EDFA's: erbium doped fiber amplifier. They're optical signal amplifiers. Due to the attenuation of the fiber, they need to be installed every so often on the fiber, under the sea. Since the equipment is cheap in comparison to the cost of repair, modern undersea amplifier boxes often contain multiple amplifiers and switchgear to MUX to a new one after it fails.
This. If you see the oceanic cables every x amount of kilometers you'll see a bump in them: that's the amplifier. There are also junction points too where cables can split off to serve locations on the route. Newer cables have the ability to dynamically reconfigure these (wavelength switching) these junctions rather than be static (the older way).
very interesting, thanks both. I'm surprised something travelling at the speed of light over a relatively short distance attenuates at all. I wonder if these amplifiers are purely optical (like mini magnifying glasses), or if they are powered (requiring running adjacent power cables)
Power is involved too. When I first visited a cable landing station I got to learn about the process to de-energize / energize the cable and coordinate with the ship and the remote side. Pretty involved but really neat to see. The stories are interesting too. One cable landing station on a small island the main tech would bring his family in during a typhoon to shelter there for days since it was a fairly protected site that had plenty of fuel for the generators.
