We present an experimental and computing analysis of the nonlinear distortions of an all-optical radiofrequency mixer based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA). Such an all-optical mixer is well suited for radio-over-fiber (RoF) applications. The simulation results are based on a SOA model developed under ADS™ software and are compared to experimental results in various cases. The good correlation between experimental and simulation results permits to demonstrate the ability of our SOA model to study mixing phenomenon by using a Harmonic Balance (HB) simulation method. Optical third-order input intercept point (IIP3) and its electrical equivalent are determined experimentally and by simulation with a good concordance. An optical IIP3 of ? dBm and a spurious free dynamic range (SFDR) of 85.7 dB/Hz^2/3 are obtained for a radiofrequency signal at 1 GHz. Moreover, simulations show that the IIP3 increases, all other parameters being equal, when the SOA active zone is shortened.