Capasso Group Develops Flat Lenses with Same Technology Used to Make Chips

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AUTUM C. PYLANT, NEWS EDITOR, [email protected]

CAMBRIDGE, Mass., July 5, 2018 —
Optics and lenses are everywhere. They’re in laptops, cameras, and telescopes. Focusing the entire visible spectrum with lenses has been a challenge because each wavelength moves through materials at different speeds. Red wavelengths will move through glass faster than blue, so the two colors will reach the same location at different times, which result in different foci. This creates image distortions known as chromatic aberrations.

Cameras and optical instruments use multiple curved lenses of different thicknesses and materials to correct these aberrations.

Members of the Capasso Group at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a single flat lens that can focus the entire visible spectrum of light in the same spot and in high resolution.

"Metalenses have advantages over traditional lenses," said Federico Capasso, Robert L. Wallace Professor of Applied Physics at Harvard. "Metalenses are thin, easy to fabricate and cost-effective. This breakthrough extends those advantages across the whole visible range of light. This is the next big step."

The metalenses developed by Capasso and his team use arrays of titanium dioxide nanofins to equally focus wavelengths of light and eliminate chromatic aberration. Previous research demonstrated that different wavelengths of light could be focused but at different distances by optimizing the shape, width, distance, and height of the nanofins. The researchers created units of paired nanofins that control the speed of different wavelengths of light simultaneously. The paired nanofins control the refractive index on the metasurface and are tuned to result in different time delays for the light passing through different fins, ensuring that all wavelengths reach the focal spot at the same time.
Flat lens on top of a thin glass wafer made by the Capasso Group. The glass wafer is .5 mm thick. Courtesy of Autum Pylant.
Flat lens on top of a thin glass wafer made by the Capasso Group. The glass wafer is 0.5 mm thick. Courtesy of Autum Pylant.

“This gives us a lot of freedom to improve the performance and to overall make very complicated systems much smaller in size and in some cases actually add functionality,” said Alex Zhu, Capasso Group member and graduate student.

In current practices, multiple lenses are required to focus all of the wavelengths in the same spot without distortion. Capasso told Photonics Media that in order to correct the distortion, six or seven lenses may be required, as is the case with cameras in cell phones.

“With a single lens or just a couple, you can actually do the work of traditional optics,” he said. “They are thinner and it’s easier to stack them and align them optically, and it’s easier to actually correct the distortions.”

Capasso added that it is also easier to machine the lenses because they don’t require the same curvature as refractive lenses. This technology could change the way that cameras are made.

Currently, different companies make the sensors and the lenses in cameras. Under Capasso’s vision, the same company that makes the sensor will also be able to make the flat lenses.

“I’m excited about this, because it’s revolutionary,” said Capasso. “We have shown that you can make these lenses with the same technology that is used to make chips.”

Capasso and three partners have started a company called Metalenz, targeting applications that do not require achromatic lenses, such as for security cameras, biometrics, authentication, and face recognition. They hope to start production in 2019. Capasso said he would eventually like to make commercial lenses that are broadband, such as those created by the Capasso Group.

Published: July 2018
integrated photonics
Integrated photonics is a field of study and technology that involves the integration of optical components, such as lasers, modulators, detectors, and waveguides, on a single chip or substrate. The goal of integrated photonics is to miniaturize and consolidate optical elements in a manner similar to the integration of electronic components on a microchip in traditional integrated circuits. Key aspects of integrated photonics include: Miniaturization: Integrated photonics aims to...
freeform optics
Freeform optics refers to the design and fabrication of optical surfaces that do not follow traditional symmetric shapes, such as spheres or aspheres. Unlike standard optical components with symmetric and rotationally invariant surfaces, freeform optics feature non-rotationally symmetric and often complex surfaces. These surfaces can be tailored to meet specific optical requirements, offering greater flexibility in designing optical systems and achieving improved performance. Key points about...
A metalens, short for "metasurface lens," is a type of optical lens that uses nanostructured materials to manipulate light at a subwavelength scale. Unlike traditional lenses made of glass or other transparent materials, metalenses do not rely on the curvature of their surface to refract or focus light. Instead, they use carefully engineered patterns of nanostructures, such as nanoscale antennas or dielectric structures, to control the phase and amplitude of light across the lens's surface....
visible spectrum
That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to 750 nm in wavelength.
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