Stability of black, gray, and bright nonlinear guided waves in a thin film bounded by a self-defocusing medium

Stability of nonlinear guided waves trapped in a thin linear film bounded by an infinite self-defocusing nonlinear medium is investigated. In addition to the trapped black and gray nonlinear guided waves, the existence of a novel class of bright nonlinear guided waves (with nonzero intensity background) is demonstrated. The gray and fundamental bright nonlinear guided waves are found stable whereas the black nonlinear guided waves are unstable to an asymmetric perturbation (but stable to a symmetric perturbation). The instability of the black nonlinear guided waves is shown to develop into various states, including stable gray and bright nonlinear guided waves, depending on initial excitations.