Imaging is an effective tool in scientific research, manufacturing, and medical practice. However, despite its importance, it is not easy to observe dynamical events that occur much faster or slower than the human time scale (found in photochemistry, phononics, fluidics, MEMS, and tribology). Unfortunately, traditional methods for imaging fall short in visualizing them due to their technical limitations. In this talk, I will introduce radically different approaches to imaging. I will first discuss ultrafast imaging and then talk about ultraslow imaging. I will show how these imaging tools help us better understand dynamical processes.

Nanoparticles in the single digit nanometer range can be easily isolated and studied with low optical powers using nanoaperture tweezers. We have studied individual proteins and their interactions with small molecules, DNA and antibodies. Recently, using the fluctuations of the trapped object, we have pioneered a new way to "listen" to the vibrations of nanoparticles in the 100 GHz - 1 THz range; the approach is called extraordinary acoustic Raman (EAR). EAR gives unprecedented low frequency spectra of individual proteins in solution, allowing for identification and analysis, as well as probing their role in biological functions. We have also used EAR to study the elastic properties, shape and size of various individual nanoparticles.

Semiconductor nanostructures are at the heart of modern-day electronic devices and systems. Due to their high refractive index, they also provide a myriad of opportunities to manipulate light. When properly sized and shaped, they can support strong optical resonances that boost light-matter interaction over bulk materials and enable their use in controlling the flow of light at the nanoscale. In this presentation, I will discuss the use of individual, resonant nanostructures and dense arrays thereof (metafilms) in a variety of optoelectronic devices and illustrate how the performance of these devices can be improved by engineering the constituent nanostructure, size, shape, and/or spacing.

We propose and demonstrate a reliable and inexpensive tool for optical characterization of photonics metamaterials and metasurfaces. Existing characterization methods of metamaterials (or more precisely negative index metamaterials), including conventional interferometry and ellipsometry, are rather complex and expensive. The “measurable” difference between, for example, positive index materials and negative index materials is that the former introduces a phase delay to transmitted light beam and the latter one introduces a phase advance. Here, we propose to use optical vortex interferometry to directly “visualize” phase delay or phase advance. In the proposed setup a laser beams at the wavelength of 633 nm is separated in two by a beam splitter. One beam is transmitted through a spiral phase plate in order to generate a beam with an orbital angular momentum, and the second beam is transmitted through a nanostructured sample. Two beams are subsequently recombined by a beam splitter to form spiral interferogram. Spiral patterns are then analyzed to determine phase shifts introduced by the sample. In order to demonstrate the efficiency of the proposed technique, we fabricated four metasurface samples consisting of metal nano-antennas introducing different phase shifts and experimentally measured phase shifts of the transmitted light using the proposed technique. The experimental results are in good agreement with numerical simulations. In summary, we report a novel method to characterize metasurfaces and metamaterials using optical vortex interferometry. The proposed characterization approach is simple, reliable and particularly useful for fast and inexpensive characterization of phase properties introduced by metamaterials and metasurfaces.

We investigate azimuthally E-polarized vortex beams with enhanced longitudinal magnetic field. Ideally, such beams possess strong longitudinal magnetic field on the beam axis where there is no electric field. First we formulate the electric field vector and the longitudinal magnetic field of an azimuthally E-polarized beam as an interference of right- and left-hand circularly polarized Laguerre Gaussian (LG) beams carrying the orbital angular momentum (OAM) states of -1 and +1, respectively. Then we propose a metasurface design that is capable of converting a linearly polarized Gaussian beam into an azimuthally E-polarized vortex beam with longitudinal magnetic field. The metasurface is composed of a rectangular array of double-layer double split-ring slot elements, though other geometries could be adopted as well. The element is specifically designed to have nearly a 180° transmission phase difference between the two polarization components along two orthogonal axes, similar to the optical axes of a half-wave plate. By locally rotating the optical axes of each metasurface element, the transmission phase profile of the circularly polarized waves over the metasurface can be tailored. Upon focusing of the generated vortex beam through a lens with a numerical aperture of 0.7, a 41-fold enhancement of the magnetic to electric field ratio is achieved on the beam axis with respect to that of a plane wave. Generation of beams with large magnetic field to electric field contrast can find applications in future spectroscopy systems based on magnetic dipole transitions, which are usually much weaker than electric dipole transitions.

In contrast with linearly polarized excitation, which necessarily has zero magnitude electrical field twice during an optical cycle, the electrical field vector of circularly polarized light has constant magnitude. During an optical cycle the electric field vector rotates in the plane normal to the wave propagation. Consequently, if plasmonic structures are resonant with circularly polarized excitation, it is possible for them to exhibit regions of strongly modified carrier density for the duration of the optical cycle. Here, we study a class of achiral toroid and ‘sun burst’ nano-patterned plasmonic surfaces that show persistent, circulating charge density waves during circularly polarized illumination. The direction of the continuously circulating wave (clockwise or counterclockwise) depends on the handedness of the incident beam. Our interest stems from whether these charge density waves can support circular electric currents (DC) manifest experimentally as static magnetic fields during illumination. Using full-wave optical modeling (FDTD method), and mechanistic calculations of the circulating potential acting on electrons in the toroid resonators, we outline the conditions that maximize optical excitation of both circulating displacement currents and electron transport currents. We show that in the limit of very weak coupling to the solenoid-like electron transport, or when < 1 x 10^-6% of the plasmonically active electron population enters the circular transport modes, relatively strong magnetic fields, > 1 G, can be expected. We discuss scanning probe measurements for monitoring the induced magnetic field, as well as the relationship between this phenomenon and the inverse Faraday effect observed in continuous media.

We have developed active metamaterials based on macroscopic quantum effects capable of quickly tuning their electrical and magnetic responses over a wide frequency range. These metamaterials are based on superconducting elements to form low insertion loss, physically and electrically small, highly tunable structures for the next generation rf electronics. The meta-atoms are rf superconducting quantum interference devices (SQUIDs) that incorporate the Josephson effect. RF SQUIDs have an inductance which includes a contribution from the Josephson inductance of the junction. This inductance is strongly tunable with dc and rf magnetic fields and currents. The rf SQUID metamaterial is a richly nonlinear effective medium introducing qualitatively new macroscopic quantum phenomena into the metamaterials community, namely magnetic flux quantization and the Josephson effect. The coherence of the metamaterials is strongly sensitive to the environment and measurement conditions. The metamaterials also display a unique form of transparency whose development can be manipulated through multiple parametric dependences. Further features such as breathers, superradiance, and self-induced transparency, along with entry into the fully quantum limit, will yield qualitatively new metamaterial phenomena. This work is supported by the NSF-GOALI and OISE Programs through Grant No. ECCS-1158644 and the Center for Nanophysics and Advanced Materials (CNAM).

Metamaterials enable the control of electromagnetic fields over sub-wavelength scales. In addition to field enhancement effects, metamaterials offer an unprecedented control over the phase of electromagnetic fields, which is of paramount importance in coherent nonlinear optical processes. Here we explore frequency conversion effects in nanostructured media. The coherent interactions arising in ensembles of nanostructures lead to a very rich phenomenology and a unique set of degrees of freedom with which to engineer the overall nonlinear response of the system. In particular we here discuss novel phase-matching schemes in ensembles of discrete nonlinear scatterers. Keywords: Metamaterials, Plasmonics, Nonlinear Optics.

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.

Hyperbolic metamaterials (HMMs) have become one of the most attractive classes of metamaterials due to their wide array of applications in combination with ease of realization. Here we will discuss our recent work on “active hyperbolic metamaterials” where demonstrate enhanced light emission and extraction from metamaterials embedded with quantum dots. We will also discuss our recent efforts on realizing tunable HMMs as well as sub-wavelength cavities.

Using effective medium theory (EMT), Bloch’s theorem (BT), and the transfer matrix method (TMM), we analyze the possibility of gain-enhanced transmission in metamaterials with hyperbolic dispersion at telecommunication frequencies. We compare different combinations of dissipative metals and active dielectrics, including noble metals, transparent conducting oxides (TCO), III-V compounds, and solid-state dopants. We find that both indium gallium arsenide phosphide (InGaAsP) and erbium-doped silica (Er:SiO2), when combined with silver, show promise as a platform for demonstration of pump-dependent transmission. On the other hand, when these active dielectrics are combined with aluminum-doped zinc oxide (AZO), a low-loss TCO, gain-enhanced transmission is negligible. Results based on EMT are compared to the more accurate BT and TMM. When losses are ignored, quantitative agreement between these analytical techniques is observed near the center of the first Brillouin zone of a one-dimensional periodic structure. Including realistic levels of loss and gain, however, EMT predictions become overly optimistic compared to BT and TMM. We also discuss the limitations to assumptions inherent to EMT, BT, and TMM, and suggest avenues for future analysis.

This is an invited presentation devoted to the Förster energy transfer in plasmonic systems. Förster energy transfer processes are now actively studied in various fields that bridge physics, biology and medicine. One can try to control the efficiency of the transfer by embedding the donors and acceptors into the structured electromagnetic environment. Available experimental studies yields contradictory reports on suppressed [1], enhanced [2] or unaffected [3] transfer. We present a rigorous Green function theory of the collective Förster energy transfer between the arrays of donor and acceptor molecules lying on the planar metallic mirror that has been previously available only for spherical nanoparticles [4]. We reveal strong modification of the effective transfer rate by the mirror. The rate can be either suppressed or enhanced depending on the relative positions between acceptor and donor arrays. This is a collective effect, completely absent for a single donor-acceptor pair put above the mirror. Our results may explain the slowdown of the transfer rate recently observed in experiment for dye molecules put on top of plasmonic mirrors and layered hyperbolic metamaterials [1]. [1] T. Tumkur, J. Kitur, C. Bonner, A. Poddubny, E. Narimanov and M. Noginov , Faraday Discuss., 2014 , DOI: 10.1039/C4FD00184B [2] C. Blum, N. Zijlstra, A. Lagendijk, M. Wubs, A. P. Mosk, V. Subramaniam, and W. L. Vos, Phys. Rev. Lett. 109, 203601 (2012). [3] P. Andrew and W. L. Barnes, Science 290, 785 (2000). [4] V.N. Pustovit, A.M. Urbas, and T.V. Shahbazyan, Phys. Rev. B 88, 245427(2013)

Efficient generation of single photons is essential for the development of photonic quantum technologies. We have demonstrated that coupling a nanodiamond nitrogen-vacancy (NV) center to CMOS-compatible nanophotonic structures results in significant reduction of the excited state lifetime, increase in the collected single–photon emission, and modification of radiation pattern. In addition, we studied the effect of increased photonic density of states on spin dependent fluorescence contrast.

We use Rytov's fluctuational electrodynamics to show that Van Der Waals interactions are fundamentally modified by metamaterials. We verify the conditions under which the effect is strongest and also show initial experimental results to prove the same. En route to developing the van der waals theory in metamaterials we have also adopted a unique approach to quantization in lossy dispersive media.

Diamond based nitrogen-vacancy (NV) centers are promising solid state defects for applications in quantum information technologies. On the one hand, there is a growing interest in enhancing their single-photon emission by coupling them to plasmonic structures. On the other hand, the dependence of emission intensity on the electron spin state enables room temperature quantum information readout. We study the fluorescence contrast resulting from the spin resonance in the conditions of an increased photonic density of states. Fluorescence observations from NV center ensembles in diamond nanocrystals coupled to structures supporting plasmonic modes experimentally confirm the analytical results.

We introduce a new "universality class" of artificial optical media - photonic hyper-crystals. These hyperbolic metamaterials with periodic spatial variation of dielectric permittivity on subwavelength scale, combine the features of optical metamaterials and photonic crystals.

A metamaterial hyperlens offers a unique solution to overcome the diffraction limit by transforming evanescent waves responsible for imaging subwavelength features of an object into propagating waves. However, the first realizations of optical hyperlenses were limited by a narrow working bandwidth and significant resonance-induced loss. Here, we report the first experimental demonstration of a non-resonant waveguide-coupled hyperlens operating in the visible wavelength range that was fabricated using a combination of top-down and bottom-up fabrication approaches. A detailed investigation of various materials systems proves that a radial fan-shaped configuration is superior to the concentric layer-based configuration in that it relies on non-resonant negative dielectric response, and, as a result, enables broadband and low-loss performance in the visible range. While the majority of applications of a hyperlens is expected to be in optical frequency range, the challenge of fabricating non-resonant radial structures at optical frequencies has not been overcome until now.

Strongly anisotropic media where principal components of the dielectric tensor have opposite signs are called hyperbolic. These materials permit highly directional, volume-confined propagation of slow-light modes at deeply sub-diffractional size scales, leading to unique nanophotonic phenomena. The realization of hyperbolic materials within the optical spectral range has been achieved primarily through the use of artificial structures typically composed of plasmonic metals and dielectric constituents. However, while proof-of-principle experiments have been performed, the high plasmonic losses and inhomogeneity of the structures limit most advances to the laboratory. Recently, hexagonal boron nitride (hBN) was identified as a natural hyperbolic material (NHM), offering a low-loss, homogeneous medium that can operate in the mid-infrared. We have exploited the NHM response of hBN within periodic arrays of conical nanoresonators to demonstrate ‘hyperbolic polaritons,’ deeply sub-diffractional guided waves that propagate through the volume rather than on the surface of a hyperbolic material. We have identified that the polaritons are manifested as a four series of resonances in two distinct spectral bands that have mutually exclusive dependencies upon incident light polarization, modal order, and aspect ratio. These observations represent the first foray into creating NHM building blocks for mid-infrared to terahertz nanophotonic and metamaterial devices. This talk will also discuss potential near-term applications stemming from these developments.

Using established nanofabrication techniques, we realize deeply subwavelength multilayer metal-dielectric nanostructures composed of silver and indium gallium arsenide phosphide (InGaAsP). In contrast to most, if not all, subwavelength multilayer metal-dielectric systems to date, the Bloch vector of the fabricated structure is parallel to the plane of the substrate, making it suitable for waveguide integration. InGaAsP multiple quantum wells (MQWs) are epitaxially grown on InP normal to the Bloch vector of the resulting multilayer. The associated carrier population of the MQWs allows for active control of the behavior of the nanostructure via external optical pumping. Individual layer thicknesses of 30nm are repeatedly achieved via electron-beam lithography, reactive ion etching of InGaAsP, and sputter deposition of silver. Resulting 60nm periods of the one-dimensional periodic structure are 25 times smaller than telecommunication wavelengths in vacuum. The realized multilayer nanostructures hold promise as a platform for active and tunable hyperbolic metamaterials at telecommunication frequencies.

The magnetically controlled planar hyperlens which consists of an InSb-PMMA multilayered structure is proposed and analyzed. The ability of the proposed hyperlens to resolve subwavelength structures at THz region is demonstrated by electromagnetic numerical simulation. The asymmetric field pattern in the hyperlens is caused by the surface magnetoplasmon (SMP) propagating in the InSb-PMMA waveguide. By using transfer matrix method and the effective medium approach of the investigated components, the role of SMP played in the super-resolution is elucidated. Furthermore, the super-resolution of the proposed device under various frequencies is accomplished by merely changing the value of external magnetic field. The proposed device would provide a practical route for multi-functional material, real-time super-resolution imaging, photolithography, and THz imaging.

An ideal hyperbolic metamaterial (HMM), which has a perfect hyperbolic dispersion curve, theoretically can support modes with indefinite wavenumbers, leading to large photon local density of states (LDOS) and many applications such as enhancing light-matter interactions, spontaneous emission and thermal radiation. Here in this presentation, HMMs based on ultrathin metal-dielectric multilayers have been studied by considering the nonlocal response of electrons in metal. Based on the hydrodynamic model of the nonlocal response, we investigate the effect of nonlocality on the performance (dispersion relation, ray refraction, LDOS and spontaneous emission) of HMMs when gradually approaching the ultrathin limit of the unit cell. We show that nonlocality will induce topological transitions of the iso-frequency surfaces and limit the wavenumber as well as LDOS for both type I and type II HMMs. Under nonlocal treatment, the iso-frequency surface of type II HMM transforms from a hyperbola to a bullet shape, while for type I HMM, the surface splits into two branches: a cylindrical-like branch at high k region and an elliptical branch at the low k region. In the high k region, the nonlocality set a cut-off k for the allowed wavenumbers in both type I and type II HMMs. This cut-off k which is defined by the electron Fermi velocity of the metal intrinsically limits the LDOS and light-matter interactions. These results indicate that in the aim of achieving high performance HMMs, merely thinning the constituent films according to the local theories is no longer valid.

Vanadium oxide (VO2) is known to undergo a semiconductor-to-metal transition at 68°C. Therefore, it can be used as a tunable component of an active metamaterial. The lamellar metamaterial designed and studied in this work is composed of subwavelength VO2 and Au layers and is predicted to have the temperature controlled transition from the hyperbolic phase to the metallic phase. The VO2 films and VO2/Au lamellar metamaterial stacks have been fabricated and studied in the electrical conductivity as well as optical (transmission, reflection) experiments. The temperature depended changes in the absorption and transmission spectra of metamaterials and films have been observed experimentally and compared with the theory predictions.

We propose the exploitation of plasmons in graphene nanoislands as a promising platform for sensing through surface-enhanced infrared absorption and Raman scattering. Our calculations indicate that the large electrical tunability of graphene enables the identification of molecular resonances by recording broadband absorption or inelastic scattering, replacing wavelength-resolved light collection by a signal integrated over photon energy as a function of the graphene doping level. Our results pave the way for the development of novel cost-effective sensors capable of identifying spectral signatures of molecules without using spectrometers and laser sources.

van der Waals (vdW) crystals consist of individual atomic planes coupled by vdW interaction, similar to graphene monolayers in bulk graphite. We investigated van der Waals heterostructures assembled from atomically thin layers of graphene and hexagonal boron nitride (hBN). We launched, detected and imaged plasmonic, phonon polaritonic and hybrid plasmon-phonon polariton waves in a setting of an antenna based nano-infrared apparatus. Hyperbolic phonon polaritons in hBN enabled sub-diffractional focusing in infrared frequencies. Because electronic, plasmonic and phonon polaritonic properties in van der Waals heterstructures are intertwined, gate voltage and/or details of layer assembly enable efficient control of nano-photonic effects.

[invited] We introduce ABC laminate metamaterials composed of layers of three different dielectrics. Each layer has zero bulk second-order optical nonlinearity, yet centro-symmetry is broken locally at each inner interface. To achieve appreciable effective bulk metamaterial second-order nonlinear optical susceptibilities, we densely pack many inner surfaces to a stack of atomically thin layers grown by conformal atomic-layer deposition. For the ABC stack, centro-symmetry is also broken macroscopically. Our experimental results for excitation at around 800 nm wavelength indicate interesting application perspectives for frequency conversion or electro-optic modulation in silicon photonics.

The development of new plasmonic materials enables novel optical devices, and they in turn assist in the progress of optical communications. As a result of the significant attention in searching for alternative materials, transparent conducting oxides (TCOs) have been proposed as promising plasmonic compounds at telecommunication wavelengths [1]. They are eminently practical materials because they are CMOS-compatible, can be grown on many different types of substrates, patterned by standard fabrication procedures, and integrated with many other standard technologies. Due to the ability of TCO nanostructures to support strong plasmonic resonance in the NIR, metasurface devices, such as a quarter wave plate, have been demonstrated whose properties can be easily adjustable with post processing such as thermal annealing [2,3]. Additionally, TCOs can be used as epsilon near zero (ENZ) materials in the NIR. From our recent study of the behavior of nanoantennae sitting upon a TCO substrate, we found that TCOs serve as an optical insulating media due to the high impedance of TCOs at the ENZ frequency, enabling emission shaping. Finally, the optical properties of TCOs can be varied by optical or electrical means. Current research is focused on studying the ultrafast carrier dynamics in doped zinc oxide films using pump-probe spectroscopy. We have shown that aluminum doped zinc oxide films can achieve a 40% change in reflection with ultrafast dynamics (<1ps) under a small fluence of 3mJ/cm2. Consequently, TCOs are shown to be extremely flexible materials, enabling fascinating physics and unique devices for applications in the NIR regime. References [1] A. Boltasseva and H. Atwater, Science 331(6015), 290-291, 2011. [2] J. Kim et al, Selected Topics in Quantum Electronics, IEEE Journal of, 19, 4601907-4601907, 2013. [3] J. Kim et al, CLEO: QELS_Fundamental Science. Optical Society of America, 2014. This work was supported by ONR MURI N00014-10-1-0942

The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. Up until recently, research in this field has been primarily focused on the use of plasmonic metals. However, the high optical losses inherent in such metal-based surface plasmon materials has led to an ever-expanding effort to identify, low-loss alternative materials capable of supporting sub-diffractional confinement. One highly promising alternative are polar dielectric crystals whereby sub-diffraction confinement of light can be achieved through the stimulation of surface phonon polaritons within an all-dielectric, and thus low loss material system. Both SiC and hexagonal BN are two exemplary SPhP systems, which along with a whole host of alternative materials promise to transform nanophotonics and metamaterials in the mid-IR to THz spectral range. In addition to the lower losses, these materials offer novel opportunities not available with traditional plasmonics, for instance hyperbolic optical behavior in natural materials such as hBN, enabling super-resolution imaging without the need for complex fabrication. This talk will provide an overview of the SPhP phenomenon, a discussion of what makes a ‘good’ SPhP material and recent results from SiC and the naturally hyperbolic material, hBN from our research group.

Inspired by the potential of designing highly efficient nanophotonic optical elements, numerous researchers are currently exploring the use of dielectric resonators in constructing meta-devices. A wide range of optical components have been demonstrated, including metasurfaces that act as two-dimensional lenses, gratings, and axicons. At the core of these devices is a dielectric building block, typically a Silicon nano-disk or nano-rod, that supports Mie-like leaky mode excitations with a geometrically tunable amplitude and phase response. Here we present a comprehensive experimental characterization of these building blocks. We elucidate their multipolar mode structure, and explain the dependence on the underlying substrate. We find that fundamentally new buried magnetic modes emerge in high-index substrates, and that Fabry-Perot effects in silicon-on-insulator platforms can be utilized to enhance or suppress specific modes. When individual resonators are arranged into arrays with sub-wavelength periodicities, inter-particle coupling leads to a shift in the resonant response. When the periodicities are on the same order as the operating wavelength, the localized resonances may couple with the global diffraction modes, leading to the possible formation of distinct high-quality-factor surface-lattice-resonant modes, similar to those encountered in plasmonic gratings. We conclude by exploring the behavior of resonators constructed out of active materials, such as polar materials that support phonon-polariton excitations, and phase-change materials with tunable dielectric constants.

Dielectric optical antenna resonators have recently emerged as a viable alternative to plasmonic resonators for metamaterials and nanophotonic devices, due to their ability to support multipolar Mie resonances with low losses. In this work, we experimentally investigate the mid-infrared Mie resonances in Si and Ge subwavelength spherical particles. In particular, we leverage the electronic and optical properties of these semiconductors in the mid-infrared range to design and tune Mie resonators through free-carrier refraction. Si and Ge semiconductor spheres of varying sizes of 0.5-4 μm were fabricated using femtosecond laser ablation. Using single particle infrared spectroscopy, we first demonstrate size-dependent Si and Ge Mie resonances spanning the entire mid-infrared (2-16 μm) spectral range. Subsequently we show that the Mie resonances can be tuned by varying material properties rather than size or geometry. We experimentally demonstrate doping-dependent resonance frequency shifts that follow simple Drude models of free-carrier refraction. We show that Ge particles exhibit a stronger doping dependence than Si due to the smaller effective mass of the free carriers. Using the unique size and doping dispersion of the electric and magnetic dipole modes, we identify and demonstrate a size regime where these modes are spectrally overlapping. We also demonstrate the emergence of plasmonic resonances for high doping levels and long wavelengths. These findings demonstrate the potential for tuning infrared semiconductor Mie resonances by optically or electrically modulating charge carrier densities, thus providing an excellent platform for tunable electromagnetic metamaterials.

Concentration of light into nanospots is greatly beneficial for heat assisted magnetic recording, biomedical imag- ing and sensing, nanolasing, etc. We propose novel, all dielectric near field transducers, which allow focusing light into a hot spot, much smaller than the wavelength without significant dissipative loss. Therefore, the detri- mental thermal effects in heat assisted recording can be significantly reduced opening new venue in the magnetic recording. In the proposed transducer electric field concentrates at the apex of the dielectric tip attached to the resonator. Thus the electric field excited in the dielectric resonator is further amplified and concentrated due to the dipole polarization of the tip.

We will present experimental studies and numerical modeling of nonlinear optical processes in plasmonic metamaterials based on assemblies of metallic nanorods and other complex geometries. Second- and third-order nonlinear optical response originating from a plasmonic component of the metamaterial will be discussed. Such plasmonic metamaterials can be used for engineering enhanced nonlinear optical properties with the required spectral and temporal response. We will also discuss a novel concept of an on-chip ultrafast all-optical modulator based on a hyperbolic metamaterial integrated in a silicon waveguide.

Graphene-based hyperbolic metamaterials (HMMs) enable new possibilities that are not attainable with conventional metal-based HMMs, such as tunability of optical properties and the ability to combine with graphene-based photodetection. A graphene HMM is made of alternating graphene-dielectric multilayers, whose properties can be understood with the effective-medium approximation (EMA). The initial experimental realization of this novel metamaterial has been demonstrated with a far-field measurement, and in this paper we investigate the light coupling from free space into a graphene HMM slab with a metallic grating using numerical simulations. We show that light can be efficiently coupled into the high-k guided modes in the HMM slab and be absorbed by the graphene layers, which can be applied to create ultrathin super absorbers.

We show that a previously derived LCR model for a plasmonic waveguide can be generalized to a model for hyperbolic metamaterials (HMMs). An analysis of previous work and a generalization into a multilayer structure is presented. The physical significance and practical applications are discussed.

Today’s technological needs are demanding for faster and smaller optical components. Optical microcavities offer a high confinement of electromagnetic field in a small volume, with dimensions comparable to the wavelength of light, which provides a unique system for the enhancement of light-matter interactions on the nanoscale. However, further reducing the size of the optical cavity (from microcavity to nanocavity) is limited to the fundamental diffraction limit. In hyperbolic metamaterials, large wave vectors can be achieved. Therefore, optical cavities, created from hyperbolic metamaterials, allow the confinement of the electromagnetic field to an extremely small volume with dimensions significantly smaller than the wavelength of light. This paper presents the results of numerical study of the optical mode confinement in nanocavities with hyperbolic dispersion using nanolayered Al/SiO2 hyperbolic metamaterial with different Al fill fractions. The fundamental properties of the optical modes and resonance frequencies for the nanocavities are studied using the finite-elementmethod numerical technique. Numerical simulations show that the light can be well confined in a disk with radius up to λ/65. This paper will also focus on other variables such as Q-factor and Al fill fraction. Potential future applications for three-dimensional nanocavities with hyperbolic dispersion include: silicon photonics optical communications networks, ultrafast LEDs and biological nanoparticles sensing.

Harnessing more energy from the sun has led to the development of materials which can efficiently trap the sun radiation in the whole spectrum and re-emit it into a narrow spectral band corresponding to the band gap of a photovoltaic device. The field of metamaterials is largely aimed at designing nanostructured surfaces with tailored absorption (emission) spectra. Many rare-earth doped crystals and glasses can efficiently absorb light throughout the whole visible and near-infrared range of the spectrum and emit radiation at longer wavelengths (1.5 to 3 microns). We report studies of absorption and thermal emission of several rare-earth doped crystals.

The terahertz and mid-infrared region of the electromagnetic spectrum is relatively new area of interest and incorporates a wide range of applications from image sensing to spectroscopy and many more yet to be discovered. In the area of metamaterials many new designs have been discovered, but “chevrons” shaped split ring resonators (ch-SRRs) in the mid-infrared region has not been studied to the best of our knowledge. This paper presents the analysis and simulation of ch-SRRs in the mid infrared region. Tunability of SRRs is important for various industrial and scientific applications and hence this paper analyzes the tunability of the ch-SRRs by variation of angle. The device is simulated in two configurations i.e., one with two chevrons shaped SRRs on the same plane of the dielectric substrate and the other with each of the two chevron shaped SRRs on the opposite plane of the substrate. Gold SRRs is used, since we are working in the terahertz region Lorentz-Drude model is employed to incorporate the losses. The ch-SRRs have been embedded upon the silicon substrate. The models are designed and simulated in COMSOL and result is shown in MATLAB. The results obtained for reflectance are of particular interest. The effective medium parameters viz. Impendence, permittivity, permeability and refractive index obtained for the split ring resonator are also evaluated. This design shows sharp results for reflectance which can be used in sensors application.

In Extraordinary Optical Transmission (EOT), a metallic film perforated with an array of [periodic] apertures exhibits transmission over 100% normalized to the total aperture area, at selected frequencies. EOT devices have potential applications as optical filters and as couplers in hybrid electro-optic contacts/devices. Traditional passive extraordinary optical transmission structures, typically demonstrate un-normalized transmission well below 50%, and are typically outperformed by simpler thin-film techniques. To overcome these limitations, we demonstrate a new breed of extraordinary optical transmission devices, by “burying” an extraordinary optical transmission grating in a dielectric matrix via a metal-assisted-chemical etching process. The resulting structure is an extraordinary optical transmission grating on top of a dielectric substrate with dielectric nano-pillars extruded through the grating apertures. These structures not only show significantly enhanced peak transmission when normalized to the open area of the metal film, but more importantly, peak transmission greater than that observed from the bare semiconductor surface. The structures were modeled using three-dimensional rigorous coupled wave analysis and characterized experimentally by Fourier transform infrared reflection and transmission spectroscopy, and the good agreement between the two has been demonstrated. The drastic enhancement of light transmission in our structures originates from structuring of high-index dielectric substrate, with pillars effectively guiding light through metal apertures.

The effect of electromagnetically induced transparency (EIT) in non-Ohmic conductors, based on the concepts of classical nonlinear optics has been studied theoretically. We report an experimental demonstration of this effect within the mid-IR wavelength range. A low-dispersion semiconductor, i.e. ZnTe, and a highly dispersive gold film were subjected to bichromatic parametric irradiation and when specific phase matching conditions are satisfied, experimental evidence for a strong signature of EIT was found.

Science thrives on analogies, and a considerable number of inventions and discoveries have been made by pursuing an unexpected connection to a very different field of inquiry. For example, photonic crystals have been referred to as “semiconductors of light” because of the far-reaching analogies between electron propagation in a crystal lattice and light propagation in a periodically modulated photonic environment. However, two aspects of electron behavior, its spin and helicity, escaped emulation by photonic systems until recent invention of photonic topological insulators (PTIs). The impetus for these developments in photonics came from the discovery of topologically nontrivial phases in condensed matter physics enabling edge states immune to scattering. The realization of topologically protected transport in photonics would circumvent a fundamental limitation imposed by the wave equation: inability of reflections-free light propagation along sharply bent pathway. Topologically protected electromagnetic states could be used for transporting photons without any scattering, potentially underpinning new revolutionary concepts in applied science and engineering. I will demonstrate that a PTI can be constructed by applying three types of perturbations: (a) finite bianisotropy, (b) gyromagnetic inclusion breaking the time-reversal (T) symmetry, and (c) asymmetric rods breaking the parity (P) symmetry. We will experimentally demonstrate (i) the existence of the full topological bandgap in a bianisotropic, and (ii) the reflectionless nature of wave propagation along the interface between two PTIs with opposite signs of the bianisotropy.

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.

The development of metasurface, capable of controlling wave-fronts through interfacial phase discontinuity, offers a fascinating methodology for designing two dimensional miniaturized optical devices. Owing to an additional advantage of the enhanced useful transmission via Bainet-inverted matasurface, we exploit them to demonstrate an intriguing concept of merging the phase-profiles of two distinct optical devices, a lens and a spiral phase plate, to realize an ultrathin nanostructured optical vortex lens. The proposed device can has multiple focal planes along the longitudinal direction; whereas the number of focal plans, corresponding topological charges and focal lengths can readily be tailored to meet any desired requirements. Meanwhile, the dual-polarity feature of the optical vertex metalens exhibits spin controlled real and virtual focal plans, while dispersionless aptitude of nanobars enables its working over the broadband. The concept unveils a novel way of employing metasurface, to engraft the phase profiles of multiple bulk devices, to achieve unique functionalities for promising applications in integrated photonics.

Plasmonic nanograting consisting of thermally-driven Au/SiO2 bimorph beams is developed that modulate birefringence for at the visible wavelength. From electromagnetic field simulation, the phase difference at 650 nm is calculated to be modulated from 68.5 to 23.5 degree by actuating bimorph beams. The phase difference of fabricated modulator was measured at the wavelength range of from 500 to 800 nm with a driving voltage of 10 V. Phase modulation is obtained, and the maximum variation is -3.3 degree at 646 nm. The maximum drive current is 100 mA.

Symmetries play a fundamental role in engineering. In this talk, I will show how symmetry considerations can enable novel nanophotonics devices with advanced functionalities. Novel electromagnetic cavities that can hold light for an infinite amount of time will be introduced as well as the design of novel metamaterials built solely from symmetry considerations. I will present a realized closed ring negative index metamaterial and a self-assembled symmetry breaking metamaterials with controllable optical response.

The use of metamaterials structures has been the subject of extensive discussions given their wide range of applications. However, a large fraction of the work available to date has been limited to simulations and proof-of-principle demonstrations. One reason for the limited success inserting these structures into functioning systems and real-world applications is the high level of complexity involved in their fabrication. Direct-write processes are ideally suited for the fabrication of arbitrary periodic and aperiodic structures found in most metamaterial and plasmonic designs. For these applications, laser-based processes offer numerous advantages since they can be applied to virtually any surface over a wide range of scales. Furthermore, laser direct-write or LDW allows the precise deposition and/or removal of material thus enabling the fabrication of novel metamaterial designs. This presentation will show examples of metamaterial and plasmonic structures developed at the Naval Research Lab using LDW, and discuss the benefits of laser processing for these applications. This work was sponsored by The Office of Naval Research.

Cone shaped resonators have been proposed to create a near perfect metamaterial reflector in the visible range (640nm-680nm). Resonators are made up of high permittivity dielectric (Si). In the considered wavelength range reflectance is above 90% with maximum value of 99.5% at 660nm. It is Mie-Resonance based structure showing magnetic and electric resonance at different wavelengths.

A Silicon Photomultiplier, SiPM, is a metasystem of Avalanche Photodiodes, APDs, which embedded in a specific purpose electronic, becomes a metadevice with unique and useful advanced functionalities to capture, transmit and analyze information with increased efficiency and security. The SiPM is a very small state of the art photo-detector with very high efficiency and sensitivity, with good response to controlled light pulses in the presence of background light without saturation. New results profit of such metadevice to propose a new receiver-emitter system useful for Visible Light Communication, VLC.

Single pixel cameras are useful imaging devices where it is difficult or infeasible to fashion focal plan arrays. For example in the Far Infrared (FIR) it is difficult to perform imaging by conventional detector arrays, owing to the cost and size of such an array. The typical single pixel camera uses a spatial light modulator (SLM) - placed in the conjugate image plane – and is used to sample various portions of the image. The spatially modulated light emerging from the SLM is then sent to a single detector where the light is condensed with suitable optics for detection. Conventional SLMs are either based on liquid crystals or digital mirror devices. As such these devices are limited in modulation speeds of order 30 kHz. Further there is little control over the type of light that is modulated. We present metamaterial based spatial light modulators which provide the ability to digitally encode images – with various measurement matrix coefficients – thus permitting high speed and fidelity imaging capability. In particular we use the Hadamard matrix and related S-matrix to encode images for single pixel imaging. Metamaterials thus permit imaging in regimes of the electromagnetic spectrum where conventional SLMs are not available. Additionally, metamaterials offer several salient features that are not available with commercial SLMs. For example, metamaterials may be used to enable hyperspectral, polarimetric, and phase sensitive imaging. We present the theory and experimental results of single pixel imaging with digital metamaterials in the far infrared and highlight the future of this exciting field.

Many conventional optoelectronic devices consist of thin, stacked films of metals and semiconductors. In this presentation, I will demonstrate how one can improve the performance of such devices by nano-patterning the constituent layers at length scales below the wavelength of light. The resulting metafilms and metasurfaces offer opportunities to dramatically modify the optical transmission, absorption, reflection, and refraction properties of devices. This is accomplished by encoding the optical response of nanoscale resonant building blocks into the effective properties of the films and surfaces. To illustrate these points, I will show how nanopatterned metal and semiconductor layers can be used to enhance the performance of solar cells, photodetectors, and enable new imaging technologies. I will also demonstrate how the use of active building blocks can facilitate the creation of active metafilm devices.

Hyperbolic metamaterial (HMM) research has led to the fabrication of devices which have unbounded k-space ellipsoids. Alternating layers of films with alternating signs of relative permittivity or permeability in a given direction enable multi-layer surfaces that are, in theory, either perfectly reflective or transmissive at an angle dependent upon the free space wave vector and ratios of the permittivity or permeability in the normal and transverse directions. By having knowledge of the electromagnetic properties of the constituent materials of a multi-layer HMM over a given bandwidth, the functionality of these structures can be altered by changing the fill fraction of the constituents. One potential device design that results is that of a flat electromagnetic wave collimator. The degree to which a multi-layer HMM collimates comes from the contrast in the magnitudes of the relative permeability or permittivity in the normal and transverse directions. With a large material parameter contrast at a given frequency, the number of transverse wave vectors that allow for successful EM wave propagation at the HMM/atmosphere interface approaches zero. This leads to propagation of a narrow angular cone of waves relative to the surface normal of the HMM. Herein we show that analytical calculations are in relatively good agreement with finite element method electromagnetic simulations performed in COMSOL’s RF module and compare dispersion relations of known materials to the resulting collimation generated in a corresponding HMM. We thereby use existing material data and predictive theories show how to tailor the frequency response of HMMs.

Unlike a semiconductor, where the absorption is limited by the band gap, a “microrectenna array” could theoretically very efficiently rectify any desired portion of the infrared frequency spectrum (25 - 400 THz). We investigated vertical metal-insulator-metal (MIM) diodes that rectify vertical high-frequency fields produced by a metamaterial planar stripe-teeth Al or Au array (above the diodes), similar to stripe arrays that have demonstrated near-perfect absorption in the infrared due to critical coupling [1]. Using our design rules that maximize asymmetry (and therefore the component of the electric field pointed into the substrate, analogous to Second Harmonic Generation), we designed, fabricated, and analyzed these metamaterial-based microrectenna arrays. NbOx and Al2O3 were produced by anodization and ALD, respectively. Smaller visible-light Pt-NbOx-Nb rectennas have produced output power when illuminated by visible (514 nm) light [2]. The resonances of these new Au/NbOx/Nb and Al/Al2O3/Al microrectenna arrays, with larger dimensions and more complex nanostructures than in Ref. 1, were characterized by microscopic FTIR microscopy and agreed well with FDTD models, once the experimental refractive index values were entered into the model. Current-voltage measurements were carried out, showed that the Al/Al2O3/Al diodes have very large barrier heights and breakdown voltages, and were compared to our model of the MIM diode. We calculate expected THz-rectification using classical [3] and quantum [4] rectification models, and compare to measurements of direct current output, under infrared illumination. [1] C. Wu, et. al., Phys. Rev. B 84 (2011) 075102. [2] R. M. Osgood III, et. al., Proc. SPIE 8096, 809610 (2011). [3] A. Sanchez, et. al., J. Appl. Phys. 49 (1978) 5270. [4] J. R. Tucker and M. J. Feldman, Rev. of Mod. Phys. 57, (1985)1055.

In this presentation we will discuss the analytical and numerical approaches to modeling electromagnetic properties of geometrically regular subwavelength 2D arrays of random resonant plasmonic particles. Amorphous metamaterials and metasurfaces attract interest of the scientific community due to promising technological implementations with cost-efficient methods of large-scale chemical nanoparticles synthesis as well as their self-organization. Random fluctuations of the particles size, shape, and/or composition are inevitable not only in the bottom-up synthesis, but also in conventional electron beam and photolithography fabrication. Despite the significant progress in large-scale fabrication, modeling and effective properties prediction of random/amorphous metamaterials and metasurfaces is still a challenge, which we address here. We present our results on analytical modelling of metasurfaces with regular periodic arrangements of resonant nanoparticles of random polarizability/size/material at normal plane-wave incidence. We show that randomness of the polarizability is related to increase in diffused scattering and we relate this phenomenon to a modification of the dipoles’ interaction constant. As a result, we obtain a simple analytical formula which describes diffuse scattering in such amorphous metasurfaces. Employing the supercell approach we numerically confirm the analytical results. The proposed approach can be easily extended from electrical dipole arrays and normal wave incidence to more general cases of electric and magnetic resonant particles and oblique incidence.

New dielectric metamaterial based on the Bragg filter comprising ten dielectric bilayers was investigated. Each bilayer is the thin films of silicone dioxide (SiO₂) and another film of zirconium dioxide (ZrO₂). The surface of the multilayer film is profiled. It has a form of periodic system of rectangles separated by the open gaps. We use the computer simulation as well as analytical solution to find the reflectance of the multilayer as a function of the wavelength and electromagnetic (em) field distribution. The multilayer system reveals the enhancement of em fields at the surface. The considered Bragg filter was modified by Raman-active structure made of gold nanoparticles with chemically attached 3,3-thio-bis(6- nitrobenzoic acid) - (TNB). The high Surface Enhanced Raman Scattering (SERS) signal was detected.

We demonstrate that a gold split-ball resonator (SBR) in the form of a spherical nanoparticle with a cut supports both optical magnetic and acoustic modes, which have strong field confinement around the cut. Such localization away from the bottom is expected to lead to an immunity to anchor loss and thus potentially high quality factors of acoustic oscillations when positioned on a substrate. As a result, when a planewave pulse excites the optical resonance, it can then efficiently drive the acoustic vibration through laser heating and/or optical forces. We estimate the overall heat variation by modelling the optical energy dissipation inside the SBR due to the dispersive and absorbing nature of gold at optical wavelengths. The optically induced force is given by the time averaged Lorentz force density. We simulate the mechanical vibrations under the optical excitation through time-dependent simulations using solid mechanics module of COMSOL software. Assuming a moderate quality factor of 10, under a plane wave pulsed laser pump which gives 100K temperature change to the SBR, both the laser heating and optical forces lead to the excitation of the acoustic mode at the same frequency with different magnitudes of 200pm and 10pm, resulting 10% and 0.5% modification of the total optical scattering, respectively. These results show that the SBRs support strong opto-mechanical coupling and are promising in applications such as surface-enhanced Raman spectroscopy and detection of localised strain.

Monte Carlo simulations have long been used to study Anderson localization in models of one-dimensional random stacks. Because such simulations use substantial computational resources and because the randomness of random number generators for such simulations has been called into question, a non-Monte Carlo approach is of interest. This paper uses a non-Monte Carlo methodology, limited to discrete random variables, to determine the Lyapunov exponent, or its reciprocal, known as the localization length, for a one-dimensional random stack model, proposed by Asatryan, et al., consisting of various combinations of negative, imaginary and positive index materials that include the effects of dispersion and absorption, as well as off-axis incidence and polarization effects. Dielectric permittivity and magnetic permeability are the two variables randomized in the models. In the paper, Furstenberg’s integral formula is used to calculate the Lyapunov exponent of an infinite product of random matrices modeling the one-dimensional stack. The integral formula requires integration with respect to the probability distribution of the randomized layer parameters, as well as integration with respect to the so-called invariant probability measure of the direction of the vector propagated by the long chain of random matrices. The non-Monte Carlo approach uses a numerical procedure of Froyland and Aihara which calculates the invariant measure as the left eigenvector of a certain sparse row-stochastic matrix, thus avoiding the use of any random number generator. The results show excellent agreement with the Monte Carlo generated simulations which make use of continuous random variables, while frequently providing reductions in computation time.

Metasurfaces composed of sub-wavelength artificial structures show promise for extraordinary light-manipulation and development of ultrathin optical components such as lenses, wave plates, orbital angular detection, and holograms over a broad range of the electromagnetic spectrum. However structures developed to date do not allow for post-fabrication control of antenna properties. We have investigated the integration of the transparent conductor indium tin oxide (ITO) active elements to realize gate-tunable phased arrays of subwavelength patch antenna in a metasurface configuration to enable gate tunable permittivity. The magnetic dipole resonance of each patch antenna interacts with the carrier density-dependent permittivity resonance of the ITO to enable phase and amplitude tunability. Operation of patch antennas and beam steering phased arrays will be discussed.

Split-ring resonator (SRR), one kind of building block of metamaterials, attracts wide attentions due to the resonance excitation of electric and magnetic dipolar response. The fundamental plasmonic properties and potential applications in novel three dimensional vertical split-ring resonators (VSRRs) are designed and investigated. The resonant properties arose from the electric and magnetic interactions between the VSRR and light are theoretically and experimentally studied. Tuning the configuration of VSRR unit cells is able to generate various novel coupling phenomena in VSRRs, such as plasmon hybridization and Fano resonance. The magnetic resonance plays a key role in plasmon coupling in VSRRs. The VSRR-based refractive-index sensor is demonstrated. Due to the unique structural configuration, the enhanced plasmon fields localized in VSRR gaps can be lifted off from the dielectric substrate, allowing for the increase of sensing volume and enhancing the sensitivity. We perform a VSRR based metasurface for light manipulation in optical communication frequency. By changing the prong heights, the 2π phase modulation can be achieved in VSRR for the design of metasurface which can be used for high areal density integration of metal nanostructures and optoelectronic devices.

In this paper, we present a computational and experimental design of a metasurface for broadband microwave antenna isolation. Our current emphasis is on the development of a high-impedance surface (HIS) that enables broadband isolation between transmit and receive antennas. For our specific HIS, we have formed a cascade of HIS unit cells and have thus expanded the isolation to provide 56 dB/meter over one octave (7.5 to 18 GHz) relative to the bare metal ground plane. Computational models are used to design the cascaded structure to assure maximum isolation amplitude and bandwidth.

Anisotropic impedance surfaces, which include metasurfaces and high impedance surfaces (HIS), can be designed to control the amplitude and propagation direction of surface electromagnetic waves and are an effective means to enhance the isolation between antennas that share a common ground plane. To date, the majority of metastructures that have been designed for antenna isolation have relied on an isotropic distribution of unit cells that possess a stop band that inhibits the propagation of surface waves between neighboring antennas. A less common approach to isolation has been through the design of a metasurface that enables the re-direction of surface waves away from the location of the antenna structure, which effectively limits the coupling. In this paper, we discuss results from our computational investigation associated with improving antenna isolation through the use of an anisotropic metastructure. Simulated results associated with the isolation performance of two simple, but similar, anisotropic structures are compared to the corresponding results from a broadband magnetic radar absorbing materials (magRAM).

Plasmonics is promising for future electronics as it can combine optical speed of operation with nanoscale size, something which is not possible with traditional optics and electronics [1]. Coupling of photons, plasmonic excitations and electrons is of key importance as it provides opportunities to monitor or control plasmonic nanocircuits electrically.

Over the past fifteen years, a lot of efforts have been focused on understanding the effective properties of metamaterials [1]. In the last few years, metasurfaces in particular have been widely investigated [2]. Several homogenization methods dedicated to them have been proposed but, due to the topic’s complexity, none have yet to be widely accepted. We considered a specific homogenization method dedicated to metasurfaces, namely Generalized Sheet Transition Conditions (GSTC, [3]). This method was chosen because it is compatible with retrieval from reflection and transmission coefficients. In this method, metasurfaces are characterized by electric and magnetic susceptibilities. In the literature, retrieved effective parameters have been shown to violate causality around resonances and this has been attributed to spatial dispersion [4]. In order to determine if spatial dispersion is the only source of this phenomenon, we have investigated the statistical properties of estimators that have been put forward for these susceptibilities. We have thus computed the Cramér-Rao lower bounds on the variance of these estimators. We have shown that this bound increases substantially around resonances making retrieval possible only for very high Signal-to-Noise Ratio (SNR, [5]). Therefore, in experiments, issues arising from spatial dispersion and noise compound and result in non-physical effective parameters. To mitigate this, we have proposed a least-squares estimator for susceptibilities that has a better performance with respect to noise. Sensitivity to noise is particularly acute for low-loss metasurfaces. It often results in required SNRs that are unachievable in practice. The present work is thus relevant to the development of loss-compensated metasurfaces for which the issues posed by retrieval will have to be closely considered for accurate and robust device characterization.

Metasurfaces offer new degrees of freedom in moulding the optical wavefronts by introducing abrupt and drastic changes in the amplitude, phase and/or polarization of electromagnetic radiation at the wavelength scale. By carefully arranging multiple subwavelength anisotropic or gradient optical resonators, metasurfaces have been shown to enable anomalous transmission, anomalous reflection, optical holograms and spin-orbit interaction. However, experimental realization of high-performance metasurfaces that can operate at visible frequency range has been a significant challenge due to high optical losses of plasmonic materials and difficulties in fabricating several subwavelength plasmonic resonators with high uniformity. Here, we propose a highly-efficient yet a simple metasurface design comprising of a single, anisotropic trapezoid-shape antenna in its unit cell. We demonstrate broadband (450 - 850 nm) anomalous reflection and spectrum splitting at visible and near-IR frequencies with 85% conversion efficiency. Average power ratio of anomalous reflection to the strongest diffraction mode was calculated to be on the order of 1000 and measured to be on the order of 10. The anomalous reflected photons have been visualized using a CCD camera, and broadband spectrum splitting performance has been confirmed experimentally using a free space, angle-resolved reflection measurement setup. Metasurface design proposed in this study is a clear departure from conventional metasurfaces utilizing multiple, anisotropic and/or gradient optical resonators, and could enable high-efficiency, broadband metasurfaces for achieving flat high SNR optical spectrometers, polarization beam splitters, directional emitters and spectrum splitting surfaces for photovoltaics.

Resonant nanostructures made of high-refractive index dielectric materials offer a new way for manipulation of light at nanoscale. Due to their inherently high magnetic and electric resonant response and low losses at optical frequencies these nanostructures offers unique functionalities, which are not achievable with conventional nanoscale plasmonics. Simple examples are strong magnetic near-field enhancement and directional scattering by nanoparticles of spherical shape, also known as a Kerker’s effect. In this talk, I will review this new rapidly developing research direction and present several new results of our team, which demonstrate a huge potential of dielectric nanoantennas for various applications. Fist will be experimental demonstration of highly localized magnetic and electric fields in silicon nanodimer antennas, which can be excited at any polarization of incoming light. Second will show low-loss light propagation in silicon nanoparticle waveguides, which can be much longer than in plasmonic waveguide of similar dimensions. Finally I will present how the light can be manipulated with almost fully transparent resonant dielectric metasurfaces having a full 2π control over the phase of incoming light at visible and near-IR wavelengths.

Quantum vacuum engineering is an active field of research. Here we use recent advances in the field of metasurface (2D-array of sub-wavelength scale nano-antennas) to construct an anisotropic quantum vacuum (AQV) in the vicinity of a quantum emitter located at some macroscopic distance from the metasurface. Such AQV can induce quantum interference among several atomic transitions, even when the transition dipole moment corresponding to the decay channels are orthogonal. Recently, there have been few theoretical proposal to use metamaterials to engineer the back-action. All these approaches, which works in the near field (few tens of nanometers from the surface), suffers from trapping an atom at these distance, surface interactions like quenching, Casimir force etc. Hence it’s pivotal to construct the back-action over macroscopic distance. We harness the polarization dependent response of a metasurface to engineer the back-action of the spontaneous emission from the atom to itself. We show strong anisotropy in the decay rate of a quantum emitter which is a manifestation of AQV. Engineering light-matter interaction over macroscopic distances opens new possibilities for long-range interaction between quantum emitters for quantum information processing, spin-optics/spintronics etc.

Recently, the use of phased array metasurfaces to control the phase and amplitude of electromagnetic waves at subwavelength dimensions have led to large number of devices ranging from flat optical elements to holographic projections. Here we analytically (and numerically using FDTD techniques) develop a design principle to form reconfigurable metasurfaces that control the phase of transmitted beam between 0 and 2π in a lossless manner. For a linearly polarized plane wave incident on a sub-wavelength array of dielectric resonators, we engineer the size of the individual resonators and the array periodicity such that the fundamental Electric and Magnetic dipole resonances of the device cross each other. This mode crossing caused by coupling of individual resonator modes with the surface lattice resonances, constructively interferes with the incident plane wave enabling us to form lossless metasurfaces. By optically pumping charge carriers into the resonators, we can tune the refractive index of the individual resonators leading to arbitrary control over the phase of the transmitted beam between 0 and 2π with less than 3dB loss in intensity. Further, we extend these strategies by redesigning the resonator elements by forming core-shell (metal-dielectric) resonators to cause the resonance matching within each resonator. This enables the mode crossing to be independent of the periodicity of the resonator elements while preserving the arbitrary control over the phase through charge carrier modulation. Such metasurfaces with spectrally overlapping electric and magnetic dipole modes may form the basis for a range of metadevices with unprecedented control over the Electromagnetic wave front.

In this paper, we present new results on the controlled directional steering and focusing of surface plasmon polaritons (SPPs) via 1D and 2 D metagratings by changing the angle of incidence, the incident wavelength and polarization. These findings build on previous work of our group on polarization controlled steering of SPPS using fishbone meta gratings and greatly expand on the functionality of the latter using novel designs. First we show that by creating a running wave of polarization along a one dimensional metallic metagrating consisting of subwavelength spaced rotated apertures that propagates faster than the SPP phase velocity, we can generate surface plasmon wakes, which are the two-dimensional analogue of Cherenkov radiation. The running wave of polarization travels with a speed determined by the angle of incidence and the photon spin angular momentum. We utilize this running wave of polarization to demonstrate controlled steering of the wakes by changing both the angle of incidence and the polarization of light, which we measure through near-field scanning optical microscopy. Next we report a simple 2D metagrating design strategy that can be used for focusing, polarization beam splitting, waveguide coupling, and even phase control at the focus of an SPP beam. We experimentally verify our 2D metasurface by creating a four wavelength plasmonic demultiplexer, which also has polarization selectivity (on/off). The wavelength demultiplexer is designed such that each of the four wavelengths is focused to a different spot outside of the structure. Coupling of free space light to SPPs is achieved by milling subwavelength apertures into a thin gold film. This methodology can be easily extended to any wavelength where SPPs exist, for an arbitrary number of wavelengths, and with polarization selectivity and phase control at the focus as well.

Thin layers of semiconductors where the permittivity crosses zero, support a particular polariton mode called epsilon-near-zero (ENZ) mode. This zero crossing can be obtained near optical phonon resonances in dielectrics or the plasma frequency in doped semiconductors. The coupling of metamaterial resonators to these ENZ modes leads to particularly large Rabi splittings. ENZ layers can be added to metamaterial-based strongly coupled systems to increase this coupling even further. I will discuss several examples of these coupled systems that include metasurfaces, phonons, intersubband transitions and ENZ modes.

We demonstrate a method to hide a Gaussian-shaped bump on a ground plane from an incoming plane wave. In essence, we use a graded metasurface to shape the wavefronts like those of a flat ground plane[1,2].The metasurface provides additional phase to the electromagnetic field to control the reflection angle. To mimic a flat ground plane, the reflection angle is chosen to be equal to the incident angle. The desired phase distribution is calculated based on generalized Snell’s laws[3]. We design our metasurface in the microwave range using sub-wavelength dielectric resonators. We verify the design by full-wave time-domain simulations and show that the result matches our theory well. This approach can be applied to hide any object on a ground plane not only at microwave frequencies but also at higher frequencies up to the infrared. 1. Jensen Li and J. B. Pendry, Hiding under the Carpet: A New Strategy for Cloaking. Phys. Rev. Lett. 101, 203901 (2008) 2. Andrea Alu, Mantle cloak: Invisibility induced by a surface. Phys. Rev. B 80, 245115 (2009) 3. Yu N, et al. Light propagation with phase discontinuities: Generalized laws of reflection and refraction. Science 334(6054):333–337 (2011)

The electromagnetic properties of vacuous curved spacetime and of a certain fictitious material in flat spacetime are noncovariantly equivalent. This fictitious medium - known as the Tamm medium - is generally bianisotropic and nonhomogeneous. The Tamm medium offers opportunities for exploring the electromagnetic properties of certain curved-spacetime scenarios that may be impractical to explore by direct methods. The realization of various Tamm mediums as homogenized composite mediums was investigated. The approach taken involved the homogenization of relatively simple component materials, with the inverse Bruggeman formalism exploited to estimate appropriate constitutive parameters, shape parameters, and volume fractions for the component materials. Typically, Tamm mediums are highly anisotropic in regions corresponding to relatively large spacetime curvature (e.g., in the vicinity of spacetime singularities). In principle, at least, such high degrees of anisotropy may be achieved by homogenizing component particles that are highly elongated. The nonhomogeneous nature of Tamm mediums can be accommodated by adopting a piecewise homogeneous approach, which is valid for appropriate wavelength regimes.

A novel metamaterial structure is presented for applications as a backward propagating Cherenkov source or Cherenkov detector. The structure comprises of a complementary split ring resonator (CSRR) metasurface loaded waveguide, which exhibits left handed behaviour between 5-6 GHz. When the left handed, TM-like mode couples with an incident electron beam, backward propagating Cherenkov radiation is observed. The structure is suitable for beam-based applications, exhibiting strong beam coupling parameters and significant excitation of longitudinal wakefields. Three dimensional particle in cell simulations are performed to identify a suitable beam for operation. High and low energy beams, with different bunch dimensions from the literature, are considered and compared to investigate the nature of the beam-wave interaction this structure can support, and to identify any required modification before beam tests can be performed. This structure can lead to new solutions for non-destructive beam diagnostics, wakefield acceleration and backward wave oscillators which can potentially be scaled to higher frequency ranges.

Resonantly absorbing thin films comprising periodically sub-wavelength structured metal surface, dielectric spacer, and metal ground plane are a topic of current interest with important applications. These structures are frequently described as “metamaterials”, where effective permittivity and permeability with dispersion near electric and magnetic resonances allow impedance matching to free space for maximum absorption. In this paper, we compare synchrotron-based infrared spectral microscopy of a single isolated unit cell and a periodic array, and we show that the resonances have little to do with periodicity. Instead, the observed absorption spectra of usual periodically structured thin films are best described as due to standing-wave resonances within each independent unit cell, rather than as due to effective optical constants of a metamaterial. The effect of having arrays of unit cells is mainly to strengthen the absorption by increasing the fill factor, and such arrays need not be periodic. Initial work toward applying the subject absorbers to room-temperature bolometer arrays is presented.

We experimentally demonstrate a classical analogue of double Fano resonances in a planar composite metamaterial possessing tripod plasmonic resonances, where a common subradiant dipole corresponding to the dark mode is coupled with two superradient dipoles corresponding to two bright modes. The composite metamaterial is structured such that four-rod resonators (FRR) are embedded inside double-split ring resonators (DSRR) superlattice. Two dipole resonances of DSRR are superradiant modes and one dipole resonance of FRR is subradiant mode. Proximity of the inner diameter of DSRR and the rod-length of FRR permits near field coherent couplings, and the composite metamaterial is a tripod metamaterial system possessing two superradiant dipole resonances of DSRR coupled coherently with one common subradiant dipole resonance of FRR in near field, similar to a tripod atomic system with four atomic levels coupled coherently by coherent optical fields. Important finding is that double Fano resonances in the composite metamaterial are correlated, showing up as a transfer of the absorbed power from one superradiant dipole to the other superradient dipole in DSRR. The general feature of plasmonic Fano resonance is examined where both superradiant and subradiant oscillators are externally driven. Analysis based on two coupled oscillators model leads to the fact that the characteristic asymmetric Fano resonance formula of plasmonic structure is kept the same with a modication in the asymmetry parameter q.

We present experimental and theoretical study of the transmission of linearly polarized microwaves through a slab of negative index of refraction metamaterials. A metamaterial slab was designed with an extended S-Shaped Split Ring Resonator (ES-SRR) to exhibit a negative index of refraction around 13.25 +/- 0.75 GHz which is a commercially leased microwave band for satellite communications. The metamaterial slab exhibits a pass-band filter transmission behavior around 12.5 GHz to 14 GHz, encompassing the Ku-band.

An array composed of six electrically small resonators and a transmission line is proposed to enhance terahertz (THz) wave transmittance. Silver is the metal of choice for the proposed array. Three thousand of the proposed arrays are fabrication on an intrinsic double-side polished silicon wafer using nano-technology tools, followed by THz time-domain spectroscopy (THZ-TDS) measurement, to validate the numerical findings experimentally.

We have fabricated a metamaterial tunable filter for dynamic frequency selection in the terahertz region. The metamaterial consists of a sandwich of two meta-surfaces grown on high resistivity silicon wafers. The first meta-surface consists of a two-dimensional array of gold double split ring resonators and the second meta-surface consisits of an array of gold cut rods. Both meta-surfaces are fabricated for a response in the terahertz region. Our terahertz pulses are produced using the standard Austin switch technique. The terahertz pulse is focused onto the two meta-surfaces which are sandwiched together to produce a transmission window. Together, with the right orientation, translation, and parallelism of the two meta-surfaces, we achieve filtering of terahertz pulses. Since the unit cells for the inclusions are on the order of 100 microns, control of the translation, orientation, and parallelism of the two meta-surfaces with respect to each other and with respect to the orientation and direction of the impinging terahertz field is a challenge. We describe our technique for doing this and present data on our frequency filtering in the terahertz.

Hybrid plasmonic nanoprisms in the form of gold (Au)-dielectric- silver (Ag) sandwich structures have been designed and simulated using Finite-difference time-domain (FDTD) simulation technique. Simulations results show two dipole resonant peaks for the hybrid sandwich structure. Also, a strong wavelength dependence of the plasmonic resonance peaks on the edge length and the thickness of gold and silver layers. The increase in edge length and thicknesses were found red shift to the plasmonic peak of the nanostructures. Furthermore, the resonant wavelengths and relative strength of the two dipole plasmonic peaks are demonstrated to be tunable.

The artificially structured metamaterials has led to many potential applications in terahertz regime, but the role in adjusting the terahertz transmission still needs to be carefully investigated. Currently, designs with split ring resonator (SRR) based metamaterials can provide a promising approach for understanding the terahertz transmission characteristics. In the experiments, a SRR-based metamaterial is proposed for presenting terahertz transmission characteristics. The substrate of the metamaterial is an n-type gallium arsenide (n-GaAs) film grown over a semiinsulating GaAs wafer. Then, the metallic film, fabricated on n-GaAs, is patterned into an arrayed four-gap microstructure according to traditional ultraviolet photolithography methods. The metal film and n-GaAs film form a Schottky contact. In the experiments, the transmission frequency spectrum of the metamaterial has an obvious fluctuation in the 0.6–1.23 THz and 1.52–2.4 THz range, and the experimental results show that the frequency region of the intensive oscillatory signal essentially agrees with that of the metamaterial characteristic transmission spectrum in the 0.5–2.5 THz range. The terahertz characteristic transmission spectrum of the fabricated metamaterial are measured at the central frequency of ~0.5, ~1.0, ~1.5, ~2.0 and ~2.5 THz, thus the oscillation characteristics can be explained by dipole resonance. The measured time-domain transmission signals and corresponding frequency responses based on the metamaterial agree well with calculated results. Therefore, our research shows a potential application of the transmission adjusting roles in terahertz regime.

In the present study, we theoretically investigate how shaping of the light distribution that illuminates a large numerical aperture lens can be used to efficiently couple light to a particular element of optical nano-circuits located at the focal region of the lens. In addition to standard plane waves, we consider illumination schemes that provide peculiar light distributions at focus, such as cylindrical vector beams. These results show that light excitation may be included as an additional degree of freedom in the optimization of optical and metatronic nano-circuitry and their coupling to conventional optical systems.

Developments in the area of metamaterial research have generated interest in toroidal moments and their treatment in the quantum regime. A quantum mechanical method of determining toroidal moments due to current circulating on a toroidal helix is presented. The Hamiltonian of a negatively charged spinless particle constrained to motion in the vicinity of a toroidal helix having loops of arbitrary eccentricity is developed. The resulting three dimensional Schr¨odinger equation is reduced to a one dimensional form inclusive of curvature effects. Low-lying eigenfunctions of the toroidal helix system are determined along with corresponding toroidal moments. A disagreement, not predicted by a classical treatment, arises between toroidal moments of elliptic toroidal helix systems when vertical and horizontal eccentricity are transposed.

Mie resonance in square arrays of dielectric rods has been reported. Arrays in square lattice of dielectric rods with very high permittivity in air have been considered. Light of transverse electric mode has been launched on the square array of cylindrical dielectric rods. Mie resonance of first two orders has been observed in the dielectric rods, due to which electric and magnetic dipoles are generated in the rods. Thus, electric resonance and magnetic resonance at different frequencies has been observed with material of high value of permittivity.

Designing metamaterials to possess extreme index values requires near resonant properties which, in turn, leads to these properties over diminishing bandwidths. Recent studies have shown that some bandwidth control might be possible by exploiting metamaterial substrates. We have demonstrated the concept in our design, and investigated the trade-offs between substrate structure, bandwidth extension and increase in losses. Loss management can be controlled by choice of metamaterial elements and replacement of metal by semiconductors. This also has the added advantage of some degree of tunability.