Negative Effective Refractive Index Research Articles

EXACT ANALYTICAL SOLUTION FOR FIELDS IN A LOSSY CYLINDRICAL STRUCTURE WITH LINEAR GRADIENT INDEX METAMATERIALS

We investigate the electromagnetic wave propagation across a finite inhomogeneous and anisotropic cylindrical metamaterial composite containing both positive and negative effective refractive index parts with linear spatial gradient. Exact analytical solutions for the electric and magnetic field distributions are obtained for a linear variation of effective refractive index across the structure. The exact analytical results for the electric and magnetic fields are compared to the numerical results obtained using the numerical simulation software HFSS. The model allows for general temporal dispersion and uniform losses within the composite.

Influence of formic acid on electrical, linear and nonlinear optical properties of potassium dihydrogen phosphate (KDP) crystals

In present investigation 0.5 and 1mol% formic acid (FA) added potassium dihydrogen phosphate (KDP) crystals have been grown by a slow evaporation technique. The cell parameters of the grown crystals were determined using single crystal X-ray diffraction analysis. The presence of different functional groups has been qualitatively analyzed by the FT-IR spectral analysis. The optical transparency and optical constants were assessed employing UV–visible studies in the range of 200–900nm. The wide optical band gap of 1mol% FA added KDP has been found to be 5eV. The frequency dependent dielectric measurements were studied for pure and KDP added FA crystals. The enhanced second harmonic generation (SHG) efficiency of grown crystals was determined by a classical Kurtz–Perry powder technique. The encouraging third order nonlinear properties were examined employing a Z-scan technique using He–Ne laser, at 632.8nm. The effective negative index of refraction and high figure of merit (FOM) essential for laser stabilization were determined for grown crystals.

Tunable Negative Refractive Index Metamaterials Based on Thermochromic Oxides

A tunable metamaterial is proposed by combining a thermochromic oxide with a fishnet structure. The reflection and transmission coefficients are calculated by finite-difference time-domain (FDTD) method. The effective electromagnetic parameters of the metamaterial are retrieved on the basis of these data. The results reveal that an effective negative refractive index is obtained by this proposed structure and the wavelength region with negative refractive index can be self-regulated by simply tuning the temperature, which is of importance to extend the applications of negative refractive index materials. The effects of structural sizes on the negative refractive index are discussed. The size-dependence indicates that the wavelength range in which the apparent refractive index is negative can be tuned to be located at the desired position by dexterously tailoring the structural parameters.

Self-biased magnetic left-handed material

We present experimental demonstrations that the material consists of self-biased Sr-ferrite rods is the lower loss left-handed material (LHM). Clear negative refractions are observed in refraction experiments with the wedge shaped samples made from this material, and negative effective refractive index n = −1 is measured. The attenuation of the sample is about 0.55 dB/cm obtained from transmission measurements much lower than other known LHMs. Our configuration avoids the bias magnetic fields required for LHMs made of soft magnetic materials and extremely high permittivity needed for making LHMs with purely dielectrics, which greatly improves its impedance mismatch with the air.

Spectral Methods and Domain Decomposition for Nanophotonic Applications

Nanophotonic applications often involve large-scale problems with excessive demand on computational resources. We develop a domain decomposition method (DDM) to reduce computer memory and central processing unit (CPU) time requirements by combining the spectral element method (SEM) and the spectral integral method (SIM) for large-scale finite periodic structures. The interior scattering subdomains within each period are modeled by the SEM while the exterior scattering problem is modeled by the SIM. The interactions between neighboring subdomains are modeled by the frequency-domain version of the Riemann solver. Numerical convergence of the Riemann solver is fast and weakly dependent on the size of the system. Two sets of examples demonstrate the typical nanophotonic applications: The first periodic system is a vertical coupling waveguide based on a photonic crystal slab which opens a way to construct and simulate optical circuits. The second periodic system is a finite-sized metamaterial with an effective negative refractive index, whose edge effects are visualized and analyzed.

Nanohole induced microfiber Bragg gratings

We demonstrate the fabrication of high-index-contrast microfiber Bragg gratings (MFBGs) using phase-mask technique under seconds' femtosecond laser ablation to drill periodic nanoholes in microfibers and study the aging properties of the gratings at room temperature. These sub-micrometer-diameter holes, benefited from the resolution of femtosecond laser micromachining beyond-diffraction limit, results in an effective negative refractive index change Δn ~-10(-3). Transmission dips over -23 dB are achieved for the gratings with excellent Gaussian apodization and 3-dB reflection bandwidths up to 1.14 nm. Moreover, the grating reflectivity increased by 3 dB, the resonant wavelength blue-shifted 1.35 nm after two weeks' placement of grating at room temperature and these gratings exhibit excellent stability in the following time. This makes them attractive elements in sensing, nanophotonics and nonlinear optics.

Ellipsometric determination of permittivity in a negative index photonic crystal metamaterial

In this work, we present the first experimental evidence of negative dielectric susceptibility in a two-dimensional silicon photonic crystal (PhC) with negative refractive index behavior. In the frequency range in which the effective refractive index neff is equal to −1, the incident light couples efficiently to the guided modes in the top surface layer of the PhC metamaterial. These modes resemble surface plasmon polariton resonances. This finding was confirmed by ellipsometric measurements, demonstrating the isotropy of the PhC resonances. Such negative index PhC materials may be of use in biosensing applications. Researchers have realized a device that exhibits negative effective refractive index on the surface of a silicon chip. The ability to control light on a semiconductor chip is important for applications that involve the interaction of electronics with light. The approach developed by Vito Mocella and colleagues from the Consiglio Nazionale delle Ricerche in Italy is based on the use of photonic crystals—in this case, a periodic array of holes etched into silicon. The holes change the way light propagates along the surface of the chip such that the structure has a negative refractive index at its resonance wavelength, which means that light bends in a direction opposite to what would usually be expected when passing from one medium to another. This effect could be used for highly sensitive biosensing applications.

Refractive properties of metamaterial composed of InGaAs layers with alternating doping densities

The aspects of light propagation through a semiconductor metamaterial (SMM) which consists of two alternating differently doped In0.53Ga0.47As layers are studied analytically and numerically. A general analytical expression for the effective index of refraction of the Poynting vector is derived for periodic structure composed of two alternating layers of absorptive and dispersive semiconductors and light propagation is simulated by finite-difference-time-domain method. Negative values of the effective refractive index with low absorption are observed in the mid-infrared frequency range. The main advantage of this design is the possibility to control the frequency region with negative effective refractive index by changing the doping densities of the layers.

Research technique of metamaterials with the controlled effective negative refractive index and their characteristics

A design of the two-beam hybrid microwave interferometer for measuring refractive indices of metamaterials is described. It is based on the branching of radiation using a waveguide directional coupler. Radiations of the interferometer waveguide arms are summed and the phase disbalance of the interferometer arms is counted on the waveguide measuring line. The frequency dispersion of the negative refractive indices of the metamaterial samples with a variable distance between its constituent plates is experimentally investigated. A possibility of controlling the refractive index of a metamaterial is demonstrated.

Negative radiation pressure and negative effective refractive index via dielectric birefringence

We show that light guided in a planar dielectric slab geometry incorporating a biaxial medium has lossless modes with group and phase velocities in opposite directions. Particles in a vacuum gap inserted into the structure experience negative radiation pressure: the particles are pulled by light rather than pushed by it. This effectively one-dimensional dielectric structure represents a new geometry for achieving negative radiation pressure in a wide range of frequencies with minimal loss. Moreover, this geometry provides a straightforward platform for experimentally resolving the Abrahams-Minkowski dilemma.

Dual-band double-negative-index fishnet metamaterial at millimeter-waves

An effective negative refractive index (NRI) is demonstrated and experimentally verified for the first two propagation bands of a fishnet-like metamaterial at millimeter-wave frequencies. The dual-band NRI behavior is achieved by engineering the diffraction order (±1, ±1) associated with the internal mode supported between holey layers to correspond with the second propagation band. In addition to the experimental interferometric technique that accounts for the handedness of the propagation, numerical results are given to predict the dual-band effective NRI and to confirm dual-band negative refraction for a prism composed of the proposed metamaterial.

银纳米颗粒复合超材料的数值和模拟研究

Electromagnetic properties of single-layer silver nano-particles of compound metamaterials are theoretically analyzed.MATLAB numerical calculation and CST simulation are used to verify the theory.The results show numerical and simulated results of 4.75 nm nano-silver arrays are basically the same,and there are Lorentz resonance.The simulated results have redshift compared to numerical results,having a weak magnetic resonance.Further simulated compounded by the use of 4.75 nm spherical to form large particles of 100 nm,the results show that there are negative real permittivity and negative real effective permeability and negative refractive index in the 300~380 THz range.That means 100 nm composite spherical particles have a strong magnetic resonance effect and consistent with the theoretical analysis.

Negative effective refractive index of metallic nanoparticles in disordered nanocomposites

An effective-medium theory is suggested, which is used to study optical properties of disordered metallodielectric nanocomposites. Expressions for the effective fields and effective parameters of nanoparticles with allowance for the electrodynamic interaction of nanoparticles have been obtained. It has been shown that the polarizing mutual influence of the structure elements of a system can give rise to regions with negative effective refractive index in the spectrum of individual particles. A model of a «left-handed» based on a field manipulation of the polarizability of nanoclusters different from the previously studied material manipulation has been put forward.

Imaging properties of a two-dimensional photonic crystal with rectangular air holes embedded in a silicon slab

Abstract We investigate the superlensing effect of a two-dimensional (2D) triangular photonic crystal (PC) slab consisting of rectangular air holes in silicon. An analysis of equal-frequency contours (EFCs) shows that geometric parameters of the PC element shape can greatly change the shape of EFCs, thus change the effective phase index of the PC structure. Moreover, an effective negative refractive index n eff = −1 can be obtained at a normalized working frequency of 0.30 × 2 π c / a by adjusting the width of the rectangular air holes. Imaging capacity of this PC slab involving both the power intensity and full width at half-maximum of image is studied by the finite-difference time-domain (FDTD) method. In order to achieve a high-quality image, an appropriate surface termination of the PC slab is chosen. Coupled-mode theory analysis shows that the optimized surface termination can excite two kinds of surface modes which can couple with the Bloch wave in the PC. With the help of these surface modes, both the intensity of image and the super resolution capacity for the PC slab lens can be improved greatly.

Viability of focusing effect by left-handed stacked subwavelength hole arrays

In this work we present advances in the design of lenses based on left-handed extraordinary transmission metamaterials which provide high transmission and focusing despite the subwavelength size of their constituent apertures. Due to the effective negative index of refraction of the close-stack of subwavelength hole arrays, concave profiles are required for focusing instead of the convex geometries of dielectric lenses. An analysis of the foci produced by plano- and bi-concave lens is carried out.

Tightly coupled tripole conductor pairs as constituents for a planar 2D-isotropic negative refractive index metamaterial

A metamaterial, arranged by stacking layers of planar constituents suitably shaped to be responsive to arbitrarily linearly polarized incident waves is here shown to exhibit 2D-isotropic effective negative refractive index (NRI). The general concept underlying this metamaterial design consists of closely pairing two metallic particles to accomplish, as a result of their tight coupling, both symmetric and antisymmetric resonance modes, whose proper superposition can lead to an effective negative refraction response. The proposed structure is composed by layers of periodically arranged pairs of face coupled loaded tripoles printed on the opposite sides of a single dielectric substrate. Through a comprehensive characterization of the transmission properties of such metamaterial, together with the analysis of its dispersion diagram, conclusive evidence that the medium exhibits effective NRI properties as well as good impedance matching to free space is provided. We also describe some guidelines to design the proposed metamaterial with a prescribed operational frequency bandwidth, dependently on the structure parameters.

Highly collimated emission from a left-handed photonic crystal with a quasi-cavity

We study the collimated emission characteristics from a dipole source inside a negative-effective-refractive-index photonic crystal with a quasi-cavity constructed by a concave photonic crystal reflector. The emissions along the ±X and −Y directions are forbidden by the quasi-cavity, so that most emissions propagate along the +Y direction. Simulation results show that a narrow collimated beam is achieved due to the near-zero negative effective refractive index. Moreover, the half-power beam width of such a collimated beam can be reduced to 3.48° by optimizing the size of the source area. Such a compact structure would have potential applications in micro-optical devices.

Negative refractive index, perfect lenses and checkerboards: Trapping and imaging effects in folded optical spaces

Abstract Newly discovered metamaterials have opened new vistas for better control of light via negative refraction, whereby light refracts in the “wrong” manner. These are dielectric and metallic composite materials structured at subwavelength lengthscales. Their building blocks consist of local resonators such as conducting thin bars and split rings driving the material parameters such as the dielectric permittivity and magnetic permeability to negative (complex) values. Combined together, these structural elements can bring about a (complex valued) negative effective refractive index for the Snell–Descartes law and result in negative refraction of radiation. Negative refractive index materials can support a host of surface plasmon states for both polarizations of light. This makes possible unique effects such as imaging with subwavelength image resolution through the Pendry–Veselago slab lens. Other geometries have also been investigated, such as cylindrical or spherical lenses that enable a magnification of images with subwavelength resolution. Superlenses of three-fold (equilateral triangle), four-fold (square) and six-fold (hexagonal) geometry allow for multiple images, respectively two, three, and five. Generalization to rectangular and triangular checkerboards consisting of alternating cells of positive and negative refractive index represents a very singular situation in which the density of modes diverges at the corners, with an infinity of images. Sine-cosecant anisotropic heterogeneous square and triangular checkerboards can be respectively mapped onto three-dimensional cubic and icosahedral corner lenses consisting of alternating positive and negative refractive regions. All such systems with corners between negative and positive refractive media display very singular behavior with the local density of states becoming infinitely large at the corner, in the limit of no dissipation. We investigate all of these, using the unifying viewpoint of transformation optics. To cite this article: S. Guenneau, S.A. Ramakrishna, C. R. Physique 10 (2009).

Acoustic collimating beams by negative refraction in two-dimensional phononic crystal

We report the realization of acoustic collimating beams by a two-dimensional phononic crystal, which has a negative effective refractive index of small magnitude. The radiation far field of a point source through the phononic crystal with a divergence angle of about 5° is obtained. The measured intensity field distribution in experiment further confirms this collimating property.

2-D Isotropic Effective Negative Refractive Index Metamaterial in Planar Technology

We present a fully printable effective negative refractive index (NRI) metamaterial responsive to arbitrarily linearly polarized incident waves. The proposed metamaterial is composed of a periodic array of tightly coupled Jerusalem cross conductor pairs printed on the opposite sides of a dielectric substrate. Each pair supports both symmetric and antisymmetric resonance modes, whose superposition can lead to an effective NRI of the composite medium. A thorough characterization of the transmission properties of such metamaterial is performed, and conclusive evidences of the medium exhibiting effective NRI properties and impedance matching to free space are presented for a range of the structure parameters.