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.