{{Short description|Light wave manipulation}} '''Phased-array optics''' is the technology of controlling the phase and amplitude of light waves transmitting, reflecting, or captured (received) by a two-dimensional surface using adjustable surface elements. An '''optical phased array''' ('''OPA''') is the optical analog of a radio-wave phased array.<ref>{{cite journal |author = McManamon P. F. |title = Optical phased array technology |journal = Proceedings of the IEEE, Laser Radar Applications |volume = 84 |pages = 99–320 |date = May 15, 1996 |publisher = IEEE |url = http://cat.inist.fr/?aModele=afficheN&cpsidt=3024704 |accessdate = 2007-02-18 |issue = 2 |display-authors=etal}}</ref> By dynamically controlling the optical properties of a surface on a microscopic scale, it is possible to steer the direction of light beams (in an OPA transmitter<ref name="Large scale OPA">{{cite journal |author = Sun J. |display-authors=etal |title = Large-scale nanophotonic phased array |journal = Nature |volume = 493 |date = January 1, 2013 |publisher = Nature Publishing Group, a division of Macmillan Publishers Limited |issue = 195 |pages=195–199 |bibcode=2013Natur.493..195S |doi=10.1038/nature11727 |pmid=23302859|s2cid=205231845 }}</ref>), or the view direction of sensors (in an OPA receiver<ref name="OPA Rx">{{cite journal |author = Fatemi R. |display-authors=etal |title = High sensitivity active flat optics optical phased array receiver with a two-dimensional aperture |journal = Opt. Express |volume = 26 |pages = 29983–29999 |date = Nov 12, 2018 |publisher = Optical Society of America |issue = 23 |doi=10.1364/OE.26.029983 |pmid=30469879 |bibcode=2018OExpr..2629983F |url=https://authors.library.caltech.edu/91516/1/oe-26-23-29983.pdf|doi-access = free }}</ref>), without any moving parts. Phased-array beam steering is used for optical switching and multiplexing in optoelectronic devices and for aiming laser beams on a macroscopic scale.
Complicated patterns of phase variation can be used to produce diffractive optical elements, such as dynamic virtual lenses, for beam focusing or splitting in addition to aiming. Dynamic phase variation can also produce real-time holograms. Devices permitting detailed addressable phase control over two dimensions are a type of spatial light modulator (SLM).
== Transmitter == An optical phased-array transmitter includes a light source (laser), power splitters, phase shifters, and an array of radiating elements.<ref name = "NitrideOPA">{{cite journal |author = Poulton C. |display-authors=etal |title = Large-scale silicon nitride nanophotonic phased arrays at infrared and visible wavelengths |journal = Opt. Lett. |volume=42 |issue=1 |pages = 21–24 |date = 2017 |publisher = Optical Society of America |doi=10.1364/OL.42.000021 |pmid=28059212 |bibcode=2017OptL...42...21P |doi-access=free}}</ref><ref name = "HashemiOPA">{{cite journal |author = Chung S. |display-authors=etal |title = A Monolithically Integrated Large-Scale Optical Phased Array in Silicon-on-Insulator CMOS |journal = IEEE Journal of Solid-State Circuits |volume=53 |issue=1 |pages = 275–296 |date = Jan 2018 |publisher = IEEE |bibcode=2018IJSSC..53..275C |doi=10.1109/JSSC.2017.2757009|s2cid=1279064 }}</ref><ref name = "HajimiriAflatouni">{{cite journal |author = Aflatouni F. |display-authors=etal |title = Nanophotonic projection system |journal = Opt. Express |volume=23 |issue=16 |pages = 21012–21022 |date = August 4, 2015 |publisher = Optical Society of America |doi=10.1364/OE.23.021012 |pmid=26367953 |bibcode=2015OExpr..2321012A |s2cid=15059522 |doi-access=free}}</ref> The output light of the laser source is split into several branches using a power splitter tree. Each branch is then fed to a tunable phase shifter. The phase-shifted light is input to a radiating element (a nanophotonic antenna) that couples the light into free space. Light radiated by the elements is combined in the far-field and forms the far-field pattern of the array. By adjusting the relative phase shift between the elements, a beam can be formed and steered.
== Receiver==
In an optical phased-array receiver,<ref name = "OPA Rx"/> the incident light (usually coherent light) on a surface is captured by a collection of nanophotonic antennas that are placed on a 1D<ref name = "OPARx1D">{{cite conference |author = Fatemi R. |display-authors=etal |title = A One-Dimensional Heterodyne Lens-Free OPA Camera |conference = Conference on Lasers and Electro-Optics, OSA Technical Digest (2016) |pages = STu3G.3 |date = 2016 |publisher = Optical Society of America |url = http://www.osapublishing.org/abstract.cfm?URI=CLEO_SI-2016-STu3G.3 |accessdate = 13 February 2019}}</ref> or 2D<ref name = "OPA Rx"/> array. The light received by each element is phase-shifted and amplitude-weighted on a chip. These signals are then added together in the optic or electronic domain to form a reception beam. By adjusting the phase shifts, the reception beam can be steered to different directions, and light incident from each direction is collected selectively.
== Applications ==
In nanotechnology, phased-array optics refers to arrays of lasers or SLMs with addressable phase and amplitude elements smaller than a wavelength of light.<ref name="Wowk B 1996 147–160">{{cite book |author = Wowk B. |authorlink = Brian Wowk |chapter = Phased Array Optics |title = Molecular Speculations on Global Abundance |editor = B. C. Crandall |publisher = MIT Press |date = 1996 |pages = [https://archive.org/details/nanotechnology00bccr/page/147 147–160] |isbn = 0-262-03237-6 |chapter-url = http://www.phased-array.com/1996-Book-Chapter.html |accessdate = 2007-02-18 |url-access = registration |url = https://archive.org/details/nanotechnology00bccr/page/147}}</ref> While still theoretical, such high-resolution arrays would permit extremely realistic three-dimensional image display by dynamic holography with no unwanted orders of diffraction. Applications for weapons, space communications, and invisibility by optical camouflage have also been suggested.<ref name="Wowk B 1996 147–160"/>
DARPA's Excalibur program aims to provide realtime correction of atmospheric turbulence for a laser weapon.<ref>{{cite web |url=http://defense-update.com/20140307_successful-excalibur-test-brings-darpa-closer-compact-high-energy-lasers.html |title=Successful EXCALIBUR Test Brings DARPA Closer to Compact High Energy Lasers |last1=Eshel |first1=Tamir |date=7 March 2014 |website=defense-update.com |publisher=Defense Update |accessdate=9 March 2014}}</ref>
The Breakthrough Starshot organisation has proposed to use phased arrays to precisely aim and steer propulsion lasers for a hypothetical gram-scale solar sail-based craft or fleet of crafts.
==See also== * Holography * Phased array * Spatial light modulator
==References== {{Reflist}}
==External links== * [http://www.phased-array.com Phased Array Optics] *[https://www.youtube.com/watch?v=VBFsisCjpBk Animation of beam steering using phased arrays on YouTube]
{{Emerging technologies|other=yes|materials=yes}}
{{DEFAULTSORT:Phased-Array Optics}} Category:Optical devices Category:Display technology Category:Hypothetical technology