Researchers develop a flat lens a thousand times thinner than a human hair

A lens a thousand times thinner than a human hair was developed in Brazil by researchers at the São Paulo School of Engineering at the University of São Paulo (EESC-USP). It can serve as a camera lens in smartphones or be used in other devices that depend on sensors.

“In the current technological context, its applications are almost limitless,” Emiliano Rezende Martins, professor at the Department of Electrical and Computer Engineering at CESE-USP and the latest author of a published article on the invention, told Agência FAPESP.

The paper is titled “On Metals with an Arbitrarily Wide Field of View” and is published in ACS Photonics. The study was supported by FAPESP via a scholarship for a research internship abroad awarded to Augusto Martins, Ph.D. candidate and lead author of the article.

The lens is made up of a single nanometric layer of silicon on arrays of nanopostes that interact with light. The structure is printed by photolithography, a well known technique used to fabricate transistors.

This type of lens is known as metalens. Metalenses were first developed ten years ago and achieve the highest resolution physically possible, using an ultrathin array of tiny waveguides called a metasurface that bends light as it passes through the lens.

According to Rezende Martins, metalenses have long faced the problem that the viewing angle is extremely small (less than 1 °). “One way to solve the problem is to combine lens metals to form complex structures,” he said.

Starting from the observation that in a conventional lens, an increase in the refractive index increases the field of vision proportional to the flatness of the lens, the authors designed a metal to imitate a totally flat lens with an infinite refractive index, this which could not be obtained with a conventional lens.

“Our lens has an arbitrary field of view, which can ideally reach 180 ° without image distortion,” said Rezende Martins. “We tested its effectiveness for an angle of 110 °. With wider viewing angles, the light energy decreases due to the shadow effect, but this can be corrected by post-processing.”

The combination of metalenses prevents super-resolution, but the resolution obtained is sufficient for all conventional applications. Martins tested the metalens with a 3-D printed camera and obtained high resolution images with a wide field of view. “So far we have only managed to shoot in green, but in the coming months we will improve the lens so that all colors are achievable,” he said.