Future trends for high capacity optically amplified submarine systems

Transatlantic and transpacific links, which stretch up to 6000 km or 9000 km raise very difficult technical questions. On such large distances, amplifier noise accumulation and propagation impairment are at a maximum and tend to set natural physical limitations on the maximum data rate and on the system cost (because noise accumulation can only be controlled by increasing the number of line repeaters). At present several solutions are under study to overcome those limitations and it is the purpose of this paper to present them and underline their potential advantages and weaknesses. We first describe the main phenomena to be taken into account for transoceanic amplified link design. “NRZ system upgrade” through WDM or bit rate increase, is presented together with soliton-type systems based on line-filtering techniques, and direct optical regeneration with the help of line intensity modulation