Erbium Doped Fiber Amplifier - EDFA

Optical fiber amplifier is capable of amplifying optical signals in the optical domain. This means the optical signal does not need to be converted to electrical signals. The amplification process happens inside the optical fiber when the signal passes through.

Erbium doped fiber amplifier is the most important optical fiber amplifiers. It uses a special type of fiber, with its core doped with rare earth element of Erbium ions. The Erbium ions act as the active gain medium. They absorb energy at wavelength around 980nm or 1480nm, being \"pumped up\" to higher energy state, and remain there for relatively long time. This feature enables the building up of large enough density of Erbium ions at the higher energy state. Therefore, when light at 1550nm passes through, the ions jump down to the lower energy level under \"stimulated radiation\" process, and generate identical photons at 1550nm.

When light is sent through long haul optical links, amplifiers are required to compensate the optical loss. Use of EDFA greatly simplified the systems and reduced the cost of long haul networks.

Three types of EDFAs are designed for the long haul transmission: power booster, inline amplifier and pre-amplifier. These amplifiers are used right after the transmitter, in the middle section of the optical link and right before the photodetector, respectively. The optical gain levels, noise properties, required power handling ability of the amplifiers are different with those three types of designs.

Miniature single channel (or narrow bandwidth) EDFA is usually designed with features such as compact size, low to medium power handling, low cost, etc. Normally there is only one single pump laser diode and single stage of optical fiber amplification. It is suitable to handle single channel or several DWDM channels.