Negative Refractive Index Media Research Articles

Light drag in a left-handed atomic medium via Cross Kerr-like nonlinearity

In this paper, we investigates the Cross Kerr-like nonlinearity effect on the quantum control of the light drag in a negative refractive index media ( NRI). Hence, we consider an atomic system in a four-level Y-type configuration, where a signal field couples the ground state to an upper level. Another weak probe field drives the intermediate transition to the excited state. The Kerr field pumps the excited state to another higher fourth transition. Therefore, we observe that the third-order optical non-linearities drastically contribute to the light drag enhancement of about 11 times. Interestingly, the light drag dynamics can be manipulated to shift from positive to negative, which allows the group delay and advancement to be fully controlled. Typically, an increase in the Kerr field, simultaneously with the detuning, induces an ultra-narrow, sharp peak in the light drag respectively at the resonance and far from the resonance with a group delay ranging from τ=−0.2 to τ=−2. The various interference pathways of light caused by the cross-kerr along with the probe, strong and signal fields not only enhance the light drag but can also be used to shift the light from subluminal to superluminal propagation under negative refraction. These results provide a framework for utilizing the Kerr-cross non-linearity to control the light drag in NRI, which is interesting in applications such as optical trapping.

Ultra-wideband Metamaterial-based Rectangular Microstrip Antenna for Sub-6 GHz 5G and other Microwave Applications

This paper presents a novel design of an ultra-wideband metamaterial-based rectangular microstrip antenna for sub-6 GHz 5G and other microwave applications. The proposed antenna consist of a rectangular microstrip patch, two metamaterial unit cells, Flame Resistant (FR-4) substrate and partial ground plane. The metamaterial unit cell comprises complementary split ring resonator (CSRR) with double negative characteristics (negative permeability and negative permittivity) as well as negative refractive index (NRI). The NRI medium enhanced the bandwidth and radiation efficiency of the antenna by reducing the surface waves and mutual coupling. The antenna operates over frequency range of 3.4009 to 11.721 GHz and 2.869 to 3.211 GHz, covering the sub-6 GHz 5G bands and other microwave applications such as Wi-Fi, WiMAX, and WLAN. Also, the proposed antenna had optimized dimensions of and exhibited good impedance matching, omnidirectional radiation pattern, and stable gain across the operating band. From simulation results, a combined bandwidth of 8.66 GHz was achieved which shows good agreement with outlined objective. The proposed antenna is suitable for sub-6 GHz 5G and other microwave applications that require ultra-wideband performance and low-profile design.

Light drag in an optically dense left-handed atomic medium

In this paper, we investigate the light drag in an optically dense negative refractive index medium. Our model is a four-level atomic system in which we demonstrate an enhancement of the light drag while keeping the negative refraction condition. Furthermore, we control the shift in the light drag by tuning both the strong coupling field and the detuning. Hence, we observe that the light drag in the negative refractive index material can be controlled to switch from subluminal to superluminal at various ranges of the detuning. Our system suggests a straightforward technique for realizing and controlling light dragging in materials with negative refractive indices, or ‘NRI,’ which might open the way for more efficient use of left-handedness in atomic systems.

Unique 3D metamaterial split ring resonator for wireless communication with high negative refractive index and for medium ratio

This article presents the unique 3D metamaterial split ring resonator (3D-MTM SRR) model with high negative refractive index and effective medium ratio at 2.45 GHz frequency. It is integrated with two layers: one square bracket structure printed on the back side of the substrate and another dual split ring with an air gap placed above the substrate. Both structures are coupled by metallic vias, which serve as connecting vias to create the 3D-MTM SRR model. Simulation and experiment results shows good agreement for high negative refractive index and effective medium ratio of −17 and 6.16, respectively. To fully comprehend the resonance phenomena of the proposed 3D-MTM model, an analogous circuit analysis is carried out. In addition, to validate the MTM activities, array topologies based on 3D-MTM cells are analyzed. Thus the unique properties of 3D-MTM SRR allow to develop the high-performance RF devices for wireless applications.

Reversing the direction of space and inverse Doppler effect in positive refraction index media

A negative refractive index medium, in which all spatial coordinates are reversed (i.e. a left-hand triplet is formed) by a spatial folding transformation, can create many novel electromagnetic phenomena, e.g. backward wave propagation, and inversed Doppler effect (IDE). In this study, we use coordinate rotation transformation to reverse only two spatial coordinates (e.g. x′ and y′), while keeping z′ unchanged. In this case, some novel phenomena, e.g. radiation-direction-reversing illusions and IDE, can be achieved in a free space region wrapped by the proposed shell without any negative refractive index medium, which is easier for experimental realization and future applications.

Symmetry relations in the generalized Lorenz–Mie theory for lossless negative refractive index media

In this paper we present a theoretical analysis of the generalized Lorenz–Mie theory for negative refractive index (NRI) media and spherical scatterers, extending the well-known concepts and definitions found in the literature involving dielectric or positive refractive index (PRI) particles. The consequences of a negative phase velocity and an anti-parallelism of the wave vector with respect to the Poynting vector are investigated and interpreted in this framework and, together with the symmetries found for the beam-shape coefficients when compared to the conventional PRI case, it is shown that the description of plane waves, Gaussian beams and, more generally, on-axis azimuthally symmetric waves along a NRI medium, their fields and all physical properties can be conveniently correlated with that of dielectric media once the electromagnetic response functions are replaced by their corresponding dielectric counterparts.

Magnetized Plasma with Ferromagnetic Grains as a Viable Negative Refractive Index Medium

Magnetized Plasma with Ferromagnetic Grains as a Viable Negative Refractive Index Medium

Origami with negative refractive index to generate super-lenses

Negative refractive index materials (NRIM) enable unique effects including superlenses with a high degree of sub-wavelength image resolution, a capability that stems from the ability of NRIM to support a host of surface plasmon states. Using a generalized lens theorem and the powerful tools of transformational optics, a variety of focusing configurations involving complementary positive and negative refractive index media can be generated. A paradigm of such complementary media are checkerboards that consist of alternating cells of positive and negative refractive index, and are associated with very singular electromagnetics. We present here a variety of multi-scale checkerboard lenses that we call origami lenses and investigate their electromagnetic properties both theoretically and computationally. Some of these meta-structures in the plane display thin bridges of complementary media, and this highly enhances their plasmonic response. We demonstrate the design of three-dimensional checkerboard meta-structures of complementary media using transformational optics to map the checkerboard onto three-dimensional corner lenses, the only restriction being that the corresponding unfolded structures in the plane are constrained by the four color-map theorem.

RESERVOIR EFFECT ON A FOUR-LEVEL LEFT-HANDED SYSTEM

In this paper, we theoretically analyze the electromagnetic properties of a negative refractive index medium configured as a four-level system under thermal bath effect. For different thermal bath coupling strengths, the system shows negative permittivity and permeability as well as a large negative refractive index. This atomic medium is stable against environmental effect in a large experimental reachable domain of parameters which makes it a potential candidate for important applications.

Optical forces in lossless arbitrary refractive index optical trapping and micromanipulation

This paper shows, using both a ray optics approach and in the framework of the generalized Lorenz–Mie theory (GLMT), what happens to the optical forces exerted on a lossless spherical particle with an arbitrary (positive or negative) relative refractive index, allowing the external medium also to be metamaterial. It is shown that the anti-parallelism between the linear momentum p of each photon and the Poynting vector S associated with the propagating wave, observed in negative refractive index media, leads to shifts in the direction of the optical force of a single ray and, consequently, to the total optical force exerted by an arbitrary-shaped laser beam. This extends the possible realizable traps and reveals how arbitrary-shaped laser beams can be used to trap particles with arbitrary refractive indices.

A Broadband Three-Dimensionally Isotropic Negative-Refractive-Index Medium

When designing negative-refractive-index (NRI) metamaterials, scientists have struggled to overcome three primary obstacles: polarization dependence, narrow bandwidth, and fabrication challenges. Here, we address these issues with the design of a three-dimensional, fully isotropic, broadband NRI medium that can be produced on a large scale. The simulated structure exhibits a NRI bandwidth of 24.1%, more than twice that achievable using a typical split-ring resonator/wire medium. A four-hundred-unit-cell slab measuring 15 cm×15 cm×6 cm is fabricated and used as a flat NRI lens. The lens produces a super- resolved focus independent of the type of source or its polarization.

Low-loss and high-symmetry negative refractive index media by hybrid dielectric resonators

Based on Maxwell's equations and Mie theory, strong sub-wavelength artificial magnetic and electric dipole resonances can be excited within dielectric resonators, and their resonant frequencies can be tailored simply by scaling the size of the dielectric resonators. Therefore, in this work we hybridize commercially available zirconia and alumina structures to harvest their individual artificial magnetic and electric response simultaneously, presenting a negative refractive index medium (NRIM). Comparing with the conventional NRIM constructed by metallic structures, the demonstrated all-dielectric NRIM possesses low-loss and high-symmetry advantages, thus benefiting practical applications in communication components, perfect lenses, invisible cloaking and other novel electromagnetic devices.

Design and Free-Space Measurements of Broadband, Low-Loss Negative-Permeability and Negative-Index Media

We present the design and measurement of broadband, volumetric negative-permeability and negative-refractive-index (NRI) media. Both of these media are fabricated using standard printed-circuit-board techniques and operate at X-band frequencies. The S-parameters of four-cell slabs of the negative-permeability and NRI media are measured, and the material parameters of the NRI lens are extracted. The four-cell-thick (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /3) NRI lens exhibits a backward-wave bandwidth of 41.2% and a total loss of 0.67 dB at the operating frequency (where μ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> ≈ -1). Super-resolved focusing in free space is also demonstrated, and spatial frequencies beyond the free-space wavenumber are recovered over a bandwidth of 7.4%. A focus with a half-power beamwidth of 0.27λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is achieved at 10.435 GHz.

Enriching the Symmetry of Maxwell Equations through Unprecedented Magnetic Responses of Artificial Metamaterials and Their Revolutionary Applications

The major issue regarding magnetic response in nature—“negative values for the permeability μ of material parameters, especially in terahertz or optical region” makes the electromagnetic properties of natural materials asymmetric. Recently, research in metamaterials has grown in significance because these artificial materials can demonstrate special and, indeed, extraordinary electromagnetic phenomena such as the inverse of Snell’s law and novel applications. A critical topic in metamaterials is the artificial negative magnetic response, which can be designed in the higher frequency regime (from microwave to optical range). Artificial magnetism illustrates new physics and new applications, which have been demonstrated over the past few years. In this review, we present recent developments in research on artificial magnetic metamaterials including split-ring resonator structures, sandwich structures, and high permittivity-based dielectric composites. Engineering applications such as invisibility cloaking, negative refractive index medium, and slowing light fall into this category. We also discuss the possibility that metamaterials can be suitable for realizing new and exotic electromagnetic properties.

High numerical aperture and low-loss negative refraction based on the fishnet rich anisotropy

In this paper we report both numerical and experimentally high numerical aperture on a mesostructure based on fishnet-like building blocks. Under the indefinite media framework, we are able to identify a negative refraction never cutoff band (3rd band of the extraordinary transmission metamaterial) with low-losses at millimeter-waves. We relate negative refraction with the diffraction modes of the periodic structure. The work is another step forward in the new but rapidly evolving subfield of negative refraction metamaterials by anisotropy. The breadth and utility of this approach suggests that metamaterials at their meso-scale may circumvent the problem associated to narrowness and losses exhibited by negative refractive index media at their subwavelength domain, while still being away from the wavelength scale of electromagnetic band-gap.

The Design of Broadband, Volumetric NRI Media Using Multiconductor Transmission-Line Analysis

Multiconductor transmission-line (MTL) analysis is used to model a broadband, volumetric negative-refractive-index (NRI) medium. Equations for the two-dimensional dispersion characteristics and the Bloch impedance are derived using a simplified periodic MTL analysis that provides insight into the operation of the NRI structure, while still accounting for spatial dispersion. Equations for the resonant points of the NRI medium are also derived, including the magnetic and electric plasma frequencies and the low-frequency backward-wave cutoff. The nature of each resonant point is discussed as well. Finally, this paper presents the modeling of finite structures with rigorous MTL analysis. Using this method, the reflection and transmission coefficients for normal incidence on a four-cell slab of the NRI medium are calculated and compared to full-wave simulation.

An anisotropic negative refractive index medium operated at multiple-angle incidences

Recently metamaterials have been demonstrating new physics to enable various unprecedented electromagnetic properties, but pratically they are so sensitive to incident angles of the external excitation that their applications are restricted. Therefore, we present an anisotropic negative refractive index medium operated at multiple-angle incidences (NRIM for MAI) to ease such a burden. Both the simulated and measured transmittance, reflectance and the corresponding material parameters indicate that our structure does possess the anisotropic negative refractive index with respect to different incident angles. In addition, the opposite directions of group and phase velocities are also demonstrated under both grazing-angle, normal and 45-degree incidences to further verify the negative refractive index of the designed monolithic NRIM structure for multiple-angle incidences.

Creating negative refractive identity via single-dielectric resonators

From a periodic array of commercially available zirconia cubes, we demonstrate artificial magnetic and electric dipoles due to the combination of displacement currents and Mie resonance. By scaling the size and periodicity of these dielectric resonators, the corresponding magnetic and electric responses are shifted to the desired frequencies. To further overlap the magnetic and electric resonances in the same frequency, we create a negative refractive index medium (NRIM) from single-dielectric resonators. Comparing with the conventional NRIM comprised of metallic or two-dielectric resonators, these single-dielectric structures present the low-loss and isotropic characteristics, and possess a further advantage to facilitate practical applications.

Imaging Properties of a Line Source Using General Anisotropic Metamaterials

We investigate the general dispersion relationship of anisotropic media theoretically. According to the dispersion relationship, we study the perfect imaging conditions by a slab of anisotropies negative refractive index media in details, Numerical results have proved our predictions for TE waves. For slab of gyrotroptic media, if a gyrotroptic parameter is small enough, the gyroteoptic slab can become nearly perfect lens using the perfect conditions of TE and TM mixed modes. We have shown that perfect imaging cannot occur in the case of larger gyrotroptic parameter.

Super-Resolution Focusing Using Volumetric, Broadband NRI Media

We describe the design, fabrication and testing of broadband negative permeability and broadband negative-refractive-index (NRI) metamaterials. The NRI metamaterial is designed to address two major limitations of current NRI media: high loss and narrow bandwidth of operation. The proposed NRI design has a backward-wave bandwidth of 44.3%. This large bandwidth allows the structure to operate away from resonant frequencies, where the loss is significantly lower. The stopband characteristics of a lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /3 slab of the negative permeability medium were measured. In addition, the focusing characteristics of the NRI medium were tested and resolution beyond the diffraction limit was experimentally observed. The slab measured in this paper achieved a resolution enhancement of 2.0 over a bandwidth of 0.33%.