Tunable Fano resonant optical forces exerted on a graphene-coated dielectric particle by a Gaussian evanescent wave
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In this paper, we investigate the optical forces exerted on a graphene-coated dielectric particle by the Gaussian beam transmitted through the prism setup systematically. It is shown that the optical force spectra exhibit significant Fano resonance under the excitation of a Gaussian evanescent wave. The magnitude and morphology of Fano resonance can be modulated effectively by the graphene coating. Also, the modification on the threshold of the Fermi energy of graphene could help to regulate the trapping behavior efficiently. The proposed work may provide a new avenue in the specific optical tweezers and nano-optics.Keywords:
Fano resonance
Wave–particle duality
Optical force
Particle (ecology)
Fano plane
Plasmonic MIM (metal-insulator-metal) waveguides based on Fano resonance have been widely researched. However, the regulation of the direction of the line shape of Fano resonance is rarely mentioned. In order to study the regulation of the direction of the Fano line-shape, a Fano resonant plasmonic system, which consists of a MIM waveguide coupled with a ring resonator and a rectangle resonator, is proposed and investigated numerically via FEM (finite element method). We find the influencing factors and formation laws of the ‘direction’ of the Fano line-shape, and the optimal condition for the generation of multiple Fano resonances; and the application in refractive index sensing is also well studied. The conclusions can provide a clear theoretical reference for the regulation of the direction of the line shape of Fano resonance and the generation of multi Fano resonances in the designs of plasmonic nanodevices.
Fano resonance
Fano plane
Line (geometry)
Rectangle
Waveguide
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The interaction between plasmonic resonances, sharp modes, and light in nanoscale plasmonic systems often leads to Fano interference effects. This occurs because the plasmonic excitations are usually spectrally broad and the characteristic narrow asymmetric Fano line-shape results upon interaction with spectrally sharper modes. By considering the plasmonic resonance in the Fano model, as opposed to previous flat continuum approaches, here we show that a simple and exact expression for the line-shape can be found. This allows the role of the width and energy of the plasmonic resonance to be properly understood. As examples, we show how Fano resonances measured on an array of gold nanoantennas covered with PMMA, as well as the hybridization of dark with bright plasmons in nanocavities, are well reproduced with a simple exact formula and without any fitting parameters.
Fano resonance
Fano plane
Plasmonic Nanoparticles
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The optical properties of plasmonic nanostructures supporting Fano resonances are investigated with an electromagnetic theory. Contrary to the original work of Fano, this theory includes losses in the materials composing the system. As a result, a more general formula is obtained for the response of the system and general conclusions for the determination of the resonance parameters are drawn. These predictions are verified with surface integral numerical calculations in a broad variety of plasmonic nanostructures including dolmens, oligomers, and gratings. This work presents a robust and consistent analysis of plasmonic Fano resonances and enables the control of their line shape based on Maxwell's equations. The insights into the physical understanding of Fano resonances gained this way will be of great interest for the design of plasmonic systems with specific spectral responses for applications such as sensing and optical metamaterials.
Fano plane
Fano resonance
Line (geometry)
Photonic metamaterial
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Plasmonic clusters can support Fano resonances, where the line shape characteristics are controlled by cluster geometry. Here we show that clusters with a hemicircular central disk surrounded by a circular ring of closely spaced, coupled nanodisks yield Fano-like and non-Fano-like spectra for orthogonal incident polarization orientations. When this structure is incorporated into an uniquely broadband, liquid crystal device geometry, the entire Fano resonance spectrum can be switched on and off in a voltage-dependent manner. A reversible transition between the Fano-like and non-Fano-like spectra is induced by relatively low (∼6 V) applied voltages, resulting in a complete on/off switching of the transparency window.
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Fano plane
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The Fano resonance of a single symmetry broken Ag nanodisk under a normal incidence was investigated by using finite-difference time-domain (FDTD) simulations. The asymmetry line shape of the Fano resonance was controlled by modifying the open angle of the nanodisk, and this Fano splitting was demonstrated as the result of the overlap between the broad dipolar and narrow quadrupolar modes, which could be strengthened by enlarging the radius of the nanodisk. A semi-analytical method was developed to calculate the plasmon hybridization, which was used to analyze the sub-process of the quadru Fano resonance. With the good agreement between theoretical calculations and FDTD simulations, the suggested method provides a way to investigate and control the Fano resonance inside a single planar nanostructure, and can be applied to the future high-performance Fano resonance sensors.
Fano plane
Fano resonance
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Fano resonances in plasmonic nanostructures are important for plasmon line shaping. Compared to a single Fano resonance, multiple Fano resonances can modify plasmon lines at several spectral positions simultaneously, but they often suffer from weak modulation depths. In this paper, plasmonic heptamer clusters comprising split nanorings are designed to form multiple Fano resonances. Three prominent Fano resonances are observed in the spectra due to the formation of multiple narrow subradiant resonances, and the multiple Fano resonances can be switched on and off by adjusting the polarization direction. Particularly, by modifying the geometry parameters, there is a large tunability of the modulation depth of each Fano resonance. Heptamer clusters comprising split nanorings are highly suitable for plasmon line shaping, and it is expected that they are useful for multiwavelength biosensing and surface-enhanced Raman scattering.
Fano resonance
Fano plane
Nanoring
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Plasmonic Fano resonances arise in bimetallic layered nanostructures (metal–dielectric–metal and dielectric–metal–dielectric–metal) are studied theoretically as the function of their geometrical parameters. Multiple Fano resonances are generated in these nanostructures where several subradiant dark modes appear due to the geometrical symmetry breaking induced by offsetting different layers. The plasmonic responses of the proposed nanoparticles with equal volumes are compared and multiple Fano resonances with large modulation depths are obtained in metal–dielectric–metal structure which is highly suitable for multi-wavelength sensing and plasmon line shaping. However, the dielectric–metal–dielectric–metal nanostructure is found to provide a slightly better tunability of higher-order plasmonic modes compared to metal–dielectric–metal nanostructure due to which it can be useful for biomedical applications.
Fano resonance
Bimetallic strip
Nanochemistry
Fano plane
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We studied the plasmonic response in graphene nanostructures consisting of double-stacked graphene nanostrip arrays with a dielectric spacer on a substrate. The finite-difference time-domain simulations show that the Fano-like resonance in the mid-IR region can be generated due to the plasmonic coupling between the upper- and lower-layer graphene nanostrips. The resonance spectrum can also be effectively controlled by adjusting the geometrical parameters of the graphene system, such as the central position of the graphene nanostrips and the coupling distance between the upper- and lower-layer graphene nanostrips. Moreover, it was found that Fano-like resonance relies on the Fermi level of graphene and polarization angle of incident light, and the spectral response can be well analyzed by using the coupled-mode theory. These results would offer a new pathway to manipulate mid-IR light at the nanoscale and realize ultrasmall graphene functional devices.
Fano resonance
Fermi energy
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Fano resonances have been achieved in a variety of complex plasmonic nanostructures. Here we propose a novel planar structure supporting higher order Fano resonances, a plasmonic nanodisk with a built-in missing sectorial slice whose slice angle varies from 0 to 360°. The numerical results reveal that higher order Fano resonances can be generated in the visible wavelength range when the slice angle locates in a certain range in this reduced-symmetry structure. Such higher order Fano resonances result from the coupling between the dipolar mode supported by the edge of the built-in missing slice and the multipolar ring modes. Furthermore, the effects of dimension and ring width of this structure on the spectral positions and intensities of the higher order Fano resonances are also studied. The line shapes of Fano resonances can be tuned flexibly by modifying the geometrical parameters of this structure.
Fano plane
Fano resonance
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