TL;DR: It’s been a little over a year since we first unveiled Half Dome—a VR headset prototype that combined mechanical varifocal displays with a wider field of view than the original Rift for improved visual immersion. Since then, an interdisciplinary team at Facebook Reality Labs (FRL) has continued pushing the limits of what’s technologically feasible to move beyond an early “proof of concept.” Today, we’re sharing some exciting updates to the Half Dome prototype that explore a new direction for varifocal and improve both physical and visual comfort—including a new electronic version of Half Dome with no moving parts.
Today at OC6, Facebook Reality Lab Chief Scientist Michael Abrash shared his vision for a virtual collaborative workspace—a space that you would be able to configure any way you wanted, with monitor-quality virtual screens, holograms, and whiteboards. It would give you the ability to interact with real surroundings and use a keyboard and mouse, to share the virtual space with other people, and to manipulate both real and virtual objects with your hands, complete with haptic feedback.
To deliver on that vision, we’d need to solve some considerable challenges. To get virtual monitors at visual parity with real-world monitors, Abrash notes, we’d need high resolution and good image quality—both of which would require very high-resolution displays and much improved optics. We’d want clear, comfortable vision within arm’s length, and we’d need a wider field of view, so that everyone in a meeting could see everyone else—a must for social presence and effective collaboration in VR.
And since we’re talking about technology that could revolutionize how we work, we’d need great ergonomics. To make it comfortable to be in VR for hours at a time, all of the necessary components need to be compact and power-efficient.
At OC6, Abrash shared some of the progress FRL has made on inventing the future in optics, including following up on varifocal and the Half Dome prototype, originally unveiled at F8 2018. That prototype headset was the result of several years of research and iterating on advanced display systems. Today, we pulled back the curtain on what’s next.
Half Dome was our first prototype to achieve two key milestones. First, using Fresnel lenses, it supports a 140° field of view. Second, by physically moving the screens based on eye tracking, it ensures that the image remains sharp, even when inspecting close objects. This was our first step toward more immersive and visually comfortable VR displays in the lab.
Today, we’re sharing a new varifocal concept prototype, Half Dome 2, built by our Display Systems Research team, working closely with several other teams across FRL.
While the original Half Dome prototype was a proof of concept that prioritized visual immersion, the Half Dome 2 prototype is targeted primarily at ergonomics and comfort, both visual and physical. It’s both substantially smaller and lighter than the original Half Dome prototype, because it manages to fold the optical path into a very small volume.
Overall, we’ve been able to improve the form factor substantially and reduce weight by a full 200 grams over Half Dome 1. While the field of view for Half Dome 2 is narrower than its predecessor, it’s still 20% wider than Oculus Quest.
The varifocal hardware has also been considerably improved. Let’s take a look inside.
The mechanical varifocal system relies on voice coil actuators and flexure hinge arrays. These reduce friction, minimize noise, and maximize the lifetime of the headset’s moving mechanical parts—all improvements on the original Half Dome prototype.
We also unveiled an electronic version in the Half Dome series of prototypes—one that replaces all of the moving mechanical parts with a new type of liquid crystal lens made from a thin, alternating stack of two flat optical elements: polarization-dependent lenses (PDLs) and switchable half-wave plates.
PDLs are special because their focal length changes based on their polarization state. By changing the voltage applied to the switchable plates, we can toggle between the two focal lengths. This could make for a great set of digital bifocals, but it doesn’t necessarily make for comfortable VR. By stacking a series of PDLs and switchable half-wave plates on top of each other, we’re able to achieve smooth varifocal that lets you comfortably and seamlessly adjust your focus in the headset.
Let’s take a look at a prototype module to understand how this works. The image on the right was recorded through the electronic varifocal module shown above—this is a real camera shot of a dinosaur figure in front of a plant. The dinosaur is nearer to the camera. On the left, we indicate that a lens is “on” by highlighting it in orange; when it’s off, its focus shifts to the far object (in this case, the plant).
As you can see, the liquid crystal lenses shift focus between different depths. To achieve smooth varifocal, we address the full stack of liquid crystal lenses, with each additional pair doubling the number of focal planes. In the example above, six liquid crystal lenses are driven to sweep through 64 focal planes, and you can see the focal depth smoothly changing at the right as we cycle through different sets of lens states.
In addition to having no moving parts, this approach allows for a significantly better form factor compared to its predecessors in the Half Dome series of prototype. When we integrate the electronic module into a complete prototype headset, it defines a new state of the art for VR ergonomics.
This is still very much research today, but here’s our standard demo, viewed in an early Half Dome 3 prototype.
As you can see, without varifocal, the tape gets blurry up close, but the electronic approach is able to replicate the smooth varifocal experience of mechanical systems at all depths—a promising sign for the future.
This latest update to the Half Dome series of prototypes digitally switches between a large number of focal states—so many, in fact, that it appears continuous, just like the mechanical varifocal displays. For the first time, we’ve achieved a more ergonomic design with a significant reduction in weight. That opens the door to a future where we can be in VR for hours at a time, collaborating with others using any number of digital whiteboards spread throughout our ideal virtual workspace. While we’re still developing the Half Dome series of prototypes at FRL, we’re excited to see where our varifocal research takes us next.