We experimentally implement a novel strategy for dielectric nanophotonics: resonant subwavelength localized confinement of light in air. We demonstrate that individual voids created in high-index dielectric host materials support localized resonant modes that do not suffer from the loss and dispersion of the host medium and are weakly dependent on the void geometry. We show that Mie void modes in dispersive dielectric materials, e.g. silicon, possess a large quality factor, comparable or larger than that for silicon resonant nanoparticles in the visible and UV. We experimentally realize resonant Mie voids by focused ion beam milling into bulk silicon wafers. We experimentally demonstrate resonant light confinement with individual Mie voids from visible down to the UV spectral range at 265 nm. We also experimentally demonstrate a high locality of optical properties of individual voids, which allows implementing them as non-interfering pixels while arranged densely in lattices. Using this property, we further experimentally utilize the bright, intense, and naturalistic colours for nanoscale colour printing.
The excitation of quasi-bound states in the continuum (quasi-BIC) in symmetry broken all dielectric metasurfaces have been vastly explored in the last years. The high Q-factor of quasi-BIC resonances make them attractive in sensing, electromagnetic induced transparency or non-linear optics. The resonance wavelength is fixed by the geometry of the metasurface, which is a constraint for applications, which require the tuning of the resonances to different spectral regions. In this work, we demonstrate the use of temperature as a means to fine-tune the quasi-BIC resonance in hydrogenated amorphous silicon (a-Si:H) metasurfaces.
Nonlinear dielectric metasurfaces provide a promising platform to control and manipulate the optical frequency conversion at the nanoscale, suggesting new applications in imaging, lasing, and sensing. Here, we engage symmetry-broken silicon metasurfaces to enhance the second- and third-harmonic generation. We design and fabricate amorphous silicon metasurfaces supporting optical bound states in the continuum and guided-mode resonances, which greatly boost light-matter interaction resulting in several-order enhancements in both second-and third-harmonic generation.
Manipulating light on the nanoscale has become a central challenge in metadevices, resonant surfaces, nanoscale optical sensors and many more, and it is largely based on resonant light confinement in dispersive and lossy metals and dielectrics. Here, we uncover a novel paradigm in dielectric nanophotonics: Resonant subwavelength confinement of light in air. Voids created in dielectric host materials support localized resonant modes confined in air and do not suffer from the loss and dispersion of the dielectric host medium. We realize these resonant Mie voids by focused ion beam milling into bulk silicon wafers and experimentally demonstrate resonant light confinement down to the UV spectral range at 265 nm (4.68 eV), highest resolution nanoscale colour printing, as well as nanophotonic refractive index sensing on the single void level with unprecedented small sensing volumes in the range of 100 attoliter and sensitivities on the order of 400 nm per refractive index unit.
We review the physics and some applications of photonic structures designed for the realization of strong nonlinear chiroptical response. We pay much attention to the recent strategy of utilizing different types of optical resonances in metallic and dielectric subwavelength structures and metasurfaces, including surface plasmon resonances, Mie resonances, lattice-guided modes, and bound states in the continuum. We summarize earlier results and discuss more recent developments for achieving large circular dichroism combined with the high efficiency of nonlinear harmonic generation.
Metal nanostructures are very lossy when they interact with light, which hinders their use in optics and photonics requiring sharp resonances. Here, we will show that employing the physics of bound states in the continuum (BICs) in all-plasmonic metasurfaces can significantly reduce/eliminate the dissipation/radiation loss in metal nanostructures, resulting in high quality-factor (Q-factor) resonances. Also, we will show that butterfly-wings-inspired plasmonic structures can support high-Q surface lattice resonances under focused light excitation. These results allow for various applications requiring compact footprint with strong-light matter interaction in nanoscales, such as lasing and quantum detection.
Topological photonics attracts attention as a fundamental framework for robust manipulation of light. Combined with an optical gain, active topological cavities hold special promise for a design of high-performance nanolasers. In this talk, we present two types of novel topological resonant modes, multipolar lasing modes from topological corner states and ultralow-threshold lasing modes using super-bound states in the continuum, for the demonstration of low-threshold lasing.
We review the physics of photonic bound states in the continuum (BICs) and their applications to metadevices, including enhancement of nonlinear response, light-matter interaction, and development of active nanophotonic devices. In particular, we discuss how BIC-empowered dielectric metastructures can be used to generate efficiently high-order optical harmonics from bulk and to boost the intrinsic nonlinearity of transition metal dichalcogenide (TMD) flakes. We explore TMD resonators composed of structured dielectric arrays and individual nanoparticles for strong light-matter coupling phenomena. We discuss the extension of metasurface functionalities for biosensing applications in biomarker detection and quantum information processing with entangled photons. Finally, we demonstrate how tunability of BICs in the momentum space can be used to realize a novel type of efficient lasing based on a finite-size cavity with a small footprint.
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.
Recent developments in the physics of Mie-resonant high-index dielectric nanostructures suggested a promising pathway to improve efficiencies of the nonlinear light conversion beyond the limits imposed by plasmonics. Here, we employ the concept of bound states in the continuum to experimentally demonstrate a sharp enhancement of the second-harmonic generation efficiency at localized states formed via destructive interference of two leaky modes. For an AlGaAs subwavelength disk with optimized parameters, pumped with a structured light and placed on an engineered multilayered substrate, we observe the record-high conversion efficiency compared to the previous demonstrations with isolated subwavelength resonators.
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 review the physics of bound states in the continuum and their applications in meta-optics and metasurfaces. First, we discuss 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. Our theoretical findings are confirmed by microwave and optical experiments for the scattering of high-index subwavelength 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. Next, we discuss how bound states in the continuum can appear in metasurfaces. We reveal that metasurfaces created by seemingly different lattices of (dielectric or metallic) meta-atoms with broken in-plane symmetry can support sharp high-Q resonances that originate from the physics of bound states in the continuum. We demonstrate a direct link between the bound states in the continuum and the Fano resonances, and discuss a general theory of such metasurfaces, suggesting the way for smart engineering of resonances for many applications in nanophotonics and meta-optics.
The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the 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. We study a strong coupling between modes of a single subwavelength high-index dielectric resonator and analyze the mode transformation and Fano resonances when the 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 a drastic change in 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 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 factors helps to extend substantially functionalities of all-dielectric nanophotonics, which opens horizons for active and passive nanoscale metadevices.
Recently, a novel class of high-Q optical resonators based on all-dielectric subwavelength nanoparticles with high refractive index has been proposed [M. V. Rybin, et al, arXiv:1706.02099, 2017]. Here we study a complex spectrum of such nanoscale resonators by means of the resonant-state expansion, treating the problem as a nonHermitian eigenproblem. We show that the high-Q features can be described within the mechanism of external coupling of open channels via the continuum. For ceramic resonators with permittivity ε = 40, we demonstrate that the quality factor of a trapped mode with a low azimuthal index could reach the value Q = 104 .
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.