Fig. 1. (a) SEM photo of Si dielectric metasurface. (b) Schematic diagram of terahertz TDPS system. (c) Structural diagram of LC-Si metasurface. d) Experimental configuration of LC-Si metasurface.

Fig. 2. Experimental results of Si metasurface without filling LC. (a) LP transmission spectra when the polarization direction of the incident LP wave is along the long axis and short axis of the Si columns. (b) Birefringence phase shifts in these two orthogonal directions. (c) Transmission spectra through the blank fused-silica LC cell, the complete blank LC cell with two graphene electrode layers, and the LC cell with LC but without Si metasurface as LC orientation along x, y, and z axes; inset figure: SEM photo of graphene electrode layer. (d) Birefringence phase shift in two orthogonal directions of this LC cell under different biased electric fields.

Fig. 3. (a) Geometric diagram of LC molecular orientation in LC-Si metasurface: when the biased electric field E=0  V/mm, the LC molecule is initially anchored in the y axis (θ=0°, γ=0°) and anchored in the x axis (θ=90°, γ=0°); when E=30  V/mm, the LC molecule is turned to the z axis (γ=90°); the long axis of the Si column is fixed along the y axis. The experimental THz time-domain signals for x−LP and y−LP components with a biased electric field applied from 0 to 30 V/mm when the LC is initially along (b) the y axis and (c) the x axis. (d) The experimental phase shift of the device under the different initial orientations and biased electric fields.

Fig. 4. Geometric diagram of LC molecular orientation in LC-Si metasurface when the LC is initially anchored θ=45° to the y axis and the angle (a) γ=0°, (b) 45°, and (c) 90° to the x−y plane, which corresponds to the biased field E=0, 15, and 30 V/mm cases, respectively. The long axis of the Si column is fixed along the y axis. (d) FDTD simulation of electric field distribution in the LC-Si metasurface when θ=45° and γ=0°, 45°, and 90° at 0.95 THz.

Fig. 5. Experimental THz time-domain signals from 1 to 7 ps delay for the four orthogonal polarization components of LC-Si metasurface, when initial LC orientation θ=45° with the biased electric field E=0–30  V/mm: (a) 45° LP incidence to 45° LP detection and (b) to −45° LP detection; (c) −45° LP incidence to −45° LP detection and (d) to 45° LP detection.

Fig. 6. Experimental transmission spectra and polarization conversion when the initial LC orientation θ=45° and LP incidence with the biased electric field E=0–30  V/mm. For the 45° LP incidence: (a) transmission spectra of LCP and RCP output components; (b) PEA and PRA spectra; (e) polarization ellipse at 0.4 and 0.8 THz. For the −45° LP incidence: (c) transmission spectra of LCP and RCP output components; (d) PEA and PRA spectra; (f) polarization ellipse at 0.4 and 0.8 THz.

Fig. 7. CP transmission spectra for LCP and RCP incidence with the biased electric field E=0–30  V/mm when the initial LC orientation θ=45°: (a) experiment Tll and Trr; (b) simulation Tll and Trr; (c) experiment Trl and Trl; (d) simulation Trl and Trl.

Fig. 8. Experimental CD spectra of LC-Si metasurface with the different biased electric fields: (a) Co-CD with E=15–30  V/mm; (b) Co-CD with E=0–15  V/mm; (c) Cross-CD with E=0–30  V/mm. Simulative CD spectra of devices with the different LC orientation angle θ corresponding to the different electric fields E in the experiment when γ=45°: (d) Co-CD with γ=45°–90°; (e) Co-CD with γ=0°–45°; (f) Cross-CD with γ=0°–45°.

Fig. 9. Experimental OA spectra of LC-Si metasurface with the biased electric fields E=0–30  V/mm: (a) Co-OA; (b) Cross-OA.