Subwavelength imaging at infrared frequencies using an array of metallic nanorods

We demonstrate that an array of metallic nanorods enables subwavelength (near-field) imaging at infrared frequencies. Using an homogenization approach, it is theoretically proved that under certain conditions the incoming radiation can be transmitted by the array of nanorods over a significant distance with fairly low attenuation. The propagation mechanism does not involve a resonance of material parameters and thus the resolution is not strongly affected by material losses and has wide bandwidth. The subwavelength imaging with ${\lambda }_0∕10$ resolution by silver rods at $30\mathrm{THz}$ and over a propagating distance of $0.6{\lambda }_0$ is demonstrated numerically using a full-wave electromagnetic simulator.

Figure 1

(Color online) Periodic array of long thin plasmonic rods arranged in a square lattice.

Figure 2

A plane wave illuminates a slab of the rod medium (side view). The thickness of the slab is $L$ and the rods are normal to the interface. The structure is periodic along the $x$ and $y$ directions.

Figure 3

Dispersion contours for the quasi-TEM mode at $30\mathrm{THz}$ for silver rods with $a=215\mathrm{nm}$ and various values of $R$.

Figure 4

Normalized attenuation constant (nonpropagating mode) at $30\mathrm{THz}$ for silver rods with $a=215\mathrm{nm}$ and different values of $R$.

Figure 5

Amplitude of the transmission coefficient as a function of $k_{\Vert }∕\beta$ for silver rods at $30\mathrm{THz}$. The “stars” represent the full wave result, the dashed line represents the analytical result, and the solid line corresponds to the analytical result with corrected $k_z^{\left(1\right)}$.

Figure 6

Phase of the transmission coefficient as a function of $k_{\Vert }∕\beta$ for silver rods at $30\mathrm{THz}$. The legend is as in Fig. 5.

Figure 7

Amplitude of the transmission coefficient as a function of $k_{\Vert }∕\beta$ for silver rods at $30\mathrm{THz}$. The length of the rods is $L=q{\lambda }_h$, where ${\lambda }_h=6.74\mu \mathrm{m}$ and $q=1.00,0.93,0.88,0.87,0.86$ (each value of $q$ is associated with a different curve).

Figure 8

Phase of the transmission coefficient as a function of $k_{\Vert }∕\beta$ for silver rods at $30\mathrm{THz}$. The length of the rods is $L=q{\lambda }_h$, where ${\lambda }_h=6.74\mu \mathrm{m}$ and $q=1.00,0.93,0.88,0.87,0.86$.

Figure 9

Amplitude of the reflection coefficient as a function of $k_{\Vert }∕\beta$ for silver rods at $30\mathrm{THz}$. The length of the rods is $L=q{\lambda }_h$, where ${\lambda }_h=6.74\mu \mathrm{m}$ and $q=1.00,0.93,0.88,0.87,0.86$.

Figure 10

Amplitude of the transmission coefficient as a function of $k_{\Vert }∕\beta$ for silver rods at different frequencies. The length of the rods is $L=5.93\mu \mathrm{m}$.

Figure 11

(Color online) Geometry of the finite-sized slab of rod medium used in the full-wave simulation. The critical parameters are given in nm.

Figure 12

(Color online) Distributions of $\mid E_z\mid$ (arbitrary units) at $29\mathrm{THz}$: (a) at the source plane, at distance $a∕2$ from the source and at the distance $a$ from the front interface, and (b) at the image plane, at distance $a∕2$ from the back interface.

Figure 13

(Color online) Distributions of $\mid E_z\mid$ (arbitrary units) at $30\mathrm{THz}$: (a) at the source plane, and (b) at the image plane.

Figure 14

(Color online) Distributions of $\mid E_z\mid$ (arbitrary units) at $31\mathrm{THz}$: (a) at the source plane, and (b) at the image plane.

Figure 15

(Color online) Distributions of $\mid E_z\mid$ (arbitrary units) at $33\mathrm{THz}$: (a) at the source plane, and (b) at the image plane.

Figure 16

(Color online) Distributions of $\mid E_z\mid$ (arbitrary units) at $36\mathrm{THz}$: (a) at the source plane, and (b) at the image plane.