Cross-Ag disk-covered GaAs microstructure for refractive index sensing by the surface plasmon resonance

This paper presents a hybrid two-dimensional (2D) microstructure, consisting of an Ag layer and a GaAs dielectric sandwich, which enhances sensing capabilities by exciting surface plasmon resonance in the metal layer, distinguishing it from conventional guided mode resonance structures. The absorption peak reaches a maximum of 99.8% with a full width at half maximum of 0.18 THz. We analyze the electric field distribution at the absorption peak and discuss the resonance mechanism based on coupled-mode theory and impedance matching. Additionally, the shifts in absorption peaks are investigated as the refractive index of the analyte varies from 1.0 to 1.3, showing a sensitivity of 4.8 THz/RIU. The proposed 2D grating structure demonstrates great potential for applications in biomedical diagnostics, food safety, and environmental monitoring.