AR HUDS. Off the shelf options.

I’ve lately acquired quite an interest in Augmented Reality (sometimes also referred to as Extended Reality), more often known by the acronym AR or XR. My particular area of interest are Head-Up Displays, or HUDs. I am currently working on an AR project that blends together a few interesting components to (hopefully!) produce interesting results. Check out my article with a brief summary of technologies used for implementing HUDs.

#AR #XR #Waveguides

In our day and age, most people would imagine a HUD as you see HUDs in video games – information projected right in your line of sight. Of course, video games never explain just how this is accomplished. But what if I told you that AR HUDs are in industrial use today, and they actually don’t feature any overly complex technologies? That’s right! The easiest, and the most pragmatic way to implement AR is to use a projector. What a brilliant idea!

There is, of course, a catch. And the catch is that in order to project a crisp and clear image at ambient lighting conditions, one needs a very powerful projector. A powerful projector means a large device, a large electricity bill and pesky heat issues. While devices of this type have been adopted for high value assembly work, they have not found purchase (pun intended!) in the lower cost segment and have left a trail of discontinued devices. See this wonderful Raspberry Pi project? You can no longer buy the projector they used. What about this, very well advertised device? Company is out of business. This is also why I am highly skeptical of the AI Pin.

Another way to achieve AR is to use a tiny LCD or LED/OLED screen and place it in your line of sight. You would normally not be able to see anything on a screen close to your eyes, but a collimating lens can parallelize the light emitted from the screen. I own a Vufine+ wearable display and it’s reasonably good, but you can also forgo the packaging and buy just the screen and driver board in China.

It is a decent way to implement AR as well as the cheapest, but you do sacrifice some of your field of view as it’s more of a picture-in-picture rather than true AR. Still, this is a robust and mature technology that I am using in one of my projects right now.

But is there a way to seamlessly project information into your line of sight without obstructing the view? There is! A very high-tech way that includes photonic waveguides and cleverly designed micro projectors. A compact projector can be place into the body or the arm of the glasses, the wave guides can steer the light to a position on the lens and that is where the magic happens! Exit gratings. Exit gratings are little interruptions in the wave guide that allow the light to escape normal to the waveguide and right into the user’s eye. What’s more, in the normal direction, the exit gratings are almost invisible, creating a non-obtrusive experience!

Is that the end-all solution to HUDs? Well, no. Maybe in the future. Devices on the market, as of writing this article and to the best of my knowledge, are low resolution, fairly low brightness and often monochrome. Such as the ActiveLook Dev kit shown above, which is just 304x256 pixels and monochrome. Companies are offering technology to offset that, good examples being Waveoptics and Exalos, but what you can buy right now is less impressive.

Well, is that it then? Not quite! While waveguide light transmission has incredible advantages, there is an alternative solution – free space transmission. This technology is a remake of the screen-in-eye approach where the source, a tiny projector, is placed away from the eye. This time, instead of using a waveguide the collimated light is projected on to an angled piece of glass, or other transparent material. The core principle is that the angle of reflection is equal to the angle incidence and so you can predict where ?the reflected will go. This allows impressive resolutions, the xReal Air 2 is 1920x1080 pixels!

So is this the ultimate AR experience? Sadly, no. There is light leaking to the outside which is undesirable and reduces the brightness you can achieve. Most commercial devices deal with this via shaded lenses on top of the screen lenses, making the device bulky and even more obtrusive. There is always a trade off!

?????????????? In short, there are no perfect options, but all of them have a niche. A projector based AR system is good for a shop floor where the work done is bringing you enough money to offset purchase and operating costs. In a scenario where cost is the driving factor, a collimated screen in front of your eye is a good solution. Think teleprompter or a teaching aid. In environments where a clear view is critical and communication is simple a waveguide solution is best. A sporting aid, a helper for an off-site repairman would be good options. Lastly, you get the free space projection glasses simply because you want a big picture!

Disclaimer: this text is not intended to guide purchasing decisions, its merely an opinion piece. But I'll probably end up owning each of the devices mentioned!