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Recently, metamaterials with near-zero refractive index have attracted much attention. Light inside these materials experiences no spatial phase change and extremely large phase velocity, makes these peculiar systems applicable for realizing directional emission, tunneling waveguides, large-area single-mode devices and electromagnetic cloaks. In addition, epsilon-near-zero (ENZ) metamaterials can also enhance light transmission through a subwavelength aperture. Impedance-matched all-dielectric zero-index metamaterials which exhibit Dirac cone dispersions at center of the Brillouin zone, have been experimentally demonstrated at microwave regime and optical frequencies for transverse-magnetic (TM) polarization of light. More recently, it has been also proved that these systems can be realized in a miniaturized in-plane geometry useful for integrated photonic applications, i.e. these metamaterials can be integrated with other optical elements, including waveguides, resonators and interferometers. In this work, using a zero-index metamaterial at the inner and outer sides of a subwavelength aperture, we numerically and experimental study light transmission through and its extraction from the aperture. The metamaterial consists of a combination of two double-layer arrays of scatterers with dissimilar subwavelength dimensions. The metamaterial exhibits zero-index optical response in microwave region. Our numerical investigation shows that the presence of the metamaterial at the inner side of the aperture leads to a considerable increase in the transmission of light through the subwavelength aperture. This enhancement is related to the amplification of the amplitude of the electromagnetic field inside the metamaterial which drastically increases the coupling between free space and the slit. By obtaining the electric field profile of the light passing through the considered NZI/aperture/NZI system at this frequency we found out that in addition to the enhanced transmission there is an excellent beaming of the extracted light from the structure. We have theoretically and experimentally shown that using a zero-index metamaterial at the inner and outer sides of a metallic subwavelength slit can considerably enhance the transmission of light through the aperture and beam its extraction, respectively. This work has been supported by TUBITAK under Project No 114E505. The author H.C. also acknowledges partial support from the Turkish Academy of Sciences.

Electromagnetic metamaterials have demonstrated unprecedented control over light matter interactions and have realized exotic responses difficult to achieve with natural materials. The ability to achieve real-time control of novel responses exhibited by electromagnetic metamaterials has led to the realization of metadevices and metasystems. Here we experimentally demonstrate two realizations of single pixel imaging systems that rely entirely on all-electronic metamaterial spatial light modulators. The metasystem enables images to be digitally encoded with various measurement matrix coefficients, thus permitting high speed and fidelity imaging.

Advances in metamaterials and metasurfaces have enabled unprecedented control of light-matter interactions. Metamaterial constituents support high-frequency electric and magnetic dipoles, which can be used as building blocks for new materials capable of negative refraction, electromagnetic cloaking, strong visible-frequency circular dichroism, and enhanced magnetic or chiral transitions in ions and molecules. However, most metamaterials to date have been limited to solid-state, static, narrow-band, and/or small-area structures. Here, we introduce the design, fabrication, and three-dimensional nano-optical characterization of large-area, dynamically-tunable metamaterials and gram-scale metafluids. First, we use transformation optics to design a broadband metamaterial constituent - a metallo-dielectric nanocrescent - characterized by degenerate electric and magnetic dipoles. A periodic array of nanocrescents exhibits large positive and negative refractive indices at optical frequencies, confirmed through simulations of plane wave refraction through a metamaterial prism. Simulations also reveal that the metamaterial optical properties are largely insensitive to the wavelength, orientation and polarization of incident light. Then, we introduce a new tomographic technique, cathodoluminescence (CL) spectroscopic tomography, to probe light-matter interactions in individual nanocrescents with nanometer-scale resolution. Two-dimensional CL maps of the three-dimensional nanostructure are obtained at various orientations, while a filtered back projection is used to reconstruct the CL intensity at each wavelength. The resulting tomograms allow us to locate regions of efficient cathodoluminescence in three dimensions across visible and near-infrared wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. Finally, we demonstrate the fabrication of dynamically tunable large-area metamaterials and gram-scale metafluids, using a combination of colloidal synthesis, protein-directed assembly, self-assembly, etching, and stamping. The electric and magnetic response of the bulk metamaterial and metafluid are directly probed with optical scattering and spectroscopy. Using chemical swelling, these metamaterials exhibit reversible, unity-order refractive index changes that may provide a foundation for new adaptive optical materials in sensing, solar, and display applications.

Transformation optics provides a geometry-based tool to create new components taking advantage of artificial metamaterials with optical properties that are not available in nature. Unfortunately, although guided electromagnetic waves are crucial for optical circuitry, transformation optics is not yet compatible with two-dimensional slab waveguides. Indeed, after determining the propagation of confined waves along the waveguide with a two-dimensional coordinate transformation, the conventional application of transformation optics results in metamaterials whose properties are insensitive to the coordinate perpendicular to the waveguide, leading to bulky, and therefore impractical, designs. In this contribution, we formulate an alternative framework that leads to feasible coordinate-based designs of two-dimensional waveguides. To this end, we characterize a guided transverse-magnetic light mode by relevant electromagnetic equations: a Helmholtz equation to account for wave propagation and a dispersion relation to impose a continuous light profile at the interface. By considering how two-dimensional conformal transformations transform these equations, we are able to materialize the coordinate-designed flows with a nonmagnetic metamaterial core of varying thickness, obtaining a two-dimensional device. We numerically demonstrate the effectiveness and versatility of our equivalence relations with three crucial functionalities, a beam bender, a beam splitter and a conformal lens, on a qualitative and quantitative level, by respectively comparing the electromagnetic fields inside and the transmission of our two-dimensional metamaterial devices to that of their three-dimensional counterparts at telecom wavelengths. As a result, we envision that one coordinate-based multifunctional waveguide component may seamlessly split and bend light beams on the landscape of an optical chip. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

While typically designed to manipulate classical light, metamaterials have many potential applications for quantum optics as well. We argue why a quantum optical effective-medium theory is needed. We present such a theory for layered metamaterials that is valid for light propagation in all spatial directions, thereby generalizing earlier work for one-dimensional propagation. In contrast to classical effective-medium theory there is an additional effective parameter that describes quantum noise. Our results for metamaterials are based on a rather general Lagrangian theory for the quantum electrodynamics of media with both loss and gain. In the second part of this paper, we present a new application of transformation optics whereby local spontaneous-emission rates of quantum emitters can be designed. This follows from an analysis how electromagnetic Green functions trans- form under coordinate transformations. Spontaneous-emission rates can be either enhanced or suppressed using invisibility cloaks or gradient index lenses. Furthermore, the anisotropic material profile of the cloak enables the directional control of spontaneous emission. MOE (Min. of Education, S’pore) Published version

The control of electromagnetic radiation in transformation optical metamaterials brings the development of vast variety of optical devices. Of a particular importance is the possibility to control the propagation of light with light. In this work, we use a structured planar cavity to enhance the thermo-optic effect in a transformation optical waveguide. In the process, a control laser produces apparent inhomogeneous refractive index change inside the waveguides. The trajectory of a second probe laser beam is then continuously tuned in the experiment. The experimental results agree well with the developed theory. The reported method can provide a new approach toward development of transformation optical devices where active all-optical control of the impinging light can be achieved.

Plasmonic metamaterial composites are often considered to be promising building blocks for a number of applications that include subwavelength light manipulation, imaging, and quantum optics engineering. These applications often rely on effective medium response of metamaterial composites and require metamaterial to operate in exotic (hyperbolic, or epsilon-near-zero) regimes. However, the behaviour of metamaterials is often different from the predictions of effective medium. In this work we aim to understand the implications of composite nature of metamaterials on their optical properties. Plasmonic nanowire metamaterials are a convenient metamaterial platform that is capable of realization of ENZ, hyperbolic, and elliptic responses depending on light frequency and metamaterial geometry. In this work we show that the response of metamaterial in elliptical regime may be strongly affected by the additional electromagnetic wave that represents collective excitation of cylindrical surface plasmons in nanowire arrays. We present an analytical description of optical properties of additional wave and analyse the effect of this mode on quantum emitters inside nanorod metamaterials.

We present experimental results on angle-dependent microwave response of the double negative microwave metamaterials. Polarization and angle-dependent transmission spectra of two microwave negative index metamaterials were measured. Two sets of S-shape single unit cells were designed for the 12.5 GHz and 20 GHz frequency ranges. Transmission spectra were measured as a function of polarization and incidence angles of the incoming electromagnetic waves.

Microwave negative index metamaterials have been recently characterized by using primarily far-field transmission of flat slabs and wedges to determine transmission losses and index of refraction, respectively. Although these methods are adequate for most purposes, a more complete characterization of spatial transmission is useful to analyze metamaterials in 3-D, for examples, to characterize irregular forms of metamaterials, such as gradients, prisms, and conformal surfaces. We report here the infrared imaging of the transmitted intensity of microwave electromagnetic waves through a prism of the negative index metamaterials.

The analytically realization of electromagnetic wave frequency conversion in a time-varying medium was shown by the two methods. The first method considers the optical analog of the electromagnetic wave redshift in the expanding universe using the transformation optics mathematical approach. The second one describes the transient process of pulse electromagnetic wave interaction with the time-varying medium using method of the second order Volterra integral equation. The frequency conversion was shown for several types of commercial laser wavelengths.

Functional optical metamaterials usually consist of absorbing, anisotropic and often non-centrosymmetric structures of a size that is only a few times smaller than the wavelength of visible light. If the structures would be substantially smaller, excitation of higher-order electromagnetic multipoles in them, including magnetic dipoles, would be inefficient. As a result, the material would act as an ordinary electric-dipole material. The required non-negligible size of metamolecules, however, makes the material spatially dispersive, so that its optical characteristics depend on light propagation direction. This phenomenon significantly complicates the description of metamaterials in terms of conventional electric permittivity and magnetic permeability tensors. In this work, we present a simple semianalytical method to describe such spatially dispersive metamaterials, which are also allowed to be optically anisotropic and non-centrosymmetric. Applying the method, we show that a strong spatial dispersion, combined with absorption and optical anisotropy, can be used to efficiently control propagational characteristics of optical beams.

Metamaterial with negative refractive index is the key phenomenon behind the concept of a cloaking device to hide an object from light in visible spectrum. Metamaterials made of two and three dimensional lattices of periodically placed electromagnetic resonant cells can achieve absorption and propagation of incident electromagnetic radiation as confined electromagnetic fields confined to a waveguide as surface plasmon polaritons, which can be used for shielding an object from in-tune electromagnetic radiation. The periodicity and dimensions of resonant cavity determine the frequency, which are very small as compared to the wavelength of incident light. Till now the phenomena have been demonstrated only for lights in near infrared spectrum. Recent advancements in fabrication techniques have made it possible to fabricate array of three dimensional nanostructures with cross-sections as small as 25 nm that are required for negative refractive index for wavelengths in visible light spectrum of 400-700 nm and for wider view angle. Two types of metamaterial designs, three dimensional concentric split ring and fishnet, are considered. Three dimensional structures consisted of metal-dielectric-metal stacks. The metal is silver and dielectric is yttrium oxide, other than conventional materials such as FR4 and Duroid. High κ dielectric and high refractive index as well as large crystal symmetry of Yttrium oxide has been investigated as encapsulating medium. Dependence of refractive index on wavelength and bandwidth of negative refractive index region are analyzed for application towards cloaking from light in visible spectrum.

In this paper, we theoretically study optical responses of tightly-coupled terahertz metamaterial. Unlike loosely-coupled one, tightly-coupled metamaterials exhibit resonant optical responses that are highly dependent on the interaction between each unit resonators. In order to predict optical response and spectral behavior of effective parameters of the metamaterials, a model based on coupled-mode theory is applied. Resonant optical response is shown to be highly dependent on the gap-size between the resonators which relates to the inter-unit coupling, and we show that this dependency implies the possibility of miniaturized metamaterials .

The transformation optics was introduced by J. Pendry and U. Leonhardt in 2006 [1,2]. In this method an initial space is transformed into a new space and this transformed space can be materialized by a material, which the electromagnetic parameters can be deduced from the metric of the transformed space. In the general case the electromagnetic parameters are anisotropic tensors. At microwave frequencies these materials can be realized using classical metamaterials like SRR form J. Pendry or ELC from D. Smith [3]. At infrared wavelengths this realization is a challenge because the dimensions of the metamaterials are much smaller than the wavelength and become nanometric. Then the design of these metamaterials must be simplified and original methods must be developed to allow the realization of these metamaterials with controlled electromagnetic properties. In this paper we describe the realization of a multilayer metamaterial working at infrared wavelength, which the permittivity and the permeability can be adjusted separately. We give some examples of realized multilayer materials operating around 150THz, with a comparison between the results of full wave simulations of these materials and their characterizations using a Fourier Transform Infrared Spectrometer.

Optical metamaterials are able to achieve optical properties that do not exist in nature. Approaches to the homogenization of optical metamaterials are becoming more and more complex in the desire to achieve accurate representation. Here we propose to modify an existing retrieval approach for metamaterials to characterize their properties. To extract the effective refractive index and material parameters from reflection and transmission coefficients for double negative metamaterial in the optical regime, the modified Nicholson-Ross-Weir (NRW) method is used. In order to obtain a true picture of these metamaterials, as a function of angle of incidence of the illumination, it is important to present not only the effective parameters of permittivity and permeability but also some other important parameters such as coupling coefficients, that represent the inherent anisotropy.

Research on chiral metamaterials has drawn much attention in recent years. By virtue of chirality, for example, it has been shown that chiral metamaterials can achieve negative refractive index without great energy dissipation. In this report, we applied effective parameter retrieval technique to study the material properties of helical metamaterial. The retrieval procedure yields electromagnetic parameters through employing finite-difference time-domain (FDTD) method under periodic boundary condition. We numerically obtain several electromagnetic parameters of the structure and show that the resonance properties and the index of refraction of the helical metamaterial have strong relationship with its circular dichroism. The optical properties of the structure are also discussed, which provides general design guidelines for engineering functional chiral metamaterials.

In this contribution we show that the fundamental diffraction limit of optical cavities can be overcome using a transformation-optical approach. Transformation optics has recently provided a new method for the design of devices to control electromagnetic fields, based on the analogy between the macroscopic Maxwell's equations in complex dielectrics and the free-space Maxwell's equations in a curved coordinate system. It offers an elegant approach to exploit the full potential of metamaterials. We show how transformation optics can be used to achieve the opposite e ect of an invisibility cloak; instead of prohibiting the electromagnetic waves from entering a predefi ned region, we encapsulate the light waves within such a finite region. This allows us to design cavities with extraordinary properties. We have been able to demonstrate theoretically the existence of eigenmodes whose wavelength is much larger than the characteristic dimensions of the device. Furthermore, our cavities avoid the bending losses observed in traditional microcavities, so the quality factor is only limited by the intrinsic absorption of the materials. Finally, we also demonstrate how the combination of radial and angular transformations allows developing cavities without bending losses using right-handed material parameters only. 1, 2

The ideas of employing the unique properties of metamaterials for cloaking and invisibility applications has been recently suggested and investigated by several groups, because they may find numerous applications in physics and technology. While many of the recent designs of the cloaking structures are based on the transformation optics and exact formulas, the original concept suggested by Tretyakov employed the periodical set of parallel-plate waveguides with the height smoothly varying from H to h in order to reduce drastically the total scattering cross-section of a given object and to obtain broadband cloaking effect. Our paper is devoted to improvement of this design to make tunability and nonlinear effect. The Tretyakov’s design was scaled for Ku-band frequencies and the cloak was placed into rectangular waveguide. The broad transmission band (“invisibility region”) was obtained. The tunability of transmission band was realized by addition the capacitors into the cloak, between metallic plates. The cloaking system was simulated numerically by CST Microwave Studio. The possibility of invisibility switching on/off was shown by changing of capacity of varactor diodes from 0.4 to 3.4 pF by incident power. The nonlinear cloak behavior was shown at microwaves.

Based on the analogy between the Maxwell equations in complex metamaterials and the free-space Maxwell equations on the background of an arbitrary metric, transformation optics allows for the design of metamaterial devices using a geometrical perspective. This intuitive geometrical approach has already generated various novel applications within the elds of invisibility cloaking, electromagnetic beam manipulation, optical information storage, and imaging. Nevertheless, the framework of transformation optics is not limited to three-dimensional transformations and can be extended to four-dimensional metrics, which allow for the implementation of metrics that occur in general relativistic or cosmological models. This enables, for example, the implementation of black hole phenomena and space-time cloaks inside dielectrics with exotic material parameters. In this contribution, we present a time-dependent metamaterial device that mimics the cosmological redshift. Theoretically, the transformation-optical analogy requires an innite medium with a permittivity and a permeability that vary monotonically as a function of time. We demonstrate that the cosmological frequency shift can also be reproduced in more realistic devices, considering the fact that practical devices have a nite extent and bound material parameters. Indeed, our recent numerical results indicate that it is possible to alter the frequency of optical pulses in a medium with solely a modulated permittivity. Furthermore, it is shown that the overall frequency shift does not depend on the actual variation of the permittivity. The performance of a nite frequency converter is, for example, not aected by introducing the saw tooth evolution of the material parameters. Finally, we studied the eect of the introduction of realistic metamaterial losses and, surprisingly, we found a very high robustness with respect to this parameter. These results open up the possibility to fabricate this frequency converting device with currently available metamaterials [V. Ginis, P. Tassin, B. Craps, and I. Veretennico, Opt. Express 18, 5350{5355 (2010) 1 ].

Metallo-dielectric structured materials, or in other words metamaterials (MTM), are in principle a well established composite to improve efficiency, functionality, and weight of micro-wave components. In recent times, it has been demonstrated that the functionalities of metamaterials can be scaled down to optical frequencies by nano structuring techniques. Examples include negative index materials in the near infrared and visible frequency range, cloaking structures, filters, and structures for improved sensing of environmental gases. The physical processes in plasmonic metamaterials depend strongly on the excitation of surface plasmons and the interaction between them. We have learned how to control the plasmon-photon and the plasmon-plasmon interaction for manipulating the electromagnetic response in a metamaterial at wavelengths well below the vacuum wavelength. Many interesting and novel optical applications and devices are expected. For instance sub-wavelength imaging, compact communication devices as polarisation splitters, slow light media structures, compact colour filters, and resonators. All-plasmonic circuits are also the basis for ultra-dense photonic integration not achievable through the conventional optical integration. With examples of several metamaterial structures we try to illustrate the application potential of MTMs and comment on their fabrication feasibility to show whether metamaterials can hold their promise. Their investigation is in any case a rewarding adventure.

The conventional metamaterials require both negative permittivity (e) and negative permeability (μ), to achieve negative refraction. Chiral metamaterial is a new class of metamaterials offering a simpler route to negative refraction. In this paper, we review the history of metamaterials and the developments on chiral metamaterials. We study the wave propagation properties in chiral metamaterials and show that negative refraction can be realized in chiral metamaterials with a strong chirality, with neither permittivity (e) nor permeability (μ) negative required. We have developed a retrieval procedure, adopting a uniaxial bi-isotropic model to calculate the effective parameters such as of the chiral metamaterials. In this paper we study the anomalous refraction at the boundary of a metamaterial medium with strong chirality. The fact that for a time-harmonic monochromatic plane wave the direction of the Poynting vector is antiparallel with the direction of phase velocity, leads to exciting features that can be advantageous in the design of novel devices and components at microwaves frequencies. This work is concerned with the propagation of electromagnetic waves in isotropic chiral media and with the effects produced by a plane boundary between two such media. In analogy with the phenomena of reflection and refraction of plane electromagnetic waves in ordinary dielectrics, the kinematical and dynamical aspects of these phenomena are studied, in situations such as the intensity of the various wave components and the change in the polarization of the wave, as it crosses the boundary. This research might be applied to the design of very high frequency microwaves and non symmetrical transmission lines. In our work, the design, numerical calculations and experimental measurements of chiral metamaterials is introduced. Strong chiral behaviours such as optical activity and circular dichroism are observed and negative refraction is obtained for circularly polarized waves in these chiral metamaterials. We show that 3D isotropic chiral metamaterials can eventually be realized.

In this review we describe the challenges and opportunities for creating magnetically active metamaterials in the optical part of the spectrum. Several techniques for extracting the effective parameters of plasmonic metamaterials are introduced and compared. The emphasis is on the periodic metamaterials whose unit cell is much smaller than the optical wavelength. The conceptual differences between microwave and optical metamaterials are demonstrated. We show that concepts for microwave metamaterials can be extended to the optical domain in a rather limited way. Whenever a metamaterial that exhibits magnetic response in the microwave part of the spectrum is scaled down in size to exhibit similar electromagnetic behavior in the optical part of the spectrum, plasmonic effects play a major role. Specifically, we demonstrate that for every unit cell's geometry of a magnetically active metamaterial, there exists the shortest wavelength I»res beyond which the magnetic response disappears. In general, the more elaborate is the unit cell (e.g., split rings with narrow inter-ring gaps, etc.), the longer is the I»res.

Features of the polarization, energy fluxes of proper inhomogeneous electromagnetic waves in a layer of absorbing uniaxial negative index metamaterial, and an exact solution of the corresponding boundary problem are investigated. A comparative analysis and modeling of optical properties of anisotropic conventional media and metamaterials is carried out. Conditions and possible advantages of a controlled transformation of the radiation characteristics by the metamaterial are analyzed.

Many optical systems used in the infrared spectrum have, so far, adopted binary optical elements (BOE) to achieve a better performance. Especially, in the middle and long infrared spectrum, binary optical elements are commonly used. Thus, limited by the manufacture technology, the applications of binary optics in the visible spectrum are rare. This tentative research aims at finding the practicability of applying BOEs in the visible spectrum. We attempted to replace the reference lens group in the interferometer with a harmonic diffractive/refractive hybrid lens group, expecting that the wave aberration be well-corrected. In this paper, the main procedure of designing a hybrid optical system is introduced with an example of “F2” lens group. After the analysis on the interference pattern and wave front, the comparison between the tested result and theoretical result can be made. It demonstrates that the hybrid optical system is capable of being applied in the visible spectrum. The analysis also discloses that raising the diffractive efficiency is the next step for us to take.

A full wave approach is developed to analyze the scattered electromagnetic fields due to fluctuations in the surface height and/or electromagnetic medium parameters such as the complex electric permittivity, conductivity, and magnetic permeability. Since the scales of the medium fluctuations considered could be significantly smaller or larger than the electromagnetic wavelengths, the familiar perturbation and physical/geometrical optics techniques based on the Kirckhoff approximations of the fields on the boundaries cannot be used nor is it possible to investigate sub- wavelength structures based on far-field measurements.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spectrum analysis of microwave signals can be performed using Bragg diffraction of light by magnetostatic waves (MSW's). MSW wave propagation must occur in a thin-film magnetic, ferrite medium, such as YIG. Since it is possible to propagate guided optical waves in the same film, rf spectrum analyzers analogous to those using guided optical wave interaction with surface acoustic waves can be constructed. Intrinsic advantages of the optical-MSW device include high center frequencies of operation, up to 20 GHz and beyond, and tunability of the center frequency. The theory of optical-MSW interactions and laboratory demonstrations of such interactions are summarized. Design considerations for a spectrum analyzer device are discussed, including materials, rf-to-MSW transduction, light sources, thin-film light coupling, and photodetectors.