Bilayered nanoantenna design improves the performance of silicon metasurfaces in the visible-wavelength region

High-transmissivity all-dielectric metasurfaces have recently attracted attention toward the realization of ultracompact optical devices and systems. Silicon-based metasurfaces, in particular, are highly promising considering the possibility of monolithic integration with complementary metal-oxide-semiconductor very large scale integration circuits. Realization of silicon-based metasurfaces operational in the visible wavelengths, however, remains a challenge. A numerical study of bilayered truncated-cone shaped nanoantenna elements is presented. Metasurfaces based on the proposed stepped conical geometry can be designed for operation in the 700- to 800-nm wavelength window and can achieve full-cycle phase response (0 to 2π) with an improved transmittance in comparison with the previously reported cylindrical geometry. A systematic parameter study of the influence of various geometrical parameters on the achievable amplitude and phase coverage is reported.