Nonlinear backward-wave photonic metamaterials

Novel concepts of nonlinear-optical (NLO) photonic metamaterial are proposed. They concern photonic materials that support backward electromagnetic or vibration waves (BWs) and provide coherent nonlinear-optical energy exchange between ordinary and BWs as applied to three- and four-wave mixing processes. Three different classes of materials which support BWs are considered: plasmonic negative-index (M) metamaterials (NIMs), metamaterials with specially engineered spatial dispersion of the nanoscopic building blocks, such as standing carbon nanotubes, and crystals that support optical phonons with negative group velocity. The possibility to exploit ordinary crystals instead of plasmonic NLO metamaterials that are very challenging to engineer is proposed. It is shown that extraordinary nonlinear optical frequency-conversion propagation processes attributed to NIMs can be mimicked in the proposed metamaterials. It is also shown that the detrimental effects of strong losses can be mitigated in the short-pulse regimes, which exhibit exotic properties when ordinary and BWs are involved in the NLO coupling. Comparative review of unparallel properties of coherent energy exchange between ordinary and backward electromagnetic waves in NIMs and between ordinary electromagnetic waves coupled through backward vibration waves is given. Unique photonic devices are proposed.