Engineering localized nonlinear-optical transport with optical phonons

We show that the medium length required for coherent energy transport from strong electromagnetic field to contra-propagating Stokes signal can be significantly reduced and the conversion efficiency sharply increased by means of three-wave mixing with optical phonons having negative group velocity. Such localization depends resonantly on the intensity of the fundamental beam and, therefore can be fit in with the given thickness of the crystal. The effect is similar to that under three-wave mixing of electromagnetic waves in frequency double domain negative/positive index plasmonic metamaterials. However, in the latter case, the effect stems from the backwardness of one of the coupled electromagnetic waves, which is provided by the extraordinary electromagnetic properties of the plasmonic meta-atoms, and is inherently strongly lossy. Basic principles of the effect are described and numerically simulated. Applications for signal processing are discussed.