定义：
光频率或传播模式对介质中相速度存在影响的效应。

色散具有多种类型，它们都涉及到在介质或者器件中光的相速度或者相位延迟与某些参数有关： 

• 色散(Chromatic-dispersion)，相速度与光频率或者波长有关。可能来自于折射率与频率有关，或者波导色散。 
• 模间色散，来自于波导（多模光纤）中高阶横向模式传播常数的差别。这会极大的限制采用多模光纤的光纤通信系统中的数据速率。 
• 偏振模式色散，来自于与偏振态有关的传播特性。采用单模光纤的光纤链路中，当数据传输速率很高时该效应比较明显。 
• 由于存在色散（Chromatic dispersion），光表面的折射角也会与频率有关，产生角色散。这一效应导致光程与频率相关，同时又带来色散。可以采用棱镜对或者衍射光栅对进行色散补偿。角色散与脉冲前沿倾斜有关。

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

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.