Lightening the load of augmented reality glasses

Augmented reality (AR) technology, which overlays digital information and virtual objects on an image of the real world viewed through a device's viewfinder or electronic display, has gained traction in recent years with popular gaming apps like Pokémon Go, and real-world applications in areas including education, manufacturing, retail and health care. But the adoption of wearable AR devices has lagged over time due to their heft associated with batteries and electronic components.

AR glasses, in particular, have the potential to transform a user's physical environment by integrating virtual elements. Despite many advances in hardware technology over the years, AR glasses remain heavy and awkward and still lack adequate computational power, battery life and brightness for optimal user experience.

In order to overcome these limitations, a team of researchers from the University of Tokyo and their collaborators designed AR glasses that receive images from beaming projectors instead of generating them.

"This research aims to develop a thin and lightweight optical system for AR glasses using the 'beaming display' approach," said Yuta Itoh, project associate professor at the Interfaculty Initiative in Information Studies at the University of Tokyo and first author of the research paper. "This method enables AR glasses to receive projected images from the environment, eliminating the need for onboard power sources and reducing weight while maintaining high-quality visuals."

Prior to the research team's design, light-receiving AR glasses using the beaming display approach were severely restricted by the angle at which the glasses could receive light, limiting their practicality -- in previous designs, cameras could display clear images on light-receiving AR glasses that were angled only five degrees away from the light source.

The scientists overcame this limitation by integrating a diffractive waveguide, or patterned grooves, to control how light is directed in their light-receiving AR glasses.

"By adopting diffractive optical waveguides, our beaming display system significantly expands the head orientation capacity from five degrees to approximately 20-30 degrees," Itoh said. "This advancement enhances the usability of beaming AR glasses, allowing users to freely move their heads while maintaining a stable AR experience."

Specifically, the light-receiving mechanism of the team's AR glasses is split into two components: screen and waveguide optics. First, projected light is received by a diffuser that uniformly directs light toward a lens focused on waveguides in the glasses' material. This light first hits a diffractive waveguide, which moves the image light toward gratings located on the eye surface of the glasses. These gratings are responsible for extracting image light and directing it to the user's eyes to create an AR image.

The researchers created a prototype to test their technology, projecting a 7-millimeter image onto the receiving glasses from 1.5 meters away using a laser-scanning projector angled between zero and 40 degrees away from the projector. Importantly, the incorporation of gratings, which direct light inside and outside the system, as waveguides increased the angle at which the team's AR glasses can receive projected light with acceptable image quality from around five degrees to around 20-30 degrees.

While this new light-receiving technology bolsters the practicality of light-receiving AR glasses, the team acknowledges there is more testing to be done and enhancements to be made. "Future research will focus on improving the wearability and integrating head-tracking functionalities to further enhance the practicality of next-generation beaming displays," Itoh said.

Ideally, future testing setups will monitor the position of the light-receiving glasses and steerable projectors will move and beam images to light-receiving AR glasses accordingly, further enhancing their utility in a three-dimensional environment. Different light sources with improved resolution can also be used to improve image quality. The team also hopes to address some limitations of their current design, including ghost images, a limited field of view, monochromatic images, flat waveguides that cannot accommodate prescription lenses, and two-dimensional images.