RSOA is considered a strong candidate to play an important role in realizing the next generation WDM PON, based on the wavelength reuse concept. Therefore, accurate and efficient modeling of RSOA is of significant importance. We present a time-domain wideband model for simulation of spatial and temporal distribution of photons and carriers in a bulk RSOA. A trade-off between the accuracy and the computational efficiency of the model is studied. Multi-objective genetic algorithm is utilized for parameter extraction. Experimental validation has been performed for continuous wave input, NRZ and QPSK signaling pulses up to 40 Gb/s of bit rate, in both amplification and remodulation regimes. Saturation, noise, chirp and signal broadening are successfully predicted, while reducing the computational time compared to other wideband models.