Electric Dipole Resonance Research Articles

Analogue of electromagnetically-induced transparency by toroidal dipole in a symmetry-breaking metamaterial

Analogue of electromagnetically-induced transparency (EIT) in metamaterials was typically based on the destructive interference between electric and magnetic dipolar resonances. In this work, a dipolar toroidal response is demonstrated by a plasmonic metamaterial composed of a ring and a disk. We theoretically demonstrate that the toroidal dipole can couple with the magnetic dipolar response (subradiant mode) and thus induce the EIT-like phenomenon by breaking the geometrical symmetry of the considered metamaterial. The result also shows a promising potential for applications of high-sensitivity resonant transmission associated with the intriguing toroidal moment.

Tunable lattice-induced transparent metasurface for dynamic terahertz wave modulation.

Tunable metasurfaces offer a promising avenue for dynamically modulating terahertz waves. Phase-change materials are crucial in this dynamic modulation, enabling precise and reversible control over the electromagnetic properties of the metasurfaces. In this study, we designed and experimentally fabricated a tunable lattice-induced transparent metasurface. This metasurface comprises two gold rod resonators exhibiting different periodic distributions, each supporting an electric dipole resonance at 2.03 THz and a surface lattice resonance at 1.51 THz, respectively. By combining these structures, we realize lattice-induced transparency. Simulation results show that the phase change of Ge2Sb2Te5 modulates these resonances, with the crystalline state significantly weakening their resonance strength intensity. The maximum modulation depth of the lattice-induced transparency peak can reach 44.4%. Experimental results of laser-induced GST phase changes confirm a modulation depth of 42.4%. This innovative metasurface design holds promise for applications in terahertz communication systems.

Enhanced light confinement in nonlocal resonant metasurfaces with weak multipolar scatterers

Stronger light confinement can be enabled by nanoantennas in the nanostructure and result in efficient control of the directionality of the scattering. We report on an observation of the well-pronounced multipolar resonances from nickel nanoantennas originating from collective effects. We show that the collective coupling of multipolar modes from weak scatterers can substantially enhance the electric dipole and quadrupole resonances. We also demonstrate the generalized lattice Kerker effect in this nanoantenna array. Resonant multipolar excitations within nickel nanoantenna arrays can significantly enhance phenomena such as magneto-optical effects, indicating promising potential for advanced applications in the field of nanophotonics and sensing.

A Mid-Infrared Perfect Metasurface Absorber with Tri-Band Broadband Scalability.

Metasurfaces have emerged as a unique group of two-dimensional ultra-compact subwavelength devices for perfect wave absorption due to their exceptional capabilities of light modulation. Nonetheless, achieving high absorption, particularly with multi-band broadband scalability for specialized scenarios, remains a challenge. As an example, the presence of atmospheric windows, as dictated by special gas molecules in different infrared regions, highly demands such scalable modulation abilities for multi-band absorption and filtration. Herein, by leveraging the hybrid effect of Fabry-Perot resonance, magnetic dipole resonance and electric dipole resonance, we achieved multi-broadband absorptivity in three prominent infrared atmospheric windows concurrently, with an average absorptivity of 87.6% in the short-wave infrared region (1.4-1.7 μm), 92.7% in the mid-wave infrared region (3.2-5 μm) and 92.4% in the long-wave infrared region (8-13 μm), respectively. The well-confirmed absorption spectra along with its adaptation to varied incident angles and polarization angles of radiations reveal great potential for fields like infrared imaging, photodetection and communication.

Observation of zero-transmission dip in a single-layer electric metamaterial with finite non-radiative loss

We propose a theory for realizing a zero-transmission dip in the transmission spectrum of a reflectionless single-layer metamaterial designed based on the Brewster effect by variably controlling the radiative loss of the metamaterial in response to the non-radiative loss. The radiative loss can be controlled while maintaining broadband zero reflection by varying the relationship between the orientation of the constituent meta-atoms and the incident electromagnetic fields. As a verification of the proposed theory, we design a reflectionless metamaterial by arranging meta-atoms that exhibit a simple electric dipole resonance in a two-dimensional lattice. The numerically calculated and experimentally measured transmission spectra of this metamaterial demonstrate that the radiative loss can be controlled by changing the arrangement of the meta-atoms without altering their structure, and that a zero-transmission dip can be observed for a certain arrangement of the meta-atoms. This study could lead to the development of material sensing, especially for lossy materials based on resonant metamaterials.

Bound state in the continuum and polarization-insensitive electric mirror in a low-contrast metasurface

High-contrast refractive indices are pivotal in dielectric metasurfaces for inducing various exotic phenomena, such as the bound state in the continuum (BIC) and electric mirror (EM). However, the limitations of high-index materials are adverse to practical applications, thus, low-contrast metasurfaces offering comparable performance are highly desired. Here, we present a low-contrast dielectric metasurface composed of radial anisotropic cylinders, which are SiO2 cylinders doped with a small amount of WS2. The cylinder exhibits unidirectional forward superscattering resulting from the overlap of the electric and magnetic dipole resonances. When a near-infrared plane wave incident normally, the metasurface consisting of the superscattering constituents manifests a polarization-insensitive EM. In contrast, when subjected to an in-plane incoming wave, the metasurface generates a symmetry-protected BIC characterized by an ultrahigh Q factor and nearly negligible out-of-plane energy radiation. Notably, the EM response of the metasurface exhibits robustness to deviation in the number and thickness of WS2 layers. Our work highlights the doping approach as an efficient strategy for designing low-contrast functional metasurfaces, thereby shedding new light on the potential applications in photonic integrated circuits and on-chip optical communication.

Highly tunable quasi-bound states in the continuum responses in subwavelength plasmonic-dielectric hybrid nanostructures

Here, we study the quasi-bound states in the continuum (Q-BIC) response in subwavelength hybrid nanostructures consisting of plasmonic antennas and subwavelength dielectric cavities. Among them, the plasmonic antennas are metal nanorods with electric dipole resonances, and the dielectric cavity is a nanodisk with an anapole mode. By reasonably adjusting the phase difference between the two modes, we can excite Q-BIC mode in the hybrid cavity. As the two modes involved in the construction of Q-BIC are on two separate structures, the Q-BIC of this hybrid nanostructure has great adjustability, and the quality factor of resonant mode can be increased several times. Our research enriches the generations of Q-BIC mode in subwavelength cavities, which may help to enhance light-matter interaction.

Active dual-control electromagnetically induced transparency analog in metal- vanadium dioxide-photosensitive silicon hybrid metamaterial

We investigate an active dual-control metamaterial leveraging electromagnetically induced transparency (EIT), exploiting near-field interactions between electric and magnetic dipole resonances. Our hybrid strip element, combining metal and vanadium dioxide, generates electric dipole resonance, while split-ring resonators integrating metal and photosensitive silicon induce magnetic dipole resonance. Simulations confirm coupling validity and demonstrate dynamic adjustability of EIT via temperature and light intensity changes. EIT modulation transitions between transparent and non-resonant states due to temperature fluctuations, or resonant states with varying light intensity. Temperature adjustments dominate when both factors are altered. Analysis via a coupled oscillator model reveals modulation of damping rates as the origin of disappearance curve variations. This innovative design enhances tunable EIT metamaterial versatility, with implications for high transmission ratios and adaptable slow-light effects in terahertz applications.

Triple-band transparency effect by multiple couplings based on toroidal dipole resonance

We explored multiple couplings properties in composite metastructure. One part is the asymmetric double rings, supporting the narrow toroidal dipole resonance, and the other component is an upright rod that excites the broad electric dipole resonance. When these two resonant modes coincide in the spectrum, dual-band plasmon induced transparency (PIT) behavior can be obtained, which is attributed to in-phase and out-of-phase couplings between the toroidal dipole and electric dipole modes. Meanwhile, the dual-band features will become a single PIT band by varying the rotation offset angle between the upper- and lower-rings. Moreover, by introducing lateral displacement of the rod with respect to the toroidal component, a triple-band PIT effect can be achieved. In particular, under a large lateral displacement, a broadband transparency window appears across a wavelength range greater than 120 nm, where the transmission exceeds 0.9. It is derived from the hybrid coupling between toroidal dipole, electric dipole and induced high-order resonance modes. The toroidal-based PIT metamaterials not only promote the understanding of toroidal dipole moment but also provide a positive reference for toroidal-based meta-devices.

Control of Quantized Spontaneous Emission from Single GaAs Quantum Dots Embedded in Huygens' Metasurfaces.

Advancements in photonic quantum information systems (QIS) have driven the development of high-brightness, on-demand, and indistinguishable semiconductor epitaxial quantum dots (QDs) as single photon sources. Strain-free, monodisperse, and spatially sparse local-droplet-etched (LDE) QDs have recently been demonstrated as a superior alternative to traditional Stranski-Krastanov QDs. However, integration of LDE QDs into nanophotonic architectures with the ability to scale to many interacting QDs is yet to be demonstrated. We present a potential solution by embedding isolated LDE GaAs QDs within an Al0.4Ga0.6As Huygens' metasurface with spectrally overlapping fundamental electric and magnetic dipolar resonances. We demonstrate for the first time a position- and size-independent, 1 order of magnitude increase in the collection efficiency and emission lifetime control for single-photon emission from LDE QDs embedded within the Huygens' metasurfaces. Our results represent a significant step toward leveraging the advantages of LDE QDs within nanophotonic architectures to meet the scalability demands of photonic QIS.

Unconventional Transverse Magneto‐Optical Kerr Effect in Cobalt Nanopillar Arrays

AbstractNovel magneto‐optical (MO) properties can be actualized through well‐designed nanostructures, greatly improving the application value of MO effects. As only p‐polarized light can generate transverse magneto‐optical Kerr effect (TMOKE) in traditional MO materials, it is quite challenging and valuable to effectuate TMOKE under s‐polarization incidence at optical frequencies. The constructed nanopillar structures in this work can realize a clear TMOKE under both s‐polarization and p‐polarization incidences, as proved by experiments and simulations. Under s‐polarized incident light with an elevation angle of 45°, electric dipole resonance (EDR) and electric quadrupole resonance (EQR) are excited, resulting in the significant enhancement of TMOKE (five orders of magnitude higher than for the planar Co film). The intensity of s‐polarized TMOKE shows an increase with the enhancing diameter and height of the nanopillar structure. The amplitude of p‐polarized TMOKE is also appreciably increased due to the excitation of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs). Moreover, the Fe and Ni nanopillars display similar reflectivity and s‐polarized TMOKE behaviors in simulations. The s‐polarized TMOKE is unexpectedly observed in ferromagnetic metals for the first time, which builds up a considerable platform for the development and application of novel MO phenomena.

SOI Based metasurface for broadband perfect reflection in visible spectrum

We propose modeling and design of a low-loss all-dielectric metasurface (DM), comprised of Silicon on Insulator (SiO2) substrate to demonstrate a perfect reflector in the visible spectrum. The proposed metasurface unit cell consists of V and W shapes arranged in a mirror image configuration, with nanometre-sized gaps (g) between them. A narrow peak with a nearly 100% reflectance and a broad perfect reflectance spectrum is observed within the visible region (400–700 nm) of the electromagnetic spectrum. The effective electromagnetic parameters were also analyzed for electric and magnetic dipole resonance. The electric and magnetic field distributions at the resonant wavelength were also analyzed for the proposed structure. By altering the gap region ‘g’, the thickness of the dielectric Silica layer (ts ), and the Si resonator (t m), the proposed structure exhibits tunable characteristics. We have successfully illustrated the consistent position of the scattering parameter’s response, regardless of the structure’s rotation, concluding the homogeneity of the designed structure across the entire visible spectrum. The all-DM exhibits a unique combination of features, including a distinct and wide reflectance spectrum as well as a tuned and enhanced electric field which makes it an ideal platform for the applications in filters, color printing, low-loss slow-light devices, and nonlinear optics.

Large and active circular dichroism in a photosensitive silicon based metasurface

Active circular dichroism (CD) is highly required for flexible polarization control in modern terahertz (THz) systems. In this work, we numerically achieve large and active CD in THz region by optically controlling photosensitive silicon in a gold/silicon hybrid cross-shape metasurface. At the incident angle of 75°, the proposed metasurface exhibits large CD. By tuning the conductivity of photosensitive silicon with an optical pump, the large CD (0.89) can be dynamically switched to 0.06 and the peak frequency is blue shifted around 0.09 THz. The simultaneous switching of CD strength and peak frequency is attributed to the variation of resonance modes between electric and magnetic dipole resonances. Our proposed active metasurface with dynamic CD has profound potential in the fields of reconfigurable THz devices.

Broadband forward-scattering of light by plasmonic balls: Role of multipolar interferences

Efficient and broadband forward-scattering is a property of prime importance for meta-atoms if they are to be used in self-assembled metasurfaces. Strong contenders include colloidal nanoresonators with tailored multipolar content to achieve proper interferences that suppress back-scattering. We consider dense plasmonic balls composed of more than a hundred silver nanoinclusions. Numerical simulations provide a full understanding of the role played by multipole moments in the scattering behavior. They are fabricated using emulsion drying and characterized optically. Strong and efficient forward-scattering is demonstrated over the entire visible range. Electric and magnetic dipole resonances of equal amplitude and phase are evidenced. Such plasmonic balls could be used as meta-atoms for bottom-up metasurface applications.

Label‐Free Imaging of Low‐Index Samples Using Substrate‐Enhanced Subwavelength‐Resolution Scattering Nanoscopy

AbstractThere is an increasing demand for label‐free imaging of subwavelength low‐index dielectric samples with high contrast and high sensitivity using a dark‐field optical microscope. However, subwavelength low‐index dielectric samples usually do not show strong Mie scattering resonance characteristics due to the weak light confining ability, which makes them difficult to clearly resolve under a traditional optical microscope. In this work, a fast, simple, and effective approach is proposed to enhance the optical response of subwavelength low‐index dielectric samples by using metallic substrate‐enhanced scattering nanoscopy. It is found that the high reflectance of a substrate can significantly enhance the electric dipole resonance of a SiO2 nanoparticle and the substrate‐nanoparticle interaction, which amplifies the scattering signal of the sample and improves the imaging contrast. Compared with the silica substrate, the Ag‐coated substrate can enhance the scattering intensity of a SiO2 nanoparticle up to 3.7 times under 540 nm wavelength illumination. Furthermore, label‐free stand‐alone 50‐nm‐radius SiO2 nanoparticles and ≈100‐nm‐thick bacterial capsules can be clearly observed when placed on Ag‐coated substrates under a conventional dark‐field optical microscope. The substrate‐enhanced subwavelength‐resolution scattering nanoscopy can enhance the scattering of low‐index subwavelength samples and benefit a significant application in biology, medical testing, and optical detection.

High performance selective light absorber based on nickel nanopillar array for photothermal conversion

Efficient absorption of solar radiation holds the key to photothermal utilization; however, realizing solar absorber designs with high absorption efficiency remains challenging. Herein, a nickel-based metamaterial selective solar absorber with a nanopillar array structure was proposed to realize nearly perfect optical absorption over a broad spectrum. The average absorbance is up to 96% in the 300–2033 nm wavelength range. Notably, a reasonably detailed analysis of the physical mechanism of the proposed absorber was performed in this paper, attributing the exceptional broadband absorption to the concurrent interaction with surface plasmon resonance, quarter-wavelength resonance, and electric dipole resonance. The absorption efficiency declines significantly when λ > 2.5 μm, with only 20% absorptivity at λ = 6 μm in the radiation-absorbing transition region. This decline is desirable, as it contributes to reducing the emissivity in the mid-infrared range and, therefore, prevents self-radiation. The results demonstrate that the selective absorber possesses the potential to capture solar energy within a broadband, while avoiding undesirable self-radiation, thereby enhancing the integral efficiency of the solar energy conversion system. Moreover, the absorption spectrum shows insensitivity to polarization and angle of incidence. The selective solar absorber proposed here offers excellent performance with a simple structure, showing great promise in the field of photothermal conversion.

Visible metasurface using an Sb[formula omitted]S[formula omitted] nanodisk structure for stretchable color application

Herein, we examine a tunable phase-change material (PCM) metasurface that features an active switchable optical response, facilitating the excitation of electric dipole resonances within the visible wavelength spectrum. The tunability of this metasurface is realized by combining a PCM with a flexible polydimethylsiloxane (PDMS) substrate exhibiting a two-dimensional configuration. By adjusting the mechanical strain of the PDMS substrate, we can actively influence the near-field interactions among the resonant dielectric components, resulting in a broad spectrum of color changes. Furthermore, the overall color spectrum of the reflected light can be dynamically switched through the Sb2S3 amorphous-to-crystalline transition. This study highlights the constraints of traditional solid dielectric designs and provides novel perspectives and approaches for the advancement of tunable optical materials and devices.

Forward and backward propagation guided-mode waves of electric dipole resonances in an h-BN metasurface

The generation of a backward propagation (BP) and forward propagation (FP) guided mode in a double ridge h-BN metasurface (DRM) is investigated. h-BN is a hyperbolic metamaterial with two Reststrahlen frequency bands (RBs). The incident wave can excite guided modes in DRM, where the Poynting vector parallel component of the FP mode is identical and the BP mode is opposite to that of the incident wave. Based on the optimized structure, the frequency range of the BP mode for TE waves was found near the type II hyperbolic band (HB II), while for TM waves, it was found in the gap between the range of HB I and HB II in h-BN. To comprehensively understand the physics underlying BP and FP modes, we present the electric and magnetic field intensities in DRM, the electric field profile of beam steering, and the radiated powers of multipole resonances. The electric dipole (ED) moment contributes most significantly to the FP and BP modes, with its power being much greater than that of other multipolar moment modes. A proportion of BP mode power and incident power decreases with increasing incident angle of TE waves. There are two peaks of the proportion with TM waves. The maximum proportion is near 75% ofTE waves and 16% ofTM waves. The DRM has shown promising potential in the field of sensors based on BP mode, with a sensitivity of 3.9675 µm/RIU of TE waves and 5.1479 µm/RIU of TM waves. These findings suggest that DRMs hold significant promise for the development of optical metasurfaces, optical switches, and high-performance sensors.

Polarization insensitive flexible ultra-broadband terahertz metamaterial absorber.

We propose a polarization insensitive, flexible ultra-broadband terahertz (THz) metamaterial absorber. It consists of a chromium composite resonator on the top, a polyimide (PI) dielectric layer in the middle, and a chromium substrate. The simulation results show that the absorption achieves more than 90% ultra-wideband absorption in the range of 1.92-4.34THz. The broadband absorption is produced by the combination of electric dipole resonance and magnetic resonance, as well as impedance matching with free space. Due to the rotational symmetry of the unit structure, the absorber is insensitive to polarization of the THz wave and has a larger range of incident angles. The total thickness of the absorber is only 13.4µm, showing highly flexible and excellent high-temperature resistance characteristics. Therefore, it has potential applications in THz wave stealth and electromagnetic shielding.

Lattice Mie resonances and emissivity enhancement in mid-infrared iron pyrite metasurfaces.

High-refractive-index antennas with characteristic dimensions comparable to wavelength have a remarkable ability to support pronounces electric and magnetic dipole resonances. Furthermore, periodic arrangements of such resonant antennas result in narrow and strong lattice resonances facilitated by the lattice. We design iron pyrite antennas operating in the mid-infrared spectral range due to the material's low-energy bandgap and high refractive index. We utilize Kirchhoff's law, stating that emissivity and absorptance are equal to each other in equilibrium, and we apply it to improve the thermal properties of the iron pyrite metasurface. Through the excitation of collective resonances and manipulation of the antenna lattice's period, we demonstrate our capacity to control emissivity peaks. These peaks stem from the resonant excitation of electric and magnetic dipoles within proximity to the Rayleigh anomalies. In the lattice of truncated-cone antennas, we observe Rabi splitting of electric and magnetic dipole lattice resonances originating from the antennas' broken symmetry. We demonstrate that the truncated-cone antenna lattices support strong out-of-plane magnetic dipole lattice resonances at oblique incidence. We show that the truncated-cone antennas, as opposed to disks or cones, facilitate a particularly strong resonance and bound state in the continuum at the normal incidence. Our work demonstrates the effective manipulation of emissivity peaks in iron pyrite metasurfaces through controlled lattice resonances and antenna design, offering promising avenues for mid-infrared spectral engineering.