The meta-surface corrects chromatic aberrations on all types of lenses

Today's optical systems – from smartphone cameras to state-of-the-art microscopes – use technology that has not changed much since the mid-1700s. Compound lenses, invented around 1730, correct chromatic aberrations that allow the lenses focus different wavelengths of light in different places. Although effective, these multi-material lenses are bulky, expensive and require polishing or precision molding as well as a very careful optical alignment. Now, a group of researchers at Harvard's School of Engineering and Applied Science (SEAS) is asking the question: is it not time for an upgrade?

SEAS researchers have developed a metacorrector, a monolayer surface of nanostructures that can correct chromatic aberrations in the visible spectrum and can be integrated into commercial optical systems, from simple lenses to high-end microscopes. The metacorrector eliminated chromatic aberrations for commercial purposes across the spectrum of visible light. The device also works for super-complex lenses with no less than 14 conventional lenses used in high-resolution microscopes.

"Our metacorrector technology can work hand-in-hand with traditional refractive optics to improve performance while dramatically reducing system complexity and footprint for a wide range of high-volume applications," he said. Federico Capasso, professor of applied physics to Robert L. Wallace. and Vinton Hayes Senior Research Scientist in Electrical Engineering at SEAS and lead author of the paper.

In previous research, Capasso and his team have demonstrated that metasurfaces, nanopillar arrays spaced by less than one wavelength, can be used to manipulate the phase, amplitude and polarization of light and allow creation of new ultracompact optical devices, including lenses. This research uses the same principles to adjust and control the effective refractive index of each nanopillar, so that all wavelengths are brought by the metacorrector to the same focal point.

"You can imagine the light as different packets delivered at different speeds as they propagate through the nanopillars.We designed the nanopillars so that all these packets arrive at the focal point at the same time and with the same time width, "said Wei Ting. Chen, research associate in Applied Physics at SEAS and first author of the article.

"The use of metacorrectors is fundamentally different from conventional methods of aberration correction, such as cascading refractive optical components or the use of diffractive elements, as it involves engineering. of nanostructures, "said Alexander Zhu, graduate student of SEAS and co-author of the study. "It means we can go beyond the material limitations of lenses and get much better performance."

The researchers then aim to increase the efficiency of high-end and miniature optical devices.