Enhanced Coupling and High-Sensitivity Multichannel Plasmonic Sensor Using Split Semicircular Ring Resonators for Refractive Index and Temperature Detection

We present a highly sensitive, multimode metal–insulator-metal (MIM) plasmonic sensor with ten resonance modes for refractive index (RI) and temperature sensing across the visible to near-infrared spectrum. The sensor consists of a resonator with paired semi-circular rings, a split gap, and a crossing air path coupled to two independent MIM waveguides (WGs). Using finite element method (FEM) simulations, we analyze the optical responses—including transmittance spectra and H- and E-field distributions—to optimize performance. The sensor generates ten distinct Fano resonance modes and operates as a high-precision plasmonic RI sensor, detecting RI variations as small as 0.01. It achieves a maximum RI sensitivity of 4500 nm/RIU and a temperature sensitivity of - 1.25 nm/°C, demonstrating exceptional performance. This work introduces a novel multimode Fano resonance-based sensor with a unique paired semicircular ring design, enabling ten resonance modes for simultaneous RI and temperature detection. The innovative structure holds great potential for high-sensitivity sensing systems and advanced nanophotonic applications.