What are the major Difference between EDFAs requirements for Terrestrial (Land) Systems and Submarine Systems?

Terrestrial(Land) system

Submarine System

•Reliability of land-based equipment is somewhat relaxed, corresponding to  a 15-year required lifetime.

• Submarine systems are designed for a 25-year lifetime and a minimum of ship repair that imply reliability and redundancy of all the critical components.

• Terrestrial equipment should enable operation over a wide temperature range of −5, +70°C (and −40, +85°C in storage conditions). 

  This wide temperature range makes it necessary to implement cooling means for the           highest temperatures and compensation means for temperature-sensitive devices.

• In submarine amplifiers, heat is dissipated from the outer side of the repeater container into the sea. Such a container is designed in order to make the heat go through the box from the pump device to the outer side, ensuring moderate temperature in all points. Temperature of the deep sea is indeed around +5°C. Specific care is taken for repeaters located at the coast or in shallow water, in order to guarantee no pump failure while avoiding Peltier cooling. 

For reliability reasons, no glue is used on the optical path. The constant temperature of the devices and the doped fiber incorporated in the amplifier makes it possible to perfectly tailor the gain spectrum of the submerged EDFAs, owing to very accurate equalizing filters and to concatenating hundreds of amplifiers. 

• The infrastructure itself of terrestrial systems determines the actual characteristics of the amplifier that needs to cope with important variations of the span loss between two amplifier sites. In addition, for economic reasons, the amplifiers cannot be tailored to cope with this nonuniform link.

• In submarine systems, the link is manufactured at the same time as the amplifiers and much attention is paid to guarantee constant attenuation loss between amplifier values, while the amplifier has been designed to perfectly adapt to the link characteristics.

• There are high gain range (20 to 35 dB) of the amplifiers incorporated in land-based systems and allowed by the margins given on the OSNR due to the reduced total link length. 

Gain equalizers therefore compensate for much larger gain excursion values than in submarine amplifiers and should therefore be located at amplifier midstage in order not to impact their equalizing loss on the amplifier output power.

• On the contrary, such filters can be placed after the single section of doped fiber that composes the amplifier in the case of submarine applications.