Half-Covered Agarose Fiber Bragg Grating for Simultaneous Measurement of Humidity and Temperature

In the paper, a temperature and relative humidity (RH) sensor based on a half-covered agarose fiber Bragg grating (HC-AFBG) is proposed and experimentally validated. A single fiber Bragg grating (FBG) is utilized as the sensing core for the sensor, with half the length of the FBG coated with humidity-sensitive agarose (AG) material. Utilizing the ability of AG to stretch or shrink with changes in humidity, the grating period of the FBG can be altered, which in turn creates new reflection peaks in the reflection spectrum. We experimented and verified the behavior of the two reflection peaks of HC-AFBG at different humidity and temperature and solved the cross-sensitivity problem. The experimental results show that the humidity sensitivity is 73.0 pm/%RH in the range of 35 %RH 65 %RH. And the temperature sensitivities of the two peaks are 13.3 pm/°C and 9.6 pm/°C in the range of 25 60 °C. Using the obtained temperature and humidity sensitivity to construct a sensitivity measurement matrix, humidity and temperature can be monitored simultaneously. This study presents a HC-AFBG sensor capable of high-sensitivity, simultaneous temperature and humidity sensing, offering a promising tool for various environmental monitoring applications.