Characterization of an ORMOCER®-coated FBG sensor for relative humidity sensing

In this paper, an ORMOCER® (OR)-coated fiber Bragg grating (FBG) sensor encapsulated with stainless steel was proposed for relative humidity (RH) sensing. Various sensing characteristics of the sensor, including RH and temperature sensitivity, hysteresis, repeatability, stability, and water resistance, were investigated systematically and compared with a polyimide (PI)-coated FBG humidity sensor. The results show that the OR-coated FBG humidity sensor can measure simultaneously the humidity and temperature, with sensitivity coefficients of 2.4 pm/%RH and 12.9 pm/°C, respectively. The OR-coated sensor has obvious advantages over the PI-coated sensor in terms of sensitivity, response speed, accuracy, and mechanical strength. Furthermore, two practical encapsulation methods were proposed for the sensor for applications in complex and harsh environments. Combined, the developed OR-coated FBG sensor provides an innovative means for RH monitoring.