The effect of enhancing the Raman gain factor on the linearity of Raman fibre amplifiers

The authors examine, for the first time, the relationship between the Raman gain factor, K_o, and the linearity properties of a Raman fibre amplifier. It is found that the two are closely related so that if the value of K_o is enhanced for example by fibre design then, in addition to lowering the required optical pump power level, the higher value of K_o also imposes a lower value for the maximum possible output signal power from the RFA if it is to function within its linear regime as an amplifier. Consequently, a higher fibre gain factor leads to a limitation on the maximum possible linear gain for a significant range of input signal levels. This has important implications for optimising the design of Raman fibre amplifiers to be used as linear gain blocks in future fibre transmission systems