Solitons in a three-wave system with intrinsic linear mixing and walkoff

A modification of the usual Type-II second-harmonic-generation model is proposed, which includes two additional features: linear conversion and walkoff (group-velocity difference) between two components of the fundamental-frequency (FF) wave. Physical interpretations of the model are possible in both temporal and spatial domains. In the absence of the intrinsic walkoff, the linear mixing makes real soliton solutions stable or unstable, depending on the relative sign of the two FF components. Unstable solitons spontaneously re-arrange themselves into stable ones. Fundamental solitons change their shape (in particular, they develop chirp) but remain stable if the intrinsic walkoff is included. In addition, quasi-stable double-humped solitary waves are found in the latter case.