The red light of a laser is coupled into the core of an optical fiber in a targeted manner (an LED is usually too weak a source to be used instead). This coupling screens the fiber and allows it to be clearly identified; by lighting up the fiber at the break, fiber breaks and damaged connectors can. An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Most are roughly the diameter of a human hair, and they may be many miles long. Fiber optic transmission systems are superior to metallic. Fiber optics is the science of transmitting data by the passage of light through thin fibers. Also, a single optical fiber can transmit signals over 60+ miles (100 kilometers), whereas attenuation – or signal degradation –.