Fiber temperature sensor based on Fabry-Pérot cavity generating optical Vernier effect

A fiber temperature sensor consisting of two cascaded reflective film-fiber-reflective film Fabry-Pérot (FP) cavities is proposed. The lengths of the two FP cavities are similar, but with small differences in their free spectral ranges (FSR) to create Vernier effect. The sensor operates similar to a Vernier caliper, where one FP cavity serves as a reference and the other as a sensing element. Experimental results demonstrate that the extinction ratios of cascaded system exceed 15 dB. The temperature sensitivity of the sensor reaches 1.14 nm/°C, offering advantages such as a wide measurement range, high sensitivity, good linearity, simple structure and low cost. Additionally, the fiber FP cavities are uncomplicated and compact, and their use as sensing elements helps avoid temperature inhomogeneity. This makes the sensor reliable, practical, and suitable for a wide range of applications.