High-sensitivity plasmonic refractive index sensor based on a split disc–ring resonator

Abstract

A highly sensitive plasmonic refractive index (RI) sensor based on a split disc–ring resonator (SDRR) is presented and numerically analyzed. The sensor comprises a split disc surrounded by a split ring, both fabricated on a SiO₂ substrate. This structure supports coupled plasmonic modes, specifically ‘bright’ and ‘dark-like’ modes, which lead to strong near-field interactions and Fano-type interference. Through extensive numerical simulations using the Finite-Difference Time-Domain (FDTD) method, we investigate the electromagnetic coupling between a radiative split-disc and a field-confining split-ring resonator. The simulations demonstrate that the Au–Au configuration exhibits the best overall sensing performance over a refractive index range of 1.33 to 1.43, achieving a maximum sensitivity (S) of 1300.1 nm/RIU, a maximum figure of merit (FOM) of 9.1292 RIU^⁻1, a maximum quality factor (Q) of 18.15, a minimum full width at half maximum (FWHM) of 142.41 nm, and a minimum theoretical, simulation-based limit-of-detection estimate (LoD) of 0.13285 RIU. Given the high linearity (R² = 0.999717), and well-defined spectral response in this RI range, these findings indicate that the proposed SDRR structure is a promising platform for numerically investigated refractometric applications.