COMBINED ERBIUM AND RAMAN AMPLIFICATION AT 1.55 MU-M IN SUBMARINE LINKS USING BACKWARD PUMPING AT 1.48 MU-M

A preamplifier system for a submarine communication link working at 1. 55 mu m is considered. It is composed of a lumped erbium-doped fibre a mplifier (EDFA) backward pumped at 1.48 mu m 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 theore tical model for the contributions to the gain from the EDFA and the SR S based on nonlinear rate equations of the EDFA coupled with the rate equations of the Raman amplification is studied. While the erbium ampl ification is calculated using a numerical technique for a backward pum ping boundary value problem, the Raman gain is obtained from a straigh tforward non-depleted pump analytical solution of the rate equations. Numerical optimization shows that there is an optimum EDFA and standar d fibre lengths that optimize the overall performance of the system. W e have introduced the standard fibre lengths in the design through the definition of a new parameter, the budget improvement. The results sh ow a good agreement with experimental results of this system.