The polarization dependence of the gain dynamics in a bulk semiconductor optical amplifier is examined using two experimental setups. The first experimental investigation is based on four-wave mixing. Using a low-pass filter model it is possible to retrieve information on the polarization dependence of the linewidth enhancement factors and recovery timeframes associated with carrier density pulsation and carrier heating, respectively. These experimental results have been confirmed using a second setup. Linearly polarized pulses (2 ps) are launched into the same SOA as a function of the angle of injection. The propagated pulse is analyzed in the frequency and time domains using the frequency resolved optical gating technique. It is found that the SOA presents a polarization dependence when the device is in the non-linear regime.