Wired: Hololens 2


Last summer, news reports emerged that Microsoft had filed a patent with the US Patent and Trademark Office back in 2016 that described expanding the field of view on a display using MEMS laser-scanning technology. MEMS refers to microelectromechanical systems, which involve miniaturized electrical and mechanical components. According to academic journals, lasers have been a part of MEMS research and applications for decades. That part of Microsoft’s patent filing wasn’t new. What was new was Microsoft’s proposed method of modulating MEMS mirrors to direct lasers in a way that created greater angles, and as a result, a larger field of view. “From an empirical standpoint, we know that field of view is critically important,” Bailenson tells WIRED. “It causes people to have a better overall experience, because they can move their head in a natural way.”

So this was obviously one of the aspects of HoloLens that Microsoft had to improve upon. And it did. The first HoloLens had a 34-degree diagonal FOV; the new headset’s field of view has “more than doubled,” Kipman says, to a 52-degree diagonal field of view. (Microsoft declined to share exact measurements for this new eyebox, saying that the x-axis and y-axis are not the best way to think about the FOV improvements. But much of the expansion was in the vertical dimension.)

The HoloLens optics team also managed to maintain a resolution of 47 pixels per degree while expanding the box. This means that, while the first HoloLens had the equivalent of two 720p displays, one for each eye, this new face computer has the equivalent of a 2K display for each eye. And the lens stack has been reduced, going from three lens plates down to two.

Both Kipman and Zulfi Alam, who manages Microsoft’s optics engineering team, acknowledge that the visual experience on HoloLens 2 isn’t totally immersive yet. It’s the mechanical method by which they’ve increased the field of view, though, that they appear to be most excited about. The MEMS mirrors that Microsoft is using are the “largest small mirrors in the world,” Alam says. The mirror looked like a speck of debris on a conference room table; when I picked it up to peer at it, I could see it was a tiny reflective disc on my finger tip.
Normally, with a DLP, LCD, or LCoS projector in a headset, light particles are spit out, refracted, bounced off of lenses, and beamed back into your eyes, essentially tricking them into seeing holograms. (The original HoloLens used a LCoS projector.) And HoloLens has enough sensors to know your head position in space, so it knows where to beam these images into your pupils into order to convince you you’re seeing things. Using the MEMS mirrors, which are strobing 54,000 times per second, HoloLens 2 is now splitting that light apart and reconstituting it at every single pixel. “It’s replicating your pupil multiple times,” Alam says.

The benefit to doing it this way, he says, is that when you want to increase the field of view, you just change the angles of the mechanical system. You don’t have to build a bigger backplane to create a bigger field of view, which would then increase the overall size of the product.