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Static cross gain saturation and dynamical small signal cross gain modulation are experimentally and theoretically investigated in order to judge the multi wavelength amplification capability of quantum dot semiconductor optical amplifiers (QD SOA). The measurements reveal the carriers in the excited states of the QDs to act as an effective reservoir, where QDs of different sizes participate in the replenishment through the indirect coupling of the excited states of all the QDs via the wetting layer. The dynamical 3 dB cross gain modulation bandwidth is presently limited to below 3.5 GHz. Thus at high data rates the cross talk between the data channels is expected to be negligible and the multi-wavelength cross talk suppression should become better the higher the bit rate is. The unique reservoir mechanism of the QD system seems to be a major advantage of QD SOA compared to conventional bulk or quantum well amplifiers.