Vector soliton associated with polarization modulational instability in the normal-dispersion regime

We investigate the dynamics of the coupled nonlinear Schrödinger equations which describe light propagation in isotropic Kerr media including polarization effects. It is shown that the phenomenon of polarization modulational instability in the normal-dispersion regime is associated with the existence of a novel type of dark vector soliton. This soliton constitutes a localized structure separating adjacent domains of orthogonal polarization eigenstates of the Kerr medium and can be viewed as a polarization domain wall.