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 habits of sunshine. A strong different to conventional, cumbersome optical elements, metasurfaces in the present day 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 College 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. Below a microscope, the brand new system seems to be like a dense array of stepped skyscrapers.
The analysis is revealed 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 gentle, wherein we will engineer all its facets corresponding to wavelength, section and polarization in an unprecedented method…It signifies a brand new avenue for metasurfaces that to this point 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 gentle. The SEAS-led metasurface revolution of the final decade has produced flat, ultra-thin buildings patterned with tens of millions of tiny parts that may manipulate gentle with nanometer precision. A putting instance expertise is the metalens: Not like typical lenses, metalenses may 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 group reported their first working metalens that may bend seen gentle, they labored with Harvard’s Workplace of Expertise Growth to license the expertise and begin an organization, Metalenz. They’ve since demonstrated a bunch of potential functions, together with an endoscope, a synthetic eye, and a telescope lens.
However the single-layer nanostructure design Capasso’s group 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 — as a way to management the sunshine’s habits.
“Many individuals had investigated the theoretical risk of a bilayer metasurface, however the true bottleneck was the fabrication,” stated Alfonso Palmieri, graduate pupil 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 tasks one picture from one aspect and a very totally different picture from the opposite.
Utilizing the services of the Heart for Nanoscale Programs at Harvard, the group 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 display the ability of their system, the group devised an experiment wherein they used their bilayer metalens to behave on polarized gentle in the identical means {that a} difficult system of waveplates and mirrors does.
In future experiments, the group might broaden into much more layers to exert management over different facets of sunshine, corresponding to excessive broadband operation with excessive effectivity throughout the complete 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 Power Workplace of Scientific Analysis beneath grant No.s FA9550-21-1-0312 and FA9550-22-1-0243. The units have been made on the Harvard College Heart for Nanoscale Programs, 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 targeted ion beam course of, and Mac Hathaway supported the atomic layer deposition course of.