Lossy mode resonance refractometer operating in the 1.55 µm waveband based on TiOxNy thin films deposited onto no-core multimode fiber by DC magnetron sputtering

Abstract

We propose and demonstrate the use of titanium oxynitrides (TiOxNy) as flexible material for lossy-mode resonance (LMR) fiber sensing applications. The LMR characteristics of TiOxNy are investigated for a fiber refractometer consisting of a multimode fiber structure, which includes a no-core fiber coated with a thin film of TiOxNy, because of transitional phases between TiN and TiO2. The material coating was achieved through the N-O exchange during the film synthesis by reactive-magnetron DC sputtering. For a suitable sputtered coating with thickness of ∼270 nm, the 2nd LMR order is generated within the 1.55 µm wavelength region, compatible with fiber optic systems. The spectral response for the 2nd and the 3rd LMR orders of the candidate fiber structure was characterized for liquid refractive index (RI) variations from a set of isopropyl alcohol (IPA)/glycerin solutions. For glycerin concentrations ranged from 0% to 35% (RI from 1.3602 to 1.4091), it was found that the 2nd LMR order is significantly more sensitive than the 3rd LMR order, whose sensitivities are of 1238.445 nm/RIU and 111.39 nm/RIU, respectively.