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Laser Illumination Could Cause LCOS to Win Out Over OLED in Near Eye AR
The conventional wisdom is that eventually OLEDs will become inexpensive and they will push out all other technologies in near eye because they will be smaller and lighter with a simple optical path. But in reading ‘Steve Mann: My “Augmediated” Life”‘ in IEEE Spectrum I was struck by his comment “It requires a laser light source and a spatial light modulator” (a spatial light modulator are devices like LCOS, transmissive panels, and DLP). The reason he gives for needing a laser light source is to support a very high depth of focus. For those that don’t believe LCOS and lasers give a high depth of focus you might want to look at my blog from last year (and the included link to a video demonstration).
Steve Mann has “lived the dream” of Augmented Reality for 35 years and (with due affection) is a geek’s geek when it comes to wearing AR technology. He makes what I think are valid points as to what he finds wrong about Google Glass including the need to have the camera’s view concentric with the eye’s view and issues of eye strain in the way the Google Glass image is in the upper corner of your field of view which can cause eye muscle strain.
But the part of Steve Mann’s article really caught my attention is the need for laser illumination to give a high depth of focus to reduce eye strain because you need what you see in the images to be in focus at the same depth as what you see in the real world. Google Glass and other LED illuminated AR generally set the focus so that the display focuses in what would be a persons far vision. Steve Mann is saying is that the focus in your eye from the display has to match that of the real world or there will be problems and the only known way to do this is to use laser illumination.
This issue of laser light having a large depth of focus when used with a panel is an important “gem” that could have a big impact in terms of the technology used in near eye AR in the future. LEDs and that includes OLEDs produce light with rays that are scattered and hard to focus. Wheres lasers produce high f-number light that is easy to focus (and requires smaller optics as well). As I said at the top of this post, the conventional wisdom is that cost is the only factor keeping OLEDs out of near eye AR, but if Steven Mann is correct, they are also prevented from being good for AR due to the physics of light. And the best technology I know of for near eye AR to mate up with laser light is LCOS.
Hi Karl, Thanks for getting back to regular posting. Another advantage of using laser illumination would be that very narrow linewidth dichroic mirror coatings could be used on the glasses to minimize their scene filtering effect while preventing “light leakage” which would be both energy inefficient and annoying to others (like an oncoming car not dipping its headlights?) And, like in laser-illuminated head-up displays, speckle wouldn’t be too much of a problem because there’s no diffusing screen.
The the idea of having narrow filters to limit the light going out of the display would seem to be a very good idea. You wouldn’t see the light in the eyepiece as happens with Google Glass. It’s not bright like a headlight, but it must be distracting to the person seeing it and they have to wonder “what are you looking at?”
Interesting about the speckle. I would think there would still be the “subjective speckle” on the retina but I haven’t studied this, but I expect you have with your company’s work on speckle (for others http://www.dyoptyka.com/).
Hi Karl, I don’t mean to derail this particular thread by getting into speckle but I might as well continue! Certainly some speckle reduction would be required in the illumination optical system to minimize “subjective speckle.” Once this is done, the perceived image quality would be good thanks to the glass being a nice smooth surface as opposed to a rough diffusing one.
Karl,
Not sure if you’re following the Unipixel story but it has many of the same promoters as MicroVision and I assume you’d have some relevant knowledge in this field (touchscreen).
You may want to come over SA and take a look. The stock has ran from $7 to near $30 since December and the stock is acting like they just re-invented the wheel.
Below are some of the proponents championing the stock. Some even claim a Billion dollar valuation in the near future..
http://seekingalpha.com/article/1242831-uni-pixel-still-the-best-investment-for-2013
http://seekingalpha.com/article/1123691-uni-pixel-independent-market-analysis-suggests-ben-wiley-has-axe-to-grind
http://seekingalpha.com/author/the-stock-miner/articles
Lasers high F# might be a disadvantage
It limits the eye box size to the size of the eye pupil
Omer,
I’m not an optical engineer and I could be wrong on this, but I don’t think the high F# will seriously affect the eye box. I will try and check and get back to you if I find out for sure.
Just to clarify,
My claim is limited to near eye applications (not projection).