Reflective Intensity-Demodulated Refractometer Based on S Fiber Taper

Abstract

A compact optical fiber refractive index (RI) sensor based on a tiny S fiber taper (SFT) cascaded with a fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The SFT can excite and recouple the cladding modes, and hence, it produces modal interference, which is sensitive to surrounding refractive index. Due to the reflection of FBG, RI measurement can be realized by monitoring the peak power change of the reflective FBG spectrum. The experimental result shows that the RI sensitivity of the sensor can be achieved as high as 366.69 dB/RIU ranging from 1.3330 to 1.3988. Moreover, this sensor possesses the temperature-insensitive characteristic. The corresponding RI measurement error is about $3.136\times 10^{-5}$ RIU/°C in the temperature range of 30 °C–70 °C.