Dispersion

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Definition: the dependence of the phase velocity in a medium on the optical frequency or the propagation mode

More specific terms: chromatic dispersion, group delay dispersion, intermodal dispersion, polarization mode dispersion, waveguide dispersion

Category: article belongs to category general optics general optics

DOI: 10.61835/9vk Cite the article: BibTex plain text HTML Link to this page LinkedIn

There are various different types of dispersion, which all involve the dependence of the phase velocity or phase delay of light in some medium or device on some other parameter:

Chromatic dispersion means that the phase velocity depends on the optical frequency or wavelength. This can result from a frequency-dependent refractive index, but also from waveguide dispersion.
Intermodal dispersion results from different propagation characteristics of higher-order transverse modes in waveguides, such as multimode fibers. This effect can severely limit the possible data rate of a system for optical fiber communications based on multimode fibers.
Polarization mode dispersion results from polarization-dependent propagation characteristics. It can be relevant in high data rate fiber-optic links based on single-mode fibers.
As a result of chromatic dispersion, refraction angles at optical surfaces can be frequency-dependent, leading to angular dispersion. This is exploited e.g. in spectrometers with prism pairs or pairs of diffraction gratings. Also, one can obtain frequency-dependent path lengths, which can again act like chromatic dispersion. In that way, prism pairs and pairs of diffraction gratings can be used for dispersion compensation. Angular dispersion is also related to the phenomenon of pulse front tilt.

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