In fiber internet, data is transmitted as light signals through thin glass or plastic fibers. These signals travel using a process called total internal reflection. 

When light moves through the fiber and hits the boundary between the fiber's core (where light travels) and the outer layer (cladding), it hits at an angle that makes it reflect back into the core instead of escaping. This angle has to be greater than a certain critical angle for total internal reflection to occur.

Because of this, the light keeps bouncing along the fiber, even if the fiber bends slightly, allowing data to travel over long distances quickly and efficiently. 

This is why fiber optic cables are so effective at delivering high-speed internet over vast distances.