Optical modulation of a photonic bandgap with two-photon excitation and the Kerr effect

Summary form only given. We experimentally demonstrate the effect of two-photon absorption (TPA) and Kerr nonlinearity on the transmission properties of a silicon-based, one-dimensional photonic crystal. The sample under study is made of five pairs of amorphous Si/SiO/sub 2/ thin layers, with a lattice period of 645 nm. Using a pump-and-probe technique with femtosecond pulses, we monitor the photonic band edge with a weak probe pulse at 1.5 /spl mu/m while modifying the refractive index with a strong pump pulse at 1.7 /spl mu/m (where the crystal is highly transparent) with an intensity of up to 20 GW/cm/sup 2/. In order to prove that optical modulation was nonlinear in origin, Z-scans were performed on the sample, which suggest that TPA far exceeds linear absorption at that intensity level. These results show that TPA and the Kerr effect can produce all-optical switching in photonic crystals and will need to be taken into account when semiconductor-based photonic crystals are used in applications where short pulses and high intensities are involved.