Terahertz multi-plasmon induced reflection and transmission and sensor devices in a graphene-based coupled nanoribbons resonators

We demonstrate numerically multi-plasmon-induced reflection (PIR), multi-plasmon-induced transparency (PIT) and propose a highly sensitive refractive index nanosensor in a novel ultra-compact graphene-based nano-device, operating in the terahertz frequency range. The base structure of the system is composed out of a bus waveguide made out of graphene coupled to resonators inserted along or aside the waveguide where each resonator is constituted by a set of two coupled graphene nano-ribbons (CGNR). The latters behave as a molecule-like entity, whose surface plasmon eigen-modes originate from the splitting of the single ribbons modes. We show that the two CGNRs can also be regarded as an effective rectangular cavity-like system, so that the insertion of the latter along or aside the graphene bus waveguide (GBW) enables the design of tunable selective or rejective filters, respectively. By inserting two identical effective cavities in the structure, into a.-like state (in analogy with three level atomic systems), we show the possibility of realizing multiple plasmon induced reflection, and highlight its fast light-features. On the other hand, if the two identical cavities are set symmetrically on each side of the GBW with slightly detuned Fermi energy levels in a V-like configuration, multi-plasmon induced transparency can be obtained. In addition, a highly sensitive refractive index nanosensor is showcased. The latter consists in a GBW, side-coupled to an effective cavity-oscillator embedded with the analyte to be detected. The sensitivity of the sensor is numerically derived. Owing to its simple structure, the proposed sensor may offer the advantage of being easily fabricated. The showcased graphene-based devices proposed in this work should help the design of tunable and highly integrated optical devices such as nano-filters, optical switches and highly sensitive nanosensors.