Engineers at Harvard University have created a bilayer metasurface made of two stacked layers of titanium dioxide nanostructures. Almost a decade ago, the engineers had unveiled the world’s first visible-spectrum metasurfaces – ultra-thin, flat devices patterned with nanostructures that could precisely control the behavior of light and enable applications in imaging systems, augmented reality, and communications. But the single-layer nanostructure design has been in some ways limiting. For example, previous metasurfaces put specific requirements on the manipulation of light’s polarization in order to control the light’s behavior. Using the facilities of the Center for Nanoscale Systems at Harvard, the engineers came up with a fabrication process for freestanding, sturdy structures of two metasurfaces that hold strongly together but do not affect each other chemically.
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