▎ 摘　　要

We investigate ultrathin metasurfaces defined by anisotropic conductivity tensors using a Green's function approach, focusing on their exciting plasmonic interactions and dramatic enhancement of light-matter interactions for hyperbolic dispersion. We apply our analytical formulation to explore several practical implementations at THz and near infrared frequencies, including electrically and magnetically-biased graphene sheets - a natural isotropic elliptic metasurface - and densely-packed arrays of graphene ribbons modelled through an effective medium approach. This latter configuration allows the electrical control of their band diagram topology - from elliptic to hyperbolic, going through the extremely anisotropic sigma -near-zero case - providing unprecedented control over the confinement and direction of plasmon propagation while simultaneously boosting the local density of states. Finally, we study the influence of the strip granularity to delimit the accuracy of effective medium theory to model the electromagnetic interactions with hyperbolic metasurfaces. Our findings may lead to the development of ultrathin reconfigurable plasmonic devices able to provide extreme confinement and dynamic guidance of light while strongly interacting with their surroundings, with direct application in sensing, imaging, hyperlensing, on-chip networks, and communications. (C) 2015 Optical Society of America