Negative Refractive Index Materials Research Articles

Feasibility study for pseudoscopic problem in integral imaging using negative refractive index materials.

To solve the pseudoscopic problem, we propose a one-step integral imaging system with negative refractive index materials, which can avoid the deterioration in resolution inherent to the optical or digital two-step processes. Specifically, the proposed method is based on the novel feature of negative refractive index materials, bending light to a negative angle relative to the surface normal. The pseudoscopic imaging property of the negative refractive index material slab is theoretically investigated. For formation of orthoscopic reconstructed images, the matching condition of the negative index lens array and the positive index lens array is deduced. Two types of conceptual prototypes of integral imaging system with negative refractive index materials are designed. Experimental results show the validity of the proposed method. To the best of our knowledge, this is the first time to explore the application of negative index materials in eliminating the pseudoscopic effect in integral imaging.

Optical delay lines using coupled slab waveguides and ring resonator with a negative refractive index core

Total delay time of a structure composed of a slab waveguide coupled with a ring resonator where negative refractive index material is replaced in the core of the structure is investigated in this work. In this paper, a two-port ring resonator (TPRR) which is made of a core with negative refractive index has been used to generate a time delay for a Gaussian-shaped pulse with 1GHz bandwidth. It is shown that the creation of the ring how causes more ng of a straight waveguide and results are compared with positive refractive index core TPRR. We have used metamaterial to make an n<0 media and have used two cascaded metamaterial rings to increase the bandwidth.

Experimental realization of an open cavity.

The design and experimental demonstration of an open cavity in the microwave region is presented. The resonance condition is achieved through the cancellation of lightpaths in positive and negative refractive index materials. The positive index material is a structured aluminium surface supporting a spoof surface plasmon mode, and the negative index material is a photonic crystal made of alumina. A resonance peak is observed in the measured spectrum at which the electric field distribution agrees with numerical simulation.

Special Section Guest Editorial: Metamaterials and Photonic Nanostructures

Center for Lasers and Photonics, Indian Institute of Technology Kanpur, Kanpur 208016, IndiaOver the past decade, scientists have learned how to manipulate the interaction of radiation withstructured materials to an unprecedented level. For decades, our world was limited to materialswith primarily positive permittivities and permeabilities, with a few exceptions such as plasmas,for example, whose permittivities can be negative. The research in metamaterials coupled withthe rapid advancements in micro- and nanofabrication technologies has removed this limitationand has opened the door to almost arbitrary material properties with some extraordinary con-sequences across the electromagnetic spectrum, ranging from radio frequencies to opticalfrequencies. These developments have been strongly complemented by the developments inperiodic dielectric photonic crystals where band-gap effects lead to mind-blowing dispersioncharacteristics and consequent effects. Almost simultaneously, the optics of metals has beenbrought to center-stage where the plasmonic excitations enable the electromagnetic radiationto interact resonantly with the structured material at very small sub-wavelength scales.These interactions prove to be the key to manipulating the optical near-field, and surprisingeffects such as sub-wavelength scale imaging by so-called super-lenses made of negative refrac-tive index or plasmonic materials have been discovered.AfocuseddiscussionmeetingonMetamaterialsandPhotonicNanostructureswasheldatIITKanpur on 16–17 August 2013 to bring researchers working on these topics to a common plat-form and to enable an interactive period for knowledge pooling. One of the intents was to takestock of theworkcarriedout in India in these frontier areas, and most of the activeresearchers inIndia contributed to the meeting. This special section consists of selected papers based on workpresented at the meeting, as well as papers contributed in response to the call for this specialsection.The special section has attracted an interesting collection of works ranging from surfaceenhanced Raman scattering from nanostructured plasmonic systems, interactions between local-ized and propagating surface plasmons in subwavelength gratings, extraordinary transmission instructured plasmonic thin films, anisotropic uniaxial metamaterials and epsilon-zero metamate-rials, fabrication techniques for embedding nondiffracting defect sites, large area nanophotonicstructures and inorganic-organic layered perovskites, to theoretical treatments of third harmonicgeneration in photonic crystals and super-continuum generation in microstructured opticalfibers. The large variety of the topics is reflective of the ever-increasing appeal and applicationsof metamaterials and nanostructured materials across optics.

Assembled Plasmonic Asymmetric Heterodimers with Tailorable Chiroptical Response

Directed nanocrystal (NC) heteroassemblies could potentially achieve tailorable multiplex circular dichroism (CD) bands. Here, for the first time, we developed assembly of nanoparticle (NP)-nanorod (NR) chiral heterodimers with chiral molecules to explore their chiroptical activities. The experimental results revealed that plasmonic CD responses were in the region from 520 to 750 nm, which was in agreement with the theoretical simulation. Importantly, the CD band could be regulated by controlling the gaps between adjacent NCs and altering the building blocks of the assemblies. These results show that the plasmonic chiroptical response of NP-NR heterodimers could come from the finger-crossed chiral construction of adjacent NC in the heterodimers and the formation of plasmonic hot-spots in the assemblies could further enhance the plasmonic CD. This work provides a new opportunity to create heterogeneous nanoscale plasmonic objects with tailorable chiroptical response for application in biosensors, in vivo chiral medical carriers and negative refractive index materials.

Molecular Split-Ring Resonators Based on Metal String Complexes

Metal string complexes or extended metal atom chains (EMACs) belong to a family of molecules that consist of a linear chain of directly bonded metal atoms embraced helically by four multidentate organic ligands. These four organic ligands are usually made up of repeating pyridyl units, single-nitrogen-substituted heterocyclic annulenes, bridged by independent amido groups. Here, in this paper, we show that these heterocyclic annulenes are actually nanoscale molecular split-ring resonators (SRRs) that can exhibit simultaneous negative electric permittivity and magnetic permeability in the UV-Vis region. Moreover, a monolayer of self-assembled EMACs is a periodic array of molecular SRRs which can be considered as a negative refractive index material. In the molecular scale, where the quantum-size effect is significant, we apply the tight-binding method to obtain the frequency-dependent permittivity and permeability of these molecular SRRs with their tensorial properties carefully considered.

Propagation properties of Gaussian beam in gradient negative index of refraction material

We apply the ABCD formalism to a gradient negative index medium (NIM) and investigate the propagation and transformation properties of Gaussian beams in this medium. First, we derive the ABCD formalism in a positive gradient NIM and obtain the propagation model. Spatial soliton and the spatial breather propagation in this medium are revealed. Our research suggests that the gradient coefficient has a significant effect on the focusing ability of slab. When the gradient coefficient increases, the quasi-lense effect becomes more prominent and notable. As a result, the focusing ability improves and the beam waist in the focal point shrinks. Second, when Gaussian beams propagate in the negative gradient NIM, the beam waist enlarges as the distance increases. There is neither spatial soliton phenomenon nor breather transmission phenomenon, which is completely different from the propagation characteristics in the positive gradient NIM.

Defect modes properties in periodic lossy multilayer containing negative index materials with symmetric and asymmetric geometric structures

In this paper, the characteristic matrix method is used to study the propagation of electromagnetic waves through one-dimensional lossy photonic crystals composed of negative and positive refractive index material layers with symmetric and asymmetric geometric structures with a defect layer at the center of the structure. First, the positive index material defect layer is considered, and the effects of the polarization and the angle of incidence on the defect mode in the transmission spectra of the both structures are investigated. The results show that the number of the defect modes in the transmission spectra depends on the geometry (symmetric or asymmetric) of the structure. In addition, it is shown that the defect mode frequency increases as the angle of incidence increases. This property is independent of the geometry of the structure. Then, for normal incidence, the negative index material defect layer is considered, and the properties of defect modes for both structures are investigated. The results can lead to designing new types of transmission narrow filters.

Negative refractive index materials for improved solar cells

Planar thin-film solar cells can exploit Fabry-Perot resonances in the spectral domain of weak absorption to make them more efficient. However, their spectral width decreases and their number increases for a thicker solar cell, both being detrimental. Here, we show that an optically complementary material, i.e., a material with a negative but otherwise identical refractive index to that of the solar cell material and with the same impedance, allows a single, spectrally immensely broad, Fabry-Perot resonance to be obtained. This is useful to enhance the absorption across the entire spectral domain of interest. If a material with the required optical response were available, a solar cell could be implemented that performs close to the Lambertian limit. However, since the idealistic material properties assumed herein cannot be achieved, an actual implementation may exploit nanostructures such as, e.g., dispersion engineered photonic crystals. In a reasonable spectral range their optical response can be close to that required.

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.

Design of a novel negative refractive index material based on numerical simulation

This paper presents a novel metamaterial constructed with wires, spheres and hollow slabs (WSHS), which simultaneously exhibits negative permittivity and permeability. An electromagnetic wave simulation is performed based on the proposed metamaterial and shows that a negative refractive index is achieved for this metamaterial. Adjusting the lattice constant of the unit cell is an easy way to manipulate the frequency of negative index of this structure. A left-hand material prism is designed composed of metamaterial unit cells and the simulation on the proposed prism proves the left-hand behavior of the designed metamaterial.

Codimension 2 and 3 situations in a ring cavity with elliptically polarized electromagnetic waves

We study pattern formation on the plane transverse to propagation direction, in a ring cavity filled with a Kerr-like medium, subject to an elliptically polarized incoming field, by means of two coupled Lugiato–Lefever equations. We consider a wide range of possible values for the coupling parameter between different polarizations, B̄, as may happen in composite materials. Positive and also negative refraction index materials are considered. Examples of marginal instability diagrams are shown. It is shown that, within the model, instabilities cannot be of codimension higher than 3. A method for finding parameters for which codimension 2 or 3 takes place is given. The method allows us to choose parameters for which unstable wavenumbers fulfill different relations. Numerical integration results where different instabilities coexist and compete are shown.

Realization of tellurium-based all dielectric optical metamaterials using a multi-cycle deposition-etch process

Tellurium (Te) dielectric resonator metamaterials for thermal infrared applications were fabricated using a multi-cycle deposition-etch process that circumvents pinch-off issues during deposition. Deposition and etching of Te were studied in detail. Metamaterial samples with varying resonator dimensions were fabricated using this technique. All the samples showed two transmission minima corresponding to magnetic and electric dipole resonances. Longer resonant wavelengths were observed as the resonator dimension was increased. Observation of spectral overlap between magnetic and electric resonances gives us the potential opportunity to realize a negative refractive index material.

Fabrication of large area flexible and highly transparent film by a simple Ag nanowire alignment

This article describes the fabrication of a flexible polymer thin film incorporating a highly aligned Ag nanowire array, resulting in high transparency and polarisation that are useful for potential applications to optical filters, electronic and optical devices and negative refractive index materials.

Three-dimensional metamaterials fabricated using Proton Beam Writing

Proton Beam Writing (PBW) is a direct write lithographic technique that has recently been applied to the fabrication of three dimensional metamaterials. In this work, we show that the unique capabilities of PBW, namely the ability to fabricate arrays of high resolution, high aspect ratio microstructures in polymer or replicated into metal, is well suited to metamaterials research. We have also developed a novel method for selectively electroless plating silver directly onto polymer structures that were fabricated using PBW. This method opens up new avenues for utilizing PBW for making metamaterials and other sub-wavelength metallic structures. Several potential applications of three dimensional metamaterials fabricated using PBW are discussed, including sensing and negative refractive index materials.

Hierarchically Structured Electrospun Fibers

Traditional electrospun nanofibers have a myriad of applications ranging from scaffolds for tissue engineering to components of biosensors and energy harvesting devices. The generally smooth one-dimensional structure of the fibers has stood as a limitation to several interesting novel applications. Control of fiber diameter, porosity and collector geometry will be briefly discussed, as will more traditional methods for controlling fiber morphology and fiber mat architecture. The remainder of the review will focus on new techniques to prepare hierarchically structured fibers. Fibers with hierarchical primary structures—including helical, buckled, and beads-on-a-string fibers, as well as fibers with secondary structures, such as nanopores, nanopillars, nanorods, and internally structured fibers and their applications—will be discussed. These new materials with helical/buckled morphology are expected to possess unique optical and mechanical properties with possible applications for negative refractive index materials, highly stretchable/high-tensile-strength materials, and components in microelectromechanical devices. Core-shell type fibers enable a much wider variety of materials to be electrospun and are expected to be widely applied in the sensing, drug delivery/controlled release fields, and in the encapsulation of live cells for biological applications. Materials with a hierarchical secondary structure are expected to provide new superhydrophobic and self-cleaning materials.

New Negative Refractive Index Material Composed of Dielectric Prisms with Metal Patterns

A two-dimensional negative refractive index material is proposed. The material has a bulky structure composed of dielectric prism cells with metal patterns. The material is expressed by an equivalent circuit. The propagation regions of two left-handed modes calculated from the equivalent circuit exist near the propagation regions obtained by electromagnetic simulation. It is confirmed by simulation that the incident plane wave goes into the material with low reflection by using the second left-handed mode and attaching metal conversion strips around the material. A negative refractive index slab lens with 15×9 cells is made to measure the field distribution of wave out of the lens. It is shown that the resolution of the slab lens exceeds the diffraction-limit.

Meta – Material Brain Biology for Information Gain

Optical properties of brain materials can be investigated based on concepts derived from physical models for signal communication, while relevantly relating them to bio systems applications. Bio system responses to ultra weak photo optic signals can prompt environment assisted behavior; and coherent cellular communication. Evolution of bio structures and materials occur as adaptations, in response to cues from the current environment, so as to enable efficient energy and information transfer functions. This is significant in an environment of ultra-weak photo emissions (UPE) and its optic signals in brain, which is reportedly related to bio energetic processes of energy metabolism; intrinsic optic signals have been associated with oscillatory functional rhythms involving calcium activity, and cellular communication. Such non–molecular signaling could couple to molecular recognition for biocontrol, and observed to have a role in bioprocess monitoring and bio imaging studies. In the case of UPE, the signals are of an ultra-weak nature and its long range propagation is hampered by bio-system absorption and scattering, despite theoretical possibilities for transmission in the mitochondrial reticular network, probably based on more simplistic assumptions. However, this possibility is limited, under physiological conditions, when bio system dissipation losses are taken into account. Some prevalent models tend to suggest limited propagation of photo-optic signals of a weak nature. It is postulated here that evolution of meta materials in brain biology in response to environment cues from UPE, would help to realize optic NIMs [Negative Refraction Index Materials]with tunability and information gain. The paper investigates the theoretical possibility for this, while relating to brain biology. The application potential of physical models for NIR and optic signaling communication, in a bio system context, is taken into account. Optical properties of brain materials are discussed in the light of concepts related to non-linear effects like negative refraction and coherent resonances and their potential application in brain biology.Such effects and behavior in brain might help to reduce biosystem scatter and dissipative losses to facilitate signal communication with long-range propagation, using ultra-weak photo optic signals.

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate (1). They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves (2). This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks (3), negative refractive index materials (4), and lenses that resolve objects below the diffraction limit (5). However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size (6-7). Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response (8). We combine the stack-and-draw technique used to produce microstructured polymer optical fiber (9) with the Taylor-wire process (10), using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 °C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

A high transmission and low loss metamaterial with negative refraction at 458 THz

In this paper using a regular 2-dimensional array of unit cells composed of two silver slabs on which silver nano rods are set, we have obtained a metamaterial exhibiting negative refraction in the near infrared electromagnetic region. Our calculations confirm that the value of FOM at 458THz is 10.7 which is, according to our knowledge, the highest value ever reported for a negative refractive index material at this frequency. This corresponds to a high transmission with a low loss at the mentioned frequency which is confirmed by the calculated transmission spectra.