Virtually a decade in the past, Harvard engineers unveiled the world’s first visible-spectrum metasurfaces — ultra-thin, flat gadgets patterned with nanoscale buildings that might exactly management the conduct of sunshine. A robust various to conventional, cumbersome optical elements, metasurfaces at present allow compact, light-weight, multifunctional functions starting from imaging techniques 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 expertise by making a bilayer metasurface, manufactured from not one, however two stacked layers of titanium dioxide nanostructures. Beneath a microscope, the brand new gadget seems 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 approach to construction mild, through which we are able to engineer all its facets equivalent to wavelength, part and polarization in an unprecedented method…It signifies a brand new avenue for metasurfaces that thus far has been simply scratching the floor.”
For hundreds of years, optical techniques 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 tens of millions of tiny components that may manipulate mild with nanometer precision. A placing instance expertise is the metalens: In contrast to typical lenses, metalenses might be fabricated with current semiconductor manufacturing, making potential compact, built-in optical techniques in gadgets like smartphones, cameras, and augmented actuality shows.
After Capasso’s staff reported their first working metalens that may bend seen mild, they labored with Harvard’s Workplace of Expertise Improvement to license the expertise and begin an organization, Metalenz. They’ve since demonstrated a number of potential functions, together with an endoscope, a man-made eye, and a telescope lens.
However the single-layer nanostructure design Capasso’s staff 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 — to be able to management the sunshine’s conduct.
“Many individuals had investigated the theoretical risk of a bilayer metasurface, however the true 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 gadgets — for instance, a system that initiatives one picture from one aspect and a totally totally different picture from the opposite.
Utilizing the amenities of the Middle for Nanoscale Techniques at Harvard, the staff 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 effectively explored in optics and metaoptics.
To reveal the facility of their gadget, the staff devised an experiment through which they used their bilayer metalens to behave on polarized mild in the identical means {that a} difficult system of waveplates and mirrors does.
In future experiments, the staff might increase into much more layers to exert management over different facets of sunshine, equivalent to excessive broadband operation with excessive effectivity throughout the whole seen and close to infrared spectrum, opening the door to much more subtle light-based functionalities.
The analysis was supported by a number of federal funding sources, together with the Workplace of Naval Analysis beneath grant No. N00014-20-1-2450, and from the Air Pressure Workplace of Scientific Analysis beneath grant No.s FA9550-21-1-0312 and FA9550-22-1-0243. The gadgets have been made on the Harvard College Middle for Nanoscale Techniques, a part of the Nationwide Nanotechnology Coordinated Infrastructure Community, which is supported by the Nationwide Science Basis beneath NSF award No. ECCS-2025158.
Employees acknowledgments: Stephan Kraemer supported the centered ion beam course of, and Mac Hathaway supported the atomic layer deposition course of.
