On gain saturation in quantum dot semiconductor optical amplifiers

We show for quantum dot (QD) semiconductor optical amplifiers (SOAs) operating in the regime where the gain is maximized, that gain saturation due to carrier depletion can be eliminated by increasing the SOA pump current density. At high pump currents, gain saturation in QD SOAs is then due to spectral hole burning. As a result, the saturation power for cw amplification can be enhanced by two orders in magnitude in QD SOAs. On the other hand, the increase of the saturation pulse energy in single pulse amplification depends strongly on the pulse duration. For pulse durations of order 100 ps, the saturation pulse energy can be increased by one order of magnitude, while a significantly smaller increase is expected for pulses of duration less than 10 ps. Simple approximate formulas are given for the gain saturation characteristics in these different regimes.