Polymer microfiber rings for high-sensitivity optical humidity sensing

We demonstrate microrings assembled with polyacrylamide (PAM) microfibers for high-sensitivity relative humidity (RH) sensing. When exposed to moisture, the PAM microfiber absorbs water molecules and inflates monotonically with the increasing humidity, resulting in evident spectral shifts of the resonance peaks of the microring. By measuring the spectral shifts, the microring shows sensitivity as high as 490 pm/%RH and a response time of about 120 ms, within a dynamic range from 5% to 71% RH.