HoloLens and Holograms

Today Microsoft announced a release window (first quarter 2016) and price (USD 3,000) for HoloLens developer kits, so suddenly HoloLens, and discussion thereof, is all over the Internet again.

Figure 1: Microsoft’s HoloLens.

I’ve already talked about HoloLens ad nauseam, but I found myself several times today trying to explain where (I think) the “Holo” in HoloLens comes from, and what HoloLens has to do with actual, real, honest-to-goodness holograms.

As it turns out, HoloLens has something to do with holograms, but not in the way that someone would initially assume: the virtual three-dimensional objects that HoloLens so cleverly inserts into a viewer’s real environments are not, in fact, real capital-H Holograms. These objects are illusions, albeit very convincing ones, created by real-time head-tracked stereoscopic rendering, the same principle underlying virtual reality headsets. I do refer to HoloLens, among others, as a “holographic display,” but that’s a specific term with a specific meaning.

What are, on the other hand, real holograms are the “lenses” that project the stereoscopic imagery that create those virtual 3D objects into the viewer’s eyes. More precisely, they are holographic wave guides, or, even more precisely, they are planar wave guides using a pair of volume holograms to direct a beam of light from a microdisplay into the wave guide on the display side, and then back out of the wave guide into the viewer’s eye on the viewer side. See Figure 2 for a (not to scale) diagram.

Figure 2: Diagram of HoloLens display system, based on best available information and not to scale.

To reiterate: The virtual 3D objects displayed by HoloLens are not holograms (they just look like holograms). The lenses themselves, on the other hand, are holograms.

So, the “lenses” in HoloLens are comprised of holograms, which makes them “holographic lenses,” or, you see where this is going, “HoloLenses.” The folks in Microsoft marketing must have had a field day with this.

While I’m on the topic: Microsoft are still sending mixed messages regarding HoloLens’ target market. On the one hand, they’ve clearly stated that they are targeting enterprise applications; on the other hand, their demonstrations are primarily focusing on consumer applications, specifically video games. That might not have been a wise choice, given the HoloLens’ dev kits rather consumer-unfriendly price of USD 3,000. If they’d focused on scientific, medical, or engineering applications, nobody would have batted an eyelash, but this way, gamers all over are upset that they’re being priced out of their hobby.

7 thoughts on “HoloLens and Holograms

  1. What’s gonna be the privacy policy of this room mapping thing? Are they gonna tell advertisers how many people are seen by the device on average? How much space you got on each room so you’ll receive ads for the biggest things that can fit in your house? Are all your activities gonna be stored in the cloud? Is the headset gonna stop watching everything when you take it off?

  2. Oliver,

    Are you sure that holographic waveguides are being used in HoloLens or is this just an educated guess? A holographic waveguide vendor claimed that HL wasn’t doing what they do.

    • It’s a guess, based on all the available information I found.

      Regarding your article: you say “[Exit pupil expansion], in turn, is probably why measuring the interpupillary distance is a large aspect of fitting people for the HoloLens.”

      I don’t think that’s the case. The waveguide exit panels, be they holographic or diffractive, look to be big enough to cover the range of interpupillary distances in the population, and I have not noticed hardware IPD adjustment knobs on the HoloLens.

      On the other hand, exact IPD is an important datum on the software side, where it’s required to project virtual objects in such a way that they correctly appear alongside real-world objects. Knowing IPD is arguably more important for AR than for VR: in the latter, wrong values will lead to wrong perception of scale that might be difficult to notice because the viewer only sees virtual objects and has no point of comparison, but in AR, virtual and real objects have to co-exist in the same space.

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