From the article:
A metalens consists of a flat surface, thinner than a micron, that is covered with an array of nanoscale objects, such as jutting pillars or drilled holes. As incident light hits these elements, many of its properties change—including its polarization, intensity, phase and direction of propagation. Researchers can precisely position the nanoscale objects to ensure that the light that exits the metalens has selected characteristics. What is more, metalenses are so thin that several can sit atop one another without a significant increase in size. Researchers have demonstrated optical devices such as spectrometers and polarimeters made from stacks of these flat surfaces.In a major breakthrough last year, researchers solved a problem called chromatic aberration. As white light passes through a typical lens, rays of its varied wavelengths get deflected at different angles and thus focus at different distances from the lens; to fix this effect, engineers today need to layer lenses in a finicky alignment. Now a single metalens can focus all the wavelengths of white light onto the same spot. Beyond creating this “achromatic” metalens, scientists have developed metalenses that correct other aberrations, such as coma and astigmatism, which cause image distortions and blurring.