Nonlinear holography

The effect of photoinduced second harmonic generation in optical fibers, bulk glasses, and crystals has been studied for four decades. The asymmetry of photoionization in the simultaneous presence of the fundamental frequency and its second harmonic results in a third-order coherent photogalvanic effect that produces strong electric fields in wideband dielectrics. The electric field-induced second-order nonlinearity oscillates with quasi-phase matching periodicity, enabling an efficient light-induced frequency converter. The recording process of the second-order nonlinear susceptibility grating and its ability to generate second harmonic light is referred to as nonlinear holography. Recent advances in low-loss photonic integrated circuits and coupled resonator cavities offer new and exciting applications for nonlinear holographic gratings. The recording approaches, available recording media, and microscopic mechanisms of nonlinear holography are reviewed in detail.