Polarization-insensitive, ultra-broadband, and compact metamaterial-inspired optical absorber via wide-angle and highly efficient performances

A non-interleaved bidirectional Janus metasurface with full-space scattering channels

Metasurfaces have attracted broad interest thanks to their unprecedented capacity for electromagnetic wavefront manipulation. The compact, ultrathin and multifunctional metasurface calls for novel design principles. Here, we propose and experimentally demonstrate a non-interleaved and non-segmented bidirectional Janus metasurface that encodes multiple functionalities in full-space scattering channels with different propagation directions and polarization in the microwave region. Specifically, by rotating and adjusting the elementary double-arrow-shaped structure within the same meta-atom, the independent phase control can be achieved in both cross-polarized transmission and co-polarized reflection components under oppositely directed incident waves. Our metasurface with broken mirror symmetry can fully exploit four independent information channels under opposite propagation directions. A series of proof-of-concept is constructed to validity of our methodology, and the simulations and experimental results further show that the proposed non-interleaved bidirectional metasurface can provide an attractive platform for various applications, ranging from structured light conversion, optical imaging, multifunctional optical information processing and others.

Near-perfect broadband infrared metamaterial absorber utilizing nickel

We propose a thin, compact, broadband, polarization and angle insensitive metamaterial absorber based on a tungsten reflector, a silicon spacer, and a top pattern composed of a double square-like ring resonator utilizing nickel (Ni). In such a structure, a high absorption (above 80%) bandwidth ∼4.8µm from 3.52 up to 8.32 µm corresponding to the relative bandwidth ∼81% can be achieved with deeply subwavelength unit cell dimensions. Here the physical origin of the broadband absorption is associated with low Q-factor dipole modes of the top pattern inner and outer sides functioning as rectangular nanoantennas. Owing to the structural symmetry, the absorber shows a good incidence angle tolerance in the relatively wide range for both transverse electric and transverse magnetic polarizations. The effective parameters of the Ni-based absorber were retrieved using the constitutive effective medium theory, and the absorption characteristics of the effective medium and metamaterial were compared.

A theoretical investigation on reciprocity-inspired wide-angle spectrally-selective THz absorbers augmented by anisotropic metamaterials

In this paper, a theoretical framework relying on the reciprocity theorem is proposed to accurately design a spectrally-selective THz superstrate-loaded metamaterial absorber (SLMA) exhibiting wide-angle feature. By leveraging high-order Floquet harmonics in a generalized transmission line model characterizing the conventional metamaterial absorbers (MAs), it is demonstrated that MAs suffer from impedance mismatch, especially at near grazing angles. From an impedance matching viewpoint, this major challenge is tackled in this paper via two different designs, exploiting a magneto-electric anisotropic Huygens' metamaterial and a multilayer dielectric structure at a certain distance over the MA plane. The numerical results corroborate well the theoretical predictions, elucidating that the proposed SLMA significantly broadens the angular performance of the MA up to near grazing angles (about 80°), where high absorptivity is still achieved in both principal planes. The deteriorating effect of diffraction modes has been comprehensively analyzed. In comparison to the previous wide-angle MA reports based on intricate particle geometries and brute-force optimizations, the proposed design features a straightforward semi-analytical algorithm, which can also be re-developed for microwave, mid-infrared, and optical frequency bands and for any type of MA element. The proposed SLMA would be very promising for various wavelength-selective applications such as sensors and imaging.

Self-biased tri-state power-multiplexed digital metasurface operating at microwave frequencies

Exploiting of nonlinearity has opened doors into undiscovered areas to achieve multiplexed performances in recent years. Although efforts have been made to obtain diverse nonlinear architectures at visible frequencies, the room is still free for incorporating non-linearity into the design of microwave metasurfaces. In this paper, a passive dual-band power intensity-dependent metasurface is presented, which is composed of two different linear and nonlinear meta-atoms accommodating a capacitor and a PIN-diode, respectively. The proposed digital metasurface has three operational states: 1) it acts as a normal reflector at low power intensities while providing a dual-band nonlinear response upon illuminating by high-power incidences where 2) it perfectly absorbs the radiations at f₁=6.7 GHz and 3) re-distributes the scattered beams by arranging the meta-atoms with a certain coding pattern at f₂=9.4 GHz. The performance of the designed coding elements has been characterized by using the scattering parameters captured in the full-wave simulations and the nonlinear analysis performed in ADS software where the accurate model of diodes is involved. The emergence of microwave self-biased metasurfaces with smart re-actions against incident waves with different power levels reveals great opportunities for designing smart windows, smart camouflage coating surfaces, and so on.

High-performance and cost-effective absorber for visible and near-infrared spectrum based on a spherical multilayered dielectric-metal structure

A broadband, polarization-insensitive, wide-angle absorber based on a spherical multilayered dielectric-metal structure is numerically designed and experimentally demonstrated in this paper. This absorber has average absorbance of 0.98 between 380 and 1910 nm, indicating a spectral width of 1530 nm with absorbance exceeding 0.9, and covering the entire visible and near-infrared spectrum. The physical mechanism leading to this broadband absorption is discussed along with the effect of structural parameters on the absorber performance. Importantly, the absorbance is hardly affected by incident angle below 45° and it still stays at a high level with incident angle up to 60°, for both transverse magnetic and transverse electric plane waves.