The characteristics of commercial RSOA, i.e. fiber-to-fiber gain and small-signal electro-optical conversion (E/O) response are measured. A numerical model for RSOA including spatial variations of carrier density and ASE noise is established and validated via experimental tests. The auger recombination coefficient and active region bulk of commercial RSOA are determined by fitting the stimulated characteristics to the experimental results numerically. Performance of RSOA with different cross-sectional areas of active region is investigated based on the numerical model. The stimulated results indicate that reducing the cross-sectional area can increase its modulation bandwidth. RSOA 3-dB bandwidth is able to increase to 10.0GHz by optimizing its active region bulk.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.