We demonstrate all-optical switching at an extremely low operating energy using silicon photonic crystal nanocavities. The operation is based on the carrier-plasma dispersion effect induced by the two-photon absorption carriers. The switching speed is less than 200ps, which is very fast for a silicon-chip-based optical modulator. In addition to the switching operation using single pulses for modulation, we show the capability of the 5-GHz RZ (Return to Zero) pulse train modulation. Such high speed is achieved because the device is extremely small. The switches can be connected in tandem by input and output waveguides, which paves the way for the realization of integrated optical logic circuits on a single chip, based on photonic crystals.
