远程光纤传感系统前向拉曼与MI耦合机制及噪声抑制技术

The gain of forward distributed fiber Raman amplification (DFRA) is used to the maximum extent to increase the fiber transmission distance without repeaters in the interferometric optical fiber sensing system.The coupling mechanism between DFRA and modulation instability(MI) as well as the noise suppression method is investigated. Considering that nonlinear Schrodinger equation cannot be used anymore because of the coexistence of elastic and inelastic nonlinear effects, the project combines the continuous multi-wave coupling equation and transient nonlinear Schrodinger equation by the distributed gain of the FRA, and a universal coupling model applicable to both elastic and inelastic effects is established, in which amplitude and phase are both considered. Based on the coupling model, the mechanism of DFRA gain, MI threshold as well as spectral shape is studied. By methods such as Amplified spontaneous emission noise mitigation and orthogonal polarization injection, the project suppresses MI in the system. For optical fiber sensing systems in which ultra-narrow linewidth laser is used, the project studies the conversion mechanism from the MI noise to sensor phase noise. A noise evaluation system is established to evaluate the effect of MI suppression and solve the problem of the parameter optimization. The project would play an important role for the practical application of the large-scale and remote optical fiber sensing network.

课题以最大限度地利用正向拉曼光放大（DFRA）增益，提升干涉型光纤传感器无中继光传输距离为目标，探索DFRA与调制不稳定型（MI）的相互耦合机制及噪声抑制机理。考虑到弹性与非弹性非线性效应共存而使经典的非线性薛定谔方程不再适用，课题拟将分布式拉曼增益作为连接稳态多波耦合方程组和瞬态非线性薛定谔方程的纽带，建立同时考虑振幅和相位的弹性与非弹性效应相统一的耦合模型。在此基础上，考察影响DFRA增益、MI阈值和谱形的内在物理机制，并将高信噪比信号光注入、退相干的光场偏振正交注入等MI抑制手段运用于光纤传感系统。通过研究MI噪声与干涉相位噪声的转换关系，建立系统噪声的综合评价体系，对MI抑制效果进行评估，最终解决系统的参数优化设计问题。课题的研究将为进一步推动大规模远程无中继光纤传感网络系统的实用化奠定基础。

干涉型光纤传感器远程无中继传输系统具有全光传输低成本、可靠性高等优点，在水声探测、地震勘探、周界安防等领域具有广阔的应用前景。本项目针对远程模拟光传输系统非线性噪声激增和光功率受限等问题，以最大限度利用前向分布式拉曼光放大（DFRA）增益、提升传输距离为目标，研究了远程传输非弹性非线性效应的存在对弹性非线性效应的影响，基于稳态的拉曼耦合方程和修改的薛定鄂方程，建立了包含调制不稳定性（MI）和前向DFRA的理论模型，结合实验验证获得修正的MI阈值及边带特性；研究了MI引起的FPU（Fermi-Pasta-Ulam）效应，通过分析中心频率光功率波动与MI边带波动的关系，获得了MI强度噪声向干涉相位噪声的转化机制；通过相干种子注入方案使远程干涉型光纤传感系统的MI阈值增加4.77dB，相位噪声抑制达25dB；研究了DFRA的分布式ASE噪声及泵浦源强度噪声引入的传感器相位噪声特性，采用前向二阶DFRA方案获得了优于一阶DFRA增益3dB的结果；提出近程非平衡匹配干涉、多波长错峰输出等光学结构，通过系统参数优化设计，实现了远程光传输线性噪声、非线性噪声以及光路拾音等噪声的综合抑制。项目的研究成果为推动大规模光纤远程传感网络的实际应用奠定了基础，具有重要的应用前景。