High performance refractive index sensor based on multi-Fano resonances in waveguide coupled cross-shaped resonator

In this paper, a novel plasmonic structure consisting of a metal-insulator-metal (MIM) waveguide which is separated in intermediate region coupled with a cross-shaped cavity (CSC) is proposed. Based on the finite element method (FEM), results are simulated by COMSOL Multiphysics software concluding three different Fano resonances peaks and an independent Lorentz peak. Theoretically, multimode interference coupled mode theory (MICMT) is used to calculated the formation of the peaks. Besides, by changing the parameters of the structure, the influence of different parameters on each resonance peak is studied. Based on the original CSC structure, the system is extended to five types of Fano resonance system by appending a semi annular (SA) structure. The research results show that the sensitivity of expanded structure can be up to 1478 nm/RIU, and the FOM value can be as high as 5×105, demonstrating its excellent nano-sensing performance and can be used as an efficient refractive index (RI) sensor.