Interaction of two dark solitons in nonlinear left-handed materials

A system of coupled nonlinear Schrödinger equations (CNLS) has dark soliton solutions. In nonlinear left-handed materials, the interaction of two of these dark solitons with the same parameter κ can generate new electromagnetic envelops that are quite different from a single soliton, even including a ‘bright’ envelop. But the new-generated envelops can also propagate steadily in the materials, we call them quasi-soliton. Numerical calculations demonstrate that varying either the parameter κ or the distance between the two solitons will change the envelop shape of the quasi-soliton remarkably. And an analysis of the phenomena is presented.