EDFA (Erbium Doped Fiber Amplifier) is a kind of fiber optic amplifier which used to re-amplify an attenuated signal without converting the signal into electrical form. Fiber amplifiers are developed to support dense wavelength division multiplexing (DWDM) and to expand to the other wavelength bands supported by fiber optics. EDFA fiber optic amplifiers function by adding erbium, rare earth ions, to the fiber core material as a dopant; typically in levels of a few hundred parts per million. The fiber is highly transparent at the erbium lasing wavelength of two to nine microns. When pumped by a laser diode, optical gain is created, and amplification occurs.