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

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.