全光纤高鲁棒性的光频梳高精度频率传递方法的研究

High precision frequency transfer technique plays important role in many applications, such as global position system, long baseline interferometry, radio telescope array, and basic physical constants measurement. Frequency transfer over fiber has the highest precision, and it is meaningful for the development of time and frequency transfer. The techniques mainly include radio frequency transfer over fiber, optical frequency transfer and optical frequency comb transfer. However, there are two bottleneck problems in high precision frequency transfer via optical fiber: The first one is end face reflection in the connection node, resulting in detection errors of phase variations; The second one is signal to noise ratio (SNR) deterioration of the round trip transmitted signal, reducing the stability of frequency transfer. At present, welding optical fiber connection nodes and wavelength division multiplexing (WDM) are applied to solve the issue of end face reflection. The phase locked loop regeneration is used for settling the later problem. There are problems that utilizing non-fiber devices and low robustness. In conclusion, we propose the technique of combination dispersion management and nonlinear optical effect with WDM to spread spectrum and filter the round trip transmitted optical comb. Thus, we accomplish wavelength conversion and ensure the coherence of the optical comb. The technique improves the SNR of the round trip transmitted signal and enhance the robustness of our system. The outcome of our project is meaningful for promoting the application of high precision optical comb frequency transfer in navigation system and next generation mobile communication system.

高精度频率传递技术在全球卫星导航、长基线干涉、射电望远镜阵列、物理基本常数测量等方面应用广泛。光纤频率传递技术精度最高，对未来时频体系发展具有重要意义，其技术实现主要有射频调制、光频直传和光频梳传递等。光纤频率传递技术面临两个瓶颈问题：一是节点的端面反射造成相位抖动检测误差；二是环回信号的信噪比恶化降低频率传递稳定度。目前，主要使用光纤熔接节点或波分复用技术解决节点的端面反射问题，利用锁相再生技术解决环回信号的信噪比恶化问题，存在使用非光纤器件、系统鲁棒性不高的问题。本项目以光频梳传递方法为基础，提出了通过色散管理、非线性光学效应与波分复用相结合的方法，对环回的光梳进行扩谱和滤波，完成波长转换，提高光梳相干性，从而提升环回信号的信噪比，增强系统的鲁棒性。本项目预期研究成果对加快光梳高精度频率传递在导航及下一代移动通信系统的等重要领域的应用具有重要意义。

高精度时频传递技术在精密导航定位、全球授时、物理学基本原理检验、长基线干涉等方面应用广泛。基于光纤的频率传递技术相比于传统的频率传递技术的精度可以提高3~5个数量级，对导航定位授时系统具有重要意义。本项目以基于光学频率梳的高精度频率传递技术为基础，提出了通过色散管理、非线性光学效应与波分复用相结合的方法，对环回的光学频率梳进行扩谱和滤波，完成波长转换，提升环回信号的信噪比，增强系统的鲁棒性。本项目实现了一种“全光纤”高精度的时频传递系统，将扩谱后再生的光频梳信号作为远端信号，该技术解决了目前光纤频率传递技术面临的端面反射造成相位抖动检测误差和环回信号的信噪比恶化降低频率传递稳定度两个瓶颈问题，并且省去了一个光学频率梳，节约系统成本。本项目验证了100公里光纤传递中的频率传递不稳定度，在1s时的频率传递不稳定度为5.1E-17，在400s时的频率传递不稳定度为7.8E-19。本项目研究实现的基于光学频率梳的“全光纤”高精度时频传递技术将成为卫星导航、深空探测及新一代精密授时网络等领域的关键技术之一。