光纤包层模受抑全内反射传感机制及液位探头设计

分析和阐释了POF光纤的包层模受抑全内反射(CMFTIR)效应及其传感机制。提出利用光纤宏弯导致模场畸变从而激发光纤包层模式的方法获得显著的CMFTIR效应并利用其实现液位传感。实验表明CMFTIR效应相对微弱,极易淹没于强背景噪声中,为此通过噪声分析提出利用宏弯耦合获得暗场信号以进一步提升信噪比。设计了双绞宏弯耦合型液位探头及其封装结构。实验结果表明,暗场耦合信号具有明显的信噪比优势,实现传感器液位区分度大于3.7 dB。相较于同类液位探头,该传感器鲁棒性好,制作更加简单且成本更为低廉。

Sensing Mechanism of Fiber Cladding Mode Frustrated Total Internal Reflection and Design of The Liquid Level Probe

The cladding mode frustrated total internal reflection (CMFTIR) effect and its sensing mechanism were analyzed and demonstrated. The method of acquiring remarkable CMFTIR effect was proposed. This method uses the distortion of fiber mode field caused by macro-bending to excite cladding mode. By using this method, the CMFTIR effect could be enhanced remarkably and be used for liquid level detection. The experiment shows that CMFTIR effect is relatively weak and easy to be submerged by strong background noises. In order to solve this problem, the method of improving signal-to-noise ratio was proposed by using macro-bend coupling and dark-field signal. Then, the twisted macro-bend coupling liquid level probe and its encapsulation structure were designed. The experiment results show that dark-field signal has obvious advantage on signal-to-noise ratio, and the sensor realizes extinction ratio above 3.7 dB. Compared with the same kind of probes, the sensor is robust, low-cost and easy to manufacture.