The ultimate AR lens guide and its implications

AR/aR manufacturer’s chosen and developed lens for its smart glasses is one of the defining features of the smart glasses. It defines price, form-factor, perceived display quality, and much more. The advancement of the waveguide lens design and the mass manufacturing thereof has brought a surge of thin and light aR/AR smart glasses, predominantly seen in the Chinese market.

The question is what are the three aR/AR lens designs. what are the differences and how has this impacted the smart glasses market in recent years?

The waveguide lens design that enables the recent surge in AR smart glasses

A technology overlooked when covering smart glasses and the rise thereof is the mass manufacturing and economies-of-scale of the waveguide lens design. A lens design, which compared to the previous Birdbath and Bug-Eye design, is more versatile, achieves higher visual clarity, and has fewer double images, known as “ghosting”.

Essentially, for augmented reality to function, light from the real world with the digital display light must enter the user’s eyes simultaneously. To achieve this, mirrors, lenses, and/or prisms are utilized based on the chosen waveguide, Birdbath, or Bug-Eye technology.

The TCL Nxt Wear Air utilizes a Holographic waveguide design, like the HoloLens 2, whereas Magic Leap One and Oppo Air Glass use the Diffractive waveguide technology. Oppositely, the Nreal Light uses a wholly different optical design called Birdbath.

The differences between Waveguide, Birdbath, and Bug-Eye are that Bug-Eye and Birdbath in the past were utilized more frequently due to lower production costs, while the waveguide options were still in R&D.

Birdbath lenses

Namely, Birdbath loses much of the light bounced from within the display to the wearer’s eyes. As a result, Birdbath AR glasses usually have darker lenses to compensate, detracting from the point of augmented reality: darkening the real world for the wearer. Additionally, the Birdbath lens is plagued with “ghosting”.

Birdbath, however, is known to have a higher FOV and can typically be manufactured at lower costs – albeit higher than Bug-Eye – and enable a slimmer form factor than that of Bug-Eye.

Bug-Eye lenses

Bug-Eye works with a one-way mirror reflecting an LCD image onto a piece of glass for the wearer to see. This means that for the FOV to be large enough, the size of the final headset must be large and clunky. But as Bug-Eye only uses a mirror, the production costs are the lowest, translating to affordable end-consumer prices effectively able to target a broader market.

In short:

1. Bug-Eye is cheapest in manufacturing cost but large and clunky in form-factor.
2. The Birdbath is more costly to produce than Bug-Eye but less than waveguide. Additionally, the Birdbath enables a slimmer design. On the other hand, the lenses are dark, and instances of ghosting are prevalent.
3. Waveguide is the most expensive in mass manufacturing and more advanced technology but enables a sunglasses-like form factor more appealing for broader audiences. Additionally, scaling production has made the waveguide less capital intensive and more accessible for aR/AR manufacturers.

Waveguide lenses

The newer waveguide option, in recent years, has seen benefits of economies-of-scale and manufacturing advancement, in effect bringing down production costs of this advanced lens design. That is why we have seen a surge in lightweight and thin AR glasses with a lower price tag, combined with consumers having a more relaxed position on privacy: something the original Google Glass was criticized for back in 2012. Furthermore, waveguide displays have a higher perceived visual quality with increased clarity and minimized ‘ghosting’.

In effect, the mass production capabilities of the waveguide, from companies such as DigiLens, which Samsung invested substantially during DigiLens’ Series D fundraiser. In effect, waveguide has brought down the cost of utilizing such lens technology: bringing on a surge of thin, stylish, and lightweight AR smart glasses to the reality market.

TL: Bug-Eye, M: Birdbath © Rob Delwo, TR: Waveguide © DigiLens

The two different waveguide designs and their differences

Before we go into the differences, let’s get the basics covered first.
The waveguide technology is explained in the name itself, in that it is a lens design guiding light around before entering into the wearer’s eyes: thereby the name “waveguide”.

Generally, the differences in waveguide design dictate how the lens itself bounces light from the display in the glass before entering the wearer’s eyes.

The geometric waveguide design

Geometric waveguide uses several transflective (a combination between transmission and reflection of light simultaneously) mirrors and prisms to bounce light from the display to the wearer’s eyes. Effectively this waveguide solution comes with mechanical tolerance, ease of form-factor and ergonomics, and generally more room for user interface designs such as touch controls.
Although, the geometric waveguide comes with a general lower light output – resulting in a perceived lower screen fidelity, even though the color differentiation itself does not impose a bias on any color. It is simply that the perceived image is poorer for the wearer. Another downside is that stripes are visible on the lenses themselves, potentially distracting the wearer from the digital reality on top of the real reality.

Diffractive waveguide designs

SRG waveguide designs

This design uses a thin layer of surface relief grating (SRG), which is a series of laser-cut valleys on the surface of the lens: see (b) in the picture below.

In other words, the orientation and depth of the valley enable light to bounce around and propel itself into the wearer’s eyes. Explained another way, think of a glass pyramid and what happens when you shine light through it. Here you see the light shone being diffracted into the full-color spectrum and directed linearly towards one area. The diffractive waveguide lens utilizes the same concept.

Interestingly, a three-layer diffractive Patented Intellectual Property got adopted by both Microsoft and Vuzix of which we now see with the new Shield glasses from Vuzix using a holographic or binocular diffractive design.

The upside in the diffractive lens technology is the ease of mass manufacturing, as it uses laser etching rather than moulding, cutting, and glueing of striped glass in the geometric design.

Further, the diffractive method enables wider interpupillary distances, meaning that different face topologies (such as eye distance) are easier to compensate for, effectively widening the potential customer base.

The downsides with the diffractive method are that the design tends to lose half the light being sent into the wearer’s eyes, while color dispersion is a known issue, lessening the perceived display quality causing what is known as the “Rainbow effect”.

Interestingly, the solution to mitigate this perceived rainbow effect is to have different layered diffractive gratings, as was adopted by Vuzix and Microsoft. But this thickens the glass itself and goes against the norm in smart glass design of thin, lightweight, and stylish. We, therefore, see innovations to compensate for this multi-layer diffractive solution onto a single-layer diffractive technology. Namely, the Finnish company Dispelix is the leader in the single-layer diffractive waveguide: a company that secured $33 million in Series-B investment in late 2021.

Holographic waveguide designs

Lastly, we have the holographic diffractive lens. This design employs a thin film of holographic material, replacing the tiny prims for nano-scale holograms to bounce the light. Like the layered SRG variant, the issue of color dispersion plagues this solution but simultaneously also comes with a haze effect and a smaller FOV.The upside is that the holographic waveguide is even more cost-effective in mass manufacturing. While it also does not have the same thickness nor perceived ripple issue.

Conclusively, the diffractive waveguide and the innovations achieved is paving the way for mass adoption in AR smart glasses. Although other customer apprehension is expected to still exist for the western market, Chinese consumers are generally laxer around privacy complications.

From virtualrealitypop.com, “Categories of waveguide technologies: a) geometric waveguide with reflective mirror array, b) diffractive waveguide with surface relief gratings, c) diffractive waveguide with volumetric holographic gratings.” Images modified from source: https://bit.ly/3zEWoty

The rise of “Air” AR/aR glasses in China

Over the past couple of years, we have seen a surge in “Air” variants of either existing or new AR/aR smart glasses devices. New iterations which pursue a slimmer, more stylish form-factor and design profile, enabled by the mass manufacturing of the waveguide design.

Oppo Air Glass

Oppo Air Glass is expected to begin a limited release in Q1-2022 in China and will differentiate itself on a monocle, waterdrop type design. Similarly, Oppo considers the category of its Air Glass to be assisted reality (aR), rather than augmented reality (AR). The difference is that aR provides relevant information on top of the lens, such as notifications, whereas AR delivers a digital interactive experience adapting itself based on the real-world environments. The former is less processing-intensive than the latter and thereby more affordable.

Nreal Air

Nreal Air is the successor to the Nreal Light and again is a slimmer and more stylish (looks like sunglasses) offering. Furthermore, Nreal strives to differentiate itself through its AR application store named Nebula.

TCL NxtWear Air

Announced at CES2022, the TCL NxtWear Air is the slimmer successor to its NxtWear G AR glasses. The new NxtWear Air strives to utilize TCL’s broad market presence in China to appeal to audiences; while targeting an entertainment-led use case. A similar strategy to Nreal, which also focuses on entertainment. Namely, Nreal found that “Consumers today are seeking lighter, but longer-lasting AR glasses exclusively for streaming media…” said CEO and founder of Nreal, Chi Xu.

Huawei X Gentle Monster Eyewear II

Although not banded “Air” and by extension the only outlier, the Huawei Eyewear II fits the trend.

Huawei has an assisted reality lineup called Eyewear, offering use cases as “your next smart personal assistant”. Huawei, through partnering with South Korean fashion-eyewear brand Gentle Monster goes for a stylish body of its Eyewear smart glasses: providing a fashion statement together with assisted reality uses. The new and lighter aR iteration is called Eyewear II, seen in the picture below.

Conclusion

In the past, augmented and assisted reality were driven by the lens designs of Birdbath and Bug-Eye, two clunky and lower quality AR solutions.
So, when mass production and economies-of-scale effects turned the new and more advanced waveguide design more accessible, a surge in aR and AR glasses were set in motion. The waveguide lens features both higher quality and a thinner and lighter AR/aR experience. Specifically, leaps in innovation have been achieved through its single-layer surface relief grating diffractive technology.

In effect, this broader use of the waveguide has resulted in a rise in thin and light aR/AR smart glasses seen mainly in the Chinese market from Chinese consumer technology brands. Assumedly due to western consumers being apprehensive regarding privacy issues stemming from the discontinued consumer-oriented Google Glass in 2012/2013. It is just a matter of time before the vast innovation of aR/AR smart glasses in China and the other Asian markets arrives in western markets.