Nonlinear Schrodinger solitons in media with non-zero second-order nonlinear susceptibility

It is demonstrated theoretically for the first time that, under the strong dispersion condition, media with non-zero second-order nonlinear susceptibility can support the soliton propagation as optical fibres do, but the nonlinear index coefficient n2 in the nonlinear Schrodinger equation should be substituted by the effective nonlinear index coefficient defined here. The results obtained here can be easily extended to discuss the other nonlinear effects connected with the nonlinear index coefficient in the media.