Virtually a decade in the past, Harvard engineers unveiled the world’s first visible-spectrum metasurfaces — ultra-thin, flat units patterned with nanoscale buildings that would exactly management the conduct of sunshine. A robust various to conventional, cumbersome optical parts, metasurfaces at this time allow compact, light-weight, multifunctional functions starting from imaging methods and augmented actuality to spectroscopy and communications.
Now, researchers within the Harvard John A. Paulson Faculty of Engineering and Utilized Sciences (SEAS) are doubling down, actually, on metasurface know-how by making a bilayer metasurface, manufactured from not one, however two stacked layers of titanium dioxide nanostructures. Below a microscope, the brand new gadget appears like a dense array of stepped skyscrapers.
The analysis is printed in Nature Communications.
“It is a feat of nanotechnology on the highest degree,” stated senior creator Federico Capasso, the Robert L. Wallace Professor of Utilized Physics and Vinton Hayes Senior Analysis Fellow in Electrical Engineering at SEAS. “It opens up a brand new option to construction mild, during which we will engineer all its features comparable to wavelength, part and polarization in an unprecedented method…It signifies a brand new avenue for metasurfaces that up to now has been simply scratching the floor.”
For hundreds of years, optical methods have relied on cumbersome, curved lenses manufactured from glass or plastic to bend and focus mild. The SEAS-led metasurface revolution of the final decade has produced flat, ultra-thin buildings patterned with thousands and thousands of tiny parts that may manipulate mild with nanometer precision. A hanging instance know-how is the metalens: Not like typical lenses, metalenses will be fabricated with current semiconductor manufacturing, making doable compact, built-in optical methods in units like smartphones, cameras, and augmented actuality shows.
After Capasso’s workforce reported their first working metalens that may bend seen mild, they labored with Harvard’s Workplace of Expertise Growth to license the know-how and begin an organization, Metalenz. They’ve since demonstrated a bunch of potential functions, together with an endoscope, a man-made eye, and a telescope lens.
However the single-layer nanostructure design Capasso’s workforce invented has been in some methods limiting. For instance, earlier metasurfaces put particular necessities on the manipulation of sunshine’s polarization — that’s, the orientation of the sunshine waves — in an effort to management the sunshine’s conduct.
“Many individuals had investigated the theoretical chance of a bilayer metasurface, however the actual bottleneck was the fabrication,” stated Alfonso Palmieri, graduate scholar and co-lead creator of the research. With this breakthrough, Palmieri defined, one might think about new sorts of multifunctional optical units — for instance, a system that initiatives one picture from one facet and a very completely different picture from the opposite.
Utilizing the services of the Heart for Nanoscale Techniques at Harvard, the workforce that included former postdoctoral researchers Ahmed Dorrah and Joon-Suh Park got here up with a fabrication course of for freestanding, sturdy buildings of two metasurfaces that maintain strongly collectively however don’t have an effect on one another chemically. Whereas such multi-level patterning has been frequent within the silicon semiconductor world, it had not been as nicely explored in optics and metaoptics.
To reveal the ability of their gadget, the workforce devised an experiment during which they used their bilayer metalens to behave on polarized mild in the identical method {that a} difficult system of waveplates and mirrors does.
In future experiments, the workforce might develop into much more layers to exert management over different features of sunshine, comparable to excessive broadband operation with excessive effectivity throughout the whole seen and close to infrared spectrum, opening the door to much more refined light-based functionalities.
The analysis was supported by a number of federal funding sources, together with the Workplace of Naval Analysis below grant No. N00014-20-1-2450, and from the Air Power Workplace of Scientific Analysis below grant No.s FA9550-21-1-0312 and FA9550-22-1-0243. The units had been made on the Harvard College Heart for Nanoscale Techniques, a part of the Nationwide Nanotechnology Coordinated Infrastructure Community, which is supported by the Nationwide Science Basis below NSF award No. ECCS-2025158.
Workers acknowledgments: Stephan Kraemer supported the centered ion beam course of, and Mac Hathaway supported the atomic layer deposition course of.
