Optical Metacages

We suggest a novel strategy for spectrally selective optical shielding of arbitrary shaped volumes by arranging specifically designed two- or three-layer nanowires around an area that needs to be protected. We show that such nanowire shields preserve their functionality for almost arbitrary geometry, and we term such structures optical metacages. We analyze several designs of such optical metacages made from either metallic or dielectric materials with experimentally measured parameters. We employ a semianalytical approach and also verify our results by numerical simulations. We further study optical properties of the introduced metacages in both near- and far-field regions, as well as analyze their frequency selectivity and the vanishing backscattering regime.

Figure 1

Demonstration of metacage functionalities for an arbitrary shape (here is an outline of Australia) made of multilayer nanowires. (a) Radiation of a point source placed inside the metacage is contained within the structure. (b) A volume inside the metacage is screened from an incident plane wave. Three-layer Si-Ag-Si nanowires are used to form the metacage. The amplitude of the electric field is plotted at $\lambda =378\mathrm{nm}$, using the commercial software CST Microwave Studio. The design parameters are found by an analytical approach, and are summarized in Table 1 (see also [29]).

Figure 2

Design of metacages. (a) Wave interaction with a single nanowire, color map shows the field profile, thin lines show the Poynting vectors. Separatrices of the energy flow divide the space into two parts, with energy flowing into the nanowire or going around it. (b) Schematics of the array of multilayer nanowires. (c) A one-dimensional chain of nanowires, which blocks the light propagation. (d) Enclosed volume shielded by nanowires, which can have an almost arbitrary shape (see, e.g., Fig. 1). Design parameters are summarized in Table 1.

Figure 3

(a) Two different hexagonal metacages designed for operation at three different wavelengths (TM polarization) by optimizing the radii of the layers. An average value of the field amplitude inside metacages remains under 0.1 of the incident wave amplitude across a considerable spectral range. Metacages are made of GaAs-Ag-GaAs multilayer nanowires with radii $R_{1–3}=72$, 165, and 200 nm and $R_{1-3}=60$, 124, and 187 nm for the red and blue curves, respectively. (b) Variation of the fields amplitude inside the metacage of (a) (red curve) vs the gap size.

Figure 4

(a) Real part of the field shows the absence of the backward reflection (the incident plane wave is propagating in the $x$ direction). (b) Metacage keeps the shielding functionality. The inset shows the far-field scattering pattern; the metacage is made of gallium arsenide and titanium nitride [44] and the design parameters are listed in the last row of Table 1.