Early systems had short range but later ones used fibers that are more transparent

Early systems had short range but later ones used fibers that are more transparent. Since the light does not leak out of the fiber, the light can go a long distance before the signal gets too weak. This is used to send telephone and internet signals within and between cities. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world.

Most optical communication systems have electrical connections. An electric signal controls a transmitter. The transmitter converts the electric signal to a light signal and sends it through the fiber to the receiver. The receiver converts the light signal back to an electric signal.
fiber cable installer
A TOSLINK plug
Fiber is sometimes used for shorter links too, such as to carry the sound signals between a compact disc player and a stereo receiver. The fibers used for these short links are often made of plastic which is less transparent. TOSLINK is the most common type of optical plug for stereos.