Backward Raman amplification used to alleviate SRS limitations in high-density WDM systems

Stimulated Raman scattering can cause depletion of higher frequency channels by the lower frequency ones. If a high power pump source is introduced, however, with frequency higher than that of all signal channels, its Raman gain can compensate for this depletion. The authors assess this arrangement analytically and find that backward Raman amplification provides improved system efficiency for the same value of pump power in the higher input signal power region (>1 mW), and the maximum relaxation value for backward pumping is much higher than that for forward pumping at the same pump power level. Further calculated results are presented illustrating how the performance of backward pumping changes with pump power and with the position of its Raman gain peak relative to the signal channels