定义：
在活性掺杂光纤中考虑吸收和放大过程后的光谱数据。
 
为了表征采用稀土掺杂光纤的光纤放大器的性质，通常需要采用Giles参数。它包含两个与波长相关的量：在激光活性离子都处于基态时光纤的吸收系数 α(λ) 和离子都处于上能级时光纤的增益因子g*(λ) （*表示完全被激发的光纤）。 

Giles参数与激光跃迁的跃迁截面还有光纤模式的交叠系数 Γ(λ)直接相关： 
 
 
得到这个方程时，我们假设了掺杂浓度在某个区域内常数，而区域外则是0。但是，这也可以适用于掺杂浓度曲线很平滑的情况。 

得到这个方程同样也假设了只考虑某一波长范围内的激光跃迁对增益或者损耗的贡献。光纤的寄生背景损耗（吸收和散射）是单独考虑的。另外也要考虑激发态吸收产生的附加效应。 
 

图1：掺铒光纤的Giles参数。 
实际中，得到确切的掺杂浓度ndop，交叠系数Γ(λ) 和光纤的跃迁截面是比较困难的。但是，可以通过测量吸收和增益直接得到Giles系数（采用增益得到的一个困难就是，在很多时候激光活性离子没有全部被激发）。这样放大器模型可以直接基于Giles参数，而不是此阿勇一些不能准确得到值的参数如， ndop, Γ(λ), σabs(λ) 和 σem(λ)。

Definition: spectroscopic data concerning absorption and amplification in an active fiber

For modeling the performance of fiber amplifiers made from rare-earth-doped fibers, so-called Giles parameters are often used. These comprise two wavelength-dependent quantities: the absorption coefficient α(λ) of the fiber with all laser-active ions in the ground state, and the gain coefficient g^*(λ) for the fiber with all laser-active ions in the upper laser level. (The star may be interpreted as indicating the fully excited fiber.)

The Giles parameters are directly related to the transition cross sections of the laser transition and the overlap coefficients Γ(λ) of the fiber modes with the doped core:

These equations are based on the assumption that the doping concentration is constant within the fiber core and zero outside it. However, the overlap factor can be generalized for smooth doping profiles.

Of course, the equations are based on the assumption that only the laser transition contributes to gain or loss in the considered wavelength range. Parasitic background losses due to absorption and scattering in the fiber may be treated separately. Possible additional effects from excited-state absorption should be kept in mind.

Figure 1: Giles parameters of an erbium-doped fiber.

In practice, it is often difficult to precisely determine the dopant concentration n_dop, the overlap coefficients Γ(λ) and the transition cross sections of a fiber. However, the Giles parameters can be obtained directly from measurements of absorption and gain. Simple amplifier models may then directly be based on the Giles parameters rather than on the not precisely known values of n_dop, Γ(λ), σ_abs(λ) and σ_em(λ).

A difficulty for the measurement of gain (g^*) is that one will usually not achieve full excitation of the laser-active ions. Even if one knew the actually achieved fraction of excited ions, one could generally not simply scale up the gain for full excitation, since for the frequently used quasi-three-level transitions the spectral shape of the net gain is influenced by reabsorption effects and thus varies with the degree of excitation.

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