Integrated FPI-FBG composite all-fiber sensor for simultaneous measurement of liquid refractive index and temperature

Abstract

A miniature and all-optical fiber sensor based on integration of Fabry–Perot interferometer (FPI) and fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of refractive index (RI) and temperature in this paper. The integrated FPI-FBG composite fiber sensor is constructed by manufacturing a micro-hole in FBG, where two parallel reflecting surfaces of micro-hole perform as cavity mirrors of FPI. Experimental results show that the temperature and RI sensitivity of spectral dip wavelength for FPI are −0.189 nm/°C and 1210.490 nm/RIU, respectively. The temperature sensitivity for FBG is 0.011 nm/°C, and the FBG is insensitive to RI. Using these different sensitivities, a matrix can be constructed and used in simultaneous measurement of RI and temperature. The resolutions of 0.1 °C and 1.5×10−5 RIU can be obtained. Owing to compact size in dimensions, the sensor can be used to measure RI and temperature simultaneously in tiny liquid environment.