Filling factor,

~F,~

is a quantity measuring the efficiency of absorption of pump in the core of a double-clad fiber.D. Kouznetsov, J. V. Moloney. Highly efficient, high gain, short wavelength and power scalable incoherent diode slab-pumped fiber laser amplifier.

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Definition

The efficiency of absorption of pumping energy in the fiber is an important parameter of a double-clad fiber laser. In many cases this efficiency can be approximated with :

1- \exp\left(  - F \frac\alpha L \right) ,

where :

~S~

is the cross-sectional area of the cladding :

~r~

is the radius of the core (which is taken to be circular) :

~\alpha~

is the

absorption coefficient The linear attenuation coefficient, attenuation coefficient, or narrow-beam attenuation coefficient characterizes how easily a volume of material can be penetrated by a beam of light, sound, particles, or other energy or matter. A coefficient valu ...

of pump light in the core :

~L~

is the length of the double-clad fiber, and :

~F~

is a

dimensionless A dimensionless quantity (also known as a bare quantity, pure quantity, or scalar quantity as well as quantity of dimension one) is a quantity to which no physical dimension is assigned, with a corresponding SI unit of measurement of one (or 1) ...

adjusting parameter, which is sometimes called the "filling factor";

~0 .

The filling factor may depend on the initial distribution of the pump light, the shape of the cladding, and the position of the core within it.

Application

The large (close to unity) filling factor is important in double-clad amplifiers; it allows them to reduce the requirements for the

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of the pump and to reduce the length of the fiber laser. Such a reduction is especially important for the power scaling of various nonlinear processes, and contributions of

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to the degradation of signal. Use of the filling factor for the estimate of the efficiency of absorption of the pump in fiber lasers allows quick estimates without performing complicated numerical simulations.

Notes

Fiber optics {{Engineering-stub

Definition

Application

See also

Notes