Lossy mode resonance-based optical fiber humidity sensor

In this work it is presented for the first time the fabrication of optical fiber relative humidity (RH) sensors by means of polymeric thin-films as lossy mode resonance (LMR) supporting coatings. In particular, LMRs have been observed thanks to the fabrication of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) polymeric coatings onto cladding-removed multimode optical fibers (CRMMF) employing the Layer-by-Layer (LbL) self assembly method. More than one LMR can be generated as a function of the coating thickness. This generation of multiple LMRs produces a band pass filter with a transmission band in the visible region. PAH/PAA film thickness and refractive index can be modified as a function of the surrounding medium relative humidity (SMRH). Thus, SMRH can be easily determined by measuring the wavelength shift of the transmission band (~15nm between 20% and 60% RH).