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Using 3D holograms polished by artificial intelligence, researchers introduce a lean, eyeglass-like 3D headset that they say is a significant step toward passing the "Visual Turing Test."

"In the future, most virtual reality displays will be holographic," said Gordon Wetzstein, a professor of electrical engineering at Stanford University, holding his lab's latest project: a virtual reality display that is not much larger than a pair of regular eyeglasses. "Holography offers capabilities that we can't get with any other type of display in a package that is much smaller than anything on the market today."

Holography is a Nobel Prize-winning 3D display technique that uses both the intensity of light reflecting from an object, as with a traditional photograph, and the phase of the light (the way the waves synchronize), to produce a hologram, a highly realistic three-dimensional image of the original object.

Wetzstein's latest holographic display, detailed in a new paper in Nature Photonics, moves the field toward a new age of lightweight, immersive, and perceptually realistic mixed reality glasses—glasses that project life-like three-dimensional moving images onto the wearer's real-world view.

From lens to screen, the display is just 3 millimeters thick. Such a tool could transform education, entertainment, virtual travel, communication, and other fields, the researchers said.

Extending reality

Holograms, Wetzstein said, provide a more visually satisfying, more realistic 3D visual experience than current stereoscopic approaches based on stereoscopic LED technology. And they come in a form that looks nothing like the bulky VR headsets of today. But, he acknowledges, it's not easy to achieve.

Wetzstein and others in the field refer to it as "mixed reality" to convey the full impact of the display's seamless melding of holographic imagery and views of the real world. One day, Wetzstein predicts, digital images and real-world scenes will be indistinguishable. In the meantime, this prototype is a "significant step" in that direction.

"Researchers in the field sometimes describe our goal as to pass the "Visual Turing Test,'" said Suyeon Choi, a postdoctoral scholar in Wetzstein's lab and first author of the paper, in reference to the AI standard named for the famed British polymath and computer scientist, Alan Turing. In AI, the Turing Test holds that machines can only be declared truly "intelligent" when one cannot distinguish whether one is chatting with a machine or a human being.

"A visual Turing Test then means, ideally, one cannot distinguish between a physical, real thing as seen through the glasses and a digitally created image being projected on the display surface," Choi said.

Thinking outside the eyebox

His group's latest headset design achieves breakthroughs in image realism and usability by integrating a custom waveguide that steers the image to the viewer's eye. The holographic image is enhanced by a new AI-calibration method that optimizes image quality and three-dimensionality.

The result is a display with both a large field of view and a large "eyebox" defined as the area in which the pupil can move and still see the entire image. This combination of large field of view and large eyebox—known in Wetzstein's world as the "étendue"—is highly coveted. The effect is a crisp 3D image that fills the user's field of view for a more satisfying and immersive 3D experience.

The leanness of the packaging cannot be overstated, Wetzstein said. The eyewear could be worn for hours at a time without the neck or eye fatigue that are a challenge with today's wearable displays.

"We want this to be compact and lightweight for all-day use, basically. That's problem number one—the biggest problem," Wetzstein said.

The other challenges are realism and immersiveness. AI helps solve the first by improving the image resolution and three-dimensional qualities of the holograph. The third challenge is achieved by the device's impressive eyebox and large field of view.

The experience is like having a bigger, more realistic screen in your home theater, Wetzstein said. "The eye can move all about the image without losing focus or image quality," he added, noting that this is "key to the realism and immersion of the system."

This latest research is the second installment in a scientific trilogy. Last year, in , Wetzstein's lab introduced the holographic waveguide that enables high image quality in the lean form factor. Now, in volume two, they have built a working prototype to bring the finer details of the engineering to life.

Volume three could still be years off, Wetzstein admits, but that ultimate piece will come in the form of a commercial product that transforms how the world thinks of virtual reality—or extended reality, as the case may be.

"The world has never seen a display like this with a large field of view, a large eyebox, and such image quality in a holographic display," Wetzstein said. "It's the best 3D display created so far and a great step forward—but there are lots of open challenges yet to solve."