<p>Reflective semiconductor optical amplifiers (RSOA) are widely used in wavelength-division-multiplexed passive optical networks (WDM-PON). RSOAs in optical network units (ONUs) are operated in the gain saturation region so that the amplitude squeezing effect can be used to erase the information on downstream signals, however, the upstream signals go through the same RSOA need to be amplified.</p> <p>In order to use one RSOA to satisfy the need of erasing the information on downstream signal by using amplitude squeezing effect and amplifying the upstream signal at the same time, an asymmetric RSOA design is proposed and demonstrated in this thesis. The ridge width becomes narrower along the traveling direction of the downstream signal so that the downstream signal can be amplified in the saturation region of the RSOA. At the same time, the ridge width increases in the traveling direction of the upstream signal, so that the modulated upstream signal can be amplified by the asymmetric RSOA. In this thesis, I mainly focus on the designing of the structure of the RSOA to enlarge the gain difference between upstream and downstream gain. Difference between wide end and narrow end effective indices, cavity length, the way that effective index changes from the wide end to the narrow end and bias current are factors that can affect the gain difference. How the device performance is affected by the factors were analyzed. An optimized structure of asymmetric RSOA is then proposed according to the effects of the factors. The performance of the asymmetric RSOA, including gain dynamic performance, saturation output power, and upstream output power, is compared with symmetric RSOA. The asymmetric RSOA shows better performance in erasing the downstream signal information as well as amplifying upstream signal.</p> / Master of Applied Science (MASc)