Fiber optics. A pair of forceps holds a fiber optic filament, while other filaments can seen in the background. Spots of colored light appear at the end of a bundle of filaments from a fiber-optic cable. Each filament (less than 1mm in diameter) is made from coated hollow glass which is flexible and has a high refractive index. A light beam entering the end of the optical fiber is internally reflected along the cylindrical surface of the core, thus traveling along the length of the fiber with little or no absorption. Fiber-optic cables can carry enormous quantities of data in digital form at the speed of light, making them invaluable in telecommunications and computing. They are used in a variety of imaging systems, including medical endoscopes, and to relay telephone or computer network data encoded as laser signals.