Research progress on hybrid vector beam implementation by metasurfaces

A dielectric metasurface based on TiO₂ nanorods^[65]. (a) Schematic diagram of laser pumping source and components based on metasurface conversion; (b) Schematic diagram of the central part and unit structural parameters of the metasurface; (c) Optical microscope images of the generated metasurfaces with topological charge l₁=10 and l₂=100; (d) Schematic diagram of generating and superimposing electric field intensities of beams with different topological charges by rotating the metasurface; (e) Generalized OAM spheres displaying different laser measurement states

Metasurfaces based on dual crystal pillar unit cell ^[61]. (a) Poincaré sphere representation of a conventional vector vortex beam and a perfect vortex vector beam, illustrating their different theoretical intensity and polarization distributions in spherical coordinates; (b) Schematic of the bilayer silicon pillar unit structure and the modulation of the incident wavefront phase, amplitude, and polarization state under oblique incidence; (c) Intensity and polarization distributions obtained from theory and experiment for different $ { {l}}_{ {0}} $ values at (θ, φ₀)=(π/2, 0) with $ { {l}}_{ {{\rm{p}}}} {} {=} {} {0} $, including the intensity after passing through an orthogonal polarizer; (d) Intensity and polarization distributions obtained from theory and experiment for different $ { {l}}_{ {0}} $ values at (θ, φ₀)=(π/3, 2π/3) with $ { {l}}_{ {{\rm{p}}}} {=0} $, including the intensity after passing through an orthogonal polarizer; (e) Intensity and polarization distributions obtained from theory and experiment for different ${ {l}}_{ {{\rm{p}}}}$ values at (θ, φ₀)=(π/2, 0) with ${ {l}}_{ {{\rm{0}}}} {} {=} {} {-2}$, including the intensity after passing through an orthogonal polarizer; (f) Intensity and polarization distributions obtained from theory and experiment for different ${ {l}}_{ {{\rm{p}}}}$ values at (θ, φ₀)=(π/3, 2π/3) with ${ {l}}_{ {{\rm{{\rm{0}}}}}} {} {=} {} {-3}$, including the intensity after passing through an orthogonal polarizer

A kind of all-medium spin-multiplexing metasurfaces for various perfect Poincaré beams^[86]. (a) Hybrid-order Poincaré sphere representation of various perfect Poincaré beams; (b) Schematic view of the metasurface composed of rectangular TiO₂ nanorods arranged on a melted silica substrate, including perspective and top views of a unit cell; (c) Schematic diagram of the phase superposition method of the metasurface; (d) Intensity distribution of optical vortex in the y-z plane at the working wavelength of 530 nm, and the ring-shaped intensity distribution of optical vortex in the x-y plane at the focal point, with a scale of 10 μm. The right side is the normalized cross-sectional distribution of the ring-shaped intensity of MF1 and MF2; (e) Normalized light intensity distribution in the y-z plane at 480 nm (blue), 580 nm (yellow), and 630 nm (red) wavelengths, and the normalized light intensity distribution at the focal point, with a scale of 10 μm

Vortex beams with longitudinal variation in topological charges based on all-dielectric metasurfaces at the incidence of circular polarization^[89]. (a) Vortex beams of longitudinal topological charge l = ±2 are generated when left-handed circularly polarized light is incident on the metasurface; (b) The spatial distribution of the field strength and phase changes with propagation distance in the x-y plane when left-handed circularly polarized light is incident; (c) Vortex beams of longitudinal topological charge l = ±1 are generated when right-handed circularly polarized light is incident on the metasurface; (d) The spatial distribution of the field strength and phase changes with the propagation distance in the x-y plane when right-handed circularly polarized light is incident

Vector vortex beam generation at the incidence of linear polarization^[89]. (a) The incident light polarized in the z-direction is converted from a vortex beam with angular polarization distribution to a vortex beam with radial polarization distribution; (b) Spatial polarization distribution changes from an angular distribution to a second-order radial distribution; (c) Spatial polarization distribution changes from a radial distribution to a second-order radial distribution

Perfect vortex light generated by the gold nanopore array^[107]. (a) Structural parameters and schematic diagram of the gold nanopore; (b) Phase curve distribution corresponding to different rotation angles; (c) Comparison of light intensity of different topological charges at different longitudinal distances under the same wavelength; (d) Phase superposition required to achieve perfect vortex light; (e) Schematic diagram of the longitudinal distribution of the generated perfect vortex light beam intensity; (f) The phase distribution and light intensity distribution of four perfect vortex lights realized on the same focal plane, with a focal length of 4 μm in the upper half and 8 μm in the lower half

Multiplexing and demultiplexing of cylindrical vector beams based on metal metasurfaces^[108]. (a) Metal metasurfaces generating multilevel diffracted topological vortex beams for different incident beams; (b) Schematic diagram of the polarization state and intensity distribution of the incident beam and different diffracted order beams; (c) The metasurface satisfies three order phase distributions in the x and y directions; (d) Phase delay generated by different incident angles; (e) Schematic diagram of multiplexing and demultiplexing using two metasurfaces, including the polarization and intensity distribution of the incident beam, multiplexed beam, and order multiplexed beam

A metal metasurface achieving second harmonic vortex beams^[112]. (a) Schematic illustration of the transformation principle of the gold nanohole array settling WS₂ layer on the beam; (b) Transmittance spectra analysis of the gold nanohole array, Au-WS₂ metasurface, and single WS₂; (c) Metasurface phase and spatial transmission schematic; (d) Distribution of different topological charges, light intensity, and phase

A three-layer metal metasurface realizing multi-channel vector holography ^[113]. (a) Schematic diagram of the three-layer metal metasurface unit structure, with PI (polyimide) medium separating each layer of metal structure; (b) Schematic diagram of the polarization rotation angle distribution of the metasurface array blocks; (c) Schematic diagram of the multi-channel vector holography effect achieved by the metasurface; (d) Schematic diagram of the experimental results, including the amplitude distribution of the hologram without selecting the polarization state for detection, and the amplitude distribution of the experiment with different channels hiding polarization states

A programmable controlled scattering metasurface^[128]. (a) FPGA controls the meta-surface coding to achieve multi-functional transformations; (b) Schematic diagram and physical picture of the metasurface unit structure; (c) Programmable metasurface achieves different topological charges of OAM beam switching, and the schematic diagram of the intensity and phase distribution

A 2-bit encoded metasurface^[127]. (a) Schematic diagram of the metasurface array and unit composition; (b) Using the metasurface to realize a single-mode OAM beam with different topological charges, including the metasurface phase distribution and simulation results; (c) Changing the code to achieve different angles of deflection for a single-mode OAM beam, as shown by the schematic diagram of the light intensity; (d) The generation and integration of multi-mode OAM beams, including the near-field and far-field light intensity distributions

Using a tunable metasurface with a photodetector to achieve various functions^[131]