coherence length

Any self-luminous body that emits visible light, UV light, or infrared light emits individual beams of light that remain coherent over a certain distance before diverging.

This light effect states that the light waves are coherent and follow each other at the same distance and phase. The distance to which these conditions are maintained is called the coherence length.

In long-distance transmission systems, the coherence length can be reduced by delay factors such as dispersion, scattering and diffraction. In optical transmission systems, the coherence length is the ratio of the square of the wavelength and the refractive index of the optical fiber and the spectral width of the light source.