Fig. 2. Metasurface design and characterization.
a Optimized metasurface phase profiles that can generate a decoupled pair of conjugate single-helix PSFs for x-polarized and y-polarized incident light, respectively. b Schematic of the metasurface that splits and focuses the light of orthogonal polarization on laterally shifted location of the photosensor with a decoupled pair of conjugate single-helix PSFs, where θ = 8° is the off-axis angle for polarization splitting. c The unit-cell of the metasurface is composed of silicon nanopillars of rectangular in-plane cross-sections on a sapphire substrate, with height H = 600 nm, period U = 350 nm, and width W and length L varying between 100 nm and 250 nm. d–f Photograph (d), optical microscopy image (e), and scanning electron microscopy image (f) of the fabricated metasurface sample, respectively. The other metalenses as shown in the photograph are fabricated for different purposes. g Calculated (green line) and measured (green star) orientation angle φ of the single-helix PSF pair as a function of the axial depth of a point object zobj. The inset shows the method to extract φ from the translation relationship of the decoupled pair of conjugate single-helix PSFs. h Calculated and experimentally measured single-helix PSFs as a function of zobj, for x-polarized and y-polarized incident light, respectively. The PSF pairs are conjugate with respect to the geometric image point (intersection point of black crosshairs). The arrows represent the vectors pointing from the geometric image point to the maximum of the PSFs.