In the area of metamaterial research, it is frequently assumed that effective medium parameters provide all the information necessary to determine the light-matter interaction. But even if the effective medium parameters can describe faithfully how the material can manipulate wave in the long wavelength limit, can the same set of parameters describe faithfully how the wave can manipulate the material? It is known that the total electromagnetic induced force acting on a metamaterial can be calculated using the Maxwell stress tensor if the light scattering property of the metamaterial can be described by standard effective medium parameters. However, we show that the optical stress inside a metamaterial systems cannot be determined by the information of effective permittivity and permeability and it can only be correctly calculated using the Helmholtz stress tensor which takes into account of electrostrictive and magnetostrictive effects. Using multiple scattering theory, we derived for the first time the analytical formulas for electrostrictive/magnetostrictive tensors for two dimensional all dielectric metamaterial systems, which are found to depend explicitly on the symmetry of the underlying lattice of the metamaterial as well as a local effective wave vector. These analytical results enable us to calculate light-induced body forces inside a composite system using the Helmholtz stress tensor within the effective medium formalism in the sense that the fields used in the stress tensor are those obtained by solving the macroscopic Maxwell equation with the microstructure of the metamaterial replaced by an effective medium. The optical stress induced by an external light source at the boundary of two metamaterials is also subtle. We investigate the optical stress induced at the interface formed by two kinds of metamaterials and it is found that the stress is strongly affected by the electrostriction and magnetostriction effects. We show that the symmetry of the underlying lattice can dramatically influence interface stress to the extent the optical stress in the interfacial area is in fact "indeterminate", in the sense for given values of effective permittivity and permeability, the interfacial stress is unknown unless we know the microscopic details or their manifestations through electrostrictive tensors. Related to this problem, we find that light in a negative-index material background in general does not pull an object immersed in it.

Metamaterials bring subwavelength resonating structures to overcome the limitations of conventional matter. The realization of active metadevices requires electrically reconfigurable components operating over a broad spectrum with a wide dynamic range. The existing capability of metamaterials, however, is not sufficient to realize this goal. Here, using large area graphene capacitors incorporated with metallic split ring resonators, we demonstrated electrically controlled metadevices on large-area flexible substrates. In this device architecture, metallic resonators are capacitively coupled to the graphene electrodes that introduce voltage-controlled dissipation. Electrostatic tuning of charge density on graphene in the order of 10¹⁴ cm^-2 enabled us to switch the resonance behavior of the split ring resonators by 50 dB with an operation voltage of 2V. Large modulation depth, simple device architecture, and mechanical flexibility are the key attributes of the graphene-enabled metadevices that could find a wide range of applications ranging from active signal processing to switchable cloaking.

As natural chiral materials demonstrate limited circularly dichroic contrasts, enhancement of these polarization dependent signals has long been the focus of chiral metamaterial research. By manipulating the geometric chirality of resonant plasmonic nanostructures, we are capable of enhancing light confinement to amplify chiral modified, nonlinear signals from quantum emitters. The metamaterial demonstrates a linear transmission contrast of 0.5 between left and right circular polarizations and a 20× contrast between second harmonic responses from the two incident polarizations. Nonlinear and linear response images probed with circularly polarized lights show strongly defined contrast. As a second set of experimentation, the chiral center of the metamaterial is opened, providing direct access to place emitters to occupy the most light-confining and chirally sensitive regions. The resulting two-photon emission profiles from circularly polarized excitation displays mirrored symmetry for the two hybrid enantiomer structures. The efficiency of the nonlinear signal directly correlates to the chiral resonance of the linear regime. The nonlinear emission signal is enhanced by 40× that of the emitters not embedded in the metamaterial and displays a 3× contrast for the opposite circular polarization. Such manipulations of nonlinear signals with metamaterials open pathways for diverse applications where chiral selective signals are monitored, processed, and analyzed.

Tunable optical metamaterials and metasurfaces are an emerging frontier, with promising applications including optical modulation, routing, and beam steering. Dynamic control in such meta-devices can be achieved by incorporating active media, e.g. liquid crystals or phase change materials, into the optical structures. Vanadium dioxide (VO₂), a prototypical phase change material, has a thermally induced insulator-metal transition that results in a considerable change in its optical properties. It has been shown that the complex refractive index of VO₂ changes drastically during phase transition.
Here we demonstrate tunable metasurfaces created using defect engineering via ion irradiation through lithographically defined masks, which locally modifies the phase transition properties on a subwavelength scale. Our metasurfaces consist of irradiated and unirradiated (intrinsic) VO₂ regions in a square checkerboard arrangement on a sapphire substrate. The phase transition properties of the metasurface are determined by the ion fluence and the duty cycle of the irradiated regions. Naively one might expect the reflectance of our metasurface to be the average of the reflectance values of the irradiated and intrinsic VO₂. Instead we observe an effective response of the metasurfaces, with an “effective phase transition temperature” between the phase transition temperature of the irradiated and intrinsic VO₂. This is due to the subwavelength nature of our patterned features. Hence we can treat the patterned VO₂ film as an effective medium which has a well-defined temperature- and wavelength-dependent complex refractive index. We apply effective medium theory to model the behavior of our metasurfaces, and observe good agreement with the experimental results. By combining defect engineering with electron-beam lithographic patterning techniques, we can design effective media with engineered anisotropy and gradient indices. Our approach will be broadly applicable to the development of tunable optical meta-devices.

We report on the realization of ultrathin free-standing all-dielectric metasurfaces, with sharply resonant optical properties in the near-infrared (telecoms) wavelength range, in which the optical forces generated among constituent elements are sufficient to induce reversible nanoscale structural deformation. With mechanical Eigenfrequencies in the hundreds of megahertz range, the optomechanical response of such structures provides for fast, strongly nonlinear tuning of optical properties at µW/µm² intensities.

We present a novel methodology to implement metasurfaces that realize the optical properties of chiral media which possess differential operation with respect to left- (LCP) and right-circular polarization (RCP). Chirality is very recurrent in biological media and organic compounds. These compounds have molecules which don&’t superimpose onto their mirror image lifting the degeneracy between LCP and RCP causing the chiroptical response. Thus, generating and sensing optical chirality is valuable to stereochemistry and molecular biology in addition to its electrodynamic applications. However, the chiroptical effect is generally weak in natural crystals and detectable only when strong phase differences between LCP and RCP accumulate over a long optical path. Strong chiroptical effects have been demonstrated in metamaterials using 3D nano-structures with broken mirror symmetry. Yet, they are complicated to implement because they require fabrication of multi-layers with angular rotations of nano-structures along successive layers. Here, we present a simplistic and efficient technique to produce chiroptical effects with gap-plasmonic metasurfaces. A planar array of metallic antennas is fabricated on top of a metallic film reflector and spaced by a dielectric layer. The metal\dielectric\metal sandwich excites slow gap-plasmonic waves that cause a significant phase and polarization change to the back-reflected beam. As a result of antennas&’ anisotropy, the metasurface responds differently to RCP and LCP. Through introducing a phase-shift between the reflected LCP and RCP components of light, the metasurface performs the chiral response of rotating polarization angle (PA) around propagation direction. We implement two metasurfaces that rotate PA of linearly polarized light by 45⁰and -45⁰, respectively. The structure doesn&’t require using complex chiral antennas. We use simple rectangular antennas, and the chiral response is obtained through superposition of reflected beam from a 16-antennas supercell by careful design of location and orientation of each antenna. We obtain a chiral effect that depends on the supercell structure rather than the properties of composite materials. Therefore, the operation is very tolerant against fabrication inaccuracies and\or temperature effects, and high quality results are experimentally obtained. Thus, gap-plasmonic metasurfaces can provide simple, compact and efficient technology for applications include bio-sensing, DNA structural analysis, crystallography, and secure quantum communications.

Symmetries play a fundamental role in physics and devices physics. In this talk, I will discuss the fundamental role of symmetries at the nanoscale resonant level in constructing nanophotonics optical devices. I will in particular discuss the possibility to construct new optical modes that do not decay despite residing the continuum of radiation modes. These modes, called bound states in the continuum, are very peculiar modes with topological properties that can enhance the functionality of nanophotonics optical devices. Their design, fabrication and characterization will be presented.

Metamaterials are artificial media that produce optical phenomena not present in naturally occurring materials. However, three-dimensional (3D) metamaterials suffer from extreme propagation losses, limiting their utility. Two-dimensional (2D) metasurfaces and, in particular, hyperbolic metasurfaces (HMSs) for propagating surface plasmon polaritons, have the potential to alleviate this problem. Because SPPs are guided at a metal-dielectric interface (rather than passing through metals), these HMSs have been predicted to have lower loss while still exhibiting phenomena observed in 3D metamaterials.
We report the first experimental realization of a hyperbolic metasurface [1] formed by lithography and etching nanostructures into sputter-deposited, single-crystalline silver films. The resulting devices display broadband negative refraction and diffraction-free propagation. Additionaly, we find that the HMS exhibits strong, dispersion-dependent spin-orbit coupling, enabling polarization- and wavelength-dependent routing of chiral SPPs. Because we begin with extremely low-loss silver films[1,2], the measured propagation distances of up to 30 mu;m in the HMS shows that the 2D nature of our devices coupled with the single-crystalline silver films offers a substantial, one to two orders of magnitude improvement over 3D metamaterials. These results provide tools for implementing high-performance plasmonic nanostructures with widespread conventional and quantum optics applications.
[1] Alexander High*, Robert C. Devlin*, Alan Dibos, Mark Polking, Dominik S. Wild, Janos Perczel, Nathalie P. de Leon, Mikhail D. Lukin and Hongkun Park. Visible-frequency hyperbolic metasurface. Nature522, 192-196 (2015). *equal contribution.
[2] S. Kolkowitz*, A. Safira*, A. A. High, R. C. Devlin, S. Choi, Q. P. Unterreithmeier, D. Patterson, A. S. Zibrov, V. E. Manucharyan, H. Park, M. D. Lukin. Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit. Science347, 1129 (2015)

Optical metamaterials are being exploited to manipulate light on the nanoscale but integrating such metamaterial structures with a nanoscale source such as a quantum dot (QD) to gain integrated multiple functions such as enhancement of QD excitation and/ or emission rates and directing the emitted photons on to a waveguide in an on-chip optical system remains a challenge. Past efforts have been largely focused on individual functions such as: (i) enhancement of excitation and/ or emission rates via incorporation of the QD in a photonic cavity [1];(ii) guiding of the emitted photons via appropriate placement of the QD by an antenna[2] directed towards (iii) a lossless waveguide[3]. Here we propose and analyze a novel design that incorporates these multiple functions simultaneously at multiple wavelengths into an architecture comprising a QD in a coupled dielectric nanoparticle resonator based optical circuit.
We realize these multiple functions by tailoring the wavelengths of the magnetic and electric multipole modes in high index dielectric nanoparticles as a function of size, shape and material parameters to control their coupling to the electronic states in the QD at the designed excitation and emission wavelengths. The optical response of the system is analytically modeled using the multipole expansion method [4] based on classical electromagnetism. We present specific results for a system comprising TiO₂ nanoparticle optical resonators and a QD excited at 532nm and emitting at 980nm. The nanoparticle radius and separations are chosen such that the magnetic hexapole (TE_3,1) mode is in resonance at the excitation wavelength of 532nm to provide local electric field enhancement at the QD while simultaneously the magnetic dipole (TE_1,1) and electric dipole (TM_1,1) modes are in resonance at the QD emission at 980nm to provide guiding. In this case we find a 20-25 fold enhancement of electric field intensity at the QD at the excitation wavelength along with simultaneous Purcell enhancement, guiding and on-chip lossless propagation at the emission wavelength. The different functionalities in our design show sufficient robustness with respect to fabrication tolerances such as nanoparticle positions which, along with the inherent lossless nature of the dielectric material makes the design suitable for scaling. Our generic analysis of the multipole resonances and light-matter interactions makes this approach readily applicable to optimization of dielectric materials and architectures relevant to optical and other wavelength regimes.
References
[1] S. Buckley et.al. Rep. Prog. Phys. 75, 126503 (2012).
[2] A. E. Krasnok et.al. Optic Express 20, 20599 (2012).
[3] A. Yariv, et.al. Optic Letters 24,11 (1999).
[4] J. M. Gerardy et.al. Phys. Rev. B 25, 6 (1982).

New apertured and apertureless methods will be described with relationship to the excitation and detection of dark and bright surface plasmon polaritons. The methods are based on interrogating meta surfaces with multiple probes. As has been very elegantly demonstrated by Xifeng Ren et al, [Applied Physics Letters 98, 201113 (2011)] an apertured Near-field Scanning Optical Microscopy (NSOM) probe acts as a point source of surface plasmon polaritons with a deterministic position and minimum requirement for the light source. On the other hand Dobman et al, [Adv. Optical Mater. 2014, DOI: 10.1002/adom.201400237 ] have shown that a second type of bound surface plasmon polariton, that cannot be excited from the far-field, propagates well across a metasurface. Such a bound plasmon polariton can only be excited, if light is used, from a near-field probe which produces all k vectors. Furthermore, point excitation of plasmons without background light and with all k vectors and all energies also will be reported using tunneling probes incorporated into a multiprobe system with scattering or collection NSOM for mapping the transport of plasmon polariton propagation on a variety of meta surfaces. All of these probes are constructed to allow for contact of one probe with another which is readily accomplished.

Photonic gradient metasurfaces are ultrathin electromagnetic wave-molding metamaterials that provide a route for realizing flat optics. Recently, we reported on a novel class of metasurfaces - spinoptical metamaterials - which gives rise to a spin-controlled dispersion due to the optical Rashba effect. The optical spin as an additional degree of freedom offers controlled manipulation of spontaneous emission, absorption, scattering, and surface-wave excitation. Spin-symmetry breaking in nanoscale structures caused by spin-orbit interaction, leading to a new branch in optics - spinoptics is presented. The spin-based effects offer an unprecedented ability to control light and its polarization state in nanometer-scale optical devices, thereby facilitating a variety of applications related to nano-photonics. However, the up-to-date metasurface design, manifested by imprinting the required phase profile for a single, on-demand light manipulation functionality, is not compatible with the desired goal of multifunctional flat optics. Here, we report on a generic concept to control multifunctional optics by disordered (random) gradient metasurfaces with a custom-tailored geometric phase. This approach combines the peculiar ability of random patterns to support extraordinary information capacity, and the polarization helicity control in the geometric phase mechanism, simply implemented in a two-dimensional structured matter by imprinting optical antenna patterns. By manipulating the local orientations of the nanoantennas, we generate multiple wavefronts with different functionalities via mixed random antenna groups, where each group controls a different phase function. Disordered gradient metasurfaces broaden the applicability of flat optics as they offer all-optical manipulation by multitask wavefront shaping via a single ultrathin nanoscale photonic device.

On-chip metamaterials with a refractive index of zero shows extreme physical properties such as infinite phase velocity and wavelength. It also has several potential integrated-photonics-related applications including super-couplers, surface emitting lasers, and phase-mismatch-free nonlinear optics. Silicon-on-insulator (SOI) platform received much attention recently due to its compatibility with complementary metal-oxide-semiconductor (CMOS) technology, which makes the mass production of photonic devices reliable. Current implementations of on-chip SOI-based zero-index metamaterials involve either metallic structures or high aspect-ratio silicon pillars, which require many processing steps, and is complicated to integrate with other photonic devices on a standard SOI wafer. Additionally, metamaterials involving metallic structures cost highly.
Here, we design an on-chip zero-index metamaterial consisting of square array of air-holes in the 220-nm thick top-silicon layer of a standard SOI wafer. This structure can be fabricated through the single-step E-beam lithography and fully-etching, which reduces the processing steps and the fabrication difficulties significantly.
Simulated effective permittivity and permeability cross zero simultaneously and linearly at the design wavelength of 1550 nm, with a finite effective impedance. Computed band structure shows that this epsilon-and-mu-zero behavior corresponds to a Dirac-cone dispersion at the center of the Brillouin zone (Gamma point), indicating a relatively isotropic zero index. This Dirac-cone dispersion is formed by the degeneracy between a quadrupole mode and two degenerate dipole modes at the Gamma point. All these results indicate that the zero index of this metamaterial is low-loss, isotropic and with a good impedance matching to free space and standard optical waveguides.
To directly demonstrate the zero index of this metamaterial, we plan to measure the refraction of a prism made of this metamaterial. We also plan to retrieve the complex index and impedance of the metamaterial from the complex transmission and reflection coefficients measured using on-chip Mach-Zehnder-interferometer-based setups.
In conclusion, we demonstrate an on-chip CMOS-compatible all-dielectric metamaterial with a low-loss, isotropic, and impedance-matched zero index at 1.55 um.

When an array of small metallic particles is embedded into a dielectric matrix one should expect a pole in the polarizability of the medium at certain energy, when the negative real part of the dielectric function of the metal compensates the double value of the positive real part of the dielectric function of the surrounding dielectric material. This gives rise to so called Froehlich resonance in the optical properties of such metamaterial.
We investigated a resonance in optical absorption, which originates from localized plasmon excitations in a self-organized system of metal AsSb nanoparticles embedded in a semiconductor AlGaAs matrix.
The AsSb-GaAlAs metamaterial was produced by a low-temperature molecular-beam epitaxy on the (001) GaAs substrates followed by a high-temperature annealing. Our transmission electron microscopy study revealed a system of almost spherical AsSb inclusions in the crystalline AlGaAs matrix. The diameter of the inclusions was 4-7, 5-8 and 6-9 nm after annealing at 400, 500 and 600C, correspondingly. The filling factor was constantly 0.17%.
The Froehlich plasmon resonance in our metamaterial was revealed at 1.48 eV with a bandwidth of 0.18 eV. The absorption coefficient within the resonant band was as large as 9000 cm-1. No significant changes in the parameters of the resonance have been observed for different particle sizes, which is consistent with Mie scattering theory. In theoretical calculations we used well documented data for the dielectric properties of AlGaAs and Drude model for the electron system of the metal AsSb nanoinclusions. A reasonably good description was achieved with plasmon resonance energy of 7.38 eV and damping time of 3 fs in bulk AsSb, which were fitting parameters of the model.

Relative placement of nanoparticles allows for fine-tuning of plasmonic, electronic, and magnetic interactions at the nanoscale. DNA-programmable assembly is a powerful means for controlling nanoparticle placement in extended crystalline materials imparting independent control over lattice size, spacing, and composition. Investigations into light-programmable matter interactions of these nanoparticle assemblies demonstrate great promise for engineering three-dimensional metamaterials by utilizing the precise materials tunability of this technique. However, these nanoparticle superlattices previously existed either as mu;m-scale aggregates or epitaxially grown structures bound to a substrate.
The desire to integrate these nanoparticle assemblies into higher order constructs has led to the investigation of transferable nanoparticle superlattice materials. We describe a novel method for synthesizing freestanding and transferrable nanoparticle superlattice sheets made through DNA-programmable techniques to flat, curved, or dimpled substrates without sacrificing the control over lattice symmetry and parameter afforded by the DNA-programmable technique. Grazing incidence small angle X-ray scattering and optical spectroscopy studies performed on these novel materials suggest preservation of nanoparticle superlattice ordering through the sheet synthesis process as well as large area uniformity. Moreover, these remarkable silica-embedded structures can withstand harsh chemical, physical, and mechanical conditions—an important discovery that will likely increase their utility.
This technique will provide an avenue for researchers to consider using such nanoparticle superlattices for a wide variety of sensor, cloaking, and light manipulating studies and devices.

In 2006 we introduced the concept of epsilon-near-zero (ENZ) structure and its supercoupling effects [M. G. Silveirinha and N. Engheta, “Tunneling of Electromagnetic Energy through Sub-Wavelength Channels and Bends Using Epsilon-Near-Zero (ENZ) Materials”, Phys. Rev. Lett., 97, 157403 (2006). Since then numerous properties of ENZ materials have been investigated extensively, and also expanded to include other extreme scenarios. One of the interesting paradigms of such extreme metamaterials are the structures in which the relative permeability attains near-zero values, while the permittivity exhibits conventional positive values. Such engineered mu-near-zero (MNZ) materials offer an interesting platform for wave-matter interaction with exciting features. In the present work, we show, both theoretically and experimentally in the microwave domain, how the supercoupling phenomenon between highly mismatched waveguide sections is different from that of the ENZ scenario. One major difference is the required height of the MNZ transition channel, which needs to be disproportionaly wider than the height of the input and output waveguides, contrary to the ENZ case where the ENZ channel had to be much narrower. Importantly, in the MNZ regime the electromagnetic field in the channel is dominantly magnetic. This offers an interesting possibility for tailoring and enhancing the radiation by small magnetic emitters, which is usually weaker than that of electric dipole emitters for which the ENZ structure is suitable. We will present our theoretical results and experimental verification of the MNZ supercoupling effects using the microwave waveguides with the transition region constructed to exhibit MNZ response. There are other intringuing features specific to the MNZ structures, which will be discussed in the presentation.

Metamaterials have become one of the most exciting fields in optics due to their exotic optical properties and important applications that are not attainable from naturally occurring materials. In particular, broken symmetry in metamaterials can lead to extremely strong effects of anisotropy (broken rotational symmetry), chirality and bianisotropy (broken mirror symmetry), which go far beyond the properties of nature materials. In this talk, I will show that by combining chirality with strong anisotropy, new topological order emerges in metamaterials leading topologically protected photonic surface states that are immune from scattering by defects and sharp edges. In addition, I will talk about our recent works on optical metasurfaces, a new type of structured surfaces showing well controlled abrupt phase discontinuities for circularly polarized incident light arising from Berry phase. A number of novel device applications have been realized based on the Berry phase metasurfaces: a dual polarity metalens that can functions either as a convex or a concave lens, a helicity switchable unidirectional surface plasmon polariton coupler, and high definition, high efficiency holograms. Finally, I will show that extending the concept of Berry phase to harmonic generations can lead to continuous phase control over the local nonlinear polarizability, which goes beyond the conventional poling technique that only manipulate the sign of the nonlinear coefficient, i.e. binary phase profile.

Optical metamaterials provide novel ways of manipulating light, allowing effects such as negative refraction,¹ optical phase tuning,² off-specular reflection following generalized Snell-Descartes laws,² enhancement of the quantum yield of light emitters and tuning of their radiation spectrum and pattern,³ near-perfect optical absorption,⁴ topological optical darkness.⁵ These optical meta-effects open the way to the development of lightweight and ultracompact photonic solutions including: flat optical components, data encryption media, integrated high efficiency lighting and optically-monitored sensors.
Most of the existing optical metamaterials operate in the near infrared to radiofrequency range and are based on noble metal plasmonic structures. Making them suitable for the visible or ultraviolet ranges is a still challenging task, since it demands a nanoscale structuration at the limit of lithography techniques. In addition, tomorrow&’s photonic solutions appeal at the development of the so-called “reconfigurable metamaterials”⁶ presenting reversibly switchable optical meta-effects under external excitation. Achieving reconfigurability together with optical meta-effects in the visible and ultraviolet requires to identify and properly assemble nano-elements, beyond the rather inert noble metals and even beyond plasmonic elements.
In this presentation, we first identify the most promising non-conventional nano-elements for building reconfigurable metamaterials at visible and ultraviolet frequencies. We make a special emphasis on those whose dielectric function is sensitive to external parameters (light, magnetic field, heat, pressure, chemical agentshellip;). Among them, semi-metallic nano-elements (Bi, Ga, Sb) are especially relevant due to: i) their solid-liquid phase transition that can be activated by thermostatic, laser, Joule or plasmonic heating, ii) the strong dielectric contrast between the solid interband polaritonic phase and liquid plasmonic phase in the ultraviolet and visible. We focus the second part of the presentation on the demonstration of optical meta-effects and reconfigurability in metamaterials built from nano-Bi.
1 Naik, G. et al.; Demonstration of Al:ZnO as a plasmonic component for near-infrared metamaterials. PNAS 2011, 109, 8834
2 Yu, N. et al.; Light propagation with phase discontinuities: Generalized laws of reflection and refraction. Science 2011, 334, 333
3 Yang, T.B. et al.; Real-time tunable lasing from plasmonic nanocavity arrays, Nature Comm.2015, 6, 1-7
4 Hägglund, C. et al.; Self-Assembly Based Plasmonic Arrays Tuned by Atomic Layer Deposition for Extreme Visible Light Absorption, Nano Lett., 2013, 13, 3352
5 Kravets, V.G. et al.; Singular phase nano-optics in plasmonic metamaterials for label-free single-molecule detection. Nature Mater. 2013, 12, 304
6 Turpin, J.; Reconfigurable and tunable metamaterials: a review of the theory and applications, Int. Journ. Ant. Prop. 2014, 429837

Metamaterials, designed composite structures with unprecedented properties and applications, have emerged as a new frontier of science and technology. As the properties of metamaterials are primarily from their structures rather than their chemical constituents, controlling geometrical effects such as symmetry and spatial arrangements play fundamental roles in metamaterials research. Metamaterial with designed symmetry that can be realized by top-down fabrication methods such as lithography, but often result in planar and small-scale metamaterials. In contrast, self-assembly approaches, may offer advantages of large scalability and cost effectiveness. However, there are significant challenges in achieving controlled assembly symmetries of metamaterials in large scale due to constraints of thermodynamics and crystal lattice mismatching between designed composites. Here we show a scalable synthesis route that enables high level control of spatial assembly symmetries, creating large-scale metamaterials with desired properties. Combing optical physics and materials chemistry, we demonstrate scalable assembly of non-trivial broken symmetries in metamaterials by optical feedback strategy. Moreover, by rational engineering symmetry configurations and coupling of unit cells, three dimensional (3D) isotropic optical negative index metamaterials can be scalable fabricated that is of paramount importance for applications such as superlens and transformation optics. Our method not only offers a scalable and sustainable manufacturing technique for 3D metamaterials, but also provides a platform for studying symmetry-based physics and applications.

Planar metal/dielectric multilayer geometries provide a unique platform to engineer the dispersion of light in many different ways. We present a novel geometry to realize a flat lens composed of a single-periodic metal/dielectric multilayer stack. We use the hyperbolic dispersion of a multilayer composed of very thin layers as a starting point, and gradually increase the layer thicknesses. We find that fully angle-independent dispersion can be achieved (wavelength 354 nm) for a multilayer composed of 53 nm silver and 25 nm titanium dioxide films, characterized by an omnidirectional negative refractive index n=-1.
Confocal and near-field microscopy show that such a thin multilayer slab acts as a flat lens, with unique features such as a submicron thickness, the absence of an optical axis and a lens-image separation of only 350 nm. The experimental data are in good agreement with analytical Green&’s tensor calculations of the focus profile above the metamaterial lens. We use analytical field calculations to calculate the direction of the Poynting vector, taking into account losses and dispersion, and find that the unit-cell and time-averaged Poynting vector of all individual harmonics of the Bloch wave are oriented in the same direction. The image is formed by the coherent superposition of refracted light from multiple harmonics in the metamaterial.
We show that by replacing the Ag layer by a transparent conducting oxide film the lens can be made to operate anywhere in the UV, visible, and near-IR spectral range. Specifically, we show that using aluminium-doped ZnO a flat lens can be made operating in the infrared telecom range near 1.5 micron. The electrical tunability of the focusing characteristics will be presented as well. The new design presented here provides the simplest flat lens geometry proposed to date.
Inspired by the versatility and elegance of the multilayer design, we present a dielectric multilayer material that serves as anti-reflection coating for stratified media, by matching the modal field profiles across the interface, thus solving the impedance matching problem often found with layered metamaterials. We then show how a dielectric multilayer structure can act as an angular filter, which can be used to control the emission characteristics of a light-emitting diode. Finally, we show how a layered metamaterial combined with a special cavity design creates a wave-attracting cavity resonance at optical frequencies. We show that for circularly polarized light the plasmonic spin-Hall effect can be exploited to achieve a deterministic wave attractor for light emitters in the cavities&’ near field

Plasmonics, which offers unparalleled capability for light confinement and guiding at the sub-wavelength scale, is an emerging technology for realization of compact devices for a wide range of applications in biosensing, energy conversion, nanofabrication, nanoscale resolution imaging and enhancement of spontaneous emission. Advances in materials synthesis has paved way for the realization of alternative plasmonic materials. Among the alternative plasmonic materials, transition metal nitrides such as TiN a