Flat Lens for a Wide Field of View

An extremely flat lens has been developed in Brazil by researchers at the Univer­sity of São Paulo’s São Carlos School of Engi­neering (EESC-USP). It can serve as a camera lens in smartphones or be used in other devices that depend on sensors. “In the present technological context, its appli­cations are almost unlimited,” Emiliano Rezende Martins, a professor in EESC-USP’s department of electrical engi­neering and computing, said.

The new metalens can be used to produce high-resolution images with a wide field of view. (Source: A. Martins, USP)

The lens consists of a single nano­metric layer of silicon on arrays of nanoposts that interact with light. The structure is printed by photo­lithography. This kind of metalenses were first developed ten years ago and achieve the highest resolution that is physically feasible, 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 angle of view is extremely small – less than one degree. “One way to solve the problem is to combine metalenses, forming complex structures,” he said.

Based on the reali­zation that in a conven­tional lens an increase in refrac­tion index increases the field of view in propor­tion to the flatness of the lens, the authors designed a metalens to mimic a totally flat lens with an infinite refrac­tion index, which could not be obtained with a conven­tional lens. “Our lens has an arbitrary field of view, which ideally can reach 180° without image distortion,” Rezende Martins said. “We’ve tested its effec­tiveness for an angle of 110°. With wider angles of view, light energy decreases owing to the shadow effect, but this can be corrected by post-processing.”

Combining meta­lenses prevents super-resolution, but the reso­lution obtained is sufficient for all conven­tional appli­cations. Martins tested the metalens with a 3D printed camera and obtained high-reso­lution images with a wide field of view. “So far we’ve only succeeded in photo­graphing in green, but in the months ahead we’ll upgrade the lens so that all colors are feasible,” he said. (Source: FAPESP)

Reference: A. Martins et al.: On Metalenses with Arbitrarily Wide Field of View, ACS Phot. 72073 (2020); DOI: 10.1021/acsphotonics.0c00479

Link: São Carlos School of Engineering, Dept. of Electrical and Computer Engineering, University of São Paulo, São Paulo, Brazil

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