Multiple-band directional excitation of surface plasmons based on electromagnetically induced transparency

We propose a structure of two metallic slits, one of which is accompanied by two non-equal length cavities. Our simulation results, conducted by finite difference time-domain method, show that there are four bands that can achieve launching surface plasmons (SPs) unidirectionally in the communication region, and each band is very narrow (between 10 nm and 30 nm). Our design method is based on SPs interference, and the phase-shift variation of SPs in the electromagnetically induced transparency wavelength region. Our design method provides a new way to manipulate SPs and control SPs' propagating direction in photonic circuits.