An optical fiber is an extremely thin strand of glass or plastic, about as thick as a human hair, that carries information as pulses of light. Instead of sending electrical signals through copper wires like traditional cables, optical fibers transmit data by bouncing light back and forth along their length, similar to how light reflects inside a crystal or a glass prism.

These fibers form the backbone of modern internet and telecommunications. When you stream a video, make a video call, or load a webpage, your data often travels part of its journey as light pulses through fiber optic cables buried underground or running along ocean floors. A single optical fiber can carry enormous amounts of information: millions of phone calls or thousands of high-definition video streams simultaneously.

The technology works because of a principle called total internal reflection. The fiber's glass core is surrounded by a special coating that keeps light trapped inside, bouncing along even when the fiber bends and curves. This allows optical fibers to transmit signals across vast distances with very little loss of quality, which is why internet companies advertise fiber optic internet as the fastest and most reliable connection available.

Doctors also use optical fibers in medical instruments to see inside the human body without surgery, and engineers use them in sensors to detect temperature changes or structural problems in bridges and buildings.