Relative humidity sensor based on no-core multimode interferometer coated with Al2O3-PVA composite films

Abstract

Abstract Herein, a simple relative humidity (RH) fiber sensor based on a multimode interferometer (MMI) with aluminum oxide nanoparticles (Al2O3 NPs) and polyvinyl alcohol (Al2O3-PVA) composite was fabricated and experimentally demonstrated. The sensor was fabricated by splicing a no-core fiber (NCF) segment between two single-mode fibers (SMF). The chemical etching method has been used with hydrofluoric (HF) acid to prepare diverse NCF diameters. This was proposed to expand the evanescent fields and enhance sensor sensitivity. A hydrophilic sensitive film based on Al2O3-PVA was coated on the surface of NC fiber using the cast-drop and evaporation technique. By altering the ambient humidity, water adsorption into the Al2O3 nanostructures occurs and therefore, the refractive index (RI) of the coated film varies inducing a 38.9 nm wavelength shift in the output spectra. The results showed that a maximum sensitivity of 0.587 nm/%RH has been achieved as the percentage of the RH increases from 30% to 100%. The simple fabrication and the high sensitivity of this sensor may prompt many potential applications in the fields of biology and chemistry.