Abstract

A base plasmonic metal-insulator-metal (MIM) waveguide structure consisting of a baffle waveguide and an obround-shaped resonator is designed to produce Fano resonance. The simulation results exhibit that double Fano resonances can be achieved. Based on this structure, an inner obround-shaped resonator is spliced to the former obround-shaped resonator through a slot resonator to form the expanded structure. Then quadruple Fano resonances are produced by the interference between the broadband continuous state arising from the baffle waveguide and the narrowband discrete state arising from the interaction among the inner obround-shaped resonator, the outer obround-shaped resonator, and the slot resonator. The Fano resonance and refractive index sensing characteristics are investigated, and the sensitivity and the figure of merit can reach 1636 nm/RIU and 33562, respectively. Furthermore, the structure filled with blood plasma can be used for detecting plasma concentrations with different refractive indices, and the sensitivity can reach ${2.88}\;{\rm{nm\cdot L/g}}$. The proposed structure with the simple baffle waveguide and obround-shaped resonators may have potential applications in biosensing and nanoscale optical sensing.

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