Researchers Develop Millimeter Flat Lens for VR and AR Platforms

Despite all the advancements in consumer technology over the past decades, one component has remained hopelessly stagnant: the optical lens. Unlike electronic devices, which have gotten smaller and more efficient over the years, the design and underlying physics of today’s optical lenses haven’t changed much in around 3,000 years.

This challenge has caused a bottleneck in the development of next-generation optical systems such as portable virtual reality displays, which require compact, lightweight and cost-effective components.

At the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), a team of researchers led by Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Principal Investigator in Electrical Engineering, developed the next generation of lenses which promise to open that bottleneck by replacing bulky curved lenses with a simple, flat surface that uses nanostructures to focus light.

In 2018, the Capasso team developed achromatic, aberration-free metal lenses that work across the entire visible spectrum of light. But these lenses were only tens of microns in diameter, too small for practical use in virtual and augmented reality systems.

Now, researchers have developed two-millimeter achromatic metal lenses capable of focusing RGB (red, blue, green) colors without aberrations and have developed a miniaturized display for virtual and augmented reality applications.

The research is published in Scientific advances.

“This state-of-the-art lens paves the way for a new kind of virtual reality platform and overcomes the bottleneck that has slowed the progress of the new optical device,” said Capasso, lead author of the article.

“Using new physics and a new design principle, we have developed a flat lens to replace the bulky lenses in today’s optical devices,” said Zhaoyi Li, postdoctoral fellow at SEAS and first author of the article. . “This is the largest RGB achromatic metal to date and is a proof of concept that these lenses can be scaled down to the size of a centimeter, mass produced and integrated into plates. – commercial forms. “

Like previous metal lenses, this lens uses titanium dioxide nanofin arrays to evenly focus wavelengths of light and eliminate chromatic aberration. By designing the shape and pattern of these nanoarrays, researchers could control the focal length of the red, green, and blue color of light. To incorporate the lens into a VR system, the team developed a near-eye display using a method called fiber scanning.

The screen, inspired by fiber-scanning endoscopic bioimaging techniques, uses an optical fiber through a piezoelectric tube. When tension is applied to the tube, the tip of the fiber scans left and right and up and down to display patterns, forming a miniaturized display. The screen features high resolution, high brightness, high dynamic range and wide color gamut.

In a VR or AR platform, the metalens would be seated directly in front of the eye, and the screen would be placed in the focal plane of the metalens. The patterns scanned by the screen are focused on the retina, where the virtual image is formed, using metalens. To the human eye, the image appears as part of the landscape in AR mode, some distance from our real eyes.

“We have demonstrated how meta-optics platforms can help solve the bottleneck of current VR technologies and potentially be used in our daily lives,” Li said.

Next, the team aims to extend the lens even further, making it compatible with current large-scale manufacturing techniques for low-cost mass production.