Fig. 1. Schematic of the spin-decoupled metasurfaces for the generation of multiple pencil-like beams with longitudinally inhomogeneous versatile polarization states and polarization-evolutive imaging. (a) A metasurface that can generate two pencil-like beams with longitudinally inhomogeneous versatile polarization states. (b) Schematic of the same metasurface for polarization-evolutive imaging.

Fig. 2. Design of metasurfaces and optical images of samples. (a) and (b) Phase maps of a meta-atom versus the structural parameters L and W under the illumination of (a) x- or (b) y-polarized THz waves. (c) and (d) Intensity maps of transmission in copolarization for (c) x- or (d) y-polarized incidence. (e) The transmission spectra of the selected meta-atom under the illumination of x- (red curve) or y-polarized (black curve) THz waves. (f) The polarization conversion efficiency (blue curve) between the transmitted RCP and incident LCP THz waves and phase difference (orange curve) between the transmitted electric fields in the x and y directions. (g), (h), and (i) Optical images of the three fabricated samples.

Fig. 3. Electric-field intensity and polarization distributions of pencil-like beams with the longitudinal polarization evolution between two orthogonal LP states. (a1)–(a3) and (h1)–(h3) The simulated and measured x-polarized (a1), (h1), y-polarized (a2), (h2), and total (a3), (h3) electric-field intensity distributions after the designed geometric metasurface. (b1)–(b5)/(c1)–(c5) and (i1)–(i5)/(j1)–(j5) The simulated and measured x-/y-polarized electric-field intensity distributions for the left pencil-like beam at the different transverse (x–y) plane. (d1)–(d5) and (k1)–(k5) The simulated and measured polarization distributions for the left pencil-like beam at the different transverse plane. (e1)–(e5)/(f1)–(f5) and (l1)–(l5)/(m1)–(m5) The simulated and measured x-/y-polarized electric-field intensity distributions for the right pencil-like beam at the different transverse (x–y) plane. (g1)–(g5) and (n1)–(n5) The simulated and measured polarization distributions for the right pencil-like beam at the different transverse plane.

Fig. 4. Polarization-switchable imaging based on the designed metasurface that shows two pencil-like beams with the longitudinal polarization evolution between two orthogonal LP states. (a) and (b) The schematic and optical images of the designed imaging sample consisting of the letters W and E. (c1)–(c3) and (e1)–(e3) The simulated and measured electric-field intensity distributions for the imaging sample located at different transverse planes of the left pencil-like beam. (d1)–(d3) and (f1)–(f3) The simulated and measured electric-field intensity distributions for the imaging sample located at different transverse planes of the right pencil-like beam.

Fig. 5. Electric-field intensity and polarization distributions of pencil-like beams with the longitudinal polarization evolution between two orthogonal CP states. (a1)–(a3) and (h1)–(h3) The simulated and measured LCP (a1), (h1), RCP (a2), (h2), and total (a3), (h3) electric-field intensity distributions after the designed geometric metasurface. (b1)–(b5)/(c1)–(c5) and (i1)–(i5)/(j1)–(j5) The simulated and measured LCP/RCP electric-field intensity distributions for the left pencil-like beam at the different transverse (x–y) plane. (d1)–(d5) and (k1)–(k5) The simulated and measured polarization distributions for the left pencil-like beam at the different transverse plane. (e1)–(e5)/(f1)–(f5) and (l1)–(l5)/(m1)–(m5) The simulated and measured LCP/RCP electric-field intensity distributions for the right pencil-like beam at the different transverse (x–y) plane. (g1)–(g5) and (n1)–(n5) The simulated and measured polarization distributions for the right pencil-like beam at the different transverse plane.

Fig. 6. Polarization-switchable imaging based on the designed metasurface that shows two pencil-like beams with the longitudinal polarization evolution between two orthogonal CP states. (a) and (b) The schematic and optical images of the designed imaging sample consisting of numbers 6 and 9. (c1)–(c3) and (e1)–(e3) The simulated and measured electric-field intensity distributions for the imaging sample located at different transverse planes of the left pencil-like beam. (d1)–(d3) and (f1)–(f3) The simulated and measured electric-field intensity distributions for the imaging sample located at different transverse planes of the right pencil-like beam.

Fig. 7. Electric-field intensity and polarization distributions of pencil-like beams with the longitudinal polarization evolution between two orthogonal LP and CP states. (a1)–(a3) and (i1)–(i3) The simulated and measured LCP (a1), (i1), RCP (a2), (i2), and total (a3), (i3) electric-field intensity distributions for the left focal point. (b1)–(b3) and (j1)–(j3) The simulated and measured LCP (b1), (j1), RCP (b2), (j2), and total (b3), (j3) electric-field intensity distributions for the right focal point. (a4) and (i4) The simulated and measured electric-field intensity distributions after the designed metasurface. (c1)–(c5)/(d1)–(d5) and (k1)–(k5)/(l1)–(l5) The simulated and measured LCP/RCP electric-field intensity distributions for the left pencil-like beam at the different transverse (x–y) plane. (e1)–(e5) and (m1)–(m5) The simulated and measured polarization distributions for the left pencil-like beam at the different transverse plane. (f1)–(f5)/(g1)–(g5) and (n1)–(n5)/(o1)–(o5) The simulated and measured x-/y-polarized electric-field intensity distributions for the right pencil-like beam at the different transverse plane. (h1)–(h5) and (p1)–(p5) The simulated and measured polarization distributions for the right pencil-like beam at the different transverse plane.

Fig. 8. Polarization-switchable imaging based on the designed metasurface that shows two pencil-like beams with the longitudinal polarization evolution between two orthogonal CP and LP states. (a) and (b) The schematic and optical images of the designed imaging sample consisting of two CP-based numbers 7 and 0. (c) and (d) The schematic and optical images of the designed imaging sample consisting of the LP-based letters H and V. (e1)–(e3) and (g1)–(g3) The simulated and measured electric-field intensity distributions for the CP-based imaging sample located at different transverse planes of the left pencil-like beam. (f1)–(f3) and (h1)–(h3) The simulated and measured electric-field intensity distributions for the LP-based imaging sample located at different transverse planes of the right pencil-like beam.

Fig. 9. Electric-field intensity and polarization distributions of three pencil-like beams with the longitudinal polarization evolution between two orthogonal LP states. (a1)–(a3) The simulated (a1) x-polarized, (a2) y-polarized, and (a3) total electric-field intensity distributions after the designed geometric metasurface. (b1)–(b5)/(c1)–(c5), (d1)–(d5)/(e1)–(e5), and (f1)–(f5)/(g1)–(g5) The simulated x-/y-polarized electric-field intensity distributions for the left, middle, and right pencil-like beams at the different transverse (x–y) plane. (h1)–(h5), (i1)–(i5), and (j1)–(j5) The simulated polarization distributions for the left, middle, and right pencil-like beams at the different transverse plane.

Fig. 10. (a), (b) Transmission spectra of metal slits and (c), (d) dual-layer chiral-structure consisting of split-ring-stripe hybrid structure and metallic gratings. The structural parameters are as follows: w=20  μm; d1=40  μm; d2=20  μm; r=60  μm; α=30; P=156  μm.

Fig. 11. Electric-field intensity and polarization distributions of three pencil-like beams with the longitudinal polarization evolution between two orthogonal CP states. (a1)–(a3) The simulated (a1) LCP, (a2) RCP, and (a3) total electric-field intensity distributions after the designed geometric metasurface. (b1)–(b5)/(c1)–(c5), (d1)–(d5)/(e1)–(e5), and (f1)–(f5)/(g1)–(g5) The simulated LCP/RCP electric-field intensity distributions for the left, middle, and right pencil-like beams at the different transverse (x–y) plane. (h1)–(h5), (i1)–(i5), and (j1)–(j5) The simulated polarization distributions for the left, middle, and right pencil-like beams at the different transverse plane.

Fig. 12. Electric-field intensity and polarization distributions of three pencil-like beams with the longitudinal polarization evolution between two orthogonal LP and CP states. (a1)–(a3) The simulated (a1) x-polarized, (a2) y-polarized, and (a3) total electric-field intensity distributions after the designed geometric metasurface. (b1)–(b5)/(c1)–(c5) and (d1)–(d5)/(e1)–(e5) The simulated x-/y-polarized electric-field intensity distributions for the left and middle pencil-like beams at the different transverse (x–y) plane. (f1)–(f5)/(g1)–(g5) The simulated LCP/RCP electric-field intensity distributions for the right pencil-like beam at the different transverse (x–y) plane. (h1)–(h5), (i1)–(i5), and (j1)–(j5) The simulated polarization distributions for the left, middle, and right pencil-like beams at the different transverse plane.