光载微波干涉分布式光纤传感方法及其应用研究

Distributed optical fiber sensor have got a lot of attention recently, as it can realize continuous measurement with no dead zone. Usually the power of Rayleigh back scattering light is quite weak, together with random statistical fluctuations, although the coherent demodulation technique can improve the sensitivity, the fiber interferometer based on such reflective light still has the problem of polarization fading. So the location accuracy, measuring range and signal bandwidth are interrelated and interact on each other in the sensing system. Microwave photonics has played an important role in optical communication, with the advantages of broadband of photonics and easier modulation of electronics at the same time, which intrigues us to explore the possibility of sensing applications. This proposal is focus on the research of distributed reflective sensing method and its application based on Optical Carrier Microwave Interferometer (OCMI), meanwhile to enhance the signal intentionally by Fresnel Reflection in the sensing fiber. A promising effort is to bring the strengths from both microwave and optics together by detecting the interference of reflected light in the microwave field. The research content include new sensing theory, signal enhancement methods and multi-parameters, dynamic and static joint sensing experiments. We will utilize advanced microwave technology to insure the stability of the interference signal, and further improve the power of reflective light through special fiber structure. This proposal with scientific significance and practical value hopes to realize a new type of distributed sensing system with longer detection range, higher positioning accuracy and faster response speed, overcoming the faults such as low Rayleigh scattering light’s random fluctuation and polarization fading.

分布式光纤传感技术能够实现连续感知和无盲区测量而获得高度关注。通常基于瑞利散射技术的信号光非常微弱，且存在随机涨落问题，虽然通过相干解调技术可以提高探测灵敏度，但光纤干涉技术还受偏振衰落等问题的困扰，使得系统的定位精度、测量长度、测量速度等指标相互制约。微波光子学将光子学的宽带特性与电子学的易控特性结合，已在通信领域发挥重要作用，本项目将拓展其在传感领域的深入应用，提出将微波加载在连续光波上，在菲涅耳反射信号增强的特种传感光纤中，通过探测反射光在微波域的干涉，实现光载微波干涉的分布式传感新方法。主要研究新型传感理论，信号增强方法和多参量、动静态联合传感的实验验证。本项目利用光纤内部的菲涅耳反射增强信号强度，运用微波干涉技术提高信号稳定性，将克服瑞利散射光信号随机涨落和偏振衰落等问题，有希望获得同时满足较长探测距离、较高空间分辨率和测量速度的新型分布式传感系统，具有重要的科学意义和实用价值。

传统的光学干涉传感系统使用窄线宽激光，传感范围受激光的相干长度限制，同时传感信号还受到激光模间干涉，偏振干涉等因素的影响。针对这一问题，本项目提出将微波光子学和分布式光纤传感技术融合，将微波加载在宽谱激光上，通过探测信号光的包络相位实现传感，这一方式能够消除传输模式、偏振及其涨落的影响，传感范围不受光波的相干长度的限制。通过研究取得以下进展：第一，基于电磁干涉理论建立了光载微波干涉的理论模型，讨论了宽谱光源的传输模式、偏振态对包络的影响。第二，建立了基于光子晶体光纤的光载微波干涉传感系统，解决了单模光纤在高温状态下测量温度时存在的光谱漂移的问题，温度实验结果表明:系统在室温到800℃温度范围内的温度测量灵敏度为76.04kHz/℃,理论上温度测量分辨率可达0.13℃,系统具有良好的温度灵敏度与稳定性；建立了一个由500个全同超弱光纤布拉格光栅组成的准分布式传感系统，该系统能够测量499根传感光纤（总范围为2.5km）在0.5–100Hz低频范围内的声信号的振幅、频率和相位，获得了22.1dB的高信噪比、良好的线性度、约0.024rad/Pa的相位灵敏度和约38dB的动态范围；第三，对光载微波干涉系统解调部分算法进行了优化，提出了一种新的迭代贝叶斯重加权(IBR)算法，并通过应用应变传感实验数据，将该算法与最大似然估计(MLE)算法进行了比较，结果表明：当轴向应变变化240με，IBR算法产生的偏差仅为36με，显著小于MLE算法产生的偏差（138με）。第四，为了使用光栅阵列反射增强光载微波信号，研究了拉丝塔光栅阵列的制作工艺，通过改变光纤内部应力得到了高反射率的拉丝塔光栅阵列。在本项目支持下，我们在国内外核心刊物与国际会议上发表学术论文19篇，其中SCI检索论文8篇，EI检索5篇，培养博士研究生1名，硕士研究生6名，圆满完成了各项任务。