Zero Dispersion Wavelength
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The zero dispersion wavelength, e.g. of an optical fiber, is the wavelength where the group delay dispersion (second-order dispersion) is zero. For standard telecom fibers, this wavelength is ≈ 1.3 μm, but by employing designs with modified waveguide dispersion it is possible to shift the zero dispersion wavelength to the 1.5-μm region (→ dispersion-shifted fibers). The dispersion is anomalous for wavelengths longer than the zero dispersion wavelength, and normal for shorter wavelengths.
For photonic crystal fibers with small mode areas, which can exhibit particularly strong waveguide dispersion, the zero dispersion wavelength can be shifted e.g. into the visible spectral region, so that anomalous dispersion is obtained in the visible wavelength region, allowing for, e.g., soliton transmission. Photonic crystal fibers as well as some other fiber designs can exhibit two or even three different zero dispersion wavelengths.
Operation of a telecom system around the zero dispersion wavelength greatly reduces dispersive broadening. At the same time, however, the signals become relatively sensitive to optical nonlinearities of the fiber, such as four-wave mixing, which can be phase matched under these conditions. It is therefore not always advantageous to operate in this regime; an improved approach is dispersion management in the form of alternatively using fibers with different dispersion.
In other situations, phase matching of nonlinearities near the zero dispersion wavelength can be useful for nonlinear devices, such as optical parametric oscillators based on the χ(3) nonlinearity of optical fibers. Also, supercontinuum generation can lead to particularly broad optical spectra when the pump light has a wavelength near the zero dispersion wavelength.
See also: chromatic dispersion, fibers, dispersion-shifted fibers, photonic crystal fibers
and other articles in the categories fiber optics and waveguides, general optics
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