Semiconductor optical amplifiers (SOAs) are key to GHz operation in the new optical telecommunication networks. Quantum dot (QD) based SOAs are outperforming their bulk and quantum well based competitors. The limiting factor in ultrahigh bit rate amplification is the ultrafast population recovery in the resonant level which is mainly limited by carrier capture and relaxation processes in the QD. We use pump-probe measurements resonant to the QDs confined states energies (ground and excited state) to investigate the response to a four fs-pulse train of 1 THz repetition rate. A deep insight about the capture process implied is then obtained, and direct capture from the wetting layer is identified as the dominant mechanism in the high current regime.

© 2007 IEEE

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