Electromagnetically-induced transparency in a multi-cavity coupled waveguide system

The plasmonic analogue of electromagnetically-induced transparency (EIT) was investigated in a plasmonic waveguide system composed of a straight waveguide, with rectangular and U-shaped (split-ring resonator) cavities. An EIT-like transparency window occurs in the transmitting spectrum of the waveguide system and the magnetic field is dramatically changed due to the destructive interference between two resonance pathways. It is demonstrated that the EIT-like spectra can be modified by varying the coupling strength and tailoring the degree of asymmetry of the structure, and we study the coupling mechanisms between the elements of the structure, including magnetic coupling, electric coupling, and inductive coupling. In addition, a cascaded structure which consists of an SRR pair with 180 degrees rotation asymmetry has been studied. It is found that the strong couplings between two asymmetric plasmonic nanostructures can lead to EIT-like transmission in both visible and near-infrared regions, simultaneously.