Anomalous terahertz transmission through double-layer metal hole arrays by coupling of surface plasmon polaritons

The transmission characteristics of the double-layer metal hole array are investigated in the terahertz (THz) region. We measured the transmission spectra with varying the layer spacing and the lateral displacement between the two layers, and observed the unexpected transmission characteristics in the range of the layer spacing below the wavelength $(\lambda \sim 1\mathrm{mm})$ of the THz wave. When the second layer is shifted laterally by a half of the lattice constant with respect to the first layer, the transmittance is enhanced by 3 times compared with that without shift. The finite difference time domain simulation is used to understand this anomalous transmission phenomenon, and it is attributed to the near-field coupling of the surface waves excited on the metal surfaces of both layers.

Figure 1

(a) Schematic diagram of the double-layer metal hole array. (b) Measured transmission spectrum for the single-layer metal hole array.

Figure 2

Measured transmission spectra for the double-layer metal hole array as a function of the layer spacing ranging from $0\text{to}2.0\mathrm{mm}$ at (a) $p=0$ and (b) $p=0.57\mathrm{mm}$. Transmission spectra at the fixed layer spacing of (c) $h=0.35\mathrm{mm}$ and (d) $h=1.25\mathrm{mm}$; solid and dashed lines are for $p=0.57$ and $p=0\mathrm{mm}$, respectively.

Figure 3

Measured transmission spectra for the double-layer metal hole array as a function of the lateral displacement between the two layers at the fixed layer spacing $h=0.35\mathrm{mm}$.

Figure 4

(a) Schematic diagram of the model used in this simulation. (b) Simulated $z$ component $E_z$ of the electric field amplitude for the single-layer metal hole array. The cross section is taken along the one of the principal axes of the triangular lattice through the center of the hole. (c) The amplitude of $E_z$ (dotted line) along the dashed line in Fig. 4b and the exponential fitting (solid line).

Figure 5

Simulated $z$ component $E_z$ of the electric field amplitude for the double-layer metal hole array at (a) $p=0$ and (b) $p=s∕2$ with the fixed layer spacing $h=0.35\mathrm{mm}$. The cross section is taken along the one of the principal axes of the triangular lattice through the center of the hole.

Figure 6

Simulated Poynting vector for the single-layer metal hole array in the $x\text{‐}z$ plane (arrows). Gray scale image shows the intensity of the $x$ component $S_x$ of the Poynting vector. The cross section is taken along one of the principal axes of the triangular lattice through the center of the hole.