better than the internationally reported 100ps uncertainty on 73km links, and meets the needs of intra-city distributed high-precision fiber-optic time transfer system.

4. In order to meet the demand of inter-city distributed high-precision fiber-optic time transfer system, extend the time transfer range and improve the short-term stability, the BWDM-TDMA optical fiber time transfer scheme based on automatic correction of dispersion deviation is proposed. The bidirectional laser with two adjacent channels in the DWDM system inhibits the influence of laser of back scattering and end-face reflection light on signal-to-noise ratio, thus extending the time transfer range and improving the short-term stability. The time transfer stability of 4.9ps@1s, 0.8ps@40000s and 9.2ps@1s, 5.4ps@40000s are obtained on 800km laboratory fiber link and 1085km field fiber link. The BWDM-TDMA optical fiber time transfer scheme is used for links less than 500 km, and the uncertainty of timing can reach 60ps, which is better than the internationally reported 250ps uncertainty on 540km links, and meets the needs of inter-city distributed high-precision fiber-optic time transfer system.

5. In order to meet the demand of inter-provincial ultra-high precision fiber-optic time transfer system, under the premise of ensuring short-term stability of time transfer, further extending the range and improving the uncertainty, it is necessary to solve the scientific problem of dispersion deviation caused by long-term drift of bidirectional wavelength in long-range optical fiber time transfer. Therefore, the BTDM-TDMA fiber-optic time transfer scheme based on wavelength tracking is proposed. The dispersion deviation caused by long-term drift of bidirectional wavelength is solved by using laser wavelength tracking technology to make the difference of bidirectional wavelength being small enough and stable for a long time. The method of measuring time interval by event timer module reduces the temperature drift and uncertainty of measurement in link delay measurement. The method of bidirectional time-division multiplexing time comparison is used to ensure that only uplink or downlink light propagates at any time in the link, avoiding the influence of rayleigh backscattering and end-face reflection, and extending the distance of single-stage transmission. The excellent phase preserving ability of the time-keeping circuit based on digital phase locked loop ensures the stability of time-division bidirectional time comparison. The time transfer stability of 4.7ps@1s, 0.4ps@40000s and the uncertainty of 8.4ps are achieved on the 750km fiber link in the laboratory. If it is on 1000km optical fiber link, the scheme can obtain the uncertainty of 10.9ps according to the analysis, which is better than the internationally reported 112ps uncertainty on 740km links, and meets the needs of inter-provincial distributed high-precision fiber-optic time transfer system.

Some key technologies studied in this paper have been applied in the construction of the distributed high-precision fiber-optic time transfer system in China. In order to further improve the accuracy of fiber-optic timing, the ultra-high accuracy fiber-optic time transfer technology based on fiber-optic microwave frequency transfer is discussed, and the initial verification is carried out through experiments. The technology of ultra-high precision time transfer based on optical frequency transfer is prospected to obtain higher fiber time transfer precision.

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