Single-layer waveguide display uses achromatic metagratings for more compact augmented reality eyewear

Augmented reality (AR), the technology that overlays digital content onto what users see around them in real-time, is now widely used in the retail, gaming and entertainment industries, as well as in some educational settings and learning environments. A key component of AR systems are so-called waveguide displays, transparent optical layers that guide light from a projector to the eyes of users, allowing them to see projected images integrated on top of their surrounding environment.

Waveguide displays, mounted on most AR headsets or smart glasses, are typically made up of several substrates and grating couplers (i.e., structures that diffract light into the waveguide). While these multi-layered waveguide displays are widely used, they can sometimes distort colors while also setting limits on the extent to which AR headsets or glasses can be reduced in size.

Researchers at Samsung Electronics and Pohang University of Science and Technology (POSTECH) have recently developed a new single-layer waveguide display that could enable the realization of more compact AR headsets for everyday use while also boosting the brightness and color uniformity of images seen by users. The new display, introduced in a paper published in Nature Nanotechnology, was fabricated using achromatic metagratings, arrays of rectangular nanostructures that diffract red, green and blue light at identical angles.

“An ideal waveguide display for AR would feature a single-layer waveguide substrate combined with dispersion-free couplers,” wrote Seokil Moon, Seokwoo Kim and their colleagues in their paper. “While metasurfaces have been explored as a potential solution for waveguide displays, severe limitations—such as low efficiency, poor uniformity and chromatic aberration—remain unresolved. We introduce a single-layer waveguide display using achromatic metagratings.”

The researchers’ newly developed waveguide display integrates achromatic metagrating couplers and advanced optical components that diffract light, directing different colors (i.e., red, green and blue light) in the same direction without distorting them. To optimize the geometric parameters in the images reproduced by these nanostructures, the researchers used a new stochastic topology optimization algorithm developed in their lab.

“The proposed metagratings comprise periodic arrays of rectangular nanostructures, diffracting red, green and blue lights in the same direction,” explained Moon, Kim and their colleagues. “Therefore, they ensure an achromatic propagation angle within the single waveguide substrate, maintaining high-quality projected images.”

The new waveguide display has several advantages that set it apart from conventional multi-layer waveguide displays and newer metasurface-based displays for AR. Firstly, it is significantly thinner than multi-layer waveguide displays, which means that it could be used to develop AR eyewear that is more compact, comfortable and easier for users to wear on a daily basis than existing headsets.

In addition, the team’s display produces better quality images than many metasurface-based and multi-layer waveguide displays, as it does not distort colors as much and allows users to see a greater proportion of their surroundings. In the future, the new display could be integrated in both existing and newly developed AR headsets, potentially facilitating their use across a wider range of everyday settings.

“As a proof of concept, we demonstrate a full-color AR waveguide display with a 500-μm-thick single-layer waveguide substrate that substantially reduces the device form factor and weight while enhancing brightness and color uniformity with a sufficient eyebox,” wrote Moon, Kim and their colleagues.

“This approach overcomes the limitations of traditional AR near-eye optical designs, which rely on multi-layer grating couplers that require complex fabrication processes and are too heavy for ergonomic head-mounted applications.”

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