Higher Order Fano Resonances and Electric Field Enhancements in Disk-Ring Plasmonic Nanostructures with Double Symmetry Breaking

Optical properties of disk-ring plasmonic nanostructures with double symmetry breaking are investigated theoretically. Tunable higher order Fano resonance is achieved, and it is sensitive to the degree of asymmetry of the nanoring, the offset and the dimension of the nanodisk. It is demonstrated that such higher order Fano resonances originate from the destructive interference between the bright mode of the displaced nanodisk and the dark mode of the asymmetric nanoring. By tunning the asymmetry degree of the nanoring, the offset, and the dimension of the nanodisk, certain higher order Fano resonances can be suppressed or enhanced. Double asymmetry breaking also allows the realization of the stronger electric field enhancement, resulting from the stronger interaction between the displaced nanodisk and the asymmetric nanoring.