Ultra-sensitive refractive index sensing enabled by high-Q hybrid plasmonic metasurface absorbers
Muhammad Ali Butt
Abstract
This work presents a high-performance hybrid plasmonic metasurface absorber (HPMSA) designed for ultra-sensitive refractive index sensing applications. The structure combines silicon nitride dielectric meta -atoms in both square and cross slot configurations with a gold back reflector, enabling strong hybrid resonances and near unity absorption. The square MS design exhibits polarization and angle-insensitive performance, achieving a refractive index sensitivity, Q-factor, and FOM of 1200 nm/RIU, 514, and 324.3, respectively. In comparison, the cross-slot design leverages quasi-bound states in the continuum (quasi-BIC) to generate ultra-narrow resonances with exceptionally high Q-factors, reaching values up to approximately 1600, and enhanced FOMs exceeding 1200. A comprehensive parametric analysis shows that adjusting the slot width in cross-slot MS allows precise tuning of the optical response, significantly enhancing field confinement and increasing sensitivity to a maximum of 1345.71 nm/RIU. These results highlight the importance of geometrical optimization in achieving superior sensing performance. When compared with prior designs, the proposed HPMSAs exhibit clear advantages in sensitivity, spectral resolution, and device compactness. The demonstrated configurations offer a powerful and scalable solution for high-precision applications in biosensing, environmental detection, and integrated photonic systems.