We theoretically show that it should be possible to demonstrate Electromagnetic-Induced-Transparency-like (EITlike) effects in the visible range by using ultra-compact plasmonic micro-ring resonators with μm 2 order foot print. By using the finite-difference time-domain (FDTD) numerical method and the coupled mode theory (CMT) collaboratively, the transmission intensity, phase, and group delay spectra of the coupled plasmonic ring resonators are theoretically calculated with the inclusion of metallic loss and dispersion through the Drude model. The interference induced transmission peak can be successfully achieved through suitable design of the plasmonic ring resonator structure.

Efficient wavelength-selective coupling of lights between sub-wavelength plasmonic waveguides and free space is theoretically investigated. The idea is based on a new type of vertical resonance coupling devices built on plasmonic metal/insulator/metal (MIM) waveguides. The device structure consists of a vertical grating coupler in a resonance cavity formed by two distributed Bragg reflectors (DBRs). With the metal loss included, maximum coupling efficiency around 50% can be obtained at the 1550 nm wavelength with a filtering 3 dB bandwidth around 20 nm (7 nm for the lossless case), demonstrating the feasibility of the idea for achieving high efficiency wavelength-selective vertical coupling through optical resonance. By utilizing this coupler, a plasmonic add-drop device is proposed and theoretically demonstrated. This kind of compact wavelength selective coupling devices shall have the potential to open up a new avenue of photonics circuitry at nanoscale.