Near-eye displays for VR use holographic optics

Technology News | July 2, 2020

By Rich Pell

Announced as a new research milestone to be presented at the virtual SIGGRAPH conference, the researchers propose a new class of near-eye displays that combine the power of holographic optics and polarization-based optical folding – an approach that could be used to develop future sunglasses-like VR hardware. These two methods, say the researchers, help keep the optics as thin as possible while making the most efficient use of space.

The new optical architecture is offered as being significantly more compact and offering the potential for better visual performance. Such lightweight and comfortable form factors, say the researchers, may enable extended VR sessions and new use cases, including productivity.

The design is demonstrated in a proof-of-concept research device that uses only thin, flat films as optics to achieve a display thickness of less than 9 mm while supporting a field of view comparable to today’s consumer VR products. The work, say the researchers, demonstrates the promise of better visual performance, as well: Laser illumination is used to deliver a much wider gamut of colors to VR displays, and progress is made toward scaling resolution to the limit of human vision.

Current VR displays have three primary components: a source of light (e.g., LEDs), a display panel that brightens or dims the light to form an image (e.g., an LCD panel), and a viewing optic that focuses the image far enough away so that the viewer’s eyes can see it (e.g., a plastic lens). As the first two components can readily be formed into thin and flat modules, most of the weight and volume go into the viewing optics.

Most VR displays share a common viewing optic: a simple refractive lens composed of a thick, curved piece or glass or plastic. The researchers propose replacing this bulky element with holographic optics. Like common holographic images, these 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, say the researchers, is a dramatic reduction in thickness and weight: The holographic optic bends light like a lens but looks like a thin, transparent sticker. However, even if the lens itself is made thin, the viewing optics as a whole may still be large – a considerable amount of empty space must be placed between the display panel and the lens to properly focus the image. Ordinarily, light from the display panel propagates forward to the lens and then continues toward the eye. However, say the researchers, when polarization-based optical folding is applied, light can be controlled to move both forward and backward within the lens so that this empty space can be traversed multiple times, collapsing it to a fraction of the original volume.

When holographic optics are applied to a VR display, say the researchers, all other optical components must be re-evaluated. Notably, holographic optics compel the use of laser light sources, which are more difficult to integrate but provide a much richer set of colors than the LEDs common in nearly all of today’s VR headsets, phones, computers, and televisions.

A common set of colors reproducible on many displays today is the sRGB color space, which can capture only a small fraction of the colors that we can actually see. In contrast, the much larger set of colors that can be reproduced using the lasers on one of the research prototype displays allows the reproduction of vivid and saturated colors.

At present, say the researchers, while their work points toward the future development of lightweight, comfortable, and high-performance AR/VR technology, it is purely research. Looking ahead, they have identified current limitations of their proposed display architecture and are discussing future areas of research that will make the approach more practical.

For more, see “Holographic Optics for Thin and Lightweight Virtual Reality.”

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