Zero-dispersion wavelength
41877
141256354
2007-06-28T21:33:52Z
Gaius Cornelius
293907
Clean up using [[Project:AWB|AWB]]
In a [[single-mode optical fiber]], the '''zero-dispersion wavelength''' is the [[wavelength]] or wavelengths at which material [[dispersion (optics)|dispersion]] and [[waveguide]] dispersion cancel one another. In all [[silica]]-based [[optical fiber]]s, minimum material dispersion occurs naturally at a wavelength of approximately 1.3 µm. Single-mode fibers may be made of silica-based glasses containing dopants that shift the material-dispersion wavelength, and thus, the zero-dispersion wavelength, toward the [[minimum-loss window]] at approximately 1.55 µm. The engineering tradeoff is a slight increase in the minimum [[attenuation coefficient]]. Such fiber is called [[dispersion-shifted fiber]].
Another way to alter the dispersion is changing the core size and the refractive indices of the mateial of [[Fiber optics#Principle of operation|core]] and [[cladding]]. Because fiber optic materials are already highly optimized for low scattering and high transparency alternative ways to change the refractive index were investigated. As a straight forward solution [[tapered fiber]]s and [[holey fiber]]s or [[photonic crystal fiber]]s (PCF) were produced. Essentially they replace the cladding by air. This improves the contrast of refractive indices by a factor of 10. Therefore the effective index is changed, especially for longer wavelengths. This type of refractive index change versus wavelength due to different geometry is called [[waveguide dispersion]].
As these narrow waveguides (~1-3µm core diameter) are combined with [[ultrashort pulse]]s at the zero-dispersion wavelength pulses are not instantly destroyed by dispersion. After reaching a certain peak power within the pulse the [[non-linear refractive index]] starts to play an important role leading to frequency generation processes like [[self-phase modulation]] (SPM), [[soliton (optics)|soliton]] generation and [[soliton fission]], [[cross phase modulation]] (XPM) and others. All these processes generate new frequency components, meaning that narrow bandwidth light literally explodes in a wide range of new colours, called [[supercontinuum generation]].
The term is also used, more loosely, in [[multimode optical fiber]]. There, it refers to the wavelength at which the material dispersion is minimum, ''i.e.'' ''essentially'' zero. This is more accurately called the '''minimum-dispersion wavelength'''.
==Zero-dispersion slope==
The rate of change of dispersion with respect to wavelength at the zero-dispersion point is called the '''zero-dispersion slope'''. [[Doubly clad fiber|Doubly]] and [[Quadruply clad fiber|quadruply clad]] single-mode fibers have two zero-dispersion points, and thus two zero-dispersion slopes.
==See also==
*[[Nonzero dispersion shifted fiber]]
==References==
*[[Federal Standard 1037C]]
*Govind P. Agrawal, ''Nonlinear Fiber Optics'', 3rd ed. (Academic Press, San Diego, CA, USA, 2001), ISBN 0-12-045143-3
[[Category:Fiber optics]]