Silicon Nitride Metalens for Optical Imaging

We report an ultrathin silicon nitride metalens for optical imaging. The meta-surface of silicon nitride provides the full phase delay in a broad range of visible wavelengths. The metalens was fabricated by using E-beam lithography, lifting-off and reactive ion etching for high aspect ratio nanostructures of silicon nitride. The beam spots focused through the metalens were experimentally measured at 405 nm, 533 nm, and 633 nm in wavelength, respectively. The captured images of the USAF chart exhibit that the metalens clearly distinguishes two line pairs with 10 μm apart. Unlike conventional metalens of titanium dioxide, the silicon nitride metalens highly compatible to further MEMS fabrication can be further utilized in optical MEMS devices for miniaturized optical imaging and illumination applications.