Abstract

Recently it has been shown experimentally¹ that nonlinearities of χ⁽²⁾ materials may create a nonlinearity-induced phase shift due to cascaded effects. These experimental results have already initiated the intensive study of bright optical solitons in diffractive (or dispersive) χ⁽²⁾ media.^2,3 Here we consider parametric interactions between the fundamental and second harmonics in a dispersive χ⁽²⁾ medium and demonstrate that dark optical solitons can also exist due to solely nonlinear parametric interactions provided the dispersion coefficients for the fundamental and second harmonics have different signs. We present novel families of stable dark two-wave solitons in a purely quadratic dispersive nonlinear medium. We also show that the solution for a dark soliton earlier reported by Hayata and Koshiba⁴ is modualationally unstable.

© 1995 IEEE