An optical fiber transmission system having Raman amplifier module for inputting a pumping signal into an optical fiber for stimulated Raman amplification of a first carrier signal. The Raman amplifier module includes a pump having two optical sources, wherein the first optical source emits a linear beam along a first polarization axis of polarization, and the second optical source emits another linear beam along a second polarization axis distinct from the first axis. The two beams are combined to for the pumping signal. The Raman amplifier module also includes a polarization tuning means arranged to superimpose in real time at least one of the polarization axes to a Polarization Dependant Loss axis.