Optical amplifiers extend the range of repeaterless submarine systems

Erbium-doped fiber amplifiers (EDFA) have seen rapid developments in the past few years, and they fit especially well the needs of repeaterless submarine links. For these links, the demand is very strong for ever longer spans, in the range of 150 km to 350 km. The applications are in continent-island, island-island, or coastal `festooned´ links. Aside from using low-loss silica-core fiber and error-correcting codes, optical amplifiers offer a practical way to increase the power budget of repeaterless links. First, an EDFA can be used to increase the transmitter output power. At the receiver end, an EDFA can be used as a preamplifier, either at the receiver site or at some distance with remote pumping from the receiver terminal, in order to obtain a better gain/noise compromise. With erbium-doped fiber amplifiers, commercial repeaterless systems up to 300 km at 622 Mbit/s or 260 km at 2.5 Gbit/s can be implemented