  Graphene has recently been shown to possess giant nonlinearity; however, the
utility of this nonlinearity is limited due to high losses and small
interaction volume. We show that by performing waveguide engineering to
graphene's nonlinearity, we are able to dramatically increase the nonlinear
parameter and decrease the switching optical power to sub-watt levels. Our
design makes use of the hybrid plasmonic waveguide and careful manipulation of
graphene's refractive index by tuning its Fermi level. The ability to tailor
the nonlinear parameter in graphene based waveguides via the Fermi level
provides a paradigm of nonlinear optics devices to be realized.
