Abstract-Bilayer Metasurfaces for Dual- and Broadband Optical Antireflection

Li Huang, Chun-Chieh Chang , Beibei Zeng, John Nogan, Sheng-Nian Luo,  Antoinette J. Taylor,  Abul K. Azad, Hou-Tong Chen,

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.7b00471?journalCode=apchd5

Optical antireflection has long been pursued for a wide range of applications, but existing approaches encounter issues in the performance, bandwidth, and structure complexity, particularly in the long-wavelength infrared regime. Here we present the demonstration of bilayer metasurfaces that accomplish dual- and broadband optical antireflection in the terahertz and mid-infrared spectral ranges. By simply tailoring the structural geometry and dimensions, we show that subwavelength metal/dielectric structures enable dramatic reduction of Fresnel reflection and significant enhancement of transmission at a substrate surface, operating either at two discrete narrow bands or over a broad bandwidth up to 28%. We also use a semianalytical interference model to interpret the obtained results, in which we find that the dispersion of the constituent structures plays a critical role in achieving the observed broadband optical antireflection.