Editing Transparency and translucency (section)

== Optical waveguides ==
{{Main|Optical fiber}}
[[Image:Optical-fibre.svg|thumb|right|Propagation of light through a multimode optical fiber]]
[[Image:Laser in fibre.jpg|thumb|right|A laser beam bouncing down an [[Acrylic glass|acrylic]] rod, illustrating the total internal reflection of light in a multimode optical fiber]]

Optically transparent materials focus on the response of a material to incoming light waves of a range of wavelengths. Guided light wave transmission via frequency selective waveguides involves the emerging field of [[fiber optics]] and the ability of certain glassy compositions to act as a [[optical medium|transmission medium]] for a range of frequencies simultaneously ([[multi-mode optical fiber]]) with little or no [[Adjacent-channel interference|interference]] between competing wavelengths or frequencies. This resonant mode of energy and data transmission via electromagnetic (light) wave propagation is relatively lossless.{{Citation needed|date=April 2021}}

An optical fiber is a [[cylindrical]] dielectric waveguide that transmits light along its axis by the process of [[total internal reflection]]. The fiber consists of a [[core (optical fiber)|core]] surrounded by a [[Cladding (fiber optics)|cladding]] layer. To confine the optical signal in the core, the [[refractive index]] of the core must be greater than that of the cladding. The refractive index is the parameter reflecting the [[speed of light]] in a material. (Refractive index is the ratio of the speed of light in vacuum to the speed of light in a given medium. The refractive index of vacuum is therefore 1.) The larger the refractive index, the more slowly light travels in that medium. Typical values for core and cladding of an optical fiber are 1.48 and 1.46, respectively.{{Citation needed|date=April 2021}}

When light traveling in a dense medium hits a boundary at a steep angle, the light will be completely reflected. This effect, called [[total internal reflection]], is used in optical fibers to confine light in the core. Light travels along the fiber bouncing back and forth off of the boundary. Because the light must strike the boundary with an angle greater than the [[total internal reflection|critical angle]], only light that enters the fiber within a certain range of angles will be propagated. This range of angles is called the [[acceptance cone]] of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding. [[Optical]] [[waveguides]] are used as components in integrated optical circuits (e.g., combined with lasers or [[light-emitting diodes]], LEDs) or as the transmission medium in local and long-haul [[optical communication]] systems.{{Citation needed|date=April 2021}}

=== Mechanisms of attenuation ===
[[File:Silica core fiber minimum attenuation.jpg|thumb|Experimentally measured record low attenuation of silica core optical fiber. At 1,550 nm, wavelength attenuation components are determined as follows: Rayleigh scattering loss ~ 0.1200 dB/km, infrared absorption loss ~ 0.0150 dB/km, impurity absorption loss ~ 0.0047 dB/km, waveguide imperfection loss ~ 0.0010 dB/km.<ref>{{Cite journal |last1=Khrapko |first1=R. |last2=Logunov |first2=S. L. |last3=Li |first3=M. |last4=Matthews |first4=H. B. |last5=Tandon |first5=P. |last6=Zhou |first6=C. |date=2024-04-15 |title=Quasi Single-Mode Fiber With Record-Low Attenuation of 0.1400 dB/km |journal=IEEE Photonics Technology Letters |volume=36 |issue=8 |pages=539–542 |doi=10.1109/LPT.2024.3372786 |issn=1041-1135|doi-access=free |bibcode=2024IPTL...36..539K }}</ref>|260x260px]]

[[Attenuation]] in [[Optical fiber|fiber optics]], also known as ''transmission loss'', is the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. It is an important factor limiting the transmission of a signal across large distances. [[Attenuation coefficient]]s in fiber optics usually use units of dB/km through the medium due to the very high quality of transparency of modern optical transmission media. The medium is usually a fiber of [[silica glass]] that confines the incident light beam to the inside. 

In optical fibers, the main source of attenuation is [[scattering]] from molecular level irregularities, called [[Rayleigh scattering]],<ref>I. P. Kaminow, T. Li (2002), Optical fiber telecommunications IV, [https://books.google.com/books?id=GlxnCiQlNwEC&pg=PA223 Vol. 1, p. 223] {{webarchive|url=https://web.archive.org/web/20130527231335/http://books.google.com/books?id=GlxnCiQlNwEC&q&f=false&pg=PA223 |date=2013-05-27 }}</ref> due to structural disorder and compositional fluctuations of the [[Amorphous solid|glass structure]]. This same phenomenon is seen as one of the limiting factors in the transparency of infrared missile domes.<ref>{{cite journal|author1=Archibald, P.S.  |author2=Bennett, H.E. |editor-first1=Stephen A. |editor-first2=Geoffery |editor-last1=Benton |editor-last2=Knight |name-list-style=amp |title=Scattering from infrared missile domes|bibcode=1978SPIE..133...71A|journal=Opt. Eng.|series=Optics in Missile Engineering |volume=17|page=647|year=1978|doi=10.1117/12.956078|s2cid=173179565 }}</ref> Further attenuation is caused by light absorbed by residual materials, such as metals or water ions, within the fiber core and inner cladding. Light leakage due to bending, splices, connectors, or other outside forces are other factors resulting in attenuation. At high optical powers, scattering can also be caused by nonlinear optical processes in the fiber.<ref>{{cite journal|author=Smith, R.G.|title=Optical power handling capacity of low loss optical fibers as determined by stimulated Raman and Brillouin scattering|journal=Appl. Opt.|volume=11|issue=11|pages=2489–94|year=1972|doi=10.1364/AO.11.002489|pmid=20119362|bibcode=1972ApOpt..11.2489S}}</ref>