Fiber amplifiers gain signal, not noise.
Daniel C. McCarthy, Senior Editor
Anybody who has blasted music from a cranked-up stereo system is probably familiar with the hiss emitting from the speakers between songs. The sound, which comes from the amplifier electronics, is usually forgotten with the first chords of the next track. That's because the signal power overcomes the amplifier's small noise factor.
The same thing happens on communications networks, except that they are much less tolerant of noise and require balanced design to maintain consistent signal quality...