In the past year, the topic of AR glasses has gradually attracted the attention of major media. Internationally, Magic Leap One and HoloLens 2 have been released. Domestic new products such as nreal, Rokid and vivo have also been unveiled, and even Huawei AR Glasses and Apple AR glasses are also on the horizon, giving people the illusion that the era of AR glasses is coming.
In fact, today’s AR display technology has been developed and applied in military and other fields for many years. However, in recent years, the optical display in AR glasses has not made any major breakthroughs, but more It is used to reduce costs, reduce size, etc. Not only that, some manufacturers claim that the AR market is 120 degrees or even larger. In this regard, Daniel Wagner, CTO of AR company DAQRI, gave a clear attitude, including AR glasses’ field of view, display effect, eyebox, etc., there may not be any big breakthroughs in the short term.
The mainstream AR optical display systems on the market include: optical see-through and video see-through. It is reported that both AR optical display systems have been explored, but the video perspective method has great limitations in the weight and volume of the head display, so most AR glasses use optical perspective solutions.
The optical see-through solution is similar to conventional glasses. You can see the real world directly, but the optical module is not completely transparent, so AR reality is achieved by superimposing real images with virtual images. The disadvantage of optical perspective solutions is that it is difficult to display black or dark colors, so shadow rendering is difficult. Scientists have made some attempts, but the practicality is not high.
There are a variety of optical principles in optical see-through solutions, among which the most common at present are: optical waveguide and transflective. Currently, most high-end AR headsets, including Magic Leap, use optical waveguide display technology. The principle of this technology is that the micro-display projects light to one side of the optical waveguide. Through the principle of total internal reflection, the light will be reflected and propagated within the optical waveguide. , then reflected from the other side, and finally reflected into the user's eyes.
The advantage of the optical waveguide is that it can achieve a smaller body size, but the disadvantage is that there are some problems with image quality. In addition, the optical efficiency of optical waveguides is low, and the requirements for microdisplays are also higher. Existing optical waveguides mainly cooperate with LCoS and Micro OLED microdisplays.
Although semi-reflective and semi-transparent is more complex to design than optical waveguide, the principle is simpler and the cost is much lower than that of optical waveguide solution. Daniel said: A common misunderstanding is that even under the premise of pursuing a large FOV, AR glasses using semi-reflective and semi-transparent optics can be smaller than Meta 2.
In terms of video perspective AR, VR headsets such as Varjo XR-1 currently have this function. The principle is to directly superimpose virtual content on the picture captured by the camera. What you watch is the "virtual content" of the screen. No visibility into the real world environment. The advantage is that it can make the integration of AR and the real environment more natural. The disadvantage is that this combination based on camera + screen has great uncertainty in terms of optical display, including contrast, brightness, field of view, etc.