Optical fiber relative-humidity sensor with evaporated dielectric coatings on fiber end-face

Abstract An optical fiber relative-humidity sensor (OFRHS) with evaporated dielectric coatings is proposed and demonstrated. The sensitive coatings, composed of multilayers of Ti 3 O 5 and SiO 2 , form an extrinsic Fabry–Perot cavity on the distal end of the multimode fiber. As the effective refractive index of the porous coatings were correlated with the change of ambient Relative-humidity (RH), which will at last result in the shift of interference fringe. By monitoring the drift of reflected interference fringe under different RH levels, the information about RH of the environment under test can be extracted. Experimental results show that the average sensitivity is 0.43 nm/% RH when environmental RH changes from 1.8% RH to 74.7% RH. The proposed sensor was proved to be high repeatability, little hysteresis and especially highly sensitive to lower moisture measure.