A lens that is a thousand times thinner than a human hair has been developed in Brazil by researchers at the University of São Paulo's São Carlos School of Engineering (EESC-USP). It can act 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,” said Emiliano Rezende Martins, professor in the EESC-USP’s Department of Electrical Engineering and Computers and the last author of a published document on the invention, Agência FAPESP.
The essay is entitled “On Metalenses with Arbitrarily Wide Field of View” and is published in ACS Photonics. The study is supported by FAPESP via a scholarship for a research internship abroad awarded to Augusto Martins, doctoral student and lead author of the thesis.
The lens consists of a single nanometric layer of silicon on matrices of nanoposts that interact with light. The structure is printed with photolithography, a well-known technique used to make transistors.
This type of lens is known as a metal one. Metalenses were first developed ten years ago and achieve the highest resolution that is physically feasible using an ultratin set of small waveguides called a metasurface that bends light as it passes through the lens.
According to Rezende Martins, metalenses have long faced the problem of the angle of view being extremely small (less than 1 °). “One way to solve the problem is to combine metal lenses and form complex structures,” he said.
Based on the realization that in a conventional lens an increase in refractive index increases the field of view in proportion to the flatness of the lens, the authors designed a metal to mimic a completely flat lens with an infinite refractive index, 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 have tested its efficiency for an angle of 110 °. With wider viewing angles, the light energy decreases due to the shadow effect, but this can be corrected by finishing. ”
Combining metal lenses prevents super-dissolution, but the resulting solution is sufficient for all conventional applications. Martins tested the metals with a 3D-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 be upgrading the lens so that all colors are feasible,” he said.
Reference: “On Metalenses with Arbitrarily Wide Field View” by Augusto Martins, Kezheng Li, Juntao Li, Haowen Liang, Donato Conteduca, Ben-Hur V. Borges, Thomas F. Krauss and Emiliano R. Martins, June 30, 2020, ACS Photonics.
DOI: 10.1021 / acsphotonics.0c00479