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

Abstract

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.