The effect of nonlinear interactions in a crystal on the polariton behavior has been investigated. A new mode in the photonic band gap in LiNbO 3 is obtained, as suggested by some recent literature. This mode is shown to be almost dispersionless, which may find application in optical communication. The Raman scattering and parametric amplification are interpreted in terms of a dielectric function, which includes nonlinearity. The scattering efficiency is shown to be a consequence of the photonic band gap. The nonlinearity is shown to lead to a soft mode-like behavior in polar crystals.
Unexpected Dependence of Photonic Band Gap Size on Randomness in Self-Assembled Colloidal Crystals