In this paper various extensions of the design strategy of transformation media are proposed. We show that it is possible to assign different transformed spaces to the field strength tensor (electric field and magnetic induction) and to the excitation tensor (displacement field and magnetic field), resp. In this way, several limitations of standard transformation media can be overcome. In particular it is possible to provide a geometric interpretation of non-reciprocal as well as indefinite materials. We show that these transformations can be complemented by a continuous version of electric-magnetic duality and comment on the relation to the complementary approach of field-transforming metamaterials.
Recent experiments have shown the viability of the metamaterial approach to dielectric response engineering for moderately enhancing the transition temperature, Tc, of a superconductor. In this report, we demonstrate the use of Al2O3-coated aluminium nanoparticles to form the recently proposed epsilon near zero (ENZ) core-shell metamaterial superconductor with a Tc that is three times that of pure aluminium. IR reflectivity measurements confirm the predicted metamaterial modification of the dielectric function thus demonstrating the efficacy of the ENZ metamaterial approach to Tc engineering. …
Nanoscale slot waveguides of hyperbolic metamaterials are proposed and demonstrated for achieving large optical field enhancement. The dependence of the enhanced electric field within the air slot on waveguide mode coupling and permittivity tensors of hyperbolic metamaterials is analyzed both numerically and analytically. Optical intensity in the metamaterial slot waveguide can be more than 25 times stronger than that in a conventional silicon slot waveguide, due to tight optical mode confinement enabled by the ultrahigh refractive indices supported in hyperbolic metamaterials. The electric fi…
We investigate the effect of anomalous field enhancement in metamaterials where the effective refractive index gradually changes from positive to negative values, i.e. transition metamaterials. We demonstrate that considerable field enhancement can be achieved in lossy optical transition metamaterials that have electromagnetic material properties obtained from experimental data. The field enhancement factor is found to be polarization-dependent and largely determined by the material parameters and the width of the transition layer.
Volumes of sub-wavelength electromagnetic elements can act like homogeneous materials: metamaterials. In analogy, sheets of optical elements such as prisms can act ray-optically like homogeneous sheet materials. In this sense, such sheets can be considered to be metamaterials for light rays (METATOYs). METATOYs realize new and unusual transformations of the directions of transmitted light rays. We study here, in the ray-optics and scalar-wave limits, the wave-optical analog of such transformations, and we show that such an analog does not always exist. Perhaps, this is the reason why many of t…
Anomalous optical coupling properties between two silicon wires in a silicon slot waveguide embedded in epsilon-near-zero (ENZ) metamaterials are proposed and demonstrated. The dependences of optical field enhancement in the slot region and transverse optical force on the slot size and the permittivity of surrounding material are studied in details. It is demonstrated that the optical field in the slot region is significantly enhanced due to the giant index contrast at the slot interface between silicon wires and ENZ metamaterials, but the optical mode coupling between silicon wires is greatly…
Optical fields in metamaterial nanostructures can be separated into bright modes, whose dispersion is typically described by effective medium parameters, and dark fluctuating fields. Such combination of propagating and evanescent modes poses a serious numerical complication due to poorly conditioned systems of equations for the amplitudes of the modes. We propose a numerical scheme based on a transfer matrix approach, which resolves this issue for a parallel plate metal-dielectric metamaterial, and demonstrate its effectiveness.
We report that the classical phenomena of optical activity and circular dichroism, which are traditionally associated with chirality (helicity) of organic molecules, proteins and inorganic structures, can be observed in non-chiral artificial media. Intriguingly, our metamaterial structure yields exceptionally strong resonant optical activity, which also leads to the appearance of a backward wave, a characteristic sign of negative-index media.
We extend the transformation-optics paradigm to a complex spatial coordinate domain, in order to deal with electromagnetic metamaterials characterized by balanced loss and gain, giving special emphasis to parity-time (PT) symmetric metamaterials. We apply this general theory to complex-source-point radiation and anisotropic transmission resonances, illustrating the capability and potentials of our approach in terms of systematic design, analytical modeling and physical insights into complex-coordinate wave-objects and resonant states.
We develop an approach to utilize anisotropic metamaterials to solve one of the fundamental problems of modern plasmonics -- parasitic scattering of surface waves into free-space modes, opening the road to truly two-dimensional plasmonic optics. We illustrate the developed formalism on examples of plasmonic refractor and plasmonic crystal, and discuss limitations of the developed technique and its possible applications for sensing and imaging structures, high-performance mode couplers, optical cloaking structures, and dynamically reconfigurable electro-plasmonic circuits.
The extraordinary properties of nonlinear optical propagation processes in double-domain positive/negative index metamaterials are reviewed. These processes include second harmonic generation, three- and four-wave frequency mixing, and optical parametric amplification. Striking contrasts with the properties of the counterparts in ordinary materials are shown. We also discuss the possibilities for compensating strong losses inherent to plasmonic metamaterials, which present a major obstacle in numerous exciting applications, and the possibilities for creation of unique ultracompact photonic dev…
We study the optical properties of metamaterials made from cut-wire pairs or plate pairs. We obtain a more pronounced optical response for arrays of plate pairs -- a geometry which also eliminates the undesired polarization anisotropy of the cut-wire pairs. The measured optical spectra agree with simulations, revealing negative magnetic permeability in the range of telecommunications wavelengths. Thus, nanoscopic plate pairs might serve as an alternative to the established split-ring resonator design.
The ability to engineer metamaterials with tunable nonlinear optical properties is crucial for nonlinear optics. Traditionally, metals have been employed to enhance nonlinear optical interactions through field localization. Here, inspired by the electronic properties of materials, we introduce and demonstrate experimentally an asymmetric metal-semiconductor-metal (MSM) metamaterial that exhibits a large and electronically tunable effective second-order optical susceptibility (\c{hi}(2)). The induced \c{hi}(2) originates from the interaction between the third-order optical susceptibility of the…
We study the propagation of electromagnetic waves in the limit of geometrical optics for a class of nearly transparent nonlinear uniaxial metamaterials for which their permittivity tensors present a negative principal component. Their permeability are assumed positive and dependent on the electric field. We show that light waves experience triple refraction -- trirefringence. Additionally to the ordinary wave, two extraordinary waves propagate in such media.
Artificially structured metamaterials have enabled unprecedented flexibility in manipulating electromagnetic waves and producing new functionalities, including the cloak of invisibility based on coordinate transformation. Here we present the design of a non-magnetic cloak operating at optical frequencies. The principle and structure of the proposed cylindrical cloak are analyzed, and the general recipe for the implementation of such a device is provided. The cloaking performance is verified using full-wave finite-element simulations.
We demonstrate that metamaterial devices requiring anisotropic dielectric permittivity and magnetic permeability may be emulated by specially designed tapered waveguides. This approach leads to low-loss, broadband performance. Based on this technique, we demonstrate broadband electromagnetic cloaking in the visible frequency range on a scale ~100 times larger than the wavelength.
Cavity array metamaterials (CAMs), composed of optical microcavities in a lattice coupled via tight-binding interactions, represent a novel architecture for engineering metamaterials. Since the size of the CAMs' constituent elements are commensurate with the operating wavelength of the device, it cannot directly utilise classical transformation optics in the same way as traditional metamaterials. By directly transforming the internal geometry of the system, and locally tuning the permittivity between cavities, we provide an alternative framework suitable for tight-binding implementations of me…
Here we theoretically show, by designing and manipulating spatially inhomogeneous, non-uniform conductivity patterns across a single flake of graphene, that this single-atom-layered material can serve as a "one-atom-thick" platform for infrared metamaterials and transformation optical devices. It is known that by varying the chemical potential using gate electric and/or magnetic fields, the graphene conductivity in the THz and IR frequencies can be changed. This versatility provides the possibility that different "patches" on a single flake of graphene possess different conductivities, suggest…
Metamaterials are being used to model various exotic "optical spaces" for such applications as novel lenses and cloaking. While most effort is directed towards engineering of continuously changing dielectric permittivity and magnetic permeability tensors, an alternative approach may be based on lattices of metamaterial waveguides. Here we demonstrate the power of the latter technique by presenting metamaterial lattice models of various 4D spaces.
We study the dispersion of electromagnetic waves in a spatially dispersive metamaterial with Lorentz-like dependence of principal permittivity tensor components on the respective components of the wave vector performing the analysis of isofrequency contours. The considered permittivity tensor describes triple non-connected wire medium. It is demonstrated that the metamaterial has four optic axes in the frequency range below artificial plasma frequency. The directions of the optical axes do not depend on frequency and coincide with the diagonals of quadrants. The metamaterial supports two propa…
Metamaterials with artificial optical properties have attracted significant research interest. In particular, artificial magnetic resonances in non-unity permeability tensor at optical frequencies in metamaterials have been reported. However, only non-unity diagonal elements of the permeability tensor have been demonstrated to date. A gyromagnetic permeability tensor with non-zero off-diagonal elements has not been observed at the optical frequencies. Here we report the observation of gyromagnetic properties in the near-infrared wavelength range in a magneto-plasmonic metamaterial. The non-zer…
Using a multiple scattering technique, we derived closed-form expressions for effective constitutive parameters and electro/magneto-strictive tensor components for 2D bi-anisotropic metamaterials. Using the principle of virtual work, we obtained the electromagnetic stress tensor that can be used to calculate the optical force density inside such media. The analytic expressions are tested against full wave numerical simulations. Our effective medium theory is essential for providing a complete macroscopic description of the optical and opto-mechanical properties of bi-anisotropic composites.
Photoacoustic imaging systems offer a platform with high resolution to explore body tissues, food, and artwork. On the other hand, plasmonics constitutes a source of resonant heating and thermal expansion to generate acoustic waves. However, its associated techniques are seriously limited to laser penetration and nonspecific hyperthermia in the sample. To address this issue, the present work adopts a paradigm shift in photoacoustics. By simulating microparticles made of random composites, the calculated pressure can be made similar or superior to that calculated via plasmonic optoacoustics. Th…
Quantum metamaterials generalize the concept of metamaterials (artificial optical media) to the case when their optical properties are determined by the interplay of quantum effects in the constituent 'artificial atoms' with the electromagnetic field modes in the system. The theoretical investigation of these structures demonstrated that a number of new effects (such as quantum birefringence, strongly nonclassical states of light, etc) are to be expected, prompting the efforts on their fabrication and experimental investigation. Here we provide a summary of the principal features of quantum me…
We propose novel quantum antennas and metamaterials with strong magnetic response at optical frequencies. Our design is based on the arrangement of natural atoms with only electric dipole transition moments at distances smaller than a wavelength of light but much larger than their physical size. In particular, we show that an atomic dimer can serve as a magnetic antenna at its antisymmetric mode to enhance the decay rate of a magnetic transition in its vicinity by several orders of magnitude. Furthermore, we study metasurfaces composed of atomic bilayers with and without cavities and show that…
Optics of metamaterials is shown to provide interesting table top models of many non-trivial space-time metrics. The range of possibilities is broader than the one allowed in classical general relativity. For example, extraordinary waves in indefinite metamaterials experience an effective metric, which is formally equivalent to the "two times physics" model in 2+2 dimensions. An optical analogue of a "big bang" event is presented during which a (2+1) Minkowski space-time is created together with large number of particles populating this space-time. Such metamaterial models enable experimental …
We examine the optical properties of two different configurations of a cylindrical device made from a hyperbolic metamaterial with optical axis defined by circular and radial director fields. The hyperbolic metamaterial is an uniaxial anisotropic medium for which the ratio between ordinary and extraordinary permittivities is negative, leading to a particular effective geometry with two timelike coordinates in the metric (Kleinian signature). By using differential geometry tools we are able to perform a comparison between a simple geometrical optics treatment and the wave formalism that shows t…
This letter discusses the importance of the nature of local fields inside a unit cell of optical metamaterials in developing a valid effective medium theory. In particular, we apply the Meier-Wokaun procedure to derive a corrected version of the Maxwell-Garnett formula for the refractive index of a medium composed by metallic rods with subwavelength cross-section. We compare this result with the values obtained using the full mode analysis calculated via numerical simulations and analyze the impact of surface plasmon polaritons in adequately determining the effective refractive index of the me…
Harnessing artificial optical magnetism requires rather complex two- and three-dimensional structures, examples include split-ring and fishnet metamaterials and nanoparticles with non-trivial magnetic properties. By contrast, dielectric properties can be tailored even in planar and pattern-free, one-dimensional (1D) arrangements, for example metal/dielectric multilayer metamaterials. These systems are extensively investigated due to their hyperbolic and plasmonic response, which, however, is considered to be limited to TM polarization, based on the general consensus that they do not possess in…
Carefully designed nanostructures can inspire new type of optomechanical interactions and allow surpassing limitations set by classical diffractive optical elements. Apart from strong near-field localization, nanostructured environment allows controlling scattering channels and might tailor many-body interactions. Here we investigate an effect of optical binding, where several particles demonstrate a collective mechanical behaviour of bunching together in a light field. In contrary to classical binding, where separation distances between particles are diffraction limited, an auxiliary hyperbol…
In this paper, we derive a model from Maxwell equations for the magnetic resonance of split-ring resonators. Using this model we revisit the scaling of split-ring resonators. Inspired by our model, we propose a new type of split-hybrid metal-dielectric ring resonator, of which the ring is made composed of moderately high index dielectric material (e.g. SiC, TiO2, ZnS) (for the major portion), while and metal (e.g. Ag) fills the gap. Such a new magnetic metamaterial is able to overcome the saturation problem of split-ring resonatorssaturation-free and therefore is able to operate at short wavel…
We present an analytical description of the nonlocal optical response of plasmonic nanowire metamaterials that enable negative refraction, subwavelength light manipulation, and emission lifetime engineering. We show that dispersion of optical waves propagating in nanowire media results from coupling of transverse and longitudinal electromagnetic modes supported by the composite and derive the nonlocal effective medium approximation for this dispersion. We derive the profiles of electric field across the unit cell, and use these expressions to solve the long-standing problem of additional bound…
The quantum optics of metamaterials starts with the question whether the same effective-medium theories apply as in classical optics. In general the answer is negative. For active plasmonics but also for some passive metamaterials, we show that an additional effective-medium parameter is indispensable besides the effective index, namely the effective noise-photon distribution. Only with the extra parameter can one predict how well the quantumness of states of light is preserved in the metamaterial. The fact that the effective index alone is not always sufficient and that one additional effecti…
We demonstrate that use of the field effect to tune the effective optical parameters of a layered hyperbolic metamaterial leads to topological transitions in its dispersion characteristics in the optical regime. Field effect gating electrically modulates the permittivity in transparent conductive oxides via changes in the carrier density. These permittivity changes lead to active extreme modulation of ~200% of the effective electromagnetic parameters along with active control of the anisotropic dispersion surface of hyperbolic metamaterials and enable the opening and closing of photonic band g…
In this paper we employ the emerging paradigm of physics-informed neural networks (PINNs) for the solution of representative inverse scattering problems in photonic metamaterials and nano-optics technologies. In particular, we successfully apply mesh-free PINNs to the difficult task of retrieving the effective permittivity parameters of a number of finite-size scattering systems that involve many interacting nanostructures as well as multi-component nanoparticles. Our methodology is fully validated by numerical simulations based on the Finite Element Method (FEM). The development of physics-in…
Precise control and manipulation of optical fields on a nanoscale is one of the most important and challenging problems in "nanophotonics". Since optical wavelength is on a much larger microscale, it is impossible to employ conventional focusing for that purpose. We show the strong optically-induced interactions between discrete meta-molecules in a metamaterial system and coherent monochromatic continuous light beam with a spatially-tailored phase profile can be used to prepare a sub-wavelength scale energy localization. Well isolated energy hot-spots as small as $λ/10$ can be created and posi…
We present a theoretical analysis of the nonlinear response of a metamaterial consisting of an array of split ring resonators coupled to a two level atomic system (2LS) without inversion. We calculated the total complex susceptibility and the linear, third and fifth-order nonlinear solution of the Maxwell Bloch equations that describe the coupled system. We analyzed the impact of the nonlinear effects on the dynamics of an active metamaterial/2LS compound in dependence of the magnitude of the external electric field when the 2LS is pumped by an external pump source and population inversion is …
We investigate the modulational instability and time-domain dynamics of nonlinear magnetic metamaterials composed of coupled split-ring resonators loaded by Kerr nonlinearity. Our results indicate that the recently proposed optical switching of local optical index based on uniform-response assumption seems fragile. We conceive two alternative schemes to utilize the valuable enhanced non- linearity, one is to focus on few-body systems and directly make use of the modulational instability (e.g., an optical comparator design), the other is to consider global switching arising from global feedback…
Ultraviolet (UV) electro-optic modulation system based on graphene-plasmonic metamaterials nanomechanical system (NEMS) with superlubricity is investigated. Due to the strong optical absorption intensity of graphene in the UV region and the combination of metamaterial structure based on surface plasmons, the modulation depth of the UV NEMS electro-optic modulator approaches as high as 8.5 times compared to the counterpart modulator in visible light region. Meanwhile, the superlubricity significantly reduces the power consumption of the UV electro-optic modulation system due to its extremely lo…
Most applications of memory effects in disordered optical media, such as the tilt-tilt and shift-shift spatial correlations, have focused on imaging through and inside biological tissues. Here we put forward a metamaterial platform not only to enhance but also to tune memory effects in random media. Specifically, we investigate the shift-shift and tilt-tilt spatial correlations in metamaterials composed of coated spheres and cylinders by means of the radiative transfer equation. Based on the single-scattering phase function, we calculate the translation correlations in anisotropically scatteri…
Materials showing electromagnetic properties that are not attainable in naturally occurring media, the so called metamaterials, have been lately, and still are, among the most active fields in optical and materials physics and engineering. Among those properties, one of the most attractive is the sub-diffraction resolving capability predicted for media having index of refraction of -1. Here we propose a fully 3D, isotropic metamaterial with strong electric and magnetic responses in the optical regime, based on spherical metallo-dielectric core-shell nanospheres. The magnetic response stems fro…
Strongly anisotropic media where the principal components of electric permittivity or magnetic permeability tensors have opposite signs are termed as hyperbolic media. Such media support propagating electromagnetic waves with extremely large wavevectors exhibiting unique optical properties. However in all artificial and natural optical materials studied to date, the hyperbolic dispersion originates solely from the electric response. This restricts material functionality to one polarization of light and inhibits free-space impedance matching. Such restrictions can be overcome in media having co…
We present the design, fabrication, and measured performance of metamaterial Anti-Reflection Cuttings (ARCs) for large-format alumina filters operating over more than an octave of bandwidth to be deployed on the Simons Observatory (SO). The ARC consists of sub-wavelength features diced into the optic's surface using a custom dicing saw with near-micron accuracy. The designs achieve percent-level control over reflections at angles of incidence up to 20$^\circ$. The ARCs were demonstrated on four 42 cm diameter filters covering the 75-170 GHz band and a 50 mm diameter prototype covering the 200-…
The extraordinary properties of resonant four-wave mixing of backward waves in doped negative-index materials are investigated. The feasibility of independent engineering of negative refractive index and nonlinear optical response as well as quantum control of the nonlinear propagation process in such composites is shown due to the coherent energy transfer from the control to the signal field. Laser-induced transparency, quantum switching, frequency-tunable narrow-band filtering, amplification, and realizing a miniature mirrorless optical parametric generator of the entangled backward and ordi…
We consider plasmonic nanoantennas immersed in active host medium. Specifically shaped metal nanoantennas can exhibit strong magnetic properties in the optical spectral range due to the excitation of Magnetic Plasmon Resonance (MPR). A case when a metamaterial comprising such nanoantennas can demonstrate both "left-handiness" and negative permeability in the optical range is considered. We show that high losses predicted for optical "left- handed" materials can be compensated in the gain medium. Gains required to achieve local generation in such magnetic active metamaterials are calculated for…
In recent years, a range of reconfigurable metamaterials controlled with thermal, electric, magnetic and optical signals have been developed for dynamically manipulating the intensity, phase and wave-front of electromagnetic radiation across the broad electromagnetic spectrum ranging from microwave to optics. Here for the first time, we demonstrate a reconfigurable metasurface performing exclusive OR (XOR) logical operation using two independent control electrical inputs and an optical read-out in the form of far-field Fano intensity states at terahertz wavelengths. At the same time, the near …
Propagation of light in a metamaterial medium which mimics curved spacetime and acts like a black hole is studied. We show that for a particular type of spacetimes and wave polarization, the time dilation appears as dielectric permittivity, while the spatial curvature manifests as magnetic permeability. The optical analogue to the relativistic Hamiltonian which determines the ray paths (null geodesics) in the anisotropic metamaterial is obtained. By applying the formalism to the Schwarzschild metric, we compare the ray paths with full-wave simulations in the equivalent optical medium.
We propose to use molecular picocavity ensembles as macroscopic coherent nonlinear optical devices enabled by nanoscale strong coupling. For a generic picocavity model that includes molecular and photonic disorder, we derive theoretical performance bounds for coherent cross-phase modulation signals using weak classical fields of different frequencies. We show that strong coupling of the picocavity {\it vacua} with a specific vibronic sideband in the molecular emission spectrum results in a significant variation of the effective refractive index of the metamaterial relative to a molecule-free s…
Photonic metamaterials with properties unattainable in base materials are already beginning to revolutionize optical component design. However, their exceptional characteristics are often static, as artificially engineered into the material during the fabrication process. This limits their application for in-operando adjustable optical devices and active optics in general. Here, for a hybrid material consisting of a liquid crystal-infused nanoporous solid, we demonstrate active and dynamic control of its meta-optics by applying alternating electric fields parallel to the long axes of its cylin…
