Variants and Other Applications of Erbium-doped Fiber Amplifiers
A high gain in a shorter length can be achieved with ytterbium-sensitized fibers (also called Er:Yb:glass fibers or ytterbium-codoped fibers). In addition to the erbium dopant, these contain some significant concentration of Yb3+ ions (typically much more ytterbium than erbium). Ytterbium ions may then be excited e.g. with 980-nm pump light (or even at longer wavelengths such as 1064 nm) and transfer their energy to erbium ions. For a proper choice of the material composition of the fiber core, this energy transfer can be fairly efficient. However, the use of pure erbium-doped fibers is more common in the telecom area, because ytterbium sensitization has no essential advantages here and possibly leads to a reduced gain bandwidth due to the modified chemical composition.
Erbium-doped double-clad fibers can be used for generating very high output powers of tens of watts or even more. As the pump absorption efficiency can be weak in this case, an ytterbium-sensitized core may again be useful.
It is also possible to amplify ultrashort pulses in the 1.5-μm region to relatively high energies, using EDFAs in the form of amplifier chains. One exploits the relatively high saturation energy of such amplifiers, particularly when using erbium-doped large mode area fibers.