Inspired by prehistoric creatures, researchers make record-setting lenses

The oceans teemed with trillions of trilobites five hundred million years ago. The compound eyes of the trilobites gave them a wide range of vision. Dalmanitina socialis was farsighted. Their bifocal eyes, each mounted on stalks and composed of two lenses that bent light at different angles, enabled these sea creatures to simultaneously view prey floating nearby as well as distant enemies approaching from more than a kilometer away.

The National Institute of Standards and Technology (NIST) has developed a miniature camera with a bifocal lens that can produce sharp images in a single photo. The camera can image objects as close as 3 centimeters and as far away as 1.7 kilometers. They created a computer program to correct for aberrations, sharpen objects at intermediate distances between these near and far focal lengths, and generate a final all-in-focus image covering this enormous depth of field.

The lightweight, large-depth-of-field cameras, which integrate photonic technology at the nanometer scale with software-driven photography, promise torevolutionizing future high-resolution images. In particular, the cameras would greatly boost the capacity to produce highly detailed images of cityscapes, groups of organisms that occupy a large field of view and other photographic applications in which both near and far objects must be brought into sharp focus.

In the April 19 issue of Nature Communications, NIST researchers, along with their colleagues from the University of Maryland in College Park and Nanjing University, describe their work.

The metalenses were fabricated by the researchers. These films are etched with groupings of pillars that are tailored to manipulate light in specific ways. To design their metalenses, Agrawal and his colleagues studded a flat surface of glass with millions of tiny, rectangular nanometer-scale pillars. The meta surface acted as a macro lens for close-up objects and a telephoto lens for distant ones, because of the shape and orientation of the nanopillars focused light.

Light that is left and right circularly polarized can be divided into two equal parts. Left circularly polarized light has an electric field that rotates counterclockwise, while right circularly polarized light has an electric field that rotates clockwise.

Depending on the orientation of the nanopillars, the light was bent left and right. The light had to travel through the longer part of the rectangle and the shorter part of the square because the team arranged the nanopillars in such a way. Light had to pass through more material in order to experience more bending. The light had less material to travel and therefore less bending for the shorter path.

Light that is bent by different amounts is brought to a different focus. The closer the light is focused, the greater the bending. The metalens produces images of both distant objects and nearby ones, depending on whether the light traveled through the longer or shorter part of the rectangular nanopillars.

Without further processing, objects at intermediate distances would be unfocused. A neural network is a computer program that mimics the human nervous system and is used to teach software to recognize and correct defects such as blurriness. The team tested its camera by placing objects of various colors, shapes and sizes at different distances in a scene of interest and applying software correction to generate a final image that was focused and free of aberrations over the entire kilometer range of depth of field.

Light-gathering ability is boosted by the metalenses developed by the team. The system has a high tolerance for error, which makes it easy for researchers to use simple, easy to fabricate designs for miniature lenses.

More information: Qingbin Fan et al, Trilobite-inspired neural nanophotonic light-field camera with extreme depth-of-field, Nature Communications (2022). DOI: 10.1038/s41467-022-29568-y Journal information: Nature Communications

The story is being republished by NIST. The original story can be read here.

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