Columbia Flat Lens Focuses on Polarization of Light The Engineer

Columbia Engineering researchers created the first flat lens to focus a wide range of colors, regardless of their polarization, on the same focal point without the need for additional lenses.

The "flat" objective of a micron is reputed to offer performances comparable to those of high-end compound lens systems. The findings of the team, led by Nanfang Yu, associate professor of applied physics at Columbia University in New York, are detailed in Light: Science & Applications.

Conventional lenses route light through different paths, so that the entire light wave arrives simultaneously at the focal point. Such lenses are made to do this by adding a longer and longer delay to the light that goes from the edge to the center of the lens.

In order to invent a leaner, lighter and cheaper goal, Yu's team took a different approach. With their expertise in optical metasurfaces – structures designed in two dimensions – to control the propagation of light in the open space, researchers have built flat targets in pixels, or "meta-atoms".

It is said that each meta-atom has a size that represents a fraction of the wavelength of light and retards the light that passes through it in a different amount. By modeling a very thin, flat layer of nanostructures on a very thin substrate, the researchers achieved the same function as a conventional system of much thicker and heavier conventional lenses.

"The beauty of our flat lens lies in the fact 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" Yu said, "And because they are so thin, they can potentially significantly reduce the size and weight of any optical instrument or device used for imaging, such as cameras, microscopes, telescopes, and even our glasses. Think of a pair of glasses of thinner thickness than a sheet of paper, to cameras for non-curved smartphones, to thin blocks of detection and imaging systems for driverless cars and drones and miniaturized tools for medical imaging applications.

Yu's team manufactured the meta-lenses – which do not require a grinding and polishing process – using standard 2D fabrication techniques similar to those used for computer chip manufacturing.

"The production of our flat lenses can be massively parallelized, which allows to obtain large amounts of high-performance and economical lenses," said Sajan Shrestha, a PhD student from the Yu Group, co-author of the 39; study. "So we can send our lens designs to semiconductor foundries for mass production and benefit from the industry-wide economies of scale."

Because the flat lens can focus light with wavelengths ranging from 1.2 to 1.7 microns in the near infrared of the same focal point, it can form "colorful" images in the near infrared band, because all colors are sharp simultaneously. is essential for color photography.

According to Columbia, the lens can focus light in any arbitrary polarization state, so that it works not only in a laboratory, where the polarization can be well controlled, but also in real applications, where the ambient light has a random polarization. It also works for transmitted light, which is convenient for integration into an optical system.

"Our design algorithm exhausts all degrees of freedom in modeling an interface into a binary pattern, so our flat lenses can achieve near-theoretical performance that a nanostructured interface can possibly achieve," he says. said Adam Overvig, the other co-lead author of the study and PhD student with Yu. "In fact, we have demonstrated some flat lenses with the best combined features theoretically possible: for a meta-lens diameter given, we got the closest focal point possible over the largest range of wavelengths. "

CLICK FOR NEWS