Metasurfaces for Optical Antireflection and Bandpass Filters

We experimentally demonstrate bilayer metasurfaces for optical antireflection. The metasurfaces consist of a square array of silicon pillars with self-aligned top gold resonators and complementary bottom gold slots, enabling near-zero reflection and simultaneously close-to-unity transmission at designed operational frequencies in the terahertz and mid-infrared spectral regions. We further demonstrate THz bandpass filters based on stacked bilayer metasurfaces, allowing fairly narrow, fast roll-off, and high-transmission bandpass performance, with an extremely clean background outside the passband.