3-D hologram moves in real-time

U. ARIZONA (US) — A new type of holographic telepresence allows the projection of a 3-D moving image without the need for 3-D glasses or other auxiliary devices.

“Holographic telepresence means we can record a three-dimensional image in one location and show it in another location, in real-time, anywhere in the world,” says Nasser Peyghambarian, an optical sciences professor at the University of Arizona who led the research effort.

The technology is likely to take applications ranging from telemedicine, advertising, updatable 3-D maps, and entertainment to a new level. The journal Nature chose the technology to feature on the cover of its Nov. 4 issue.

“Holographic stereography has been capable of providing excellent resolution and depth reproduction on large-scale 3-D static images,” the authors wrote, “but has been missing dynamic updating capability until now.”

“At the heart of the system is a screen made from a novel photorefractive material, capable of refreshing holograms every two seconds, making it the first to achieve a speed that can be described as quasi-real-time,” says Pierre-Alexandre Blanche, an assistant research professor of optical sciences and lead author of the Nature paper.

The prototype device uses a 10-inch screen, but Peyghambarian’s group is already successfully testing a much larger version with a 17-inch screen. The image is recorded using an array of regular cameras, each of which views the object from a different perspective. The more cameras that are used, the more refined the final holographic presentation will appear.

That information is then encoded onto a fast-pulsed laser beam, which interferes with another beam that serves as a reference. The resulting interference pattern is written into the photorefractive polymer, creating and storing the image. Each laser pulse records an individual “hogel” in the polymer. A hogel (short for holographic pixel) is the three-dimensional version of a pixel, the basic units that make up the picture.

The hologram fades away by natural dark decay after a couple of minutes or seconds depending on experimental parameters. Or it can be erased by recording a new 3-D image, creating a new diffraction structure and deleting the old pattern.

Peyghambarian explains: “Let’s say I want to give a presentation in New York. All I need is an array of cameras here in my Tucson office and a fast Internet connection. At the other end, in New York, there would be the 3-D display using our laser system. Everything is fully automated and controlled by computer. As the image signals are transmitted, the lasers inscribe them into the screen and render them into a three-dimensional projection of me speaking.”

The overall recording setup is insensitive to vibration because of the short pulse duration and therefore suited for industrial environment applications without any special need for vibration, noise or temperature control.

One of the system’s major hallmarks never achieved before is what Peyghambarian’s group calls full parallax: “As you move your head left and right or up and down, you see different perspectives. This makes for a very life-like image. Humans are used to seeing things in 3-D.”

The system is a major advance over computer-generated holograms, which place high demands on computing power and take too long to be generated to be practical for any real-time applications.

Currently, the telepresence system can present in one color only, but Peyghambarian and his team have already demonstrated multi-color 3-D display devices capable of writing images at a faster refresh rate, approaching the smooth transitions of images on a TV screen. These devices could be incorporated into a telepresence set-up in near future.

The work is a result of a collaboration between the UA and Nitto Denko Technical, or NDT, a company in Oceanside, Calif.

More news from the University of Arizona: http://uanews.org/

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