Fano resonance sensing characteristics of MIM waveguide coupled Square Convex Ring Resonator with metallic baffle

A metal-insulator-metal (MIM) waveguide coupled a Square Convex Ring Resonator (SCRR) with single metallic baffle structure is proposed based on the transmission characteristics of the surface plasmonic polaritons in sub-wavelength structures. Fano resonance is an asymmetric spectral line formed by the destructive interference between the narrower discrete state formed by the SCRR and the wider continuous state formed by the baffle. Compared with the no-defect square ring, the convex part changes the original transmission path in the cavity, thus which shows the novel Fano resonance sensing characteristic. The coupled mode theory (CMT) is adopted to analyze the transmission characteristics. Using finite element method (FEM) to simulate the waveguide structure and to analyze the relationship between structural parameters and refractive index sensing characteristics. The proposed sensor yields sensitivity higher than 1120 nm/RIU and a Figure Of Merit (FOM) of 2.68 x 10(5) by optimizing the geometry parameters. The structure can provide theoretical basis for the integration of photonic devices and the design of refractive index sensors.