On July 12, YVR launched its brand-new VR glasses YVR 2. According to official data, this VR all-in-one machine adopts ultra short focal optical design. Combined with the backstage comments received by Xiao P during this period, today we will take a good look at the ultra short focal optical folding optical path (pancake).

Although at present, major manufacturers try to make VR head displays as light and thin as possible, in VR head displays with Fresnel lens as the optical scheme, the host weight of meta quest2 is 503G, and HTC vive focus3 is close to 800g. Too heavy equipment will lead to poor wearing comfort of users, so the pancake scheme that can make the head display “lose weight” came into being.

What is pancake optical solution?

From the disassembly of VR head display, we can divide the display unit into display screen and lens. The image light source of the display screen is magnified into our glasses through the Fresnel lens, thus forming an image. At present, most VR head displays on the market adopt the scheme of display screen + Fresnel lens. However, one of the disadvantages of Fresnel lens is that it is too thick, which is not in line with the development trend of lightweight VR in the future.

In order to enlarge the area of a light source as much as possible within a limited distance, one way is to use a magnifying glass; Another method requires the help of two mirrors for reflection. When the same light area is obtained, the route of the latter will be shorter than that of the former. With this knowledge, we can better understand the principle of pancake imaging.

For VR head display based on pancake technology scheme, after the image source enters the lens with semi reflective and semi transparent function, the light turns back many times between the lens, phase delay plate and reflective polarizer, and finally shoots out from the reflective polarizer. At the same time, the lens group does not need to keep a certain distance from the display screen, which can reduce the thickness of VR head display, make it more compact, and the overall volume will be smaller.

Advantages and disadvantages of pancake scheme

Compared with the Fresnel lens scheme, the pancake scheme, in addition to the above-mentioned lightness, can also improve the problems of blurred vision edge, picture distortion, edge glare and so on, and bring users better visual effects.

 

At the same time, the pancake folding optical scheme also has unresolved defects. On the one hand, it is more difficult to fit the screen with the folded light path, which leads to the high price of VR glasses adopting this scheme; On the other hand, for VR devices based on 2p pancake scheme, the maximum field angle that can be achieved is 95-100 °. It is rumored that Apple’s first generation apple ar/mr will be equipped with two 3P pancake modules, which will improve the field of view.

Among the VR head displays that have been launched at present, the main ones that adopt pancake ultra short focus optical solutions are Huawei VR glass, HTC vive flow and arpara 5K. These three products are split VR glasses, which require external devices such as mobile phones and computers to provide power supply units and computing units. Starting this year, we will also see VR all-in-one machines equipped with this scheme. For example, yvr2, Pico’s next-generation high-end devices, meta quest pro, arpara AIO, and Apple’s highly anticipated Mr headset.

Finally, it should be noted that although pancake ultra short focus will gradually become the mainstream optical solution of VR all-in-one machine in the second half of this year, it is mainly medium and high-end products. When the demand for pancake Scheme continues to expand and the production capacity advantage is improved, the cost is expected to decline, and finally benefit consumers, so as to gradually replace VR head display with Fresnel lens scheme.

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