Abstract : Many alternatives to classical intensity modulation schemes have recently been proposed for optical communications. Coherent systems, using the optical phase as the information carrier, have many advantages over their counterparts : better sensitivity, higher nonlinear effect tolerance. Nevertheless, they show a different behavior to noise accumulated during the propagation. The Kerr effect induces a nonlinear phase noise which limits performances.
In the first part, a fast estimation, either analytical or semi-analytical, of these fluctuations is proposed for two different cases. The results given by the moment method and the perturbation theory are compared with numerical simulations of the propagation. We have also conducted an experimental study of the influence of the dispersion map on phase noise.
In the second part, we propose and study a new modulation format based on continuous differential phase modulation to improve spectral efficiency. This format consists in modulating the optical phase with a 3 level (duobinary) signal. Its performances are compared with those of standard formats in a 10 Gbit/s recirculating loop experiment.