Combined erbium and Raman amplification at ? in submarine links using backward pumping at ?

A preamplifier system for a submarine communication link working at is considered. It is composed of a lumped erbium-doped fibre amplifier (EDFA) backward pumped at spaced from the detector by a span length of a standard fibre. The standard fibre shows a bonus gain to the system due to stimulated Raman scattering (SRS). A theoretical model for the contributions to the gain from the EDFA and the SRS based on nonlinear rate equations of the EDFA coupled with the rate equations of the Raman amplification is studied. While the erbium amplification is calculated using a numerical technique for a backward pumping boundary value problem, the Raman gain is obtained from a straightforward non-depleted pump analytical solution of the rate equations. Numerical optimization shows that there is an optimum EDFA and standard fibre lengths that optimize the overall performance of the system. We have introduced the standard fibre lengths in the design through the definition of a new parameter, the budget improvement. The results show a good agreement with experimental results of this system.