5. Repeater and sea connection unit

5.1 Repeater

The underwater repeater has the following specific features.

• High reliability

  The number of repeater failures must be limited to three in 25 years per link. This means that for a link of around 150 repeaters, the failure rate per hour of a repeater is 9 × 10 ^–8 i.e. 90 in 10 ⁹ h, or 90 FIT (Failure In Time ). Since the most critical components in terms of reliability are the laser pump diodes at 980 nm, these are coupled together to power a pair of EDFAs: thus, in the event of failure of one of the pump diodes, the output power of the EDFAs decreases (3 dB loss in the event of failure of 50% of the pump diodes),...