WDM optical transmission system and WDM optical transmission method

A WDM optical transmission system in which a WDM signal light including at least one intensity-modulated optical signal and at least one phase-modulated optical signal is transferred via an optical transmission path;

• said WDM optical transmission system comprising:
• an optical waveform detecting section which detects an optical waveform of the intensity-modulated optical signal adjacent to the phase-modulated optical signal in a wavelength range;
• a signal processing section which determines a state of phase modulation of said phase-modulated optical signal affected by said adjacent intensity-modulated optical signal in said optical transmission path, based on the optical waveform detected by said optical waveform detecting section, and calculates a phase modulation drive waveform capable of canceling the phase modulation;
• and
• a phase modulating section which additionally phase-modulates said phase-modulated optical signal synchronously with said adjacent intensity-modulated optical signal, according to the drive waveform calculated by said signal processing section.