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Short for erbium-doped fiber amplifier. EDFA is an optical repeater device that is used to boost the intensity of optical signals being carried through a fiber optic communications system. An optical fiber is doped with the rare earth element erbium so that the glass fiber can absorb light at one frequency and emit light at another frequency. An external semiconductor laser couples light into the fiber at infrared wavelengths of either 980 or 1480 nanometers. This action excites the erbium atoms. Additional optical signals at wavelengths between 1530 and 1620 nanometers enter the fiber and stimulate the excited erbium atoms to emit photons at the same wavelength as the incoming signal. This action amplifies a weak optical signal to a higher power, effecting a boost in the signal strength.

Fiber optic use in the 1980s required the light signals to be converted back into electronic signals at the data's final destination. EDFA removes this step from the process: all the steps of its operation are the actions of photons, so there is no conversion of optical signals to electronic signals.

Erbium had little commercial uses before the age of fiber-optic telecommunications. Now it is an important constituent of signal repeaters in long-distance telephone cables.

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