System evaluation of optical M-QAM modulation driven by multilevel and binary waveforms

We compare M-QAM optical modulation schemes driven by multilevel and binary electrical waveforms assuming the noise accumulated over a long-distance link. While the architecture driven by multilevel electrical signals requires a power back-off to avoid modulator nonlinearities, the option driven by binary waveforms exhibits higher intrinsic losses. The system performance is evaluated by Monte-Carlo simulation under additive noise. The results indicate that both options yield equivalent maximum system reaches. However, the architecture based on binary systems requires in general higher driving voltages.