Fabry–Pérot Cavity Based on a High-Birefringent Fiber Bragg Grating for Refractive Index and Temperature Measurement

A fiber-optic sensor for simultaneous measurement of refractive index and temperature is described. The refractive index measurement is based on the visibility variations of a Fabry-Pérot interferometer. It is formed with the interfering waves generated from a low reflectivity Bragg grating inscribed on a Panda fiber and from the fiber end tip (Fresnel reflection) in contact with the liquid. The sensor is characterized by immersing the fiber tip in distilled water with different concentrations of ethylene glycol. A linear relation of the interferometer fringe visibility with refractive index variation is observed. The temperature is determined by the wavelength shift of the FBG peaks. Results show the feasibility of simultaneous measurement of refractive index and temperature and also the possibility of adjusting fringe visibility via polarization control.