How does the holographic grating in a Near Eye Waveguide work? I'm an electrical engineer who recently started working with these near eye optics like this one https://www.trulifeoptics.com/  It looks like a microscope slide but it's a waveguide that transports a display from a little LCD screen to a clear section in front of the users eye.  I understand that it combined with the pupil of the eye generates the image that I see.

I understand waveguides from an electrical point of view (and somewhat of an optical one).  What I'm curious about is how they make these holographic gratings that couple the image in and out of the waveguide.  I don't even know what they are.  Are they grinding tiny little aberrations into a sheet of glass, or is it an etching process, or laser?  I guess if it was plastic it could be molded like a CD is? 
I'm also curious about how why it's called holographic.  Holographic just conjures up images of credit cards security stickers and Nova programs from the late 80s for me :)
 A: 
I'm also curious about how why it's called holographic. 

Holograms are basically complex diffraction gratings, designed to form an image. Often, even non-imaging diffractive components are called holograms (for example, the colorful sheets that reduced the need for backlighting behind LCDs in the 1990's). So a better word for this device might be "diffractive optics", but "holographic" has better name recognition, so that's what you're going to see in marketing materials.

What I'm curious about is how they make these holographic gratings that couple the image in and out of the waveguide. I don't even know what they are. Are they grinding tiny little aberrations into a sheet of glass, or is it an etching process, or laser? I guess if it was plastic it could be molded like a CD is?

Diffractive optics can be made by any of these processes. They could also be made with something like a photographic emulsion on the surface of the glass, or by a photosensitive material embedded in the glass. Either of which would be exposed to light in an appropriate pattern to form the grating as part of the manufacturing process.
Which process provides adequate resolution for this application at lowest cost is a question of engineering, not physics. Based on the image, I suspect this device uses some kind of plastic film, possibly stamped with the grating pattern, layered on one side of the glass.
