Facebook’s virtual reality research division presents a smaller virtual reality optics prototype than we’ve seen so far for the annual SIGGRAPH computer graphics conference.
The ideas behind the “near-eye holographic display” might one day allow sunglasses form factor VR headsets, but for now this is only limited research.
Why are VR headsets so bulky?
The primary driver of size and most of today’s VR headsets is the optical design. Extending a screen over a wide field of view requires a large, thick lens, and focusing at a visible distance requires a long space for the screen. After adding the necessary casing to hold this system, even the smallest designs end up over 350 grams.
The standalone Oculus Quest, with a battery, mobile chip, and lens separation adjustment, weighs 571 grams. Many people find that their face hurts after a few minutes.
Panasonic and Pico have shown prototypes of compact headphones with “pancake-like lenses,” and Huawei has already launched it as a product in China. Without a tracking system or battery, these headphones end at around 150 grams.
However, these current pancake lens designs have a number of unsolved flaws. They block about 75 percent of the light, which can make the image appear dim and blurry. They can also show faint phantom versions of the image slightly misaligned, and this “phantom effect” only worsens when you try to enhance the image with a brighter font.
Holographic lenses
Facebook Reality Labs’ new focus is a thin film where the focus is done using holographic optics instead of most of the lens. ‘Hologram’ in this context only means a physical “recording” of how light interacts with an object, in this case a lens rather than a scene.
Facebook claims that the research may be able to “offer a field of view comparable to today’s VR headsets using only a thin film for a thickness of less than 9mm.” The total weight of the display module is stated as only 18 grams. However, this does not include the actual laser source or any of the images Facebook provided. “For our prototype green sunglasses, we measured an overall maximum field of view of approximately 92 ° × 69 °,” according to the research paper.
Using polarized-based optical folding, these ultralight lenses can be placed directly in front of the display source.
Because holographic elements scatter light, the only practical lighting source is lasers used at specific angles and wavelengths. The researchers were able to “inject” laser light onto a 2.1 ″ 1600 × 1600 LCD, replacing the backlight.
The prototype is currently monochrome, only capable of displaying the color green. The researchers have a table-size proof of concept for various colors, and believe that bringing this to the sunglasses prototype is “feasible” with more engineering.
The color gamut laser light can offer (known as the color gamut) is significantly wider than LCD displays and in fact slightly wider than even OLED, so this would represent a major achievement if it could be moved to a head system.
Early research, high goals
It is important to understand that what is presented here is only an early investigation for a new type of display system. If it ever becomes a product, you will also need a tracking system. And unless you connect to your phone with a cable, you probably need a battery and a mobile chipset, too.
Facebook describes this research as being on the same miniaturization research “path” as Half Dome 2 and 3, which featured on Oculus Connect 6 in October.
Those headphones are much larger than what is shown here, but they achieved a wider field of view while also having eye tracking and variable focus. FRL says that future versions of this prototype sunglasses could also be varifocal by moving the lenses in a range of just 1 millimeter. In theory, this could be accomplished with small piezoelectric actuators.
In order for virtual reality to reach Mark Zuckerberg’s lofty goal of a billion users, headphones must feel much more comfortable and increase realism. While designs like the Rift S “halo strap” can redistribute weight, this is more of a bandage than actually addressing the issue of volume.
Like all initial research, this idea can never work. Practical problems may arise. Facebook is simultaneously exploring a series of new compact display architectures. If you can make one work, you could do in virtual reality what LCD panels did with CRT monitors and televisions.
Facebook’s research paper concludes:
“Lightweight, high-resolution, sunglasses-like virtual reality displays can be the key to enabling the next generation of demanding virtual reality applications that can be leveraged anywhere and for long periods of time. We are making 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 compatible technologies to demonstrate a full-color display, form factors similar to sunglasses. and high resolution on a series of hardware prototypes. Many practical challenges remain: We must achieve a full-color screen with a form factor similar to that of sunglasses, obtain a larger vision box and work to suppress ghost images. By doing so, we hope to be one step closer to achieving ubiquitous and immersive computing platforms that increase productivity and reduce physical distance. “
