Facebook shows thin VR glasses with holographic optics and pancake lens

Facebook’s research arm has shown a proof of concept version of VR goggles, combining holographic optics with polarization-based optical folding to create a much flatter VR goggle. These glasses look more like thick sunglasses than current VR glasses.

The largest reduction in the thickness of the VR glasses is due to the use of polarization-based optical folding. Facebook Reality Labs writes that modern VR glasses must be so thick, because there must be a considerable distance between the light source and the lens. This distance is necessary to focus the image properly. With current VR glasses, the light source goes in one direction towards the lens. However, when polarization-based optical folding is used, the light is first reflected once through the lens, only to be reflected back through the lens to the eye via the display panel.

As a result, the light effectively passes through the space between the display panel and the lens three times, which can drastically reduce this space. Facebook does indicate that with these pancake optics, half the light intensity is lost with every reflection. When the light beam reaches the eye, only a quarter of the light intensity is left. In addition, the light can ‘leak’ at pancake optics, which can cause ghosting. Finally, for pancake optics, a lot of glass or plastic is usually used in order to be able to focus the image properly.

Instead of using a lot of plastic or glass to focus the image, FRL suggests using holographic optical elements. These are thin, flat sheets with a negligible weight. Facebook calls it a lens the size of a sticker. In the proof of concept, Facebook uses a laser backlight and an LCD panel to achieve the specific spectral bandwidth of between 0.1nm and 1nm required for a holographic lens. The lens of the proof of concept is 9mm thick and offers ‘comparable’ fov compared to current VR glasses.

The larger color space that Facebook says is possible

Another advantage of the setup used is that the laser backlight can provide a much larger color space, Facebook writes. The research department shows in an image the color space that the Prototype Display Lasers could display, making a comparison with the sRGB color space of many current VR glasses. The resolution of the concept model is comparable to other VR glasses, according to the company, although FRL is working on getting this closer to ‘the limit of the human eye’.

With the lighter and flatter concept, Facebook hopes that people will be able to use VR glasses for longer sessions. This would allow the glasses to offer more options for use. Facebook Reality Labs emphasizes that the work is pure research at this point. For example, the concept glasses currently only display the color green and the concept cannot yet be practically used for use with two eyes. Facebook says more work is needed to integrate a full color display.