Almost a decade ago, Harvard engineers unveiled the world’s first visible-spectrum metasurfaces – ultra-thin, flat devices patterned with nanoscale structures that could precisely control the behavior of light. A powerful alternative to traditional, bulky optical components, metasurfaces today enable compact, lightweight, multifunctional applications ranging from imaging systems and augmented reality to spectroscopy and communications.
Now, researchers in the Harvard John A. Paulson School of Engineering and Applied Sciences(SEAS) are doubling down, literally, on metasurface technology by creating a bilayer metasurface, made of not one, but two stacked layers of titanium dioxide nanostructures. Under a microscope, the new device looks like a dense array of stepped skyscrapers. ...
“It opens up a new way to structure light, in which we can engineer all its aspects such as wavelength, phase and polarization in an unprecedented manner…
“Many people had investigated the theoretical possibility of a bilayer metasurface, but the real bottleneck was the fabrication,” said Alfonso Palmieri, graduate student and co-lead author of the study. With this breakthrough, Palmieri explained, one could imagine new kinds of multifunctional optical devices – for example, a system that projects one image from one side and a completely different image from the other. ...
See the full story here: https://seas.harvard.edu/news/2025/04/doubling-down-metasurfaces