Fig. 1. (a) Schematic of the reconfigurable THz wavefront modulator. The structure consists of a double C-shaped gold antenna array and a 5×5 array of graphene capacitors composed of 10 graphene ribbons. (b) Top view of one unit cell with the double C-shaped antenna. The centers of the large antenna and small antenna are located at (0 μm,0 μm) and (75 μm, −75  μm), while the opening directions are −45° and +45°, respectively. (c) Side view of the structure.

Fig. 2. (a) Simulated transmission spectra of the two individual C-shaped antennas (top) and transmission spectrum of the double C-shaped antenna (bottom). The purple rectangles correspond to the transmissions predicted by the TCMT through fitting the simulated results. (b) Simulated transmission spectrum of the double C-shaped antenna with different outer radii R′ of the smaller antenna. (c) Conversion efficiency of the double C-shaped antenna and single C-shaped antenna without graphene and with graphene for f=0.504  THz. (d) Conversion efficiency of the double C-shaped antenna and single C-shaped antenna versus different graphene chemical potentials for f=0.504  THz.

Fig. 3. (a)–(c) Illustration of 5×5  pixels of the reconfigurable modulator with three graphene chemical potential distribution modes A′,B′, and C′, respectively. The colors represent different graphene chemical potentials. (d)–(f) Simulation results of transmitted amplitude distributions in the x-z plane under the three chemical potential modes.

Fig. 4. (a) Schematic of the device fabrication. (b) Fabrication process of the metasurface. (c) Fabrication process of graphene ribbons. (d), (e) Optical image of fabricated metasurface and ablated graphene by laser cutting. (f) Raman spectra of the uncut (red and blue lines) and cut (yellow line) areas.

Fig. 5. (a)–(d) Experimental results of field distribution on the y-z plane when the voltages are applied in four modes: A, B, C, and D. The intensities are normalized by the maximum intensity of mode B. (e) Broadband performance of the device. (f) Relationship between the applied gate voltage and graphene chemical potential.

Fig. 6. (a) Phase spectra of the large C-shaped antenna and small C-shaped antenna in x and y polarizations (Δφy=0.07π and Δφx=0.97π). (b) Relation between the Q-factor of QBIC and the width of the small C-shaped antenna. (c), (d) Instantaneous directions of surface magnetic field (Hx) and their distributions at frequencies of f=0.504  THz and f=0.497  THz, respectively. The gray dotted line denotes the outline of the gold antennas (top view). (e) Instantaneous directions and absolute value distribution of the electric field (|E|) at the frequency of f=0.504  THz in the y-z plane (side view). (f) Phase spectra of transmitted y-polarized wave corresponding to EF=0.04  eV, EF=0.4  eV, EF=0.56  eV, and EF=0.68  eV.

Fig. 7. Ablation of graphene under different laser fluences.

Fig. 8. (a) Graphene ribbons after laser cutting. (b) Resistance test of one graphene ribbon. The resistance is 28.9  kΩ. (c) Resistance test of adjacent graphene ribbons demonstrating electrical isolation.

Fig. 9. (a) Fabricated metasurface and graphene ribbons mounted on PCB. (b) Fabricated graphene ribbons connected to PCB by silver paste. (c) THz focal plane imaging system.

Fig. 10. (a), (b) Phase profile obtained by simulation and experiment, respectively. (c) Gate-dependent electrical resistance of graphene on the metasurface. (d)–(f) FWHM and focusing efficiency of modes A, B, and C, respectively.

Table 1. Gate Voltages Applied on Graphene