Fano Resonance in the Plasmonic Structure of MIM Waveguide with r-Shaped Resonator for Refractive Index Sensor

A plasmonic structure of metal-insulator-metal (MIM) waveguide consisting of a baffle waveguide and an r-shaped resonator is designed to produce Fano resonances. The finite element method is used to analyze the transmission characteristics and magnetic field distributions of the plasmonic structure. The simulation results show that two Fano resonances can be achieved by the interference between a continuum state in the baffle waveguide and a discrete state in the r-shaped resonator. The Fano resonances can be tuned by changing the geometrical parameters of the plasmonic structure. The refractive index sensing is investigated and it is found that the sensitivity is strongly dependent on the geometrical parameters. The maximum sensitivity is 1333 nm/RIU, with the figure of merit of 5876. The results of the designed plasmonic structure offer high sensitivity and nano-scale integration, which are beneficial to nano-scale refractive index sensors, biosensors, and photonic devices.