Ultrafast pulse-pair amplification in InGaAs quantum-dot amplifiers

Semiconductor optical amplifiers (SOAs) are important devices for optical communications being low- cost and having small size, high gain, and large amplitude and phase nonlinearities. However, slow dynamics of the gain nonlinearities in conventional bulk and quantum well SOAs (mainly due to carrier heating) usually limit the performance of these amplifiers for optical signal processing at high bit rates (>10Gb/s). Using a pump-probe differential transmission technique in heterodyne detection with sub-picosecond time resolution we have measured the GS ultrafast gain recovery dynamics in electrically-pumped InGaAs/GaAs QD SOAs operating near 1.3 mum at room temperature in the presence of a pump pulse pair. Here, we have introduced a pre-pump at a variable delay time relative to the pump pulse, which can be independently adjusted in intensity and modulated separately. The results suggest a dominant effect of an inhomogeneous distribution of recovery times, as could be expected from a microstate model, rather than the effect of ES depletion. From the application point of view, our findings indicate that a pulse sequence of 2 THz repetition rate would undergo ultrafast amplification.