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 ( ∼ 120 fJ ) , small energy absorption ( ∼ 10 fJ ) , fast on-off response ( ∼ 15 ps ) , limited only by carrier lifetime, and a minimum 10 dB modulation depth suggest practical all-optical switching applications at high repetition rates.