Filling factor,

~F,~

is a quantity measuring the efficiency of absorption of pump in the core of a

double-clad fiber Double-clad fiber (DCF) is a class of optical fiber with a structure consisting of three layers of optical material instead of the usual two. The inner-most layer is called the ''core''. It is surrounded by the ''inner cladding'', which is surr ...

.D. Kouznetsov, J. V. Moloney. Highly efficient, high gain, short wavelength and power scalable incoherent diode slab-pumped fiber laser amplifier. IEEE Journal of Quantum Electronics, v.39, No.11, p.1452-1461 (2003)

Definition

The efficiency of absorption of pumping energy in the fiber is an important parameter of a

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 val ...

of pump light in the core :

~L~

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

~F~

is a

dimensionless Dimensionless quantities, or quantities of dimension one, are quantities implicitly defined in a manner that prevents their aggregation into units of measurement. ISBN 978-92-822-2272-0. Typically expressed as ratios that align with another sy ...

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

brightness Brightness is an attribute of visual perception in which a source appears to be radiating/reflecting light. In other words, brightness is the perception dictated by the luminance of a visual target. The perception is not linear to luminance, and ...

of the pump and to reduce the length of the fiber laser. Such a reduction is especially important for the

power scaling Power scaling of a laser is increasing its output power without changing the geometry, shape, or principle of operation. Power scalability is considered an important advantage in a laser design. This means it can increase power without changing outs ...

of various nonlinear processes, and contributions of stimulated scattering 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