Theoretical Analysis of Tunable Multimode Coupling in a Grating-Assisted Double-Layer Graphene Plasmonic System

A double-layer graphene hybrid system is proposed to investigate the multimode coupling at far-infrared frequencies. With the assistance of metallic grating, the upper- and lower-layer graphene surface plasmons as well as the magnetic polaritons can be excited simultaneously, resulting in selective localization of electromagnetic energy. By tuning the thickness of the spacer, the mutual conversion between strong coupling and weak coupling can be achieved, giving rise to hybrid modes and Rabi splitting. The dynamic control of multimode coupling is also investigated via varying the Fermi energy of graphene. The hybrid coupling behaviors exhibit unique energy-transfer and multiband light trapping as well as mode splitting characteristics, which can be well described by the classical coupled oscillator model. Our work may inspire related studies on graphene-based light matter interaction, and the proposed hybrid system provides a good paradigm for designing many plasmonic devices, including tunable optical switches, thermal emitters, multiband absorbers, sensors, etc.