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长距离高精度光纤时频传递技术研究
其他题名High Precise Frequency Transfer and Time Synchronization over Ultra-Long Distance
刘琴
学位类型博士
导师韩申生
2016
学位授予单位中国科学院上海光学精密机械研究所
关键词光纤时频传递 光纤延迟线 双向光放大 级联系统
摘要高精度时间频率传递技术在多方面有着重要应用,如时间频率计量、导航定位、基础物理、粒子加速器、天文学等。现有的高精度时间频率传递技术主要基于卫星实现,例如GPS共视时间、双向卫星时间频率传递等。但随着原子钟尤其光钟的发展,基于卫星的传递方法已经不能完全满足需求。光纤最大的特点是受外界环境的影响较小和损耗低,其传输频率的短期稳定度较自由空间好。另一方面,已经建成的光纤通信网络(涉及大量的技术和基础设施)既可以用于进行高稳定度的频率传输,又可以用于进行高精度的时间同步。所以用光纤来实现高精度中远程时频传递技术已经成为国际热点。对于长链路高精度光纤时频传递,一方面,调制的光信号因为链路中的各种吸收和散射而产生损耗,会导致接收端的信号信噪比太低,影响时频传递的稳定性,如果链路距离超过了探测器可探测范围,甚至无法接收到时频信号,所以必须对光信号进行放大,同时基于单纤中信号双向还回主动反馈补偿方式,放大也必须满足双向放大且放大对称要求。另一方面,由于补偿带宽和噪声抑制比随着链路长度的增加而下降,导致超长链路传递系统中有部分噪声无法通过补偿系统进行反馈抑制,需要采用级联补偿方法来解决。 本文面向长距离光纤时间频率传递的应用需求提出了基于波分复用和光学补偿技术的时频同传系统,并在实际超长链路中验证了级联传递系统,主要的研究内容如下: 1. 设计了一种应用于高精度光纤时频传递的压控光纤延迟线。该光纤延迟线的延迟时间连续可调、动态范围大,制作的1km光纤延迟线测试温度变化范围为68℃,时延量变化为2.6ns,10km光纤延迟线温度变化范围为46℃,时延量变化为16.1ns。 2. 提出了一种基于光学补偿和波分复用方案的时间和频率信号同时传递方法,并实验验证了系统的可靠性。在实验室内60km链路上实现了1.9×10-14@1s,2.5×10-17@10000s的频率稳定度;经过400s平均时间后,时间信号的稳定度为1.4 ps,时间同步不确定度为22 ps。 3. 设计了一种应用于高精度光纤时频传递的低噪声高对称性的双向光放大器。该双向光放大器的放大倍数在-15bdm输入时为26.2db,引入的不对称绝对时延为1.75ns,时延抖动只有0.8ps@1000s。 4. 研制了多套光纤时频同传系统工程样机。一套应用于某地的两个原子钟房之间的交互比对,目前已经持续运转了一年多,仍然保持良好的工作状态。一套应用在某处的城市光纤网络中实现了三点的时频同传和两点的时间同步,将中心站氢钟的10MHz频率信号以及生成的1PPS信号同时传递到距离为14km和110km的两个远地天线站。其中14km链路最后达到的频率稳定度为3.0×10-14 @1 s,1.4×10-17 @10000 s, 110km链路为8.3×10-14@1 s,1.7×10-17 @10000 s。理论计算两个远地端与本地的时间同步精度分别达到了38.5ps (14 km)和 38.7 ps(110km)。 5. 在京沪光纤骨干网苏州段通过级联方式,进行了目前国内外已知的最长距离的微波时频同传实验, 链路分为280km和150km两段。实际测试中,远地端频率传递稳定度达到了1.02×10-13@1s和8.24×10-17@10000s,本次实验准确地验证了远地端的时间同步精度达到了94ps。
其他摘要Remote transfer of ultra-stable frequency and time standards is of great importance in many areas such as metrology, navigation, basic physics, paticles accelatrator and astronomy. Due to the rapid development in stability of frequency and time standards, especially the optical clocks, the widely used methods like global positioning satellite system (GPS) carrier phase and two-way satellite time and frequency transfer (TWSTFT) techniques will not fully satisfy the high requirement. Owing to the characteristics of high bandwidth, low attenuation and resistance to external interference, optical fiber has become an attractive alternative to satellite links. In addition, the exsiting fiber network which is involved in many mature technologies and fundamental facilities can be well exploited to not only realize the transfer of frequency signal but also time synchronization. Nowadays, adopting optical fibers for such transfer presents much better performance and has became an international hotspot. As for long-distance transfer, on one hand, because of obsortion and scattering, the signal-to-noise ratio of transmitted signal recovered in the remote end will be too low to maintain the stability of transferring. What’s more, the signal cannot be detected by the photo detector in the remote end when the total loss along fiber link is big enough. So optical amplification must be considered. However, in a round-trip fiber transfer of joint frequency and time (FTFT) signals system in which the signals will be sent forth and back along the same fiber link, the amplification should be bidirectional. On the other hand, the link loss and the cumulative noise increase with the distance of fiber link, while the compensation bandwidth and noise suppression ratio decrease with the increase of the link length, resulting in that some noise cannot be compensated by the system in long-distance transfer. This can be solved by exploiting cascaded system. In view of the applications of FTFT in long fiber link, the simultaneous frequency and time transmission system based on DWDM technology and optical compensation method is proposed. At the same time, using cascaded method, ultra-long distance transfer is also demonstrated in field network.The main contents are as follows: 1. A voltage-controlled fiber delay line for high precise time or frequency transfer via optical fiber is described and made. The delay of the fiber delay line is adjustable and with large range. The tested temperature and delay range of the made 1km fiber delay line are 68℃and 2.6ns. Those of 10km fiber delay line are 46℃and 16.1ns. 2. A simultaneous time and frequency dissemination system based on optical compensation and DWDM is described. The system is experimentally examined to be reliable via a 60 km spooled fiber link. After compensation, the final frequency stability of 1.9×10-14 @1 s and 2.5×10-17 @10000 s is achieved. The stability of the one pulse per second (1PPS) is 1.4 ps at the averaging time of 400 s. The uncertainty of time synchronization is 22 ps. 3. A specific bi-directional erbium-doped fiber amplifier (Bi-EDFA) is designed and applied to compensate for the loss of the link with low noise and high symmetry simultaneously. The amplification gain of Bi-EDFA can reach 26.2db when the input power is -15bdm. The calibrated time of the propagation delay difference of Bi-EDFA is 1.750ns and the delay fluctuation caused by the asymmetry of the Bi-EDFA in two directions is only 0.8ps at averaging time of 1000s. 4. Several engineering prototype of the fiber-optic joint time and frequency transfer are developed in this thesis. One is used in time comparison between two atomic clock rooms and it has been kept running for more than one year with effective working. One is adopted to disseminate two 1PPS signals and one frequency signal (10 MHz) of hydrogen maser from the central location to two remote antenna locations, as far away as 14 km and 110 km. The frequency stability of 14 km link reaches 3.0×10-14 @1 s and 1.4×10-17 @10000 s while the stability of 110 km link is 8.3×10-14 @1 s and 1.7×10-17@10000 s. The time signals at the two remote locations are synchronized with each other. The accuracies of synchronization are estimated to be 38.5 ps for the 14km link and 38.7 ps for the 110 km link. 5. Frequency transfer and time synchronization are simultaneously realized over a compensated cascaded fiber link of 430km, which is a part of Beijing-Shanghai optical fiber backbone network. The entire cascaded system consists of two stages with fiber links of 280km and 150km, respectively. It is the longest distance fiber-based joint time and radio frequency transfer in China. The frequency stability of 430 km link reaches 1.02×10-13 averaged in 1 s and 8.24×10-17 in 10000 s. The accuracy of synchronization is 94 ps.
语种中文
文献类型学位论文
条目标识符http://ir.siom.ac.cn/handle/181231/15954
专题学位论文
推荐引用方式
GB/T 7714
刘琴. 长距离高精度光纤时频传递技术研究[D]. 中国科学院上海光学精密机械研究所,2016.
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