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An erbium-doped fiber amplifier (EDFA) is a device that amplifies an optical fiber signal. It is used in the telecommunications field and in various types of research fields. An EDFA is "doped" with a material called erbium. The term "doping" refers to the process of using chemical elements to facilitate results through the manipulation of electrons.
The EDFA was the first successful optical amplifier and a significant factor in the rapid deployment of fiber optic networks during the 1990s.
In general, EDFA works on the principle of stimulating the emission of photons. With EDFA, an erbium-doped optical fiber at the core is pumped with light from laser diodes. This type of setup in telecom systems can help with fiber communications, for example, boosting the power of a data transmitter. An EDFA may also be used to maintain long spans of a passive fiber network and may also be used for some types of equipment testing.
Pump lasers, known as pumping bands, insert dopants into the silica fiber, resulting in a gain, or amplification. EDFA amplification occurs as the pump laser excites the erbium ions, which then reach a higher energy level. Photons are emitted as erbium ion levels decrease, or decay. This decaying process creates an interaction between the phonons and the glass matrix, which are vibrating atomic elastic structures.
The EDFA rate, or amplification window, is based on the optical wavelength range of amplification and is determined by the dopant ions' spectroscopic properties, the optical fiber glass structure and the pump laser wavelength and power. As ions are sent into the optical fiber glass, energy levels broaden, which results in amplification window broadening and a light spectrum with a broad gain bandwidth of fiber optic amplifiers used for wavelength division multiplex communications. This single amplifier may be used with all optic fiber channel signals when signal wavelengths are in the amplification window. Optical isolator devices are placed on either side of the EDFA and serve as diodes, which prevent signals from traveling in more than one direction.
EDFAs are usually limited to no more than 10 spans covering a maximum distance of approximately 800 kilometers (km). Longer distances require an intermediate line repeater to retime and reshape the signal and filter accumulated noise from various light dispersion forms from bends in the optical fiber. In addition, EDFAs cannot amplify wavelengths shorter than 1525 nanometers (nm).