All-optical modulation with ultrafast recovery at low pump energies in passive InGaAs/InGaAsP multiquantum well waveguides

We report on the observation of ultrafast (<1 ps) recovery of all-optical modulation based on below band gap, optically induced excess absorption using pump pulse energies of less than 4 pJ. At higher pump pulse energies, the hot carriers produced by two-photon absorption significantly reduce the recovery rate. The increase in absorption recovery times at the higher densities of hot carriers is consistent with a contribution to the nonlinear absorption change from hot electron assisted absorption. The measured hot electron assisted absorption cross section of 2×10^-20 m² is in good agreement with the theoretical value.