Optical fiber transatlantic repeater reduction

From "couple hundred yards" range for early fibers to "thousands of miles without losing more than half" today, enabling sparse undersea repeater stations.

The original glass fibers, which didn't have all this great functionally graded material, might transmit light a couple hundred yards. Now we have glass fibers that will transmit light thousands of miles without losing more than half. So when you're going to bury undersea cable, you don't want to have repeater stations very often. Corning developed this process to make big rods with functionally graded glass composition that changes the index of refraction, so you always get internal reflections to keep the photons in the container of glass.

Layered fiber design (clear core + reflective cladding) enables single-shot transatlantic transmission.

When they first started doing this in the late '60s and 1970s, they would try to lay an optical fiber across the Atlantic Ocean and they'd have to have repeater stations about every 10 kilometers. They got better and better until I think you can go all the way across the Atlantic with no repeater station now, because they've improved their transmissivity by orders of magnitude. They essentially make layers — you have a central core of clear glass, but then you have layers that will reflect the light, because the light might be coming through at a slight angle. You want it to reflect back, and it just bounces down this waveguide, this light guide.