A. A. Bogdanov

Hybrid waves localized at hyperbolic metasurfaces

ITMO University, St. Petersburg 197101, Russia(Dated: March 2, 2015)We reveal the existence of a new type of surface electromagnetic waves supported by hyperbolicmetasurfaces, described by a conductivity tensor with an inde nite signature. We demonstrate thatthe spectrum of the hyperbolic metasurface waves consists of two branches corresponding to hybridTE-TM waves with the polarization that varies from linear to elliptic or circular depending on thewave frequency and propagation direction. We analyze the e ect of losses of the surface waves andderive the corresponding analytical asymptotic expressions.I. INTRODUCTION

Surface plasmon polariton assisted optical pulling force

We demonstrate both analytically and numerically the existence of optical pulling forces acting on particles located near plasmonic interfaces. Two main factors contribute to the appearance of this negative recoil force. The interference between the incident and reflected waves induces a rotating dipole with an asymmetric scattering pattern, while the directional excitation of surface plasmon polaritons (SPPs) enhances the linear momentum of scattered light. The strongly asymmetric SPP excitation is determined by spin–orbit coupling of the rotating dipole and surface plasmon polariton. As a result of the total momentum conservation, the force acting on the particle points in a direction opposite to the incident wave propagation. We derive analytical expressions for the force acting on dipolar particles placed in the proximity of plasmonic surfaces. Analytical expressions for this pulling force are derived within the dipole approximation and are in excellent agreement with results of electromagnetic numerical calculations. The forces acting on larger particles are analyzed numerically, beyond the dipole approximation.

Optical forces in nanorod metamaterial

Optomechanical manipulation of micro and nano-scale objects with laser beams finds use in a large span of multidisciplinary applications. Auxiliary nanostructuring could substantially improve performances of classical optical tweezers by means of spatial localization of objects and intensity required for trapping. Here we investigate a three-dimensional nanorod metamaterial platform, serving as an auxiliary tool for the optical manipulation, able to support and control near-field interactions and generate both steep and flat optical potential profiles. It was shown that the ‘topological transition’ from the elliptic to hyperbolic dispersion regime of the metamaterial, usually having a significant impact on various light-matter interaction processes, does not strongly affect the distribution of optical forces in the metamaterial. This effect is explained by the predominant near-fields contributions of the nanostructure to optomechanical interactions. Semi-analytical model, approximating the finite size nanoparticle by a point dipole and neglecting the mutual re-scattering between the particle and nanorod array, was found to be in a good agreement with full-wave numerical simulation. In-plane (perpendicular to the rods) trapping regime, saddle equilibrium points and optical puling forces (directed along the rods towards the light source), acting on a particle situated inside or at the nearby the metamaterial, were found.

Topological transition in coated wire medium

Employing nonlocal homogenization approach, we investigate the properties of a metamaterial consisting of parallel metallic wires with dielectric coating. We demonstrate that manipulation of dielectric contrast between wire dielectric shell and host material at fixed frequency results in dynamic switching of metamaterial dispersion regime from elliptic to the hyperbolic one, i.e. the topological transition takes place. It is proved that such transition can be induced by the variation of the metamaterial temperature. Our findings thus pave a way to the implementation of a tunable ‘elliptic-hyperbolic’ metamaterial.

Dark-field imaging as a noninvasive method for characterization of whispering gallery modes in microdisk cavities

Whispering gallery mode microdisk cavities fabricated by direct laser writing are studied using dark-field imaging and spectroscopy in the visible spectral range. Dark-field imaging allows us to directly visualize the spatial intensity distribution of whispering gallery modes. We extract their azimuthal and radial mode indices from dark-field images, and find the axial mode number from the dispersion relation. The scattering spectrum obtained in the confocal arrangement provides information on the density of optical states in the resonator. The proposed technique is a simple noninvasive way to characterize the optical properties of microdisk cavities.

Direct imaging of isofrequency contours in all-dielectric optical metasurface

We study the properties of optical surface waves in all–dielectric anisotropic metasurface represented by an array of silicon slabs. We employ back focal plane microscope with solid immersion lens for direct imaging of isofrequency contours of surface waves of the metasurface to reveal both elliptic and hyperbolic–like regimes and reconstruct the dispersion curves for transverse and longitudinal directions.

Visualization of Isofrequency Contours of Strongly Localized Waveguide Modes in Planar Dielectric Structures

An experimental method has been proposed to study the dispersion properties of optical surface and waveguide modes in planar structures. An experimental setup involves a microscope with a high numerical aperture objective and a hemispherical solid immersion lens made of zinc selenide in contact with the sample surface. The reflection from the sample is detected in the back focal plane of the system. Such a configuration makes it possible to study strongly localized states with an effective refractive index up to 2.25 in the visible and near infrared spectral ranges. For a thin silicon layer deposited on a glass substrate, the possibility of visualization of isofrequency contrours with polarization resolution and the reconstruction of dispersion of waveguide modes depending on the direction of their propagation has been demonstrated.

Optical binding of two nanoparticles near interface

In this work we investigate lateral optical binding of two dielectric nanoparticles placed above a metallic substrate. We consider both longitudinal and lateral components of the optical binding force. Dyadic Greens function was used to describe analytically field distribution in the near and far field zone. Equilibrium positions for dielectric particles were calculated and contribution of metallic substrate was analyzed.

Demultiplexing surface waves with silicon nanoantennas

We demonstrate directional launching of surface plasmon polaritons on thin gold film with a single silicon nanosphere. The directivity pattern of the excited surface waves exhibits rapid switching from forward to backward excitation within extremely narrow spectral band (i 50u2005nm), which is driven by the mutual interference of magnetic and electric dipole moments supported by the dielectric nanoantenna.

Effect of substrate on optical bound states in the continuum in 1D photonic structures

Optical bound states in the continuum (BIC) are localized states with energy lying above the light line and having infinite lifetime. Any losses taking place in real systems result in transformation of the bound states into resonant states with finite lifetime. In this work, we analyze properties of BIC in CMOS-compatible one-dimensional photonic structure based on silicon-on-insulator wafer at telecommunication wavelengths, where the absorption of silicon is negligible. We reveal that a high-index substrate could destroy both off-Γ BIC and in-plane symmetry protected at-Γ BIC turning them into resonant states due to leakage into the diffraction channels opening in the substrate.