Metamaterials最新文献

In this paper, we numerically demonstrate that plasmonic covers designed through the scattering cancellation approach can be successfully used to enhance the performance of near-field scanning optical microscopy (NSOM) systems based on the employment of aperture tip probes. The material used to partially cover the tip exhibits a near-zero value of the real part of the permittivity function at the working frequency and is designed in such a way to dramatically reduce the undesired electromagnetic coupling between the sample to be imaged and the metallic coating of the aperture tip. We show that minimizing such an unwanted interaction may lead to enhance the maximum achievable resolution of the NSOM system. The approach proposed is numerically tested at optical frequencies through a proper set of full-wave simulations, taking into account material losses and frequency dispersion. The proposed results represent a proof-of-concept and can be scaled at lower frequencies (infra-red and THz), where fabrication issues are more relaxed and possible implementation can be made practical using alternating plasmonic/non-plasmonic multi-layers or even some natural materials.

In this paper, it is demonstrated that transmission lines loaded with a combination of open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs) are useful for the design of high-order band pass filters subjected to standard responses. Specifically, we present a 7-pole Chebyshev band pass filter in coplanar waveguide technology. The device is compact and filter performance is good, including a wide stopband response. With this work, we extend our previous work on the applications of OSRR- and OCSRR-loaded lines to the design of highly selective filters.

We determine the rigorously calculated scattered field of meta-atoms and decompose it into spherical harmonics with complex amplitudes. Transforming these spherical harmonics into a Cartesian base reveals all multipole moments in this coordinate system, i.e. all electric and magnetic dipole, quadrupole and any higher order moments can be completely determined. We show that these multipole moments provide a deeper understanding on how light interacts with the considered meta-atoms. After sketching the analytical framework, we investigate exemplarily two well-established meta-atoms and show the applicability of our approach.

The transfer function of some in-plane periodic split-ring metamaterial slab lenses is analyzed for several configurations across the slab. The transfer function is obtained by means of full-wave electromagnetic computations using the simulation software CST Microwave Studio, and it is compared with the transfer function obtained analytically for a continuous slab of reference. Significant differences are found in the transfer function of the analyzed structures. The closest behavior to the continuous slab lens was found for the partially open structure comprising an integer number of periods across the slab. Experiments are provided which confirms the theoretical results.

We present our investigations into the direct laser writing of a novel germanium-containing hybrid sol–gel photosensitive material for optical applications at micro scale. We employ this material in the fabrication of photonic micro-structures, such as aspheric lenses and prisms; these are well-shaped and provided good optical performance. The material exhibits good transparency and structurability, and three-dimensional structures with sub-100 nm resolution are achieved. We demonstrate the suitability of the direct laser writing method for the rapid production of custom shaped microoptical components. Since germanium glasses are widely used in fiber optics, the combination of direct laser writing with this specially designed, functional material opens an interesting way in fabricating structures for controlling light flow.

Abstract

We present a method for homogenizing tensor transmission-line (TL) metamaterials. These are metamaterials consisting of loaded transmission-line networks, that can possess magnetically anisotropic (tensor) effective material parameters. The homogenization employs a local field averaging procedure to compute the effective material parameters. These effective material parameters can be dispersive or non-dispersive. For the tensor metamaterials possessing dispersive effective material parameters, the homogenization method takes advantage of the circuit topology of tensor transmission-line metamaterials to predict material parameters over a frequency range.

We analyze in this paper symmetry properties of planar arrays in long-wave approximation and for normal incidence. Using group-theoretical methods we define all the possible magnetic groups for such structures. For some practical cases, we calculate the scattering matrices for nonmagnetic and magnetic arrays and discuss their properties.

Through analyzing the transmission properties of metallic plates with periodic arrays of subwavelength apertures in different shapes, we found two conditions for such structures to work as super lenses. The working wavelength dictated by the aperture's shape resonance should be much larger than the array's periodicity, meanwhile the coupling between the aperture's waveguide modes and external radiations should be as small as possible. These two conditions contradict with each other for a square-shape aperture so that high index materials should be inserted into the apertures, while a fractal-shape aperture satisfies these two conditions simultaneously without using high-index insertions. Numerical simulations were performed to illustrate the imaging properties of these plasmonic lenses.

A simple model of near-field pixel-to-pixel image transfer using magneto-inductive arrays is presented. The response of N-dimensional rectangular arrays is first found as an excitation of eigenmodes. This analytical method involves approximating the effect of sources and detectors, and replaces the problem of solving large numbers of simultaneous equations with that of evaluating a sum. Expressions are given for the modal expansion coefficients, and in the low-loss case it is shown that the coefficient values depend only on the difference in reciprocal frequency space of the operating frequency from the resonant frequency of each mode. Analytic expressions are then derived for quasi-optical quantities such as the spatial frequency response, point-spread function and resolving power, and their implications for imaging fidelity and resolution are examined for arrays of different dimension. The results show clearly that there can be no useful image transfer for in-band excitation. Out-of-band excitation allows image transfer. Provided the array is larger than the expected image by at least the size of the point spread function, the effect of the array boundaries may be ignored and imaging is determined purely by the properties of the medium. However, there is a tradeoff between fidelity and throughput, and good imaging performance using thick slabs depends on careful choice of the operating frequency. The approximate analytic method is verified by comparison of exact numerical solution of the full set of coupled equations, and the conditions for its validity are identified.

Recent metamaterial (MM) research faces several problems when using metal-based plasmonic components as building blocks for MMs. The use of conventional metals for MMs is limited by several factors: metals such as gold and silver have high losses in the visible and near-infrared (NIR) ranges and very large negative real permittivity values, and in addition, their optical properties cannot be tuned. These issues that put severe constraints on the device applications of MMs could be overcome if semiconductors are used as plasmonic materials instead of metals. Heavily doped, wide bandgap oxide semiconductors could exhibit both a small negative real permittivity and relatively small losses in the NIR. Heavily doped oxides of zinc and indium were already reported to be good, low loss alternatives to metals in the NIR range. Here, we consider these transparent conducting oxides (TCOs) as alternative plasmonic materials for many specific applications ranging from surface-plasmon-polariton waveguides to MMs with hyperbolic dispersion and epsilon-near-zero (ENZ) materials. We show that TCOs outperform conventional metals for ENZ and other MM-applications in the NIR.