Gap solitons in three wave mixing nonlinear media

Summary form only given. Parametric waveguides with Bragg resonances allow the generation of gap-simultons, i.e. multi-color localized energy states propagating at low or even zero speed. Such solitonic pulses can be excited by a single frequency input, collide, slow-down and stop, enabling the realization of optically controlled delay lines and buffers. We review the theoretical/numerical progress in the field with specific reference to second harmonic generation.