May 15 2014
Giles parameters are used to design fiber amplifiers that are made of rare-earth-doped fibers.
These parameters are comprised of two wavelength-dependent factors: the gain coefficient g*(λ) of the fiber, with laser-active ions in the upper excited level, and the absorption coefficient α (λ) of the fiber, having ground state filled with laser-active ions.
Giles parameters are the function of the overlap coefficients ⎡ (λ) of the fiber modes, and the transition cross-sections of the laser transition, which are represented by the following equations:
α (λ) = σ abs (λ) ⎡ (λ) ndop
g*(λ) = σem (λ) ⎡ (λ) ndop
The above equations are derived based on the assumption that the doping concentration remains constant within a specific volume, and becomes zero outside it. while deriving the equations it is necessary to consider the additional effects resulting from excited-state absorption, and losses due to absorption and scattering in the fiber.
In general the quantities, such as the transition cross-sections of a fiber, the overlap coefficients ⎡ (λ), and the dopant concentration ndop, are difficult to determine. However, measurements of gain and absorption are directly used to derive Giles parameters.
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