One of the most important technical advances in fiber optic telecommunication systems has been the optical fiber amplifier (OFA). The use of an all-optical fiber optic amplifier instead of a semiconductor optical amplifier has many inherent advantages. For example, the most popular erbium-doped fiber amplifiers (EDFAs) have a broad range of optical amplification in the 1550-nm window; these erbiumdoped fibers are easy to incorporate directly into an allâfiber optic telecommunication system. Today the erbium-doped silica fibers are the most common rare-earth (RE)-doped fiber amplifiers, as they have high gain and low noise. EDFAs are quite versatile in that they may be used as preamplifiers, in-line and booster amplifiers, as well as sources. They can provide more than 20 dB of gain across a broad wavelength band, which enables them to be extremely useful as components in dense wavelength-division multiplexed (DWDM) systems. Additionally, they may be pumped with 800-, 980-, and 1480-nm sources and their quantum efficiency can be quite high.
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