Erbium Doped Fiber Amplifier. These optical amplifiers work much like a laser: a length of erbium-doped optical fiber is connected to a coupler so that an input signal is fed into it along a pumping wavelength. Erbium atoms inside the fiber are excited by the pump, and the signal is amplified by stimulated emission. EDFAs are of course widely used in optical telecommunications and photonics in general, the frequency band where the amplification is interesting being coincident with silicium's low absorption frequency band.