Improvement of SPM tolerance for phase-modulated duobinary transmissions using phase modulator with postfiltering technique

We theoretically investigate self-phase modulation (SPM) tolerance of a new duobinary signals employed a phase modulator and optical filter, referred to as phase-modulated (PM) duobinary signals. For the conventional duobinary transmission (DBT) with electrical low-pass filters, fiber input power is strongly limited due to SPM. However, our results suggest that SPM tolerance can be improved while maintaining high dispersion tolerance using PM-DBT, since the signals with a constant power are transmitted over fibers. Adjusting the phase difference between mark and space levels of phase modulators, we can further improve SPM tolerance, compared with the conventional DBT.