The 3-D images and video created are visible from a wide range of viewing angles.
In theaters, 3-D movies are everywhere. But how about a 3-D holographic movie on your mobile phone?
At Hewlett Packard Laboratories, a team led by physicist David Fattal has found a way to make 3-D, hologram-like displays for tiny screens -- no glasses required. And they've done it using inexpensive, readily available parts.
The still images and video created are visible from wide angles, unlike other 3-D imaging technologies, which tend to limit how far to one side the viewer can be from the hologram. The research appears today in the journal Nature.
"For a mobile device, it needs a wider angle [than a television] because you are more likely to tilt your hand, and we want the feeling of a virtual object in the screen in front of you," Fattal said at a press briefing.
The HP team built the display using a thin piece of glass, a liquid-crystal display and light-emitting diodes (LEDs). First, the researchers etched 500,000 circles – essentially pixels -- into the surface of the glass, each one comprised of a striped grating pattern made from sub-micrometer-sized grooves.
Next, they put a layer of liquid crystal display on top of the glass. Then the scientists surrounded the glass with the LEDs. Light from the LEDs was directed into the glass from the side. Once inside, the light bounced around the thin layer of glass and then escaped out the top through the 500,000 etched pixels.
When the light escaped, it came into contact with the grating patterns, which altered the light's direction. The LCD layer was used to control each pixel's brightness.
Different groups of pixels shining in different directions made one part of a 3-D image. In fact, 14 different images are combined to make a three-dimensional picture of say, a turtle.
Physicists from HP made hardly any modifications to the glass layer, the LEDs and the LCD used to make a three-dimensional image.Hewlett Packard
"When a viewer moves his head or the display, he or she will see a succession of different images," Fattal said. Each image is from a slightly different perspective, creating the illusion of 3D.
The glass layer, the LEDs and the LCD were all used with little modification. So any 3-D display using this design would be much cheaper to make than a true holographic system, which requires a complex systems of lasers.
HP's system also gives it an edge over some of the more complicated systems of mirrors used in other 3-D video displays. HoloAd, for example, is a big and bulky system that relies on projecting images onto glass – not very convenient for a mobile device. There are other complex systems involving exotic technologies such as bubbles and ultrasonic vibrations. None of these are practical for mobile devices.
A simpler system also reduces the computing power needed to create images and video.
Pierre Alexandre Blanche, an assistant research professor in the College of Optical Sciences at the University of Arizona, said that the use of gratings to control the light is a departure from previous attempts to build similar systems. Ordinarily, he said, engineers tried to control the light by putting lenses on top of the glass layer. "This is original, and could be interesting because the light can eventually be better controlled than with lenses," he wrote in an email.
Fattal added that the number of images could be boosted to 64, making the 3-D effect even smoother. And because the light beams that make up the image are all projected in specific directions, the viewing angle is big – approaching 180 degrees. That's an improvement over other attempts at 3-D holograms, many of which require the viewer to be directly in front of the image in order to see the illusion.
Having a wide view is an important characteristic for 3-D imaging on mobile devices, Fattal said, because a phone or tablet is more likely to be held at different angles at different times.
Raymond Beausoleil, an HP Fellow in the Intelligent Infrastructure Lab and a co-author on the paper thinks the first applications will likely be in signage or displays that help people visualize complex data.
"The point of the paper is that there is an approach to 3-D displays that is relatively easy to mock up and seems ideal for small form factor," he said.