Relative Humidity Sensor Based on SMS Fiber Structure With Two Waist-Enlarged Tapers

An all-fiber relative humidity (RH) sensor based on single-mode-multimode-single-mode fiber structure with two waist-enlarged tapers is proposed and experimentally demonstrated. It is fabricated by waist-enlarged splicing a section of multimode fiber (MMF) between two single-mode fibers. A thin layer of polyvinyl alcohol is dip-coated onto the MMF and two bitapers. The proposed sensor resonance wavelength peak shifts to longer wavelengths with the RH increasing. The sensitivity of the RH measurement of 0.223 nm/% RH in the range from 35% to 85% RH is experimentally achieved.