基于单模异芯光纤结构的液位传感器

Liquid Level Sensor Based on a Single-Mode Hetero-Core Fiber Structure

提出了一种新颖的光纤液位传感器。在普通单模光纤（SMF）中间熔接一段细芯单模光纤（TCSMF），构成共轴光纤马赫一曾德尔干涉仪（MZI）。液位的变化引起包层模与芯模的相位差发生改变，从而导致干涉仪的透射光谱发生改变。对传感器的工作原理和测量灵敏度及精度进行了理论分析，实验结果显示透射光谱中特征峰波长漂移量跟液位变化量呈较好的线性关系，且灵敏度随待测液体折射率的增大而增高，与理论分析结果相一致。测量得到纯水和饱和氯化钠溶液的测量灵敏度分别为0．160nm／mm和0．228nm／mm。该传感器采用全光纤结构，制备简单、测量精度高，可适用于折射率低于光纤包层折射率液体的高精度液位测量。

A novel liquid level sensor is proposed. A segment of thin-core single-mode fiber （TCSMF） is inserted in a single-mode fiber （SMF） by splicing to form an in-line Mach-Zehnder interferometer （MZI）. The phase difference between cladding modes and core mode is changed with the change of liquid level, and then the transmission spectrum of MZI is changed. The principle and sensitivity of the sensor are analyzed theoretically, and experimental results show that the shift of the peak wavelength is almost linearly proportional to the change of liquid level and the sensitivity increases with the refractive index （RI） of tested liquid, which is content with the analyzed results. The sensitivities of 0. 160 nm/mm and 0. 228 nm/mm are obtained in pure water and saturated salt water, respectively. The sensor is characterized by full optical fiber structure, easy fabrication and high sensitivity, and it is promising in measuring accurately the level of liquid with refractive index less than that of cladding.