material dispersion
Material dispersion is due to the different propagation velocities and refractive indices of light waves in solids. The refractive index describes the shortening factor, the Nominal Velocity of Propagation( NVP), i.e. the reduction of the phase velocity of an electromagnetic wave in optical fibers compared to propagation in vacuum.
The velocity of propagation is due to the physical and chemical composition of the glass and causes dispersion, which depends on the wavelength.
That is why it is also called chromatic dispersion. This dispersion is also influenced by the radiation of the light source. In the case of light sources with a small spectral width, the material dispersion is very small. The material dispersion of fused silica is particularly favorable at wavelengths of 1,300 nm because its characteristic is zero at this wavelength. It is material-dependent, occurring in single- mode and multimode fiber, and depends on the doping of the core glass.
The material dispersion coefficient (M), given in `lambda`, results from the pulse broadening per unit length and the unit for the spectral width. It is usually calculated in picoseconds (ps) per (nanometer x kilometer).