基于OTDR的光纤液体泄漏检测的研究

通过应用光时域反射仪（OTDR)测量多模光纤（MMF）反射光强变化，提出一种检测液体泄漏的光纤传感器，并对其进行理论仿真和实验研究。众所周知，OTDR具有小巧、精密、智能化、便于移动的特点，能有效避免常规光纤传感器设备复杂笨重不可以移动的问题。使用一定溶度的氢氟酸（HF）溶液腐蚀多模光纤作为传感部件，易于设计和制作。当多模光纤的纤芯直径减小到一定程度时，将其暴露在空气或待测液体中。裸露的芯层周围介质折射率的变化，将会影响传感区域内光的模场分布，改变透射光的强度，故该结构可以有效检测环境中液体的泄漏。本文设计制作了两个远距离的光纤传感器。第一个传感器仅带有一个光纤传感结构。连接带有传感结构的长光纤和OTDR。设置OTDR的扫描脉宽30ns、扫描时间3min，光源的脉冲信号强度约为15dB、扫描距离5km。以水为检测对象。首先，将传感结构暴露在空气中，OTDR的反射曲线在检测处的损耗为2.893dB。当检测到水时，OTDR的反射曲线的损耗为0.631dB。因此，检测到水时，光损耗减小，反射光强变大。实验结果和仿真结果一致。第二个传感器是有两个传感结构的分布式复用传感器，将其检测两处的环境情况。两个传感结构都能很灵敏的检测出是否存在水，证明了传感器的复用特性。因此，该液体泄漏检测光纤传感器能够广泛应用于工程实践中。

Research on optical fiber liquid leakage detection based on OTDR

By using optical time domain reflection (OTDR) to measure the intensity of the reflected light intensity of multi-mode fiber (MMF), we propose a fiber optic sensor which can detect the leakage of liquid, and carry on the theoretical simulation and experimental study. As we all know, OTDR has the characteristics of small size, precision, intelligent, easy to move, and can effectively avoid the problem that the conventional, complicated and heavy optical fiber sensor devices cannot move. Use a certain concentration of hydrofluoric acid (HF) solution to etch multimode fiber as sensor components, which is easy to design and manufacture. When the core diameter of multimode fiber decreases to a certain degree, we expose it in the air or liquid under test. The change of the refractive index of the surrounding medium will affect the mode field distribution of the optical field and the intensity of the transmitted light. Therefore, the structure can effectively detect the leakage of external environment liquid. We design and make two sensors in this paper. The first sensor is only with a sensing structure. Connect OTDR and the long fiber with the sensing structure. Set the scanning pulse width of 30ns, the scan time of 3min, the strength of the light pulse signal about 15dB, the scan distance of 5km on the OTDR. Take water as test object. First, the sensing structure is exposed in the air, reflection loss curve of OTDR is 2.893dB, when it detects water，reflection loss curve of OTDR was 0.631dB. Therefore, when it detects water, the loss of OTDR is decreased, and the intensity of the reflected light is large. The experimental results are in agreement with the simulation results. The second sensor with two sensing structures is made into the distributed multiplex sensor for detecting water of different regional environment, the two sensor structures can detect water sensitively, which prove the multiplexing characteristic of the sensor. Therefore, the liquid leakage detection optical fiber sensor can be widely used in engineering practice.