Effect of localized loss on distributed fiber Raman amplifiers

The effect of localized loss in fiber transmission line on DFRA has been examined using computer simulation based on the measured Raman gain coefficient. The output power level of DFRA strongly depended not only on the position of localized loss but also on the loss level. The impact was most serious when the loss point was close to the signal output side in OLA site. Therefore, it is necessary to measure OTDR trace of the transmission line to figure out the loss distribution before DFRA design or deployment. However, the Raman gain profile of DFRA can be made robust against loss change simply by balancing the C/L-band output power as long as the localized loss is outside the effective length of pump. This fact provides DFRA with design flexibility and allows the use of a fixed gain flattening filter.