Simultaneous Measurement of Temperature and Humidity based on Phase-Shifted Fiber Bragg Grating and Fabry-Perot

A dual-parameter sensor for temperature and humidity based on phase-shifted fiber grating (PS-FBG) with polymethylmethacrylate (PMMA) microsphere Fabry-Perot (FP) cavity is designed. The sensor consists of PMMA microspheres forming the FP cavity in cascade with PS-FBG. The results show that the FP cavity exhibits a high sensitivity of 83.38 pm/%RH with excellent linearity of 0.9982 in the range of 35% to 85%RH, while the PS-FBG humidity response is zero. The temperature sensitivities of the FP cavity and PS-FBG are -87.26 pm/°C and 12.05 pm/°C, respectively, when the temperature increased from 25 ~ 50°C. The 3dB ultra-narrow bandwidth characteristic (0.022nm) based on the PS-FBG realizes the high-precision temperature measurement, which is conducive to reducing humidity measurement error during the dual-parameter measurement. Moreover, the scheme of utilizing the sensitivity coefficient matrix to realize the simultaneous measurement of temperature and humidity is experimentally verified, and the maximum temperature and humidity errors are, respectively, 0.21°C and 1.98%RH. The sensor combines the features of high sensitivity, high precision temperature compensation, simple structure, and excellent repeatability.