Editing Dispersion (optics) (section)

== Material and waveguide dispersion ==
Most often, chromatic dispersion refers to bulk material dispersion, that is,  the change in [[refractive index]] with optical frequency. However, in a [[waveguide]] there is also the phenomenon of ''waveguide dispersion'', in which case a wave's [[phase velocity]] in a structure depends on its frequency simply due to the structure's geometry. More generally, "waveguide" dispersion can occur for waves propagating through any inhomogeneous structure (e.g., a [[photonic crystal]]), whether or not the waves are confined to some region.{{dubious|date=October 2014}} In a waveguide, ''both'' types of dispersion will generally be present, although they are not strictly additive.{{Citation needed|date=October 2014}} For example, in fiber optics the material and waveguide dispersion can effectively cancel each other out to produce a [[zero-dispersion wavelength]], important for fast [[fiber-optic communication]].