Fig. 3: Design and experimental realization of 0D singularity array.

a Geometry of the phase-only metasurface to generate the singularity array upon illumination by λ = 760 nm light. The Cartesian directions are also indicated. b Longitudinal (z) phase gradient along the optic axis at the 0D singularity array, demonstrating large (compared to the free-space wavenumber k₀) and uniform phase gradients at the singularity locations. c Inverse-designed metasurface phase profile as a function of metasurface radial position that achieves the 0D singularity array. The phases have been unwrapped to show the long-range variation. d Scanning electron microscope image of the TiO₂ nanopillars on SiO₂ at the center of the fabricated metasurface that achieves the phase profile in (c). Inset: close-up of the nanopillars demonstrate vertical sidewalls. e Experimental setup to generate and characterize the 0D singularity array. Dotted lines indicate the positions of the pinholes and power meter used in characterizing the absolute transmission intensity.