Fig. 1. (a) Graphene-loaded metal wire grating modulator in TIR geometry. The graphene device was deposited on a high-resistivity SiO2/Si substrate and placed on a Si prism. The conductivity of graphene was adjusted by the voltage between the ground (GND) and the metal grating. The incident THz signal was in s polarization. (b) Diagram of the metal grating loaded graphene structure in (a). The medium below the metal grating is the dense medium (n1), and above the metal grating is the less dense medium (n2). The THz signal is incident from the dense medium to the less dense medium in s polarization at an angle of θ. The period of the metal grating is P, and the gap width is g. The red dashed lines represent the integration loop of the electric field.

Fig. 2. (a) Simulation and calculation results of reflected intensity from a graphene/metal grating. The solid lines are calculation results, and the dots are simulation results with different enhancement factors (η). The black dashed lines are the calculation results without a metal grating. (b) Simulation structure of a metal grating in TIR geometry without graphene. The simulation electric field is polarized along the x direction. The black dashed line is to monitor the electric field amplitude in the simulations. (c) Simulated E-field enhancement of a THz wave with a metal grating with various grating parameters (η=2, 3, 10).

Fig. 3. Schematic of the experimental setup and photograph of the metal grating integrated graphene device. (a) Schematic of the graphene modulator in TIR geometry. (b) and (c) are photographs of the metal grating structure. (d) Photograph of the graphene area, showing clearly the graphene covered metal grating area and bare graphene area (white dashed outline).

Fig. 4. THz peak-to-peak images of two metal gratings without graphene in TIR geometry. The peak-to-peak values are calculated from the reflected THz electric field signal from the top surface of the devices. The direction of the electric field is represented by a red double-arrow line. The slit orientation of the grating is represented by golden lines. The white dashed outlines in the images highlight the grating areas. (a), (b) Images of the 30–15 μm grating with electric field perpendicular and parallel to the silt direction. (c), (d) Images of the 30–10 μm grating with electric field perpendicular and parallel to the slit direction.

Fig. 5. Experimental results of the metal grating integrated graphene device. (a), (b) THz peak-to-peak images of 30–15 μm and 30–10 μm grating devices without applying voltage. The graphene transferred on the metal grating is highlighted with white dashed lines. The right side of the graphene area is with a metal grating; the left side of the graphene area is without a covering metal grating. (c) and (d) are reflected waveforms by changing the gate voltages from −60  V to +60  V for 30–15 μm and 30–10 μm grating devices with (solid) and without a grating (dashed). Four insets in (c) and (d) show the peak value changes of the time-domain signal. The waveforms are shifted horizontally for clarity.

Fig. 6. (a) and (b) are MDs of the two devices in TIR and transmission geometries (T90). The red solid line is the MD of graphene integrated with a 30–10 μm grating; the blue solid line is the MD of graphene integrated with a 30–15 μm grating; the green dashed line is the MD of graphene without a metal grating.