基于SBS矢量特性的单端宽带动态应变测量方法研究

To solve the problems that Brillouin optical time domain analysis (BOTDA) systems with double-ended structure are too complicated and their applications are limited, and to broaden the measurement frequency range, enhance the sensitivity and spatial resolution simultaneously, a new method, which bases on the vector characteristics of stimulated Brillouin scattering (SBS) and single-ended structure, is proposed to realize the fast and accurate measurement of dynamic strain along the fiber with wide frequency range, high sensitivity and high spatial resolution. This project aims at putting forward some new methods as follows..Modeling and verification methods for strain dependence of amplitude and phase shift generated by the SBS effect between Rayleigh scattering from the microwave-modulated incident base and pump pulse..Theoretical modeling, evaluating and improving methods for single-ended vector BOTDA system through employing the techniques of double-sideband structure, pulsed pre-pump coding and self-heterodyne detection..Evaluating, improving and amending methods for the influence of fiber dispersion and nonlinear effect on system performance by mathematical modeling..By detecting SBS phase shift and adopting single-ended structure, the system requires no frequency sweep and can realize the nondestructive measurement with low cost. The proposed method can greatly improve signal-to-noise ratio and measurement speed of the system, realize the dynamic strain measurement with wide frequency range, high sensitivity and high spatial resolution by employing double-sideband structure, pulsed pre-pump coding and self-heterodyne detection, which has wide application prospects in the development of geophysics, acoustics and other disciplines, and the fields of online monitoring geological disaster and large engineering structures of electric power, railway.

针对双端结构BOTDA系统结构复杂、应用场合受限且无法同时实现动态应变的宽带、高灵敏度、高空间分辨率测量的问题，提出一种基于SBS矢量特性的单端结构的宽带动态应变测量方法，实现沿光纤动态应变的宽带、高灵敏度、高空间分辨率的快速、准确测量。主要内容：微波调制入射信号基底产生的瑞利散射与泵浦脉冲SBS作用的幅度和相移与应变关系建模及验证；双边带结构、脉冲预泵浦编码、自外差检测单端矢量BOTDA系统建模评价和性能提高方法；光纤色散、非线性效应对系统性能影响的建模和校正方法。该方法利用SBS相移检测，无需频率扫描；采用单端结构可实现非破坏性的低成本测量；利用双边带结构、脉冲预泵浦编码和自外差检测技术，可大大提高系统信噪比和测量速度，实现宽带、高灵敏度和高空间分辨率测量，在地球物理、声学等学科发展及地质灾害和电力、铁路等行业大型结构在线监测领域具有广阔的应用前景。

为了解决双端矢量布里渊光时域分析(BOTDA)系统在光纤断裂时无法检测的问题，本项目提出了将光纤产生的背向瑞利散射作为探测光的单端矢量BOTDA动态应变传感系统。通过对单端BOTDA系统的受激布里渊散射(SBS)作用机理及外差检测的建模分析，完成了光纤矢量SBS耦合波方程的解析及相移谱与应变的敏感机理研究，搭建了外差矢量单端BOTDA动态应变传感系统；为了实现空间分辨率和测量精度的同时提高，将脉冲预泵浦概念引入单端矢量BOTDA动态应变测量系统；为了提高系统的应变灵敏度、减小光源频率漂移的影响，将双边带结构和自外差检测引入测量系统。为了解决系统性能指标相互制约的问题，对脉冲编码单端BOTDA系统进行了理论和实验研究；提出了波长扫描单端BOTDA系统，实现了相干瑞利噪声的降低；研究了基于高阶相位调制技术和平衡探测技术的传感系统，实现了信噪比的提升。搭建基于BOTDA的海缆振动信号监测模拟实验系统，提出TSA-VMD-MPE对振动信号降噪；利用单模光纤中的双折射效应，建立了光纤振动监测模型，并进行仿真和实验验证。为了准确实时地提取布里渊散射谱，提出采用极限学习机、优化的神经网络、优化的互相关、相似匹配及非线性最小二乘拟合的线性转化等方法，并对布里渊增益谱特征参数提取准确性的影响因素进行研究；提出一种三芯光纤三维形态重构算法。提出采用宽带光源、相移键控脉冲编码、基于多频探测光和频移平均技术以提高BOTDR系统性能。此外，设计了弯曲容忍的分布式光纤传感器以克服弯曲造成的传感性能降低。由于SBS阈值是限制单端BOTDA系统入纤功率和信噪比的主要因素，完成了单端BOTDA系统的阈值特性的研究；为了研究光纤色散对系统性能的影响，探索了相干光时域反射(COTDR)系统中干涉衰落噪声的产生机理，通过对基于COTDR的分布式光纤传感的研究，完成了色散对脉冲宽度及系统性能影响的研究。