Facebook Researchers Reveal Methods for Design & Fabrication of Compact Holographic Lenses

By
Ben Lang
-
15

Researchers from Facebook Reality Labs have shared new methods for the design & fabrication of compact holographic lenses for use in XR headsets.

The lenses used in most of today’s XR devices are typical refractive lenses which can be fairly bulky, especially as they are optimized for certain optical characteristics. Fresnel (ridged) lenses are frequently used in XR headsets to improve optical performance without adding too much bulk.

In theory, holographic lenses are a promising approach for XR optics thanks to their ability to perform the same (or even more advanced) functions of a traditional lens, but in the space of a wafer-thin film. However, designing and fabricating holographic lenses with high optical performance is far more difficult today than it is with typical refractive optics.

In an effort to move us one step closer to the practical use of holographic lenses in XR devices, Facebook Reality Labs researchers Changwon Jang, Olivier Mercier, Kiseung Bang, Gang Li, Yang Zhao, and Douglas Lanman have detailed new methods for creating them. This could go a long way toward making it possible to build, at scale, the kind of compact XR glasses Facebook recently demonstrated.

In a paper published in the peer-reviewed journal ACM Transactions on Graphics (Vol. 39, No. 6, Article 184) in December, titled Design and Fabrication of Freeform Holographic Optical Elements, the researchers write, “we present a pipeline for the design and fabrication of freeform [Holographic Optical Elements (HOEs)] that can prescribe volume gratings with complex phase profiles and high selectivity. Our approach reduces image aberrations, optimizes the diffraction efficiency at a desired wavelength and angle, and compensates for the shrinkage of the material during HOE fabrication, all of which are highly beneficial for VR/AR applications. We also demonstrate the first full-color caustic HOE as an example of a complex, but smoothly-varying, volume grating.”

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Specifically the paper covers optimization methods for establishing a theoretical holographic lens design, and two approaches for actually manufacturing it.

One uses a pair of freeform refractive optics to create the target hologram; the paper proposes the method for creating the refractive optics such that they accurately form the target hologram within the holographic film. The other involves a holographic printer used to create the target hologram from tiled holographic patches; again the paper proposes the method for optimizing the process to most accurately recreate the target hologram within the holographic film with this specific approach, which they say is a completely different challenge from the first method.

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The first method of creating holographic lenses with a pair of refractive optics | Image courtesy Facebook Reality Labs
The second method of creating holographic lenses with a holographic printer | Image courtesy Facebook Reality Labs
Image courtesy Facebook Reality Labs

While the paper didn’t explore quite this far, the authors say that future research could attempt to apply these same methods to curved, rather than flat, surfaces.

“For some VR/AR applications, it could be beneficial to create HOEs with physically curved form-factors, for example, for HOEs laminated on curved windshields or glasses. We expect our fabrication framework to expand well to such cases, since neither the printer or the [refractive lens] approaches require the HOE to be flat, and the optimization method of Algorithm 1 could be adapted to intersect rays with a curved surface […],” the researchers write. “Optimizing the shape of the HOE as part of our method would provide us with more degrees of freedom and would broaden applications, but we leave this as future work.”

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Ben Lang
Ben is the world's most senior professional analyst solely dedicated to the XR industry, having founded Road to VR in 2011—a year before the Oculus Kickstarter sparked a resurgence that led to the modern XR landscape. He has authored more than 3,000 articles chronicling the evolution of the XR industry over more than a decade. With that unique perspective, Ben has been consistently recognized as one of the most influential voices in XR, giving keynotes and joining panel and podcast discussions at key industry events. He is a self-described "journalist and analyst, not evangelist."
  • xyzs

    I love to see all these RnD big announcements. Really.

    But when we learn that the Rift 2 with half dome advanced tech was cancelled for purely business strategy reasons – and that today, Oculus’ very latest Quest 2 relies on the exact same tech we had in the first Rift, if not inferior on many points like its single LCD screen and its cheaper build quality – I am really wondering what’s the plan with all that shiny futur tech brag ?

    The only parts that improve the oculus products (except insight) are the parts that are not made by Oculus, like the soc. For the rest, the VR part, we are getting lower and lower quality hardware. As of today, more than 5 years later, Quest 2 is still a gen 1 VR product, with still the same FOV, less good IPD adjustments, still zero eye tracking, still no varifocal tech, now with LCD single screens instead of dual OLED (at least they are RGB and not pentile anymore), and a less good build quality compared to older products.

    So yeah cool, Quest are cheap for what they offer and you have good stuff in your lab, but in the end, nothing exciting gets real.

    Prove me wrong.

    • kontis

      And their best FOV device was DK1 released in 2013.

      You are right that it’s disappointing, but what they are doing is quite smart and makes sense.

      15+ years ago almost nobody was interested in a $500+ (let alone $1000+) cellphone, but then iPhone came and it was becoming more and more important device in people’s lives.

      The actual Facebook XR goal is the iPhone killer – the Smartglasses. They can easily cost $1000+ and once they become improtant in people’s lives even $2000 won’t be outrageous. In a few decades when most people won’t even own a car (or have a driving license) investing $20K into customized XR + neural interface to be competitive in the job market and live a middle class standard life might become a very common if not necessary thing.

      However, a VR equivalent of a toy today, a gaming console like Nintendo Switch cannot cost more than $400.
      So they are not pushing it in that high end tech direction, because it’s not the market that can sustain it. They are preparing for their actual goal. Their current products are not that.

    • VirtualRealityNation

      When I bought my N-Vis S60 with tracker for $28,000 back in 2006 I thought I was buying a Gen 1 VR product. Showing clients all over the US how well this 2006 VR solution worked I got lots of flack about it’s quality, cost, weight, and it’s huge garden hose cable connected to it. 15 years later the Quest 2 seems like a dream come true to all of those complaints. Sure, it’s not perfect and could definitely improve on a host of issues. However, most successful product lines improve to stay relevant. The Quest 2 is a marvel compared to tech of just a few years back when you consider what it can do in a self contained system. And that will continue. Facebook will have a long run with XR tech. Some product lines will go cheap and others will bring incredible advances. I believe they both will have their place.

      • Rogue Transfer

        Yes, Qualcomm did a remarkable job building the XR2 system-on-a-chip and making a VR reference design for companies, like Facebook to use.

        Facebook did add improvements for the camere-on-headset, outside-in LED controller tracking, which proved pivotal to its success.

        • psuedonymous

          Other way around: While the XR2 was a nice performance boost for Quest 2, Quest came before using a regular Snapdragon 835 with the same feature set as Quest 2 (position tracking, hand tracking, reprojection, etc).

    • wheeler

      From what I can tell, the major features of Half Dome like vari-focal and eye-tracking (good enough for vari-focal) are still not solved problems and it’s certainly not a matter of not trying. Only very recently did a FB researcher claim that vari-focal is “almost ready for prime time” (paraphrasing) and even that didn’t include the eye-tracking part (which is essential for practical vari-focal with traditional VR displays so even the original claim is kind of dubious). Less than a year ago Abrash stated that there is no eye-tracking in existence good enough for vari-focal or foveated rendering and that it remains to be seen if it’s even possible. Carmack’s latest statements about foveated rendering make Abrash’s original predictions seem like pie in the sky stuff. And other things have become much more sobering as well, e.g. the expected FOV of Half-Dome decreased with each iteration–to the point where it’s something very reasonable for today’s standards.

      There was a ton of hype back then. They were trying to sell not just consumers on VR but likely many other stakeholders within and outside of the company. Who knows, they may have actually believed it themselves (when you have a bunch of smart people together and basically unlimited resources, it can seem like anything is possible), or they may have felt stretching the truth is an essential part of the process for impatient stakeholders–doesn’t make much of a difference. The Rift 2 or whatever probably would have been quite similar to the Valve Index: a great headset for enthusiasts by maxing out certain aspects of the tech well into the realm of diminishing returns but still the same fundamental technology–still a “Gen 1” technology.

      • Rogue Transfer

        Only very recently did a FB researcher claim that vari-focal is “almost ready for prime time”

        For clarity, it wasn’t ‘very recently’, it was last July too. Just before Abrash stated that ‘it remained to be proven possible to do [eye-tracking] robustly and accurately enough to enable that tech’.

        The researcher was enthusing about their work, showing pride in it, but we clearly should take their Half Dome research prototype with a pinch of salt, as it was never demonstrated to anyone outside the company(and in fact, FRL refused a request to do so to the media or developers). We have no idea if the varifocal quality would hold to consumer standards. In fact, we know it likely couldn’t because of that refusal to demo it, even privately.

        • wheeler

          I think you’re right about them being cagey about showing just any old dev or media person the prototype (which, regardless of whether or not the tech has long term promise, can make sense). But there was individual that was commenting in these roadtovr disqus sections named “lieisacake” that claimed to have tried some of these varifocal prototypes. They described some of the problems they suffered from in the parlance of a researcher or engineer that was familiar with the technologies and the common pitfalls. Unfortunately I can no longer find those comments because they deleted those comments and their profile. But some individuals outside of the company may have gotten to try them–probably under NDA. Unfortunately archive.org doesn’t appear to grab disqus comments

      • Rupert Jung

        There a multiple headsets out there with working eye tracking solutions. Here’s the review of an add-on, two years ago: https://youtu.be/lxsLOnY9Yg4?t=145

        • wheeler

          I’m aware of that, but there’s a big difference between that and something that is suitable for vari-focal (at least vari-focal with traditional displays) and the kind of gains we were hyped up on for foveated rendering years ago. With current tech you can use it for modest performance gains via foveated rendering, a certain degree of pupil swim correction and CA mitigation, for social features, and as an imprecise input device

          • alxslr

            A modest precission in foveated rendering could lead to a very remarcable push in graphics and also allow wider fow with same graphics power. I think they were just aiming too high.

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    • Blaexe

      Rift 2 was probably more like the Index. Nowhere does it say it included “advanced half dome tech”. That’s just a wrong assumption.

      Eye Tracking is not solved today, let alone 2018. Varifocal wasn’t either (and probably isn’t today given that the mechanical solution was probably never meant to be used in a product).

    • Julia Norris

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  • I like this research, but “HOE” is probably the worst acronym ever