Te-Tm Coupling of Spatial Solitons in Planar Waveguides With Cascaded Second-Order Nonlinearity

Second-order nonlinearity is traditionally associated with second-harmonic generation and was not, until recently1-7, 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.