3D holograms show off their backside

AUTHOR: Inavate

The telepresence industry was shaken up last week when a university research team unveiled a new type of holographic projection that creates a 3D, moving image. Nasser Peyghambarian of the University of Arizona College of Optical Science unveiled the system that creates an image that can be viewed from different perspectives. The developers claim “dynamic updating capability” sets it apart from existing telepresence systems.

The research group says one of the system's major hallmarks is something they call 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 3D."

When used in a telepresence environment this feature could allow people participating in a conference to view the front, sides and even back of the hologram.

Optical sciences professor Peyghambarian says the technology is likely to find a home in applications ranging from telemedicine, advertising, updatable 3D maps and entertainment.

"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 Peyghambarian.

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

The technology
"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 a paper recently published in Nature.

The prototype device uses a 10-inch screen, but Peyghambarian's group is already successfully testing a much larger 17-inch version. 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. Alternatively it can be erased by recording a new 3D image, which serves to create a new diffraction structure and delete the old pattern.

Peyghambarian explained: "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 3D 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.

The work is a result of a collaboration between the UA and Nitto Denko Technical, or NDT, a company in Oceanside, Calif. NDT provided the polymer sample and media preparation. "We have made major advances in photorefractive polymer film fabrication that allow for the very interesting 3D images obtained in our upcoming Nature article," said Michiharu Yamamoto, vice president at NDT and co-author of the paper.

Potential applications of holographic telepresence include advertising, updatable 3D maps and entertainment. Telemedicine is another potential application: "Surgeons at different locations around the world can observe in 3D, in real time, and participate in the surgical procedure," the authors wrote.

Currently, the telepresence system can present in one colour only, but Peyghambarian and his team have already demonstrated multi-colour 3D 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.