A hybrid self-growing polymer microtip for ultracompact and fast fiber humidity sensing

Abstract A hybrid self-growing polymer microtip is firstly proposed and fabricated as an ultracompact fiber-tip Fabry-Perot interferometer (FPI) with enhanced figure of merit (FoM). The hybrid microtip FPI is based on a sharp polymer microtip grown on an ultraviolet (UV) cured polymer film at the fiber end, which has exhibited significant interferometric visibility with high fringe contrast up to 30 dB in the reflection spectra. Using this tiny FPI, an optical fiber relative humidity (RH) sensor with the enhanced FoM of ∼ 0.95/%RH was demonstrated, which is ∼30 times higher than the previous optical fiber-based humidity sensors, and the achieved sensitivity is high enough to perform real-time human breath observation. Furthermore, the humidity sensor exhibited excellent performance in monitoring human breath with fast response time of ∼ 0.6 s. This new type of photonic microtip RH sensing element has shown advantages of compactness, flexibility, fast-response and high sensitivity, which provides a promising platform for potential applications in environmental and biological RH sensing, especially in a restricted space environment.