Editing Material dispersion coefficient (section)

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In an [[optical fiber]], the '''material dispersion coefficient''', ''M''(λ), characterizes the amount of [[pulse broadening]] by material [[dispersion (optics)|dispersion]] per unit length of fiber and per unit of [[spectral width]]. It is usually expressed in [[picosecond]]s per ([[nanometre]]·[[kilometre]]). 

For many optical fiber materials, ''M''(λ) approaches zero at a specific [[wavelength]] λ<sub>0</sub> between 1.3  and 1.5 [[μm]]. At wavelengths shorter than λ<sub>0</sub>, ''M''(λ) is negative and increases with wavelength; at wavelengths longer than λ<sub>0</sub>, ''M''(λ) is positive and decreases with wavelength. 

Pulse broadening caused by material dispersion in a unit length of optical fiber is given by the product of ''M''(λ) and [[spectral width]] (Δλ).