High-Sensitivity Compact Fiber-Optic Temperature Sensor Based on Online Tunable High-Order Harmonic Vernier Effect

This work proposes a compact Fabry-Perot interferometer (FPI)-type fiber-optic temperature sensor based on the high-order harmonic Vernier effect. The sensor is constructed by forming a polydimethylsiloxane film on the end face of a single-mode fiber (SMF) to build up the FPI. Another SMF end face on the opposite side is used as a third reflective interface. The air cavity length can be precisely adjusted with the help of a displacement stage to produce on-line tunable orders of harmonic Vernier. This design not only features a compact structure and adjustable properties but also significantly enhances the sensor's sensitivity by utilizing the high-order harmonic Vernier effect. The experimental results show that within the temperature range of 31 - 34 °C, the sensitivity of the Vernier inner envelope is as high as 27.38 nm/°C. The uncertainty of the temperature sensitivity is 1.65 nm/°C.