Multilayer Metamaterials Research Articles

Wide-angle broadband near-perfect all-dielectric metamaterial reflector

Compact nonabsorbing reflectors are useful in numerous important applications, such as surface protection against high-power irradiation, low-loss mirrors in laser cavities, and improvement of signal-to-noise ratios in bioimaging and nanosensing. We exploit the Mie resonance in periodically arranged silicon nanospheres to design a wide-angle broadband near-perfect all-dielectric metamaterial reflector. First, we obtain the reflectance of a semi-infinite dilute medium of dielectric spheres arranged in a simple-cubic lattice in air and deduce criteria such as the radius and period required to obtain a near-perfect mirror. Next, we construct a near-perfect broadband mirror using the metasurfaces in the near-infrared wavelength range for the period-to-radius ratio of ∼2.54 for normal incidence. Finally, we study the reflection characteristics of the multilayer nanosphere metamaterials. A near-perfect mirror is designed, which is independent of polarization, and the permitted incident-angle width reaches 40 deg for three layers of metamaterial. This is the first study to address the optimal structure parameters for metasurfaces and the reflection characteristics of multilayer metamaterials. Our findings provide guidelines for the design of photonic devices based on dielectric metamaterials.

Magnetic Properties of Fibonacci-Modulated Fe-Au Multilayer Metamaterials.

Herein we experimentally study magnetic multilayer metamaterials with broken translational symmetry. Epitaxially-grown iron-gold (Fe-Au) multilayers modulated using Fibonacci sequence—referred to as magnetic inverse Fibonacci-modulated multilayers (IFMs)—are prepared using ultra-high-vacuum vapor deposition. Experimental results of in-situ reflection high-energy electron diffraction, magnetization curves, and ferromagnetic resonance demonstrate that the epitaxially-grown Fe-Au IFMs have quasi-isotropic magnetization, in contrast to the in-plane magnetization easy axis in the periodic multilayers.

Design and Analysis of Compound Multilayer Metamaterial Filter in THz Region

A periodic microstructure with dielectric and metal layers is proposed to obtain a bandpass filter. The multilayer microstructure is compounded of ring cross slot and cross slot. The center frequency of the filter is 0.338THz with a 3dB bandwidth of 75.62GHz. The maximum insertion loss in the pass band reaches 0.60dB. The bandedge transitions of the rejection bands are 232dB/THz and 176dB/THz, respectively. Furthermore, the physical mechanism of near field distribution and the influence of two factors (the number of metal layer and dielectric layer) on the passband have been studied. Meanwhile, the frequency response is analyzed for different incident angles and polarizations. The frequency response characteristic is insensitive to the polarization, and a good performance for incident angle of the transmission is obtained. It can be applied to THz atmospheric communication system.

Graphene oxide on magnetron sputtered silver thin films for SERS and metamaterial applications

Abstract In the last years the potential of combining the attractive materials characteristics of graphene related materials and silver nanostructures for SERS and metamaterials has emerged. Here, we report of graphene oxide thin films deposited by dip-coating on magnetron sputtered silver thin films. Our work represents a novelty in the field of the study of graphene oxide- silver composites, since magnetron sputtering deposition is an alternative way to silver thin films fabrication; previous works used instead silver nitrate aqueous solution mixed with the graphene oxide. Micro-Raman technique, morphological analysis and variable angle spectroscopic ellipsometry were performed. The final SERS signal intensity was investigated and we found Raman peaks dependent on the intensity of the laser and the thickness of silver and GO films. These results could open somestudies on plasmonics and on the reduction of graphene oxide mediated by silver thin films. Moreover, effective medium theory calculations show the possible use of these graphene oxide/silver thin films in multilayer hyperbolic metamaterials for optical applications.

Broadband angle- and permittivity-insensitive nondispersive optical activity based on planar chiral metamaterials

Because of the strong inherent resonances, the giant optical activity obtained via chiral metamaterials generally suffers from high dispersion, which has been a big stumbling block to broadband applications. In this paper, we propose a type of planar chiral metamaterial consisting of interconnected metal helix slat structures with four-fold symmetry, which exhibits nonresonant Drude-like response and can therefore avoid the highly dispersive optical activity resulting from resonances. It shows that the well-designed chiral metamaterial can achieve nondispersive and pure optical activity with high transmittance in a broadband frequency range. And the optical activity of multi-layer chiral metamaterials is proportional to the layer numbers of single-layer chiral metamaterial. Most remarkably, the broadband behaviors of nondispersive optical activity and high transmission are insensitive to the incident angles of electromagnetic waves and permittivity of dielectric substrate, thereby enabling more flexibility in polarization manipulation.

Dual-band and polarization-independent infrared absorber based on two-dimensional black phosphorus metamaterials.

Two-dimensional (2D) black phosphorus (BP) with direct band gap, bridges the characteristics of graphene with a zero or near-zero band gap and transition metal dichalcogenides with a wide band gap. In the infrared (IR) regime, 2D BP materials can attenuate electromagnetic energy due to losses derived from its surface conductivity. This paper proposes an IR absorber based on 2D BP metamaterials. It consists of multi-layer BP-based nano-ribbon pairs, each formed by two orthogonally stacked nano-ribbons. The multi-layer BP metamaterials and bottom gold mirror together form a Fabry-Perot resonator that could completely inhibit light transmission to create strong absorption through the BP metamaterials. Unlike previously reported BP metamaterial absorbers, this new structure can operate at two frequency bands with absorption > 90% in each owning to the first-order and second-order Fabry-Perot resonant frequencies. It is also polarization independent due to the fourfold rotational structural symmetry. To our best knowledge, this is the first report on using BP metamaterials in an absorber that operates independent of polarization and in dual bands.

Матричные методы расчета характеристик многослойных планарных метаматериалов при наличии киральности и пространственной дисперсии

Матричные методы расчета характеристик многослойных планарных метаматериалов при наличии киральности и пространственной дисперсии

Klein tunneling near the Dirac points in metal-dielectric multilayer metamaterials

The Klein tunneling of optical waves near the Dirac points in the metal-dielectric multilayer metamaterials is theoretically investigated and demonstrated through the coupled-mode theory under the tight-binding approximation and the rigorous band structure analysis based on the transfer-matrix method. The optical analogue of Klein tunneling for the relativistic electrons passing across a potential barrier is revealed by the iso-frequency contour analysis and numerical simulation to describe the optical beam propagation and refraction across the interface of two metal-dielectric multilayer metamaterial stacks. The transmission and reflection spectra of the Klein tunneling of optical waves are also explained by the coupled mode theory.

Enhancement and interplay of first- and second-order spatial dispersion in metamaterials with moderate-permittivity inclusions

We investigate a class of multilayered metamaterials characterized by moderate-index inclusions and low average permittivity. Via first-principle calculations, we show that in such scenario first- and second-order spatial dispersion effects may exhibit a dramatic and non-resonant enhancement, and may become comparable to the local response. Their interplay gives access to a wealth of dispersion regimes encompassing additional extraordinary waves and topological phase transitions. In particular, we identify a novel configuration featuring bound and disconnected isofrequency contours. Since they do not rely on high-index inclusions, our proposed metamaterials may constitute an attractive and technologically viable platform for engineering nonlocal effects in the optical range.

Freestanding optical negative-index metamaterials of green light.

A freestanding, multilayered fishnet metamaterial is reported to experimentally exhibit a negative refractive index in the green-light spectral range. The realization of a negative refractive index at such a high frequency range mainly originates from low-loss magnetic resonance and interactions between the neighboring functional layers. Based on a good agreement between the numerically simulated and experimentally measured transmittance and reflectance spectra, a single negative refractive index of -0.76 with a figure-of-merit of 0.5 is achieved for the metamaterial at the wavelength of 532nm.

Limits of imaging with multilayer hyperbolic metamaterials.

The multilayer hyperbolic metamaterials are known to be capable of imaging with sub-wavelength resolution. In this work performance of these "hyperbolic lenses" is analyzed in depth by employing commonly used transfer matrix method as well as the eigen-mode approach, the latter offering a clear physical insight into the operation of hyperbolic imagers and revealing their fundamental limitations. The resolution of multilayer structures is shown to decrease with the number of layers not only due to increased loss but also because of the severe suppression of large spatial frequencies caused by the cancellation between symmetric and antisymmetric eigen-modes. Additionally, the resolution is strongly affected by the granularity and fill ratio. In the end, hyperbolic metamaterials can create an image with subwavelength resolution only at very close distance to the object and hence limiting their utility.

Cermet based metamaterials for multi band absorbers over NIR to LWIR frequencies

Cermets or ceramic-metals are known for their use in solar thermal technologies for their absorption across the solar band. Use of cermet layers in a metamaterial perfect absorber allows for flexible control of infra-red absorption over the short wave infra-red, to long wave infra-red bands, while keeping the visible/near infra-red absorption properties constant. We design multilayered metamaterials consisting of a conducting ground plane, a low metal volume fraction cermet/ZnS as dielectric spacer layers, and a top structured layer of an array of circular discs of metal/high volume metal fraction cermet that give rise to specified absorption bands in the near-infra-red (NIR) frequencies, as well as any specified band at SWIR–LWIR frequencies. Thus, a complete decoupling of the absorption at optical/NIR frequencies and the infra-red absorption behaviour of a structured metamaterial is demonstrated.

Integrated 2D-Graded Index Plasmonic Lens on a Silicon Waveguide for Operation in the Near Infrared Domain.

In this article we address the nanoscale engineering of the effective index of silicon on insulator waveguides by using plasmonic metasurface resonances to realize a graded index lens. We report the design, implementation, and experimental demonstration of this plasmonic metasurface-based graded index lens integrated on a silicon waveguide for operation in the near-infrared domain. The 2D-graded index lens consists of an array of gold cut wires fabricated on the top of a silicon waveguide. These gold cut wires modify locally the effective index of the silicon waveguide and allow the realization of this gradient lens. The reported solution represents a promising alternative to the bulky or multilayered metamaterials approach in the near IR domain. This enabling technology may have found its place in silicon photonic applications by exploiting the plasmonic resonances to control the light at nanoscale.

Numerical study of tunable enhanced chirality in multilayer stack achiral phase-change metamaterials.

We numerically demonstrate a multiband circular dichroism (CD) by tilting achiral metamaterials (MMs) composed of an elliptical nanoholes array (ENA) penetrating through metal/ phase-change material (PCM) /metal multilayer stack, with respect to the incident light. The CD spectrum can be actively tuned across a wide range from the near-infrared (NIR) to mid-infrared (MIR) regime by transiting the state of the PCM (Ge2Sb2Te5) from amorphous to crystalline. Thus, it can switch on/off a multiband chiroptical response in the infrared region. Our simulation also elucidates that the achiral multilayer stack MMs, which have strong magnetic resonances, can enhance the optical chirality inside the elliptical apertures for both amorphous and crystalline states. The switching of the enhanced chirality may pave the way to manipulate electromagnetic waves, such as tunable circular polarizers, chiroptical spectroscopy, and chiral biosensors.

Broadband multi-layer metamaterial design based on quasi-log-periodic split-ring resonators

This paper proposes an efficient broadband multi-layer metamaterial (MM) design based on quasi-log-periodic split-ring resonators (SRRs) array. The arrangement of the quasi-log-periodic structure variables of the split-ring resonator is discussed for high attenuation and wide bandgap applications. The five-layer SRR–MM is designed, analyzed, and fabricated. The waveguide method is used to measure the transmission characteristics, and the measured results are in good agreement with the simulated ones. The suppression frequency bandwidth is about 40% from 8.5 to 12.5 GHz. The results show that the wide bandgap characteristics can be effectively obtained using the quasi-log-periodic multi-layer metamaterial design.

Closed Form Kramers–Kronig Relations to Extract the Refractive Index of Metamaterials

Closed form expressions of the Kramers–Kronig and of the multiply subtractive Kramers–Kronig relations are derived to predict the real part of the refractive index from the imaginary part, which is given in discrete frequency points. The accuracy and the convergence rate of the closed form expressions are investigated by calculating the refractive index of a hypothetical double negative metamaterial with predefined parameters. Then, a two-step procedure is presented, which utilizes the subtractive Kramers–Kronig relation to uniquely retrieve the effective refractive index of metamaterials even when the Kramers–Kronig relation fails. The developed procedure is demonstrated by extracting the effective parameters of multilayer fishnet metamaterials.

Quantum input-output relations for lossy and anisotropic multilayer magnetodielectric meta-material

In this paper, we quantize electromagnetic field in, lossy, dispersive and anisotropic magnetodielectric media by using phenomenological approach. We obtain quantum input– output relations for anisotropic multilayer metamaterials. As an application of our approach, we investigate the dissipative and anisotropic effects of an anisotropic magnetodielectric slab on the quantum properties of incident input states. For this purpose, quadrature squeezing and Mandel parameter of output states has been calculated by modeling the anisotropic magnetodielectric slab through Lorentz model for a situation in which the incident states on the right and left side of the magnetodielectric slab are two- mode coherent states and quantum vacuum state, respectively

Asymmetric transmission of linearly polarized waves in terahertz chiral metamaterials

We experimentally demonstrate the asymmetric transmission of linearly polarized waves in a multilayer chiral metamaterial in the terahertz (THz) regime. The chiral metamaterial is constructed by two stacked orthogonal metallic layers embedded in polyimide dielectric layers. Simulated and measured results show that the proposed multilayer chiral metamaterial can achieve dual-band direction-dependent cross-polarization conversions for both x- and y-polarized THz waves. The polarized wave passing through the metamaterial will be converted into its orthogonal polarization state, while the same polarized wave is blocked along the reversed propagation direction. In addition, the asymmetric transmission band may be effectively engineered to other frequencies by slightly adjusting the gap width. We believe that our findings are beneficial in manipulating the polarization state of THz waves and exploring polarization-sensitive THz devices.

A Design of Functional Layer with Robust Constitutive Parameters for Multilayer Metamaterials

We propose a functional layer design with robust effective parameters for multilayer metamaterial. The functional layer is consisting of two identical dielectric material layers and one layer of metallic structures sandwiched in between. The symmetric design ensures that, following standard retrieval technique, effective parameters retrieved for a single functional layer in vacuum can be used to characterize its electromagnetic contribution when stacked in a multilayer system. When applied to the fishnet structures, effective parameters of the symmetric functional layer system show great robustness against the varying of the number of layers. The symmetric functional layer design is also investigated on multilayer metamaterials consisting of several layers of different kinds of metallic structures. Transmission and reflection spectra are obtained for real structures and their effective models by finite-differential-time-domain simulation and transfer matrix method calculation, respectively. It turns out that the effective model shows great equivalency to the real structures, and the effective parameters of symmetric functional layer design are robust at both normal and oblique incident cases. Our work provides a practical approach to design and characterize multilayer metamaterials with the well-known effective parameters retrieval technique.

Near-Field Heat Transfer between Multilayer Hyperbolic Metamaterials

Abstract We review the near-field radiative heat flux between hyperbolic materials focusing on multilayer hyperbolic meta-materials. We discuss the formation of the hyperbolic bands, the impact of ordering of the multilayer slabs, as well as the impact of the first single layer on the heat transfer. Furthermore, we compare the contribution of surface modes to that of hyperbolic modes. Finally, we also compare the exact results with predictions from effective medium theory.