Optimization of Gap Plasmonic Waveguides for Nonlinear Applications

Highly nonlinear waveguides are essential components for all-optical signal processing. Many promising nonlinear waveguides utilize the Kerr nonlinearity, the strength of which is determined not only by the material properties, but also by geometrical factors, quantified by the waveguide's nonlinear effective area A(eff). In an all-optical switch, the switching threshold power is proportional to A(eff), so optimization of the nonlinear waveguide is equivalent to minimization of A(eff). Recent studies have shown that dielectric slot waveguides can confine optical energy far below the diffraction limit, with nonlinear effective areas considerably less than those attainable in total internal reflection waveguides. In this work, we instead consider the use of a gap plasmonic waveguide (GPW) for deep sub-wavelength optical confinement. Using finite element methods, we compare optimized slot waveguides with GPWs of identical geometry. We show that the GPW achieves a nonlinearity more than an order of magnitude superior to the corresponding dielectric slot waveguide, and that a further optimization of the GPW is possible.