Fig. 1. Schematic diagram for generation of a structured light beam with polarization variation along arbitrary spatial trajectories using tri-layer metasurface.

Fig. 2. Schematic diagram of design concept for structured light beams. (a) The phase distribution at the input plane. (b) Spatial transmission trajectory of cylindrical helical path. (c) Polarization distributions on the input plane. (d) The polarization states corresponding to different propagation distances z on the Poincaré sphere for linear longitudinal polarization variations. (e) Polarization distributions on the input plane. (f) The polarization states corresponding to different propagation distances z on the Poincaré sphere for nonlinear longitudinal polarization variations.

Fig. 3. Schematic and characteristics of the designed unit cell. (a) Concept of the designed tri-layer metasurface and the metallic structure of each layer. (b, c) Microscope images of fabricated sample 1 and sample 2, respectively. The scale bar is 200 μm. (d) Amplitude and phase modulation of the 128 selected antennas at 0.75 THz.

Fig. 4. Schematic of experimental setup. L, lens; PM, parabolic mirror; TP, THz polarizer; TQWP, THz quarter wave plate; BS, beam splitter; HWP, half-wave-plate; P, polarizer, QWP; quarter wave plate; WP, Wollaston prism; CCD: charge-coupled device.

Fig. 5. Experimental results for a structured light beam with linear longitudinal polarization variations along a helical transmission trajectory. (a, b) Cross-sectional intensity profiles of the electric field at a propagation distance of z=15 mm for the simulation and experiment, respectively. (c) Cross-sectional intensity profiles (red and blue solid lines) extracted from (a) and (b) at the locations of white dashed lines. (d) The electric field component intensity and electric field intensity at different distances. (e, f) Amplitudes and phase difference of electric field components E_x and E_y at different propagation distances. (g) Theoretical, simulated and experimental transmission trajectories.

Fig. 6. Experimental results of a structured light beam with nonlinear longitudinal polarization variations along a helical transmission trajectory. (a) Intensity distributions for E_x, E_y, and total electric field at different distances. (b) Simulated and experimental amplitudes and (c) phase difference of electric field components E_x and E_y at different propagation distances. (d) Theoretical, simulated and experimental transmission trajectories.