We present the blueprint for a novel negative-index metamaterial. This structure is fabricated via three-dimensional two-photon direct laser writing and silver shadow evaporation. The comparison of measured linear optical spectra with theory shows good agreement and reveals a negative real part of the refractive index at around 3.85 micrometer wavelength - despite the fact that the metamaterial structure is bi-anisotropic due to the lack of inversion symmetry along its surface normal.
We investigate the influence of different metals on the electromagnetic response of fishnet metamaterials in the optical regime.We found, instead of using a Drude model, metals with a dielectric function from experimentally measured data should be applied to correctly predict the behavior of optical metamaterials. Through comparison of the performance for fishnet metamaterials made with different metals (i.e., gold, copper, and silver), we found silver is the best choice for the metallic parts compared to other metals, because silver allows for the strongest negative-permeability resonance and…
Near-infrared epsilon-near-zero (ENZ) metamaterial slabs based on silver-germanium (Ag-Ge) multilayers are experimentally demonstrated. Transmission, reflection and absorption spectra are characterized and used to determine the complex refractive indices and the effective permittivities of the ENZ metamaterial slabs, which match the results obtained from both the numerical simulations and the optical nonlocalities analysis. A rapid post-annealing process is used to reduce the collision frequency of silver and therefore decrease the optical absorption loss of multilayer metamaterial slabs. Furt…
An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of t…
We further miniaturize a recently established silver-based negative-index metamaterial design. By comparing transmittance, reflectance and phase-sensitive time-of-flight experiments to theory, we infer a real part of the refractive index of -0.6 at 780 nm wavelength -- which is visible in the laboratory.
Hyperbolic metamaterials show exceptional optical properties, such as near-perfect broadband absorption, due to their geometrically-engineered optical anisotropy. Many of their proposed applications, such as thermophotovoltaics or radiative cooling, require high-temperature stability. In this work we examine Ag/a-Si multilayers as a model system for the thermal stability of hyperbolic metamaterials. Using a combination of nanotomography, finite element simulations and optical spectroscopy, we map the thermal and optical instability of the metamaterials. Although the thermal instability initiat…
In the metamaterial with hyperbolic dispersion (an array of silver nanowires in alumina membrane) we have observed six-fold reduction of the emission life-time of dye deposited onto the metamaterials surface. This serves as the evidence of the earlier predicted high density of photonic states in hyperbolic metamaterials.
We verify the extraordinary transmission enhancement and collimation induced by the material loss in anisotropic near-zero permittivity (ENZ) metamaterials, and reveal the physical mechanism of this exotic electromagnetic phenomenon via the iso-frequency contour (IFC) analysis. In addition, we demonstrate the possibility in realization of such loss enhanced transmission of Gaussian beam in realistic silver-germanium multilayered structures by applying full-wave numerical simulations.
A well-established, silver fishnet design has been further miniaturized to function as a negative-index material at the shortest wavelength to date. By studying the transmittance, reflectance, and corresponding numerical simulations of the sample, we report in this paper a negative refractive index of -0.25 at the yellow-light wavelength of 580 nm.
We propose a design for a plasmonic copper metamaterial with a negative index of refraction at visible/near-infrared wavelengths. Using numerical simulations, we demonstrate negative refraction by a copper metamaterial prism, and perform a parameter extraction technique to verify the sign of the effective, electric permittivity and magnetic permeability. Our proposed design has a figure of merit comparable to similar silver-based metamaterials operating in the visible/near-infrared range. These findings have implications for the design of low cost plasmonic devices and negative-index metamater…
Internal physical structure can drastically modify the properties of waveguides: photonic crystal fibers are able to confine light inside a hollow air core by Bragg scattering from a periodic array of holes, while metamaterial loaded waveguides for microwaves can support propagation at frequencies well below cutoff. Anisotropic metamaterials assembled into cylindrically symmetric geometries constitute light-guiding structures that support new kinds of exotic modes. A microtube of anodized nanoporous alumina, with nanopores radially emanating from the inner wall to the outer surface, is a manif…
Optical metamaterials (OMs) at visible wavelengths have been extensively developed. OMs reported recently are all composed of periodic structure, and fabricated by top-down approaches. Here demonstrated are the colored visible light frequency metamaterials composed of double layer array disordered and geometrical variational dendritic cells as well as fabricated by a novel bottom-up approach. The experiment demonstrates that the OMs composed of random silver dendritic cells which caused the appearance of multiple transmission passbands at red and yellow light frequencies. Moreover, the slab fo…
The race to engineering metamaterials comprising of a negative refractive index in the optical range has been fueled by the realization of negative index materials for GHz frequencies six years ago. Sheer miniaturization of the GHz resonant structures is one approach. Alternative designs make use of localized plasmon resonant metal nanoparticles or nanoholes in metal films. Following this approach, a negative refractive index has been realized in the optical range very recently. We review these recent results and summarize how to unambiguously retrieve the effective refractive index of thin la…
Noble metals such as gold and silver are the primary metallic building blocks of metamaterial devices. Making subwavelength-sized structural elements from these metals seriously limits the optical performance of a device, however, and complicates the manufacturing process of nearly all metamaterial devices in the optical wavelength range. As an alternative to noble metals, we propose to use heavily-doped oxide semiconductors that offer both functional and fabrication advantages in the near-infrared. In this letter, we report an experimental demonstration of negative refraction in a near-infrar…
Metamaterials are artificial composite materials that, by virtue of their microstructure, exhibit properties not exhibited by their component materials. Much excitement has been generated by negatively refracting metamaterials, typically consisting of coupled, metallic, subwavelength elements that simulate electric and magnetic dipoles, because of their unusual ability to manipulate visible light, infrared waves and microwaves. In such a metamaterial, an electromagnetic wave propagates so that the direction of its energy flow is opposed to its phase velocity, a condition captured by the real p…
The trapped rainbow effect has been mostly found on tapered anisotropic metamaterials (MMs) made of low loss noble metals, such as gold, silver, etc. In this work, we demonstrate that an anisotropic MM waveguide made of high loss metal tungsten can also support the trapped rainbow effect similar to the noble metal based structure. We show theoretically that an array of tungsten/germanium anisotropic nano-cones placed on top of a reflective substrate can absorb light at the wavelength range from 0.3 micrometer to 9 micrometer with an average absorption efficiency approaching 98%. It is found th…
Materials showing electromagnetic properties that are not attainable in naturally occurring media, the so called metamaterials, have been lately, and still are, among the most active fields in optical and materials physics and engineering. Among those properties, one of the most attractive is the sub-diffraction resolving capability predicted for media having index of refraction of -1. Here we propose a fully 3D, isotropic metamaterial with strong electric and magnetic responses in the optical regime, based on spherical metallo-dielectric core-shell nanospheres. The magnetic response stems fro…
In the present paper, a half-wave plate (HWP) based on a birefringent metamaterial is numerically designed to operate in the visible range. The proposed structure consists of an array of double-pattern perpendicular rectangular aperture (RAA) engraved into opaque silver film deposited on a glass substrate. One of the apertures is glass filled. The operating principle of this plate is based on the excitation and the propagation of one guided mode inside each aperture but with different effective index. At the output side, a phase difference is obtained whose value mainly depends on the metal th…
The development of metamaterials, data processing circuits and sensors for the visible and UV parts of the spectrum is hampered by the lack of low-loss media supporting plasmonic excitations and drives the intense search for plasmonic materials beyond noble metals. By studying plasmonic nanostructures fabricated on the surface of topological insulator $\mbox{Bi}_{1.5}\mbox{Sb}_{0.5}\mbox{Te}_{1.8}\mbox{Se}_{1.2}$ we found that it is orders of magnitude better plasmonic material than gold and silver in the blue-UV range. Metamaterial fabricated from $\mbox{Bi}_{1.5}\mbox{Sb}_{0.5}\mbox{Te}_{1.8…
Three-dimensional metallic microstructures find applications as stents in medicine, as ultrabroadband antennas in communications, in micromechanical parts or as structures of more fundamental interest in photonics like metamaterials. Direct metal printing of such structures using three-dimensional laser lithography is a promising approach, which is not extensively applied yet, as fabrication speed, surface quality, and stability of the resulting structures are limited so far. In order to identify the limiting factors, we investigate the influence of light-particle interactions and varying scan…
