Plasmonic metasurfaces, made up of two-dimensional metallic meta-atom arrays, are advantageous because of their ultrathin thicknesses, ease of fabrication, versatile functionality, field confinement beyond the diffraction limit, and superior nonlinearity. Their efficiency, however, is limited due to Ohmic heat loss during resonance. Huygens meta-atoms can break the scattering symmetry and improve transmission efficiency, but transmission efficiency is limited at visible frequencies. Macroscopically, a dielectric Pancharatnam-Berry phase metasurface (PB-phase metasurface) is an optically anisotropic medium similar to a birefringent structure. As meta-atoms’ dimension is close to the incident light wavelength, the metasurface should be considered an inhomogeneous but not a homogeneous, anisotropic medium.
Researchers proposed a hetero-nano-fin structure to improve the efficiency of PB-phase metasurface. MgF2/GaN and MgF2/Nb2O5 hetero-nano-fins were investigated. The overall polarization conversion efficiency (PCE) of the MgF2/GaN nano-fin improved from 52.7 to 54% compared to the bare GaN nano-fin. The Nb2O5 nano-overall fin’s PCE was 1.7 times that of the GaN nano-fin.
After applying MgF2 antireflection, the overall PCE increased from 92.4% to 96%. Furthermore, antireflection improves efficiency by 4.3% on average in wavelengths ranging from 450 to 700 nm. Although the energy increase appears minor, antireflection is critical for a metasurface, improving efficiency and reducing a meta-device’s background signal.
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