Researchers develop a flat millimeter lens for VR and AR platforms

Despite all the advances in consumer technology in recent decades, one component has remained frustratingly stagnant: optical lenses. 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 nearly 3,000 years.

This challenge caused a bottleneck in the development of next generation optical systems, such as wearable screens for virtual reality, which require compact, lightweight and economical components.

At 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 Senior Researcher in Electrical Engineering, is developing the next generation of lenses that promise to open this bottleneck by replacing bulky curved lenses with a simple, flat surface that uses nanostructures to focus light.

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

Now, the researchers have developed achromatic metalones of two millimeters that can focus RGB colors (red, blue, green) without aberrations and developed a miniaturized screen for applications of virtual and augmented reality.

The research is published in Advances in Science.

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

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

Like previous metalenses, this lens uses arrays of titanium dioxide nanofins to focus equally on the wavelengths of light and eliminate chromatic aberration. By designing the shape and pattern of these nano-arrays, the researchers were able to control the focal length of the red, green and blue colors of light. To incorporate the lens into a VR system, the team developed a close-up viewfinder using a method called fiber scanning.

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

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

“We demonstrate how meta-optics platforms can help to solve the bottleneck of today’s VR technologies and potentially be used in our daily lives,” said Li.

The team then plans to scale the lens further, making it compatible with current large-scale manufacturing techniques for mass production at a low cost.