From the disassembly of Meta and the revelations about Apple glasses, take a look at the "non-sci-fi but useful" AR glasses

Have you ever worn AR glasses?

Not the smart glasses like Ray-Ban Meta or Xiaomi glasses that can only play audio but not display visuals, nor the bulky XR headsets like Meta Quest or Apple Vision Pro. Instead, they are glasses that look no different from ordinary ones but come with a display screen.

▲ Meta Ray-Ban Display Image source: YouTube @Mrwhosetheboss

This kind of device, once exclusive to science - fiction movies and laboratories, has now become a battleground for tech brands big and small. Meta, Apple, and Google are all brewing new products and even regard it as the next - generation interaction to replace smartphones.

If previous AR glasses products were still in a relatively immature stage with many unsolved flaws in the user experience, then from the second half of this year to the year after next, AR glasses will enter a stage of "wild growth". We will see a large number of more practical solutions gradually implemented in products.

Install a "periscope" in the lens

Meta's first pair of glasses with a display, the Ray - Ban Display, released last month, has attracted a lot of attention. As the AR glasses with the best form and most mature technology at present, those who tried on the Ray - Ban Display couldn't help but exclaim that "the future is here".

People wearing the Meta Ray - Ban Display may not notice it, but outsiders will find a very significant difference between this AR glasses and other similar products -

When the glasses screen is lit, outsiders can't see any reflection or light leakage on the lenses at all. It looks no different from a pair of ordinary glasses without a screen.

▲ The Display worn by @Myra won't show obvious screen light leakage from a similar angle

According to the on - site experience of ifanr and @Myra, only when looking from the side can one notice the reflection of the waveguide screen wires on the glasses.

Almost all current AR glasses products or prototypes suffer from lens light leakage. The Meta Ray - Ban Display can be said to be the first pair of glasses that truly solves this problem.

The famous teardown institution iFixit discovered the secret behind this technology from the lenses of the Ray - Ban Display.

Essentially, AR glasses are like a small "projector" (optical engine) on the frame. It projects light onto the lens and then uses waveguide technology to "trap" the light in the transparent material, guiding the light to travel and finally reach our eyes.

There are two waveguide solutions for AR smart glasses: diffractive waveguide and geometric waveguide. Currently, most AR glasses products use the former, while the Ray - Ban Display uses the latter.

Diffractive waveguide creates a large number of parallel scratches on the lens through nano - imprinting or photolithography. The areas between the scratches are opaque, while the smooth parts between two scratches can transmit light. The diffractive direction of light is changed through the regular nano - structure. These scratches are the "gratings".

▲ The left is the input grating, and the right is the output grating. Image source: Nature

These gratings can be simply understood as the "entrance" and "exit" of light. After the light from the optical engine is brought into the lens by the input grating, it will travel in a regular and directional "total reflection" inside the lens. When it reaches the output grating, the direction of light travel is changed again and is directed towards the human eye.

▲ Image source: Bilibili @AK

Since light is reflected and transmitted densely inside the lens, a lot of energy is lost in the process. Not all photons can enter the human eye as guided by the scratches. Many photons deviate from the expected direction and appear in unexpected positions, resulting in the light leakage phenomenon visible from the outside of the lens.

▲ Light travels in "total reflection" inside the lens

The principle of geometric waveguide is actually much simpler than that of diffractive waveguide: it uses two kinds of mirrors to accurately guide light from the optical engine to the eyeball.

▲ The light leakage phenomenon of the Thunderbird X3 Pro

Careful observation of the Ray - Ban Display will reveal eleven relatively obvious "scratches" on the edge of the lens. That is the first prism, which guides the light from the optical engine to the central area of the lens. There are also some almost invisible mirrors in that area. Each mirror reflects about 5% of the light and accurately conducts the light to the human eye.

▲ The lens of the Ray - Ban Display. Light will be accurately transmitted inside the lens. Image source: iFIxit

This way of accurately conducting light using two kinds of mirrors is similar to the structure of a periscope. The advantage is that the density of light reflection and transmission inside the lens is greatly reduced, and the amount of light deviating from the expected path is also significantly reduced. Most of the light can reach the mirror in the center of the lens smoothly, so light leakage is less likely to occur.

▲ The structure of a periscope

Light - leakage prevention is not the biggest advantage of geometric waveguide. Due to the low - loss characteristic of geometric waveguide, an LCoS optical engine can be selected. Compared with the micro - LED and laser solutions of traditional diffractive waveguide AR glasses, the cost and energy consumption are much lower, which happen to be the two major shortcomings of current AR glasses.

However, at present, the geometric waveguide solution is still difficult to become a mainstream solution. Currently, only one optical company, SCHOTT, has the mass - production ability of geometric waveguide lenses. Compared with the mature diffractive waveguide production, geometric waveguide lenses require very precise processing technology to accurately control the angle and position of the mirrors. If there is an error in the angle, it may affect the imaging.

▲ Image source: iFixit

In addition, due to the micro - mirror structure inside the lens, geometric waveguide lenses have a certain thickness. Currently, the minimum is 2 - 3mm, while diffractive waveguide lenses can be made as thin as 1mm. In terms of the field of view, the geometric solution is also inferior to the diffractive waveguide, which means the display area will be a little smaller.

Therefore, there has always been a debate in the industry about which is better, geometric waveguide or diffractive waveguide. Meta's adoption of the geometric waveguide solution in the Ray - Ban Display is more of a technological experiment.

However, in the long run, the "light - leakage prevention" characteristic of geometric waveguide has more far - reaching value.

After the rise of smart glasses in the past two or three years, more and more people feel a little uncomfortable when they notice that someone around them is wearing a pair of "smart glasses".

▲ Meta Orion. Image source: TechRadar

This "intrusive feeling" brought by smart devices existed in the early days of the rise of BlackBerry phones and wireless earphones. Others can clearly sense that you are using a device and may doubt whether your attention is still on the current situation.

For smart glasses, this feeling is even more obvious - screen light leakage will block the eye contact between the user and the outside world, and eye contact is a very important part of modern communication and social interaction.

▲ If everyone wears a headset

Therefore, Apple's Vision Pro is specially designed with an "EyeSight" function to simulate and display the user's "eyes" when wearing the headset, aiming to preserve the user's sense of presence when using this immersive device.

The reason why we are reluctant to wear a bulky headset when going out is not only because of its weight and form but also because we hope to still look like "humans" rather than an extension of a machine.

The best tech products often make people unaware of the existence of technology, both for themselves and for others.

If it can't be the iPhone, then be the Apple Watch first

If the Meta Ray - Ban Display explores a new idea in the hardware form of smart glasses, what Apple is brewing is a software solution for smart glasses.

Due to the compact form of glasses limiting their performance, it will be very difficult to equip them with a complete graphical interface operating system like iOS. Currently, the AR smart glasses products with good reputations are basically equipped with a very simple system. Their functions and interfaces are similar to those of feature phones with buttons, and they don't emphasize the concept of "Apps".

▲ The Meta Ray - Ban Display is more like providing a visual interface for Meta AI

Apple is preparing to equip its AR glasses with the same visionOS system as the Vision Pro, but not an independent "full - version".

▲ visionOS

For the first - generation Apple Glasses, Apple obviously doesn't want to make a device that can replace the iPhone overnight. It is more like the Apple Watch, which can be paired with the iPhone and Mac and directly utilize the existing computing power and performance of the latter two.

If paired with the iPhone, the glasses will display a more streamlined interface to reduce resource consumption; when paired with the MacBook, a full - fledged visionOS experience