Improving Performance of Higher-Order Codirectional Raman Amplifiers Using Phase-Modulated Signals -- Functional Principle

Existing unrepeatered submarine links are increasingly upgraded to the most advanced modulation format currently available for commercial applications. Quite often the use of third-order codirectional Raman amplifiers is necessary. Power fluctuations of the involved high-power pump induces phase shifts in phase modulated signals via the nonlinear Kerr effects. An approach for reducing the impact of this effect on system performance is explained in this document.