Facebook’s VR research division presents prototypes of VR optics smaller than anything else we’ve seen for the annual SIGGRAPH computer graphics conference.
The ideas behind the “holographic display near the eye” may one day enable the VR earphones with form factor to sunglasses, but for now this is only a search with limits.
Why are VR headphones so bulky?
The main driver of the size and mass of today’s VR headphones is the optical design. Magnifying a display over a wide field of view requires a large, thick lens, and focusing at a visible distance requires a long space on the display. After adding the housing needed to hold this system, even the most minimal designs end up over 350 grams.
Autonomous Oculus Quest, with battery, mobile chip and lens separation adjustment, weighs 571 grams. Many people find it hurts after a few minutes.
Panasonic and Pico showcased compact headset prototypes using “pancake lenses” and Huawei has already launched this product in China. Without a tracking system or battery, these headphones end up for around 150 grams.
However, these current models of pancake lenses have a number of unresolved defects. They block about 75 percent of the light, which can make the image blurry and faded. They may also show slight misalignments of the phantom versions of the image, and this “ghosting” only gets worse when trying to improve the image with a brighter source.
The new approach of Facebook Reality Labs is a thin film in which the focus is performed from the holographic perspective rather than from most of the lens. “Hologram” in this context simply means a physical “recording” of how light interacts with an object, in this case a goal rather than a scene.
Facebook says the research may be able to “offer a field of view comparable to today’s VR headphones using only a thin film for a thickness of less than 9 mm”. The total weight of the display module is only 18 grams. However, this does not include the actual laser source and none of the images provided by Facebook. “For our prototype green-only sunglasses, we measured a maximum overall field of view of approximately 92◦ × 69◦,” according to the research paper.
Using polarization-based optical folding, these ultralight lenses can be positioned directly in front of the display source.
Since holographic elements scatter light, the only practical source of illumination are lasers used at specific angles and wavelengths. The researchers were able to “inject” the laser light into a 2.1 ″ 1600 × 1600 LCD, replacing the backlight.
The prototype is currently monochromatic, capable of displaying only the green color. Researchers have proof of the multi-color tabletop concept and believe that wearing this prototype sunglasses is “feasible” with further engineering.
The range of colors that laser light can provide (known as color gamut) is significantly wider than LCD displays, and in fact slightly wider than even the OLED, so this would be a milestone if it could be moved into a worn-out system.
Early research, high goals
It is important to understand that what is presented here is only a first search for a new type of display system. If it ever becomes a product, it will also need a tracking system. And unless you connect to the phone with a cable, you will probably also need a battery and a mobile chipset.
Facebook describes this research as being on the same “path” of miniaturization research as Half Dome 2 and 3, which it presented at Oculus Connect 6 in October.
Those headphones are much larger than what is shown here, but have achieved a wider field of view while also having variable eye tracking and focus. FRL states that future iterations of this sunglasses prototype could also be varifocal by moving the lenses over a radius of just 1 millimeter. This could theoretically be achieved with small piezoelectric actuators.
In order for virtual reality to reach Mark Zuckerberg’s high milestone of 1 billion users, headsets must become significantly more comfortable by increasing realism. While designs like the Rift S “halo strap” can redistribute weight, this is more of a bandage than truly tackling the problem of mass.
Like all early research, this idea may never go out. Practical problems may emerge. Facebook is simultaneously exploring a number of new compact display architectures. If it can get even one to work, it could do VR what LCD panels have done to CRT monitors and televisions.
Facebook’s research paper concludes:
“Light, high-resolution, sunglasses-like VR displays can be the key to enabling the next generation of demanding virtual reality applications that can be exploited anywhere and for long periods of time. We have made progress towards this goal by proposing a new design space for virtual reality displays that combines polarization-based optical folding, holographic optics and a host of supporting technologies to demonstrate color displays, glasses-like form factors and high resolution in a series of hardware prototypes. Many practical challenges remain: we have to get a color display in a form factor similar to sunglasses, get a wider eye box and work to suppress ghost images. In doing so, we hope to be a step forward towards achieving ubiquitous and immersive computing platforms that increase productivity and bridge physical distance. “