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100-Petabit Internet Backbone Coming Into View
lostinbrave notes laboratory work that could lead to long-haul network cables capable of exceeding 100 Petabits per second.kilometer. "Alcatel-Lucent said that scientists at Bell Labs have set an optical transmission record that could deliver data about 10 times faster than current undersea cables, resulting in speeds of more than 100 Petabits per second.kilometer. This translates to the equivalent of about 100 million Gigabits per second.kilometer, or sending about 400 DVDs per second over 7,000 kilometers, roughly the distance between Paris and Chicago. ... The transmissions were not just faster, they were accomplished over a network whose repeaters are 20 percent farther apart than commonly maintained in such networks, which could decrease the costs of deploying such a network."
I think I read that only 10% of undersea cable capacity was/is being used. Can't get you a source, but I remember reading it when I got off on a tangent after the last undersea cable damage.
Given that optical fibre capacity is limited by dispersion (different parts of the signal travelling at different speeds, causing adjacent symbols to overlap), it's a reasonable number - both a longer distance and a faster symbol rate make the problem worse. So if this is what's limiting you, you can double the distance by halving the speed, or vice versa. Of course, that's not the only limiting factor, and IIRC some forms of dispersion don't scale proportionally with distance, so it's not the only relevant factor.