An optical transmission system having optical fibres having dispersion of alternate sign greater, in absolute value, than 1 ps/(nm km) arranged in an optical path in accordance with a dispersion map appropriate for the transmission of DM solitons at a wavelength λc. The system has a transmission station and a receiver station connected to the optical path. The transmission station launches on the optical path at least a first optical pulse RZ. At least one phase conjugation device is located along the optical path to invent the spectrum of at least the first pulse. This phase conjugation device is located in a chirp cancellation portion of the optical path which includes a point at which the chirp of a DM solition of wavelength λc is cancelled out.