Enhancement of second harmonic generation in nonlinear photonic crystals with two defective layers

The second harmonic generation in one-dimensional nonlinear photonic crystals with two defective layers was theoretically investigated by using the transfer matrix method. The nonlinear defect layers were introduced at the center of the photonic crystals. The forward and backward second harmonic conversion efficiencies are found to be a function of the separation width between the two defect layers. By optimizing the separation width using the simulated annealing algorithm, huge forward and backward conversion efficiencies are obtained for one of the defect modes and its associated second harmonic wave is located at the edge of a photonic band gap.