Unrepeated WDM Transmission Systems Based on Advanced First-Order and Higher Order Raman-Copumping Technologies

We compare standard fiber Raman laser and new high-power- and low relative-intensity-noise (RIN)-copumping technologies for long-span unrepeated wavelength-division-multiplexing (WDM) transmission systems. We show that, by using enhanced forward-error-correction techniques and by optimizing the transmission-system parameters in terms of signal power per channel, dispersion map, and copropagating on- off Raman gain, both copumping technologies allow successful transmission of 8 10-Gb/s WDM channels over more than 70 dB of standard single-mode fiber. However, transmission experiments point out that only the newly proposed high-power and low-RIN lasers can guarantee realistic system margins and can potentially provide further span-reach enhancement when used in optimized higher order copumping configurations.