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 x 10-Gb/sWDM 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.