Facebook’s Reality Labs and its Oculus brand have been developing a streamlined VR headset. Their latest effort is, they claim, the "thinnest VR display demonstrated to date". It's basically a pair of easy-to-wear VR sunglasses, though they're just a proof-of-concept device at this stage.

Facebook demos the thinnest VR headset to date with holographic displays image 2
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The VR headset uses holographics with flat films for the optics. The displays are less than 0.35 inches thick, helped by polarisation-based optical folding that moves the light forward and back multiple times. Here's how Facebook's Reality Labs described the technology:

"To significantly reduce the overall size and weight of VR displays, we combine two techniques: Holographic optics and polarization-based optical folding. Most VR displays share a common viewing optic: A simple refractive lens composed of a thick, curved piece or glass or plastic. We propose replacing this bulky element with holographic optics. You may be familiar with holographic images seen at a science museum or on your credit card, which appear to be three-dimensional with realistic depth in or out of the page. Like these holographic images, our holographic optics are a recording of the interaction of laser light with objects, but in this case the object is a lens rather than a 3D scene. The result is a dramatic reduction in thickness and weight: The holographic optic bends light like a lens but looks like a thin, transparent sticker."

Facebook's Reality Labs said its current prototype outputs in monochrome, but it's hoping to one day deliver a wider colour range with upgraded imagery. "In our technical paper, we identify the current limitations of our proposed display architecture," explained Facebook's Reality Lab, and we "[Discuss] future areas of research that will make the approach more practical". 

The unit hopes to improve the resolution to the “limit of human vision", which could lead to VR glasses you can wear for long periods of time.