Resonances of sandwiched optical antenna

We calculate the resonant properties of the sandwiched triangle and bowtie antennas using finite difference time domain technique and compare with one-layer structures. The sandwiched antennas possess two tunable resonances corresponding to the symmetric and antisymmetric modes for dipole excitation, which can be understood by the hybridization of the plasmons supported by the two golden layers of the antennas. We obtain a giant field enhancement and a full width at half maximum as larger as 385 nm for the sandwiched bowtie antenna.