Fig. 1. Functional diagram and characterization of the LC cascaded metalens. (a), (b) Functions of the LC cascaded metalens when the LC optical axis is along the y-axis and x-axis, and the inset is a physical photo of the LC cascaded metalens. (c) Schematic diagram of N/F-STS system. (d) Schematic diagram and dimensions of each metaatom. (e) SEM image of the LC cascaded metalens.

Fig. 2. Simulation and experimental results of the intensity distribution of the emitted LCP and RCP waves in the focal plane, modulated by θ in simulation (a) and applied voltage in the experiment (b).

Fig. 3. Normalized intensity distribution curve and FWHM values at the focal plane. (a) Specified measurement position. θ of 0° (b), (d) and 90° (c), (e) for emitted LCP and RCP waves in the simulation. Voltage of 0 V (f), (h) and 200 V (g), (i) for emitted LCP and RCP waves in the experiment.

Fig. 4. Spatial polarization state distribution on the focal plane: spatial light field and polarization ellipses distributions in (a) simulation for varying θ and (b) experiment for different voltages, as well as ellipticity variation in (c) simulation and (d) experiment.

Fig. 5. Experimental spectral response characteristics at different focal points: transmission spectra of RCP output wave at positions (a) F1, (b) F2, (c) F4, and LCP output wave at positions (d) F1, (e) F2, (f) F4 by applying different voltages.

Fig. 6. Broadband response characteristics of the LC integrated dynamic THz multi-focal metalenses experiment: spatially separated spin-beam optical field distributions under voltage of (a) 0 V and (c) 200 V, and normalized total output power under voltage of (b) 0 V and (d) 200 V.

Fig. 7. Ordinary and extraordinary refractive indices (a) and the absorption coefficient (b) of the HTD028200 LCs.

Fig. 8. (a) Experimental results of refractive index variation with voltage in the range of 0.3–0.7 THz. (b) Corresponding curve of the LC refractive index with respect to voltage and angle at 0.5 THz.