Four wave mixing in ultra long transmission systems incorporating linear amplifiers

This paper examines the impact of four wave mixing on a typical transoceanic system consisting of erbium doped fibre amplifiers (EDFAs), dispersion shifted fibre, and a multiplex of four coherent channels. The constraints imposed upon the system by this effect are discussed, and comparisons made with the constraints imposed by other effects, such as the noise performance of the EDFA chain. Theoretical considerations show that ultralong span systems could be operated with less than 1dB penalty if the signal phases were misaligned adequately at each amplifier output