In-fiber Fabry-Perot temperature sensor using silicone-oil-filled the quartz capillary tube

In this study, a highly sensitive temperature sensor based on a Fabry–Perot interferometer (FPI) filled with the silicone oil was designed and demonstrated. The FPI temperature sensor comprised an in-line sandwiched structure, i.e., single mode fiber – capillary – single mode fiber. A microchannel was processed on the capillary wall with a femtosecond laser. The capillary was filled with the silicone oil through the microchannel using the immersing method. Through theoretical analysis, the sensitivity of FPI temperature sensor is mainly determined by the thermo-optical coefficient of silicone oil. Owing to the high TOC of the silicone oil, the optical path difference (OPD) in the FP cavity varied strongly with temperature, which consequently induced a drastic wavelength shift of the reflection spectrum. Thus, FPI temperature sensor has high sensitivity. The temperature response, repeatability and stability of the sensor are studied experimentally. The results show that the temperature sensitivity of FPI sensor filled with silicon oil reaches −0.4102 nm/°C, which is about 205.1 times compared to that of the FPI sensor unfilled with silicon oil. The proposed sensor has the advantages of simple manufacturing, good robustness and stability. In addition, the total length of the sensor head is small, which is compact size and can be used flexibly in limited space and harsh environment.