Fig. 2: The BVML design and characterization.

a Schematic of the designed metasurface. Unit cell structure is composed of rectangular shaped α-Si nanopillars on a SiO₂ substrate, with the long axis L = 150 nm, the short axis W = 80 nm, the height H = 400 nm, and the period P = 250 nm. b Schematic top view of the super-pixel realizing complex amplitude modulation. c The complex amplitude value as the function of the rotation angles of the two groups of nanopillars in the super-pixel. The abbreviation “Amp.” has the full name of “Amplitude”. d The optical photographs of the fabricated metasurfaces corresponding to the first- to fourth-order BVMLs, respectively. Scale bars: 200 μm. e Top and tilted views of the SEM images of the α-Si nanopillar arrays. Scale bars: 500 nm. f–i Experimentally measured PSF of the first- to fourth-order BVMLs at the wavelength of 633 nm. Scale bars: 10 μm. j–m The experimental CTF curves for these BVMLs extracted from (f–i), respectively, and fitted by the corresponding order polynomial. The abbreviation “Exp” has the full name of “Experiment”.