Antireflection of optical anisotropic dielectric metasurfaces

We propose a hetero-nano-fin structure to further improve the efficiency of Pancharatnam-Berry phase metasurfaces. Two hetero-nano-fin types, MgF₂/GaN and MgF₂/Nb₂O₅, were investigated. The overall polarization conversion efficiency (PCE) improved from 52.7 to 54% for the MgF₂/GaN nano-fin compared with the bare GaN nano-fin. The overall PCE of the Nb₂O₅ nano-fin was 1.7 times higher than that of the GaN nano-fin. The overall PCE improved from 92.4% up to 96% after the application of MgF₂ antireflection. Moreover, the antireflection improves efficiency by an average of 4.3% in wavelengths from 450 to 700 nm. Although the increment of energy seems minimal, antireflection is crucial for a metasurface, not only enhancing efficiency but also reducing background signal of a meta-device.