Re: someone explaining
"So for a US-UK fibre, the landing station in the UK might generate +1000V DC, with the 0V line from the power supply connected to the ground. Then the landing station in the US generates -1000V DC, with the 0V line from the power supply connected to the ground. "
I think you're missing a zero in those numbers - IIRC the Southern Cross cable, on its NZ to Hawaii section, feeds somewhere in the region of 12.5kV from each end.
A rough idea of the required total feed voltage (at least for the cables I'm familiar with) can be determined by the formula 'cable length'/n, where n = 50 (volts needed to power each amplifier) times 60 (km, the approximate distance between amplifiers).
Optical amplifiers are based on a short (a few metres) of optical fibre that has been doped with a small amount of Erbium atoms - hence the the fact that they are normally referred to as EDFAs - Erbium Doped Fibre Amplifier. Other dopants can be used, which produce amplifiers that have a different working frequency range.
A 'pump laser' (up to three) within the amplifier is used to excite some of the electrons in the Erbium atoms up from their normal rest energy level to a level that is two steps more energetic. The electrons which have been pushed up then almost immediately drop back one level, leaving them in the level that is one step up from their rest state - they are comparatively stable at this level. The initial drop back from the highest level generates spurious photons, which cause noise in the optical signal and limit the amount of amplification stages you can have while still retaining a workable signal to noise ratio.
The electrons that have been left sitting in a stable state, one level higher than their rest state, will, when struck by a photon from the incoming signal drop back to their rest state, in the process of which they emit a photon that is an exact copy of the signal photon that collied with them. This new photon, plus the original one, then go on to repeat the process, causing the desired signal to be amplified.
Needless to say, there's a hell of a lot of devil in the details between my simple description above and actually building a field deployable EDFA, but in any DWDM system they are probably the most common optical block present.
No, I'm not the Orange Idiot at 1600 Pennsylvania Ave., I just spent many years working for a vendor of such toys as a support engineer for DWDM systems.