Plasmonic nanostructures can overcome Abbe's diffraction limit to generate strong gradient fields, enabling efficient optical trapping of nano-sized particles. However, it remains challenging to achieve stable trapping with low incident laser intensity. Here, we demonstrate a Fano resonance-assisted plasmonic optical tweezers (FAPOT), for single nanoparticle trapping in an array of asymmetrical split nano-apertures, milled on a 50 nm gold thin film. Stable trapping is achieved by tuning the trapping wavelength and varying the incident trapping laser intensity. A very large normalized trap stiffness of 8.65 fN/nm/mW for 20 nm polystyrene particles at a near-resonance trapping wavelength of 930 nm was achieved. We show that trap stiffness on resonance is enhanced by a factor of 63 compared to off-resonance conditions. This can be attributed to the ultra-small mode volume, which enables large near-field strengths and a cavity Purcell effect contribution. These results should facilitate strong trapping with low incident trapping laser intensity, thereby providing new options for studying transition paths of single molecules, such as proteins, DNA, or viruses.
Optical manipulation has attracted remarkable interest owing to its versatile and non-invasive nature. However, conventional optical trapping remains inefficient for the nanoscopic world. The emergence of plasmonics in recent years has brought a revolutionary change in overcoming limitations due to diffraction and the requirements for high trapping laser powers. Among the near-field optical trapping cavity-based systems, Fano resonant optical tweezers have a robust trapping capability. In this work, we experimentally demonstrate sequential trapping of 20 nm particles through the use of metamat…
In recent years, a range of reconfigurable metamaterials controlled with thermal, electric, magnetic and optical signals have been developed for dynamically manipulating the intensity, phase and wave-front of electromagnetic radiation across the broad electromagnetic spectrum ranging from microwave to optics. Here for the first time, we demonstrate a reconfigurable metasurface performing exclusive OR (XOR) logical operation using two independent control electrical inputs and an optical read-out in the form of far-field Fano intensity states at terahertz wavelengths. At the same time, the near …
Mechanism of the Fano resonances in planar metamaterials demonstrate based on the coupled two-oscillator model. We have described the optical spectrums like reflectance and transmittance near the resonances of bright mode (continuum mode) and dark mode (discrete mode) and explained their optical properties by the Fano formulism. the Fano formulism of the resonances in the planar metamaterials can predict the asymmetric shape line and radiative properties occurring in reflectance and transmittance from the coupling between bright and dark modes.
We investigate numerically Fano resonances excited in periodic arrays of dielectric, metallic and left-handed cylinders. Of particular interest are Fano resonances excited in the linear array of cylin- ders. We analyze spatial distribution and symmetry of electromagnetic field and discuss the relation between observed Fano resonances and frequency spectra of two-dimensional arrays of cylinders.
We demonstrate that both linear and nonlinear Fano resonances can be realized on two dimensional magnetic metamaterials. The Fano resonance comes from the interference between localized magnetic plasmon resonance and propagating surface plasmon polaritons. When studying the linear optical response of the metamaterial structure, this interference phenomenon was observed in the ellipsometric spectrum. By finely tailoring the geometrical parameters of the magnetic metamaterial device, the nonlinear Fano response was tuned to a near-infrared wavelength (1.61-1.8 μm) of femtosecond pump laser, and …
We present the first study of disorder in planar metamaterials consisting of strongly interacting metamolecules, where coupled electric dipole and magnetic dipole modes give rise to a Fano-type resonant response and show that positional disorder leads to light localization inherently linked to collective magnetic dipole excitations. We demonstrate that the magnetic excitation persists in disordered arrays and results in the formation of "magnetic hot-spots".
We studied the transmission characteristics of a planar metamaterial consisting of an array of electric split-ring resonators (eSRRs) with double periodicity. Because of coupling between different resonant modes induced by different lattice periods in metamaterials with double periodicity, the appearance of Fano resonance can be expected in the same manner as that in the case of coupled classical oscillators. We fabricated complementary eSRRs and verified that a Fano-like spectral shape appeared in the transmission spectra of eSRRs with double periodicity in the terahertz region.
By embedding four-rod resonators inside double-split ring resonators superlattice, a planar composite metamaterial possessing tripod plasmonic resonances is fabricated. Double Fano resonances are observed where a common subradiant driven oscillator is coupled with two superradiant oscillators. As a classical analogue of four-level tripod atomic system, the transmission spectrum of the composite metamaterial exhibits a double Fano-based coherent effect. Transfer of absorbed power between two superradiant oscillators is controlled by manipulating two coupling strengths conjugated through the pol…
We propose a concept of a low-symmetry three-dimensional metamaterial exhibiting a Double- Continuum Fano (DCF) optical resonance. Such metamaterial is described as a birefringent medium supporting a discrete "dark" electromagnetic state weakly coupled to the continua of two nondegen- erate "bright" bands of orthogonal polarizations. It is demonstrated that light propagation through such DCF metamaterial can be slowed down over a broad frequency range when the medium param- eters (e.g. frequency of the "dark" mode) are adiabatically changed along the optical path. Using a specific metamaterial…
We study the scattering of magnetoinductive plane waves by internal (external) capacitive (inductive) defects coupled to a one-dimensional split-ring resonator array. We examine a number of simple defect configurations where Fano resonances occur and study the behavior of the transmission coefficient as a function of the controllable external parameters. We find that for embedded capacitive defects, the addition of a small amount of coupling to second neighbors is necessary for the occurrence of Fano resonance. For external inductive defects, Fano resonances are commonplace, and they can be tu…
Graphene has emerged as a promising building block in the modern optics and optoelectronics due to its novel optical and electrical properties. In the mid-infrared and terahertz (THz) regime, graphene behaves like metals and supports surface plasmon resonances (SPRs). Moreover, the continuously tunable conductivity of graphene enables active SPRs and gives rise to a range of active applications. However, the interaction between graphene and metal-based resonant metamaterials has not been fully understood. In this work, a simulation investigation on the interaction between the graphene layer an…
A simple metamaterial absorber suitable for fabrication over large areas associated with a Fano like resonance is proposed. The proposed designed of the metamaterial absorber consists of photoresist disk arrays on a silicon substrate followed by the deposition of a tri layer of Au, ZnS and Au on the top of the structure. Due to the tri layer, there is a formation of a cavity between the substrate and gold layer on the top of photoresist disk and a waveguide in the ZnS layer in between the gold layers on the substrate and the ZnS layer itself. The Fano like resonance arises due to the interfere…
Metamaterials and meta-surfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, nonlinear optics, and even spaser lasing. Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field. The simplicity of free-space light coupling into sharply-resonant meta-surfaces with high resonance quality factors Q>>1 is a significant practical advantage over the extremely angle-sensitive diffractive structures or inherently inhomogeneous high-Q …
Metasurface analogues of electromagnetically induced transparency (EIT) have been a major focus of the nanophotonics field over the past several years due their ability to produce high quality factor (Q-factor) resonances for applications such as low-loss slow light devices and highly sensitive optical sensors. However, Ohmic loss limits the achievable Q-factors in conventional plasmonic EIT metasurfaces to values less than 10, significantly hampering device performance. Here, we report experimental demonstration of a classical analogue of EIT using all-dielectric silicon-based metasurfaces. D…
Fano resonance is a unique feature of interacting quantum systems, exhibiting resonance shapes distinctively different from conventional symmetric resonance curves. Recently, Fano resonances have been found in plasmonic nanoparticles, photonic crystals, and electromagnetic metamaterials. Here we report Fano-like photoluminiscence curves in nanodiamond solutions as a result of incoherent combination of two or more scattering and fluorescence processes. We argue that, analogously to Fano resonances, the steep asymmetric dispersion of the photoluminiscence profile in nanodiamond solutions, in com…
Ultrasensitive terahertz sensing of highly absorptive aqueous solutions remains challenging due to strong absorption of water in the terahertz regime. Here, we experimentally demonstrate a cost-effective metamaterial-based sensor integrated with terahertz time-domain spectroscopy for highly absorptive water-methanol mixture sensing. This metamaterial has simple asymmetric wire structures that support multiple resonances including a fundamental Fano resonance and higher order dipolar resonance in the terahertz regime. Both the resonance modes have strong intensity in the transmission spectra wh…
High quality factor resonances are extremely promising for designing ultra-sensitive refractive index label-free sensors since it allows intense interaction between electromagnetic waves and the analyte material. Metamaterial and plasmonic sensing has recently attracted a lot of attention due to subwavelength confinement of electromagnetic fields in the resonant structures. However, the excitation of high quality factor resonances in these systems has been a challenge. We excite an order of magnitude higher quality factor resonances in planar terahertz metamaterials that we exploit for ultrase…
We report on a bistable light transmission through a planar metamaterial composed of a metal pattern of weakly asymmetric elements placed on a nonlinear substrate. Such structure bears the Fano-like sharp resonance response of a trapped-mode excitation. The feedback required for bistability is provided by the coupling between the strong antiphased trapped-mode-resonance currents excited on the metal elements and the intensity of inner field in the nonlinear substrate.
The build-up dynamics of a continuous spectrum under the action of a weak laser field on a Fano resonance with the use of the pulses with the Lorentz spectrum and ultrashort pulses in the wavelet form is investigated. A dispersion-time excitation dependence of the Fano resonances in a He atom, in an InP impurity semiconductor, in longitudinal optical LO-phonons of a shallow donor exciton in pure ZnO crystals, and in metamaterials are calculated. The numerical simulation of the dynamics has shown time-dependent formation a Fano spectral profile in the systems of different physical natures under…
A perfect metal film with a periodic arrangement of cut-through slits, an anisotropic metallic metamaterial film, mimics a dielectric slab and supports guided electromagnetic waves in the direction perpendicular to the slits. Here, we introduce metallic metasurface superlattices that include multiple slits in a period, and demonstrate that the superlattices support the Fano resonances and bound states in the continuum. The number of Fano resonances and bound states depend on the number of slits in a period of superlattices. The metallic metasurface superlattices provide new mechanisms to manip…
We report on a bistable light transmission through a bilayer "fish-scale" (meander-line) metamaterial. It is demonstrated that an all-optical switching may be achieved nearly the frequency of the high-quality-factor Fano-shaped trapped-mode resonance excitation. The nonlinear interaction of two closely spaced trapped-mode resonances in the bilayer structure composed with a Kerr-type nonlinear dielectric slab is analyzed in both frequency and time domains. It is demonstrated that these two resonances react differently on the applied intense light which leads to destination of a multistable tran…
We discuss the similarity between the nature of resonant oscillations in two nonlinear systems, namely, a chain of coupled Duffing oscillators and a bilayer fish-scale metamaterial. In such systems two different resonant states arise which differ in their spectral lines. The spectral line of the first resonant state has a Lorentzian form, while the second one has a Fano form. This difference leads to a specific nonlinear response of the systems which manifests itself in appearance of closed loops in spectral lines and bending and overlapping of resonant curves. Conditions of achieving bistabil…
We present a metamaterial-based terahertz (THz) sensor for thickness measurements of subwavelength-thin materials and refractometry of liquids and liquid mixtures. The sensor operates in reflection geometry and exploits the frequency shift of a sharp Fano resonance minimum in the presence of dielectric materials. We obtained a minimum thickness resolution of 12.5 nm (1/16000 times the wavelength of the THz radiation) and a refractive index sensitivity of 0.43 THz per refractive index unit. We support the experimental results by an analytical model that describes the dependence of the resonance…
We observe toroidal response from a planar metamaterial comprised of asymmetric split ring resonators (ASRRs). It is showed that a toroidal-molecule can be constructed through rational arrangement of planar ASRRs as meta-atoms via manipulating structural symmetry of the meta-atoms. Field maps clearly indicate that the toroidal resonance paves new electromagnetic confinement style in a subwavelength scale. Planar scheme of manipulating the coupling among the ASRRs may stimulate research in optical region involving toroidal multipoles. Toroidal geometry together with the Fano resonance made high…
We propose, solve, and discuss a simple model for a metamaterial incorporating optical gain: A single bosonic resonance is coupled to a fermionic (inverted) two-level-system resonance via local-field interactions. For given steady-state inversion, this model can be solved analytically, revealing a rich variety of (Fano) absorption/gain lineshapes. We also give an analytic expression for the fixed inversion resulting from gain pinning under steady-state conditions. Furthermore, the dynamic response of the 'lasing SPASER', i.e., its relaxation oscillations, can be obtained by simple numerical ca…
Transmission through a subwavelength terahertz fiber, which is positioned in parallel to a frequency selective surface, is studied using several finite element tools. Both the band diagram technique and the port-based scattering matrix technique are used to explain the nature of various resonances in the fiber transmission spectrum. First, we observe that spectral positions of most of the transmission peaks in the port-based simulation can be related to the positions of Van Hove singularities in the band diagram of a corresponding infinite periodic system. Moreover, spectral shape of most of t…
Fano resonance exhibiting an asymmetric spectral line shape is a universal phenomenon observed in diverse physical systems. Here we experimentally establish a direct link between the spectral asymmetry parameter and a physically realizable phase factor of interference between a continuum and a discrete mode that leads to Fano resonance. Using a specially designed metamaterial, namely waveguided plasmonic crystal with a spatially varying orientation axis of plasmonic grating, we demonstrate control on the spectral asymmetry of the Fano resonance through changes in the geometric phase of polariz…
The Fano line profiles, originally discovered in the context of photoionization, have been found to occur in a large class of systems like resonators, metamaterials, plasmonics. We demonstrate the existence of such resonances in cavity optomechanics by identifying the interfering contributions to the fields generated at antiStokes and Stokes frequencies. Unlike the atomic systems, the optomechanical systems provide great flexibility as the width of the resonance is controlled by the coupling field. We further show how the double cavities coupled by a single optomechanical mirror can lead to th…
Weak measurement enables faithful amplification and high precision measurement of small physical parameters and is under intensive investigation as an effective tool in metrology and for addressing foundational questions in quantum mechanics. Most of the experimental reports on weak measurements till date have employed external symmetric Gaussian pointers. Here, we demonstrate its universal nature in a system involving asymmetric spectral response of Fano resonance as the pointer arising naturally in precisely designed metamaterials, namely, waveguided plasmonic crystals. The weak coupling ari…
We demonstrate tunable pulling and pushing optical forces on plasmonic nanostructures around Fano resonance. The plasmonic nanostructure containing a spherical core with optical gain and a metallic shell shows much larger optical pulling force than a pure gain sphere. One can obtain large field enhancement and giant pulling force at the emerged quadrupole mode. The introduction of optical pump compensate the dissipative loss from metal shell, thus enable the strong coupling between a narrow quadrupole mode and a board dipole mode, giving rise to Fano resonance. The giant negative forces origin…
Orthogonal Flatbands-Enabled Robust Fano Resonances through Brillouin-Zone Folding
Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences（中国科学院深圳先进技术研究院）；The Hong Kong University of Science and Technology (Guangzhou)（香港科技大学（广州））
Hyperbolic-enhanced Raman scattering in van der Waals MoOCl2: from Fano resonances to picomolar detection
XPANCEO；University of Chemistry and Technology Prague（布拉格化工大学）；National Graphene Institute (NGI), University of Manchester（曼彻斯特大学国家石墨烯研究所）；National University of Singapore（新加坡国立大学）
The full control of the fundamental photophysics of nanosystems at frequencies as high as few THz is key for tunable and ultrafast nano-photonic devices and metamaterials. Here we combine geometrical and ultrafast control of the optical properties of halide perovskite nanoparticles, which constitute a prominent platform for nanophotonics. The pulsed photoinjection of free carriers across the semiconducting gap leads to a sub-picosecond modification of the far-field electromagnetic properties that is fully controlled by the geometry of the system. When the nanoparticle size is tuned so as to ac…
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 tha…
Understanding vanishing transmission in Fano resonances in quantum systems and metamaterials, and ultralow transmission in disordered media is key to elucidating optical interactions. Using analytic theory and numerical simulations, we discover the topological structure and motion under deformation of transmission zeros in the complex energy plane. We demonstrate the zeros can be controlled to create ultranarrow Lorentzian lines in spectra of transmission time and diverging rates of frequency change of transmission zeros as they converge. This suggests a new approach to ultrasensitive detectio…
We study the propagation of waves in a quasi 1D homogeneous host medium filled with various resonators. We first prove that a far field coupling between the elements explains its dispersive nature. This coupling is interpreted as a Fano interference between the incoming wave and the waves re-radiated by each resonator, which experience a phase shift at resonance. We propose a simple formalism that gives the complete dispersion relation of the medium in terms of the far field response of a single resonator. We prove that our approach applies to and unifies various domains such as metamaterials,…
Conventional approaches to control and shape the scattering patterns of light generated by different nanostructures are mostly based on engineering of their electric response due to the fact that most metallic nanostructures support electric resonances in the optical frequency range. Recently, fuelled by the fast development in the fields of metamaterials and plasmonics, artificial optically-induced magnetic responses have been demonstrated for various nanostructures. This kind of response can be employed to provide an extra degree of freedom for the efficient control and shaping of the scatte…
