HoloLens was shocking when it was launched, but as time goes by, there are more and more products of the same type on the market, and compared to similar products showing larger and larger angles of view, the small field of view of HoloLens is a bit unsatisfactory. . However, Microsoft recently published a patent that said it can greatly expand the field of view.
According to the description in the patent, it uses a MEMS laser scanner for near-eye displays. This is a projection display technology solution that combines RGB three-color laser modules with micro-electromechanical systems (ie MEMS). It can also be said that the projection display of a pure laser light source is combined with a scanning projection display.
In simple terms, its principle is to use a micro-electromechanical two-dimensional scanning galvanometer and RGB three-primary-color lasers to form images by laser scanning, and its output resolution depends on the scanning frequency of the MEMS micromirror. When the scanning projection display is combined with the laser, a faster frame rate can be achieved. According to one case in the patent, it can reach a rate of 60 frames per second, which is sufficient for the human eye.
Let's take a look at its specific structure. The following picture is a perspective view of the main part of the structure. The one marked as 140 is a laser emitting device, which generally emits the RGB light source that composes the image. The optical element marked 102 is an optical element, which plays a role of reflecting the light emitted by the light source, and can be any suitable specular reflector or Bragg polarization grating.
Another important part is the MEMS drive device. These two drive devices are similar to many MEMS scanners. Both drive the entire device to rotate at high frequencies in the x-axis and y-axis directions. In the figure, there are 120 and 122 Indicates that the coupling is controlled by 124.
The principle that the patent can expand the field of view is actually to expand the FOV supported by the MEMS laser scanner. In some cases, the MEMS laser scanner consists of multiple laser diode display engines, including the red, green and blue wavelengths. The light-emitting device, the light subsequently emitted is guided to the optical mirror or Bragg polarization grating (that is, the optical element in the foregoing) for reflection and polarization.
The optical element here can be deflected to a certain degree around two axes, which are called x and y axes in the patent. We can also see in the previous structural diagrams. Taking one of these axes as the x axis, the first moment , It may polarize the light received from the display in the first orientation, and when it reaches the second moment, it has rotated a certain angle around the axis, and it will polarize the light received in the second orientation.
In other words, the light is reflected in the first direction of the optical mirror, depicting the first part of the overall image. The light then traces the second part of the overall image in the second direction of the optical mirror. The first and second parts of this image can be combined to create an effect that looks like the overall FOV is enlarged. To put it simply, the FOV is stretched in both vertical and horizontal directions through reflections in different directions. I have to say that the effect of "stretching" is also very good. In some cases, the field of view has reached 70 degrees, which is double that of Hololens.
It must be noted that MEMS laser scanning display itself is not a new solution. It is said that Remote EyeSight AR glasses use this display technology. Opus Microsystems developed high-definition two-dimensional MEMS scanning mirrors and AR laser head-up displays in 2016. In addition, , There are also vehicle-mounted HUDs that use this scheme. The reason why Microsoft's patent is valued this time is that it can extend the field of view to a large extent.
All in all, as mentioned at the beginning, the field of view of Hololens is indeed smaller than that of glasses on the market now. The next-generation product called Sydney is under development and is likely to be launched next year. Then, the appropriate expansion of FOV should be possible. This is what Hololens considers. If there is no better solution, perhaps MEMS laser scanning is also a good choice.
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