Analysis of D-shaped optical fiber based corrosion sensor using LMR and SPR effects

Abstract

This article presents the proposed structure and the simulation results from analytical and numerical modeling of two corrosion sensor elements in D-shaped optical fiber: one based on the lossy mode resonance (LMR) effect and the other based on the effect of surface plasmon resonance (SPR). In the first sensor element, a bilayer of titanium dioxide - aluminum (TiO2-Al) is deposited on the D-shaped region, operating in LMR conditions, while, in the second sensor element, an aluminum(Al) monolayer is deposited under D-shaped region, operating in SPR condition. The sensor elements can operate separately, enabling simultaneous two-parameter measurements at two different points, or they can operate in cascade configuration, increasing the operating range and sensitivity of the sensor set. The D-shaped region of the optical fiber is modeled with an analytical model based on the Fresnel formulation, and also with a numerical model, which uses the finite element method with the COMSOL Multiphysics 5.2 software. The transmission of light through the D-shaped region causes peculiar variations in each light polarization in each sensor element, depending on the metal thickness. Both regions are subject to a corrosive environment. The sensor elements are evaluated separately and in cascade configuration, using polarized and non-polarized light. Finally, the obtained results show two resonance valleys for the same operating wavelength, resulting in a higher operating range with high sensitivity, compared to other corrosion sensor structures found in the literature.