Nonuniform doping of graphene for plasmonic tapers

A numerical study of graphene plasmons (GPs) propagating along various doping profiles of the graphene sheet is proposed. We show that the GP reflection at an abrupt doping interface is a simple function of the doping difference, consistent with a Fresnel model. In addition, improved transmission is obtained with a tapered interface and we find an optimal size for the transition zone. By considering localized inhomogeneities we describe a Fabry-Perot type cavity leading to an absorption above 60%. Furthermore, an alternative design of a 6 nm length cavity is proposed achieving 100% absorption. These results may lead to novel optical switches, circuits or nano-sensors.