Abstract

Second-order nonlinearity is traditionally associated with second-harmonic generation and was not, until recently^1-7, seen as a source of intensity dependent phenomena. The rejection of second-order materials, as envelope or spatial soliton hosts, appears to have been centred upon a phase-matching argument¹. This view has now changed and the back-mixing ^1,2,⁷, or down-mixing [cascading], of the second-harmonic with the fundamental wave to create useable third-order nonlinearity in the form of an intensity-dependent refractive index is opening up exciting prospects. Featuring strongly among these are spatial soliton interactions. Such excitations depend upon the competing roles of diffraction and nonlinearity⁸,⁹ and have already received some attention¹⁰.

© 1995 Optical Society of America