Highly Sensitive D-Shaped Optical Fiber Surface Plasmon Resonance Refractive Index Sensor Based on Ag-α-Fe 2 O 3 Grating

Abstract

This work proposed the simulation of a highly sensitive surface plasmon resonance (SPR) optical fibre sensor equipped with a hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ) layer coated with silver gratings on the surface of a D-shaped optical fibre. $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterial film was utilised as the sensing layer. Free electrons on the metal surface were stimulated via evanescent waves on the fibre surface to generate surface plasmon waves. The resonance absorption peaks were monitored to determine the changes in refractive index (RI). The SPR fibre sensor was optimised using the finite element method to analyse the structural parameters of the D-shaped optical fibre and silver gratings. This method was also applied to examine the effect of the thickness of the hematite sensing layer on sensor sensitivity (S). The hematite-coated silver gratings significantly enhanced the sensor as revealed by the simulation outcomes. In this work, the maximum response S of the sensor can reach $6.4~\mu \text{m}$ /RIU when the external RI was changed from 1.33 to 1.39 with 45 nm thick silver grating, 50 nm width air gaps and 12 nm thick hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ). The results suggest the high potential of $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterials in optical fibre-sensing applications.