Symposium FF
Electromagnetic Metamaterials and Metasurfaces: Recent Research Achievements and New Paradigms


FF-1:IL01  New Trends for Hybrid Metamaterials and Metasurfaces
M. Lapine, University of Technology Sydney, Ultimo, Australia

Recent progress in metasurfaces and metamaterials poses a number of challenges for theory and experiments. In this talk, two aspects of the novel trends will be addressed: the response of patterned metasurfaces and the description of multi-layered structures. Patterned metasurfaces, produced as a periodic array of various repeated features, such as nano-bumps, nano-jets or nano-holes, will be shown to provide pronounced resonances, well-controllable by the specific shape of the nano-pattern as well as the period of the array, which a geometrical interplay of all the parameters being crucial for plasmonic resonance. Multilayered structures, produced as a sequence of nano-layers of altering materials, will be shown to exhibit remarkable spatial dispersion and can only be described with additional boundary conditions, specific for relative thickness of the layers and for the way of structure termination; these findings help to explain numerous recent experimental mismatches observed for hyperbolic metamaterials. The reported findings are essential for further development of multilayered and patterned metasurfaces for optical and infrared frequency ranges.

FF-1:IL02  Around the Plasmonic Nanoparticle Cycle: From a New Chiral Optical Effect to Applications in Quantum Optics
V.K. Valev, Department of Physics, University of Bath, Bath, UK

This talk will focus on three absorbing lines of research into nanophotonics. It will begin with the first experimental observation of a chiroptical effect that was predicted 40 years ago.[1,2] Our team recently demonstrated that in chiral metal nanoparticles (those that lack mirror symmetry) the intensity of light, scattered at the secondharmonic frequency, is proportional to the chirality. This effect was predicted 40 years ago, it is >10,000 more sensitive than corresponding linear optical effects and it could enable safer pharmaceuticals. Next, it will consider the smallest backjets (‘nanojets’) ever created and will discuss how they can serve to assemble novel metamaterials based on nano metalworking.[3,4] Nano metalworking is an exciting, emerging field that is largely unexplored. Finally, it will illustrate how a vapour stabilization technique can greatly enhance quantum sensors.[5]
REFERENCES [1] Phys Rev. X 9, 011024 (2019). [2] J. Chem. Phys. 70, 1027 (1979). [3] Adv. Mater. 24, OP29-OP35 (2012). [4] Nat. Commun. 5, 4568 (2014). [5] Nat. Commun. 10, 2328 (2019).

FF-1:L04  Spatial Multiplexing Method for Multiwavelength Metalens
SANGWON BAEK1, J. Kim2, Y. Kim2, J. Rho2, J.-l. Lee1, 1Department of Materials Science and Engineering, Pohang University of Science and Technology, South Korea; 2Department of Mechanical Engineering, Pohang University of Science and Technology, South Korea

We theoretically demonstrate a multiwavelength metalens that operates concurrently at three visible wavelengths (λ = 450, 532, 633, and 700 nm). Multiwavelength metalenses are designed by a simple integration of metalens components by a spatial interleaving method (SIM). The designed metalenses focus light to the same focal distance at three visible wavelengths with near diffraction-limited full width at half-maximum. We also successfully fabricated SIM metalens by using low-loss hydrogenated amorphous silicon. These methods can provide a simple guideline to increase the operating wavelengths of metalenses.

FF-2:IL01  Nanopillars Arrays as Anisotropic Metamaterials and Metasurfaces
A.V. Lavrinenko1, E. Shkondin1, O. Takayama1, R. Malureanu1, M. E. Aryaee Panah1, O.Y. Yermakov2, A.A. Bogdanov2, S. Chatterjee3, G. Strangi3, 1Technical University of Denmark, Kgs. Lyngby, Denmark; 2ITMO University, Saint Petersburg, Russia; 3Case Western Reserve University, Cleveland, USA

Traditionally nanopillars are one of the building blocks in many conceptual designs of nanophotonics, like photonic crystals, optical metamaterials, metasurfaces and gratings. Arrays of nanopillars can exhibit either diffractive or metamaterials properties leading in the latter case to anisotropic and with proper engineering even to hyperbolic dispersion. We overview, first, fabrication of such arrays consisting of nanopillars and nanotubes. Then we report on homogenization procedures and extraction of effective parameters. The lecture will be concluded with the examples of applications of nanopillars metamaterials and metasurfaces as switching devices, absorption elements and sensors.

FF-2:IL03  Topological Slow Light beyond the Time-bandwidth Limit
K.L. Tsakmakidis, K. Baskourelos, Department of Physics, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, Greece

Topologically protected transport has recently emerged as an effective means to address a recurring problem hampering the field of slow light for the past two decades: Its keen sensitivity to disorders and structural imperfections. With it, there has been renewed interest in efforts to overcome the delay-time–bandwidth limitation usually characterizing slow-light devices, on occasion thought to be a 'fundamental' limit. What exactly is this limit, and what does it imply? Can it be overcome? If yes, how could topological slow light help, and in what systems? What applications might be expected by overcoming the limit? In our talk will shall overview recent progress in this emerging new sub-field, addressing the above, and other related, questions while pointing to important new functionalities, both, for classical and quantum devices, that overcoming the limit can enable.

FF-2:L05  Ultrathin Suspended Membrane Metasurfaces for Efficient Terahertz Light Absorption and Modulation
A. OTTOMANIELLO, V. Mattoli, Center for Materials Interfaces, Istituto Italiano di Tecnologia, Pontedera, Italy; P. Vezio, A. Tredicucci, Dipartimento di Fisica, University of Pisa, Pisa, Italy; S. Zanotto, A. Pitanti, Laboratorio NEST Scuola Normale Superiore, and Istituto Nanoscienze CNR, Pisa, Italy

Optical metasurfaces are a very promising platform to go beyond traditional metamaterials in terms of both compactness and functionality. Here, we propose a design of membrane metasurfaces which can allow (near-)perfect light absorption in an ultrathin thickness (<1 µm) at terahertz frequencies. The suspended membranes consist of a dielectric thin film encapsulated into two metallic layers. By inscribing in the top metallization a terahertz metasurface made of connected split ring resonators, an absorption resonance is introduced, whose depth can be strongly enhanced by the presence of the homogeneous bottom metallization. Regulating the thickness of the dielectric material, high levels of absorption are theoretically demonstrated in an ultra-subwavelength thickness (<λ/100). The potential and versatility of this device concept is broadened by the freedom of choice for the inner dielectric material, which can be fabricated with low mechanical dissipation, stimuli responsive or ultra-conformable media to achieve a dynamic manipulation of light. Owing to the capacitor-like geometry, light detection can be possible by electrically measuring the photothermally induced capacitive perturbation, and with a modulation speed limited by the ultrathin membrane heat capacity.

FF-2:IL06  Superemission and Superabsorption Effects in Metamaterials
S.I. MASLOVSKI, Instituto de Telecomunicações and Department of Electronics, Telecommunications and Informatics, University of Aveiro, Aveiro, Portugal

The absorption cross section of a resonant body can be much greater than its geometric area. The principle of resonant absorption is widely used, e.g. in conjugate-impedance matched antennas. By impedance matching of a metamaterial body to its environment we show that there is no upper limit on the absorption cross section of a resonant metamaterial object. On the other hand, hot absorbing bodies emit thermal radiation such as the black body radiation governed by Planck's law. We develop a general approach to maximize the power emitted by a metamaterial body. We prove that in the conjugate-impedance matched metamaterials the radiated power can become super-Planckian even when the objects that exchange radiative heat are optically large and separated by distances much greater than the radiation wavelength. Such metamaterial superemitters and superabsorbers can find applications in future thermophotovoltaic systems. We outline possible realization strategies for super-Planckian emitters and superabsorbers and discuss recent modeling, simulations, and experiments related to the superemission and superabsorption effects in metamaterials.
This work is funded by FCT/MCTES through national funds and when applicable co-funded by EU funds under the project UIDB/50008/2020-UIDP/50008/2020.

FF-2:L07  Hierarchically Structured Functional Ceramic Composites for Microwave Absorption using Graphene Augmented Inorganic Nanofibers
A. SAFFAR Shamshirgar1, R.E. Rojas Hernández1, G.C. Tewari2, J.F. Fernández3, R. Ivanov1, M. Karppinen2, I. Hussainova1, 1Department of Mechanical and Industrial Engineering, Tallinn University of Technology, Tallinn, Estonia; 2Department of Chemistry and Materials Science, Aalto University, Aalto, Finland; 3Institute of Ceramics and Glass (ICV-CSIC), Madrid, Spain

Graphene has shown remarkable potential for various applications such as EMI shielding and thermoelectric applications due to its tunable nature and unique properties. This work focuses on the design and characterization of alumina based functional multilayers using graphene augmented inorganic nanofibers (GAIN). Homogeneous composites of GAIN/α-Al2O3 with various filler contents were processed using spark plasma sintering. Presence of various defects and scattering points, the conductive-dielectric core-shell structure of GAIN, and their integration into the α-Al2O3 matrix ensured a significant increase in the complex permittivity as a function of GAIN tested at X-band. The outcome of this increased permittivity was remarkable electromagnetic shielding effectiveness of the structures, which was correlated to high surface scattering. In order to decrease the surface scattering phenomenon and enhance microwave absorption, a multilayer structure with a gradient in GAIN content and layer thickness was fabricated and tested using transmission line method in a rectangular waveguide under the fundamental TE10 mode. The result has shown a significant enhancement of the absorption (>90%) at X-band with a narrowband peak of -40 dB corresponding to 99.99 % absorption centered at 9.6 GHz.

FF-3:IL03  Multipole Analysis and Tuning of All-dielectric Metasurfaces Supporting High-quality Optical Resonances and Quasi-trapped Mode Responses
A.B. Evlyukhin, Institute of Quantum Optics, Leibniz Universität Hannover, Hannover, Germany

Theoretical approach to the multipole analysis of the extinction and scattering spectra of arbitrary shaped particles and the reflection and transmission spectra of metasurfaces composed from them is demonstrated and discussed. The method is applied to high refractive-index nanoparticles with isotropic and bianisotropic optical properties supporting optical resonances. Multipole resonances of single nonspherical silicon nanoparticles are investigated. It is demonstrated how specially configured scattering diagrams are connected with overlapping of different multipole modes resonantly excited in the nanoparticles and how small shape defects can generate bianisotropic optical response of the single nanoparticles. It is shown how trapped modes of metasurfaces composed from the nanoparticles with bianisotropic properties can be implemented and can provide high-quality optical resonances in the transmission and reflection spectra. A semi-analytical method based on the coupled-dipole equations with inclusion bianisotropic polarizabilities is demonstrated. Finally, a general strategy for the realization of electric and magnetic quasi-trapped modes located at the same spectral position is presented.

FF-4:IL02  Temporally Modulated Metasurfaces for Extreme Control of Light and Electromagnetic Radiation
Xuchen Wang, A. Díaz Rubio, V. Asadchy, G. Ptitcyn, M. Mirmoosa, S. Tretyakov, Department of Electronics and Nanoengineering, Aalto University, Espoo, Finland

Temporal modulation of macroscopic parameters of materials, such as permittivity and surface impedance, gives us an exceptional opportunity for extreme manipulation of electromagnetic radiation. Consequently, extraordinary functionalities can be obtained including virtual absorption, nonreciprocity, and harmonic generation. In this talk, we present our recent results on this intriguing and novel research area, focusing on temporally modulated metasurfaces. First, we show that such metasurfaces are providing nonreciprocity. Subsequently, we indicate that they can be engineered such that tunable and multifunctional nonreciprocal devices are realized. Here, in contrast to other concurrent studies, we suppose that the modulation function of the surface impedance is not a time-harmonic signal. Such important assumption gives rise to an additional freedom for controlling of nonreciprocity. Thus, a variety of nonreciprocal devices like isolators, gyrators and circulators can be incorporated in a uniform hardware platform only by changing the modulation functions. Finally, we show that spatial modulation is not a necessary condition for achieving nonreciprocity. If the metasurfaces are bianisotropic, modulating such structures only in time can also induce strong nonreciprocity.

FF-4:IL03  Novel Devices based on Active and Tunable Dielectric Nanoantennas
A.I. Kuznetsov, Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), Singapore

Dielectric nanoantennas and metasurfaces have recently emerged as a novel approach in nanophotonics. Due to their low absorption losses and the possibility to use industry-friendly semiconductor materials, they pave the way for nanophotonics to reach industrial applications in the near future. In this talk, I will present applications of the dielectric nanoantenna concepts to design active and tunable nanoantenna devices. First, active dielectric nanoantenna concept will be presented. Due to their highly tailorable resonances and strong emission properties, nanoantennas made of active III-V semiconductor materials can be used to achieve directional LED and laser light sources. Directional nanoscale lasers based on arrays and single nanoantennas will be discussed. Second, I will focus on the concept of tunable dielectric nanoantennas and metasurfaces. In particular, I will show how individual electrical control of different nanoantenna pixels embedded into liquid crystal can achieve functionalities of nanoscale spatial light modulators able to steer the laser beam in 1D at >20 degrees angle and experimental efficiencies >35%. Such devices can find applications in solid-state LIDAR and 3D sensing technologies.

FF-4:IL05  Conformable Holographic Metasurfaces
A. DI FALCO, School of Physics and Astronomy, University of St Andrews, UK

Optical metasurfaces (MSs) can be fabricated in flexible substrates. Flexibility brings additional advantages to MSs respect to their rigid counterpart, in terms of scalability, conformability, and tunability. When metasurfaces are used as supports to encode computer generated holograms, flexibility allows to harness the shape and topology of the target substrate as an additional degree of freedom to encode the holographic information. Here we show that this platform can be scaled from the visible to the mm-wave range. This in turn opens the way to the exploitation of flexible holographic metasurfaces for a large number of applications, from security holograms that display the correct image only when the substrate has a determined shape, to the possibility to interface the metamaterials technology to biophotonics systems or to create holographic patches to retrofit existing antennas infrastructures for telecommunication applications.

FF-5:IL01  Topologically Protected Transport in Photonic Crystals

Photonic topological insulators offer the possibility to eliminate backscattering losses and improve the efficiency of optical communication systems. First, we combine the properties of a planar silicon photonic crystal (PC) and the concept of topological protection to design, fabricate and characterize an optical topological insulator (TI) that exhibits the valley Hall effect. We show that the transmittances are the same for light propagation along a straight topological interface and one with four sharp turns. This result quantitatively demonstrates the suppression of backscattering due to the non-trivial topology of the structure. Second, we propose a straightforward way to dynamically tune the transmission in a silicon-based topological PC using all-optical free-carrier excitation that allows for fast refractive index modulation. Tunability is important for many applications, including modulators, switches, and optical buffers. The proposed PC-based approach offers significant advantages compared with other realizations of photonic TI, such as lower propagation losses, a larger operating bandwidth, a much smaller footprint, compatibility with CMOS technology, and the fact that it allows for operation at telecommunications wavelengths.

FF-5:IL05  Nonlinear Optical Switching and Tunability in AlGaAs Nanoantennas and Metasurfaces
C. De Angelis, D. Rocco, Department of Information Engineering, University of Brescia, Brescia, Italy

Optical modulators play a significant role in applications ranging from energy harvesting, sensor and imaging devices. Here, we investigate the directionality of the second harmonic signal emitted from a metasurface of AlGaAs nanocylinders embedded into liquid crystals. We numerically demonstrate that by changing the liquid crystal orientation it is possible to modulate both the power and the directionality of the nonlinearly generated photons. Our results open important opportunities for tunable metadevices such as nonlinear holograms and dynamic displays.

FF-5:IL06  Topological Photons and Phonons in Nanophotonic Architectures
E. VERHAGEN, Center for Nanophotonics, AMOLF, Amsterdam, The Netherlands

Recent years have seen a surge of interest in bringing the concepts of topological physics to the photonic and acoustic domains. In this talk, I will discuss our efforts to manipulate the on-chip transport of light and sound (mechanical vibrations) to induce unusual behavior in topological states at the nanoscale. We induce this behavior by suitably breaking temporal and spatial symmetries in nanophotonic architectures. On the one hand, we directly observe photonic topological edge states in photonic crystals that exploit spatial symmetry breaking. We test the robustness of topological light propagation and study photonic spin-orbit coupling at the nanoscale. On the other hand, we create optomechanical systems in which time-reversal symmetry is broken through optomechanical interactions. We demonstrate the resulting emergence of quantum-Hall physics for phonons in optically-coupled networks of mechancial resonators. Moreover, by introducing optomechanical squeezing interactions we study the unique states that arise due to the interplay of chirality and non-Hermiticity.

FF-6:IL02  Controlling the Parity and Time-reversal Symmetry of Metasurfaces in Current-driven Graphene Dirac Plasmons
TAIICHI OTSUJI, Research Institute of Electrical Communication, Tohoku University, Sendai, Japan

Graphene is an exotic atomically thin 2D material featured by massless Dirac-Fermionic plasmons. Recent study on topological insulators has brought a groundbreaking discovery on observation of massless Kane Fermions in HgCdTe (MCT) a zinc-blend bulk 3D crystal. Metamaterial/metasurface design enables controlling the topological phase state transitions at the surface/interface of 2D/3D materials, dramatically increasing the order of freedom in manipulating electromagnetic responses. Recently introduction of controlling the parity and time-reversal (PT) symmetry of metamaterials/metasurfaces has been emerging, which has opened a new paradigm. This presentation deals with recent advancement and latest hot-topic on such trends and streamlines of controlling the PT symmetry of metasurfaces in current-driven graphene Dirac plasmons (GDPs). The device is realized by actively controlling the PT symmetry of the GDP metasurface under electrical bias applications in the authors’ original dual-grating-gate graphene channel field effect transistor (DGG-GFET) structure. Practical device design and numerically simulated performance projections will be presented.

FF-6:IL03  Broadband Active Control of Light-matter Interactions with Metal-dielectric Nanocavities
N. MACCAFERRI, Department of Physics and Materials Science, University of Luxembourg, Luxembourg, & Department of Physics, Umeå University,  Umeå, Sweden

Confining and controlling electromagnetic radiation over sub-diffraction limited volumes is of extreme importance to widen our understanding of nanoscale light-matter interactions. Surface plasmon polaritons (SPPs) are collective oscillations of a material free electron gas at its interface, leading to strongly enhanced electromagnetic field confinement below the diffraction limit of light, opening up excellent opportunities in single-molecule detection and sequencing, energy harvesting, and opto-electronics. Metal-dielectric multilayers composed by nm-thick films support a wide landscape of sub-diffraction optical modes, which can be excited via coupling with nanoscale diffraction gratings [1] or by local excitations, for instance by using high-energy electron beams [2]. In this framework, we experimentally demonstrate how disc-shaped multilayered metal-dielectric nanostructures can couple to far-field radiation and enable a full control of absorption and scattering of light at visible and near-infrared frequencies [3]. At the same time, we show that these nanostructures can enable a resonant magnetically induced modulation of the light polarization by exciting either electric or magnetic optical modes [4]. Moreover, the exploitation of the metal-dielectric interface-induced symmetry breaking has been explored as possible route to achieve enhanced nonlinear optical emission [5], largely independent from the exciting polarization and angle of incidence, unlocking promising applications of these structures as solvable nanostructures to generate visible light by using near-infrared (NIR) radiation. These multilayered metal-dielectric nanoparticles exhibit also a high (> 70%) absorption efficiency in the NIR region, and their light-to-heat conversion is demonstrated by a much larger temperature increase than that of metallic nanostructures with the same geometry and volume. As proof-of-concept, we introduce an approach for efficient in vitro hyperthermia of living cells with negligible cytotoxicity [6]. This type of architectures can also be used for a plenty of applications spanning from the detection of deep sub-wavelength deformation [7] and ultra-high-resolution imaging [8], to temperature sensing [9] and tailored ultrafast all-optical switching of light states with a relative modulation depth exceeding 100% [10].
[1] N. Maccaferri et al., APL Photonics 5(7), 076109 (2020);  [2] T. Isoniemi et al., Adv. Opt. Mater. 8(13), 2000277 (2020); [3] N. Maccaferri et al., Nano Lett. 19(3), 1851–1859 (2019); [4] J. Kuttruff et al., Phys. Rev. Lett. in press (2021); [5] N. Maccaferri et al., ACS Photonics 8(2), 512-520 (2021); [6] Y. Zhao et al., arXiv:2005.13296 (2020); [7] A. Carrara et al., Adv. Opt. Mater. 8(18), 2000609 (2020); [8] V. Caligiuri et al., ACS Appl. Nano Mater. 3(12), 12218-12230 (2020); [9] A. Gabbani et al., in preparation (2021); [10] J. Kuttruff et al., Comm. Phys. 3, 114 (2020).


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