Dielectric multilayer-based fiber optic sensor enabling simultaneous measurement of humidity and temperature

A multilayer-based fiber optic sensor enabling simultaneous measurement of humidity and temperature is proposed and demonstrated. The sensitive elements were multilayer coatings consisting of nano-porous TiO(2) and SiO(2) films, which were deposited on fiber end-face to form a Fabry-Perot (F-P) filter structure. Relative-humidity (RH) sensing is correlated with the shift of interference fringe due to the change of effective refractive index of porous coatings when exposed to different RH environments. The sensor is sealed in a glass tube in case of temperature measurement. Experimental results show that the average sensitivity are 0.43nm/%RH and 0.63nm/°C respectively when environmental RH changes from 1.8%RH to 74.7%RH and temperature changes from 21.4°C to 38.8°C. The proposed sensors present high repeatability, and especially highly sensitive to lower moisture measure.