Graphene Plasmonics: Propagation control for optoelectronic applications

Graphene plasmonics created a tremendous interest in the last few years since it offers a simple way to control light on the sub-wavelength scale. These properties stem from the low loss and strongly confined graphene plasmons, combined with a large tunability of graphene via electrostatic or chemical doping.
However, even if the technology seems promising for optoelectronic circuitry, graphene plasmons propagating under various doping profiles have not been studied extensively. Performing finite-element method simulations and semi-analytical models, we show that the reflection of graphene plasmons at abrupt doping interfaces is a simple function of the doping difference. Furthermore, an improved transmission is obtained with specific tapered doping profiles, and an optimal size for tapering is found. This planar system leads to Fabry-Perot type cavities (Figure 1) with absorption above 60%. A deeply sub-wavelength 6nm length cavity achieving 100% absorption is proposed.
A more complex graphene structuring can also offer a strong control of the light: we model a grating of finite graphene ribbons at the end of a graphene sheet, and discuss the reflection as a function of their length and width. Critical zero-reflection points are observed and explained via the ribbon mode dispersion.