Modulational instability of copropagating light beams induced by cubic–quintic nonlinearity in nonlinear negative-index material

Abstract

We study the modulational instability (MI) of the continuous wave propagating through negative-index materials, based on the coupled cubic–quintic nonlinear Schrödinger equations. A comparison is made with the already available results on MI without including the quintic term. We find that this term helps in achieving MI, in otherwise impossible combinations of dispersion and nonlinearity. For example, spatial MI can occur in the focusing regime, and temporal MI becomes possible in the anomalous dispersion for defocusing nonlinearity, while in the case of the normal dispersion regime, it occurs for focusing nonlinearity, and spatiotemporal MI can occur in the focusing nonlinearity and normal dispersion. Moreover, this additional term provides extra freedom to control the amplitude of the MI gain profile.