Symposium E
Progress in Metamaterials Research

ABSTRACTS

Session E-1 - Physics and Modelling of Metamaterials Systems

E-1:IL01  Some Perspectives in Non-Hermitian Metamaterials
V. GALDI, University of Sannio, Benevento, Italy

Inspired by the concept of parity-time symmetry in quantum mechanics, "non-Hermitian" optical scenarios, characterized by spatial modulation of loss and gain, have recently elicited a growing attention in both theoretical and application-oriented studies. From the theoretical viewpoint, the interest is motivated by the possibility to conceive optical "testbeds" for the (otherwise impossible) experimental study of controversial quantum-physics effects. From the application viewpoint, a variety of anomalous light-matter interaction effects (e.g., unidirectional invisibility, coherent perfect absorption, negative refraction and focusing) have been demonstrated and observed that could set the stage for the development of novel optical devices. Here, we review some recent results in the field of non-Hermitian metamaterials. In particular, we present a complex-coordinate extension of the transformation-optics framework, which naturally handles media featuring loss and gain and, in conjunction with the well-established "complex source point" formalism, provides an insightful interpretation in terms of the manipulation of beam-like wave objects. Moreover, we also illustrate certain interesting tunneling and waveguiding phenomena that can occur in parity-time symmetric bi-layers.


E-1:L03  Validity of Effective Medium Approximation in Deeply Subwavelength All-dielectric Multilayers
A.V. LAVRINENKO, S.V. ZHUKOVSKY, A. ANDRYIEUSKI, O. TAKAYAMA, E. SHKONDIN, R. MALUREANU, F. JENSEN, Technical University of Denmark, Kgs. Lyngby, Denmark

Dielectric multilayers with individual layers thicknesses much thinner than the wavelength of light have been traditionally regarded as the optimal case for the application of the effective medium approximation. Indeed, in such structure the field variation inside a single layer is very small, leading to negligibly weak interference effects. Therefore, a light wave interacts with the structure as a whole rather than with its individual layers. The structure can thus be treated as a piece of homogeneous material characterized by effective parameters. However, recent publication by Sheinfux et al. (Phys. Rev. Lett. 2014, v.113, 243901) disavows the validity of this commonly accepted assumption in certain circumstances. We report on a thorough experimental check of the effective index approximation accuracy. In particular, we demonstrated that the approximation breaks even for deeply subwavelength layer thicknesses (less than 1/30 of the light wavelength). Such breakdown manifests itself as the difference in the reflectance spectra of structures with different layer thickness or different layer ordering. The measured reflectance difference spectra expose deviations in reflectance as big as 0.5, putting special constrains on application of the effective medium approximation.


Session E-2 - Microwave and THz Metamaterials

E-2:IL01  Digital Metamaterials for Terahertz Single Pixel Imaging
W.J. PADILLA, Duke University, Department of Electrical and Computer Engineering, Durham, NC, USA

Spatial light modulators are useful for a host of applications including imaging and holography. We utilize metamaterial digital spatial light modulators to enable single pixel imaging in the terahertz regime. The theory of coded aperture imaging is discussed and the future potential applications of this exciting field are discussed.


E-2:L03  Enhanced Chirality in the Near-field of Electromagnetic Metamaterials
L.E. BARR, A.P. HIBBINS, E. HENDRY, XM2 Centre for Doctoral Training in Metamaterials, University of Exeter, Exeter, Devon, UK

Quantifying a chiroptical interaction in a manner consistent across a range of systems is a difficult task, since in evanescent fields, spin and orbital angular momenta are not clearly defined [1]. In this contribution we define a chiral electromagnetic field as one that has electric and magnetic fields with parallel components and a π/2 phase difference [2]. Using this definition, we experimentally and computationally study a chiral metamaterial consisting of an array of barely sub-wavelength metallic helices, considering the interaction with both evanescent [3] and propagating chiral EM fields in the microwave regime, elucidating the underlying physics.
[1] L. Allen et al, Progress in Optics, 39, 291 (1999); [2] Y. Tang and A. Cohen, Phys. Rev. Lett. 104, 163901 (2010); [3] E. Hendry et al, Nano Lett. 12, 3640 (2012)


E-2:L04  RF Plasmonic State and Negative Permittivity Properties of Random Percolative Composites
RUNHUA FAN, College of Ocean Science and Engineering, Shanghai Maritime University, Shanghai, P.R.China; and School of Material Science and Engineering, Shandong University, Jinan, P.R. China

Double negative materials (DNMs) with simultaneously negative permittivity and negative permeability have attracted extensive attention worldwide in recent years because of their various potential applications in electronic, microwave and optics. Different from metamaterials which gain their double negative properties not from their composition but from their exactingly-designed structures, random DNMs is proposed from the point of view of materials, i.e. intrinsic properties determined by chemical composition and microstructure. We have prepared a series of conductor-insulator composites for the DNMs. Interestingly, plasmonic negative permittivities are obtained in the percolative composites. And, unique fano-like plasmon resonances that switch the permittivity from negative to positive are also observed in the dielectric spectra. Further investigations indicated that, the fano-like dielectric frequency dispersion can be attributed to the interference between the electromagnetic radiations emitted by the LC resonance of the composites and the external high frequency electromagnetic field. The realization of negative permittivity in percolative composites will have great significance on the development of double negative materials.


E-2:L05  Mode Index Tunable Moiré Pattern Metasurfaces
R.C. MITCHELL-THOMAS, J.R. SAMBLES, A.P. HIBBINS, Electromagnetic and Acoustic Materials Group, Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, UK

Metasurfaces have been shown to be of significant benefit in the pursuit of antenna miniaturisation. Reduction of the volume and weight of communications systems is highly advantageous for application in the aerospace and aeronautical sectors. One area where metasurface-based antennas are not as well developed as their traditional counterparts is beam steering. This relies on tunability of the properties of the metasurface, either from electronic or mechanical tuning. This presentation will focus on the possibility of using Moiré interference patterns to mechanically tune the mode index of a metasurface. This is done by rotating two sets of equivalent metasurfaces with respect to one another. Upon rotation, the pattern becomes perfectly periodic only at discrete angles, and numerical simulations can be performed to calculate the dependence of the mode index on frequency for these angles. Using a lithographic fabrication technique, samples will be manufactured, and the dispersion characteristics of these structures will be studied both at, and in between the aforementioned discrete periodic angles, allowing an insight into the behaviour of the aperiodic metasurfaces.


E-2:IL08  Metasurfaces with Electric, Magnetic and Magneto-electric Properties
A. GRBIC, B. TIERNEY, C. PFEIFFER, Dept. of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA

Metamaterials have provided unprecedented control over electromagnetic fields. However, their notable thickness has often led to fabrication challenges and added loss. This has motivated the development of metasurfaces. Metasurfaces are surfaces textured at a subwavelength scale to achieve tailored electromagnetic properties. Here, we describe how metasurfaces with tailored electric, magnetic and magneto-electric surface parameters can be realized. Such metasurfaces offer extreme field control to realize desired transmission and reflection characteristics, guidance properties, and polarization conversions. A systematic approach to designing these metasurfaces is outlined, and a pragmatic approach to realizing them is described. The approach involves cascading anisotropic electric sheets (patterned metallic surfaces) across a subwavelength thickness. In contrast to earlier metasurface designs, complex 3D geometries such as omega and helical particles are not needed to achieve the magneto-electric responses. The cascaded electric sheets can be fabricated using planar fabrication processes. This is attractive since it allows the realization of microwave (optical) metasurfaces using standard microfabrication (nanofabrication) strategies.


E-2:L09  Resonant Transmission through Thin Metal Layers using Two Dimensional Arrays
M. CAMACHO-AGUILAR, A.P. HIBBINS, J.R. SAMBLES, University of Exeter, Exeter, UK

Thin (< skin-depth) metal layers are known to almost completely screen a microwave electromagnetic field due to the near perfect response of the electrons at these frequencies. Nevertheless, it has recently been shown possible to resonantly transmit microwaves through a 60 nm-thick aluminium layer by surrounding it with an array of thin resonant cavities. In this work, in order to provide the necessary impedance matching, we employ a thin dielectric sheet coated with a variety of different metallic patterns and resonant structures to maximise the magnitude of the transmitted signal. We explore the angle dependence of transmission and absorption, and our experimental results compare well with the predictions of numerical finite element method models. This type of structure could be used in a device that works as a very narrow band-pass filter for microwaves with either unknown polarisation or relative position to the source such as in satellite applications.


E-2:L10  Exploring the Interactions in Systems of Densely Packed Split Ring Resonators
S. SEETHARAMAN, I.R. HOOPER, W.L. BARNES, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, Devon, UK

Split Ring Resonators (SRRs) are a fundamental building block of many electromagnetic metamaterials. Typically, the response of the metamaterial is assumed to be independent of interactions between the SRRs of which they are comprised. Here we show that SRRs in close proximity exhibit a rich coupling that involves both electric and magnetic interactions. We study experimentally and computationally the strength and nature of the coupling between two identical metallic split ring resonators operating at microwave frequencies. By placing two SRRs in a waveguide we measure the frequency dependent transmission as a function of SRR separation and relative orientation. We characterize the length scales of the electric and magnetic couplings and find that, depending on their relative orientation, the couplings can either reinforce each other or act in competition. These results will be important in designing and exploiting densely packed metamaterial systems, for example those used to mimic the molecular aggregates employed in photosynthesis.


Session E-3 - All-dielectric Metamaterials and Metasurfaces

E-3:IL01  High Quality Factor Silicon-based Metasurfaces
J. VALENTINE, YUANMU YANG, Vanderbilt University, Nashville, TN, USA; A. BOULESBAA, I.I. KRAVCHENKO, D.P. BRIGGS, A. PURETZKY, D. GEOHEGAN, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA

While plasmonic metasurfaces have seen much development over the past decade, they still face throughput limitations due to ohmic losses. On the other hand, all-dielectric metasurfaces can eliminate the issue of ohmic loss while still providing the freedom to engineer the optical properties of the composite. In this talk, I will describe the use of silicon-based metasurfaces possessing sharp Fano resonances possess experimental Q-factors approaching 500 in the near-infrared regime, much larger than their plasmonic counterparts. The high-Q resonance is accomplished by employing Fano-resonant unit cells in which both radiative and non-radiative damping are minimized and is magnified by coherent interactions among the resonators. Along with a large Q-factor, the electromagnetic field is enhanced in the metamaterial. We take advantage of this fact to demonstrate sensing with a figure of merit above 100. We also examine nonlinear conversion enhancement demonstrating a third harmonic conversion enhancement factor of 10^5 with respect to an unstructured silicon slab.


E-3:IL02  Dielectric Nanoantennas and Metasurfaces based on Si Nanoparticles
A.I. KUZNETSOV, Data Storage Institute, A*STAR, Innovis, Singapore

Research on nanoantennas and metasurfaces based on high-index dielectric and semiconductor materials form a new branch in nanophotonics. Thanks to their strong interaction with both electric and magnetic components of light, resonant dielectric nanostructures provide a variety of opportunities, which were not possible in plasmonics. Silicon is now considered as one of the most promising materials for nanoantenna design. Having relatively small feature size (around 100-200 nm for resonances in the visible), resonant silicon nanostructure have a number of advantages compared to their plasmonic counterparts, including: very low losses in near-IR and visible spectrum; strong magnetic dipole response (much stronger than electric dipole in the certain wavelength range) and compatibility with CMOS nanofabrication. In this talk, I will review several recent results of our team, which demonstrate a huge potential of resonant dielectric nanostructures for a variety of applications. This will include: (i) magnetic near-field enhancement in silicon nanoantennas, (ii) low-loss light guiding in resonant Si nanoparticle chains, (iii) highly-efficient visible light bending with dielectric metasurfaces, and (iv) generalized Brewster effect in dielectric metasurfaces with strong magnetic response.


E-3:IL03  Resonant Dielectric Huygens’ Metasurfaces
I. STAUDE, Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-University Jena, Jena, Germany; K.E. CHONG, M. DECKER, D.N. NESHEV, Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, ACT, Australia; I. BRENER, Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, NM, USA; YU. S. KIVSHAR, Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, ACT, Australia

Resonant optical metasurfaces tailored to impose a spatially variant phase shift onto an incident wavefront have developed as a breakthrough concept for advanced wave-front engineering. However, reflection and/or absorption losses as well as low polarization-conversion efficiencies pose fundamental obstacles for achieving the high transmission efficiencies that are required for practical applications. A way to overcome these challenges is provided by the use of high-refractive-index dielectric nanoresonators as meta-atoms. In addition to exhibiting very low absorption losses, such nanoresonators can be tailored to emulate the behavior of the forward-propagating elementary wavelets known from Huygens’ principle. This is possible based on the simultaneous excitation of electric and magnetic dipole resonances. My talk will review our recent advances in lightwave control with dielectric Huygens’ metasurfaces, demonstrating that high transmittance efficiencies, full phase coverage, and a polarization insensititve response can be realized at NIR frequencies using arrays of silicon nanodisks as meta-atoms. Various examples of wavefront control will be discussed, including beam shaping and holographic imaging, both of which we have experimentally demonstrated with high efficiency.

 
Session E-4 - Nonlinear, Tunable and Active Metamaterials

E-4:IL02  Optimizing the Second Harmonic Chiroptical Effects in Plasmonic Nanostructures
V.K. VALEV, Department of Physics, University of Bath, Bath, UK

Strong second harmonic generation (SHG) chiroptical effects result from the interaction of light with chiral plasmonic nanostructures. Due to the favorable power-law scaling of near-field enhancements, the nonlinear optical properties of chiral plasmonic nano- and metasurfaces are of prime fundamental and practical interest. Moreover, modern nanofabrication techniques allow us to endow the surfaces of nanostructured metal films with virtually any possible symmetry we can imagine. For a surface/interfaces technique, such as SHG, this freedom in design presents novel opportunities to probe material properties. We will discuss a range of nano/meta-material geometries that have been investigated with SHG and, in particular, we will seek to optimize the second harmonic circular dichroism (SHG-CD) response. Both chiral and achiral contributions will we discussed and the relationship between superchiral light and SHG will be demonstrated.


E-4:IL03  Thermally Tunable Self-assembled Metamaterials
C. ROCKSTUHL, Institute of Theoretical Solid State Physics, Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany; M. FRUHNERT, Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany; W. LEWANDOWSKI, J. MIECZKOWSKI, E. GÓRECKA, Faculty of Chemistry, University of Warsaw, Warsaw, Poland

Self-assembled metamaterials promise to mitigate some deficiencies of traditional metamaterials made by top-down techniques. Specifically, they can be fabricated at large scales, at low costs and usually come with the advantage of having an isotropic optical response. Many interesting material properties have been demonstrated, e.g. a strong magnetic response or negative index. However, what is missing in most bottom-up materials is the ability to dynamically tune their response, i.e. once the material is available the optical response shall be reversibly switched. Here, we discuss such material where tunability is achieved by a liquid crystal that shows a pronounced thermal response. Covering metallic nanoparticles with this liquid crystal allows the reversible switch between well distinguishable material phases. While identifying a lamellar and an amorphous phase, we show that the modified interaction of the metallic nanoparticles in the two phases causes a pronounced change in the optical response. As shown by experiment and theory, the material possesses a tunable Lorentzian response in the effective permittivity in the blue part of the visible spectrum. Such material is the first of its kind and might be at the heart of future devices that rely on tunable metamaterials.


E-4:IL04  Tunable Metamaterials: Conceptual Overview and Recent Highlights
M. LAPINE, University of Technology Sydney, NSW, Australia

At the early stages of metamaterial research, people were fascinated with the impressive range of exciting possibilities they may offer. Clearly, having a dynamic control over their properties, so that these can be adjusted 'on the fly' for a given device or sample, provides a great practical significance. I will review a range of approaches on how tunability and reconfigurability can be added to metamaterial design. Particular emphasis will be given to power-driven tunability in nonlinear metamaterials, occurring via nonlinear self-action; mechanical tunability in dense arrays, enabled by enhanced lattice effects; structural nonlinear tuning, resulting from dynamic interaction between electromagnetics and mechanics; as well as some exotic tunability methods based on a combination of quite different physical properties within one meta-atom. Specific effects emerging in finite samples due a strong influence of the boundaries, will also be pointed out. The selection of examples will include both resonant and non-resonant metamaterials, involving radio-frequency, microwave, and optical signals; and routes towards practical applications will be discussed.


E-4:IL05  Enhanced Optical Nonlinearities from Metasurfaces Coupled to Semiconductors
I. BRENER, Sandia National Labs and Center for Integrated Nanotechnologies, Albuquerque, NM, USA

I will present an overview of some recent results where nonlinear optics is combined with both metallic and dielectric metasurfaces. Record second order nonlinearities can be obtained when metallic metasurfaces are coupled with resonant electronic transitions in semiconductors such as intersubband transitions. Additionally, since the nonlinear unit in this case is a single resonator coupled to the semiconductor heterostructure, additional functionality can be obtained at the second harmonic beam. This phenomena can be described as a phased-array source. Using this principle, we have created beam and polarization splitters operating at the second harmonic wavelength. This is new functionality that has no counterpart in conventional nonlinear optical materials. Another interesting case is the combination of all-dielectric metasurfaces with optical nonlinearities, both bulk and surface enhanced. All-dielectric metasurfaces provide a platform to engineer magnetic and electric resonant modes in wavelength-scale nanoresonators. Fabricating such dielectric metasurfaces from different types of semiconductors can be used to enhance their second and third order nonlinearities by several orders of magnitudes.


E-4:IL06  Nonlinear and Tunable Metamaterials
MINGKAI LIU1, KEBIN FAN2, W. PADILLA2, D.A. POWELL1, XIN ZHANG3, I.V. SHADRIVOV1, 1Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra ACT, Australia; 2Duke University Department of Electrical & Computer Engineering, Durham NC, USA; 3Department of Mechanical Engineering, Boston University, Boston, MA, USA

We propose a new type of nonlinear and tunable metamaterial, a meta liquid crystal, which is made of thin elongated dielectric particles with chains of meta-atoms, and these particles are dispersed in a liquid environment. These elements reorient in response to static electric field, directing the axis of anisotropy, thus tuning the electromagnetic response of the whole structure. This is a truly three-dimensional metamaterial in a liquid phase that can occupy arbitrarily shaped volumes. There is considerable freedom to design the electromagnetic properties through the appropriate choice of the meta-atom geometry, and the electrodynamic and electrostatic responses can differ greatly. We fabricate such tunable meta liquid crystals and demonstrate that they can modulate both the amplitude and phase of transmitted terahertz signals. We find that significant modulation contrast and linear birefringence can be achieved even for very small volume densities. We study three different designs and compare their performance. Our study demonstrates the feasibility of meta liquid crystals as a novel form of three dimensional tunable metamaterial.
 

E-4:IL07  Alternative Materials and Solutions for Next Generation Plasmonic Technology
M. FERRERA, School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA, & School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, Scotland, UK

With the fast development of plasmonics and metamaterial technologies, after the initial pioneering studies focused on noble metal-based devices and structures, a tremendous need for alternative, versatile, and CMOS-compatible compounds is arising in order to upgrade metadevices from a lab concept to a practical reality. Recently, significant attention has been given to new platforms such as Transition Metal Nitrides (TMNs) and Transparent Conductive Oxides (TCOs), which overcome many of the intrinsic limitations of gold and silver namely lack of CMOS compatibility, ultra thin film fabrication constrains, and lack of tunability of their optical properties. TMNs (e.g. titanium and zirconium nitride -TiN, ZrN), from an optical point of view, closely resemble gold but they have a tailorable plasma frequency falling in the visible/ultraviolet region. TMNs are very durable materials with exceptionally thermal, chemical, and mechanical stability, and they represent the best option for heat-assisted plasmonic applications. In my talk I will give a general overview of the huge potentials behind these novel compounds plus provide many examples of recent results mostly focused on TCO-based applications.


Session E-5 - Applications of Metamaterials and Metadevices

E-5:IL01  Optomechanical Metamaterials
E. VERHAGEN, FOM Institute AMOLF, Amsterdam, The Netherlands

By structuring material at the nanoscale, strong interactions between light and the motion of nanomechanical resonators can be established. Combining many optomechanical systems in two-dimensional arrays creates effective optomechanical metamaterials, which promise unprecedented control over light as well as acoustical degrees of freedom. These can be used for multiplexed mechanical sensing, efficient electro-optic conversion, and extreme optical nonlinearities. Moreover, exploiting the dynamics of optomechanical resonators allows to break time-reversal symmetry to create nonreciprocal response. We show our experimental efforts to create the basic building blocks of such metamaterials. We demonstrate record-strength optomechanical interactions achieved by confining photons at subwavelength scales in plasmonic and photonic crystal systems. Moreover, we study high-quality photonic resonators that allow nonreciprocal propagation of light due to its radiation-pressure induced interaction with mechanical motion.


E-5:IL02  Metamaterial based Nanobiosensors and Nanophotodetectors
E. OZBAY, Nanotechnology Research Center, Bilkent University, Bilkent, Ankara, Turkey

In this talk, we will present how metamaterials can be used for nanobiosensors and nanophotodetector applications. Our results show that a plasmonic structure can be successfully applied to bio-sensing applications and extended to the detection of specific bacteria species. A highly tunable design for obtaining double resonance substrates to be used in Surface Enhanced Raman Spectroscopy will also be presented. Surface Enhanced Raman Scattering experiments are conducted to compare the enhancements obtained from double resonance substrates to those obtained from single resonance gold truncated nano-cones. We will present a UV plasmonic antenna integrated metal semiconductor metal (MSM) photodetector based on GaN. We also report the design, fabrication, and measurement of a device comprising a split ring resonator array on epitaxial graphene. We obtained resonance broadening and tuning of split ring resonators by utilizing an epitaxial graphene transistor with transparent top-gate. Metallic split ring resonator (SRR) structures are used in nanophotonics applications in order to localize and enhance incident electromagnetic field. Electrically controllable sheet carrier concentration of graphene provides a platform where the resonance of the SRRs fabricated on graphene can be tuned. The reflectivity spectra of SRR arrays shift by applying gate voltage, which modulates the sheet carrier concentration, and thereby the optical conductivity of monolayer graphene. We experimentally and numerically demonstrated that the tuning range can be increased by tailoring the effective mode area of the SRR and enhancing the interaction with graphene.


E-5:IL03  Metamaterials as a Platform to study Localised and Propagating Toroidal Excitations
N.I. ZHELUDEV, V.A. FEDOTOV, N. PAPASIMAKIS, V. SAVINOV, T.A. RAYBOULD, University of Southampton, Southampton, UK

The ability to engineer the electromagnetic space with metamaterials provides a unique opportunity to study localised and propagating toroidal excitations. We overview metamaterial structures supporting electromagnetic toroidal modes, examine interaction of structured light with such metamaterials, discuss the effect of toroidal excitations on the bulk material properties and outline challenges for spectroscopy of such excitations. We also present the analysis of propagating toroidal electromagnetic perturbations in free-space, their interactions with nano-objects and examine metamaterial-based solution to launching such excitations, also know as flying doughnuts.


E-5:L06  High Temperature Stability of Oxide Photonic Structures
R. JANSSEN1, R. PASQUARELLI1, P.N. DYACHENKO2, A. PETROV2, M. EICH2, 1Institute of Advanced Ceramics and 2Institute of Optical and Electronic Materials, Technische Universität Hamburg-Harburg, Germany

Highly reflective coatings can be created using ordered pores in matrices with high refractive index, e.g. ‘inverse opals’ obtained by inversion of the colloidal crystals can provide more pronounced photonic bandgap properties since a stronger photonic interaction is expected in these structures. For reflecting radiation energy, structures with pores size around the µm range are interesting as they can be considered as candidates for thermal barrier coatings or selective emitter in thermophotovoltaics. At temperature >1000°C, however, these structures can exhibit significant undesired microstructural changes (due to phase changes, grain growth, sintering, etc.) that result in a loss of the desired photonic properties. At present, we focus on TiO2 and Al2O3 inverse opals which have been prepared from templates by vertically self-assembled PS monospheres, ALD infiltration and subsequent calcination. In the presentation we will report the synthesis, microstructure as well as resultant photonic properties by reflectance spectra. The results confirm that both mass transport by diffusion as well as phase changes are the key parameters for structural stability at elevated temperatures of the structures, and that by respective tailoring these coatings can serve at T>>1000°.

 
Session E-6 - Antenna, Nanoantenna and Waveguide Applications, Transformation Optics, Superlenses

E-6:IL01  Plasmonic Waveguides: Challenges and Perspectives
S. BOZHEVOLNYI, Department of Technology and Innovation, University of Southern Denmark, Odense M, Denmark

Recent years have seen a rapid expansion of research into nanophotonics based on surface plasmon–polaritons. These electromagnetic waves are bound to and propagate along metal–dielectric interfaces, and can be guided by metallic nanostructures beyond the diffraction limit. This remarkable capability has unique prospects for the design of highly integrated photonic signal-processing systems, nanoresolution optical imaging techniques and sensors. This talk summarizes the basic principles and major achievements of plasmonic waveguiding, and details the current state-of-the-art in subwavelength plasmonic waveguides, passive and active nanoplasmonic components for the generation, manipulation and detection of radiation, including configurations for the nanofocusing of light. Potential future developments and applications of nanophotonic devices and circuits in optical signals processing and nanoscale optical devices are also discussed.


E-6:IL02  Transformation Optical Applications with Pseudo-magnetic Field
JENSEN LI, University of Birmingham, School of Physics and Astronomy, Birmingham, UK

Conventional transformation optics bends light by changing sizes and shapes of the local dispersion surfaces. Here, we examine an alternative route in bending light by shifting the centers of the local dispersion surfaces, which can be realized using metamaterials with tilted anisotropy. A gradient of this shifting corresponds to a pseudo magnetic field, which can be used for generating one-way edge states and optical spin-Hall effect. Based on this additional bending power, we design an alternative cylindrical invisibility cloak. The asymmetry of light bending direction from a pseudo-magnetic field makes the cloak more tolerable to a truncation of the singular materials near the inner surface of the cloak. As another example, such an asymmetry allows us to design an omnidirectional retroreflector, with asymmetric transmission power.
 

E-6:L03  Imaging and Spectroscopy of Plasmonic and Phonon Polariton Modes with the Photothermal Induced Resonance (PTIR) Technique
A. CENTRONE, National Institute of Standard and Technology, Gaithersburg, MD, USA

The development of nanostructures that sustain, either sub-diffraction plasmonic or phonon-polariton resonances in the mid-IR generate interest for sensing (via the SEIRA effect) and narrow-band thermal emission, respectively. For example gold resonators and hexagonal boron nitride (hBN) nanocones gives rise to localized plasmonic and phonon polaritonic modes, respectively that are wavelength-tunable as a function of structural parameters. Photo Thermal Induced Resonance (PTIR) employs an AFM tip as a local detector to transduce the thermal expansion of the sample induced by light absorption into large cantilever oscillations. Our PTIR setup combines an AFM microscope with three lasers providing wavelength-tunability from 500 nm to 16000 nm. Local absorption spectra (electronic or vibrational) and maps are obtained with a wavelength-independent resolution as high as 20 nm. The PTIR technique will be used: 1) to map and quantify SEIRA enhanced in plasmonic resonators as a function of the nanostructure size, shape and arrangement. 2) 2o obtain maps and spectra of phonon-polariton modes in hBN nanocones that are naturally hyperbolic, i.e. have a dielectric function of opposite sign along orthogonal crystal axes, conferring both metallic and dielectric-like properties simultaneously.

E-6:IL04  Optical Antennas
M. AGIO, Laboratory of Nano-Optics, University of Siegen, Siegen, Germany

The dramatic advances of nanotechnology have enabled us to fabricate subwavelength architectures that function as antennas for improving the exchange of optical energy with nanoscale matter. In fact, the amount of activities on this topic has grown very rapidly in various fields of research, spanning physics, chemistry, and biology to cite a few. At a more fundamental level, these systems provide a handle on atoms and molecules, a concept that dates back to the onset of field-enhanced spectroscopy. We describe the main features of optical antennas for enhancing quantum emitters and review designs that increase the spontaneous emission rate by orders of magnitude from the ultraviolet up to the near-infrared spectral range. Furthermore, we show how these nanostructures may direct fluorescence into guided modes and light beams with a high efficiency. We conclude by exploring how these approaches may expand the detection limits of nanoscale objects, with particular attention on the enhancement of light-matter interaction, coherent detection as well as damping and dephasing processes.


E-6:IL05  Integrated Hyperlens in the Visible Spectral Range
N.M. LITCHINITSER,  JINGBO SUN, M.I. SHALAEV, University at Buffalo, The State University of New York, Buffalo, NY, USA

A metamaterial hyperlens offers a 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 significant resonance-induced losses. We experimentally demonstrate a non-resonant waveguide-integrated hyperlens with a radially oriented layered structure in the visible frequency range. We perform a detailed investigation of various materials systems and prove that a radial (fan-shaped) configuration is superior to the concentric layers- based configuration. Indeed, the radial configuration with a negative component of dielectric permittivity orientated along the layers and positive permittivity being normal to the layers relies on non-resonant negative dielectric response and results in a low loss performance in the visible range. In this structure, the evanescent-wave components of a wave vector from the subwavelength slits are converted into the propagating waves and then out-coupled to the free space in the far field. Such devices are likely to revolutionize many fields ranging from clinical diagnostics and single molecule spectroscopy to nanoscale lithography.


E-6:L06  Nanoantenna-based Stokes Polarimeter on a Silicon Chip
A. ESPINOSA-SORIA, Nanophotonics Technology Center, Universitat Politècnica de València, Valencia, Spain; F.J. RODRÍGUEZ-FORTUÑO, King’s College London, London, UK; A. GRIOL, A. MARTÍNEZ, Nanophotonics Technology Center, Universitat Politècnica de València, Valencia, Spain

We present an on-chip polarimeter working at telecom wavelengths that obtains the full state of polarization (SoP) of an incoming light beam. We make use of a subwavelength scatterer (acting as a nanoantenna) coupled to silicon waveguides. As a result of the spin-orbit interaction taking place in the evanescent region of the silicon waveguides, the nanoantennas response polarization-dependent, allowing to map out the incoming SoP into a well-defined scattering path. Our approach allows to get the SoP in real time and over an ultrabroad bandwidth, enabling spectropolarimetry, and due to the small scattering losses, it could be used in an in-line configuration. We demonstrate experimentally the concept at telecom wavelengths using a circuit fabricated with standard silicon technology, which would ultimately enable low-cost fabrication in high-volumes. Our approach is universal and valid for any wavelength range and technological platform so it could be applied to a wide variety of disciplines, including biochemistry, spectrometry or optical communications.

 
Session E-7 - Acoustic and Mechanical Metamaterials

E-7:L02  Direct Observation of Ultrasonic Cut-off Frequency for Holes with Pressure-release Walls
T. GRAHAM, J.R. SAMBLES, A.P. HIBBINS, S.A.R. HORSLEY, Department of Physics and Astronomy, University of Exeter, Exeter, UK

A cylindrical waveguide with pressure-release boundaries has an acoustic cut-off frequency, below which no acoustic signal may propagate, that is dependent on its radius. Using ultrasonic signals underwater, with the sound incident upon cylindrical holes cut through flat sheets of closed cell polyurethane foam, we experimentally observe this cut-off frequency. In addition we show that arrays of these holes support bound surface modes. A combination of Fabry-Perot-like resonances and their mixing with these trapped surface modes dictate the acoustic response. Areas of application for this research are the reduction of underwater noise pollution as well as the control of ultrasound emission and reflection from vessels.


E-7:L03  Nonlinear Vibration Damping in Mechanical/Electrical Periodic Structures Featuring Switched Piezoelectric Elements
BIN BAO, M. LALLART, D. GUYOMAR, Laboratoire de Génie Electrique et Ferroélectricité, INSA de Lyon, Villeurbanne Cedex, France

In piezoelectric periodic metamaterial beams, a periodic array of piezoelectric transducers is uniformly distributed through the structure. Traditionally, the electronic networks applied to the periodic array for elastic wave propagating control consist in locally resonant electrical shunts using linear R (resistance) or RL (resistance and inductance) circuits or broadly resonant electronic networks using negative capacitance shunts with external energy supplies. In this paper, a new type of nonlinear two-connected synchronized switching passive electronic networks is proposed and introduced in the periodic array. Numerical results show that the phononic metamaterial beam with the proposed electrical networks exhibits relatively broad band gaps. Especially, band gap hybridization (near-coupling between Bragg scattering mechanism and broadband resonance mechanism caused by nonlinear synchronized switching electrical networks) of the proposed electrical networks outperforms the independent synchronized switching electronic networks (switching shunts independently connected to PZTs). In addition, the proposed electrical networks have technical simplicity, with only half of the number of electronic switches required compared to independent synchronized switching electronic networks.


E-7:L04  Mechanical Metamaterials with Hierarchical Structure
A. KRUSHYNSKA, M. MINIACI, F. BOSIA, Department of Physics, University of Torino, Torino, Italy; B. MORVAN, LOMC UMR CNRS 6294, Université du Havre, Le Havre, France; N.M. PUGNO, Laboratory of Bio-Inspired & Graphene Nanomechanics, Department of Civil, Environmental and Mechanical Engineering - University of Trento, Trento, Italy

The property of phononic crystals (PCs) and acoustic metamaterials (AMMs) of inhibiting elastic wave propagation, i.e. exhibiting band gaps (BGs) at various frequency ranges, is mainly derived from their overall structure rather than their constituent properties. In this study, we propose to introduce hierarchical structural complexities, i.e. to create PCs/AMMs with several structural levels at different length scales. As a result, exceptional mechanical properties appear related to BGs nucleation/annihilation/shifting phenomena because of functional adaptation of the structure at all the hierarchical levels on multiple frequency scales. This study analyses the main changes in the band structures of viscoelastic PCs/AMMs. Hierarchy allows to extend the effective attenuation frequency ranges compared to a non-hierarchical case and simultaneously to reduce the total material mass. Results are complemented numerically by performing time-transient FE analyses and experimentally by Scanning Laser Vibrometer measurements, which capture the decrease of the transmission power spectrum with the number of the material unit cells and hierarchical levels in the PCs and AMMs. Results reveal unique opportunities for hierarchical-structured PCs/AMMs to open BGs at multiple frequency scales.


E-7:IL05  Parity-time Synthetic Phononic Media
J. CHRISTENSEN, M. WILLATZEN, DTU, Kgs. Lyngby, Denmark

In this presentation we show how active acoustic media can be engineered and tuned to work as a Parity-time (PT) synthetic phononic system. With colorful examples we demonstrate the rich physics involved and the broad landscape for applications associated with the PT properties.


E-7:L06  Boundary Layer Effects on Acoustic Transmission Through Narrow Slit-cavities
G.P. WARD, R.K.LOVELOCK, A.R.J. MURRAY, A.P. HIBBINS, J.R. SAMBLES, J.D. SMITH, Exeter University, Exeter, Devon, UK

We explore the slit-width dependence of resonant transmission of sound in air through both a slit-array formed of aluminium slats, and a single open-ended slit-cavity in an aluminium plate. By studying Fabry-Perot-like cavity resonances, we find significant attenuation of the transmitted signal, and a reduction of the effective speed of sound through the slits by as much as 18%, for slit sizes narrowed below ~2% of the free space wavelength. Our experimental results agree with numerical modelling and with theory which stems from Lord Rayleigh, concerning how viscous and thermal boundary layers at the slit walls effect the acoustic wave across the whole slit-cavity.


Session E-8 - Novel Concepts and Applications of Metasurfaces and Metadevices

E-8:IL02  Photonic Spin Hall Effect with nearly 100% Efficiency based on Gradient Metasurface
SHULIN SUN1, WEIJIE LUO2, SHIYI XIAO2, QIONG HE2,3, LEI ZHOU2,3, 1Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Green Photonics and Department of Optical Science and Engineering, Fudan University, Shanghai, China; 2State Key Lab. of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai, China; 3Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai, China

Photonic spin hall effect (PSHE), that spin-polarized photons can be laterally separated in transportation, gains increasing attention from both science and technology, but available mechanisms either require bulky systems or exhibit very low efficiencies. Here we demonstrate that a giant PSHE with ~100% efficiency can be realized at certain meta-surfaces with deep-subwavelength thicknesses. Based on rigorous Jones-Matrix analysis, we establish a general criterion to design meta-surfaces that can realize 100%-efficiency PSHE. The criterion is approachable from two distinct routes at general frequencies. As a demonstration, two microwave meta-surfaces are fabricated and then experimentally characterized, both showing ~90% efficiencies for the PSHE. Our findings pave the road for many exciting applications based on high-efficiency manipulations of photon spins, with a polarization detector experimentally demonstrated here as an example.


E-8:IL03  Topological Notions and Pseudo-spin in Electromagnetic Waves
W.-J. CHEN1, M. XIAO1, Z.-Q. ZHANG1, J.-W. DONG2, C.T. CHAN1, 1Department of Physics and the Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, China; 2State Key Laboratory of Optoelectronic Materials and Technologies and School of Physics and Engineering, Sun Yat-Sen University, Guangzhou, China

Topological insulators have been extensively studied for the exotic properties due to the topology of the bulk bands. A signature of quantum spin Hall insulator is the spin-filtered edge states whose spin is locked to the momentum. The edge transport is robust against nonmagnetic impurities as they do not induce spin flip. Quantum spin Hall insulator has been mapped to photonic systems. Spin-filtered edge states are protected by the nontrivial topology of bulk states. These pseudospin states can be achieved in carefully designed photonic crystals or bulk metamaterials which are usually difficult to fabricate. The natural question is whether “pseudospin” transport is possible without using any bulk material. Here, we propose a new paradigm in which symmetry-protected pseudospin states are guided in air inside a channel, and the pseudospin is enforced simply by imposing perfect electric and perfect magnetic conductor boundary conditions. Wave propagation is robust against deformations that do not induce spin flip. To achieve a broad bandwidth, one can also employ an “all PEC” configuration where additional symmetries mimic an effective PMC boundary. We generate several conceptual designs and experimentally demonstrate symmetry-protected pseudospin transport in the microwave regime.


E-8:L04  Metastructures for Passive Broadband Vibration Suppression and Energy Harvesting
J.D. HOBECK, D.J. INMAN, University of Michigan, Department of Aerospace Engineering, Ann Arbor, MI, USA

The research presented in this paper focuses on a unique multifunctional structural design that not only absorbs broadband vibration, but also extracts significant amounts of electrical energy. This is accomplished by first designing an array of low-frequency resonators to be integrated into a larger host structure. This array of resonators can contribute not only to static requirements, e.g., stiffness, strength, mass, etc., of the host structure but the array also functions as a distributed system of passive vibration absorbers. Structures having these distributed vibration absorber systems are known as metastructures. Here, the authors present a unique absorber design referred to as a zigzag beam, which can have a natural frequency an order of magnitude lower than that of a basic cantilever beam of the same scale. It will be shown that the zigzag beams can be designed with an added layer of piezoelectric material which allows them to harvest significant amounts of electrical power as they suppress vibration of the host structure. Details discussed in this paper include those both for analytical and numerical modeling and also for experimental analysis used to validate the proposed modeling methods.


Poster Presentations

E:P02  Group Velocity Anomaly Modes in Hybrid Bands in Photonic Crystals made of Ferroelectrics
M.W. TAKEDA1, M. ARIKAWA1, R. ARAKI1, Y. NAKATA1, F. MIYAMARU1,2, 1Department of Physics, Faculty of Science, Shinshu University, Matsumoto, Japan; 2Center for Energy and Environmental Science, Shinshu University, Nagano, Japan

In the materials periodically arranged with different index of refraction, the electromagnetic waves have the band gap in a wavelength corresponding to the lattice constant. On the other hand, the electromagnetic wave coupled with polar phonons in ferroelectrics forms a phonon-polaritons, in which an additional band gap appears between TO and LO phonon frequencies. When the photonic crystal is constructed by ferroelectrics, the emergence of hybrid bands where new band gaps must appear at the Brilluion zone center and boundary is expected. Here, the group velocity anomaly modes in the polariton brunches are expected to be found out. In the present paper, we report the FDTD numerical analyses and experimental results of propagation characteristics of the group velocity anomaly modes in the hybrid band of the one-dimensional photonic crystal fabricated by ferroelectrics Li2Ge7O15 and Sr2Ta2O7 single crystals by using a terahertz time-domain spectroscopy. Moreover, the localization properties of the group velocity anomaly modes in the two- and three-dimensional photonic crystals made of ferroelectric spheres are discussed.


E:P03  Microwave Surface Waves on Graphene-like Metasurfaces
Y.N. DAUTOVA, A.P. HIBBINS, J.R.SAMBLES, Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, Devon, UK

The study of structured metallo-dielectric metamaterials has been highly topical in recent years, thanks to the growing interest and application in engineering artificial electromagnetic properties across the whole spectrum. Whereas much work was carried out with cm-scale-structuring around the middle of the 20th century, working in the microwave regime is advantageous even today as it allows for concepts to be tested that would be impractical and expensive at higher frequencies. We fabricate a graphene-inspired honeycomb array comprised of metallic circular holes in a thin (15 micron) metal layer which supports TM surface waves. We experimentally study dispersion and eigenmodes of this metasurface and compare results with predictions of a full electromagnetic finite-element solver. Our samples show linear dispersion, similar to well-celebrated Dirac cones in graphene. Then, we substitute circle holes with triangular-shaped holes and introduce inversion asymmetry by rotating meta-atoms on two sub-lattices of the honeycomb structure antiparallel to each other. This structural change results in modification of dispersion including opening of a bandgap. The size of induced bandgap can be controlled by changing the respective angle of the triangular elements on the two sub-lattices.
 

Cimtec 2016

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