Observation of edge bound states in the continuum at truncated silicon pillar photonic crystal.

Bound states in the continuum are optical modes with extremely high-quality factors and narrow resonances, which exist in the dispersion spectrum of the radiative region above the light line. A unique bound state in the continuum is supported at the edge of truncated photonic crystals, which is a type of a Fabry-Pérot type bound state in the continuum, but has never been observed in experiments. Here, we demonstrate the bound states in the continuum supported at the edge array of silicon (Si) pillars whose diameter is bigger than that of the rest of a Si-pillar two-dimensional photonic crystal.

Pedestal High-Contrast Gratings for Biosensing.

High-contrast gratings (HCG) are an excellent candidate for label-free detection of various kinds of biomarkers because they exhibit sharp and sensitive optical resonances. In this work, we experimentally show the performance of pedestal HCG (PHCG), which is significantly enhanced in comparison with that of conventional HCG. PCHGs were found to provide a 11.

Momentum considerations inside near-zero index materials.

Near-zero index (NZI) materials, i.e., materials having a phase refractive index close to zero, are known to enhance or inhibit light-matter interactions.

Method of lines for the analysis of tunable plasmonic devices composed of graphene-dielectric stack arrays.

Due to the increasing interest in emerging applications of graphene or other 2D material-based devices in photonics, a powerful, fast and accurate tool for the analysis of such structures is really in need. In this paper, the semi-analytical method of lines (MoL) is generalized for the diffraction analysis of tunable graphene-based plasmonic devices possessing three dimensional periodicity. We employ Floquet's theorem to handle analytically propagation of waves in the periodicity of the graphene-dielectric arrays in the direction of the layers stacking.

Polarization-Dependent All-Dielectric Metasurface for Single-Shot Quantitative Phase Imaging.

Phase retrieval is a noninterferometric quantitative phase imaging technique that has become an essential tool in optical metrology and label-free microscopy. Phase retrieval techniques require multiple intensity measurements traditionally recorded by camera or sample translation, which limits their applicability mostly to static objects. In this work, we propose the use of a single polarization-dependent all-dielectric metasurface to facilitate the simultaneous recording of two images, which are utilized in phase calculation based on the transport-of-intensity equation.

Hyperbolic surface waves on anisotropic materials without hyperbolic dispersion.

We theoretically analyze directional surface electromagnetic waves supported at an interface between an isotropic medium and anisotropic metal with effective uniaxial negative permittivity. We identify two types of surface wave solutions, resulting in unique hyperbolic dispersion in the wavevector space. Such anisotropic metal can be realized by alternating dielectric and metallic layers with deep subwavelength thicknesses or metallic nanowires in dielectric host.

Plasmonic nanojet: an experimental demonstration: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 3244 (2020)OPLEDP0146-959210.

Hydrogen gas sensing using aluminum doped ZnO metasurfaces.

Hydrogen (H) sensing is crucial in a wide variety of areas, such as industrial, environmental, energy and biomedical applications. However, engineering a practical, reliable, fast, sensitive and cost-effective hydrogen sensor is a persistent challenge. Here we demonstrate hydrogen sensing using aluminum-doped zinc oxide (AZO) metasurfaces based on optical read-out.

Plasmonic nanojet: an experimental demonstration.

We propose and study a microstructure based on a dielectric cuboid placed on a thin metal film that can act as an efficient plasmonic lens allowing the focusing of surface plasmons at the subwavelength scale. Using numerical simulations of surface plasmon polariton (SPP) field intensity distributions, we observe high-intensity subwavelength spots and formation of the plasmonic nanojet (PJ) at the telecommunication wavelength of 1530 nm. The fabricated microstructure was characterized using amplitude and phase-resolved scattering-type scanning near-field optical microscopy.

Investigation of effective media applicability for ultrathin multilayer structures.

Multilayer hyperbolic metamaterials (HMMs) are highly anisotropic media consisting of alternating metal and dielectric layers with their electromagnetic properties defined by the effective medium approximation (EMA). EMA is generally applied for a large number of subwavelength unit cells or periods of a multilayer HMM. However, in practice, the number of periods is limited.

Epsilon-Near-Zero Grids for On-chip Quantum Networks.

Realization of an on-chip quantum network is a major goal in the field of integrated quantum photonics. A typical network scalable on-chip demands optical integration of single photon sources, optical circuitry and detectors for routing and processing of quantum information. Current solutions either notoriously experience considerable decoherence or suffer from extended footprint dimensions limiting their on-chip scaling.

Photonic spin Hall effect in hyperbolic metamaterials at visible wavelengths.

The photonic spin Hall effect in transmission is a transverse beam shift of the out-coming beam depending on polarization of the incoming beam. The effect can be significantly enhanced by materials with high anisotropy. We report, to the best of our knowledge, the first experimental demonstration of the photonic spin Hall effect in a multilayer hyperbolic metamaterial at visible wavelengths (wavelengths of 520 and 633 nm).

Effective surface conductivity of optical hyperbolic metasurfaces: from far-field characterization to surface wave analysis.

Metasurfaces offer great potential to control near- and far-fields through engineering optical properties of elementary cells or meta-atoms. Such perspective opens a route to efficient manipulation of the optical signals both at nanoscale and in photonics applications. In this paper we show that a local surface conductivity tensor well describes optical properties of a resonant plasmonic hyperbolic metasurface both in the far-field and in the near-field regimes, where spatial dispersion usually plays a crucial role.

Benchmarking five numerical simulation techniques for computing resonance wavelengths and quality factors in photonic crystal membrane line defect cavities.

We present numerical studies of two photonic crystal membrane microcavities, a short line-defect cavity with a relatively low quality (Q) factor and a longer cavity with a high Q. We use five state-of-the-art numerical simulation techniques to compute the cavity Q factor and the resonance wavelength λ for the fundamental cavity mode in both structures. For each method, the relevant computational parameters are systematically varied to estimate the computational uncertainty.

Direct Amplitude-Phase Near-Field Observation of Higher-Order Anapole States.

Anapole states associated with the resonant suppression of electric-dipole scattering exhibit minimized extinction and maximized storage of electromagnetic energy inside a particle. Using numerical simulations, optical extinction spectroscopy, and amplitude-phase near-field mapping of silicon dielectric disks, we demonstrate high-order anapole states in the near-infrared wavelength range (900-1700 nm). We develop the procedure for unambiguously identifying anapole states by monitoring the normal component of the electric near-field and experimentally detect the first two anapole states as verified by far-field extinction spectroscopy and confirmed with the numerical simulations.

Optical reconfiguration and polarization control in semi-continuous gold films close to the percolation threshold.

Controlling and confining light by exciting plasmons in resonant metallic nanostructures is an essential aspect of many new emerging optical technologies. Here we explore the possibility of controllably reconfiguring the intrinsic optical properties of semi-continuous gold films, by inducing permanent morphological changes with a femtosecond (fs)-pulsed laser above a critical power. Optical transmission spectroscopy measurements show a correlation between the spectra of the morphologically modified films and the wavelength, polarization, and the intensity of the laser used for alteration.

Enhancing Optical Forces in InP-Based Waveguides.

Cantilever sensors are among the most important microelectromechanical systems (MEMS), which are usually actuated by electrostatic forces or piezoelectric elements. Although well-developed microfabrication technology has made silicon the prevailing material for MEMS, unique properties of other materials are overlooked in this context. Here we investigate optically induced forces exerted upon a semi-insulating InP waveguide suspended above a highly doped InP:Si substrate, in three different regimes: the epsilon-near-zero (ENZ), with excitation of surface plasmon polaritons (SPPs) and phonons excitation.

Matter-Wave Tractor Beams.

Optical and acoustic tractor beams are currently the focus of intense research due to their counterintuitive property of exerting a pulling force on small scattering objects. In this Letter we propose a matter-wave tractor beam and utilize the de Broglie waves of nonrelativistic matter particles in analogy to "classical" tractor beams. We reveal the presence of the quantum-mechanical pulling force for the variety of quantum mechanical potentials observing the resonant enhancement of the pulling effect under the conditions of the suppressed scattering known as the Ramsauer-Townsend effect.

Pulling cylindrical particles using a soft-nonparaxial tractor beam.

In order to pull objects towards the light source a single tractor beam inevitably needs to be strongly nonparaxial. This stringent requirement makes such a tractor beam somewhat hypothetical. Here we reveal that the cylindrical shape of dielectric particles can effectively mitigate the nonparaxiality requirements, reducing the incidence angle of the partial plane waves of the light beam down to 45° and even to 30° for respectively dipole and dipole-quadrupole objects.

Near-field characterization of bound plasmonic modes in metal strip waveguides.

Propagation of bound plasmon-polariton modes along 30-nm-thin gold strips on a silica substrate at the free-space wavelength of 1500 nm is investigated both theoretically and experimentally when decreasing the strip width from 1500 nm down to the aspect-ratio limited width of 30 nm, which ensures deep subwavelength mode confinement. The main mode characteristics (effective mode index, propagation length, and mode profile) are determined from the experimental amplitude- and phase-resolved near-field images for various strip widths (from 30 to 1500 nm), and compared to numerical simulations. The mode supported by the narrowest strip is found to be laterally confined within ~ 100 nm at the air side, indicating that the realistic limit for radiation nanofocusing in air using tapered metal strips is ~ λ/15.

Third-order susceptibility of gold for ultrathin layers.

This Letter presents an experimental study of nonlinear plasmonic effects in gold-stripe waveguides. The optical characterization is performed by a picosecond laser and reveals two nonlinear effects related to propagation of long-range surface plasmon polaritons: nonlinear power transmission of plasmonic modes and spectral broadening of plasmonic modes. The experimental values of the third-order susceptibility of the gold layers are extracted.

Boosting Local Field Enhancement by on-Chip Nanofocusing and Impedance-Matched Plasmonic Antennas.

Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nanosized volumes by reducing the cross sections of propagating modes far beyond the diffraction limit, that is, by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging, and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths.

Experimental Demonstration of Effective Medium Approximation Breakdown in Deeply Subwavelength All-Dielectric Multilayers.

We report the first experimental demonstration of anomalous breakdown of the effective medium approximation in all-dielectric deeply subwavelength thickness (d∼λ/160-λ/30) multilayers, as recently predicted theoretically [H. H. Sheinfux et al.

Dark-field hyperlens: Super-resolution imaging of weakly scattering objects.

We propose a device for subwavelength optical imaging based on a metal-dielectric multilayer hyperlens designed in such a way that only large-wavevector (evanescent) waves are transmitted while all propagating (small-wavevector) waves from the object area are blocked by the hyper-lens. We numerically demonstrate that as the result of such filtering, the image plane only contains scattered light from subwavelength features of the objects and is completely free from background illumination. Similar in spirit to conventional dark-field microscopy, the proposed dark-field hyperlens is shown to enhance the subwavelength image contrast by more than two orders of magnitude.