Holographic display
A holographic display is a type of display that utilizes light diffraction to create a virtual three-dimensional image.  Holographic displays are distinguished from other forms of 3D displays in that they do not require the aid of any special glasses or external equipment for a viewer to see the image.

Timeline

1947 - Hungarian scientist Dennis Gabor first came up with the concept of a hologram while trying to improve the resolution of electron microscopes.  He derived the name for holography, with "holos" being the Greek word for "whole," and "gramma" which is the term for "message."

1960 - The world's first laser was developed by Russian scientists Nikolay Basov and Alexander Prokhorov, and American scientist Charles H. Townes.  This was a major milestone for holography because laser technology serves as the basis of some modern day holographic displays.

1962 - Yuri Denisyuk invented the white-light reflection hologram which was the first hologram that could be viewed under the light given off by an ordinary incandescent light bulb.

1968 - White-light transmission holography was invented by Stephen Benton.  This type of holography was unique because it was able to reproduce the entire spectrum of colors by separating the seven colors that create white light.

1972 - Lloyd Cross produced the first traditional hologram by using white-light transmission holography to recreate a moving 3-dimensional image.

1989 - MIT spatial imaging group pioneered electroholography, which uses magnetic waves and acoustic-optical sensors to portray moving pictures onto a display

2005 - The University of Texas developed the laser plasma display, which is considered the first real 3D holographic display.

2010 - Hollow pyramid shaped prisms are released into the consumer market, which if placed over a flat screen (or smartphone), can emulate a three-dimensional image by means of 2-D light refraction.

2012 - The first holographic display is implemented in a car's interactive navigation display system.  The technology was showcased through the exclusive luxury car, the Lykan HyperSport.

2013 - MIT researcher Michael Bove predicts that holographic displays will enter the mass market within the next ten years, adding that we already have all the technology necessary for holographic displays.

2021 - Researchers at Light Field Lab have a prototype of a touchable holographic display. The company claims to use "broad-spectrum complex-amplitude dense converging wavefront".

Types of holographic displays

Laser plasma 

Laser plasma displays, developed in 2005 by the University of Texas, utilize a series of powerful lasers that focus light in desired positions in order to create plasma excitations with the oxygen and nitrogen molecules in the air.  This type of holographic display is capable of producing images in thin air, without the need for any sort of screen or external refraction media.  The laser plasma display is able to depict very bright and visible objects, but it lacks in terms of resolution and picture quality.

Micromagnetic piston display 

The piston display, invented by Belgian company IMEC in 2011, utilizes a MEMS (micro-electro-mechanical system) based structure.  In this type of display, thousands of microscopic pistons are able to be manipulated up and down to act as pixels, which in turn reflect light with a desired wavelength to represent an image.  This developing technology is currently in the prototype phase, as IMEC is still developing the mechanism that will mobilize their "pixels" more effectively.  Some of the limitations of this type of this display include the high cost, difficulty of creating large screens, and its susceptibility to mechanical failures due to the relatively large amount of moving parts (microscopic pistons).

Holographic television display 

The holographic television display was created by MIT researcher Michael Bove in 2013.  Dr. Bove used a Microsoft Kinect camera as a relatively effective way to capture subjects in a three-dimensional space.  The image is then processed by a PC graphics card and replicated with a series of laser diodes.  The produced image is fully 3-dimensional and can be viewed from all 360 degrees to gain spatial perspective.  Bove claims that this technology will be widespread by 2023, and that the technology will cost as much as today's ordinary consumer TV's.

Touchable holograms 

Touchable holograms were originally a Japanese invention that became further developed by American microprocessor company Intel.  Touchable hologram technology is the closest modern representation of the holographic displays that one might see in sci-fi movies such as Star Wars and particularly in the Star Trek television franchise.  This display is unique in that it can detect a user's touch by sensing movements in the air.  The device then provides haptic feedback to the user by sending an ultrasonic air blast in return.  In Intel's demonstration of this technology, the display was showcased representing a touchless, responsive piano.  A possible implementation for this technology would be interactive displays in public kiosks; because this type of display does not require a user to physically touch a screen, it ensures that bacteria and viruses do not get transmitted.

Technologies used

Laser 

Most modern day holograms use a laser as its light source.  In this type of hologram, a laser is shone onto a scene that is then reflected onto a recording apparatus.  In addition, part of the laser must shine directly onto a specific area of the display to act as a reference beam.  The purpose of the reference beam is to provide the recording device with information such as background light, picture angle, and beam profile.  The image is then processed to compensate for any variation in picture fidelity, and then sent to the display.

Electroholography 

Electroholographic displays are digital displays that transmit stored image data using an electromagnetic resonator.  These signals are then read by an acoustic-optic modulator and converted into a legible image and displayed on an RGB laser monitor.  Electroholographic displays hold an advantage over traditional displays in terms of picture accuracy and range of color.

Full parallax/HPO/VPO 

Full parallax holography is the process of delivering optical information in both the x and y directions.  The resulting image will therefore provide the same perspective of a scene to all viewers regardless of viewing angle.

Horizontal Parallax Only (HPO) and Vertical Parallax Only (VPO) displays only deliver optical information in two dimensions.  This method of display partially compromises the image in certain viewing angles, but it requires much less computational power and data transfer.  Because humans' eyes are positioned side by side, HPO displays are generally preferred over VPO displays, and sometimes preferred over full parallax displays due to their lesser demand on processing power.

MEMS 

MEMS technology allows holographic displays to incorporate very small moving parts into its design.  The prime example of a MEMS-enabled display is the piston display, listed in the above section.  Micropistons used in the display can behave like pixels on a computer monitor, allowing for sharp image quality.

Hologram-like display

Mitsubishi is developing a hologram-like 'aerial display'.

See also
 Holographic screen

References 

Display technology
Holography
3D imaging
Emerging technologies