High-contrast all-optical switching by using cascading in the Cerenkov regime

The interest in χ(2) materials and related nonlinear wave-propagation effects has been driven for a long time by potential applications in efficient blue-light generation by second harmonic generation (SHG) and electro-optical switching.1 Recently additional interest has been raised by advances in polymeric χ(2) materials, which promise large nonlinear phase shifts by the cascading of second-order effects.2 This offers possibilities for tackling problems that have been traditionally thought to need third-order nonlinearities: all-optical switching. From a practical point of view, the interest in SHG and cascading has been dominated by guided-mode/guided-mode interactions. Guided-mode/radiation-mode interactions have been studied as well,3 but analytical relations are difficult to obtain because of the problems associated with normalization of radiation modes. Consequently, most work has concentrated primarily on the efficiency of SHG. However, interactions with radiation modes can be easily studied by means of the SHG beam-propagation method.4 This method, an extension of normal BPMs, consists of a split-step approach in which the calculation of the propagation of the fields at the two wavelengths is alternated by the calculation of the nonlinear interactions.