title: High-performance humidity sensor based on a polyvinyl alcohol-coated photonic crystal cavity.
abstract: We demonstrate a high-performance relative humidity (RH) sensor by coating a photonic crystal (PC) cavity with polyvinyl alcohol (PVA). Because a PC cavity's evanescent field strongly interacts with the coated moisture-sensitive PVA film, the resonant wavelength is modified remarkably under varying RH levels ranging from 30% to 90%. In a PC cavity coated with a 720 nm thick PVA, the sensor exhibits a linear spectrum sensitivity exceeding 129 pm/%RH over 40-90%RH, and the power interrogation presents a high sensitivity as 0.77 dB/%RH. The resolvable humidity variation could be much less than 0.1%RH. Relying on the sub-micron thick PVA, the sensor promises a response time less than 300 ms and good repeatability. The dependence of the sensor performances on the PVA thickness is studied as well, indicating a tradeoff between the sensing dynamic range and the response time.
authors.forename: Chenyang
authors.initials: C
authors.lastname: Zhao
authors.forename: Qingchen
authors.initials: Q
authors.lastname: Yuan
authors.forename: Liang
authors.initials: L
authors.lastname: Fang
authors.forename: Xuetao
authors.initials: X
authors.lastname: Gan
authors.forename: Jianlin
authors.initials: J
authors.lastname: Zhao