Repeaters

A cylinder that brightens the light

Even light grows dim after a long trip through glass. So the cable has a cylinder called a repeater about every 60 to 80 km. When the faded light passes through a repeater, it becomes bright again. Crossing the Pacific, the light passes more than 100 of these repeaters.

Why?Even very clear glass soaks up a little light, just as a voice sounds quieter the farther away it is. Without repeaters, the light would become too weak to read the 1s and 0s after a few hundred kilometers.

Learn moreA repeater does not turn the light into electricity. It brightens the light as light. The electricity that runs the repeaters is sent from land through the copper in the cable. The light in the picture moves slowly, but in real life it passes this stretch in the blink of an eye — far faster, in fact.

Time

30 ms → 36 ms

Simplified route · light in glass at about 200,000 km per second