Fiber is already used in: 90% of all long distance telephony; 50% of all local telephony; most CATV networks; most LAN (computer network) backbones and many video surveillance links. Optical fiber is comprised of a light carrying core surrounded by a cladding which traps the light in the core by the principle of total internal reflection. Fiber optic systems transmit using infrared light, invisible to the human eye, because it goes further in the optical fiber at those wavelengths.