Erbium Doped Fiber Amplifier
Erbium Doped Fiber Amplifier (EDFA) is an optical amplifier that amplifies a modulated laser beam directly, without optoelectronic or electro-optical conversion. The device uses a short length of optical fiber doped by rare-earth element erbium. When the signal-carrying laser beams pass through this fiber, external energy is applied, usually at Infra Red wavelengths. This is so called pumping excites the atoms in the erbium-doped section of optical fiber, increasing the intensity of the laser beams passing through.
Erbium doped fiber amplifier consist of the core material that is a glass based on SiO3-GeO2 and some other glass forming oxides such as Al2O3. The most popular optical amplifier is based on the erbium (Er3+ ion) doped amplifier (EDFA). The core region of an optical fiber is doped with Er3+ ions. Other rare earth ion dopants can also be used such as a neodymium (Nd3+).
Optical amplifiers use external current injection to excite electrons to higher energy levels which it called optical pumping. In this process, one uses photons to directly raise electrons into excited states. EDFA works in three energy levels. The top energy level to which the electron is elevated must lie energetically above the desired lasing level.
References :
Agrawal, G.P. (2002), Fiber-Optic Communication Systems, 3rd edition, John Wiley and Sons, New York
Rahmasari, Lita (2008), Study of Amplification on Erbium Doped Fiber Amplifier, Thesis, Universiti Teknologi Malaysia, Johor Bahru