spatial nonlinearity in anisotropic metamaterial plasmonic slot waveguides

We study the main nonlinear solutions of plasmonic slot waveguides made from an anisotropic metamaterial core with a positive kerr-type nonlinearity surrounded by two semi-infinite metal regions. first, we demonstrate that for a highly anisotropic diagonal elliptical core, the bifurcation threshold of the asymmetric mode is reduced from the gw/m level for the isotropic case to 50 mw/m level indicating a strong enhancement of the spatial nonlinear effects. in addition, the slope of the dispersion curve for the asymmetric mode remains positive, at least near the bifurcation, suggesting a stable mode. second, we show that for the hyperbolic case, there is no physically meaningful asymmetric mode, and that the sign of the effective nonlinearity can become negative.