An Erbium Doped Fiber Amplifier

What is an EDAF? An Erbium Doped Fiber Amplifier (EDFA) consists of a piece of fiber of length L, whose core is uniformly doped with Erbium ions.

Such ions can be thought of as simple two-level systems, i.e., they can have only two energy states: 1) a fundamental state and 2) an excited state. A strong ``pump'' laser light at the proper wavelength (usually 980 nm or 1480 nm) is propagated into the core of the fiber in order to excite its ions. Excited ions, when ``hit'' by an input ``signal'' photon, have a certain probability (depending on the wavelength of the input photon) of releasing by stimulated emission a photon identical to the hitting one. The release of the energy of the stimulated photon brings the excited ion to its fundamental state. Hence from one input ``signal'' photon we can obtain, by an avalanche process along the fiber core, an average of G photons at the fiber output, i.e., the signal photon has been amplified by a factor G, known as the Gain.

June 17, 2011

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