Holographic Display Adds Movement

Holographic imaging technology that can depict a scene in another location and update ot every two seconds has been demonstrated for the first time. The technology, known as three-dimensional telepresence, could lead to new uses of holographic 3-D images in telemedicine, videoconferencing and entertainment, among other applications.

Nasser Peyghambarian with a refreshable holographic image of an F-4 Phantom Jet created on a photorefractive polymer at the University of Arizona College of Optical Sciences in Tucson. (Photo: gargaszphotos.com/University of Arizona)

The technology was developed at the University of Arizona College of Optical Sciences and is featured on the cover of the Nov. 4 issue of the journal Nature. "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."

Their new type of holographic telepresence allows the projection of a 3-D moving image without the need for special eyewear such as 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," said optical sciences professor Nasser Peyghambarian, who led the research effort.

The success of 3-D films such as "Avatar" has generated a lot of interest in 3-D image rendering from the public, the media and industry. Since its appearance in the original "Star Wars" film in 1977 ("Help me, Obi-Wan Kenobi, you're my only hope"), 3-D telepresence has been a source of fascination, but the absence of a large, updatable holographic recording medium meant the potential was never realized.

"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," said Pierre-Alexandre Blanche, an assistant research professor in the UA College of Optical Sciences and lead author of the paper. Two-dimensional images were taken at multiple angles in one location and sent to another location via an Ethernet connection, then printed with the hologram setup.

Pictures of a hologram recorded with the 3-D telepresence system. (Image: Blanche et al Nature)

The prototype device uses a 10-in. screen, but Peyghambarian's group is already successfully testing a much larger version with a 17-in. screen. The image is recorded using an array of regular cameras, each of which views the object from a different perspective. The more cameras 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 3-D version of a pixel, the basic units that comprise the picture.
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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.

"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," Peyghambarian explained.

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 lifelike image. Humans are used to seeing things in 3-D."

The work is a result of a collaboration between the university and the company Nitto Denko Technical (NDT) of Oceanside, Calif. NDT provided the polymer sample and media preparation.

Potential applications of holographic telepresence include advertising, updatable 3-D maps and entertainment. In a telemedicine application, "Surgeons at different locations around the world can observe in 3-D, in real time, and participate in the surgical procedure," the authors wrote.

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 system can present in one color only, but Peyghambarian and his team have already demonstrated multicolor 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 setup in the near future, he said.

This work builds on a 2008 Nature paper by the same group, which reported an updatable 3-D holographic display; however, the hologram was monochrome and could only be updated every four minutes.

The research was funded through grants from the Air Force Office of Scientific Research, DARPA and the National Science Foundation's Engineering Research Center on Integrated Access Networks.

For more information, visit: www.arizona.edu

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