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In physics, coherence length is the propagation distance from a coherent source to a point where an electromagnetic wave maintains a specified degree of coherence. The significance is that interference will be strong within a coherence length of the source, but not beyond it. This concept is also commonly used in telecommunication engineering. Image File history File links Portal. ... The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density. ... Wave propagation refers to the ways waves travel through a medium (waveguide). ... Coherence is the property of wave-like states that enables them to exhibit interference. ... Electromagnetic radiation is a propagating wave in space with electric and magnetic components. ... In optics, correlation functions are used to characterize the statistical and coherence properties of an electromagnetic field. ... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ... Copy of the original phone of Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ...

In long-distance transmission systems, the coherence length may be reduced by propagation factors such as dispersion, scattering, and diffraction. In telecommunications, transmission is the act of transmitting electrical messages (and the associated phenomena of radiant energy that passes through media). ... Dispersion of a light beam in a prism. ... In particle physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

In optical communications, the coherence length L is given approximately by L = λ²/(n Δλ), where λ is the central wavelength of the source, n is the refractive index of the medium, and Δλ is the spectral width of the source. In telecommunications, information transfer is the process of moving messages containing user information from a source to a sink. ... The wavelength is the distance between repeating units of a wave pattern. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... Free space is the most simple and elementary electromagnetic medium. ... In telecommunication, spectral width is the wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. ...

Coherence length is usually applied to the optical regime.

Source: from Federal Standard 1037C in support of MIL-STD-188 Federal Standard 1037C entitled Telecommunications: Glossary of Telecommunication Terms is a U.S. Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ... MIL-STD-188 is a series of U.S. military standards relating to telecommunications. ...

The expression above is a frequently used approximation. Due to ambiguities in the definition of spectral width of a source, however, the following definition of coherence length has been suggested:

The coherence length is the optical path length difference of a self interfering laserbeam which corresponds to a 50% fringe visibility, where the fringe visibility is defined as V = (I_max - I_min)/(I_max + I_min) and I is the fringe intensity. In optics and telecommunication, the term optical path length has the following meanings: In a medium of constant refractive index, n , the product of the geometric distance and the refractive index. ...

Helium-neon lasers have a typical coherence length of 20 cm, while semiconductor lasers reach some 100 m. Fiber lasers can have coherence lengths exceeding 100 km. A helium-neon laser, usually called a HeNe laser, is a type of small gas laser. ... A laser diode is a laser where the active medium is a semiconductor p-n junction similar to that found in a light-emitting diode. ... A fiber laser or fibre laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium or ytterbium. ...