Plasmonic-induced transparency in a MIM waveguide with two side-coupled cavities

We investigate numerically the classical analogue of electromagnetically induced transparency (EIT) in a nanoplasmonic structure constituted by two side-coupled cavities. Two configurations are considered: (1) two cavities connected symmetrically on each side of the waveguide; (2) two cavities situated on the same side. In the first case, the EIT resonance occurs as a consequence of the destructive interference between the two cavities (playing the role of two coupled radiative oscillators), whereas in the second situation, the phenomenon arises due to a coupling between dark and radiative resonators. By detuning the sizes of the two cavities (i.e., the length difference ΔL, keeping their width w similar), we show that the position, width and quality factor of the EIT resonance depend strongly on ΔL. The effect of the metal gap separating the two cavities from the waveguide is also discussed. These results may have important applications for designing integrated devices such as narrow-frequency optical filters, novel sensors and high-speed switches.