Researchers develop millimeter-sized flat lens for VR and AR platforms

Despite all the advances in consumer technology in recent decades, one component has stagnated frustratingly: the optical lens. Unlike electronic devices, which have become smaller and more efficient over the years, the design and underlying physics of today’s optical lenses have not changed much in about 3,000 years.

This challenge has caused a bottleneck in the development of next-generation optical systems, such as portable virtual reality screens, 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 Senior Research Fellow in Electrical Engineering, developed the following. generation lenses that promise to open the 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 light spectrum. But these lenses were only ten microns in diameter, too small for practical use in VR and augmented reality systems.

The researchers have now developed a two-millimeter achromatic metal lens that can focus RGB (red, blue, green) colors without deviations and develop a miniaturized display for virtual and extended reality applications.

The research is published in Scientific progress.

“This modern lens opens the way to a new kind of virtual reality platform and overcomes the bottleneck that has slowed the progress of new optical devices,” said Capasso, the senior author of the article.

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

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

The show, inspired by fiber-scanning-based endoscopic biopsy techniques, uses an optical fiber through a piezoelectric tube. When a voltage is applied to the tube, the fiber tip scans left and right and up and down to display patterns, forming a miniature display. The screen has high resolution, high brightness, high dynamic range and a wide color gamut.

In a VR or AR platform, the metalworkers would sit directly in front of the eye and place the screen within the focal plane of the metalwork. The patterns scanned by the screen are focused on the retina, where the virtual image forms, using the metalwork. To the human eye, the image appears as part of the landscape in AR mode, some distance from our real eyes.

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

Next, the team wants to enlarge the lens even further, making it compatible with current large-scale mass-production techniques at low cost.