Well, I stand corrected. I had read several articles about undersea fibre and they said that it required a repeater every few km. Looking this up, it says that modern cables can go upward of 100 km between repeaters. Across the Atlantic that still adds up though, if my electro-optical assumption were true. Second, I guessed that it was electro-optical because I know the cables carry voltage to power the repeaters. I just wasn't aware that continuous amplification was even possible, especially at the extremely high bit rates that fibre runs at. Thank you for the correction.