Extended modulational instability and new type of solitary wave in coupled nonlinear Schroedinger equations

We investigate the dynamics of the incoherently coupled nonlinear Schroedinger equations describing the propagation of two waves interacting through a third order nonlinearity. We show that the phenomenon of extended modulational instability induced by incoherent coupling is associated with the existence of a new type of solitary wave. This solitary wave consists of a bound state of two interacting semi-infinite symmetric kink waves. (orig.)