Wednesday, November 3, 2010

3D Holographic Display

A new holographic display can transmit three-dimensional movies from one location to another almost in real time. If Princess Leia had to send her “Help me Obi-Wan Kenobi, you’re my only hope” message from Earth today, it would now be technologically possible.

“We can take objects from one location and show them in another location in 3-D in near real time,” said optical scientist Nasser Peyghambarian, and project leader from the University of Arizona in a press conference Nov. 1. “It is no longer something that is science fiction, it is actually something that you can do today.”
Holographic movies have been a dream since at least 1966, when the first hologram was transmitted over a television system by Bell Labs. Updatable holographic displays have been around for decades as well; the first was developed by Stephen Benton at the MIT Media Lab in 1989.
The new device projects a color 3-D image onto a sheet of special plastic using a fast-flashing laser. The image can be updated once every two seconds, fast enough to give a sense of movement.
“In the past, other holograms you have seen are static images,” said Pierre-Alexandre Blanche of the University of Arizona, lead author of a study in the Nov. 4 Nature describing the device. “Now, with a 2-second lag, it starts to become something more tangible.”
The image can also be transmitted over the internet in less than a second, which would allow a near real-time window into distant events, something the authors call “holographic telepresence.”
Peyghambarian and colleagues set an array of 16 webcams in a semicircle around the objects they wished to project, which included a model airplane, a vase of flowers and the researchers’ heads. Each camera captured the object from a different perspective, making the ultimate image more lifelike.
“If you go to a 3-D movie like Avatar, you would see only two perspectives, one for one eye and one for the other eye,” Peyghambarian said. “In our case, we have demonstrated 16 perspectives, but the technology has the potential to show hundreds of perspectives. So it’s very close to what humans can see.”
The cameras sent the images to another room, where they were encoded into pulsed laser that flashes 50 times per second. Each laser pulse encodes one holographic pixel, or “hogel.”
Then the researchers trained the laser onto a newly developed plastic called a photoreactive polymer, which is coated with a material that converts light into electrical charges that create and store the image. The charges move around the plastic in such a way that when light bounces off the material, it reaches your eyes as if it had bounced off the toy plane or the researcher’s head.
“With this material, since you can move the charge around, you can erase the hologram and write another hologram on it,” Blanche said.
Two years ago, Peyghambarian’s team made a similar material that could only refresh the image every four minutes. The images in that material were also disturbed by vibrations and temperature changes, so the screen had to be kept in a highly controlled box.
The new material rewrites every two seconds, a 100-fold improvement, and isn’t bothered by changes to its environment, the researchers say.
Beyond entertainment and fighting the Empire, the display could have important medical and military applications, Peyghambarian says.
“Different doctors from different parts of the world can participate [in surgery] and see things just as if they were there,” he said. The device could even be used for telecommuting. “People from Europe don’t have to come to the U.S. to participate in a conference, it would be as if they were there.”
“This is mostly a materials advance,” said optical scientist Michael Bove of the MIT Media Lab, who was not involved in the new research but is collaborating with Peyghambarian on another project. “The material is faster and more sensitive than what had previously been reported.”
Given the small size of the screen and the two-second lag time, “some people in the field object to the term ‘telepresence,’” Bove said.
Blanche agrees that the hologram’s lag time is too long. “Quite frankly, it’s a bit annoying, and we know that,” he said.
For truly real-time video, the image would need to refresh 30 times a second. That would take either a much more sensitive material or a “very big, very nasty” laser, Blanche said. The team hopes to push the material to produce video quality holographs in the next two years, and the technology could be ready for your living room within the decade.
“In two years we improved the speed by a factor of 100. If we can improve the speed by the same factor, we will be over video rate,” Blanche said. “It will be done.”


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