fiber-optic cable 
Fiber-optic cables consist of thin filaments of glass (or other transparent materials) that can 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 cables, optical fibers can transmit data greater distances without amplification. But because the glass filaments are fragile, optical fiber must be run underground rather than overhead on telephone poles.