Highly sensitive temperature sensing probe based on two cascaded Fabry–Perot interferometers and Vernier effect

Abstract

In this paper, a temperature sensing probe is designed using two cascaded Fabry-Perot interferometers (FPIs). FPI1 is made by splicing single-mode optical fiber (SMF)-no-core optical fiber-capillary-SMF in turn, and then drilling a micro-hole on the capillary wall of FPI 1 with femtosecond laser, and injecting dimethyl silicone oil (DSO) into the capillary through the micro-hole with immersion method. FPI 2 is made by splicing SMF-capillary-SMF sequentially. Due to the thermal sensitivity of DSO, the temperature sensitivity of a single FPI 1 reaches −0.3674 nm/°C. When the free spectral ranges of FPI 1 and FPI 2 are close, their cascaded sensor will produce a Vernier effect for improving the sensitivity. The experimental results show that the sensitivity of the sensing probe is as high as 1.8456 nm/°C. In addition, the sensor has a compact structure and can be used flexibly in confined space temperature measurement.