Showing papers by "Yuri S. Kivshar published in 2017"
TL;DR: In this article, a broad range of resonant electromagnetic effects by using two effective coupled oscillators, including the Fano resonance, electromagnetically induced transparency, Kerker and Borrmann effects, and parity-time symmetry breaking, are reviewed.
Abstract: The importance of the Fano resonance concept is recognized across multiple fields of physics. In this Review, Fano resonance is explored in the context of optics, with particular emphasis on dielectric nanostructures and metasurfaces. Rapid progress in photonics and nanotechnology brings many examples of resonant optical phenomena associated with the physics of Fano resonances, with applications in optical switching and sensing. For successful design of photonic devices, it is important to gain deep insight into different resonant phenomena and understand their connection. Here, we review a broad range of resonant electromagnetic effects by using two effective coupled oscillators, including the Fano resonance, electromagnetically induced transparency, Kerker and Borrmann effects, and parity–time symmetry breaking. We discuss how to introduce the Fano parameter for describing a transition between two seemingly different spectroscopic signatures associated with asymmetric Fano and symmetric Lorentzian shapes. We also review the recent results on Fano resonances in dielectric nanostructures and metasurfaces.
1,234 citations
TL;DR: In this article, the authors review the recent developments in meta-optics and nanophotonics and demonstrate that the Mie resonances can play a crucial role offering novel ways for the enhancement of many optical effects near magnetic and electric multipolar resonances.
Abstract: Scattering of electromagnetic waves by subwavelength objects is accompanied by the excitation of electric and magnetic Mie resonances that may modify substantially the scattering intensity and radiation pattern. Scattered fields can be decomposed into electric and magnetic multipoles, and the magnetic multipoles define magnetic response of structured materials underpinning the new field of all-dielectric resonant meta-optics. Here we review the recent developments in meta-optics and nanophotonics and demonstrate that the Mie resonances can play a crucial role offering novel ways for the enhancement of many optical effects near magnetic and electric multipolar resonances, as well as driving a variety of interference phenomena which govern recently discovered novel effects in nanophotonics. We further discuss the frontiers of all-dielectric meta-optics for flexible and advanced control of light with full phase and amplitude engineering, including nonlinear nanophotonics, anapole nanolasers, quantum optics, ...
477 citations
TL;DR: It is revealed that isolated subwavelength dielectric resonators support states with giant Q-factors similar to bound states in the continuum formed via destructive interference between strongly coupled eigenmodes and characterized by singularities of the Fano parameters.
Abstract: Recent progress in nanoscale optical physics is associated with the development of a new branch of nanophotonics exploring strong Mie resonances in dielectric nanoparticles with a high refractive index. The high-index resonant dielectric nanostructures form building blocks for novel photonic metadevices with low losses and advanced functionalities. However, unlike extensively studied cavities in photonic crystals, such dielectric resonators demonstrate low quality factors (Q factors). Here, we uncover a novel mechanism for achieving giant Q factors of subwavelength nanoscale resonators by realizing the regime of bound states in the continuum. In contrast to the previously suggested multilayer structures with zero permittivity, we reveal strong mode coupling and Fano resonances in homogeneous high-index dielectric finite-length nanorods resulting in high-Q factors at the nanoscale. Thus, high-index dielectric resonators represent the simplest example of nanophotonic supercavities, expanding substantially the range of applications of all-dielectric resonant nanophotonics and meta-optics.
460 citations
TL;DR: In this article, a 3D photonic topological metacrystal based on an all-dielectric metamaterial platform shows robust propagation of surface states along 2D domain walls, making it a promising solution for photonics applications.
Abstract: The theoretical study of a 3D photonic topological metacrystal based on an all-dielectric metamaterial platform shows robust propagation of surface states along 2D domain walls, making it a promising solution for photonics applications. The proposed metacrystal design might also open the way for the observation of elusive fundamental physical phenomena.
265 citations
TL;DR: In this paper, the authors demonstrate electrical tuning of the spectral response of a Mie-resonant dielectric metasurface consisting of silicon nanodisks embedded into liquid crystals.
Abstract: We demonstrate electrical tuning of the spectral response of a Mie-resonant dielectric metasurface consisting of silicon nanodisks embedded into liquid crystals. We use the reorientation of nematic liquid crystals in a moderate applied electric field to alter the anisotropic permittivity tensor around the metasurface. By switching a control voltage “on” and “off,” we induce a large spectral shift of the metasurface resonances, resulting in an absolute transmission modulation of up to 75%. Our experimental demonstration of voltage control of dielectric metasurfaces paves the way for new types of electrically tunable metadevices, including dynamic displays and holograms.
236 citations
TL;DR: Not only the scattering by individual particles and particle clusters, but also the manipulation of reflection, transmission, diffraction, and absorption for metalattices and metasurfaces are discussed, revealing how various optical phenomena observed recently are all ubiquitously related to the Kerker concept.
Abstract: The original Kerker effect was introduced for a hypothetical magnetic sphere, and initially it did not attract much attention due to a lack of magnetic materials required. Rejuvenated by the recent explosive development of the field of metamaterials and especially its core concept of optically-induced artificial magnetism, the Kerker effect has gained an unprecedented impetus and rapidly pervaded different branches of nanophotonics. At the same time, the concept behind the effect itself has also been significantly expanded and generalized. Here we review the physics and various manifestations of the generalized Kerker effects, including the progress in the emerging field of meta-optics that focuses on interferences of electromagnetic multipoles of different orders and origins. We discuss not only the scattering by individual particles and particle clusters, but also the manipulation of reflection, transmission, diffraction, and absorption for metalattices and metasurfaces, revealing how various optical phenomena observed recently are all ubiquitously related to the Kerker's concept.
217 citations
TL;DR: A spontaneously polarized nanolaser able to couple light into waveguide channels with four orders of magnitude intensity than classical nanolasers, as well as the generation of ultrafast pulses via spontaneous mode locking of several anapoles is demonstrated.
Abstract: Nanophotonics is a rapidly developing field of research with many suggestions for a design of nanoantennas, sensors and miniature metadevices Despite many proposals for passive nanophotonic devices, the efficient coupling of light to nanoscale optical structures remains a major challenge In this article, we propose a nanoscale laser based on a tightly confined anapole mode By harnessing the non-radiating nature of the anapole state, we show how to engineer nanolasers based on InGaAs nanodisks as on-chip sources with unique optical properties Leveraging on the near-field character of anapole modes, we demonstrate a spontaneously polarized nanolaser able to couple light into waveguide channels with four orders of magnitude intensity than classical nanolasers, as well as the generation of ultrafast (of 100 fs) pulses via spontaneous mode locking of several anapoles Anapole nanolasers offer an attractive platform for monolithically integrated, silicon photonics sources for advanced and efficient nanoscale circuitry
185 citations
TL;DR: In this paper, the authors review the recent progress in physics of tunable and reconfigurable nanophotonic structures of different types, focusing on three platforms based on metallic, dielectric and hybrid resonant photonic structures such as nanoantennas, nanoparticle oligomers and nanostructured metasurfaces.
Abstract: Interaction of light pulses of various durations and intensities with nanoscale photonic structures plays an important role in many applications of nanophotonics for high-density data storage, ultra-fast data processing, surface coloring and sensing. A design of optically tunable and reconfigurable structures made from different materials is based on many important physical effects and advances in material science, and it employs the resonant character of light interaction with nanostructures and strong field confinement at the nanoscale. Here we review the recent progress in physics of tunable and reconfigurable nanophotonic structures of different types. We start from low laser intensities that produce weak reversible changes in nanostructures, and then move to the discussion of non-reversible changes in photonic structures. We focus on three platforms based on metallic, dielectric and hybrid resonant photonic structures such as nanoantennas, nanoparticle oligomers and nanostructured metasurfaces. Main challenges and key advantages of each of the approaches focusing on applications in advanced photonic technologies are also discussed.
164 citations
TL;DR: In this article, high-index dielectric nanoparticles are used to generate a strong magnetic response that can be leveraged in designing metasurfaces with unidirectional scattering, as well as efficient metadevices.
Abstract: In nanophotonics, subwavelength localization of light is usually associated with plasmonics, the collective excitation of electrons and electromagnetic waves at metallic surfaces. Recent developments in the physics of high-index dielectric nanoparticles, however, suggest an alternative mechanism of light localization: low-order dipole and higherorder multipole Mie resonances. These resonances can generate a strong magnetic response that can be leveraged in designing metasurfaces with unidirectional scattering, as well as efficient metadevices. Indeed, as the power of this approach becomes increasingly apparent, high-index nanomaterials could complement, or even substitute for, plasmonic materials in a range of devices—and could spur a new era in nonlinear nanophotonics.
159 citations
TL;DR: It is demonstrated, both experimentally and theoretically, that resonantly excited nanocrystalline silicon nanoparticles fabricated by an optimized laser printing technique can exhibit strong second-harmonic generation (SHG) effects.
Abstract: Recent trends to employ high-index dielectric particles in nanophotonics are motivated by their reduced dissipative losses and large resonant enhancement of nonlinear effects at the nanoscale. Because silicon is a centrosymmetric material, the studies of nonlinear optical properties of silicon nanoparticles have been targeting primarily the third-harmonic generation effects. Here we demonstrate, both experimentally and theoretically, that resonantly excited nanocrystalline silicon nanoparticles fabricated by an optimized laser printing technique can exhibit strong second-harmonic generation (SHG) effects. We attribute an unexpectedly high yield of the nonlinear conversion to a nanocrystalline structure of nanoparticles supporting the Mie resonances. The demonstrated efficient SHG at green light from a single silicon nanoparticle is 2 orders of magnitude higher than that from unstructured silicon films. This efficiency is significantly higher than that of many plasmonic nanostructures and small silicon nan...
150 citations
TL;DR: In this article, an all-dielectric metasurface with sharp resonances by achieving interference between magnetic dipole and electric quadrupole modes of constituted nanoparticles arranged in a 2D lattice is shown.
Abstract: All-dielectric metasurfaces provide a powerful platform for a new generation of flat optical devices, in particular, for applications in telecommunication systems, due to their low losses and high transparency in the infrared. However, active and reversible tuning of such metasurfaces remains a challenge. This study experimentally demonstrates and theoretically justifies a novel scenario of the dynamical reversible tuning of all-dielectric metasurfaces based on the temperature-dependent change of the refractive index of silicon. How to design an all-dielectric metasurface with sharp resonances by achieving interference between magnetic dipole and electric quadrupole modes of constituted nanoparticles arranged in a 2D lattice is shown. Thermal tuning of these resonances can cause drastic but reciprocal changes in the directional scattering of the metasurface in a spectral window of 75 nm. This change can result in a 50-fold enhancement of the radiation directionality. This type of reversible tuning can play a significant role in novel flat optical devices including the metalenses and metaholograms.
TL;DR: In this paper, the organic cation part of perovskites is alloyed with nano-printing to achieve a significant enhancement of both linear and nonlinear photoluminescence.
Abstract: Recent developments in the physics of high-index resonant dielectric nanostructures suggest alternative mechanisms for subwavelength light control driven by Mie resonances with a strong magnetic response that can be employed for the design of novel optical metasurfaces. Here we demonstrate metasurfaces based on nanoimprinted perovskite films optimized by alloying the organic cation part of perovskites. We reveal that such metasurfaces can exhibit a significant enhancement of both linear and nonlinear photoluminescence (up to 70 times) combined with advanced stability. Our results suggest a cost-effective approach based on nanoimprint lithography and combined with simple chemical reactions for creating a new generation of functional metasurfaces that may pave the way toward highly efficient planar optoelectronic metadevices.
TL;DR: An all-dielectric sensing platform based on silicon nanodisks with strong optically-induced magnetic resonances is demonstrated, able to detect a concentration of streptavidin of as low as 10-10 M (mol L-1) or 5 ng mL-1, thus pushing the current detection limit by at least two orders of magnitudes.
Abstract: Biosensing based on nanophotonic structures has shown a great potential for cost-efficient, high-speed and compact personal medical diagnostics. While plasmonic nanosensors offer high sensitivity, their intrinsically restricted resonance quality factors and strong heating due to metal absorption impose severe limitations on real life applications. Here, we demonstrate an all-dielectric sensing platform based on silicon nanodisks with strong optically-induced magnetic resonances, which are able to detect a concentration of streptavidin of as low as 10−10 M (mol L−1) or 5 ng mL−1, thus pushing the current detection limit by at least two orders of magnitudes. Our study suggests a new direction in biosensing based on bio-compatible, non-toxic, robust and low-loss dielectric nanoresonators with potential applications in medicine, including disease diagnosis and drug detection.
TL;DR: In this paper, the peculiarities of light scattering from subwavelength particles made of high-refractive-index materials caused by the coexistence of particular anapole modes of both electric and magnetic character were investigated.
Abstract: We investigate the peculiarities of light scattering from subwavelength particles made of high-refractive-index materials caused by the coexistence of particular anapole modes of both electric and magnetic character. The similarities and differences of such anapole modes are discussed in detail. We also show that these two types of anapole modes can be supported simultaneously by subwavelength high-index spherical dielectric particles.
TL;DR: In this article, spectrally diverse multiple magnetic dipole resonances can be excited in all-dielectric structures lacking rotational symmetry, in contrast to conventionally used spheres, disks, or spheroids.
Abstract: We demonstrate that spectrally diverse multiple magnetic dipole resonances can be excited in all-dielectric structures lacking rotational symmetry, in contrast to conventionally used spheres, disks, or spheroids. Such multiple magnetic resonances arise from hybrid Mie-Fabry-Perot modes, and can constructively interfere with induced electric dipole moments, thereby leading to novel multifrequency unidirectional scattering. Here we focus on elongated dielectric nanobars, whose magnetic resonances can be spectrally tuned by their aspect ratios. Based on our theoretical results, we suggest all-dielectric multimode metasurfaces and verify them in proof-of-principle microwave experiments. We also believe that the demonstrated property of multimode directionality is largely responsible for the best efficiency of all-dielectric metasurfaces that were recently shown to operate across multiple telecom bands.
TL;DR: By engineering such waves, scientists have designed an optical system that enhances this confinement, producing a compact laser that emits a high-quality beam.
Abstract: Light in a laser is confined in the form of standing waves. By engineering such waves, scientists have designed an optical system that enhances this confinement, producing a compact laser that emits a high-quality beam. See Letter p.196
TL;DR: This work distinguishes experimentally the contribution of electric and magnetic nonlinear response by analyzing the structure of polarization states of vector beams in the second-harmonic radiation and provides a direct observation of nonlinear optical magnetism through selective excitation of multipolar nonlinear modes in nanoantennas.
Abstract: Nonlinear effects at the nanoscale are usually associated with the enhancement of electric fields in plasmonic structures Recently emerged new platform for nanophotonics based on high-index dielectric nanoparticles utilizes optically induced magnetic response via multipolar Mie resonances and provides novel opportunities for nanoscale nonlinear optics Here, we observe strong second-harmonic generation from AlGaAs nanoantennas driven by both electric and magnetic resonances We distinguish experimentally the contribution of electric and magnetic nonlinear response by analyzing the structure of polarization states of vector beams in the second-harmonic radiation We control continuously the transition between electric and magnetic nonlinearities by tuning polarization of the optical pump Our results provide a direct observation of nonlinear optical magnetism through selective excitation of multipolar nonlinear modes in nanoantennas
TL;DR: Polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain.
Abstract: Recently introduced field of topological photonics aims to explore the concepts of topological insulators for novel phenomena in optics. Here polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain. It is observed experimentally and described how theoretically topological phase transitions at the nanoscale define a change from trivial to nontrivial topological states when the edge mode is excited.
TL;DR: In this paper, the authors observed the breakup dynamics of an elongated cloud of condensed atoms placed in an optical waveguide and compared the number of localized spatial components observed in the breakup with the number predicted by a plane-wave stability analysis of the nonpolynomial nonlinear Schrodinger equation.
Abstract: We observe the breakup dynamics of an elongated cloud of condensed $^{85}\mathrm{Rb}$ atoms placed in an optical waveguide The number of localized spatial components observed in the breakup is compared with the number of solitons predicted by a plane-wave stability analysis of the nonpolynomial nonlinear Schr\"odinger equation, an effective one-dimensional approximation of the Gross-Pitaevskii equation for cigar-shaped condensates It is shown that the numbers predicted from the fastest growing sidebands are consistent with the experimental data, suggesting that modulational instability is the key underlying physical mechanism driving the breakup
TL;DR: In this paper, a multipole decomposition of the electromagnetic field is proposed to describe the scattering intensity of an arbitrary nanoscale object, which can be characterized by a multi-particle decomposition.
Abstract: Scattering of electromagnetic waves by an arbitrary nanoscale object can be characterized by a multipole decomposition of the electromagnetic field that allows one to describe the scattering intens...
TL;DR: It is revealed that an isotropic, homogeneous, subwavelength particle with high refractive index can produce ultra-small total scattering and the invisibility effect could be useful for the design of highly transparent optical materials.
Abstract: We reveal that an isotropic, homogeneous, subwavelength particle with high refractive index can produce ultra-small total scattering. This effect, which follows from the inhibition of the electric dipole radiation, can be identified as a Fano resonance in the scattering efficiency and is associated with the excitation of an anapole mode in the particle. This anapole mode is non-radiative and emerges from the destructive interference of electric and toroidal dipoles. The invisibility effect could be useful for the design of highly transparent optical materials. This article is part of the themed issue ‘New horizons for nanophotonics’.
TL;DR: The results demonstrate that waveguide-integrated nanoantennas have the potential to be used as ultra-compact polarization-demultiplexing on-chip devices for high–bit rate telecommunication applications.
Abstract: Optical nanoantennas provide a promising pathway toward advanced manipulation of light waves, such as directional scattering, polarization conversion, and fluorescence enhancement. Although these functionalities were mainly studied for nanoantennas in free space or on homogeneous substrates, their integration with optical waveguides offers an important "wired" connection to other functional optical components. Taking advantage of the nanoantenna's versatility and unrivaled compactness, their imprinting onto optical waveguides would enable a marked enhancement of design freedom and integration density for optical on-chip devices. Several examples of this concept have been demonstrated recently. However, the important question of whether nanoantennas can fulfill functionalities for high-bit rate signal transmission without degradation, which is the core purpose of many integrated optical applications, has not yet been experimentally investigated. We introduce and investigate directional, polarization-selective, and mode-selective on-chip nanoantennas integrated with a silicon rib waveguide. We demonstrate that these nanoantennas can separate optical signals with different polarizations by coupling the different polarizations of light vertically to different waveguide modes propagating into opposite directions. As the central result of this work, we show the suitability of this concept for the control of optical signals with ASK (amplitude-shift keying) NRZ (nonreturn to zero) modulation [10 Gigabit/s (Gb/s)] without significant bit error rate impairments. Our results demonstrate that waveguide-integrated nanoantennas have the potential to be used as ultra-compact polarization-demultiplexing on-chip devices for high-bit rate telecommunication applications.
Abstract: We demonstrate both experimentally and numerically multifold enhancement of magneto-optical effects in subwavelength dielectric nanostructures with a magnetic surrounding exhibiting localized magnetic Mie resonances. We employ amorphous silicon nanodisks covered with a thin nickel film and achieve the 5-fold enhancement of the magneto-optical response of the hybrid magnetophotonic array of nanodisks in comparison with a thin nickel film deposited on a flat silica substrate. Our findings allow for a new basis for active and nonreciprocal photonic nanostructures and metadevices, which could be tuned by an external magnetic field.
TL;DR: Enhanced second-harmonic generation (SHG) from a hybrid metal-dielectric nanodimer consisting of an inorganic perovskite nanoparticle of barium titanate coupled to a metallic gold (Au) nanoparticle is shown.
Abstract: We show enhanced second-harmonic generation (SHG) from a hybrid metal–dielectric nanodimer consisting of an inorganic perovskite nanoparticle of barium titanate (BaTiO3) coupled to a metallic gold (Au) nanoparticle. BaTiO3–Au nanodimers of 100 nm/80 nm sizes are fabricated by sequential capillarity-assisted particle assembly. The BaTiO3 nanoparticle has a noncentrosymmetric crystalline structure and generates bulk SHG. We use the localized surface plasmon resonance of the gold nanoparticle to enhance the SHG from the BaTiO3 nanoparticle. We experimentally measure the nonlinear signal from assembled nanodimers and demonstrate an up to 15-fold enhancement compared to a single BaTiO3 nanoparticle. We further perform numerical simulations of the linear and SHG spectra of the BaTiO3–Au nanodimer and show that the gold nanoparticle acts as a nanoantenna at the SHG wavelength.
TL;DR: In this paper, a quantitative model is developed to identify and disentangle the three physical processes that govern the ultrafast changes of the nanobrick optical properties, namely, two-photon absorption, free-carrier relaxation, and lattice heating.
Abstract: We report on the broadband transient optical response of anisotropic, amorphous silicon nanobricks that exhibit Mie-type resonances. A quantitative model is developed to identify and disentangle the three physical processes that govern the ultrafast changes of the nanobrick optical properties, namely, two-photon absorption, free-carrier relaxation, and lattice heating. We reveal a set of operating windows where ultrafast all-optical modulation of transmission is achieved with full return to zero in 20 ps. This is made possible because of the distinct dispersive features exhibited by the competing nonlinear processes in transmission and despite the slow (nanosecond) internal lattice dynamics. The observed ultrafast switching behavior can be independently engineered for both orthogonal polarizations using the large anisotropy of nanobricks, thus allowing ultrafast anisotropy control. Our results categorically ascertain the potential of all-dielectric resonant nanophotonics as a platform for ultrafast optica...
TL;DR: In this article, the angularly resolved transmission properties of dielectric metasurfaces consisting of silicon nanodisks which support electric and magnetic dipolar Mie-type resonances in the near-infrared spectral range were investigated.
Abstract: We experimentally and numerically study the angularly resolved transmission properties of dielectric metasurfaces consisting of silicon nanodisks which support electric and magnetic dipolar Mie-type resonances in the near-infrared spectral range. First, we concentrate on Huygens' metasurfaces which are characterised by a spectral overlap of the fundamental electric and magnetic dipole resonances of the silicon nanodisks at normal incidence. Huygens' metasurfaces exhibit a high transmitted intensity over the spectral width of the resonances due to impedance matching, while the transmitted phase shows a variation of as the wavelength is swept across the width of the resonances. We observe that the transmittance of the Huygens' metasurfaces depends on the incidence angle and is sensitive to polarisation for non-normal incidence. As the incidence angle is increased starting from normal incidence, the two dipole resonances are shifted out of the spectral overlap and the resonant features appear as pronounced transmittance minima. Next, we consider a metasurface with an increased nanodisk radius as compared to the Huygens' metasurface, which supports spectrally separate electric and magnetic dipole resonances at normal incidence. We show that for TM polarisation, we can shift the resonances of this metasurface into spectral overlap and regain the high resonant transmittance characteristic of Huygens' metasurfaces at a particular incidence angle. Furthermore, both metasurfaces are demonstrated to reject all TM polarised light incident under angles other than the design overlap angle at their respective operation frequency. Our experimental observations are in good qualitative agreement with numerical calculations.
TL;DR: This work studies the third-harmonic generation from dimers composed of pairs of two identical silicon nanoparticles and demonstrates that the multipolar harmonic modes generated by the dimers near the Mie resonances allow the shaping of the directionality of nonlinear radiation.
Abstract: Recent progress in the study of resonant light confinement in high-index dielectric nanostructures suggests a new route for achieving efficient control of both electric and magnetic components of light. It also leads to the enhancement of nonlinear effects near electric and magnetic Mie resonances with an engineered radiation directionality. Here we study the third-harmonic generation from dimers composed of pairs of two identical silicon nanoparticles and demonstrate, both numerically and experimentally, that the multipolar harmonic modes generated by the dimers near the Mie resonances allow the shaping of the directionality of nonlinear radiation.
TL;DR: In this paper, the authors introduced the multiparticle Wannier states for interacting systems with cotranslational symmetry, which provided an orthogonal basis for constructing effective Hamiltonians for the isolated bands.
Abstract: The study of topological effects in physics is a hot area of research, and only recently have researchers been able to address the important issues of topological properties of interacting quantum systems. But it is still a great challenge to describe multiparticle and interaction effects. Here, we introduce the multiparticle Wannier states for interacting systems with cotranslational symmetry, which provide an orthogonal basis for constructing effective Hamiltonians for the isolated bands. We reveal how the shift of multiparticle Wannier state relates to the Chern number of the multiparticle Bloch band and study the Thouless pumping of two interacting bosons in a one-dimensional superlattice. In addition to the Thouless pumping of bound states when two bosons move unidirectionally as a whole, we describe topologically resonant tunneling when two bosons move unidirectionally, one by the other, provided the neighboring-well potential bias matches the interaction energy. Our work creates a paradigm for multiparticle topological effects and provides a way to detect topological states in interacting multiparticle systems.
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TL;DR: In this paper, a quantitative model is developed to identify and disentangle the three physical processes that govern the ultrafast changes of the nanobrick optical properties, namely two-photon absorption, free-carrier relaxation, and lattice heating.
Abstract: We report on the broadband transient optical response from anisotropic nanobrick amorphous silicon particles, exhibiting Mie-type resonances. A quantitative model is developed to identify and disentangle the three physical processes that govern the ultrafast changes of the nanobrick optical properties, namely two-photon absorption, free-carrier relaxation, and lattice heating. We reveal a set of operating windows where ultrafast all-optical modulation of transmission is achieved with full return to zero in 20 ps. This is made possible due to the interplay between the competing nonlinear processes and despite the slow (nanosecond) internal lattice dynamics. The observed ultrafast switching behavior can be independently engineered for both or- thogonal polarizations using the large anisotropy of nanobricks thus allowing ultrafast anisotropy control. Our results categorically ascertain the potential of all-dielectric resonant nanophotonics as a platform for ultrafast optical devices, and reveal the pos- sibility for ultrafast polarization-multiplexed displays and polarization rotators.
TL;DR: In this article, a novel type of metamaterial is introduced, where the structural symmetry can be controlled by optical forces, and the effect is employed to transform a planar achiral metasurface into a stereoscopic chiral structure.
Abstract: A novel type of metamaterial is introduced, where the structural symmetry can be controlled by optical forces. Since symmetry sets fundamental bounds on the optical response, symmetry breaking changes the properties of metamaterials qualitatively over the entire resonant frequency band. This is achieved by a polarized pump beam, exerting optical forces which are not constrained by the structural symmetry. This new concept is illustrated for a metasurface composed of zig-zag chains of dipole meta-atoms, in which a highly asymmetric optical force exists for an appropriate incident polarization. The effect is employed to transform a planar achiral metasurface into a stereoscopic chiral structure. Importantly, the handedness of the induced chirality can be actively switched by changing the incident polarization. The proposed concept can be employed to achieve dynamic spatial control of metamaterials and metasurfaces at infrared and optical frequencies with subwavelength resolution.