The saturation behavior of a quantum-dot semiconductor optical amplifier (QD- SOA) is governed by a complex combination of ground state and excited state replenishment in saturation condition. Also, due to inhomogeneously broadened gain of a QD-SOA, various spectral regions are coupled via the common quantum dot (QD) reservoir, i.e., wetting layer, and the barrier layer. Hence, a frequency domain model has been developed to effectively exhibit the saturation properties of a QD-SOA in this article. Based on performed experimental tests, and also, developed model we exploit gain dynamic, gain saturation characteristics and noise suppression capability at different SOA operation conditions. The effect of an external beam on different characteristics of QD-SOAs has been investigated experimentally when the applied beam is in the gain or transparency region of the amplifiers. Also, based on different external beam power levels, the performance of the discussed method is characterized in terms of signal- to-noise ratio at the input of the QD-SOA, and output quality factor, which directly quantifies the level of intensity noise. A comprehensive comparison is performed between the quality factor of noisy input bit stream and the output data which contains the pattern effect at higher bit rates. Finally, noise suppression specification of the device at different bias currents is discussed.