Highly Sensitive Humidity Sensor Based on Optical Fiber Fabry-Perot Interferometer

An ultra-sensitive optical fiber humidity sensor based on an extrinsic Fabry-Perot interferometer is proposed and experimentally demonstrated in this paper. The Fabry-Perot cavity is constructed by a section of humidity-sensitive metal-paper coil and an optical fiber endface. Taking advantage of the hydrophilicity of the metal-paper coil, the cavity length of the Fabry-Perot cavity varies with humidity due to the deflection of the metal-paper section. The fabricated sensor shows a linear response to relative humidity (RH) spanning from 50%RH to 73%RH. More prominently, an ultra-high sensitivity of 32.5 mu m/%RH (change in cavity length/change in RH) or 63.5 nm/%RH (wavelength shift/change in RH) was achieved over other optical fiber humidity sensors previously reported, to our knowledge.