[hwillis]

> Wouldn't the display application here be something like a scanning AR/VR headset which constructs an image directly on your retina with a small number of beams moving very quickly (kinda like an old CRT display)?

That would only work if the display stays exactly (.01 degrees) in the same spot relative to your eyes. What's it going to do, project a million images, each the width of your pupil? You'd need extremely good eye tracking. You can't put this on a contact lens because the substrate is too thick, in addition to all the manufacturing problems.

> 1/0.17 = 5.9 ppd is about half the angular resolution of the commercial Index VR headset, so it does still need a bit more progress before it would be competitive.

Factors of two is a massive underestimate. The screen in a VR headset is waaaaaay bigger than your retina, which you're projecting onto. Not only that, but you're really concerned about projecting onto the fovea, which has about 1 "pixel" per 20 microns. At 10 cm (4"), 20 microns width would be .011 degrees per pixel. The beam is actually pretty sharp, so halving the beamwidth would lower the bleed to <<10%, which is fine. All together that's ~30x improvement in beamwidth.

[nshepperd]

That would be what is required for an ideal display. Current VR displays get closer to 0.1 degrees per pixel so it would be a ~3x improvement to be competitive with existing tech, as I said.

[hwillis]

No, I'm talking about what is required to get to the same as current VR. Beamwidth and pixels per degree are NOT equivalent. Beamwidth causes adjacent pixels to blur into each other, which is a much bigger issue when projecting onto the eye because it's such a smaller surface. The equivalent factor for a display would be the diffraction blur introduced by a pixel.

Back of the envelope math: at 10 pixels per mm, 500 nm light through a circular aperture[1] has a half-power beamwidth of .0013 degrees, so two orders of magnitude better than this technology. That is what you'd need for an ideal display. The bare minimum is just that the blurring at the retina does not cause pixels three rows over to bleed into each other.

[1]: https://www.cv.nrao.edu/course/astr534/2DApertures.html