Triple Fano resonances induced by a square-elliptical cavity coupled with an MIM waveguide for high-sensitivity gas refractive index sensing

The proposed structure of a baffled metal–insulator–metal (MIM) waveguide coupled with a square cavity and a silver elliptical cylinder is designed to excite triple Fano resonances. The transmittance spectrum and electric field distribution at the resonance peaks produced by the structure are simulated using the finite difference time domain (FDTD) method. The simulation results of the transmittance spectrum are fitted by the multimode interference coupled-mode theory (MICMT). By analyzing the variations in the transmittance spectrum, the formation mechanism of the Fano resonances is investigated. The structure generates triple Fano resonances within the near-infrared spectrum, and its potential for gas refractive index sensing is investigated. The sensor demonstrated a sensitivity of up to 1942 nm/RIU and a figure of merit (FOM) of 1.10×10 5 . These promising results suggest that the structure holds significant potential for applications in biochemical sensing.