Erbium-Doped Fiber Amplifier (EDFA)

Techopedia explains Erbium-Doped Fiber Amplifier (EDFA)

The trace impurity is known as a dopant, and the process of inserting the impurity is known as doping or being doped. Pump lasers, known as pumping bands, insert dopants into the silica fiber at a 980 or 1480 nanometer (nm) wavelength, resulting in a gain, or amplification, in the 1550 nm range, which is the optical C-band. The 1480 nm band is usually used in amplifiers with greater power. Pump lasers operate bidirectionally.

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).

The optical fiber amplifier was invented in the early 1980s by H. J. Shaw and Michel Digonnet at Stanford University in California (U.S.).