[epmaybe]

I watched the Verge video this morning where they tried to explain how the hologram projector works, but I am still confused. How can it ensure a sharp image shining directly through your own intraocular lens (not the glasses themselves) to the retina? If you have a "longer" or "shorter" eyeball the light ray's focus point will not be on the retina itself.

[defterGoose]

Laser light is "coherent" both spatially and temporally. Spatial coherence allows the beam to be "collimated", which basically just means that it looks like a cylinder and not a cone. That's why you can shine a laser at the moon and see the spot; most of the energy from the laser makes it to the same place, bounces back to your eyes, and you get a bright spot. Shining a flashlight doesn't work because the light spreads out too much. Technically some of the light still gets to the moon and back to your eyes, it's just below the threshold of your eye's ability to distinguish differences in brightness.

For the glasses, the laser is probably being scanned using a mems mirror (like how a DLP tv works, sorta), and modulated in brightness periodically to create the pixels. Since there's only one "point" of contact between your lens and the beam, the lens doesn't distort the beam like it would an image. That's where the idea of focus comes in. If you were looking at a photograph with your eye, there would be many sources and colors of light. Since the lens refracts incoming light based on direction, position, and color, your lens' job is to make sure the "pixels" of the photograph stay spatially organized with respect to each other. That's what being in focus means. And since the laser has only one color and one direction, all that light stays together and makes a nice dot on your retina. The only thing left to do is make a correction to the overall distortion pattern your lens introduces ,which is similar for pretty much everyone. Same reason you need to add barrel distortion before sending video to an HMD. I think that's what they were showing with that "warping" red image of the glasses' display.

[epmaybe]

Thank you for the explanation! I had figured that laser light was indeed different than normal light rays, but couldn't remember my undergrad optics to explain why.

[imcoconut]

Thank you for the excellent description

[epmaybe]

In reading the article I see that they are using VCSE Laser. Does that answer the question?

[mojomark]

Just think of it this way: all natural light (i.e. the typical incoherent light you see reflected or emitted off of surfaces in your environment) emit wavefronts that eminate spherically from each reflection (or emission) point. As such, the spherical wavefronts from light eminating from objects close towards your eye (i.e. less than ~8m away, a.k.a optical infinity), will have a curvature that the optics of your eye (i.e. your cornea and lens) work or morph in order to focus into a point on your retina. The closer the object is to your eye, the greater the curvature (i.e. the higher the angle of divergence). However, objects further from your eye (i.e. greater than ~8m, or optical infinity), from your eye's perspective, will have a wavefront that is still curved, but that is essentially flat, such that your eye's optics do not have to morph to focus thes objects. All objects past optical infinity appear "in focus" unless your eye attempts to focus (i.e. the lens morphs or "accomodates") on an object in the foreground. A laser beam essentially emulates a flat wavefront because the photons comprising the beam have a very small angle of divergence. Thus, light eminating from a laser will appear in focus just like an object placed at optical infinity. Actually, this is part of the principle underpinning the accomodation-vergence conflict.