title: Intensity-modulated relative humidity sensing with polyvinyl alcohol coating and optical fiber gratings.
abstract: A relative humidity (RH) sensor in reflection mode is proposed and experimentally demonstrated by using a polyvinyl alcohol (PVA)-coated tilted-fiber Bragg grating (TFBG) cascaded by a reflection-band-matched chirped-fiber Bragg grating (CFBG). The sensing principle is based on the RH-dependent refractive index of the PVA coating, which modulates the transmission function of the TFBG. The CFBG is properly designed to reflect a broadband of light spectrally suited at the cladding mode resonance region of the TFBG, thus the reflected optical signal passes through and is modulated by the TFBG again. As a result, RH measurements with enhanced sensitivity of ∼1.80  μW/%RH are realized and demodulated in the range from 20% RH to 85% RH.
authors.forename: Jingyi
authors.initials: J
authors.lastname: Yang
authors.forename: Xinyong
authors.initials: X
authors.lastname: Dong
authors.forename: Kai
authors.initials: K
authors.lastname: Ni
authors.forename: Chi Chu
authors.initials: CC
authors.lastname: Chan
authors.forename: Perry Ping
authors.initials: PP
authors.lastname: Shun