Fig. 1. Schematics of hypersurface cells. (a) Main view; (b) top view

Fig. 2. Co-polarized transmission amplitude and transmission phase of designed hypersurface cells for perpendicular incidence of x-polarized and y-polarized waves. (a) Transmission amplitude; (b) transmission phase

Fig. 3. Transmission amplitude and transmission phase of hypersurface unit for LCP vertical incidence with different rotation angles. (a) Transmission amplitude; (b) transmission phase

Fig. 4. 2-bit coded elements with phase gradient. (a) Coding element “00”; (b) coding element “01”; (c) coding element “10”; (d) coding element “11”

Fig. 5. Coding sequences used to generate topological charges and phase distributions of l=-1 and l=-2. Coding sequences of (a) l=-1 and (b) l=-2; phase distributions of (c) l=-1 and (d) l=-2

Fig. 6. Far-field scattering with l=-1 and far-field scattering with l=-2 of single-mode vortex wave-encoded phase gradient metasurface at a frequency of 2.0 THz for LCP incidence. (a) Far-field scattering with l=-1; (b) far-field scattering with l=-2

Fig. 7. Encoded sequences and phase distribution used to generate two-beam encoded phase gradient metasurface. (a) Encoded sequences; (b) phase distribution

Fig. 8. Far-field scattering from two split beams in the -x-direction at LCP wave incidence for split-beam encoded phase gradient metasurface at a frequency of 2.0 THz

Fig. 9. Split-beam coding sequences are Fourier-convoluted with the l=-1 vortex wave coding sequence and the l=-2 vortex wave coding sequence, respectively, to produce the coding sequences and phase distributions of the two split-beam vortex waves of the same mode. (a) Vortex wave coding sequence with l=-1; (b) vortex wave coding sequence with l=-2

Fig. 10. Far-field scattering from a two-split-beam single-mode coding phase gradient metasurface at frequency of 2.0 THz. (a) l=-1; (b) l=-2

Fig. 11. Two split-beam vortex waves with l=±1 and l=±2 in x direction at 2.0 THz for LP incidence. (a) Two split-beam vortex waves with l=±1; (b) two split-beam vortex waves with l=±2

Fig. 12. Phase distributions of coding phase gradient metasurface. (a) Phase distribution of two split-beam vortex waves with l=-1 in -x direction; (b) phase distribution after calculating inverse matrix of two split-beam vortex waves with l=-2 in -x direction; (c) multibeam multimodal vortex wave phase distribution

Fig. 13. Far-field scattering and angle for vertical incidence of LP waves. (a) Far-field scattering of the encoded phase-gradient hypersurface at 2.0 THz; (b) pitch angle θ and azimuth angle φ corresponding to vortex waves in the -x and -y directions,respectively; (c) pitch angle θ and azimuth angle φ corresponding to +x and +y directions, respectively