Dispersion(色散)

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:

• Chormatic dispersion (波长色散) 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 (模间色散) 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 （偏振模色散）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.