Gain and phase dynamics of InAs/GaAs quantum dot semiconductor optical amplifiers

Ultrafast spectroscopy of quantum dot semiconductor optical amplifiers (SOAs) provides valuable information about the potential of these devices for emerging applications such as multi-wavelength regeneration while giving insight on their unique carrier dynamics. Pump-probe spectroscopy was used to analyse the carrier dynamics in InAs/GaAs quantum dot amplifiers. We have developed a "two-colour" experimental configuration that allows us to pump and probe different parts of the Amplified Spontaneous Emission spectrum and develop a detailed picture of the relevant carrier processes in both absorption and gain regimes of QD-SOAs. The study has revealed that hole recovery and intradot electron relaxation occur on a picosecond timescale, while the electron capture time is on the order of 10 ps. The relaxation of the wetting layer carrier density was shown to have a strong effect on the phase dynamics of both ground and excited state transients, while having a much weaker effect on the gain dynamics. Such behaviour is strongly encouraging for reduced pattern effect operation in high speed optical networks.