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.