Ultra-short fiber optic temperature sensor based on fiber Bragg grating Fabry-Perot interferometer

Fiber optic temperature sensors for small-scale heat sources have an urgent need in many industrial fields. We first propose and demonstrate an ultra-short fiber optic temperature sensor based on a Fabry-Perot (FP) interferometer which combines a fiber Bragg grating (FBG) with Fresnel reflection on the fiber end face. The FBG with a grating length of 50 mu m was inscribed by a femtosecond laser line-by-line scanning technology. This FBG exhibits a resonant wavelength of 1548.8 nm and a broad full width at half maximum (FWHM) bandwidth of 12.4 nm. The selected dip wavelength of the FBG-FP cavity sensor changes linearly with the temperature increase, corresponding to the temperature sensitivity of 10.8 pm/degrees C. Moreover, the FBG-FP cavity sensor can be used to measure the temperature of the small-scale laser spot due to its compact structure. The experimental results show the temperature at different positions of laser exposure area are 138.4 degrees C, 111.5 degrees C and 74.4 degrees C, respectively.