All-optically Control of Light Propagation in Valley-Hall Topological Waveguides of Graphene Metasurfaces

We study the influence of graphene Kerr effect on valley-Hall topological modes of a graphene plasmonic crystal waveguide. Extra air holes are introduced to break the spatial-inversion symmetry of the plasmonic metasurface, which can be performed using e-beam lithography. As a result, a gapless Dirac cone and topologically protected edge modes form inside the nontrivial frequency bandgap. Taking advantage of the fact that graphene is a nonlinear optical material possessing an extremely large Kerr coefficient, we demonstrate that an all-optical switch can be implemented in this topological photonic system by controlling an optical signal propagating in the waveguide via a pump beam injected into the bulk modes of the metasurface. This work may lead to new graphene-based active topological photonic nanodevices.