A Semiconductor Optical Amplifier is essentially a laser diode (LD) with no feedback from its input and output ports and hence is also referred to as a Traveling-Wave Amplifier (TWA). SOAs have proven to be versatile and multifunctional devices that are key building blocks for optical networks. Semiconductor Optical Amplifiers should have the highest gain appropriate to the application. Wide optical bandwidth is also desirable so that the Semiconductor Optical Amplifier (SOA) can amplify a wide range of signal wavelengths.