Gain recovery dynamics are studied in electrically pumped quantum dot (QD) based semiconductor optical amplifiers (SOAs) after amplification of double femtosecond laser pulses using ultrafast pump-probe spectroscopy with heterodyne detection. The authors observe a distinct change in gain recovery in the ground state when a significant excited state population is achieved. A complete gain recovery is found when two 150fs pulses with 5ps time delay pass through the SOA in resonance to the ground state under high injection currents of 80–100mA. The obtained results open the way for ultrafast (>200GHz) operation in p-doped QD based SOAs at 1.3μm telecommunications wavelengths.

The application of quantum dot (QD) semiconductor optical amplifiers (SOAs) in above 100-Gbit Ethernet networks demands an ultrafast gain recovery on time scales similar to that of the input pulse approximately 100 GHz repetition frequency. Microscopic scattering processes have to act at shortest possible time scales and mechanisms speeding up the Coulomb scattering have to be explored, controlled, and exploited. We present a microscopic description of the gain recovery by coupled polarization- and population dynamics in a thermal nonequilibrium situation going beyond rate-equation models and discuss the limitations of Coulomb scattering between 0D and 2D-confined quantum states. An experiment is designed which demonstrates the control of gain recovery for THz pulse trains in InGaAs QD-based SOAs under powerful electrical injection.

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