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One model shows a prototype form factor for a virtual reality holographic display.
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An elevated shot highlights the 9mm thickness of the prototype screen.
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The transparent film of the prototype screen, embedded in the glasses case.
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An animated Facebook GIF that shows the difference between holographic film VR screens and traditional screens that use bulkier lenses (click if animation doesn’t load).
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A view of “holographic directional backlight”, which projects an image onto 1mm film that appears as a “virtual light source” at an apparent distance of 13mm.
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The display module for the prototype of sunglasses.
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The current “sunglasses” prototype uses green lasers to create an image like the one on the left. A larger “desktop” prototype with a color LCD screen can create images like the one on the right.
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Close-up highlighting the resolution of the prototype screens.
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A close-up of a test image shows how the laser-based display allows small details to be distinguished.
For all the advances in virtual reality technology in recent years, one important factor that still holds back space is the size and relative discomfort of today’s headphone design. Even today’s most compact and comfortable VR headsets still resemble a cross between ski goggles and a motorcycle helmet, requiring massive headbands to secure a heavy screen that protrudes several inches from the face. Reference designs for “glasses” -type virtual reality displays help a little, but still look like Coca-Cola bottle glasses from a steampunk cosplay event (and provide a limited field of view to begin with).
Now, Facebook Reality Labs researchers are using a holographic film to create a virtual reality screen prototype that is less like ski goggles and more like lightweight sunglasses. At less than 9mm overall thickness, and without significant compromises in field of view or resolution, these displays could one day make today’s bulky VR headphone designs completely obsolete.
In the recently released ACM Siggraph document, Thin and Light Holographic Optics for Virtual Reality, researchers Andrew Maimone and Junren Wang detail the optics behind their lightweight prototype. The key to thinness is a series of flat, polarized films that use a “pancake optical” light folding technique to reflect the displayed image multiple times in a small space.
That design effectively extends the apparent focal length of the image (which is key to the comfort of the user’s eye) without the need for a large physical space for light to travel. The holographic films used to focus the image on the eye also eliminate the need for the types of bulky refractive lens systems found in today’s headphones.
How does it look?
Despite the thinness, the prototype screen can provide a horizontal field of view of approximately 90 degrees in testing. That’s a huge improvement over thin-film AR screens like Microsoft’s Hololens or Magic Leap, and it’s comparable to VR headsets like Oculus Rift and Quest (but less than high-end headsets like HTC Vive and Valve Index). .
Since Facebook’s prototype screen uses lasers instead of LCDs to create an image, it is difficult to make a traditional pixel-based resolution measurement. The screen resolution also varies as you move away from the center, with what the researchers describe as “significant phantom effect” once you leave a 60-degree central field of view.
That said, the researchers say the images in the center of their prototype screen can clearly define details just a little larger than an arc minute in apparent size. That is approaching the limits of 20/20 human vision, a level of detail that would require ridiculous pixel densities on a traditional LCD headset.
A coming revolution?
While there is a lot of potential here, there are also many limitations for today’s holographic display prototypes. For one thing, the current model only displays content in multiple shades of green, creating an effect somewhat similar to the red-tinted 3D images of Nintendo’s failed Virtual Boy (you can see a video of this green-tinted screen in action in this Facebook research blog post).
Obtaining full-color images in that form factor will require the integration and overlapping of red and blue lasers, which will require careful design and engineering work. On the plus side, though, those lasers should be able to provide a wider color gamut than the usual sRGB LCD screens on today’s VR headsets.
Today’s holographic prototypes also download everything except a single monocular screen out of the frame of the “sunglasses” to avoid extra bulk. As the researchers note, “A truly portable and practical display would integrate a pair of display modules, a computing platform, batteries, positional trackers, and all external components in a frame similar to sunglasses.”
All that said, the prototype discussed here sounds like a revolutionary and fully doable new direction for future virtual reality displays, one that could smash virtual reality out of the meaningful bounds of its cumbersome current form factor. While we are a long way from this type of technology reaching consumer-level products, it’s nice to see that Facebook, owner of Oculus, drives the state of the art for virtual reality visualization.
Listing image from Facebook Research
