Dispersion

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

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 effect can subsequently lead to frequency-dependent path lengths, which can again act like chromatic dispersion. This is exploited e.g. in prism pairs or pairs of diffraction gratings for dispersion compensation. Angular dispersion is also related to the phenomenon of pulse front tilt.

See also: chromatic dispersion, intermodal dispersion, polarization mode dispersion, dispersion compensation, waveguide dispersion, pulse front tilt

Category: general optics

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