Pump-pump four-wave mixing in distributed Raman amplified systems

This paper describes the four-wave mixing (FWM) interaction of several Raman pumps and its effect on optical-signal-to-noise ratio and Raman gain. In this paper, the modeling of the combined Raman and FWM effects is explained and is used for the impairment investigation. We compare the relative importance of amplifier parameters. In particular, the paper shows how wide pumps increase the regions of forbidden zero-dispersion wavelength and increase the penalty regions in the signal band. Fiber parameters beyond zero-dispersion wavelength (dispersion slope, effective area, and Rayleigh scattering) are also investigated but show little impact. Finally, the paper considers nonuniform spans and shows that the use of short cables makes pump-pump FWM a likely problem.