Defective photonic crystals with greatly enhanced second-harmonic generation

A one-dimensional defective photonic crystal structure is proposed with the aim of studying its nonlinear optical properties. In such a structure, extremely enhanced second-harmonic generation with an efficiency ~5 orders of magnitude higher than that of ordinary films is demonstrated in a numerical simulation. Extraordinary phase conditions of the process in such a structure were explored, and efficient forward and backward second-harmonic generation could be achieved simultaneously. The mechanism of the enhancement is the high field intensity and efficient wave coupling introduced by light localization in defect states, from which many other nonlinear processes can also benefit.