Strong enhancement of terahertz transmission for a three-layer heterostructure of metal hole arrays

The transmission characteristics of the three-layer metal hole array (MHA) are investigated in the subterahertz region. While the transmittance of the single-layer subwavelength MHA, the diameter of which is much smaller than the wavelength, is extremely low, the transmittance can be increased significantly by attaching the MHAs of the larger diameter on both sides of the subwavelength MHA. The finite-difference time-domain simulation is used to understand the mechanism of such a transmission enhancement phenomenon, and it is attributed to the enhancement of the electric field of the surface waves which are excited strongly on the surface of the outer-layer MHA.

Figure 1

Measured transmission spectra for the MHA of the diameter $d=0.20$, 0.40, 0.60, and 0.80 mm. The cutoff frequencies for the MHAs are shown by the arrows.

Figure 2

(Color online) Schematic diagram of the 3L-MHA. The spacing $s$ between the holes and the diameter $d$ of the center MHA are $s=1.13\mathrm{mm}$ and $d=0.20\mathrm{mm}$, respectively. Thickness $t$ of the MHA is $t=0.25\mathrm{mm}$ for all layers.

Figure 3

(a) Measured transmission spectra for the 3L-MHAs of the diameter $d_{\mathrm{out}}$ of the outer MHA $d_{\mathrm{out}}=0.40$, 0.60, and 0.80 mm. (b) Enhancement factor for the peak transmittance of the 3L-MHAs of $d_{\mathrm{cent}}=0.20\mathrm{mm}$ (circle) and 0.30 mm (cross) as a function of the diameter of the outer MHA $d_{\mathrm{out}}$.

Figure 4

Simulated $z$ component $E_z$ of the electric-field amplitude at 0.28 THz for the single MHA of the diameter (a) $d=0.20$, (b) 0.40, (c) 0.60, and at 0.25 THz for (d) 0.80 mm. The cross section is taken along one of the principal axes of the triangular lattice through the center of the hole.

Figure 5

Simulated $z$ component $E_z$ of the electric-field amplitude for the 3L-MHAs at 0.29 THz. The diameter of the center MHA is $d_{\mathrm{cent}}=0.20\mathrm{mm}$ for all 3L-MHA. The diameters of the outer MHAs are (a) $d_{\mathrm{out}}=0.40$, (b) 0.60, and (c) 0.80 mm. The cross section is taken along one of the principal axes of the triangular lattice through the center of the holes.

Figure 6

Peak frequencies of transmission spectra for the 3L-MHA (open circle and open square) and the single MHA (solid circle and square) as a function of the incident angle. The polarization of the incident THz wave is TM and along one of the principal axes of the triangular structure.