Semiconductor optical amplifier (SOA) is a favorable element like booster or pre-amplifier in most optical communication networks. In this paper SOA is used as nonlinear element to induce phase difference between data pulses. Switching characteristics are investigated by using a numerical method that describes the dynamic gain response of the SOA to ultrashort optical pulses. By reducing the input pulsewidth to subpicosecond regime, higher speeds and capacities for the optical telecommunications can be achieved.