A fiber laser or fibre laser is a laser in which the active gain medium is an optical fiber doped with
rare-earth elements such as erbium, ytterbium, neodymium, dysprosium,
praseodymium, and thulium.
The term fiber laser is usual for the optical fiber which just provides the light of high brightness. In the case of
application of the Light Amplification by Stimulated Emission for some informational purposes, the term Doped fiber amplifier is more common.
Design and manufacturing of fiber lasers
Fiber nonlinearities, such as stimulated Raman
scattering or four-wave mixing can also provide gain and thus serve in effect as
gain media. Unlike most other types of lasers, the laser cavity in fiber laser is
constructed monolithically by fusion splicing the different types of fibers; most
notably fiber Bragg gratings replace here conventional dielectric mirrors to provide optical feedback. To pump
fiber lasers, semiconductor laser diodes or other fiber lasers are used almost exclusively.
Fiber lasers can have several kilometer-long active regions and provide very high optical gain. They can support kilowatt level
of continuous output power because the fiber's high surface area to volume ratio allows efficient cooling. The fiber waveguiding properties reduce
or remove completely thermal distortion of the optical path thus resulting in typically diffraction-limited high-quality optical beam. Fiber lasers also feature compact layout compared to
rod or gas lasers of comparable power, as the fiber
can be bent to small diameters and coiled. Other advantages include high vibrational stability, extended lifetime and
maintenance-free turnkey operation.
Many high-power fiber lasers are based on double-clad fiber. The gain medium forms
the core of the fiber, which is surrounded by two layers of cladding. The lasing mode
propagates in the core, while a multimode pump beam propagates in the inner
cladding layer. The outer cladding keeps this pump light confined. This arrangement allows the core to be pumped with a much
higher power beam than could otherwise be made to propagate in it, and allows the conversion of pump light with relatively low
brightness into a much higher-brightness signal. As a result, fiber lasers and amplifiers are
occasionally referred to as "brightness converters."
There is important question about shape of the double-clad fiber; fiber with circular symmetry seems to be worst possible
design[1][2][3][4][5] [6]. The design should allow core to be small
enough to convert the pump to only few (or even one) mode, to provide the cladding large enough to allow the confinement of pump
and to allow most of pump to be used in the core in relatively short piece of the fiber.
One of configurations of fiber lasers is the fiber disk laser]. In such a laser, the
pump is not confined in the cladding of the fiber (as in the double-clad fiber), bit
goes across the roped core many times, as it is coiled. This configuration is suitable for the power scaling, while anyway many sources of pump are used, and there is no reason to make all the pump
propagate along all the length of the fiber [7][8][9][10]
Application of fiber lasers
Applications of fiber lasers include material processing, telecommunications, spectroscopy, and medicine. The advantage of the fiber laser is that the light is already coupled into the fiber and can be
easily delivered movable focusing element. Such a coupling is important for laser cutting or laser welding or laser folding of
metals and polymers.
References
- ^ S. Bedo; W. Luthy, and H. P. Weber
(1993). "The effective absorption coefficient in double-clad fibers". Optics Communications 99: 331-335.
- ^ A. Liu; K. Ueda (1996). "The absorption characteristics of circular, offset, and rectangular double-clad fibers".
Optics Communications 132: 511–518.
- ^ Kouznetsov, D.;
Moloney, J.V. (2003). "Efficiency of
pump absorption in double-clad fiber amplifiers. 2: Broken circular symmetry". JOSAB 39 (6): 1259-1263.
- ^ Kouznetsov, D.;
Moloney, J.V. (2003). "Efficiency of
pump absorption in double-clad fiber amplifiers.3:Calculation of modes". JOSAB 19 (6): 1304-1309.
- ^ Leproux, P.; S. Fevrier, V. Doya,
P. Roy, and D. Pagnoux (2003). "Modeling and optimization of double-clad fiber amplifiers using chaotic propagation of pump".
Optical Fiber Technology 7 (4): 324-339.
- ^ D.Kouznetsov; J.Moloney
(2004). "Boundary behaviour of modes of a Dirichlet Laplacian". Journal of Modern Optics 51: 1362-3044.
- ^ K. Ueda; A. Liu (1998). "Future of High-Power Fiber Lasers". Laser Physics 8:
774-781.
- ^ K. Ueda (1999). "Scaling physics of disk-type fiber
lasers for kW output". Lasers and Electro-Optics Society 2: 788-789.
- ^ Ueda; Sekiguchi H., Matsuoka Y.,
Miyajima H. , H.Kan (1999). "Conceptual design of kW-class fiber-embedded disk and tube lasers". Lasers and
Electro-Optics Society 1999 12th Annual Meeting. LEOS '99. IEEE 2: 217-218.
- ^ Hamamatsu K.K. (2006).
"The Fiber Disk Laser explained". Nature Photonics sample: 14-15.
See also
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