The present work concerns the study of pulsed laser systems containing a fibre amplifier for boosting optical output power. In this paper, this fibre amplification device is included into a MOPFA laser, a master oscillator coupled with fibre amplifier, usually a cladding-pumped high-power amplifier often based on an ytterbium-doped fibre. An experimental study has established that the observed nonlinear effects (such as Kerr effect, four waves mixing, Raman effect) could behave very differently depending on the characteristics of the optical source emitted by the master laser. However, it has not been yet possible to determine from the experimental data if the statistics of the photons is alone responsible for the various nonlinear scenarios observed. Therefore, we have developed a numerical simulation software for solving the generalised nonlinear Schrödinger equation with a stochastic source term in order to validate the hypothesis that the coherence properties of the master laser are mainly liable for the behaviour of the observed nonlinear effects.