Terahertz plasmon-induced transparency and absorption in compact graphene-based coupled nanoribbons

We investigate theoretically and numerically the possibility of realizing plasmon-induced transparency (PIT) and plasmon-induced absorption (PIA) in a novel compact graphene-based nanostructure. The main graphene bus waveguide is coupled to two graphene nanoribbons (GNRs). The PIT effect is obtained by setting the two GNRs in an inverted L-shape aside of the main waveguide, giving rise to lambda-like configuration in analogy with three atomic-level systems. The possibility of improving the quality factors of PIT-like resonances is shown and the associated slow light effects are showcased. The mechanism behind the observed transparency windows is related to mode splitting also known as Autler-Townes splitting phenomenon. Two PIA resonances are also demonstrated by the same system. This is achieved by inserting the two GNRs, forming an inverted T-shape, inside the main waveguide. Here the two GNRs are also set in a lambda-like configuration. We indicate the possibility of improving the Q-factor of the PIA resonances and showcase their fast light features. The PIA absorption bands are shown to be essentially caused by interference phenomena between three states as in electromagnetic-induced transparency. The proposed system may help the design of tunable integrated optical devices such as sensors, filters or high speed switches.