Any phenomenon in which the velocity of propagation of an electromagnetic wave is wavelength dependent. Note 1: In communication technology, "dispersion" is used to describe any process by which an electromagnetic signal propagating in a physical medium is degraded because the various wave components ( i.e., frequencies) of the signal have different propagation velocities within the physical medium. Note 2: In an optical fiber , there are several significant dispersion effects, such as material dispersion, profile dispersion, and waveguide dispersion, that degrade the signal. Note 3: In optical fiber communications , the incorrect terms "multimode dispersion" and "intermodal dispersion" should not be used as synonyms for the correct term " multimode distortion ." Note 4: In classical optics, "dispersion" is used to denote the wavelength dependence of refractive index in matter, ( dn/d , where n is the refractive index and is the wavelength) caused by interaction between the matter and light . "Dispersion," as used in fiber optic communications , should not be confused with "dispersion" as used by optical lens designers. Note 5: Three types of dispersion, relating to optical fibers, are defined as follows:
material dispersion: In optical fiber communication, the wavelength dependence of the velocity of propagation (of the optical signal ) on the bulk material of which the fiber is made. Note 1: Because every optical signal has a finite spectral width , material dispersion results in spreading of the signal. Note 2: Use of the redundant term "chromatic dispersion" is discouraged. Note 3: In pure silica , the basic material from which the most common telecommunication -grade fibers are made, material dispersion is minimum at wavelengths in the vicinity of 1.27 m (slightly longer in practical fibers).
profile dispersion: In an optical fiber , that dispersion attributable to the variation of refractive index contrast with wavelength . Profile dispersion is a function of the profile dispersion parameter.
waveguide dispersion: Dispersion, of importance only in single- mode fibers, caused by the dependence of the phase and group velocities on core radius, numerical aperture , and wavelength . ( 188 ) Note 1: For circular waveguides, the dependence is on the ratio, a / , where a is the core radius and is the wavelength. Note 2: Practical single-mode fibers are designed so that material dispersion and waveguide dispersion cancel one another at the wavelength of interest.