Revolutionary ultra-thin meta-lens enables full-color imaging

The first flat lens capable of correctly focusing a large range of colors of any polarization.

Top panels: Scanning electron micrographs of sections of broadband meta-lenses. They are composed of silicon nanopillars with various cross-sectional shapes patterned on a glass substrate. Bottom panel: Photo showing two elements of a multi-element meta-lens imaging system. Credit: Sajan Shrestha, Adam Overvig, Nanfang Yu/Columbia Engineering
Top panels: Scanning electron micrographs of sections of broadband meta-lenses. They are composed of silicon nanopillars with various cross-sectional shapes patterned on a glass substrate. Bottom panel: Photo showing two elements of a multi-element meta-lens imaging system. Credit: Sajan Shrestha, Adam Overvig, Nanfang Yu/Columbia Engineering

Light of various colors goes at various speeds in various materials and structures. This is the reason we see white light split into its constituent colors subsequent to refracting through a prism, a marvel called dispersion. A normal lens can’t focus light of various colors to a single spot because of dispersion.

This implies distinctive hues are never in a center in the meantime, thus a picture framed by such a basic focal point is definitely blurred. Traditional imaging frameworks tackle this issue by stacking different focal points, yet this arrangement comes at the expense of expanded many-sided quality and weight.

Columbia Engineering analysts have made the first flat lens prepared to do effectively centering a vast scope of shades of any polarization to the equivalent central spot without the requirement for any extra components. Just a micron thick, their progressive “flat” lens is considerably more slender than a sheet of paper and offers execution similar to top-notch compound lens systems.

Nanfang Yu, associate professor of applied physics said, “The beauty of our flat lens is that by using meta-atoms of complex shapes, it not only provides the correct distribution of delay for a single color of light but also for a continuous spectrum of light. And because they are so thin, they have the potential to drastically reduce the size and weight of an optical instrument or device used for imaging, such as cameras, microscopes, telescopes, and even our eyeglasses.”

Illustration showing a comparison between two types of flat lenses. In the foreground, a new type of flat lens focuses all colors of light to the same spot. As a comparison, the flat lens in the background is not color-corrected. Credit: Adam Overvig/ Columbia Engineering
Illustration showing a comparison between two types of flat lenses. In the foreground, a new type of flat lens focuses all colors of light to the same spot. As a comparison, the flat lens in the background is not color-corrected. Credit: Adam Overvig/ Columbia Engineering

“Think of a pair of eyeglasses with a thickness thinner than a sheet of paper, smartphone cameras that do not bulge out, thin patches of imaging and sensing systems for driverless cars and drones, and miniaturized tools for medical imaging applications.”

Scientists fabricated the meta-lenses utilizing standard 2-D planar fabrication systems like those utilized for manufacturing computer chips. They say the procedure of mass assembling meta-lenses ought to be significantly less complex than delivering computer chips, as they have to characterize only one layer of nanostructures—in comparison, modern computer chips require various layers, some upwards of 100.

Unlike conventional lenses, this flat meta-lens do not need to go through the costly and time-consuming grinding and polishing processes.

Sajan Shrestha, a doctoral student in Yu’s group who was a co-lead author of the study said, “The production of our flat lenses can be massively parallelized, yielding large quantities of high performance and cheap lenses. We can, therefore, send our lens designs to semiconductor foundries for mass production and benefit from economies of scale inherent in the industry.”

Because the flat lens can focus light with wavelengths ranging from 1.2 to 1.7 microns in the near-infrared to the same focal spot, it can form “colorful” images in the near-infrared band because all of the colors are in focus at the same time—essential for color photography.

Adam Overvig, the study’s other co-lead author said, “Our design algorithm exhausts all degrees of freedom in sculpting an interface into a binary pattern, and, as a result, our flat lenses are able to reach performance approaching the theoretic limit that a single nanostructured interface can possibly achieve.”

“In fact, we’ve demonstrated a few flat lenses with the best theoretically possible combined traits: for a given meta-lens diameter, we have achieved the tightest focal spot over the largest wavelength range.”

University of Pennsylvania H. Nedwill Ramsey Professor Nader Engheta said, “This is an elegant work from Professor Nanfang Yu’s group and it is an exciting development in the field of flat optics. This achromatic meta-lens, which is the state-of-the-art in the engineering of metasurfaces, can open doors to new innovations in a diverse set of applications involving imaging, sensing, and compact camera technology.”

The study is published in the journal Light: Science & Applications.