New Raman pump module for reducing pump-signal four-wave-mixing interaction in co-pumped distributed Raman amplifiers

We propose a new Raman pump module that effectively reduces four-wave-mixing (FWM) nonlinear interaction among longitudinal pump modes and wavelength-division-multiplexed (WDM) signals in co-pumped distributed Raman amplifiers based on nonzero dispersionshifted fibers (NZ-DSFs). Theory and experiments confirm that the proposed pump module structure, based on polarization- and wavelength-multiplexed Fabry-Perot lasers, allows distributed amplification with high co-propagating on-off Raman gain, providing a key technology for all-Raman-based dense-WDM ultralong-haul transmission.