Wide-angle infrared absorber based on a negative-index plasmonic metamaterial

A metamaterial-based approach in making a wide-angle absorber of infrared radiation is described. The technique is based on an anisotropic perfectly impedance-matched negative-index material (PIMNIM). It is shown analytically that a PIMNIM that is subwavelength in all three dimensions enables absorption close to 100% for incidence angles up to $45°$ to the normal. A specific implementation of such frequency-tunable PIMNIM based on plasmonic metamaterials is presented. Applications to infrared imaging and coherent thermal sources are described.

Figure 1

(Color online) Angular dependence of the absorption coefficient for the idealized structure with ${\mu }_{zz}={ϵ}_{yy}=-1+i$, ${\mu }_{xx}=1$, $L_x=\infty$ (dashed line), and $L_x=200\text{nm}$ (dashed-dotted line), barely distinguishable from the $L_x=\infty$ line. Solid line: same for the specific implementation of the metamaterial absorber shown in Fig. 2. A schematic of the idealized wide-angle metamaterial absorber is given in the inset; $s$-polarized incident wave is assumed.

Figure 2

(Color online) Schematic of the PIMNIM structure. Unit cell for electromagnetic and electrostatic simulations is inside the dashed rectangles.

Figure 3

(Color online) Electrostatic magnetically active plasmon resonance of the PIMNIM structure shown in Fig. 2 with the scalable geometric proportions corresponding to (in nm) $L_y=320$, $w_y=200$, $t_x=80$, $w_z=50$, $d_z=80$, $h_x=20$, $v_x=10$, and $h_z=20$. The resonance occurs at ${ϵ}_m/{ϵ}_d=-26.8$. Arrows: electric field; color: electrostatic potential.

Figure 4

(Color online) (a) Reflectance, transmittance, and absorbance at normal incidence of a single PIMNIM layer. (b) Extracted effective dielectric permittivity ${ϵ}_{\text{eff}}$ and magnetic permeability ${\mu }_{\text{eff}}$ of the PIMNIM structure. Reflectance vanishes at $\lambda =1.5\mu \text{m}$ because ${ϵ}_{\text{eff}}={\mu }_{\text{eff}}$. Parameters (in nm): $L_y=326$, $w_y=208$, $t_x=80$, $w_z=46$, $d_z=78$, $h_x=21$, and $h_z=20$.

Figure 5

(Color online) Maximum field enhancement, $\left|\mathit{E}\right|/\left|E_0\right|$, in the PIMNIM vs wavelength. It is noted that the enhancement is maximized at the absorption peak and has no features corresponding to the electric resonance at $\lambda =1380\text{nm}$.

Figure 6

(Color online) Field enhancement, $\left|\mathit{E}\right|/\left|E_0\right|$, in the PIMNIM. Field is plotted on $y\text{−}z$ slices at (a) $x=0$ and (b) $x=-8\text{nm}$. Although the largest enhancement is near the edges and corners, a relatively large area experiences significant enhancement.