Independently Tunable Triple Fano Resonances in Plasmonic Waveguide Structure and Its Applications for Sensing

A surface plasmon polaritons (SPPs) waveguide structure composed of a metal-insulator-metal (MIM) waveguide with a baffle, a special square cavity (SSC) and a ring cavity (RC), is proposed to realize independent tuning of triple Fano resonances. Using the finite element method (FEM), the magnetic field distributions and optical transmission spectra of the structure are analyzed in detail. The simulation results show that the structure achieves triple Fano resonances originated from two different mechanics. One of Fano resonances occurs in the RC, and the others occur in SSC. By regulating the structural parameters of the SSC and RC, respectively, these Fano resonances can be well tuned independently, which provides flexibility for the structure to be applied to optical devices. In addition, the structure exhibits great performances in refractive index sensing and bio-sensing. The maximum sensitivity of refractive index sensing achieves 2350 nm/RIU, and there is a good linear relationship between resonance wavelength and refractive index. Due to great sensitivity and independent tunability, the SPPs waveguide structure may be potentially used in micro-nano optical devices, especially in optical on-chip sensor.