Improvements in the Linearity of Semiconductor Optical Amplifiers as External Modulators

Semiconductor optical amplifiers (SOAs) can be advantageously utilized as external modulators because they can simultaneously perform two functions: amplification and modulation. When the SOA is used in a subcarrier multiplexed system, the modulation linearity is a crucial property. In this paper, theoretical and experimental investigations are presented with the result of improved modulation linearity. By proper adjustment of the operation point and by careful optical matching, a significant improvement in the modulation linearity and also in the spurious-free dynamic range is achieved, along with high modulation sensitivity and wide bandwidth.