We present a numerical analysis of the impact of the optical amplification by semiconductor optical amplifiers (SOAs) in a Coherent Optical-Orthogonal Frequency Division Multiplexing (CO-OFDM) transmission link at 100 Gb/s. The numerical modeling of SOA is developed to be able to simulate all of nonlinear effects of the SOA, particularly four-wave mixing (FWM) effect. This model is integrated into a co-simulation platform to perform a simulation at a system level. Error Vector Magnitude (EVM) measurement is given with respect to the number of subcarriers and phase-amplitude coupling. We show also the dependence of the EVM at the signal wavelength by performing our simulations on a wide optical bandwidth, taking into account the main parameters of the SOA - such as the phase-amplitude coupling factor, the saturation power and the noise figure (NF) - that influence the non-linear effects.