Metallic Resonators Research Articles

Strong Light-Matter Coupling in Lead Halide Perovskite Quantum Dot Solids.

Strong coupling between lead halide perovskite materials and optical resonators enables both polaritonic control of the photophysical properties of these emerging semiconductors and the observation of fundamental physical phenomena. However, the difficulty in achieving optical-quality perovskite quantum dot (PQD) films showing well-defined excitonic transitions has prevented the study of strong light-matter coupling in these materials, central to the field of optoelectronics. Herein we demonstrate the formation at room temperature of multiple cavity exciton-polaritons in metallic resonators embedding highly transparent Cesium Lead Bromide quantum dot (CsPbBr3-QD) solids, revealed by a significant reconfiguration of the absorption and emission properties of the system. Our results indicate that the effects of biexciton interaction or large polaron formation, frequently invoked to explain the properties of PQDs, are seemingly absent or compensated by other more conspicuous effects in the CsPbBr3-QD optical cavity. We observe that strong coupling enables a significant reduction of the photoemission line width, as well as the ultrafast modulation of the optical absorption, controllable by means of the excitation fluence. We find that the interplay of the polariton states with the large dark state reservoir plays a decisive role in determining the dynamics of the emission and transient absorption properties of the hybridized light-quantum dot solid system. Our results should serve as the basis for future investigations of PQD solids as polaritonic materials.

Design of a Dual‐Band Waveform‐Selective Metasurface Absorber Based on the Combination of Two Resonator Structures Loaded with Nonlinear Circuits

AbstractIn this paper, a design scheme for a dual‐band waveform‐selective metasurface absorber (MSA) is presented based on the combination of two metal resonator structures loaded with nonlinear circuits. Dual‐band MSAs with four different configurations are constructed by loading capacitor/inductor‐based nonlinear circuits into the gaps of two square‐patch (SP) and two square‐ring (SR) resonators, all of which can achieve selective absorption of short pulses and continuous waves (CWs) at two frequencies independently. As a typical example, the dual‐band MSA with the SP resonator loaded with the inductor‐based nonlinear circuit and the SR resonator loaded with the capacitor‐based nonlinear circuit is systematically studied. First, the selective absorption performance of the dual‐band MSA for CWs and pulses under different input powers is demonstrated. Second, the selective absorption properties of the dual‐band MSA for pulses with different pulse widths are studied. Third, the waveform‐selective absorption characteristics of the dual‐band MSA for oblique TE and TM waves are also illustrated. Finally, the influence of circuit component parameters on the selective absorption properties of pulses and CWs is systematically studied. The proposed dual‐band MSAs have potential application areas such as antenna design, wireless communications, and electromagnetic compatibility.

Energy efficient microwave curing of carbon fiber reinforced polymer via metamaterial matching and advanced electromagnetic exposure control

Abstract This study proposed an effective and sustainable technique for the curing of carbon fiber reinforced polymers (CFRPs) using microwaves. The method involves applying a metallic resonance coating layer to envelop the CFRP composite’s surface. Next, the composite is positioned within a multi-mode cavity, which is used as an applicator, and is powered by four 250 W solid-state power amplifiers. To ensure precise control over the heating pattern and achieve uniform heating of the composite, a sophisticated control algorithm is developed. This algorithm can independently regulate the phase, power level, and frequency of each power amplifier. The experimental results confirm the effectiveness of this proposed approach in achieving precise control over the microwave-based curing process for CFRPs.

Bifunctional flexible metasurface based on graphene and vanadium dioxide for polarization conversion and absorption

A bifunctional flexible metasurface with high polarization conversion ratio (PCR) and absorptivity based on graphene and vanadium dioxide (VO2) is proposed in microwave band, which consists of metallic resonator with two VO2 films in the diagonal direction, graphene resistance film layer, two polyimide (PI) dielectric layers and copper ground plate. The proposed metasurface can be switched from a polarization converter to an absorber by employing insulator-to-metal transition in VO2, and the PCR and absorptivity are dynamically manipulated by the graphene. When the conductivity of VO2 (σvo2) is 10 S/m (room temperature) and the square resistance of graphene (Rg) is 900 Ω/sq., the metasurface becomes a broadband polarization converter with the PCR exceeding 90 % in 6.97–17.62 GHz and the corresponding relative bandwidth (RB) is 86.62 %. Once the temperature is high enough and VO2 is in its fully metallic state (σvo2 = 2 × 105 S/m and Rg = 30 Ω/sq), the metasurface efficiently absorbs normally incident electromagnetic (EM) waves in 13.33–19.47 GHz with the absorptivity exceeding 90 % (RB = 37.44 %). The influence of geometric and EM parameters and incident angles on its bifunctional features are also investigated. Moreover, the proposed metasurface exhibits polarization insensitivity under dual functions. The designed bifunctional metasurface is expected to be applied in the fields of wireless communication systems, radar and sonar systems and EM stealth technology.

Sculpting ultrastrong light-matter coupling through spatial matter structuring.

The central theme of cavity quantum electrodynamics is the coupling of a single optical mode with a single matter excitation, leading to a doublet of cavity polaritons which govern the optical properties of the coupled structure. Especially in the ultrastrong coupling regime, where the ratio of the vacuum Rabi frequency and the quasi-resonant carrier frequency of light, ΩR/ω c, approaches unity, the polariton doublet bridges a large spectral bandwidth 2ΩR, and further interactions with off-resonant light and matter modes may occur. The resulting multi-mode coupling has recently attracted attention owing to the additional degrees of freedom for designing light-matter coupled resonances, despite added complexity. Here, we experimentally implement a novel strategy to sculpt ultrastrong multi-mode coupling by tailoring the spatial overlap of multiple modes of planar metallic THz resonators and the cyclotron resonances of Landau-quantized two-dimensional electrons, on subwavelength scales. We show that similarly to the selection rules of classical optics, this allows us to suppress or enhance certain coupling pathways and to control the number of light-matter coupled modes, their octave-spanning frequency spectra, and their response to magnetic tuning. This offers novel pathways for controlling dissipation, tailoring quantum light sources, nonlinearities, correlations as well as entanglement in quantum information processing.

Dual-band terahertz reflective-mode metasurface for the wavefront manipulation of independent linear and circular polarization waves

Metasurfaces (MSs) are being extensively researched owing to their ability to modulate the polarization and wavefront of electromagnetic (EM) waves in a flexible manner, which usually offer significant advantages including ultra-thinness, low losses, and easy fabrication. However, conventional MSs typically operate well only with a single polarization. Here, we propose a novel design strategy for a terahertz (THz) reflective-mode MS that relies on a single unit-cell arrangement combining propagation phase and geometric phase. Our designed MS can achieve multiple wavefront manipulations in reflection mode, not limited to circular polarization (CP) transformation, but also enabling linear polarization (LP) conversion. The MS we propose consists of a periodic array of bilayered metal patterned resonator structures sandwiched by a dielectric substrate. The metallic resonator is made of the outer single-split-ring (SSR) and C-shaped slot (CSS), inner double-split-ring (DSR), and its complementary structure. With this design, the MS is capable of converting a LP wave to its orthogonal counterpart at lower frequency (f1=0.7THz) after reflection. Additionally, at higher frequency (f2=1.4THz), the proposed MS can also convert the right-handed CP (RCP) to left-handed CP (LCP) upon reflection or vice versa. The 2π phase full coverage of the orthogonal LP and CP waves can be achieved independently and simultaneously by adjusting the opening and orientation angles of the SSR based on propagation phase, and orientation angle of the DSR based on geometric phase. We numerically demonstrate beam deflection, planar focusing, and the vortex beam for both reflected orthogonal LP and CP waves with three representative MSs to provide proof of concept. These findings reveal the great potential for multifunctional devices for dual-polarization in imaging and communication systems.

Near-Perfect Infrared Transmission Based on Metallic Hole and Disk Coupling Array for Mid-Infrared Refractive Index Sensing

Nanostructured color filters, particularly those generated by the extraordinary optical transmission (EOT) resonance of metal–dielectric nanostructures, have been intensively studied over the past few decades. In this work, we propose a hybrid array composed of a hole array and a disk array with the same working period within the 3–14 μm mid-infrared band. Through numerical simulations, near-perfect transmission (more than 99%) and a narrower linewidth at some resonance wavelengths were achieved, which is vital for highly sensitive sensing applications. This superior performance is attributed to the surface plasmon coupling resonance between the hole and disk arrays. A high tunability of the near-perfect transmission peak with varying structural parameters, characteristics of sensitivity to the background refractive index, and angle independence were observed. We expect that this metallic hole and disk coupling array is promising for use in various applications, such as in plasmon biosensors for the high-sensitivity detection of biochemical substances.

A Dual Band 28/38 GHz Metamaterial Absorber for 5G Applications

A dual-band metamaterial absorber (MMA) for fifth-generation (5G) applications is discussed in this work. The suggested absorber works at frequency bands of 28 GHz and 38 GHz. The suggested MMA unit cell with a size of 5.8 mm × 5.8 mm (0.54 λ0 × 0.54 λ0 at 28 GHz) is designed on 1.5 mm (0.14 λ0) low-cost FR4 substrate and composed of two metallic ring resonators. The suggested MMA is investigated to validate its performance for different polarization for transverse electric (TE) and transverse magnetic (TM). Both normal and oblique angles are studied. The MMA has a simple structure with a compact size. Different parameters such as the currents, electric field distributions, and normalized impedance are studied. The array of 10 × 10 unit cells is utilized to verify the simulated outcomes. The suggested MMA is fabricated and tested, and its outcomes are compared to the simulated outcomes. The MMA is operated at dual bands 28/38 GHz with high absorption rates of 98 and 98.4%, respectively, under the normal incidence for both outcomes. A good matching between the two outcomes is observed, which supports the MMA for 5G applications.

Supercavity mode in a single metallic resonator

Bound states in the continuum are exotic nonradiating modes with very high quality factors enabling enhanced wave-matter interactions. While they typically require array-type of systems, versions of such states have been reported in single dielectric resonators, giving rise to suppressed scattering states termed supercavity modes. In this work, we experimentally demonstrate a supercavity mode in an all-metallic resonator open for probing by free-space microwaves. Our design exploits careful tailoring of the boundaries around the resonator, which supports an octupole mode fostering a significant increase in the quality factor. The main advantage of the resonator is its simplicity and robustness, and it may be utilized as a stand-alone unit for energy harvesting and sensing or as an element for advanced functional material designs.

Submicrometer optical frequency combs based on SPPs metallic multi-ring resonators

Optical frequency combs (OFCs) have great potential in communications, especially in dense wavelength-division multiplexing. However, the size of traditional OFCs based on conventional optical microcavities or dispersion fibers is at least tens of micrometers, far larger than that of nanoscale electronic chips. Therefore, reducing the size of OFCs to match electronic chips is of necessity. Here, for the first time to our knowledge, we introduce surface plasmon polaritons (SPPs) to the construction of OFCs to realize a miniature device. The thickness of our device is reduced below 1 μm. Though the presence of SPPs may induce ohmic and scattering loss, the threshold of the device is obtained as 9 μW, comparable to the conventional device. Interestingly, the response time is 13.2 ps, much faster than the optical counterparts. This work provides a feasible strategy for the miniaturization of OFCs.

Tri-band and high FOM THz metamaterial absorber for food/agricultural safety sensing applications

Multi-band based terahertz metamaterial absorber is of great importance in current research and applications because of its ability to achieve multi-band absorption of electromagnetic waves and multi-point matching of detection material information. In this paper, a three-band terahertz metamaterial absorber based on metal split-opening ring is proposed, which produces harp peaks with high Q values due to the resonant response of the metal resonator matched with the surface lattice resonance. By optimizing the structure parameters, the Q-factor is as high as 528 and the FOM value is 153.2, which is better than the FOM of the currently reported absorbers. The sensing performance of absorber as refractive index sensor and thickness sensor is studied, and the results show that it can be used for refractive index sensing and thickness sensing detection of analytes. Finally, five pesticides were simulated and tested. The maximum frequency shift of the absorber was 16ghz when the refractive index changed by 0.02 steps, which proved its ability to recognize different pesticides. The detection of proline solutions of 2–10 g/100 ml proves that the absorber could detect analytes with a refractive index difference of 0.003. These results show that the absorber has high sensitivity, high Q factor, ultra-high FOM, and polarization-insensitive characteristics, which can be used for detecting food/agricultural safety testing and other fields.

Photo‐Mediated Cascade Growth of Ag Nanocrystals in Flow Reactors for High‐Performance Flexible Transparent Electrodes

AbstractPhoto‐mediated synthesis wielding localized surface plasmon resonance (LSPR) of nanoscale metal is widely applied to sculpt silver (Ag) nanocrystals with controllable dimensions and morphologies. However, this photo‐mediated strategy remains underutilized owing to low efficiency and inferior quality in conventional batch reactors. Here, the effective synthesis of Ag nanocrystals is demonstrated via flow reactors and elucidates the photo‐mediated anisotropic growth mechanism. The investigation reveals that the intersection between excitation wavelengths and LSPR of Ag nanocrystals is a prerequisite for their growth. The final morphology is highly correlated with excitation wavelengths, which modulate the redox potential (reaction barrier) of Ag nanocrystals featuring distinct defective structures. Thus, by utilizing tandem‐connected flow reactors, size‐controllable Ag nanoplates can be yielded in a highly efficient cascade growth manner. In addition, composite conductive ink (submicron/nano‐Ag particles) is employed to create high‐performance flexible transparent electrodes. A sixfold conductivity enhancement especially under low sintering temperature (<80 °C), along with superior transmittance (over 90%), and distinguished cyclic durability (negligible resistance change over 1000 cycles) are achieved simultaneously. The study not only establishes comprehensive insights into the acquisition of well‐defined Ag nanocrystals in flow reactors but also ushers in enormous feasibility toward high‐performance and cost‐effective flexible electronics.

Optimized polarization-independent Chand-Bali nano-antenna for thermal IR energy harvesting

A novel, polarization-independent, wide-angle reception Chand-Bali nano-antenna is proposed. An adjoint-based optimization algorithm is used to create the same resonance at both linear polarizations of the incident radiation. The nano-antenna optimal parameters reveal that two hot spots with a strong field enhancement are created. These hot-spots could be integrated with metal–insulator–metal (MIM) diodes to form a rectenna for infrared (IR) energy harvesting. The metallic resonators allow for selecting several materials to facilitate the fabrication of the nano-antenna and the MIM diode. The Chand-Bali-based IR rectennas are investigated and simulations demonstrate an improvement of more than one order of magnitude in efficiency compared to ones using traditional nano-antennas.

A graphene-metal hybrid biosensor for SEIRA spectroscopy applications

Detecting the building blocks of all living organisms plays a vital role in medical diagnosis and biological research. Infrared (IR) spectroscopy is one of the techniques for detecting biomolecules, such as DNA, RNA, and lipids, through their vibrational fingerprints. IR spectroscopy provides biosensing by directly measuring changes in absorption spectra; however, nanometric-size molecules reveal a weak signal-to-noise ratio with IR light, which is a disadvantage for sensitive bio-detection. Surface-Enhanced Infrared Spectroscopy (SEIRA) based on different structures and materials has been widely used to overcome this problem. In this study, a SEIRA platform based on a hybrid graphene-metal nanoantenna array is designed by combining the enhanced sensitivity of graphene with its electrical tunability and strong-field enhancement with metallic structures. The plasmonic resonance of graphene nano-slit is dynamically tuned to detect fingerprints of protein monolayer at different frequencies. The same detection behavior has been statically demonstrated by metallic antennas. Our results indicate that the sensitivity of the SEIRA sensor platform is quite high due to the combination of graphene and metal hybrid structure compared to the metal resonator alone because of the strong light confinement in the graphene layer. The proposed biosensor can detect the Amid-I and Amid-II bonds, which create relatively strong vibrational fingerprints, as well as the Amide-III bond, which is a very weak bond of a monolayer protein-goat-mouse Immunoglobulin (IgG) protein. It can also be a very useful characterization tool for identifying the molecular fingerprints of unknown chemicals and molecules with its capability to span a large spectral range either dynamically or statically. The strong light absorption via metallic structures compensates for the large areal coverage of graphene sheets, which is quite a challenge for dynamic tuning in real applications.

Photocatalytic Water Splitting Driven by Surface Plasmon Resonance

AbstractSurface plasmon resonance (SPR) in metals results in unique optical properties and photoelectric functions, which are helpful for light harvesting in photocatalysis. Additionally, the plasmon‐associated charge transfer process gives a complementary platform to understand the charge dynamics at a fundamental level. This Review focused on the recent developments of water splitting by plasmonic metals/semiconductor photocatalysts. Firstly, the basic characteristics of SPR and the plasmon‐enhanced photocatalysis mechanisms including plasmon resonance energy transfer and interfacial charge transfer are introduced, highlighting the recent understanding of the plasmonic electron‐hole separation, distribution, and the reaction sites for water splitting. Then, advances in the strategies to improve the quantum efficiency of plasmon‐induced water splitting are summarized by considering modulation in metals, interface contacts, and bulk properties of semiconductors. Finally, we discuss future prospects in the development of high‐efficiency plasmonic metal/semiconductor photocatalysts for water splitting.

Terahertz metamaterials for biomolecule sensing based on symmetry-broken unit resonators

Terahertz waves have gained attention owing to their potential for various bio-applications, including broadband spectroscopy, imaging, and sensing. For development of practical applications in clinical fields, highly sensitive molecular detection is essential. Notably, the molecular sensitivity of optical sensing can be enhanced by utilizing localized electromagnetic waves in metallic optical resonators. In this study, we theoretically design terahertz (THz) metamaterial sensors based on the Fano resonance, enabling highly sensitive and selective molecular sensing without additional molecular labeling. The metamaterial sensors consisting of symmetry-broken unit resonators are designed to support Fano resonances with strongly localized electromagnetic waves through coupling of the resonators. The key concept behind the design is to match the Fano resonance with the characteristic resonance in the target molecules, leading to pronounced changes in the transmission spectra of THz waves through the metamaterial with the analytes. We numerically demonstrate the sensing performance by considering steroids as the target molecules and explain the sensing mechanism using both temporal coupled-mode theory and FDTD numerical simulations.

Anapole state revealed by cloaking metallic cylinders with split ring resonators

This paper proposes the experimental demonstration of an anapole-based cylindrical electromagnetic cloaking scheme. An anapole state is excited by arranging around a cylindrical metallic target vertical split-ring resonators, forming an equivalent surface admittance boundary condition able to suppress the scattering. Using Mie formalism and multipole scattering theory, we identify the actual reason behind the cloaking operation, characterizing the anapole condition by the scattering contributions from toroidal and electric dipole moments. Numerical results are verified using full-wave simulation softwares and subsequently validated with back-scattering measurements inside an anechoic chamber.

Near-field imaging and spectroscopy of terahertz resonators and metasurfaces [Invited

Terahertz (THz) metasurfaces have become a key platform for engineering light-matter interaction at THz frequencies. They have evolved from simple metallic resonator arrays into tunable and programmable devices, displaying ultrafast modulation rates and incorporating emerging quantum materials. The electrodynamics which govern metasurface operation can only be directly revealed at the scale of subwavelength individual metasurface elements, through sampling their evanescent fields. It requires near-field spectroscopy and imaging techniques to overcome the diffraction limit and provide spatial resolution down to the nanoscale. Through a series of case studies, this review provides an in-depth overview of recently developed THz near-field microscopy capabilities for research on metamaterials.

Visible light driven hydrogen generation and pollutant degradation with Au loaded 2D/2D heterojunctional nanocomposite of MoS2 and g-C3N4

The growing energy crises and accumulating organics in water have caused significant threats to the economy and environment in the current time. To minimize the impact of these problem, here we established a 2D/2D interaction between MoS2 and g-C3N4 through simple hydrothermal and calcination processes and was further loaded with Au nanoparticles. The visible light driven photocatalysis was arrived by splitting water and degrading hazardous pollutant in wastewater. The large surface to surface interaction exceedingly increased the charge transfer and separation for highly speedy photocatalysis. About 220 μmol H2 was available from 2Au/9MS/CN nanocomposite in 1 h which was 24.44 times higher than the amount available from bare g-C3N4. Further, all the photocatalysts delivered acceptable eradication activity for 2-chlorphenol and 68% pollutant was removed in 1 h. The highly accelerated photocatalysis with 2Au/9MS/CN nanocomposite is related to the extended visible light purchasing due to the surface plasmon resonance of the Au metal and enhanced charge separation arrived from the well-established 2D/2D heterojunction. We hope that this work will attract major attention of the researchers towards the preparation of dimension-matched 2D/2D heterojunctional nanocomposites for energy production and eradication of organics from water.

Tunable slow light device based on a graphene metasurface.

Slow light devices have significant applications in memory, switching, and quantum optics. However, the design and fabrication of slow light devices with large tunable group delay are still challenging. Here, a graphene-based slow light device that can electrically modulate the group delay of terahertz (THz) waves is proposed and experimentally demonstrated. The unit cell of the device consists of a U-shaped metal resonator and an Ω-shaped metal resonator, with three graphene ribbons embedded between the two resonators. Under electrical stimuli, a relatively high amplitude modulation depth of 74% is achieved and the maximum transmission amplitude is as high as 0.7 at the transmission peak of 0.6 THz. Most importantly, the maximum group delay variation reaches 5 ps at 0.76 THz and the maximum group delay amplitude is as high as 8.8 ps. The experiment shows good agreement with simulation. This study paves a new way for developing novel switchable nanophotonic devices and slow light devices.