Complex modes in plasmonic nonlinear slot waveguides

We analyze linear and nonlinear modes of metal-dielectric-metal slot waveguides taking into account the effect of losses at the metallic cladding. First, we study a linear core and then assume it to be nonlinear with a Kerr-type nonlinear response. In the linear case, we summarize the earlier results of the frequency dispersion analysis showing the mode transformation when losses are increasing. For the nonlinear case, after a brief review of the earlier results on the lossless plasmonic slot waveguides, we demonstrate that losses lead to the existence of complex nonlinear modes which we describe through the dependence of mode power on the propagation constant. We show that losses bring many novel features into this nonlinear system resulting in novel bifurcations and novel types of nonlinear guided modes, as well as the existence of limiting values for the propagation constant and the modes with an unlimited power. We also study the mode stability by means of numerical simulation using the finite difference time domain method.