[[Image:Zblan transmit.jpg|thumb|Light attenuation by ZBLAN and silica fibers]]
[[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. Attenuation coefficients 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. Attenuation is an important factor limiting the transmission of a signal across large distances. In optical fibers the main attenuation source is scattering from molecular level irregularities ([[Rayleigh scattering]])<ref>I. P. Kaminow, T. Li (2002), Optical fiber telecommunications IV, [https://books.google.com/books?id=GlxnCiQlNwEC&q&f=false&pg=PA223#v=onepage&q&f=false 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{{Citation needed|date=November 2010}}. 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.<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><ref>{{cite journal|author1=Archibald, P.S. |author2=Bennett, H.E. |name-list-style=amp |title=Scattering from infrared missile domes|bibcode=1978SPIE..133...71A|journal=Opt. Eng.|volume=17|page=647|year=1978|doi=10.1117/12.956078|s2cid=173179565 }}</ref>
