Metal–insulator–metal waveguide structure coupled with T-type and ring resonators for independent and tunable multiple Fano resonance and refractive index sensing

Abstract

This study proposes a metal–insulator–metal (MIM) waveguide structure coupled with symmetric T-type resonators for exciting double Fano resonances. Furthermore, the proposed structure can generate an additional independent Fano resonance mode when one of the T-type resonators is replaced with a ring resonator. We employed the finite difference time domain method to simulate the transmission spectrum of the structure and the electric field distribution at resonant wavelengths. The formation mechanism of the Fano resonance is explained using the standing wave theory and multimode interference coupled mode theory. After studying the sensing characteristics of the designed structure, we achieved a maximum sensitivity of 1012 nm/RIU and a figure of merit of 5.57 × 104, which is higher than that of most of the structures reported recently. The proposed structure has broad application prospects in the field of nano sensing.