The actual fiber data cables are just like any other, super thin like a human hair. 5 to 10 microns in diameter for the core of a single-mode fiber strand which

The actual fiber data cables are just like any other, super thin like a human hair. 5 to 10 microns in diameter for the core of a single-mode fiber strand which is used for long distances. They can carry hundreds of gigabits per second. It's not so much the fibers that allow this: the cables don't need to be replaced to increase capacity; the physics behind the cables doesn't really change, they just carry pulses of light. It's the equipment modulating the signal on both sides that is upgraded to allow for increasingly higher bandwidth. Any of the thickness past those few microns is just shielding.