Phase-shifted Fiber Bragg Grating Based Humidity Sensor

A humidity fiber optic sensor based on phase-shifted (PS) fiber Bragg Gratings (FBG) is demonstrated in this paper. The sensor (PS-FBG) is coated with a moisture sensitive polyimide. When this thin coating is exposed to moisture its swells, hence inducing tensile stress on the PS-FBG and affecting its Bragg wavelength. Due to its intrinsic properties, the PS-FBG sensor presents the same trend of wavelength variation as standard fiber Bragg Grating sensor but with higher measurement resolution, and reliable measurements can be obtained in different humidity and temperature environments. This paper assesses the suitability, including sensitivity and response time, of the phase-shifted FBG sensor approach for humidity sensing. By monitoring this change, it is demonstrated that the humidity level of the environment can be accurately monitored.