Light squeezing through arbitrarily shaped plasmonic channels and sharp bends

We propose a mechanism for optical energy squeezing and anomalous light transmission through arbitrarily-shaped plasmonic ultranarrow channels and bends connecting two larger plasmonic metal-insulator-metal waveguides. It is shown how a proper design of subwavelength optical channels at cutoff, patterned by plasmonic implants and connecting larger plasmonic waveguides, may allow enhanced resonant transmission inspired by the anomalous properties of epsilon-near-zero (ENZ) metamaterials. The resonant transmission is shown to be only weakly dependent on the channel length and its specific geometry, such as possible presence of abruptions and bends.

Figure 1

(Color online) Geometry of plasmonic ultranarrow channels connecting two larger plasmonic (metal-insulator-metal) planar waveguide sections. (Here only one of the unit cells in the $x$ direction is shown. The problem is periodic in the $x$ direction). The figure displays the three-dimensional (3D) view (top), transverse cross section of the channel (bottom left), and longitudinal cross section (i.e., side view) at the middle of the channel (bottom right).

Figure 2

Calculated cut-off width $b$ versus frequency for the rectangular plasmonic waveguide formed by the narrow channel in Fig. 1 for $a_{\text{ch}}=20\text{nm}$. The black curve refers to Eq. (2), calculated assuming that the waveguide has four walls made of realistic silver, the red line neglects the presence of silver on the lateral walls, and the blue line refers to the case of ideal perfectly conducting walls for a rectangular waveguide of the same size.

Figure 3

Dispersion of the guided wave number (real and imaginary parts) in a rectangular plasmonic channel with $a_{\text{ch}}=20\text{nm}$ and $b=200\text{nm}$ (black), compared with the dispersion in a parallel-plate metal-insulator-metal waveguide with $a_{\text{ch}}=20\text{nm}$ (red).

Figure 4

Calculated dispersion of the cut-off frequency vs (a) $$$a_{\text{ch}}$ for fixed $$$b=200\text{nm}$ and (b) $b$ for fixed $a_{\text{ch}}=20\text{nm}$.

Figure 5

(Color online) (a) Transmission and (b) reflection coefficients and (c) phase of the transmission for the channels in Fig. 1 with $a_{\text{ch}}=20\text{nm}$, $a=b=200\text{nm}$, and $t=50\text{nm}$ for three different values of $l_{\text{ch}}$.

Figure 6

(Color online) (a) Electric and (b) magnetic field distributions (snapshots in time) for the geometry in Fig. 3 with $l_{\text{ch}}=1\mu \text{m}$ at the frequency $f_0$. The distribution is on the plane at the center of the rectangular waveguide

Figure 7

(Color online) Abrupt bending in the channels in Fig. 4, showing how the channel geometry does not influence the tunneling properties of the anomalous tunneling at frequency $f_0$.