All‐dielectric nanophotonics attracts ever increasing attention nowadays due to the possibility of controlling and configuring light scattering on high‐index semiconductor nanoparticles. It opens a ...room of opportunities for designing novel types of nanoscale elements and devices, and paves the way for advanced technologies of light energy manipulation. One of the exciting and promising prospects is associated with utilizing the so‐called toroidal moment, being the result of poloidal currents excitation, and anapole states, corresponding to the interference of dipole and toroidal electric moments. Here, higher‐order toroidal moments of both types (up to the electric octupole toroidal moment) are presented and investigated in detail via the direct Cartesian multipole decomposition allowing new near‐ and far‐field configurations to be obtained. Poloidal currents can be associated with vortex‐like distributions of the displacement currents inside nanoparticles, revealing the physical meaning of the high‐order toroidal moments and the convenience of the Cartesian multipoles as an auxiliary tool for analysis. High‐order nonradiating anapole states accompanied by the excitation of intense near‐fields are demonstrated. It is believed that the results are of high importance for both the fundamental understanding of light scattering by high‐index particles and a variety of nanophotonics applications and light governing on nanoscale.
Recently, toroidal moments and anapole states have opened up new horizons for dielectric nanophotonics. The toroidal moments of both types up to the electric octupole toroidal moment are investigated in detail via the irreducible Cartesian multipole decomposition. High‐order nonradiating anapole states manifested in vanishing contribution to the far‐field accompanied by the excitation of intense near‐fields are demonstrated.
Nonradiating current configurations attract attention of physicists for many years as possible models of stable atoms. One intriguing example of such a nonradiating source is known as 'anapole'. An ...anapole mode can be viewed as a composition of electric and toroidal dipole moments, resulting in destructive interference of the radiation fields due to similarity of their far-field scattering patterns. Here we demonstrate experimentally that dielectric nanoparticles can exhibit a radiationless anapole mode in visible. We achieve the spectral overlap of the toroidal and electric dipole modes through a geometry tuning, and observe a highly pronounced dip in the far-field scattering accompanied by the specific near-field distribution associated with the anapole mode. The anapole physics provides a unique playground for the study of electromagnetic properties of nontrivial excitations of complex fields, reciprocity violation and Aharonov-Bohm like phenomena at optical frequencies.
Rapid progress in nanophotonics is driven by the ability of optically resonant nanostructures to enhance near-field effects controlling far-field scattering through intermodal interference. A ...majority of such effects are usually associated with plasmonic nanostructures. Recently, a new branch of nanophotonics has emerged that seeks to manipulate the strong, optically induced electric and magnetic Mie resonances in dielectric nanoparticles with high refractive index. In the design of optical nanoantennas and metasurfaces, dielectric nanoparticles offer the opportunity for reducing dissipative losses and achieving large resonant enhancement of both electric and magnetic fields. We review this rapidly developing field and demonstrate that the magnetic response of dielectric nanostructures can lead to novel physical effects and applications.
Directional light scattering by spherical silicon nanoparticles in the visible spectral range is experimentally demonstrated for the first time. These unique optical properties arise because of ...simultaneous excitation and mutual interference of magnetic and electric dipole resonances inside a single nanosphere. Such behaviour is similar to Kerker's-type scattering by hypothetic magneto-dielectric particles predicted theoretically three decades ago. Here we show that directivity of the far-field radiation pattern of single silicon spheres can be strongly dependent on the light wavelength and the nanoparticle size. For nanoparticles with sizes ranging from 100 to 200 nm, forward-to-backward scattering ratio above six can be experimentally obtained, making them similar to 'Huygens' sources. Unique optical properties of silicon nanoparticles make them promising for design of novel low-loss visible- and telecom-range metamaterials and nanoantenna devices.
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.
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.
Via controlling the temperature and employing the right combination of the electric and magnetic resonant responses of the metasurfaces, drastic and reciprocal interchanges in directional scattering are demonstrated experimentally and theoretically. At 1425 nm forward to backward ratio variation from 1 to >50 can be obtained. The results provide an important step toward tunable nanophotonic components and all‐optical circuitry on a chip.
The scattering of nanoparticles plays a profound role in the recently flourishing fields of plasmonics and metamaterials. However, current investigations into nanoparticle scattering are based on the ...electric and magnetic resonances only, where their toroidal counterparts are usually not considered. The inclusion of toroidal terms can render new explanations for some fundamental scattering properties and thus may stimulate further breakthroughs in both scattering‐related basic researches and applications. Here we revisit the most fundamental problem of Mie scattering by individual spherical nanoparticles and show that compared to conventional interpretations in terms of electric and magnetic responses, the roles played by their toroidal counterparts are indispensable. Based on the demonstration of efficient toroidal dipole excitation in homogeneous dielectric particles, we reveal that the extensively studied scattering transparencies of core–shell nanoparticles can actually be classified into two categories: (i) the trivial transparency with no effective multipole excitations and (ii) the non‐trivial transparency induced by the destructive interferences of excited electric and toroidal multipoles. The incorporation of toroidal multipoles offers new insights into the study of nanoparticle scattering in both near and far fields, which may shed new light on many applications, such as biosensing, imaging, nanoantennas, photovoltaic devices, and so on.
We show decisively the crucial roles played by toroidal multipoles for individual scattering nanoparticles and demonstrate two categories of scattering transparencies: the trivial transparency with no effective multipole excitations and the non‐trivial one induced by the destructive interferences of electric and toroidal multipoles excited.
Functional and nonlinear optical metasurfaces Minovich, Alexander E.; Miroshnichenko, Andrey E.; Bykov, Anton Y. ...
Laser & photonics reviews,
March 2015, Letnik:
9, Številka:
2
Journal Article
Recenzirano
Optical metasurfaces are thin‐layer subwavelength‐patterned structures that interact strongly with light. Metasurfaces have become the subject of several rapidly growing areas of research, being a ...logical extension of the field of metamaterials towards their practical applications. Metasurfaces demonstrate many useful properties of metadevices with engineered resonant electric and magnetic optical responses combined with low losses of thin‐layer structures. Here we introduce the basic concepts of this rapidly growing research field that stem from earlier studies of frequency‐selective surfaces in radiophysics, being enriched by the recent development of metamaterials and subwavelength nanophotonics. We review the most interesting properties of photonic metasurfaces, demonstrating their useful functionalities such as frequency selectivity, wavefront shaping, polarization control, etc. We discuss the ways to achieve tunability of metasurfaces and also demonstrate that nonlinear effects can be enhanced with the help of metasurface engineering.
Metasurfaces have become the subject of several rapidly growing areas of research. They show many useful properties of metadevices with engineered resonant electric and magnetic optical responses combined with low losses of thin‐layer structures. The basic concepts of this rapidly growing research field are introduced and enriched by the recent development of metamaterials and subwavelength nanophotonics. The most interesting properties of photonic metasurfaces are reviewed and their useful functionalities are demonstrated.
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