Ultrafast all-optical switching of 3D photonic band gap crystals

We present ultrafast optical switching experiments on 3D photonic band gap crystals. Switching the Si inverse opal is achieved by optically exciting free carriers by a two-photon process. We probe reflectivity in the frequency range of second order Bragg diffraction where the photonic band gap is predicted. We observe a large frequency shift of up to 1.5% of all spectral features including the peak that corresponds to the photonic band gap. We also demonstrate large, ultrafast shifts of stop bands of planar GaAs/AlAs photonic structures. We briefly discuss how our results can be used in future switching and modulation applications.