Ultrafast all-optical modulation in GaAs photonic crystal cavities

We demonstrate all-optical modulation based on ultrafast optical carrier injection in a GaAs photonic crystal cavity using a degenerate pump-probe technique. The observations agree well with a coupled-mode model incorporating all relevant nonlinearities. The low switching energy $(∼120fJ)$⁠, small energy absorption $(∼10fJ)$⁠, fast on-off response $(∼15ps)$⁠, limited only by carrier lifetime, and a minimum 10 dB modulation depth suggest practical all-optical switching applications at high repetition rates.