Abstract

The existence of χ⁽²⁾ optical solitons was suggested long ago [1], but at that time this idea failed to attract much attention. However, about four years ago it was demonstrated experimentally that a nonlinearity-induced phase shift can be achieved in χ⁽²⁾ materials (ie optical materials without inversion symmetry) due to cascaded effects [2]. This activates many efforts to analyse a variety of χ⁽²⁾-induced nonlinear effects (previously well understood only for χ⁽³⁾ materials) such as modulational instability, self-focusing or self-defocusing, and optical solitons. As has been already demonstrated theoretically (see, eg, Refs [3,4] to cite a few), both (1 + 1) and (2+1) dimensional bright and dark solitons can exist in materials in the form of two-wave localised modes of the strongly coupled fundamental and second-harmonic fields. The first experimental verifications of χ⁽²⁾ self-guided beams in (1 + 1) and (2+1) dimensions have also been reported [5,6].

© 1996 Optical Society of America