(Erbium-Doped Fiber Amplifier) A device that boosts the signal in an optical fiber. Introduced in the late 1980s, the EDFA was the first successful optical amplifier. It was a major factor in the rapid development of fiber-optic networks in the 1990s, because it extended the distance between costly regenerators. In addition, an EDFA amplifies all the channels in a WDM signal simultaneously, whereas regenerators require optical to electrical conversion for each channel.A Laser Without MirrorsFunctioning like a laser without mirrors, the EDFA uses a semiconductor pump laser to introduce a powerful beam at a shorter wavelength into a section of erbium-doped fiber several meters long. The pump light excites the erbium atoms to higher orbits, and the input signal stimulates them to release excess energy as photons in phase and at the same wavelength. EDFAs boost wavelengths in the 1550 nm range, and the pump light is typically 1480 nm or 980 nm. See EDWA, WDM, Raman amplifier and optical amplifier.
A type of amplifier used in fiber optic transmission systems (FOTS) and comprising a short length of fiber that has been doped with erbium and spliced into the operating single-mode fiber (SMF) in a configuration known as discrete amplification, or lumped amplification. A three-port wavelength division multiplexer (WDM) is used, with one incoming port connected to the operating fiber carrying the primary signal in the 1550 nm window, one incoming port attached to a pump laser operating at 980 nm or 1480 nm, and the one outgoing port connected to the operating fiber (see Figure E-2).The pump laser excites the erbium atoms.Weak incoming light from the operating system causes the erbium atoms to drop from their excited state. As they do so, they release the extra energy, which transfers to the primary signal and amplifies it. An EDFA can simultaneously amplify a number of wavelengths in an operating range around 1550 nm, which is in the optical C-Band.A single-pump EDFA involves a pump laser on the upstream side of the erbium-doped fiber section and provides a gain varying from +10 dB (1,000%, or 10:1), to as much as approximately +17 dB (approximately 8,000 percent, or 80:1). A double-pump EDFA involves one pump laser on the upstream side and another on the downstream side of the erbium-doped fiber section, and provides a gain of close to 30 dB (100,000 percent, or 1,000:1). Note: The pump lasers can operate in either direction. Optical isolators, placed on both sides of the EDFA, act like diodes, serving to prevent optical signals from traveling in more that one direction. EDFAs are highly effective and less costly than optical repeaters, but generally are limited to no more than 10 spans over a total distance of 800 km or so. At that point a repeater must be applied to retime and reshape the signal, thereby filtering out the accumulated noise caused by various forms of dispersion. EDFAs are further limited by their inability to amplify wavelengths shorter than 1525 nm. An EDFA performs a type of amplification known as lumped amplification, as it is concentrated in a single point. See also amplifier, C-Band, diode, dispersion, dopant, erbium, FOTS, lumped amplification, noise, repeater, SMF, WDM, and window.