The respective effects of direct and indirect couplings on the plasmon-induced transparency in waveguide systems

We investigate respectively the effects of direct and indirect couplings on electromagnetically induced transparency (EIT)-like in a Metal-Insulator-Metal (MIM) bus waveguide coupled to two aperture-resonators (ARS). Adjusting the intensity of direct and indirect couplings, we can intentionally realize, modulate and eliminate the EIT-like transmission in the proposed plasmonic structures. The consistency between theoretical results and finite-difference time-domain (FDTD) simulations indicates that the direct coupling can give rise to EIT-like phenomenon in symmetrical structure. Moreover, the EIT-like transmission dips can be shifted back to the original resonant frequency when the two couplings offset each other. These results may provide a helpful guideline for the control of light in highly integrated optical circuits.