Sensor based on multiple Fano resonances in MIM waveguide resonator system with silver nanorod-defect

Abstract

The triple Fano resonance via a plasmonic waveguide system which is composed of an isosceles-triangular resonator coupled with a nanorod-defect is presented. The Fano resonance originates from the narrow discrete resonances and the broad continuous state of the isosceles-triangular resonator and the nanorod-defect, respectively. Multimode interference coupled-mode theory (MICMT) and finite difference-time domain method (FDTD) are proposed to explain the triple Fano resonance. Results show that the Fano line shapes can be independently tuned by the geometrical parameters, such as the radius of nanorod-defect, the height or the base length of the isosceles-triangle resonator. The transmittance of the system can sharply decrease from peak to dip with wavelength shifts of only 8 nm for FR2. The sensitivity and FOM* (figure of merit) of the FR2 can be up to 1250nm/RIU and 88.68, respectively. In comparison to other similar sensors, the proposed plasmonic structure has relatively comparable sensitivity and FOM*, which may have application in slow light device, nanoscale filter, refractive index sensor and other related plasmonic devices.