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The field of nonlinear optics is a well-established discipline that relies on macroscopic media and employs propagation distances longer than a wavelength of light. Recent progress with electromagnetic metamaterials has allowed for the expansion of this field into new directions of new phenomena and novel functionalities. In particular, nonlinear effects in thin, artificially structured materials such as metasurfaces do not rely on phase-matching conditions and symmetry-related selection rules of natural materials; they may be substantially enhanced by strong local and collective resonances of fields inside the metasurface nanostructures. Consequently, nonlinear processes may extend beyond simple harmonic generation and spectral broadening due to electronic nonlinearities. This article provides a brief review of basic concepts and recent results in the field of nonlinear optical metasurfaces.

Rapid progress in miniaturizing vortex devices is driven by their integration with optical sensing, micromanipulation, and optical communications in both classical and quantum realms. Many such efforts are usually associated with on-chip micro- or nanoscale structures in real space and possess a static orbital angular momentum. Recently, a new branch of singular optics has emerged that seeks phase singularities in multiple dimensions, realizing vortex beams with compact nanodevices. Here, we review the topological phase singularities in real space, momentum space, and the spatiotemporal domain for generating vortex beams; discuss recent developments in theoretical and experimental research for generation, detection, and transmission of vortex beams; and provide an outlook for future opportunities in this area, ranging from fundamental research to practical applications.

Bound states in the continuum (BICs) represent dark modes trapped in the radiation continuum. BICs received significant attention in optics and photonics as a simple tool to achieve giant quality factors by transforming them into quasi-BICs. Here, we report the observation of high-harmonic generation in dielectric metasurfaces hosting BICs. The metasurface is composed of a square lattice with parallel Si bars of a slightly different width placed on a transparent substrate. The structure is engineered to support a quasi-BIC in the mid-IR with a high quality factor. We tune the metasurface asymmetry to enable the optimal coupling condition that provide the highest high-harmonic generation efficiency. In the experiment, we demonstrate the generation of odd optical harmonics from the 3rd to the 11th order in the BIC regime and study their polarization dependence. We measure the dependence of the high-harmonic signal on the input intensity. The concept of metasurfaces with highly localized light boosted by BIC resonances provides a new degree of freedom to control experimentally strong nonlinear optical response.

Coupling of light into optical fibers is important for many applications, while for commonly used step-index optical fibers it massively drops for oblique incident angles

We demonstrate experimentally perfect absorbers for arbitrary polarization (linear, circular, or elliptical) in the mid-IR based on plasmonic diatomic metasurfaces, which provide perfect absorption for any specific polarization and almost total reflection for the orthogonal polarization.

We report on the formation of high-Q localized states in finite arrays of Mie resonators overcoming the previously predicted values by at least two-orders of magnitude, which becomes possible due to destructive interference of band-edge modes.

We design and demonstrate dramatic suppression of reflection from MAPbBr3 halide-perovskite metasurfaces. We employ the Kerker effect and engineer both electric and magnetic Mie resonances in each dielectric meta-atom to achieve a broadband performance.

Nonlinear metasurfaces incorporate many of the functionalities of their linear counterparts such as wavefront shaping, but simultaneously they perform nonlinear optical transformations. This dual functionality leads to a rather unintuitive physical behavior which is still widely unexplored for many photonic applications. The nonlinear processes render some basic principles governing the functionality of linear metasurfaces. Exemplarily, the superposition principle and the geometric optics approximation become not directly applicable to nonlinear metasurfaces. On the other hand, nonlinear metasurfaces facilitate new phenomena that are not possible in the linear regime. Here, we study the imaging of objects through a dielectric nonlinear metalens. We illuminate objects by infrared light and record their generated images at the visible third-harmonic wavelengths. We revisit the classical lens theory and suggest a generalized Gaussian lens equation for nonlinear imaging, verified both experimentally and analytically. We also demonstrate experimentally higher-order spatial correlations facilitated by the nonlinear metalens, resulting in additional image features.

Electromagnetic response of dielectric resonators with high refractive index is governed by optically induced electric and magnetic Mie resonances facilitating confinement of light with the amplitude enhancement. However, strong subwavelength trapping of light was associated traditionally only with plasmonic or epsilon-near-zero structures which however suffer from losses. Recently, an alternative localization mechanism was proposed to trap light in individual subwavelength optical resonators with a high quality factor in the regime of a supercavity mode. Here, we present the experimental observation of the supercavity modes in subwavelength ceramic resonators in the radiofrequency range. We demonstrate experimentally that the regime of supercavity mode can be achieved via precise tuning of the resonator's dimensions resulting in a huge growth of the quality factor reaching the experimental values up to 1.25x10^4, being limited only by material losses in dielectrics. We reveal that the supercavity modes can be excited efficiently by both near- and far-fields by means of dipole sources and plane waves, respectively. In both the cases, the supercavity mode manifests itself clearly via characteristic peculiarities of the Fano resonance and radiation patterns. Our work paves the way for future compact practical devices in photonics and radiophysics., Comment: 11 pages, 4 figures

We describe the scattering properties of planar metasurfaces composed of arrays of dielectric resonators supporting both electric and magnetic Mie resonances. We focus on the study of metasurfaces with such functionalities as perfect reflection, perfect transmission, and perfect absorption of light at the normal or oblique incidence. Each effect is presented in its simplest form for the cases of electric and magnetic dipole resonances. Generalizations to higher orders and higher numbers of multipoles are discussed as well.

Nanostructured metasurfaces demonstrate extraordinary capabilities to control light at the subwavelength scale, emerging as key optical components to physical realization of multitasked devices. Progress in multitasked metasurfaces has been witnessed in making a single metasurface multitasked by mainly resorting to extra spatial freedom, for example, interleaved subarrays, different angles. However, it imposes a challenge of suppressing the cross-talk among multiwavelength without the help of extra spatial freedom. Here, we introduce an entirely novel strategy of multitasked metasurfaces with noninterleaved single-size Si nanobrick arrays and minimalist spatial freedom demonstrating massive information on 6-bit encoded color holograms. The interference between electric dipole and magnetic dipole in individual Si nanobricks with in-plane orientation enables manipulating six bases of incident photons simultaneously to reconstructed 6-bit wavelength- and spin-dependent multicolor images. Those massively reco...

Metasurfaces, two-dimensional lattices of nanoscale resonators, offer unique opportunities for functional flat optics and allow the control of the transmission, reflection, and polarization of a wavefront of light. Recently, all-dielectric metasurfaces reached remarkable efficiencies, often matching or out-performing conventional optical elements. The exploitation of the nonlinear optical response of metasurfaces offers a paradigm shift in nonlinear optics, and dielectric nonlinear metasurfaces are expected to enrich subwavelength photonics by enhancing substantially nonlinear response of natural materials combined with the efficient control of the phase of nonlinear waves. Here, we suggest a novel and rather general approach for engineering the wavefront of parametric waves of arbitrary complexity generated by a nonlinear metasurface. We design all-dielectric nonlinear metasurfaces, achieve a highly efficient wavefront control of a third-harmonic field, and demonstrate the generation of nonlinear beams at a designed angle and the generation of nonlinear focusing vortex beams. Our nonlinear metasurfaces produce phase gradients over a full 0-2π phase range with a 92% diffraction efficiency.

Most optical metamaterials fabricated and studied to date employ metallic components resulting in significant losses, heat and overall low efficiencies. A new era of metamaterial physics is associated with all-dielectric meta-optics, which employs electric and magnetic Mie resonances of subwavelength particles with high refractive index for an optically induced magnetic response, thus underpinning a new approach to design and fabricate functional and practical metadevices. Here we review the recent developments in meta-optics and subwavelength dielectric photonics and demonstrate that the Mie resonances can play a crucial role in the realization of the unique functionalities of meta-atoms, also driving novel effects in the fields of metamaterials and nanophotonics. We discuss the recent research frontiers in all-dielectric meta-optics and uncover how Mie resonances can be employed for a flexible control of light with full phase and amplitude engineering, including unidirectional metadevices, highly transparent metasurfaces, non-linear nanophotonics and topological photonics.

We study the third-harmonic generation by structured light in subwavelength silicon nanoparticles which support both electric and magnetic multipolar Mie resonances. By tailoring the vectorial structure of the pumping light, we may control both strength and polarization composition of the excited harmonic fields. In this way, we generate nonlinear fields with radial or azimuthal polarizations by addressing selectively a different type of multipolar Mie resonances, also enhancing or suppressing the optically induced nonlinear magnetic response.

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.

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 nanoparticles in the visible range, and it can be useful for a design of nonlinear nanoantennas and silicon-based integrated light sources.

We report on the experimental and numerical results for the second-harmonic generation spectroscopy by doughnut-shaped cylindrical vector beams of azimuthal and radial polarizations in individual subwavelength AlGaAs particles, which support multipolar Mie resonances at the fundamental and double frequencies. We observe high-Q resonant optical modes associated with bound states in the continuum for the azimuthally polarized pump beam with the record-high efficiency (0.1%) of the up-conversion nonlinear optical process due to a strong electromagnetic field confinement. Our findings provide an important step towards a design of resonant subwavelength all-dielectric nanostructures with tailored efficiencies of nonlinear optical phenomena at the nanoscale.

We present a novel optical effect where the scattered light on dielectric particles is suppressed simultaneously in the forward and backward directions. In contrary to the quadrupolar generalized Kerker conditions, this effect requires the coherent dipoles to be with pi phase with their quadruple counterparts. Electric dipole Fano profile and quadruples long-wavelength characteristics together set the physical environment to satisfy these conditions at a certain spectral position. The metasurface constructed from transverse scatterers is extraordinary transparent for the incident light where neither the phase nor the amplitude is perturbed.

We study, both theoretically and experimentally, tunable metasurfaces supporting sharp Fano-resonances inspired by optical bound states in the continuum. We explore the use of arsenic trisulfide (a photosensitive chalcogenide glass) having optical properties which can be finely tuned by light absorption at the post-fabrication stage. We select the resonant wavelength of the metasurface corresponding to the energy below the arsenic trisulfide bandgap, and experimentally control the resonance spectral position via exposure to the light of energies above the bandgap., 7 pages, 5 figures

Dielectric metasurfaces allow us to realize many unique effects in optics, and they can serve as the building blocks of the modern photonic technologies. Here, we suggest theoretically and demonstrate experimentally the effect of high transparency of all-dielectric metasurfaces with meta-atoms supporting the so-called transverse Kerker effect. In contrast to the well-known Huygens' metasurfaces, in our case both phase and amplitude of the incoming wave remain unperturbed at the resonant frequency and, consequently, our novel metasurfaces totally operate in the high-transparency regime. We prove experimentally, in the microwave frequency range, that both phase and amplitude of the waves transmitted through these metasurfaces remain almost unaffected. Also, we demonstrate numerically and experimentally and explain theoretically a novel mechanism for achieving a perfect absorption of the incident light enabled by the resonant response of the dielectric metasurfaces placed on a conducting substrate. In the subdiffractive limit, we show that these effects are mainly determined by the optical response of the constituting meta-atoms rather than collective lattice contributions. With the spectrum scalability, our finding can be extended to the optical frequencies to be employed for energy harvesting, nonlinear phenomena, and filtering of light.

Recently emerged new field of meta-optics aims at the manipulation of strong optically-induced electric and magnetic Mie resonances in high-index dielectric nanostructures. Unique advantages of dielectric resonant nanostructures over their metallic counterparts are low losses, enhancement of both electric and magnetic fields, and unique resonances that provide competitive alternatives for plasmonic structures such as nanoantennas and metasurfaces. This talk will summarize our recent results on Mie-resonant dielectric meta-optics and metasurfaces.

All-dielectric nanophotonics attracts more and more attention nowadays due to the possibility to control and configure light scattering on high-index semiconductor nanoparticles. It opens a room of opportunities for designing novel types of nanoscale elements and devices, paving the way to advanced technologies of light energy manipulation. One of the most pespective and interesting effects is directive light scattering provided by the so-called Kerker and anti-Kerker effects giving a possibility to realize Huygens light sources, fully transparent metasurfaces, different types of nanoantennae etc. Another one corresponds to the realization of so-called “anapole states” providing near-zero scattering accompanied with strong near-fields. Here we briefly review some new results on the induced invisibility regarding fully transparent metasurfaces based on the simultaneous cancellation of the forward and backward scatteringvia particular optical responses of multipoles (similar to Kerker effect), and invisible objects and structures governed by the novel type of anapoles - hybrid anapole states.

Metamaterials---artificial electromagnetic media that are structured on the subwavelength scale---were initially suggested for the realisation of negative-index media, and later they became a paradigm for engineering electromagnetic space and control¬ling propagation of waves. However, applications of metamaterials in optics are limited due to inherent losses in metals employed for the realisation of artificial optical magnetism. Recently, we observe the emergence of a new field of all-dielectric resonant meta-optics aiming at the manipulation of strong optically-induced electric and magnetic Mie-type resonances in dielectric and semiconductor nanostructures with relatively high refractive index. Unique advantages of dielectric resonant nanostructures over their metallic counterparts are low dissipative losses and the enhancement of both electric and magnetic fields that provide competitive alternatives for plasmonic structures including optical nanoantennas, efficient biosensors, passive and active metasurfaces, and functional metadevices. This talk will summarize the most recent advances in all-dielectric Mie-resonant meta-optics including active nanophotonics as well as the recently emerged fields of topological photonics and nonlinear metasurfaces.

By controlling interference of Mie resonance modes of various nanostructures, we can achieve a large number of nontrivial effects in nanophotonics. In this work, we propose a cylindrical structure in which the spectral overlap of the Mie-type modes can be controlled by drilling a hole parallel to the axis, thus changing unidirectional scattering. We further demonstrate that the scattering patterns can be tailored by rotating the structure to achieve almost arbitrary scattered wave direction.

Angle-multiplexed dielectric metasurfaces enable sensitive molecular fingerprint detection without the need for spectrometry., Infrared spectroscopy resolves the structure of molecules by detecting their characteristic vibrational fingerprints. Subwavelength light confinement and nanophotonic enhancement have extended the scope of this technique for monolayer studies. However, current approaches still require complex spectroscopic equipment or tunable light sources. Here, we introduce a novel metasurface-based method for detecting molecular absorption fingerprints over a broad spectrum, which combines the device-level simplicity of state-of-the-art angle-scanning refractometric sensors with the chemical specificity of infrared spectroscopy. Specifically, we develop germanium-based high-Q metasurfaces capable of delivering a multitude of spectrally selective and surface-sensitive resonances between 1100 and 1800 cm−1. We use this approach to detect distinct absorption signatures of different interacting analytes including proteins, aptamers, and polylysine. In combination with broadband incoherent illumination and detection, our method correlates the total reflectance signal at each incidence angle with the strength of the molecular absorption, enabling spectrometer-less operation in a compact angle-scanning configuration ideally suited for field-deployable applications.

We study both linear and nonlinear propagation of pulses in waveguides composed of high-index dielectric nanoparticles supporting both electric and magnetic resonances. We reveal that short pulses (∼100 fs) broaden significantly in the linear regime after propagating only several tens of micrometers, due to a strong waveguide dispersion. In the nonlinear regime, the pulses propagating in the chains of spherical nanoparticles broaden even more strongly than in the linear regime due to defocusing nonlinearity. However, for the chains of nanodisks the pulse broadening can be compensated by the nonlinear effect, due to the interplay of the electric and magnetic resonances that can change the sign of the group-velocity dispersion for some frequencies, making possible the formation and propagation of solitary waves and effective generation of the new frequencies. Our results demonstrate that considered systems can serve as a promising platform for nonlinear and ultrafast nanophotonics, allowing the observation ...

We study a plasmonic directional coupler with a metallic cladding and dielectric core in the presence of balanced gain and loss, and demonstrate that such a photonic structure can possess the parity-time (PT) symmetry even when optical losses in metal are taken into account. We analyze the modal dispersion of the coupler when losses in metal are negligible and then study how substantially increased losses modify the modal dispersion and coupler's properties. For realistic parameters, we demonstrate a novel approach for recovering the property of the PT-symmetry by introducing unbalanced loss and gain in both cores of the coupler.

We study the third-harmonic generation from metal–dielectric–metal layered fishnet metamaterials and identify experimentally the multipolar contributions to the generated nonlinear harmonic fields by analyzing the radiation patterns of the emission. We observe that the third harmonic radiated from the fishnet structure is a result of the interference of the electric and magnetic dipoles and the electric quadrupole modes. Our results provide direct evidence of the importance of higher order multipoles in the nonlinear response of fishnet metamaterials, opening new opportunities for enhanced nonlinearities and controlled directionality of nonlinear processes in metamaterials.

A spaser is a nanoplasmonic counterpart of a laser, with photons replaced by surface plasmon polaritons and a resonant cavity replaced by a metallic nanostructure supporting localized plasmonic modes. By combining analytical results and first-principle numerical simulations, we provide a comprehensive study of the ultrafast dynamics of a spaser. Due to its highly-nonlinear nature, the spaser is characterized by a large number of interacting degrees of freedom, which sustain a rich manifold of different phases we discover, describe and analyze here. In the regime of strong interaction, the system manifests an irreversible ergodic evolution towards the configuration where energy is equally shared among all the available degrees of freedom. Under this condition, the spaser generates ultrafast vortex-like lasing modes that are spinning on the femtosecond scale and whose direction of rotation is dictated by quantum noise. In this regime, the spaser acquires the character of a nanoparticle with an effective spin. This opens up a range of interesting possibilities for achieving unidirectional emission from a symmetric nanostructure, stimulating a broad range of applications for nanoplasmonic lasers as unidirectional couplers and random information sources.

Metasurfaces have shown great promise for the control of optical wavefronts, thus opening new pathways for the development of efficient flat optics. In particular, Huygens’ metasurfaces based on all-dielectric resonant meta-atoms have already shown a huge potential for practical applications with their polarization insensitivity and high transmittance efficiency. Here, we experimentally demonstrate a polarization-insensitive holographic Huygens’ metasurface based on dielectric resonant meta-atoms capable of complex wavefront control at telecommunication wavelengths. Our metasurface produces a hologram image in the far-field with 82% transmittance efficiency and 40% imaging efficiency. Such efficient complex wavefront control shows that Huygens’ metasurfaces based on resonant dielectric meta-atoms are a big step toward practical applications of metasurfaces in wavefront design related technologies, including computer-generated holograms, ultrathin optics, security, and data storage devices.

We study functional hybrid metasurfaces consisting of metal–dielectric nanoantennas that direct light from an incident plane wave or from localized light sources into a preferential direction. The directionality is obtained by carefully balancing the multipolar contributions to the scattering response from the constituents of the metasurface. The hybrid nanoantennas are composed of a plasmonic gold nanorod acting as a feed element and a silicon nanodisk acting as a director element. In order to experimentally realize this design, we have developed a two-step electron-beam lithography process in combination with a precision alignment step. The optical response of the fabricated sample is measured and reveals distinct signatures of coupling between the plasmonic and the dielectric nanoantenna elements that ultimately leads to unidirectional radiation of light.

We review the basic physics and applications of a special class of planar metamaterials, often called metasurfaces, which are composed of optically thin and densely packed planar arrays of resonant or nearly resonant subwavelength elements. Electromagnetic properties and functionalities of such metasurfaces are defined by the structure and specific features of the subwavelength elements and their coupling type and strength, and they are often influenced by an underlying substrate. Metasurfaces may provide a full control of the reflected and transmitted fields, and they can be designed to possess many required properties replacing bulky optical components. Here, we describe different types of metasurfaces suggested in the past and recent years for a broad range of the operational wavelengths ranging from microwaves to the visible, and emphasize their important functionalities. We demonstrate that, despite a wide functional and structural diversity, all suggested metasurfaces can be associated with only several broad classes depending on intrinsic physical mechanisms of their polarizability. We suggest the functionality-based classification of metasurfaces, and clarify a link between their polarization response and field control capabilities. We also suggest a general approach to an optimal design of metasurfaces for many specific applications.

All-dielectric nanophotonics attracts more and more attention nowadays due to the possibility to control and configure light scattering on high-index semiconductor nanoparticles. It opens a room of opportunities for the designing novel types of nanoscale elements and devices, and paves a way to advanced technologies of light energy manipulation. One of the most perspective and interesting effects is directive light scattering provided by the so-called Kerker and anti-Kerker effects giving a possibility to realize Huygens source of light, fully transparent metasurfaces, different types of nanoatennae etc. Another one corresponds to the realization of so-called “anapole states” providing near-zero scattering accompanied with strong near-fields. Here we briefly review some new results on the induced invisibility regarding fully transparent metasurfaces based on the simultaneous cancellation of the forward and backward scattering via particular optical responses of multipoles (similar to Kerker effect), and invisible objects and structures governed by the novel type of anapoles – hybrid anapole states.

With recent advances in nanophotonics, metasurfaces based on nano-resonators have facilitated novel types of optical devices. In particular, the interplay between different degrees of freedom, involving polarization and spatial modes, boosted classical polarization measurements and imaging applications. However, the use of metasurfaces for measuring the quantum states of light remains largely unexplored. Conventionally, the task of quantum state tomography is realized with several bulk optical elements, which need to be reconfigured multiple times. Such setups can suffer from decoherence, and there is a fundamental and practical interest in developing integrated solutions for measurement of multi-photon quantum states. We present a new concept and the first experimental realization of all-dielectric metasurfaces with no tuneable elements for imaging-based reconstruction of the full quantum state of entangled photons. Most prominently, we implement multi-photon interferometric measurements on a sub-wavelength thin optical element, which delivers ultimate miniaturization and extremely high robustness. Specifically, we realize a highly transparent all-dielectric metasurface, which spatially splits different components of quantum-polarization states. Then, a simple one-shot measurement of correlations with polarization-insensitive on-off click detectors enables complete reconstruction of multi-photon density matrices with high precision. In our experiment, we prepare sets of polarization states and reconstruct their density matrices with a high fidelity of over 99% for single photon states and above 95% for two-photon states. Our work provides a fundamental advance in the imaging of quantum states, where multi-photon quantum interference takes place at sub-wavelength scale.

Metasurfaces based on resonant nanophotonic structures have enabled novel types of flat-optics devices often outperforming the capabilities of bulk components, yet these advances remain largely unexplored for quantum applications. We show that non-classical multi-photon interferences can be achieved at the subwavelength scale in all-dielectric metasurfaces. We simultaneously image multiple projections of quantum states with a single metasurface, enabling a robust reconstruction of amplitude, phase, coherence, and entanglement of multi-photon polarization-encoded states. One- and two-photon states are reconstructed through nonlocal photon correlation measurements with polarization-insensitive click-detectors positioned after the metasurface, and the scalability to higher photon numbers is established theoretically. Our work illustrates the feasibility of ultra-thin quantum metadevices for the manipulation and measurement of multi-photon quantum states with applications in free-space quantum imaging and communications., 19 pages, 14 figures

We analyze stability of spatiotemporal solitons in multimode fibers in graded-index waveguides. We find the area of stable soliton-like dynamics of initial Gaussian pulse and study pulse propagation by direct three-dimensional numerical modeling.

All-dielectric resonant nanophotonics lies at the heart of modern optics and nanotechnology due to the unique possibilities to control scattering of light from high-index dielectric nanoparticles and metasurfaces. One of the important concepts of dielectric Mie-resonant nanophotonics is associated with the Kerker effect that drives the unidirectional scattering of light from nanoantennas and Huygens' metasurfaces. Here we suggest and demonstrate experimentally a novel effect manifested in the nearly complete simultaneous suppression of both forward and backward scattered fields. This effect is governed by the Fano interference between an electric dipole and off-resonant quadrupoles, providing necessary phases and amplitudes of the scattered fields to achieve the transverse scattering. We extend this concept to dielectric metasurfaces that demonstrate zero reflection with transverse scattering and strong field enhancement for resonant light filtering, nonlinear effects, and sensing.

© 2018 The Author(s). We demonstrate experimentally the generation of sum-frequency signal and heralded photons with non-classical correlations via spontaneous parametric down-conversion in AlGaAs nanodisks.

We demonstrate Si-based metasurfaces for third-harmonic generation of an arbitrary wavefront. The nonlinear metasurfaces produce phase gradients within a full 0–2π phase range. We achieve 92% diffraction efficiency of the nonlinear wavefront control.

We study light emission from square arrays of Mie-resonant silicon nanoantennas situated on a fluorescent glass substrate. When the spectral positions of the silicon nanoantennas' resonances overlap with the intrinsic emission from the glass, the emission is selectively enhanced for certain spectral and spatial frequencies detemined by the design of the nanoantenna array. We measure the emission spectra of the coupled system for a systematic variation of the nanoantenna geometry, showing that the spectral maximum of the emission coincides with the antenna resonance positions observed in linear-optical transmittance spectra. Furthermore, we study the directionality of the emission by back focal plane imaging and numerical calculations based on the Fourier modal method and the reciprocity principle. We observe that the nanoantenna array induces a reshaping of the resonantly enhanced emission in the air half-space into a narrow lobe directed out of the substrate plane. This reshaping is explained by coherent scattering of the emitted light in the nanoantenna array. Our results demonstrate that combining emission enhancement by magnetic dipolar Mie-type resonances of silicon nanoantennas with diffractive coupling in the periodic arrangement allows for the creation of flat light sources with tailored spectral and directional emission properties.

It is known that the nonlinear optical properties of photonic nanostructures can be modified substantially due to strong field confinement and optical resonances. In this contribution, we study third-harmonic generation from low-loss subwavelength silicon nanodisks arranged in the form of trimer oligomers with varying distance between the nanoparticles. Each of the nanodisks exhibits both electric and magnetic Mie-type resonances that are shown to affect significantly the nonlinear response. We observe the third-harmonic radiation intensity that is comparable to that of a bulk silicon slab and demonstrate a pronounced reshaping of the third-harmonic spectra due to interference of the nonlinearly generated waves augmented by an interplay between the electric and the magnetic dipolar resonances.

Here we suggest and realize an ultracompact plasmonic spectral-band demultiplexer for telecommunication wavelengths integrated onto an optical waveguide that couples two wavelength-encoded optical signals in the O- and the C-band in opposite directions of a silicon waveguide. In this way, we demonstrate a plasmonic key element for on-chip optical data processing that can also be used as a functional link between on- and off-chip optical signals.

Optical metasurfaces have developed as a breakthrough concept for advanced wave-front engineering enabled by subwavelength resonant nanostructures. However, reflection and/or absorption losses as well as low polarization-conversion efficiencies pose a fundamental obstacle for achieving high transmission efficiencies that are required for practical applications. Here, for the first time to our knowledge, highly efficient all-dielectric metasurfaces are demonstrated for NIR frequencies using arrays of silicon nanodisks as metaatoms. The main features of Huygens' sources are employed, namely, spectrally overlapping crossed electric and magnetic dipole resonances of equal strength, to demonstrate Huygens' surfaces with full transmission-phase coverage of 360° and near-unity transmission. Full-phase coverage combined with high efficiency in transmission are experimentally confirmed. Based on these key properties, all-dielectric Huygens' metasurfaces can become a new paradigm for flat optical devices, including beam-steering, beam-shaping, and focusing, as well as holography and dispersion control.

© 2017 IEEE. We suggest and realize experimentally dielectric metasurfaces with high transmission efficiency for quantum multi-photon tomography, allowing for full reconstruction of pure or mixed quantum polarization states across a broad bandwidth.

All-dielectric particles with small and large aspect ratio supporting Mie modes and hybrid Mie-Fabry-Perot modes are experimentally studied in microwave frequency range. The all-dielectric bianisotropic and multimode unidirectional metasurfaces based on such particles are designed and experimentally investigated. We demonstrate the all-dielectric bianisotropic metasurface composed of the particles with broken symmetry exhibits different phase of the reflection coefficient being excited from the opposite directions. The all-dielectric metasurfaces based on the particles with large aspect ratio responsible for the existence of multiple magnetic dipole resonances reveal the multimode unidirectionality when the Kerker conditions are satisfied.

Metasurfaces are ultra-thin patterned photonic structures that emerged recently as planar metadevices capable of reshaping and controlling incident light. They are composed of resonant subwavelength elements distributed across a flat surface. Due to the resonant scattering, each element can alter the phase, amplitude and polarization of the incoming light. Many designs and functionalities of metasurfaces suggested so far are based on plasmonic planar structures, however most of these metasurfaces demonstrate low efficiencies in transmission due to losses in their metallic components. In contrast, all-dielectric resonant nanophotonic structures avoid absorption losses, and can drastically enhance the overall efficiency, especially in the transmission regime. Here we utilize this platform to create flat optical elements such as vector beam q-plates, holograms and quantum polarization tomography devices. Holograms, in particular, showcase a potential of the metasurface platform as they rely on a complex wavefront engineering. Metasurface platform enables a new way to create highly efficient holograms with single-step patterning. Here, we design and realize experimentally greyscale meta-holograms with superior transmission properties. Another promising area for implementation of all-dielectric metasurfaces is quantum optics. We suggest and develop experimentally a new concept of quantum-polarization measurements with a single all-dielectric resonant metasurface. A metasurface enables full reconstruction of the state of entangled photon pairs based on the photon correlations with single-photon detectors. The subwavelength thin structure provides an ultimate miniaturization, scalability to a larger number of entangled photons, and gives the possibility to study the dynamics of quantum states in real-time.

Optical nanoantennas possess great potential for controlling the spatial distribution of light in the linear regime as well as for frequency conversion of the incoming light in the nonlinear regime. However, the usually used plasmonic nanostructures are highly restricted by Ohmic losses and heat resistance. Dielectric nanoparticles like silicon and germanium can overcome these constrains [1,2], however second harmonic signal cannot be generated in these materials due to their centrosymmetric nature. GaAs-based III-V semiconductors, with non-centrosymmetric crystallinity, can produce second harmonic generation (SHG) [3]. Unfortunately, generating and studying SHG by AlGaAs nanocrystals in both backward and forward directions is very challenging due to difficulties to fabricate III-V semiconductors on low-refractive index substrate, like glass. Here, for the first time to our knowledge, we designed and fabricated AlGaAs nanoantennas on a glass substrate. This novel design allows the excitation, control and detection of backwards and forwards SHG nonlinear signals. Different complex spatial distribution in the SHG signal, including radial and azimuthal polarization originated from the excitation of electric and magnetic multipoles were observed. We have demonstrated an unprecedented SHG conversion efficiency of 10-4; a breakthrough that can open new opportunities for enhancing the performance of light emission and sensing [4]. References [1] A. S. Shorokhov et al. Nano Letters 16, 4857 (2016). [2] G. Grinblat et al. Nano Letters 16, 4635 (2016). [3] S. Liu et al. Nano Letters 16, 7191 (2016). [4] R. Camacho et al. Nano Lett. 16, 7191 (2016).

We study guided modes in non-Hermitian optical waveguides with dielectric layers having either gain or loss. For the case of a three-layer waveguide, we describe stationary regimes for guided modes when gain and loss compensate each other in the entire structure rather than in each layer. We demonstrate that, by adding a lossless dielectric layer to a double-layer waveguide with the property of parity-time (PT) symmetry, we can control a ratio of gain and loss required to support propagating and nondecaying optical guided modes. This novel feature becomes possible due to the modification of the mode structure, and it can allow using materials with a lower gain to balance losses in various optical waveguiding structures. In addition, we find a non-PT-symmetric regime when all guided modes of the system have their losses perfectly compensated.

We show directional light routing and high–bit rate data transmission using a nanoantenna integrated on a low-loss waveguide., 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.