Shaping sub-wavelength plasmonic funnels

For ten years graphene has attracted a continuously growing interest due to its amazing electronic properties. This material is not only extremely thin, it also presents a tunable conductivity controlled by varying the doping level e.g. via electrostatic gating. More recently, graphene is under study for its curious optical properties. Graphene plasmons for example exhibit a relatively tight confinement and long lifetime, compared to noble metal plasmons. Moreover, at normal incidence 2.3 percent of the light is absorbed by the one atom thick layer! This remarkably strong and broadband interaction can be exploited in complex photonic structures such as modulators, metamaterials and optical sensors. Before examining complete devices, we need to study the fundamental modes in basic structures such as nano-ribbons, rings, disks, cavities etc. This is achieved by describing graphene through its dielectric function, determined via the conductivity within the random phase approximation. The numerical calculations are handled by COMSOL using the finite-element method. Once the basic structures are understood, we aim to model more complex and functional components such as photovoltaic cells, integrated components and light emitting devices.