An optical fiber is a glass or plastic fibre that carries light along its length without much attenuation or loss.
The glass used to make optical fibers is pure.
The repeater distances on long haul routes for optical fibers varies from 50 to 150 k
WHY OPTICAL FIBERS ?
In todays world where the spectrum of signals being communicated (Viz voice data, graphic, video, images etc) is incresing continously as also the fact that communication need is getting more & more real time, bandwidth of the communication medium is becoming more and more critical.