How does the Glass display project the image onto the lens?

Google Glass uses a Field Sequential Color LCOS to project the rendered image through a lens and into the retina, as first determined by Karl Guttag in March 2013.

Basically, the image of each single color channel is synthesized by an LCOS array on a chip, while the illumination source is rapidly cycled through pure red, green, and blue LEDs, in synchronization with the color channel switching.

Each of these sequential images is passed through a series of lens elements that direct the resultant image to the user’s retina via the Glass display.  The result is that the user percieves a small translucent screen hovering at about arms length distance, as extended up and outward from the right eye. Since the colors are cycling very very quickly, the user perceives a full color video stream.

Here is a diagram of both the LCOS image generator, as well as the RGB lamps, and the lensing system:

structure of an FSC LCOS image generator

The determination of Glass utilizing an FSC LCOS is based on detailed analysis of the Google Glass Fashion Week video by Karl Guttag:

Sequential Red, Green, +Blue Fields Captured From Google YouTube Video DVF [through Glass]

sources:

Karl Guttag Glass Investigation:
Google Glass Is Using Field Sequential Color (FSC) LCOS (Likely Himax)

Himax LCOS displays:
: About Himax Display : :

original post: Quora

 

2 thoughts on “How does the Glass display project the image onto the lens?”

  1. Karl Guttag

    Thanks for the reference to my site in your blog. I would like to point out that the diagram you showed with an X-Cube color combiner is not what anyone would use for near eye displays. For near eye field sequential color LCOS, they normally use a stack of films and maybe a Fresnel lens to spread the light from a set of red, green, and blue LEDs (some manufactures have the 3 leds in one package). Then the beam splitter is usually either a flat or curve polarizing “film” (sheet of plastic) that is very low cost and inexpensive.

    I took a diagram from a 2001 patent and labeled the key components. This is not exactly what Google is doing (as the diagram was from back in 2001) but it is probably similar.

    http://www.kguttag.com/wp-content/uploads/2013/03/Simple-LCOS-Optical-Engine-2.png

    1. acroyogi Post author

      Thanks so much for both the original research and the clarification, Karl!

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