Editing Volumetric display (section)

== Types ==

Many different attempts have been made to produce volumetric imaging devices.<ref>[http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2Fsearch-bool.html&r=0&f=S&l=50&TERM1=volumetric+display&FIELD1=&co1=AND&TERM2=&FIELD2=&d=ptxt US Patent Office]</ref> There is no officially accepted "[[taxonomy (general)|taxonomy]]" of the variety of volumetric displays, an issue which is complicated by the many [[permutation]]s of their characteristics. For example, illumination within a volumetric display can either reach the eye directly from the source or via an intermediate surface such as a mirror or glass; likewise, this surface, which need not be tangible, can undergo motion such as oscillation or rotation. One categorization is as follows:

=== Swept-volume display ===

Swept-surface (or "swept-volume") volumetric 3D displays rely on the human [[persistence of vision]] to fuse a series of slices of the 3D object into a single 3D image.<ref>Gately, Matthew, et al. "[https://www.osapublishing.org/viewmedia.cfm?uri=jdt-7-9-503&se.. A three-dimensional swept volume display based on LED arrays]." Journal of Display Technology 7.9 (2011): 503-514.</ref> A variety of swept-volume displays have been created.

For example, the 3D scene is computationally decomposed into a series of "slices", which can be rectangular, disc-shaped, or helically cross-sectioned, whereupon they are projected onto or from a display surface undergoing motion. The image on the 2D surface (created by projection onto the surface, LEDs embedded in the surface, or other techniques) changes as the surface moves or rotates. Due to the persistence of vision, humans perceive a continuous volume of light. The display surface can be reflective, transmissive, or a combination of both.

Another type of 3D display that is a candidate member of the class of swept-volume 3D displays is the varifocal mirror architecture. One of the first references to this type of system is from 1966, in which a vibrating mirrored drumhead reflects a series of patterns from a high-frame-rate 2D image source, such as a vector display, to a corresponding set of depth surfaces.

An example of a commercially available Swept-volume display is the Voxon VX1 from Voxon Photonics. This display has a volume area that is {{Convert|18 x 18 x 8|cm|abbr=on}} deep and can render up to 500 million voxels per second. Content for the VX1 can be created using [[Unity (game engine)|Unity]] or using standard 3D file types such as [[Wavefront .obj file|OBJ]], [[STL (file format)|STL]] and [[DICOM]] for medical imaging.

[[File:VX1 DICOM.jpg|thumb|A Voxon VX1 volumetric display showing DICOM medical data]]

=== Static volume ===

So-called "static-volume" volumetric 3D displays create imagery without any macroscopic moving parts in the image volume.<ref>Blundell, Barry G., and Adam J. Schwarz. "[https://pdfs.semanticscholar.org/10a6/a67290ee81cb339e226de35c4a58c4ab76fb.pdf The classification of volumetric display systems: characteristics and predictability of the image space]." IEEE Transactions on Visualization and Computer Graphics 8.1 (2002): 66-75.</ref> It is unclear whether the rest of the system must remain stationary for membership in this display class to be viable.

This is probably the most "direct" form of volumetric display. In the simplest case, an addressable volume of space is created out of active elements that are transparent in the ''off'' state but are either opaque or luminous in the ''on'' state. When the elements (called [[voxel]]s) are activated, they show a solid pattern within the space of the display.

Several static-volume volumetric 3D displays use laser light to encourage visible radiation in a solid, liquid, or gas. For example, some researchers have relied on two-step [[Photon upconversion|upconversion]] within a [[rare-earth]]-[[Doping (semiconductor)|doped]] material when illuminated by intersecting infrared laser beams of the appropriate frequencies.<ref>{{cite web |title = Volumetric Display |author = Joseph A. Matteo |url = http://www.stanford.edu/~matteoja/volume.html |work = Lecture notes for the Applied Vision and Imaging Systems class at [[Stanford University]] |date = 16 March 2001 |archive-url = https://web.archive.org/web/20050909205829/http://www.stanford.edu/~matteoja/volume.html |archive-date = 2005-09-09 }}</ref><ref name="Downing1996"/>

Recent advances have focused on non-tangible (free-space) implementations of the static-volume category, which might eventually allow direct interaction with the display. For instance, a [[fog display]] using multiple projectors can render a 3D image in a volume of space, resulting in a static-volume volumetric display.<ref>[https://www.youtube.com/watch?v=yzIeiyzRLCw 3D Multi-Viewpoint Fog Projection Display]</ref><ref>{{cite web |url = https://www.engadget.com/2011/03/17/3d-fog-projection-display-brings-purple-bunnies-to-life-just-in/ |author = Tim Stevens |date = 17 March 2011 |title = 3D fog projection display brings purple bunnies to life, just in time to lay chocolate eggs (video) |work = [[Engadget]] }}</ref>

<!-- Deleted image removed: [[Image:Laser plasma volumetric display.jpeg|framed|A pulsed laser creates points of glowing plasma in air]] -->
A technique presented in 2006 does away with the display medium altogether, using a focused [[pulse]]d [[infrared]] [[laser]] (about 100 pulses per second; each lasting a [[nanosecond]]) to create balls of glowing [[plasma (physics)|plasma]] at the [[Focus (optics)|focal point]] in normal air. The focal point is directed by two moving [[mirror]]s and a sliding [[lens (optics)|lens]], allowing it to draw shapes in the air. Each pulse creates a popping sound, so the device crackles as it runs. Currently it can generate dots anywhere within a cubic metre. It is thought that the device could be scaled up to any size, allowing 3D images to be generated in the sky.<ref>{{cite web |url = https://www.newscientist.com/article/dn8778-3d-plasma-shapes-created-in-thin-air.html |title = 3D plasma shapes created in thin air |date = 27 February 2006 |author = David Hambling |work = [[New Scientist]] }}</ref><ref>{{cite web |url = http://www.physorg.com/news11251.html |title = Japanese Device Uses Laser Plasma to Display 3D Images in the Air |date = 27 February 2006 |work = Physorg.com }}</ref>

Later modifications such as the use of a neon/argon/xenon/helium gas mix similar to a plasma globe and a rapid gas recycling system employing a hood and vacuum pumps could allow this technology to achieve two-colour (R/W) and possibly RGB imagery by changing the pulse width and intensity of each pulse to tune the emission spectra of the luminous plasma body.

In 2017, a new display known as the "3D Light PAD" was published.<ref>Patel, S. K.; Cao, J.; Lippert, A. R. [https://www.nature.com/articles/ncomms15239 "A Volumetric 3D Photoactivatable Dye Display"]. Nature Commun. 2017, in press.</ref> The display's medium consists of a class of photoactivatable molecules (known as spirhodamines) and digital light-processing (DLP) technology to generate structured light in three dimensions. The technique bypasses the need to use high-powered lasers and the generation of plasma, which alleviates concerns for safety and dramatically improves the accessibility of the three-dimensional displays. UV-light and green-light patterns are aimed at the dye solution, which initiates photoactivation and thus creates the "on" voxel. The device is capable of displaying a minimal voxel size of 0.68&nbsp;mm<sup>3</sup>, with 200&nbsp;μm resolution, and good stability over hundreds of on–off cycles.