Fig. 1. (a) Schematic diagram of the broadband SPW excitation in the multi-APSR. Left corners are the detailed diagrams of paired slits and one single APSR structure. (b) Functions of broadband APSR. (c) Simulated and experimental transmission spectra of slits with different geometric sizes. (d) Simulated Ez near-field (real part) distribution and (e) phase maps of SPWs excited by each APSR at 0.35, 0.40, 0.50, and 0.60 THz.

Fig. 2. (a) Structure of THz LC-integrated APSR on-chip metadevices. The photo of practical broadband APSR and its micrographs are shown in the right dotted frame. (b) Schematic diagram of the working principle of LC-integrated SP metadevices. (c) Near-field scanning with THz microprobe. The details of two microprobe types for transversal and longitudinal near-field detection are shown on the right. The antenna gap directions in probe spikes are along the y direction and the z direction. (d) Near-field scanning-terahertz time-domain spectroscopy (NFS-THz-TDS) system.

Fig. 3. Transversal near-field detection on the broadband APSR. (a) Normalized transmittance spectra of Ey components in the near field of broadband APSR at the scanning points from P1 to P8. (b) Experimental and (c) simulated near-field Ey component intensity distributions.

Fig. 4. Longitudinal near-field detection of the APSR. (a) Near-field Ez spectra of broadband and narrowband APSR in focusing and defocusing cases. (b) The simulated near-field Ez intensity distributions of the broadband and narrowband APSR under the LCP incidence. (c) The corresponding experimental results. (d) The simulated near-field Ez intensity distributions of the longitudinal focusing along the x direction and the transverse focusing along the y direction on the focal spot at 0.475 THz. (e) The corresponding experimental results.

Fig. 5. (a) Diagram of active energy distribution in the LC-integrated broadband APSR on-chip metadevice. (b) Simulated and (c) experimental near-field Ez intensity distributions for active unidirectional focusing of SPWs when the LC is orientated along the y-axis (0 V/mm) and x-axis (12 V/mm). (d) Measured time-domain signals at the left focal spot under the electric field of 0 V/mm and 12 V/mm. (e) Experimental near-field Ez spectra of LC-integrated broadband metadevice in focusing and defocusing cases. x-cutting line through the focal spots when the LC orientation is along (f) the y-axis and (g) the x-axis.

Fig. 6. At 0.45 THz, the near-field Ez intensity distribution with the dynamic modulation of SPWs at the left and right focal spots: (a) as the LC rotates from y- to x-axis in the simulation; (b) as the external electric field is enhanced in the experiment. (c) Simulated and (d) experimental near-field Ez intensity distribution along the y-cutting line through the focal spots on the left and right sides.

Fig. 7. (a) Optical micrographs of slit array metasurfaces. The geometric sizes of slits are 140  μm×50  μm,160  μm×50  μm, 180  μm×50  μm, and 200  μm×50  μm. (b) Diagram of narrowband APSR structure. The actual device and optical micrographs are shown on the right.

Fig. 8. (a) Normal refractive index no and extraordinary refractive index ne of LC and its birefringence coefficient. (b) Experimental polarization conversion spectra of the LC layer from a 45°-LP to LCP state.

Fig. 9. (a) Transmission and (b) phase spectrum of QWP. The diagram illustrates the polarization conversion characteristics varying with the angle β by the mechanical rotation of its fast-axis. (c) Near-field Ez distribution on broadband APSR under LP incidence and (d) under RCP incidence, and that on (e) narrowband APSR under RCP incidence, at 0.35, 0.475, and 0.60 THz.