分布式光纤振动传感器的研究

【作者】 范登华；

【导师】 刘永智；

【作者基本信息】 电子科技大学 ， 光学工程， 2009， 硕士

【摘要】 分布式光纤传感技术是应用光纤纵向特性进行测量的技术,它把被测参量作为光纤长度的函数,可以在整个光纤长度上对沿光纤几何路径分布的外部物理参量进行连续的测量,为工业和研究领域提供了同时获得被测物理参量的空间分布状态和随时间变化信息的手段,在智能飞行器、智能桥梁、高速公路、重要建筑、煤气管道监测以及光缆监测等领域获得了广泛的应用。本文主要研究了分布式光纤振动传感器,具体对基于Sagnac结构的分布式光纤振动传感器和基于Michelson结构的光时域反射仪两种结构进行了深入的分析和试验研究。文中详细分析了基于Sagnac结构的分布式光纤振动传感系统的基本原理,与传统的Sagnac干涉环不同,系统用3×3耦合器分光和引入相位偏置,用1×2光纤耦合器将光返回,采用直线型光纤传感,采用波长为1316.7nm的LD脉冲光源,既解决了连续光源的低功率入射问题,又回避了受激布里渊散射阈值的限制。通过探测干涉光强的交流分量的零点频率,就能定位出振动发生的位置。在此系统结构下,本文进一步分析了系统的探测灵敏度、最大可探测距离。用PZT相位调制器模拟振动源进行实验,结果表明:此系统的实验结果与理论分析完全相符,在振动源为5.245km时,系统的相对误差为2.6%,理论上最大监测距离大于100km。利用传输光纤中存在的后向瑞利散射光携带有光纤位置、外界振动等信息的特点,采用光纤迈克尔逊结构构成干涉型光时域反射仪,有望分布式传感沿光纤的微小振动信号。文中设计了一种新型结构的分布式光纤振动传感器,该传感器用3dB耦合器将1310nm激光分为两路相干光:参考光纤和传感光纤,它们中的后向瑞利散射光在耦合器处发生干涉,干涉信号的变化点对应着振动点所在位置。将没有振动信号、加微小振动信号和加损耗干扰三种情况分别作用于传感光纤进行试验对比,结果表明:在微小振动的情况下,光强变化微弱;加损耗时光强变化显著,初步试验定位准确度在92%以上,通过进一步软件校正还可大大提高此准确度。更多还原

【Abstract】 Distributed optical fiber sensor technology is based on the lengthways characteristic of the fiber. It puts the measured parameters as a function of fiber length, and can maintain the external physical parameters throughout the fiber path continuously. It offers a way to measure the physical parameters of the spatial distribution and time-varying state at the same time for industry and research fields, and it has been widely used in intelligent vehicles, smart bridges, highways, major buildings, gas pipeline monitoring and fiber optic cable monitoring.The distributed optical fiber vibration sensors are studied in this dissertation. Two specific structures, which are based on Sagnac structure and Michelson structure OTDR respectively, are analyzed and studied in detail.The basic principle of a distributed optical fiber vibration sensor based on Sagnac structure is studied in this dissertation. Different from traditional Sagnac ring, this system uses a 3×3 fiber coupler to divide the laser and to bring a phase bias, a 1×2 fiber coupler to return the laser, a straight optical fiber as sensor component and a LD pulse light source. The laser’s wavelength is 1316.7nm. It not only resolves a low-power incidence problem of the continuous light source, but also evades the stimulated Brillouin scattering threshold limit. By detecting the exchange component of the interference light intensity, finding out the zero frequency, the vibration spot can be located. The detection sensitivity and the maximum detection range of this system structure are also further analyzed. The experiment by using a PZT phase modulator to simulate the vibration demonstrates: the experimentation result accords with the theoretical analysis; when the vibration is 5.245km far away from the 1×2 fiber coupler, the relative error of location is 2.6% and the largest monitoring distance is more than 100km in theory.Since the Rayleigh backscattering in optical fiber contains some information, just as the location of dispersion and vibration, an OTDR with fiber Michelson structure is designed, in order that the tiny vibration along the sensor fiber could be monitored. A simple novel distributed vibration sensor system is proposed is this dissertation. In this system, the 1310nm laser source is divided by a 3dB coupler into two coherent light beams: the sensing light beam and the reference light beam. When the Rayleigh Backscattering in the two optical fibers transmits back to the coupler, it would interfere. The place where the interference light changes is the place where vibration occurs. Under the three conditions of no vibration, tiny vibration and a light-loss on fiber, we experiment respectively and observe the difference. Conclusion: Under the condition of tiny vibration, the light is changed faintly, but the light is changed obviously and the location is precise with a light loss.更多还原