基于少模-无芯-少模光纤结构的高灵敏度折射率传感器

光纤折射率传感器广泛应用于各种复杂环境的监测。设计了一种基于少模光纤（fewmode fiber,FMF）–无芯光纤（coreless fiber,CLF）–FMF结构的高灵敏度折射率传感器。该传感器由2小段FMF之间熔接1段减薄的CLF组成马赫-增德尔干涉仪（Mach–Zehnder interference,MZI），测量外界折射率，利用光纤布拉格光栅（fiber Bragg grating,FBG）进行温度补偿。MZI干涉光谱中的谐振波谷同时受折射率和温度影响，FBG只受温度的影响。利用MZI和FBG的折射率和温度灵敏度系数构建灵敏度矩阵，实现折射率和温度的同步测量。实验结果表明，MZI折射率灵敏度为345.66 nm/RIU，温度灵敏度为0.013 4 nm/℃；FBG的温度灵敏度为0.010 4 nm/℃。

High-sensitivity refractive index sensor based on FMF-CLF-FMF optical fiber structure

Optical fiber refractive index sensor is widely used for monitoring in various complex environments. A high-sensitivity refractive index sensor based on the structure of few-mode fiber (FMF)-coreless fiber (CLF)-FMF was designed, and the experimental verification was carried out. The sensor consisted of a thinned section of CLF fused between two small sections of FMF to form a Mach-Zehnder interferometer (MZI) for measuring external refractive index, and the fiber Bragg grating (FBG) was used for temperature compensation. The resonance trough of interference spectrum generated by MZI structure was affected by both refractive index and temperature, while FBG was only affected by temperature. The sensitivity matrix was constructed by using the refractive index and temperature sensitivity coefficients of MZI and FBG to realize the simultaneous measurement of refractive index and temperature. Experimental results show that the refractive index sensitivity of MZI is 345.66 nm/RIU, and the temperature sensitivity is 0.0134 nm/℃. Meanwhile, the temperature sensitivity of FBG is 0.0104 nm/℃.