Researchers have developed holey dielectric metasurfaces that achieve high nanostructure aspect ratios and that are mechanically robust. It opens a possible path to achieving large diameter achromatic metalenses by expanding the accessible range of group delays.
The dielectric metasurfaces comprise ultradeep via-holes through a thin membrane with aspect ratios approaching 30:1. As the material around each hole forms a contiguous structure, the device is inherently robust and can be deployed without a supporting substrate, expanding the application range of this metasurface platform to cases where a substrate cannot be used, such as in ultrafast optics, where a substrate introduces unwanted dispersion.
The meta-atoms used in the dielectric metasurfaces have the potential to achieve even larger aspect ratios beyond the proof-of-concept reported. Micrometer-sized holes with aspect ratios exceeding 100:1 have been fabricated in silicon microelectromechanical systems, and nanoporous anodic alumina membranes can achieve aspect ratios larger than 25000:1.