The efficiency of optical communication system operation is limited by the low operation rate and relatively complicated realization of electronic components. The transparent and fast optical signal processing becomes very important for the modern optical communication networks in order to overcome the electronic "bottleneck". In this work, we consider two examples of all-optical signal processing based on the unique nonlinear optical characteristics of semiconductor optical amplifiers (SOAs). We developed a theoretical model of all-optical logic gates based on quantum dot SOAs (QD-SOAs), which are the most promising candidates for up to 100 Gb/s optical networks. We also proposed a novel method of the all-optical automatic gain control (AGC) of erbium doped fiber amplifiers (EDFA) based on the application of semiconductor optical amplifiers (SOAs).