Magnetic Mie Resonances Research Articles

Far-Field Analysis on Reflecting Colors of Dielectric Nanosphere Metasurface

Photonic resonances in nanostructures have been exploited in reflective or transmission color filters, which can provide vivid colors. Metallic nanostructures have been widely studied to demonstrate a variety of color filters based on strong light interaction due to plasmonic resonances. However, because of the severe absorption loss of metal in visible light, dielectric nanoparticles having Mie resonances are a popular study focus in recent years to achieve vivid colors. In contrast to the behaviors of point-like electric dipole in metallic nanoparticle, the interplay of the electric and magnetic Mie resonances in dielectric nanoparticle enables a large degree of freedom in manipulating the directivity of light scattering, reflecting/transmitting color, and spontaneous emission rates. Here, we propose a color reflector based on an array of silicon nanoparticles that shows reflectance greater than 70% and vivid colors over the entire visible spectrum range, which covers sRGB color area. Viewing angle dependencies of the color and brightness are also investigated by calculating color-resolved far-field patterns, while exhibiting maintenance of the color and high reflectance over a broad viewing angle.

Tunable ferrite-dielectric metamolecule with Fano resonance

Actively controllable material properties are desirable for applications in materials science and microwave engineering. We design and fabricate a magnetically-coupled metamolecule with ferrite for X-band microwave frequencies that shows tunable responses to external magnetic fields. When compared with the metamolecule’s magnetic Mie resonance, superior field sensitivity is observed in the vicinity of the Fano resonance through analysis of the transmission spectra. The mechanism is investigated by emulating the field distributions, and the phenomenon is attributed to specially coupled magnetic dipoles. The simulation results are verified experimentally. This work substantiates the metamaterial’s enhanced electromagnetic properties for potential application to tunable microwave devices.

Large-Scale and Low-Cost Fabrication of Silicon Mie Resonators.

High index dielectric nanoparticles have been proposed for many different applications. However, widespread utilization in practice also requires large-scale production methods for crystalline silicon nanoparticles, with engineered optical properties in a low-cost manner. Here, we demonstrate a facile, low-cost, and large-scale fabrication method of crystalline silicon colloidal Mie resonators in water, using a blender. The obtained nanoparticles are polydisperse with an almost spherical shape and the diameters controlled in the range 100-200 nm by a centrifugation process. Then the size distribution of silicon nanoparticles enables broad extinction from UV to near-infrared, confirmed by Mie theory when considering the size distribution in the calculations. Thanks to photolithographic and drop-cast deposition techniques to locate the position on a substrate of the colloidal nanoparticles, we experimentally demonstrate that the individual silicon nanoresonators show strong electric and magnetic Mie resonances in the visible range.

Nanophotonic enhancement and improved electron extraction in perovskite solar cells using near-horizontally aligned TiO2 nanorods

While vertically oriented metal oxide nanowires have been intensely researched for use as electron transport layers (ETLs) in halide perovskite solar cells (HPSCs), horizontal nanowires (oriented roughly parallel to the substrate) have received much less attention despite their higher photonic strength due to overlapping electric and magnetic dipolar Mie resonance modes. Herein, we demonstrate the fabrication of an assembly of horizontally aligned TiO2 nanorods (HATNRs) on FTO substrates via a facile hydrothermal route. The HATNRs are employed as the ETL to achieve 15.03% power conversion efficiency (PCE) in HPSCs which is higher than the PCE of compact TiO2 based devices (10.12%) by a factor of nearly 1.5. A mixed halide, mixed cation organometal perovskite FA0.83MA0.17Pb(Br0.17I0.83)3 with optimized composition is used as the active layer. The excellent refractive index matching between the perovskite and TiO2, coupled with strong Mie scattering in the nanorod geometry results in broadband near-zero backscattering and high forward scattering, upon coating of HATNRs with perovskite. The maximum suppression of backscattering is found at ∼600 nm. The HATNRs ETL also improves the extraction of electrons from the perovskite layer and results in superior blocking of carrier recombination at the perovskite layer/FTO interface.

Bound states in the continuum and Fano resonances in the strong mode coupling regime

The study of resonant dielectric nanostructures with high refractive index is a new research direction in nanoscale optics and metamaterial-inspired nanophotonics. Because of the unique optically-induced electric and magnetic Mie resonances, high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications. Here we study strong coupling between modes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances when resonator's aspect ratio varies. We demonstrate that strong mode coupling results in resonances with high quality factors, which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich-Wintgen scenario of destructive interference. We explain the physics of these states in terms of multipole decomposition and show that their appearance is accompanied by drastic change of the far-field radiation pattern. We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra. Our theoretical findings are confirmed by microwave experiments for the scattering of a high-index cylindrical resonators with a tunable aspect ratio. The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high quality factor helps to extend substantially functionalities of all-dielectric nanophotonics that opens new horizons for active and passive nanoscale metadevices.

Enhanced Second-Harmonic Generation with Structured Light in AlGaAs Nanoparticles Governed by Magnetic Response

We employ structured light for the second-harmonic generation from subwavelength AlGaAs nanoparticles that support both electric and magnetic multipolar Mie resonances. The vectorial structure of the pump beam allows addressing selectively Mie-resonant modes and control the strength of the generated nonlinear fields. We observe experimentally the enhancement of the second-harmonic generation for the azimuthally polarized vector beams near magnetic dipole resonance, and match our observations with the numerical decomposion of the Mie-type multipoles for the fundamental and generated second-harmonic fields

Magnetic hot-spot generation at optical frequencies: from plasmonic metamolecules to all-dielectric nanoclusters

Abstract The weakness of magnetic effects at optical frequencies is directly related to the lack of symmetry between electric and magnetic charges. Natural materials cease to exhibit appreciable magnetic phenomena at rather low frequencies and become unemployable for practical applications in optics. For this reason, historically important efforts were spent in the development of artificial materials. The first evidence in this direction was provided by split-ring resonators in the microwave range. However, the efficient scaling of these devices towards the optical frequencies has been prevented by the strong ohmic losses suffered by circulating currents. With all of these considerations, artificial optical magnetism has become an active topic of research, and particular attention has been devoted to tailor plasmonic metamolecules generating magnetic hot spots. Several routes have been proposed in these directions, leading, for example, to plasmon hybridization in 3D complex structures or Fano-like magnetic resonances. Concurrently, with the aim of electromagnetic manipulation at the nanoscale and in order to overcome the critical issue of heat dissipation, alternative strategies have been introduced and investigated. All-dielectric nanoparticles made of high-index semiconducting materials have been proposed, as they can support both magnetic and electric Mie resonances. Aside from their important role in fundamental physics, magnetic resonances also provide a new degree of freedom for nanostructured systems, which can trigger unconventional nanophotonic processes, such as nonlinear effects or electromagnetic field localization for enhanced spectroscopy and optical trapping.

Exclusive Magnetic Excitation Enabled by Structured Light Illumination in a Nanoscale Mie Resonator.

Recent work has shown that optical magnetism, generally considered a challenging light-matter interaction, can be significant at the nanoscale. In particular, the dielectric nanostructures that support magnetic Mie resonances are low-loss and versatile optical magnetic elements that can effectively manipulate the magnetic field of light. However, the narrow magnetic resonance band of dielectric Mie resonators is often overshadowed by the electric response, which prohibits the use of such nanoresonators as efficient magnetic nanoantennas. Here, we design and fabricate a silicon (Si) truncated cone magnetic Mie resonator at visible frequencies and excite the magnetic mode exclusively by a tightly focused azimuthally polarized beam. We use photoinduced force microscopy to experimentally characterize the local electric near-field distribution in the immediate vicinity of the Si truncated cone at the nanoscale and then create an analytical model of such structure that exhibits a matching electric field distribution. We use this model to interpret the PiFM measurement that visualizes the electric near-field profile of the Si truncated cone with a superior signal-to-noise ratio and infer the magnetic response of the Si truncated cone at the beam singularity. Finally, we perform a multipole analysis to quantitatively present the dominance of the magnetic dipole moment contribution compared to other multipole contributions into the total scattered power of the proposed structure. This work demonstrates the excellent efficiency and simplicity of our method of using Si truncated cone structure under APB illumination compared to other approaches to achieve dominant magnetic excitations.

Dielectric Metasurface-Based High-Efficiency Mid-Infrared Optical Filter.

Dielectric nanoresonantors may generate both electric and magnetic Mie resonances with low optical loss, thereby offering highly efficient paths for obtaining integrated optical devices. In this paper, we propose and design an optical filter with a high working efficiency in the mid-infrared (mid-IR) range, based on an all-dielectric metasurface composed of silicon (Si) nanodisk arrays. We numerically demonstrate that, by increasing the diameter of the Si nanodisk, the range of the proposed reflective optical filter could effectively cover a wide range of operation wavelengths, from 3.8 μm to 4.7 μm, with the reflection efficiencies reaching to almost 100%. The electromagnetic eigen-mode decomposition of the silicon nanodisk shows that the proposed optical filter is based on the excitation of the electric dipole resonance. In addition, we demonstrate that the proposed filter has other important advantages of polarization-independence and incident-angle independence, ranging from 0° to 20° at the resonance dip, which can be used in a broad range of applications, such as sensing, imaging, and energy harvesting.

Pairing Toroidal and Magnetic Dipole Resonances in Elliptic Dielectric Rod Metasurfaces for Reconfigurable Wavefront Manipulation in Reflection.

A novel approach for reconfigurable wavefront manipulation with gradient metasurfaces based on permittivity‐modulated elliptic dielectric rods is proposed. It is shown that the required 2π phase span in the local electromagnetic response of the metasurface can be achieved by pairing the lowest magnetic dipole Mie resonance with a toroidal dipole Mie resonance, instead of using the lowest two Mie resonances corresponding to fundamental electric and magnetic dipole resonances as customarily exercised. This approach allows for the precise matching of both the resonance frequencies and quality factors. Moreover, the accurate matching is preserved if the rod permittivity is varied, allowing for constructing reconfigurable gradient metasurfaces by locally modulating the permittivity in each rod. Highly efficient tunable beam steering and beam focusing with ultrashort focal lengths are numerically demonstrated, highlighting the advantage of the low‐profile metasurfaces over bulky conventional lenses. Notably, despite using a matched pair of Mie resonances, the presence of an electric polarizability background allows to perform the wavefront shaping operations in reflection, rather than transmission. This has the advantage that any control circuitry necessary in an experimental realization can be accommodated behind the metasurface without affecting the electromagnetic response.

Enhancement of the intensity magneto-optical effect in magnetophotonic metasurfaces

Intensity magneto-optical response enhancement is shown numerically in magnetophotonic metasurfaces. Spectral overlapping of magnetic and electric dipole Mie resonances leads to increase of the effect and to modification of the resonance line shape.

Strong Coupling in Si Nanoparticle Core - 2D WS2 Shell Structure

Two-dimensional semiconducting transition metal dichalcogenides (TMDCs) are attractive materials for optoelectronics. In this paper, a strong coupling regime in Si nanoparticle covered by single layer WS2 system at the magnetic optical Mie resonance is observed. This regime is achieved owing to the symmetry of the magnetic dipole Mie mode, polarized along the TMDC surface, and low dissipative losses of the Si nanoparticle. A Rabi splitting energy exceeding 110 meV is obtained.

Giant Nonlinear Response at the Nanoscale Driven by Bound States in the Continuum

Being motivated by the recent prediction of high-Q modes in subwavelength dielectric resonators inspired by bound states in the continuum (BIC), we study the second-harmonic generation from isolated subwavelength AlGaAs nanoantennas. We reveal that nonlinear effects at the nanoscale can be enhanced dramatically provided the resonator parameters are tuned to the BIC regime. We predict a record-high conversion efficiency for nanoscale resonators that exceeds by 2 orders of magnitude the conversion efficiency observed at the magnetic dipole Mie resonance, thus opening the way for highly efficient nonlinear metasurfaces and metadevices.

Electromagnetic dipole resonant characteristics of all-dielectric one dimensional grating in terahertz region

Mie-type magnetic and electric resonances in an all-dielectric one-dimensional grating are theoretically demonstrated in terahertz region. It is found that strong polarization-sensitivity and frequency-selection behaviors of resonances can be excited in all dielectric subwavelength grating structure. This all dielectric grating with less absorption loss can be carefully designed as broadband reflectors and polarization beam splitters. The coupling effects of the array silicon pillar and the electromagnetic field distribution were numerically calculated by use of finite element method. The effective constitutive parameters of subwavelength grating, including in the effective refractive index, effective permittivity, effective permeability, and effective impedance, can be extracted by using the standard retrieval method of inversion algorithm. Magnetic and electric Mie resonances can be revealed by enhanced effective parameters at resonant frequencies.

All-dielectric two-dimensional metasurfaces based on electric and magnetic dipolar Mie resonances

We present a design paradigm of two-dimensional metasurfaces composed of homogenous dielectric nanowires only, which can reliably work at the near-infrared and visible-light frequencies. The design principle is based on the coherent interference between electric and magnetic dipolar modes of a single nanowire, in conjunction with the near-field coupling interactions between neighbouring nanowires in a periodic array. No complicated refractive index profiles or lossy metallic components are needed. By assembling different nanowires into a super cell structure and choosing an appropriate lattice constant, we present an actual physical implementation of the Huygens surface. An effective manipulation on the transmitted wave direction is achieved with a close-to-unity transmittance. A metasurface-based planar lens with short focal distance is unambiguously demonstrated, and potential applications in the related fields are expected.

Tunable Resonance Coupling in Single Si Nanoparticle-Monolayer WS2 Structures.

Two-dimensional semiconducting transition metal dichalcogenides (TMDCs) are extremely attractive materials for optoelectronic applications in the visible and near-infrared range. Coupling these materials to optical nanocavities enables advanced quantum optics and nanophotonic devices. Here, we address the issue of resonance coupling in hybrid exciton-polariton structures based on single Si nanoparticles (NPs) coupled to monolayer (1L)-WS2. We predict a strong coupling regime with a Rabi splitting energy exceeding 110 meV for a Si NP covered by 1L-WS2 at the magnetic optical Mie resonance because of the symmetry of the mode. Further, we achieve a large enhancement in the Rabi splitting energy up to 208 meV by changing the surrounding dielectric material from air to water. The prediction is based on the experimental estimation of TMDC dipole moment variation obtained from the measured photoluminescence spectra of 1L-WS2 in different solvents. An ability of such a system to tune the resonance coupling is realized experimentally for optically resonant spherical Si NPs placed on 1L-WS2. The Rabi splitting energy obtained for this scenario increases from 49.6 to 86.6 meV after replacing air by water. Our findings pave the way to develop high-efficiency optoelectronic, nanophotonic, and quantum optical devices.

Enhancement of Raman scattering in dielectric nanostructures with electric and magnetic Mie resonances

Resonantly enhanced Raman scattering in dielectric nanostructures has been recently proven to be an effcient tool for developing nanothermometry and experimental determination of their mode- composition. In this paper, we develop a rigorous analytical theory based on the Green's function approach to calculate the Raman emission from crystalline high-index dielectric nanoparticles. As an example, we consider silicon nanoparticles which have a strong Raman response due to active optical phonon modes. We relate enhancement of Raman signal emission to Purcell effect due to the excitation of Mie modes inside the nanoparticles. We also employ the numerical approach to the calculation of inelastic Raman emission in more sophisticated geometries, which do not allow a straightforward analytical form of the Green's function description. The Raman response from a silicon nanodisk has been analyzed within the proposed method, and the contribution of the various Mie modes has been revealed.

All-dielectric meta-optics and non-linear nanophotonics

Abstract 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.

Dielectric Materials Containing Active Dielectric-Metal Composite Nanoparticles as Double Negative Materials in the Visible

In the visible spectral range, Mie resonance-based double negativity has still not been observed in all-dielectric metamaterials due to the lack of dielectrics with sufficiently high refractive indices. In this work, the dielectric materials containing nanospheres of gain-metal nanocomposites are proposed as double negative materials operating in the visible. They are embedded with two types of composite nanospheres: one contributes to the negative permeability via magnetic Mie resonance facilitated by gain-assisted high indices of composite nanospheres and the other one to the negative permittivity via plasmonic dipolar resonance in the same spectral range. The figure-of-merit of these materials reaches up to infinity or even can be negative, implying the gain, depending on the structural and material parameters. The proposed materials can find broad applications as loss-free negative index materials in the visible and near-infrared.

Selective Third-Harmonic Generation by Structured Light in Mie-Resonant Nanoparticles

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.