Optical fiber relative-humidity sensor using Fabry–Perot cavity formed by e-beam evaporated dielectric films

A fiber optic relative-humidity sensor with a low-fineness Fabry-Perot cavity is proposed and demonstrated. Manufactured by e-beam evaporation, the Fabry–Perot cavity composed of five-layer dielectric oxides has columnar and porous structures, which is sensitive to relative-humidity change of environment. Experimental investigation shows that the proposed sensor exhibits a sensitivity of 0.42 nm/%RH when the ambient relative humidity changes from 15.2%RH to 74.3%RH.