Dipole Resonance Mode Research Articles

Isovector giant dipole resonance mode with an improved propagation approach in the framework of EQMD model

Isovector giant dipole resonance mode with an improved propagation approach in the framework of EQMD model

Single-double-band switchable optical circular polarizers based on surface plasmon resonance.

A single-double-band switchable circular polarization filter based on surface plasmon resonance exhibits significant potential for applications in fields such as communication and sensing due to its adjustable, low-cost, and easy integration features. In this study, we propose a bi-layer rod nanostructure and use FEM simulation to study the transmission spectra of the structure. The results demonstrate that the structure exhibits both single- and double-band circular polarization filtering effects, which can be switched by varying geometric parameters such as the distance between the two layers and the width of nanorods. Furthermore, the filtering effects of both single- and double-band are highly dependent on the length of the nanorods, with average extinction rates reaching 486 and 2020/129, respectively; the operating bandwidths (defined as extinction ratio >10) can reach 170nm and 35nm/70nm, respectively. The underlying physical mechanisms are clarified by analyzing the electric dipole, magnetic dipole resonance modes, and induced chiral fields on nanostructures.

Dielectric light-trapping nanostructure for enhanced light absorption in organic solar cells

Dielectric scatterers where Mie resonances can be excited in both electric and magnetic modes have emerged as a promising candidate for efficient light trapping (LT) in thin-film solar cells. We present that light absorption in organic solar cells (OSCs) can be significantly enhanced by a front-sided incorporation of a core–shell nanostructure consisting of a high-refractive-index dielectric nanosphere array conformally coated with a low-refractive-index dielectric layer. Strong forward light scattering of the all-dielectric LT structure enables the absorption in an organic semiconductor to be remarkably boosted over a broad range of wavelengths, which is attributed to interference of a simultaneous excitation of the electric and magnetic dipole resonant modes. The OSC with the LT structure shows the short-circuit current density (Jsc) of 28.23 mA/cm2, which is 10% higher than that of a flat OSC. We also explore how the LT structure affects scattering cross-sections, spectral multipole resonances, and far-field radiation patterns. The approach described in this work could offer the possibility for the improvement of characteristic performances of various applications, such as other thin-film solar cells, photodiodes, light-emitting diodes, and absorbers.

VIS-NIR TMOKE enhanced dielectric-metal hybrid structure for high performance dual-channel sensing.

Magneto-plasmon sensors based on the transverse magneto-optical Kerr effect (TMOKE) have been extensively studied in recent years. In this paper, we theoretically propose a hybrid structure composed of a one-dimensional bismuth iron garnet: yttrium iron garnet (BIG: YIG) nanowire arrays and thin film stack, which is grown on an infinite thick silicon wafer. The thin film stack, from top to bottom, consists of the following layers: BIG: YIG, SiO2, and Au. By exciting the magnetic dipole resonance mode between the cylindrical nanowires and the SPP mode on the surface of the Au film, dual-channel sensing has been achieved in both visible and infrared spectra. The results demonstrate that the TMOKE response spectrum of the structure supports ultra-narrow linewidths of 0.03 nm in the visible light range and 1.54 nm in the infrared range. By changing the refractive index of the analyte, the detected sensitivity of the sensor system in visible and infrared bands is 553 nm RIU-1 and 285 nm RIU-1, and the Figure of merit (FOM) can reach up to 69125 RIU-1 and 303 RIU-1, respectively. This work provides a theoretical basis and a feasible approach for the design of dual channel gas sensors.

Ti3C2/Ni2P/triphenyl phosphite as antioxidative microwave absorbers with excellent photothermal property

Microwave absorbers with the high-efficiency photothermal conversion performance are currently lacking but significantly desired as they can provide a sufficient heat energy besides the absorption property. Herein, Ti3C2/Ni2P/triphenyl phosphite (TPOP-Ti3C2/Ni2P) composite was synthesized by an ingenious one-pot solution-phase reaction and proved to be a superior antioxidative microwave absorbent with excellent photothermal properties. Ni2P can effectively optimize the impedance match of Ti3C2 MXene and consequently improve its microwave absorption (MA) performance. Results show that the minimum reflection loss value of TPOP-Ti3C2/Ni2P is −57.87 dB at 10.88 GHz, the maximum effective absorption bandwidth is 5.04 GHz, and the thickness is merely 1.8 mm. Notably, TPOP on the MXene surface can serve simultaneously as an antioxidative stabilizer and a capping agent to improve its hydrophobicity and chemical stability. The average water contact angle of TPOP-Ti3C2/Ni2P is prompted to 96.59°, while the average oil contact angle is 26.02°. Moreover, compared with the pure Ti3C2, TPOP-Ti3C2/Ni2P has an obvious antioxidant stability in aqueous solution. Additionally, Ni2P nanoparticles exhibit a dipole resonance mode under illumination conditions, which enhances the surface absorption capability of visible light. The surface temperature of the natural rubber film after introducing TPOP-Ti3C2/Ni2P increased rapidly under simulated light, showing a high photothermal conversion ability. Furthermore, the MA performance of the composite film remains basically unchanged, whether is repeatedly bent or exposed under a harsh sun. This study provides a new strategy for manufacturing MA materials with efficient photothermal properties for the possible application to design wearable devices that can combine electromagnetic protection and self-generated heat.

Multiple poles resonances coupling with high sensitivity sensing for multiple bulging black phosphorus-based metasurface

Herein, a multiple bulging black phosphorus (BP)-based metasurface is proposed for studying its reflection responses and sensing performances through the finite-difference time-domain simulation method. It is shown that, the reflection dips are caused by the coupling between dipole resonance modes and poly-poles resonance modes. Moreover, the dipoles resonance modes and poly-poles resonance modes can mutually enhance and inhibit each other, and tunable reflection spectra can be realized by symmetrically and asymmetrically adjusting the bulging of the proposed BP-based metasurface. In addition, the reflection spectra as a function of the polarization of incident light are discussed. We can find that a dipole resonance mode on the vertical side at the direction of ZZ for BP is gradually fully excited, resulting in an additional obvious reflection dip as the polarization angle θ increases from 0° to 90°. Especially, the sensing performance with the maximum of sensitivity S = 1.5 μm/RIU can be realized in the proposed BP-based metasurface. The results may provide a way to design micro-nano plasmonic devices.

Optically controlled and polarized sensitivity adjustable terahertz metamaterial absorber

A photoactive terahertz (THz) absorber is designed based on the quadruple rotational symmetrical metamaterial structure combined with the GaAs bars. For the bare metallic metamaterial structure, the THz absorber shows a polarization insensitive property with two perfect absorption peaks at 0.62 THz and 0.84 THz, and the absorption rates are 98.80 % and 99.97 %, respectively. For the GaAs functionalized metamaterial structure, the hybrid THz absorber is equivalent to the metallic resonator in the absence of the pump light since the GaAs bars are in an insulated state with the conductivity of 100 S/m. Further, the GaAs bars turn into a metallic state as the conductivity increases to 5 × 105 S/m under pump light. The hybrid THz absorber becomes an axisymmetric structure with a polarization sensitive property, which could excite two new perfect absorption frequencies at 0.71 THz and 2.24 THz, and the corresponding absorptivity are 99.80 % and 99.90 %. The simulated electronic field distribution and surface current distribution indicate that the perfect absorption is due to the dipole resonant modes. The proposed optically controlled and polarization tunable THz metamaterial absorber provides potential applications in the related fields of THz switches, detectors, and imaging.

Theoretical study of extremely narrow plasmonic surface lattice resonances observed by MIM nanogratings under normal incidence in asymmetric environments

Nanoarray structures can support plasmonic surface lattice resonances (SLRs) with extremely narrow linewidths and huge electric field enhancement features, which are attractive applications in nanolasers, biochemical sensors, and nonlinear optics. However, current nanoarray structures located in an asymmetric dielectric environment with a refractive index contrast of 1.00/1.52 of the superstrate/substrate excite much poorer SLRs under normal incidence, which largely limits their application range. In this work, we report extremely narrow SLRs supported by one-dimensional metal–insulator–metal nanograting in asymmetric dielectric environments. The simulation results show that an SLRs with linewidth of 3.26 nm and quality factor of 233.2 can be excited under normal incidence. This high-quality SLRs is attributed to the interference formation between the out-of-plane dipole resonance mode and the out-of-plane quadrupole resonance mode. We also show that the resonance wavelength and quality factor can be tuned by changing the structure geometry and period, and we calculate the normal incidence SLRs quality factor to be up to 248 in 1.33/1.52 and 250 in 1.45/1.52. We expect the SLRs of this work to find potential applications in asymmetric dielectric environments.

Coexistence of circular dichroism and asymmetric transmission in Babinet-complementary metamaterials.

Chiral metamaterials with circular dichroism (CD) or asymmetric transmission (AT) draw enormous attention for their attractive applications in polarization transformers, circular polarizers, and biosensing. In this study, a feasible trilayer chiral metamaterials (TCM) is designed and investigated in theory and simulation. The proposed TCM is composed of a nanoslit layer and a Babinet-complementary nanorod layer separated by a nanoslit spacer. Owing to symmetry breaking by the tilted nanoslit in metal film, the TCM shows simultaneous CD and AT effects in the near-infrared region. The simulated electric charge distributions prove that the chirality arises from the excitation of asymmetric electric dipole resonant modes due to the coupling of adjacent unit cells. Moreover, CD and AT can be tuned by the tilted angle of the nanoslit and the thickness of the spacer, the fitting functions of which are consistent with the theoretical formulas based on transmittance matrix analysis. The proposed nanostructure offers a potential strategy for manipulating metamaterials with simultaneous CD and AT effects, allowing a multitude of exciting applications such as ultra-sensitive polarization transformer and biosensor.

Engineering negative coupling and corner modes in a three-dimensional acoustic topological network

Higher-order topological insulators have aroused massive attention due to their fancy topological properties. Artificial metamaterials, with their exquisite fabrications and measurements, offer an ideal approach to investigate topological properties in classical systems. Therein lower-dimensional corner states obtained in the three-dimensional (3D) Su-Schrieffer-Heeger (SSH) model and the octupole insulator have been extensively explored in acoustic systems. However, the existing acoustic negative couplings in the quantized multipole topological phases are mostly formed by shifting the connecting waveguides between every two resonators, which support a restricted dipole resonance mode. Here we establish subwavelength acoustic third-order topological insulators based on the theoretical frame of acoustic transmission lines and provide an innovative way for freely engineering acoustic negative couplings that work in arbitrary resonance modes. Furthermore, topological invariant calculations and numerical simulations in analogous acoustic networks validate the occurrence of topological corner states in both the 3D SSH model and octupole insulator. We foresee that the proposed methodology will broaden future avenues for studying atypical topological quantum effects with negative couplings in the classical macroscale context.

Multifunctional resonant graphene four-port for THz and far IR regions

A new multifunctional resonant device for THz and far-infrared regions based on surface plasmon-polariton graphene resonator and waveguides is suggested and analyzed in this paper. The device consists of a circular graphene resonator and four nanoribbons serving as waveguides. Every waveguide is front-coupled to the resonator with a small gap between them. The waveguides are oriented with the angle 90∘ between them. The graphene elements are deposited on a dielectric substrate. The Fermi energy of graphene can be dynamically varied by applying an electrical potential difference between the graphene and a thin polysilicon layer which acts as an electrode. The resonator can work with dipole and quadrupole resonant modes. They are used to provide the functions of tunable band-pass filter, tunable power divider and switch. Using the scattering matrix description of the four-port, the circuit theory representation and full-wave analysis, we show that for the central frequency 14.52 THz the parameters of the developed device are as follows: the Q-factor due to use of resonant structure is (6÷8), the matching in the pass-band with return loss of − 17 dB and low insertion loss of about − 1.0 dB. The component provides a tunability of the central frequency and the power ratio between the three output ports can be projected in a wide range. In the OFF regime, the transmission coefficients to output ports are lower than − 42 dB.

Polarization‐independent dual narrow‐band perfect metamaterial absorber for optical communication

AbstractIn this paper, we demonstrate a dual narrow‐band perfect metamaterial absorber for optical communication, where a silicon nano‐disk array is placed on a thin gold film separated by a dielectric layer. Numerical results reveal that dual narrow‐band perfect absorption peaks, which are attributed to waveguide mode and magnetic dipole resonance mode, are achieved at 1310 and 1550 nm, respectively. The results show that the absorption of the two peaks is higher than 99% under the normal incidence of both TE and TM polarizations and the bandwidth is 5 and 15 nm, respectively. Moreover, the absorption peak at 1310 nm can be independently tuned by varying the thickness of the dielectric layer. These findings imply that the proposed absorber can be used in the field of optical communication, frequency‐selective photodetection, and intersatellite laser communication.

Low-Profile Shared-Structure Dual-Polarized Yagi–Uda Antennas

Low-profile shared-structure dual-polarized (DP) Yagi–Uda antennas are proposed, which are formed by three kinds of basic components, namely DP driven element, DP director, and DP reflector. An open-cavity dipole is utilized as the DP driven element to generate DP endfire radiations. The quarter-wave resonance mode for vertical polarization (VP) and half-wave dipole resonance mode for horizontal polarization (HP) are excited by differential feeding structures in the DP driven element. The open-cavity element is adopted as the DP director or reflector to enhance endfire gain. For the proposed design, two polarization radiators are integrated into one structure, realizing structure sharing, and thus a low profile. Three-element (Ant. 1) and seven-element (Ant. 2) antennas with a profile of 0.1 λ₀ are designed, fabricated, and measured. The measured overlapped bandwidth of the Ant. 1 is from 4.11 to 4.83 GHz (16%) with ports isolation higher than 30 dB, and the measured VP and HP gains are from 5 to 6 dBi and 5 to 7 dBi, respectively. The Ant. 2 further increases the DP endfire gain by 2–3 dBi at the overlapped bandwidth of 16.3%.

Single-layer all-dielectric quarter-wave plate and half-wave plate metasurfaces for polarization conversion in the visible light region

Metasurfaces have the characteristics of ultra-thin volume, light weight, and planar structure, which can also effectively control the polarization state of electromagnetic waves. We propose single-layer all-dielectric quarter-wave plate (QWP) and half-wave plate (HWP) metasurfaces that work in the visible light region in transmission mode. The designed QWP can convert y-linearly polarized (YLP) light into left-handed circularly polarized light, whereas the HWP can convert YLP light into x-linearly polarized light. Moreover, the designed wave plates have a certain wide band working ability. When the incident angle is <30 deg for the QWP and <28 deg for the HWP, the polarization conversion performance shows strong robustness. The effects of fabrication tolerance, the height of elliptic-shaped pillar, and lattice constant on the polarization conversion performance are analyzed. In addition, the physical mechanism of polarization conversion is revealed by simulating the distribution of magnetic field and electric field inside unit structures. The results indicate that nanostructures of different sizes will excite different magnetic dipole resonance modes so as to realize the function of different polarization state conversions. It is believed that all-dielectric wave plate metasurfaces will become a good alternative for controlling the polarization state of electromagnetic waves.

Theoretical simulation of nonlinear regulation of wall thickness dependent longitudinal surface plasmon in pentagonal gold nanotubes

In this paper, the longitudinal plasmon mode optical properties and localized electric field distribution of a single pentagonal gold nanotube are investigated for the first time by the discrete dipole approximation. It is found that pentagonal gold nanotube has stronger electric field distribution compared with circular gold nanotubes when the incident wavelength is located at the plasmon resonance peak. Additionally, we observed that the longitudinal plasmon resonance peak can blue shift nonlinearly with increasing wall thickness, but red shifts linearly with the increase of the length of the pentagonal gold nanotube. The localized electric field analysis reveals that the longitudinal plasmon peak of the pentagonal gold nanotube originates from the dipole resonance mode. The local electric field intensity is controlled by the wall thickness and length. Notably, the effect of wall thickness on the longitudinal plasmon resonance and electric field enhancement can be attributed to the change of the plasmon coupling position and intensity. This work has enriched the theoretical research of pentagonal gold nanotubes and provided ideas for the preparation of high sensitivity nanoprobes biosensors.

Excitations of Multiple Fano Resonances Based on Permittivity-Asymmetric Dielectric Meta-Surfaces for Nano-Sensors

We have designed an all-dielectric device based on permittivity-asymmetric rectangular blocks on meta-surfaces, yielding multiple Fano resonances with high sensitivity and high figure of merit (FOM) in the near-infrared regime. By introducing different materials to break the permittivity-symmetry, three sharp Fano peaks are generated with high Q-factors arising from the interference between the sub-radiant modes and the magnetic dipole resonance modes. Combining the field distributions and the multipole decomposition in Cartesian coordinates, the resonance modes are analyzed to be magnetic quadrupoles (MQs) and magnetic dipoles (MDs). Furthermore, the dependence on materials and geometric parameters has been studied. The maximal sensitivity, FOM and Q-factor reach 394 nm&#x002F;RIU, 4925 and 14437, respectively. This proposed structure provides a good alternative to geometry-asymmetric meta-surface structures and may be used for multichannel sensing, nonlinear optical devices, and laser.

Highly sensitive refractive index sensor for detection of Hg2+ based on Fano-like resonance in metal–dielectric–metal meta-structure

We experimentally and theoretically investigate Fano-like resonance in a large-area Au/SiO2/Au nano-patches meta-structure, which originates from the coupling between Fabry–Perot resonance and magnetic dipole resonance modes. A highly sensitive refractive index sensor based on the lineshape analysis is obtained. The extracted wavelength shift with the amount of substance of Hg2+ changing from 10–3 pmol to 1 nmol has a linear dependence, and the sensitivity can reach to ultra-low limit of detection (LOD) as 10–3 pmol. This study may provide an approach for the development and modification in sensing.

Quadrupole resonator mode versus dipole one in photonic crystal ferrite circulators

We propose a photonic crystal circulator based on quadrupole resonance of a magnetized ferrite cylinder. This device consists of a T-junction composed by three waveguides in a two-dimensional photonic crystal with square lattice. The ferrite cylinder is placed in the center of the T-junction. The scattering matrix, analytical model and the numerically calculated frequency characteristics of the circulator for the central frequency 94.5 GHz are presented. This device is compared with the previously suggested T-type circulator based on the dipole resonance mode. In particular, we show that the use of the quadrupole resonance permits to reduce the necessary DC magnetic field in comparison with dipole mode case by six times and this is important at THz frequencies where the necessary field is excessively high. Besides, quadrupole resonance requires the higher diameter of the ferrite resonator. The ferrite cylinders are produced by a special technology, and higher dimensions lead to a better reproducibility of such elements. However, these advantages are achieved at the expense of higher insertion losses and lower bandwidth of the circulator.

Study on mode shifts of localized surface plasmon cavity in Ag nanowire tetramer

The interaction between noble metal nanowires can induce the local surface plasmonic resonance effect, thereby enhancing the distribution of electric field in the nanostructures, which is of very important significance in improving the fluorescence characteristics and enhancing the sensitivity of sensors. In this study, we design several types of tetramers based on precious metals Ag nanostructures, including cylindrical and prismatic Ag tetramers, and by changing the arrangement and the rotation angle of prism nanowires, we simulate the rotation-angle dependent electric field distribution and electric field intensity of &lt;i&gt;X&lt;/i&gt; component , and also discuss the physical mechanism of the relationship between the resonant peak position of absorption spectrum and the change of mode volume. The results show that in the Ag nanowires tetramer structure, the electric field in the cylindrical structure is not enhanced obviously, but the electric field in the prismatic structure is greatly enhanced, and an electric dipole resonance mode is produced in the gap between tetramers. The polarization of plasma resonant cavity revels that the morphology plays a decisive role in generating the hot spots, After changing both the combination mode of tetramer nanowires and the rotation angle of the four-prism, the local surface exciton resonance of the unrotated asymmetric tetramer structure is most ideal and has resonance intensity higher than the that of symmetrical four-prism structure. Therefore, our results provide a structural model and theoretical parameters for the enhancement of electric field intensity by local surface plasmon resonance effect.

Whispering-gallery mode resonance-assisted plasmonic sensing and switching in subwavelength nanostructures

Whispering-gallery modes (WGMs), confining the resonant photons in nanoscale volumes, have been known to exhibit high-quality factor and sensitivity for electromagnetic waves in the field of nanophotonics. Here, we numerically demonstrate that a metasurface, which consists of periodic arrays with concentrically hybrid rectangular-slot (RS) and circular-ring-aperture (CRA) unit cells, supports polarization-dependent plasmonic sensing and switching in the visible and near-infrared regions. In particular, it is shown that the magnetic plasmon-induced transparency (PIT) effect arises from the coupling between a wideband WGM resonance and a narrowband magnetic dipole resonance mode in the hybrid metasurface. It is of great interest to find that the resonance mode broadening and mode shift sensing can be realized by varying the polarization angle of incident light and the length of the RS structure, respectively. Moreover, a novel and easy-fabricated plasmonic switching can be implemented in the visible and near-infrared regions. By changing the inner radius of the CRA structure, we reveal that the operating wavelength of the plasmonic switching can be extended to the telecom O- or E-band with an optimal ON/OFF ratio being 18.35 dB. Our results provide a path toward designing compact and tunable PIT device and could expand the application range of subwavelength nanostructures to the realm of optical communications and information process.