MIM waveguide structure consisting of a baffle and a ring cavity embedded in a square metal layer

This paper presents a design for a tunable plasmon refractive index nanosensor based on Fano resonance. The proposed structure comprises a metal-insulator-metal waveguide featuring a silver baffle and a ring cavity embedded in a square (RCSQ). This innovative structural configuration effectively excites dual Fano resonances by leveraging the unique properties of its constituent elements and geometry. The transmission spectrum and electric field at the resonance were simulated using the finite element method (FEM) in two-dimensional space, providing an in-depth explanation of the formation mechanism of the Fano resonance, as well as analyzing how various structural parameters influence sensor characteristics. Simulation results indicate that the Fano peak can be readily tuned by adjusting cavity parameters and refractive indices. Common tuning of the Fano resonance is achievable through modifications to the proportionality constant of the RCSQ. Finally, we optimize and analyze the sensor characteristics of this structure, achieving sensitivity levels up to 2750 nm/RIU with a figure of merit (FOM) of 3.48×10⁴. Consequently, this structure holds significant potential for applications in optical nanosensors.