Refractive Index Sensor Based on the Symmetric MIM Waveguide Structure

Abstract

A surface plasmon polariton refractive index sensor which is composed of a metal–insulator–metal (MIM) waveguide, coupled with two stubs and one ring resonator, is proposed. The transmission characteristics of this plasmonic structure are numerically studied based on the finite element method. The simulation results display that a typical Fano profile is exhibited in the transmission spectra, and that the Fano resonance results from the coupling between broadband spectrum resonance (bright mode) in two stubs and the narrowband spectrum resonance (dark mode) in the ring resonator. Furthermore, the effect of various geometric parameters of this proposed structure and the refractive index sensitivity of the system based on Fano resonance is investigated. The investigations demonstrate that the spectral positions of the Fano resonances are highly sensitive to the radius of the ring resonator and the refractive index of the filling medium. The maximum sensitivity and the figure-of-merit of this structurer are 1268 nm/RIU and 280, respectively. These results provide a reference for achieving high-sensitivity sensors in MIM waveguide coupled systems based on the Fano resonance effect.