Semiconductor Optical Amplifier-Enabled Intensity Modulation of Adaptively Modulated Optical OFDM Signals in SMF-Based IMDD Systems

Detailed numerical investigations of the transmission performance of adaptively modulated optical orthogonal frequency division multiplexed (AMOOFDM) signals are undertaken, for the first time, in optical amplification- and chromatic dispersion compensation-free SMF IMDD systems using semiconductor optical amplifiers (SOAs) as intensity modulators. A theoretical model describing the characteristics of the SOA-based intensity modulators is developed, based on which optimum SOA operating conditions are identified. It is shown that the optimized SOA-based intensity modulators support a 30 Gb/s AMOOFDM signal transmission over a 80 km SMF, which doubles the transmission performance offered by directly modulated DFB lasers. The aforementioned performance enhancement is mainly due to a considerable reduction in the frequency chirp effect, resulting from the strong SOA gain saturation-induced decrease in SOA effective carrier lifetime. Relatively low extinction ratio and clipping of the SOA modulated signals are identified to be the key factors limiting the maximum achievable AMOOFDM transmission performance. In addition, results also indicate that both the optimum SOA operating conditions and the AMOOFDM transmission performance are insusceptible to variations in SOA parameters.