Optical fiber humidity sensor based on lossy mode resonances supported by TiO2/PSS coatings

In this work it is presented the fabrication of titanium dioxide (TiO ₂) and poly(sodium 4-styrenesulfonate) (PSS) resonance supporting coatings onto optical fibers and their utilization as transducers for relative humidity (RH) sensing. The fabrication of the TiO ₂/PSS coatings has been performed by means of the layer-by-layer (LbL) electrostatic self-assembly technique using the core of optical fibers as the substrate, which permits to generate several resonances in the visible and infrared spectral region. These resonances vary as a function of the refractive index of the medium in contact with the TiO ₂/PSS layer. Moreover, the water vapor content of the surrounding medium produces a shift of the resonances that enables the monitorization of the RH. This characteristic permits to obtain an optical fiber sensing device based on wavelength detection with fast response times and good repeatability as well as the possibility to perform self-referenced measurements by means of monitoring two resonances.