High-sensitivity optical fiber relative humidity probe with temperature calibration ability

A high-sensitivity optical fiber relative humidity (RH) sensing probe with the ability of temperature calibration is proposed and experimentally demonstrated. It consists of a simple Fabry–Perot interferometer constructed by coating a layer of thin polyimide (PI) film on the end face of single-mode fiber and an upstream fiber Bragg grating (FBG). PI is one of the organic polymer humidity-sensitive materials with good comprehensive properties. The cascaded FBG is used for temperature calibration and elimination of the temperature cross-sensitivity in the process of measuring RH. Experimental results show that this sensing probe can realize simultaneous measurement of temperature and RH. The RH response sensitivity reaches up to 986.25 pm/%RH. This sensing probe with the advantages of simple structure, compact size, high sensitivity, easy packaging, and dual-parameter measurement has an extensive application prospect.