Fig. 1. Schematic of the spin-decoupled metalens with intensity-tunable multiple focal points. Under the illumination of LCP THz waves, two RCP focal points are generated, while two LCP focal points can be observed for the incident RCP THz waves. The intensity between two RCP focal points and two LCP focal points can be arbitrarily modulated with different weights of LCP and RCP incident THz waves.

Fig. 2. Schematic, principle, and fabrication of the spin-decoupled metalens. (a) Schematic of the spin Hall metalens consisting of a variety of silicon microrods with identical shape but different orientations. (b) Unit cell of the microrod. (c) The transmission spectra of microrods under the illumination of TE and TM THz waves. (d) The corresponding phase difference between the transmitted TE and TM THz waves. (e) and (f) Optical images of the fabricated spin-decoupled metalenses that can generate transversely distributed and longitudinally distributed RCP and LCP multiple focal points, respectively.

Fig. 3. Electric-field intensity distributions (|E|2) for the spin-decoupled metalens that can generate transversely distributed multiple focal points. (a1), (a2), (b1), (b2), (c1), (c2), (d1), (d2), and (e1), (e2) are the corresponding electric-field intensity distributions at the x−y plane (z=3.75  mm) for the incidence of LCP, LECP, LP, RECP, and RCP THz waves, respectively. (a3), (a4), (b3), (b4), (c3), (c4), (d3), (d4), and (e3), (e4) are the corresponding electric-field intensity distributions at line y=1.5  mm (z=3.75  mm) for the incidence of LCP, LECP, LP, RECP, and RCP THz waves, respectively.

Fig. 4. Electric-field intensity distributions (|E|2) for the spin-decoupled metalens that can generate longitudinally distributed multiple focal points. (a1), (a2), (b1), (b2), (c1), (c2), (d1), (d2), and (e1), (e2) are the corresponding electric-field intensity distributions at the x−z plane (y=0  mm) for the incidence of LCP, LECP, LP, RECP, and RCP THz waves, respectively. (a3), (a4), (b3), (b4), (c3), (c4), (d3), (d4), and (e3), (e4) are the corresponding electric-field intensity distributions at line z=3.75  mm for the incidence of LCP, LECP, LP, RECP, and RCP THz waves, respectively.

Fig. 5. Calculated and measured electric-field intensity distributions at line y=−1.5  mm (z=3.75  mm) for the incidence of (a1), (b1) LCP, (a2), (b2) LECP, (a3), (b3) LP, (a4), (b4) RECP, and (a5), (b5) RCP THz waves.

Fig. 6. Electric-field intensity distributions (under the illumination of THz waves with polarization switched from LCP to RCP) at the x−z plane for the spin-decoupled metalens that can generate transversely distributed multiple focal points.

Fig. 7. Simulated electric-field intensities (|E|2) at the focal plane. (a) The electric-field intensities (|E|2) at point (1.5, 1.5, 3.75 mm) (red curve) and point (−1.5, 1.5, 3.75 mm) (blue curve) with different ellipticity of the THz waves. (b) The electric-field intensities (|E|2) at point (1.5, −1.5, 3.75 mm) (orange curve) and point (−1.5, −1.5, 3.75 mm) (dark yellow curve) with different ellipticity of the THz waves.

Fig. 8. Calculated and measured electric-field intensity distributions at line z=5.75  mm (x=0  mm), for the incidence of (a1), (b1) LCP, (a2), (b2) LECP, (a3), (b3) LP, (a4), (b4) RECP, and (a5), (b5) RCP THz waves, respectively.

Fig. 9. Electric-field intensity distributions (under the illumination of THz waves with polarization switched from LCP to RCP) at the x−y plane (z=3.75  mm) for the spin-decoupled metalens that can generate longitudinally distributed multiple focal points.

Fig. 10. Electric-field intensity distributions (under the illumination of THz waves with polarization switched from LCP to RCP) at the x−y plane (z=5.7  mm) for the spin-decoupled metalens that can generate longitudinally distributed multiple focal points.

Fig. 11. Simulated electric-field intensities (|E|2) at the focal plane. (a) The electric-field intensities (|E|2) at point (0, 1.0, 3.75 mm) (red curve) and point (0, −1.0, 3.75 mm) (blue curve) with different ellipticity of THz waves. (b) The electric-field intensities (|E|2) at point (0, 1.5, 5.7 mm) (orange curve) and point (0, −1.5, 5.7 mm) (dark yellow curve) with different ellipticity of the THz waves.