Subsea Optical Amplifier Fundamentals - Part 2

Picture below shows subsea amplfiers aboard a cable ship. They cost roughly $250K a piece, can support up to 40 Tbps, and are spaced every 70 kilometers or 42 US miles. These remarks apply to these specific amplifiers.

As noted in Part 1 of this series, erbium doped fibre eliminated optical-electrical-optical (OEO) conversions for amplifiers. So the limiting factor of computer hardware involved in the conversions was eliminated. The result was a 'transparent' technology that placed no limits on submarine termination equipment upgrades. Subsea cables became highly scable because the amplifiers could easily handle higher throughput achieved via DWDM improvements.

These amplifiers are tough buggers. They must withstand severe pressure at depths as great 8,000 meters for 25 years as well as nasty seawater corrosion. The amplifier hull is generally made of titanium or a special beryllium copper alloy, C17200, which conducts heat and electricity very well and is highly resistant to salt-driven corrosion. Conducting heat is important because the pump lasers generate a lot of it. Redundancy is also the name of the game with several spare lasers backing up several active pumps.

In general, life span has been excellent. Moreover, the pumps rarely fail. So repairs of repeater units is exceptionally rare. In fact, I have never even heard of a repeater requiring repair. It just doesn't happen.

Here are references for those who wish to dig deeper into the subject:

1. https://hackaday.com/2023/08/08/under-the-sea-optical-repeaters-for-submarine-cables/

2.https://www.laserfocusworld.com/fiber-optics/article/16551090/optical-amplifiers-speed-data-flow-undersea

3.https://www.ingentaconnect.com/content/mts/mtsj/2015/00000049/00000006/art00008?crawler=true&mimetype=application/pdf