Ari Grobman is the Chief Executive Officer at Lumus.
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In the technology world, there’s a strong consensus that the metaverse is moving closer every day. But what is the metaverse, exactly? For many, the metaverse means living every day in virtual reality—wearing headsets, immersed in fantastic worlds—or maybe sitting in virtual conference rooms, chatting with the avatars of colleagues from around the globe.
Augmented reality offers a vision of the metaverse that’s closer to our physical life. AR glasses will be the next indispensable mobile device, a “quasi-successor” to phones and tablets. Ordinary-looking AR eyewear can project images on a transparent virtual screen directly in front of the eyes, displaying everything from navigation, translation, games and movies to email and spreadsheets. The transparent screen doesn’t obscure the real environment or the real people in it. The transparent screen will be part of the physical world, for AR offers an elegant bridge between the virtual and physical worlds.
Curiously, the most advanced augmented reality employs a time-tested technology: the mirror. It’s just an everyday object to most of us, but there’s an amazing history behind the looking glass: For instance, Egyptians were using mirrors around 2900 B.C., bronze mirrors were made in China circa 2000 B.C. and mirrors made of polished stone have been traced back to 6000 B.C. Now, simple mirrors are the unexpected key to the technology of AR eyeglasses.
How is it that today’s most futuristic application depends on one of history’s most ancient technologies?
How Augmented Reality Works
Waveguide architecture is one of the more prevalent AR technologies today; however, not all waveguides employ mirrors. Reflective 2-D waveguide architectures use an array of partially reflective mirrors to reflect a virtual image into the wearer’s eye. The image travels through a microprojector to a lens in front of the eye, creating a transparent display that layers the virtual image over the view of the real world.
Light enters the waveguide through a small aperture in the microprojector, which is hidden in the temple of the eyeglasses, and leaves the waveguide through a larger aperture at the other end. The exit aperture is centered in front of the eye, where it redirects light and projects it toward the eye.
Within the waveguide, cascading mirrors redirect and expand light. Light moves from mirror to mirror in a uniform sequence, so the eye always sees the complete image as it moves left to right and up and down. The mirrors are micro-thin and embedded into the lens, not visible, so the eyeglasses look normal and have a slim profile. The alternative of using a single mirror would require a thick lens—resulting in bulky, unstylish AR glasses.
Why Mirrors Matter
One major alternative to reflective waveguides is diffractive waveguides, which use gratings rather than mirrors. (A diffraction grating is an optical element that divides light composed of many different wavelengths into separate light components according to wavelength.) Reflective waveguides are considered optically superior to diffractive ones. While mirrors reflect light in one direction and treat all colors alike, gratings disperse light, diffracting different colors in different directions from different angles. This creates some fundamental problems unique to diffractive optics.
For instance, the way diffractive waveguides disperse colors creates a rainbow effect, and the eye sees red, green and blue separately. In contrast, mirrors don’t break up colors but reflect them uniformly. The diffractive gratings are inefficient, too, projecting less light into the eye while up to 50% escapes outward. This issue, called forward light leakage or waveguide glow, produces the startling effect of bright multi-colored lights shooting from the eyewear. That’s a bad look for the wearer—and it can compromise privacy and security by projecting personal information to onlookers.
Designing mirrors into waveguides has evolved significantly in recent years, with each breakthrough making waveguides smaller, lighter and thinner. Several important distinctions benefit AR users: a bright virtual display that’s easy to view even outdoors in full sunlight, a distortion-free image with both uniform color and a true white and better battery efficiency.
Making History With AR
Regardless of how well waveguides may perform, the industry still faces crucial challenges before it can reach a “glasses for the masses” moment. Mapping the user interface (UI) or user experience (UX) to manage a potentially overwhelming stream of content from the metaverse is critically important. None of us want to suffer input overload from wearing AR glasses. The key to making AR a rich and rewarding user experience is the right content at the right time and no more. Or, as Albert Einstein is credited with saying, “Everything should be made as simple as possible, but not simpler.”
Consumer demand for fashion is another hurdle to clear. The industry will be asking users to wear these devices on their faces. Some AR experts call this “sacred space,” and for good reason. Most of us choose eyeglasses or sunglasses quite carefully, with considerable deliberation in front of a (regular) mirror. Whether manufacturers use mirrors (reflective waveguides) or other solutions, they must meet the challenge of creating aesthetically appealing designs before mass adoption can become a reality.
Mirrors are essential to many applications today, including high-definition television, massive telescopes and solar power plants. Even so, they may seem simplistic in the modern world. Other, more exotic technologies could be tapped to bring the benefits of a virtual world to our real world via augmented reality. Yet the most sophisticated AR applications are relying on one of the most elementary options. In a way, mirrors are taking us back to basics with a completely new way to use very old technology. There’s something genuinely satisfying about that.
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