Directional Polaritonic Excitation of Circular, Huygens and Janus Dipoles in Graphene-Hexagonal Boron Nitride Heterostructures

—Polariton assisted tunable directionality provides an intrinsic ingredient to various micro/nano integrated optical systems. Their capabilities of light manipulation in mesoscopic structures allow numerous beneficial properties in information processing. The realization of active near-field directionality by tuning the input signal of system bias is more preferable than that by reconfiguring the nanostructures. Recent progresses on the multiple hybrid dipole radiations ensure another methodology in realizing tunable directionality. Here we investigate some exotic near-field phenomena in a 5-layer waveguide consisted of graphene and hexagonal boron nitride ( h BN) illuminated by hybrid dipole sources such as a Circular dipole, a Huygens dipole or a Janus dipole. We demonstrate divergent behaviors of hybrid polariton excitations subject to various source types and the tunability of switching between phonon-like polaritons and plasmon-like polaritons. We also show that the flipping of the group velocity of excited hybrid polaritons can be used to flexibly tune the transportation direction away from the dipolar sources. To be specific, when the group velocity of supported polariton flips its sign, the energy flow will shift to the opposite side accordingly. Such phenomena are promising in the design of reconfigurable and multifunctional nanophotonic devices.