Editing Gradient-index optics (section)

== Applications ==
The ability of GRIN lenses to have flat surfaces simplifies the mounting of the lens, which makes them useful where many very small lenses need to be mounted together, such as in [[photocopier]]s and [[image scanner|scanner]]s.<ref name=engineering360>{{cite web|url=https://www.globalspec.com/learnmore/optics_optical_components/optical_components/grin_lenses|title=Gradient Index Lenses Selection Guide: Types, Features, Applications|website=Engineering360|access-date=2021-07-11}}</ref> The flat surface also allows a GRIN lens to be easily optically aligned to a [[optical fiber|fiber]], to produce [[collimated light|collimated]] output, making it applicable for [[endoscopy]] as well as for ''in vivo'' [[calcium imaging]] and [[Optogenetics#Identification of particular neurons and networks|optogenetic stimulation]] in brain.<ref>{{cite web|url=https://www.mightexbio.com/in-vivo-calcium-imaging/#text-block-37|title=In Vivo Calcium Imaging: The Ultimate Guide|date=2019|access-date=2021-07-11|publisher=Mightex}}</ref>

In imaging applications, GRIN lenses are mainly used to reduce aberrations. The design of such lenses involves detailed calculations of aberrations as well as efficient manufacture of the lenses. A number of different materials have been used for GRIN lenses including optical glasses, plastics, [[germanium]], [[zinc selenide]], and [[sodium chloride]].<ref name=engineering360 />

Certain optical fibres ([[graded-index fiber|graded-index fibres]]) are made with a radially-varying refractive index profile; this design strongly reduces the [[dispersion (optics)|modal dispersion]] of a [[multi-mode optical fiber]]. The radial variation in refractive index allows for a sinusoidal height distribution of [[ray (optics)|rays]] within the fibre, preventing the rays from leaving the [[Core (optical fiber)|core]]. This differs from traditional optical fibres, which rely on [[total internal reflection]], in that all modes of the GRIN fibres propagate at the same speed, allowing for a higher temporal bandwidth for the fibre.<ref name=moore>{{cite journal|last1=Moore|first1=Duncan T.|date=1980|title=Gradient-index optics: a review |url=https://www.osapublishing.org/ao/abstract.cfm?URI=ao-19-7-1035|journal=Applied Optics|volume=19|issue=7|pages=1035–1038|doi=10.1364/AO.19.001035|url-access=subscription}}</ref>

Antireflection coatings are typically effective for narrow ranges of frequency or angle of incidence.  Graded-index materials are less constrained.<ref>{{cite journal|last1=Zhang|first1=Jun-Chao|last2=Xiong|first2=Li-Min|last3=Fang|first3=Ming|last4=He|first4=Hong-Bo|title=Wide-angle and broadband graded-refractive-index antireflection coatings|journal=Chinese Physics B|date=2013|volume=22|issue=4|page=044201|doi=10.1088/1674-1056/22/4/044201|url=http://cpb.iphy.ac.cn/fileup/PDF/2013-4-044201.pdf|access-date=13 May 2016|bibcode=2013ChPhB..22d4201Z}}</ref>

An axial gradient lens has been used to concentrate sunlight onto solar cells, capturing as much as 90% of incident light when the sun is not at an optimal angle.<ref>{{Cite web |last=Irving |first=Michael |date=2022-06-28 |title=Pyramid lenses catch light from any angle to boost solar cell efficiency |url=https://newatlas.com/energy/agile-pyramid-lenses-boost-solar-cell-efficiency/ |access-date=2022-06-28 |website=New Atlas |language=en-US}}</ref>