On February 27, 2023, Xiaomi officially released the Discovery Edition of Xiaomi Wireless AR Glasses at the 2023MWC World Mobile Communications Conference . This product is equipped with an innovative digitally controlled electrochromic lens , which can adapt to different light environments. The shading mode can be more immersive when watching movies, and the transparent mode can make the AR experience of combining virtual reality more vivid.
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In this issue of Tech Talk, we invited Xiaomi material process engineer - Zhao Jing , to introduce the application and working principle of electrochromism (EC) technology in AR glasses.
Hard core index: ⭐⭐⭐⭐⭐
Hobby index: ⭐⭐⭐⭐
Reading time: about 7 minutes
1. Technical background and innovation
Xiaomi Wireless AR Glasses Discovery Edition is a human-centered design of AR glasses. The weight of the whole machine is extremely light. It is the first to adopt wireless distributed computing. It has a retina-level light environment adaptation display. , a complete large-screen application ecosystem, and rich interconnection scenarios.
Xiaomi Wireless AR Glasses Explorer Edition
>>>> 1.1 AR display effect that perfectly blends digital and real world
AR technology, that is, augmented reality technology, superimposes the projected virtual image and the real environment perceived by the user on the same screen or space in real time, so as to realize the fusion of the surrounding visual environment and the virtual graphic information, presenting a richer perceptual effect to the user. new environment.
One of the core experiences of AR glasses is its virtual imaging effect , which requires clear and bright virtual images through the design of optomechanical and optical display modules. However, under strong and complex outdoor light conditions, the imaging of AR glasses will be seriously disturbed. Due to the limitation of the brightness of the light machine and the light effect of the light display module, it is impossible to present clear and bright images in a strong light environment as under indoor light. AR images, this is the imaging problem faced by AR glasses.
So, how to make the glasses clear and bright as the real thing when users look at the glasses under different ambient light conditions?
AR imaging effect is related to ambient light conditions
>>>> 1.2 Innovative solution for intelligently adjusting the light transmittance of the lens with numerical control electrochromic technology
In order to solve this imaging problem, the industry usually equips an additional black shade lens hood as an accessory of AR glasses to reduce the interference of external ambient light on imaging and improve the relative brightness of the display module. However, this solution requires additional accessories, which increases the volume and weight, and is inconvenient in actual use. It needs to be carried with you, and it needs to be manually installed and disassembled in different environments. The user experience is poor.
In response to this problem, Xiaomi has developed a brand-new numerical control electrochromic technology solution to intelligently adjust the light transmittance of the lens. This technology applies electrochromic materials to display module lenses, controls electrochromic materials to exhibit different light transmittances under different electric fields, and can quickly switch between different transmittances to cope with the external environment. The ambient light changes .
For example, in an indoor environment or when the light is not strong, adjusting the lens to a transparent mode with high light transmittance will not affect the virtual imaging effect, but also enable users to better perceive the display environment, and the experience of AR combining virtual and real is more vivid; and When you come to an outdoor environment with strong light, adjust the lens to the low light transmittance shading mode to reduce the interference of external ambient light on imaging, display clear images, and make users more immersed in watching movies.
One-key switch between shading/transparency mode
2. Analysis of technical principles
The principle of CNC electrochromic materials is that the optical properties of materials (reflectivity, transmittance, absorptivity, etc.) can undergo stable and reversible color changes under the action of an external electric field, and the appearance is manifested as color and transmittance. The reversible change of light rate, so as to realize the digital control of color change.
The electrochromic lens developed this time adopts an inorganic all-solid-state complementary electrochromic structure, strictly controls the laser processing technology and packaging technology, realizes excellent photoelectric performance and reliability, and can achieve four-speed light transmission under low driving voltage The light transmittance/shading rate can reach the highest range of current industry products, and can achieve a fast response in seconds.
>>>> 2.1Inorganic all-solid-state complementary electrochromic structure
The electrochromic lens used in this product adopts an inorganic all-solid-state complementary electrochromic scheme, which contains a total of 8 layers.
The electrochromic lens consists of a transparent substrate and a first transparent conductive layer deposited on the substrate using a magnetron sputtering process, an anode ion storage layer (NiOx), a solid electrolyte layer, a cathode electrochromic layer (WO 3 ), a second transparent Conductive layer, and use OCA glue to bond with the transparent cover, and finally package to avoid the infiltration of water and oxygen, so as to achieve high reliability and cycle life.
>>>> 2.2 光The chemical modulation amplitude can reach the highest range of current industry products, achieving high light transmittance/shading rate
In order to achieve a higher optical modulation amplitude, the electrochromic solution developed this time integrates two types of electrochromic materials to participate in the color change together to realize the superposition of the color change effect of the two materials, which is called a complementary electrochromic device. .
Compared with the electrochromic device with only one electrochromic film, this complementary electrochromic device using the combination of anodic and cathochromic layers has a larger light modulation range, greater charge storage capacity and cycle Excellent performance such as longer service life . The optical modulation range of the lens developed this time can reach the highest range of current industry products.
>>>> 2.3 Accurate digital voltage four-speed control
The voltage rise and fall curve is adjusted by the control circuit, so that the precise control of the color changing effect can be realized through the regulation of the voltage. When a forward voltage is applied, the ion storage layer of the electrochromic lens is pressurized, so that the ions stored in it are released in a controlled manner, and are transported to the electrochromic layer through the electrolyte layer. The oxide of nickel presents a brown oxidation state, and WO 3 presents In the blue reduction state, the overall lens color is deepened, and the light transmittance decreases. Conversely, when the reverse voltage is applied, the ion storage layer of the electrochromic lens is depressurized, and the ion storage layer returns all or part of the ions in the electrochromic layer, and the nickel oxide and WO 3 layers begin to fade to the set state , the overall lens color becomes lighter and the light transmittance increases.
Compared with the usual two-level adjustment, this solution sets up four-level adjustment. By matching the Gamma curve of the human eye, a more flexible four-level adjustment is set based on the final brightness perceived by the human eye to adapt to complex external light Environment, to bring consumers a more comfortable experience.
>>> 2.4 seconds fast response, realize any switching of four gears
At present, the photochromic scheme is widely used in the field of sunglass protection. The photosensitive material inside the lens changes color under the irradiation of outdoor ultraviolet light. There are also attempts to apply it in the field of AR glasses, but this passively driven form of light has a long time to change color. Usually 2~3min. In contrast, the electrochromic lens developed this time can achieve rapid response through precise control of the electric field, color change in seconds, and smooth switching of any gear within four gears to achieve a fast and uniform color change effect.
3. Future evolution of technology
Electrochromic technology is a typical cross-disciplinary technology with complex preparation process. Its current commercial application is immature, and continuous optimization iterations are needed to meet increasingly stringent technical requirements.
Achieve a larger dimming range to meet a wider range of needs;
Achieve higher shading efficiency to shorten response time and improve user experience;
Achieve higher structural stability to prolong cycle life and improve reliability in use;
Realize the intelligent adjustment of pixel level and area, and realize the fusion of virtual reality with consistent lighting through the combination of materials, software, algorithms and sensors, and interact with real scenes.
It is believed that with the evolution of technology, electrochromic technology will be more widely used in the field of AR glasses in the future to provide users with a better AR experience.
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