optical fiber 
A medium used for high-bandwidth data transmission in telecommunications and networking. Optical-fiber cables consist of bundles of thin glass or plastic filaments that carry beams of light. A laser transmitter encodes frequency signals into pulses of light and sends them down the optical fiber to a receiver, which translates the light signals back into frequencies. Less susceptible to noise and interference than other kinds of cable, optical fibers can transmit data for greater distances without requiring signal amplification. But because the filaments are fragile, optical-fiber cables must be run underground, which makes them expensive to install.