Fig. 1. Schematic of the cascaded metasurface for dynamic wavefront control. (a) Sketch of the dynamic wavefront controlling process in which the direction and polarization state of the transmitted wave are evolving simultaneously over the time t. The whole system is composed of multilayer metasurfaces with different phase distributions Φi(ri) and angular speeds α˙i(t) (where the i indicates the layer number). The inset to panel (a) illustrates the local coordinate of a meta-atom and the global coordinate. Such a meta-atom can transmit a normally incident wave with (b) an averaged transmission phase Φavi(ri) and (c) different polarization states (described by the point |σfi(r,t)⟩ on Poincaré’s sphere) evolving simultaneously over the time t.

Fig. 2. Illustration of the dynamic controlling process. Two identical transparent metasurfaces with (a) phase distribution of Φui(ri) and (b) phase distribution of Φvi(ri) are employed to illustrate the process. (c) The total phase Φav(r,t) of the device and (d) the scattered |E|-field distributions calculated by the Green’s function approach for a transmitted beam at a distance d=λ above the surface for a normally incident LCP wave at five different time instants, with (e) the orientation angles {α1(t),α2(t)} evolving over time t. Ellipses in (c) and (d) illustrate the polarization patterns at different locations inside the transmitted beam at a distance d=0 and d=λ above the surface.

Fig. 3. Meta-atom designs for both the phase and polarization manipulations. (a) Schematic of the designed meta-atom for independent phase and polarization controlling. FDTD-computed (b) transmission phase difference ΔΦi and (c) average transmission amplitude |tavi| versus wx and h3 for the bottom post under illuminations of u^- and v^-polarized beams, with fixed wy=40μm. (d) Simulated average transmission phase Φavi and (e) average transmission amplitude |tavi| versus l and h1 for the whole meta-atom with ΔΦi=−π/2 after optimization of the bottom post. Other geometrical parameters of the meta-atoms are fixed as P=130μm and h2=110μm.

Fig. 4. Beam-steering process of transmitted waves along different paths. The phase diagrams of (a) polar angle θ and (b) azimuth angle φ as functions of α1(t) and α2(t). The θ and φ change as functions of t when the beam direction varies on (c) Path I and (d) Path II.

Fig. 5. Experimental and simulated results of the dynamic beam-steering metadevice. (a) Schematics of the metadevice consisting of two layers of transmissive metasurfaces aligned by a motorized rotation stage, as shown in the lower left inset. The upper left inset shows the side-view SEM pictures of a single metasurface, which consists of top and bottom layers. (b) Top-view (left) and (c) bottom-view (right) SEM pictures of the fabricated metadevice. (d) Schematics of the experimental setup to characterize the metadevice. (e) Experimental and (f) simulated far-field scattering power distributions as the metadevice is illuminated by an LCP light at 0.7 THz, as the metadevice evolves along Path I at different time instants. (g) Evolution of directions for transmitted waves on the sphere of k direction as the metadevice moves along Path I and Path II, with solid line (star-symbols) denoting the simulated (experimental) results. Here, the blue region denotes the solid angle for beam-steering coverage.

Fig. 6. Experimental and simulated results of the metadevice for simultaneous beam-steering and polarization manipulation. (a) Rotation operations on Poincaré’s sphere for an LCP incident wave passing through the two-layer cascaded metasurfaces. (b) The phase distribution of Φui(ri) and Φvi(ri) of two identical anisotropic metasurfaces. (c) SEM images of the top and bottom of the designed meta-atoms. The evolution of (d) directions on a sphere of k direction and (e) the polarization states on Poincaré’s sphere for transmitted waves varying over time, where the blue region denotes the beam-steering and polarization coverage and the star-symbols represent the k and polarization state at three different time instants [t=0,(1/2)T,andT]. (f)–(h) Experimental (blue circles) and simulated (blue line) far-field scattering patterns (left panel) and polarization states (right panel) of the transmitted wave of three certain time instants.