Experimental and theoretical observations of the slow-light effect on a tunable photonic crystal

We describe how the susceptibility of a nonlinear material, such as lithium niobate, can change when the material is nanostructured. Indeed, we show, by the calculation of the local-field factor inside a photonic crystal, a significant augmentation of the susceptibility, especially at the edges of the photonic bandgap. In addition, and for the case of lithium niobate, we observe an increase of the second-order nonlinear coefficient. The experimental realization of an electro-optic tunable photonic crystal, based on a square lattice of holes, shows that the measured phenomenon completely agrees with the theoretical predictions.