Recently the performance of Semiconductor Optical Amplifiers (SOA) in 1.3μn fiber communication systems has been intensively studied and a 10 Gbit/s RZ - transmission over 500 km has been demonstrated in the field and over 1500 km in a re-circulating fiber loop set up using MQW-SOA. It turned out that the performance of such systems is primarily limited by three factors: the fast growth of Amplified Spontaneous Emission (ASE), the pattern effect and the nonlinear impulse-phase distortions in SOA which are caused by the low saturation energy of SOA, the gain recovery time comparable with the bit period and by the strong nonlinearity of SOA. The effects are also important in other systems where cascaded SOA are used, for example, as optical gates. With increasing bit rate in TDM systems and with number of channels in WDM, the effects became stronger and the maximum propagation distances decrease. So in the case of a 4×10 Gbit/s WDM system a 80 km transmission has been experimentally demonstrated and up to 200 km predicted from numerical simulations. The limiting effects and consequently the performance are similar in systems with both NRZ or RZ modulation formats. But using other modulation formats like Phase Shift Keying (PSK) or Frequency-Shift Keying (FSK), where the signal power is constant, it would be possible to avoid these specific for SOA, harmful effects and to approach the performance in the 1.5 μm window. In this paper we present the results on a single channel 10 Gbit/s Differential Binary PSK - Direct Detection (DBPSK-DD) transmission in a 1.3 μm system with in-line MQW-SOA amplifiers. The format has been chosen because of simplicity of the transmitter and receiver designs.