Three-dimensional, holographic displays have been a dream of technophiles for decades, and there’s been a lot of progress in the last few years, from Microsoft’s Holoflector prototype to efforts at movies.
Concept devices and scientific research is one thing, but a consumer device is another. For that to happen, holograms have to be as cheap as current display technologies and so far they aren’t. But now a group of MIT researchers have found a way to develop the core electronics for a holographic display at a cost of about $10. Other devices costs thousands of dollars.
The idea came from Daniel Smalley, a graduate student in MIT’s Media Lab and lead author on a paper that was published in the journal Nature last week. He built a color holographic video display that’s as sharp as a standard-definition TV and updates images at the same rate.
If it works as Smalley and his team hope, then holographic televisions and communications (think Face Time in 3D) could become a reality.
Ordinarily, to make a holograms, one uses a laser. A beam is fired at an object or a person you want to get a picture of. The beam is split, and one half illuminates the target. The illumination beam reflects off of the target and hits a photographic plate. Meanwhile the other half of the beam, which hasn’t hit anything, also hits the photographic plate.
The two beams will interfere with each other and create a ripple pattern on the plate. The ripples scatter any light that hits it in such a way that it reproduces the original image. Because the scattering, called diffraction, changes depending on the viewing angle, it creates an illusion of a 3-D image.
Creating holographic video is hard because in order to get the same light-scattering effect, it’s necessary to control the light waves as they emerge from each pixel. In addition, the pixels in the image have to be close to the size of light waves, and there isn’t a video display technology that exists yet which can do that easily or cheaply.
To get around this, Smalley used a crystal of a material called lithium niobate. Just under the surface of the crystal are tiny channels that confine and guide the light that passes through them. Each channel, or waveguide, also has a small electrode, which slightly distorts the shape of the crystal. It can do that because lithium niobate is piezoelectric, meaning that it changes shape when a current is run through it.
As the electrode alters the crystal’s shape, some wavelengths of light get filtered out and others will pass. That creates the scattering effect necessary for the 3-D image.
Because it only needs one waveguide for each pixel, rather than three (one for each color) the cost is much reduced, and the use of relatively simple crystals brought the costs down even more. A single-pixel system also allows the images to refresh faster, and reduces the power consumption. Waveguides are also not a new technology in themselves; they are used in all kinds of electronics such as communications gear.
The images the team made with their first device refreshed at five frames per second and had dimensions of about 420 by 420 pixels, with a depth of 156. The next one will be closer to a cube four times as large.
Credit: Nature / Daniel Smalley