Q. What is EDFA ?

ERBIUM DOPED FIBER AMPLIFIERS (EDFA)

In optical communication network, signals travel through fibers for very large distances without significant attenuation. However, when distances become hundreds of kilometers, it becomes necessary to amplify the signal during transit. Optical fiber amplifiers provide in-line amplification of optical signals by effecting stimulated emission of photons by rare earth ions implanted in the core of the optical fiber. Erbium is the preferred rare earth for this purpose though amplifiers using Praseodymium are also in use. EDFAs are used to provide amplification in long distance optical communication with fiber loss less than 0.2 dB/km by providing amplification in the long wavelength window near 1550 nm. The principle of rare earth doped fiber amplifier is the same as that of lasers excepting that such amplifiers do not require a cavity whereas a cavity is required for laser oscillation.

Advantages of EDFA are as follows:

• It provides in-line amplification of signal without requiring electronics i.e., the signal does not need to be converted to electrical signal before amplification. The amplification is entirely optical.
• It provides high power transfer efficiency from pump to signal power.
• The amplification is independent of data rate.
• The gain is relatively flat so that they can be cascaded for long distance use.

On the debit side, the devices are large, there is gain saturation and there is also presence of amplified spontaneous emission (ASE).