Ultrafast all-optical switching in a silicon-based photonic crystal

We study the effect of two-photon absorption and Kerr nonlinearity on the optical properties of a one-dimensional photonic crystal made with amorphous silicon and SiO2. A stop band appearing near 1.5 mum is monitored with a weak probe beam and modulated by changes in the refractive index caused by a pump pulse at 1.71 mum with 18 GW/cm(2) peak intensity. Nonlinear optical characterization of the sample using Z-scan points out to two-photon absorption as the main contributor to free carrier excitation in silicon at that power level. Modulation in the transmittance near the band edge is found to be dominated by the optical Kerr effect within the pulse overlap (similar to 400 fs) whereas free carrier index changes are observed for 12 ps. (C) 2000 American Institute of Physics. [S0003-6951(00)02551-1].