We have analysed the output pulse characteristics of semiconductor optical amplifier (SOA). They can be modified due to the variation of input parameters, such as, gain, input pulsewidth and internal loss imposed by the medium. In our model, the effect of self-phase modulation (SPM) has taken into consideration to improve the accuracy of simulation results. The proper output pulse characteristics can be achieved by controlling the mentioned parameters. We used a simplified nonlinear Schrodinger equation (SNSE) to model the behaviour of SOAs. The SNSE is solved using the finite-difference beam propagation method (FDBPM).