Visible-Range Double Fano Resonance Metal-Insulator-Metal Plasmonic Waveguide for Optical Refractive Index Sensing

A metal-insulator-metal (MIM) structure consisting of a semi-circular resonant cavity (SCRC) and a circular split-ring resonator (SRR) is proposed and designed for optical sensing applications. The coupling between the SCRC and SRR can create dual Fano resonances in the visible range. The optical responses of the structure including transmittance spectra and magnetic field distributions are investigated using finite-difference time-domain (FDTD) method. According to the calculated transmittance spectra, the proposed optical sensor can support double Fano resonances as a result of the interaction between the narrow-band mode of SRR and broadband mode of SCRC. The light-matter interaction at the Fano resonance frequencies is highly enhanced so that a maximum sensitivity and figures of merit (FOM) of 579 nm/RIU and 12.46 are obtained, respectively. Our proposed design also exhibits a great linearity R-2 value of 0.999987. For the sake of completeness, it is shown that the structure can result in an optical delay of about 0.05 ps corresponding to a group index of 14.6 that is potentially useful for plasmonic nanosensors and slow-light devices in the visible range of the spectrum.

Automated summary

A metal-insulator-metal (MIM) structure consisting of a semi-circular resonant cavity (SCRC) and a circular split-ring resonator (SRR) is proposed and designed for optical sensing applications. The coupling between the SCRC and SRR can create dual Fano resonances in the visible range. The structure exhibits a high sensitivity and figures of merit, making it potentially useful for plasmonic nanosensors and slow-light devices.