Which phenomenon explains why optical fibers can transmit signals over long distances?

Optical fibers transmit signals over long distances primarily due to total internal reflection. This phenomenon occurs when light travels from a denser medium, such as glass or plastic, into a less dense medium (like air) at a sufficiently shallow angle. When the angle of incidence exceeds a specific threshold known as the critical angle, all of the light is reflected back into the denser medium instead of passing through the boundary. This allows for the continuous reflection of light within the fiber, preventing signal loss and ensuring that data can be transmitted efficiently over long distances.

The structure of optical fibers, which consists of a core with a high refractive index surrounded by a cladding with a lower refractive index, is designed to facilitate this total internal reflection, thereby enabling effective signal transmission in telecommunications and other applications. The ability to keep the light within the fiber ensures that even over long stretches, the signal remains strong and intact.