Graphene ribbons for tunable coupling with plasmonic subwavelength cavities

Since graphene supports low loss plasmonic guided modes in the infrared range, we theoretically investigate the coupling of these modes in patterned sheets with nanocavities. We calculate cavity modes and (potentially critical) coupling in filter-type circuits, with resonances observed as multiple minima in the reflection spectrum. The origin and properties of the cavity modes are fully modeled by coupled mode theory, exploring for various positions of the cavity with respect to the access waveguide. A useful resonance frequency shift is examined by modifying the graphene doping (e.g., via voltage tuning). The deep subwavelength cavity modes reach quality factors up to 42 for ribbons of 30 nm width around 5 mu m wavelength. These resonances provide opportunities for ultracompact optoelectronic circuits. (C) 2014 Optical Society of America