Fig. 1. Schematic of the space-time digital coding metasurface, which can independently control the wavefronts of the fundamental and high-order harmonics by adjusting the phase φA, and the time delay t1 of the periodic reflectivity.

Fig. 2. Reflection amplitudes and phases of Γpq(t) in each period (left column) and the calculated reflection spectra (right column) under different combinations of φA and t1, when the coding sequence 000011111111 is employed. (a) φA=0°, t1=0, (b) φA=180°, t1=0, (c) φA=0°, t1=T/2.

Fig. 3. (a) Perspective view, (b) top view, and (c) bottom view of the metaatom. (d) The simulated reflection spectra of the metaatom under the normal incidence. (e) The scattering patterns of the metaatom for the on and off states. The geometric parameters of the metaatom are p=14, h1=0.8, h2=4, d0=0.7, x1=2, y1=4, x2=0.4, y2=0.6, x3=0.15, and x4=0.8  mm.

Fig. 4. (a) Required phase distributions of the different harmonics. (b) The corresponding far-field scattering patterns. (c), (d) Near-field amplitude and phase distributions for the −1st, 0th, and 1st order harmonics.

Fig. 5. (a) Front view and (b) back view of the proposed space-time digital coding metasurface. (c) Measured reflection spectra for the on and off states of the PIN diodes. (d) Measured harmonic amplitude distributions under two coding sequences 111100000000 and 000011111111, respectively.

Fig. 6. (a) Schematic of the experimental setup for measuring the harmonic near-field distributions. (b) Photograph of the nonlinear near-field experiment environment. (c) The coaxial probe for near-field detection. (d) The waveguide antenna as the excitation of the metasurface. (e), (f) Measured amplitude and phase distributions of the fundamental and ±1st order harmonics.

Table 1. Combination Values (ω0t1, φA) and Calculated Harmonic Phases in the Eight Zones of the Metasurface