The present invention provides a WDM optical communication system, comprising input means and output means for an optical signal, an optical fibre path connecting signal-transmissively said input and output means, wherein the optical signal is amplified by means of Raman amplification and said optical fibre path comprises at least one Raman amplifier, further comprising WDM means for coupling at least two polarized pump radiation wavelengths with wavelengths less than the signal radiation wavelength into said Raman amplifier, wherein one pump radiation wavelength has a selected different polarization with respect to the polarization of the other pump radiation wavelengths.