[AZLiberty]

Cable "burn thru" is one possible cause of the failure. Most long US undersea fiber cables are DC powered using the ocean as a return path for the DC power.

This doesn't make sense to me. Fiber-optic cables are passive: you just shine light down them and pick it up at the other end. Or is the power for repeaters along the cable?

[ASOC]

The cable is is (from inside to out) 4 fiber strands
a Teflon wrap
a copper 'pipe' to carry voltage
another layer of Teflon. In places the cable may be unarmored and about 5/8 of an inch thick.

Armored cable can be 2 or 3 inches in diameter.

The amplifiers, which sit about every 100kM or so, are used to boost signal levels, get their power from the coper in the cable.

See my earlier post for erbium doped amplifiers - they are really quantum state energy pumps - cool sorta new (1999) tech -- also used on land based systems as well.

An interesting sidenote, since the cables from AK to CONUS are DC powered, the copper inside the cable acts almost like a 3,000 kM antenna.

During magnetic storms, system feed voltages can vary by about 100 VDC as the earths magnetic fields 'cut' the antenna and induce voltage, acting like a big generator.