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Spin-selective reflection metadevices are usually realized by using chiral metamirrors that can reflect one state of circularly polarized (CP) waves and restrain the other one. However, most of the chiral metamirrors only exhibit chirality in a narrow band, which may impede their potential applications. Here, we propose a Pancharatnam–Berry (PB) coding metasurface composed of the spin-decoupled elements to realize broadband spin-selective reflections with arbitrary wavefront manipulations. The spin-selective anomalous reflection is designed and measured to validate the performance of the proposed PB coding metasurface. Both simulation and experiment results show that the designated CP wave can be efficiently reflected without reversing the spin state, while at the same time, its orthogonally polarized wave is suppressed by random diffusion, in a broad band from 16 to 24 GHz. The results also reveal that the proposed PB coding metasurface has the chiral-like characteristics, even though it is composed of nonchiral meta-elements.

Information metasurfaces have attracted much attention in recent years due to the capability to link the physical world and information science. However, most of the current information metasurfaces are either phase-only coding or amplitude-only coding, limiting their functions and applications. Here, a broadband and programmable amplitude-phase-joint-coding (APJC) information metasurface is proposed and experimentally demonstrated, from which the phase and amplitude of reflected electromagnetic waves can be independently controlled by adjusting the bias voltage of PIN diode integrated in the meta-atom. In particular, the reflection amplitude can be continuously controlled from 0.1 to 0.9, and the reflection phase can be switched between two states with about 180° phase difference. Thus, the proposed metasurface is capable of realizing independent 1-bit or multibit amplitude coding and 1-bit phase coding, and both of them can be reprogrammed in real time in broad band from 8 to 13 GHz. The abilities of the programmable APJC information metasurface in manipulating the electromagnetic waves are demonstrated by both numerical simulations and experiments, including to suppress the sidelobes of scattering beam, generate the diffractive waves with arbitrary magnitudes, and so on. These results show unique advantages of APJC information metasurface in real-time independent controls of energy allocation and wavefront tailoring of the electromagnetic waves in a wide frequency band.

The development of chiral metasurfaces with spin-selective reflection or transmission provides a new way to control the circularly polarized (CP) waves. However, it is still a great challenge to independently manipulate the polarization, frequency, and phase of the spin-selective reflected waves in different operating bands, which may have potential applications in improving the data capacity of microwave and optical communication systems. Here, a dual-band chiral metasurface is proposed to generate gigantic intrinsic chirality with strong circular dichroism (CD) in two different frequency bands by piecing two typical mono-chiral units together. The polarization, frequency and phase of the spin-selective reflected waves can also be independently designed in the two operating bands by adjusting the configuration of the chiral unit structures. Based on the proposed chiral structures, a dual-band chiral metasurface with spin-selective anomalous reflections is designed and demonstrated by both simulations and experiments. The results show that the polarization of spin-selective reflected waves can be customized by selecting appreciate chiral structures, while the wavefront of the spin-selective reflected waves can be further controlled by designing their arrangement.

A leaky-wave antenna (LWA) is proposed on the basis of an ultrathin spoof surface plasmonic (SSP) waveguide, which can convert SSP waves into spatial multi-polarized radiation waves. The SSP waveguide is composed of a metallic strip line with periodic unit cells, and each unit consists of two orthogonally beveled slots. The feature of the single-conductor SSP waveguide determines that the leaky-wave radiation pattern is omnidirectional in the azimuth direction around LWA. Due to the design of orthogonally beveled slots, different polarized radiations can be achieved along the azimuth direction. Simulation results show that left-handed circularly polarized (LHCP), right-handed circularly polarized (RHCP), and linearly polarized (LP) radiations are achieved in different azimuth directions simultaneously, which are further validated by the experimental measurement. We also demonstrate a purely single polarized radiation by placing a metal reflector close to LWA, and the polarization is reconfigurable among LHCP, RHCP, and LP by mechanically rotating LWA.

A dual-mode ultrawideband (UWB) antenna is proposed in this communication. The proposed antenna is composed of a monopole and a dipole sharing the same structure, which is excited by a coplanar waveguide (CPW) in even mode and odd mode, respectively. To achieve this kind of excitation, we present a dual-mode feeding structure with high isolation. Because the field distributions for the odd and even modes in CPW are opposite, and far-field patterns radiated by the two modes are orthogonal, this antenna has high isolation between two feeding ports. Fabricated antennas are measured, and good agreement with the simulation results is observed. The achieved impedance bandwidths of 10 dB return loss are 2.8–20 GHz and 4.4–17.6 GHz, with the isolation of 15 dB over the entire operating bandwidth, making it a good candidate for UWB multiple-input-multiple-output applications.

We propose a supercompact and ultrawideband (UWB) bandpass filter for spoof surface plasmonic polariton (SSPP) mode. By using meander-line technology, the electrical size of the proposed SSPP structure is reduced dramatically, which is only about 1/4 of the traditional rectangular-groove structure with the same geometry. Based on the proposed SSPP structure, we construct a supercompact UWB bandpass filter working in the frequency range of 0.25–4.5 GHz, whose geometric size is only $87.5\times12.8$ mm2. The upper cutoff frequency of the passband can be controlled by changing the meander-line design of the SSPP unit, and the lower cutoff frequency of the passband is determined by the capacitive coupling of the feeding structure. Both the simulation and experimental results show that the UWB SSPP bandpass filter is centered at 2.4 GHz with an extremely wide relative bandwidth of 174%, whose electrical size is only $0.7\lambda \,\,\times 0.1\lambda $ at the central frequency.

Surface plasmon polaritons (SPPs) are interactions between incident electromagnetic waves and free electrons on the metal–dielectric interface in the optical regime. To mimic SPPs in the microwave frequency, spoof SPPs (SSPPs) on ultrathin and flexible corrugated metallic strips were proposed and designed, which also inherit the advantages of lightweight, conformal, low profile, and easy integration with the traditional microwave circuits. In this paper, we review the recent development of SSPPs, including the basic concept, design principle, and applications along with the development from unwieldy waveguides to ultrathin transmission lines. The design schemes from passive and active devices to SSPP systems are presented respectively. For the passive SSPP devices, the related applications including filters, splitters, combiners, couplers, topological SSPPs, and radiations introduced. For the active SSPP devices, from the perspectives of transmission and radiation, we present a series of active SSPP devices with diversity and flexibility, including filtering, amplification, attenuation, nonlinearity, and leaky-wave radiations. Finally, several microwave systems based on SSPPs are reported, showing their unique advantages. The future directions and potential applications of the ultra-thin SSPP structures in the microwave and millimeter-wave regions are discussed.

Nonlinear absorption is a significant topic in classic nonlinear sciences. Today, a growing interest in this area is drawn by increasingly severe interferences associated with strong microwaves. Although conventional absorbers may help mitigate the harmful effects, they unavoidably cause a huge loss to small useful signals. Here, a novel nonlinear absorbing metasurface is proposed targeting spatial waves. Based on an active nonlinear mechanism, the input impedance of the metasurface is highly dependent on the wave intensity. When the waves get stronger, the impedance-match between the meta-surface and free space is improved, so they are preferably allowed to enter the structure and be dissipated inside. A prototype is fabricated and measured in a microwave anechoic chamber, and its intriguing characteristics such as wide incident angle scope, dual polarizations, and wide instantaneous bandwidth are demonstrated, which are in good agreement with theoretical and simulated anticipations. With an ultralow profile and a simple direct-current-supplying strategy, the proposal can find potential applications in various scenarios to reinforce the protection of the weak against the strong. This work was supported by National Natural Science Foundation of China (61801117, 61722106, 61731010, 62071117), National Key Research and Development Program of China (2018YFA0701900, 2018YFA0701904, 2017YFA0700201, 2017YFA0700202, 2017YFA0700203), Fundamental Research Funds for the Central Universities (2242021R40009, 2242021R10109), International Cooperation and Exchange of National Natural Science Foundation of China (61761136007), the 111 Project (111-2-05), High Level Personnel Project of Jiangsu Province (JSSCBS20210098), Zhishan Young Scholar Program of Southeast University, and Zijin Scholar Program of Southeast University.

A leaky-wave antenna (LWA) based on reconfigurable spoof surface plasmon polaritons (SSPP) is proposed for beam scanning in the Ka band, which consists of a reconfigurable SSPP waveguide and a periodic array of metal rectangular split rings. Both numerical simulations and experimental measurements show that the reconfigurable SSPP-fed LWA has good performance in the frequency range from 25 to 30 GHz. Specifically, as the bias voltage changes from 0 to 15 V, we can achieve the maximum sweep range of 24° at a single frequency and 59° at multiple frequency points, respectively. Owing to the wide-angle beam-steering feature, as well as the field confinement and wavelength compression properties derived from the SSPP architecture, the proposed SSPP-fed LWA possesses great potential applications in the compact and miniaturized devices and systems of the Ka band.

A double-layer graphene hybrid system is proposed to investigate the multimode coupling at far-infrared frequencies. With the assistance of metallic grating, the upper- and lower-layer graphene sur...

A dual-band fixed-frequency beam-scanning leaky-wave antenna (LWA) based on a corrugated microstrip line (CML) has been proposed. The proposed CML includes a series of uniform grooves that are alternately loaded by capacitors and varactors. The unit cell of the CML supports two kinds of modes in two different frequency bands. In each band, the dispersion characteristics of the CML can be electronically tuned by changing the capacitance loaded in the unit cell. Therefore, by simply changing the bias voltage of the loaded varactor diodes in the CML, the surface impedance of the LWA is dynamically reconfigured, and moreover, the radiation beams of the LWA are electronically steerable at a fixed frequency in each band. The experimental results show that at 4.25 and 5.75 GHz, the designed dual-band LWA can electronically steer the radiation beams in the maximum range of 80° and 22°, respectively, by changing the bias voltage from 0 to 10 V.

Multimode interaction in nanostructures plays a significant role for enhancing light-matter interactions. Here we investigate the hybrid electromagnetic couplings among graphene sheet plasmons (GSP) and magnetic polaritons (MP) in a coupled multimode system theoretically. The results both from the finite element method and coupled oscillator model reveal that the superposition of the resonance peaks generated by plasmonic hybridization can achieve multispectral perfect absorption. The electromagnetic energy at different resonance frequencies can be selectively localized at different positions of the nanostructure on purpose, exhibiting unique energy-transfer characteristics. The GSP mode can interact with MP modes by dynamically tuning the chemical potential of graphene, resulting in two distinct Rabi splitting phenomena with mode splitting energies of 10.34 meV and 16.54 meV, respectively. The strong coupling between GSP and MP can lead to the formation of multiple hybrid modes. Moreover, we further study the coupled four-mode system from both theoretical and simulation aspects, indicating that the general characteristics of mode interaction can be applied to more complicated multi-mode coupled systems. The presented results should be useful for multimode interaction studies, and have potential applications in highly tunable graphene-based plasmonic devices, such as thermal emitters, detectors, optical switches, multiband absorbers, etc.

A planar wavefront transformation lens based on gradient-index metamaterials is proposed. The designed lens is composed of isotropic and inhomogeneous metamaterials and can reach impedance matching with free space. Based on the impedance-matching metamaterial lens, we present a compact high-gain and high-aperture-efficiency horn-based lens antenna working from 8 to 12 GHz. At the center working frequency of 10 GHz, the performance of the antenna is significantly improved and the measured gain increases to 17.7 dBi, which is 6.5 dBi higher than that of the original H-plane horn antenna. The half-power beamwidth and sidelobe level in the H-plane reduces to 6.2° and 15.3 dB, respectively, and the aperture efficiency reaches 94%. Such performance is much better than that of the conventional optimal H-plane horn antenna.

Huygens’ metasurfaces, which can tailor both electric and magnetic dipole resonances, have been draw widespread concern. Here, a three-dimensional Huygens’ metasurface holographic imaging with enhanced quality is designed whose thickness is only 0.033λ. The presented Huygens’ metasurface hologram may provide inspirations for the design of high-resolution imaging, ultrathin imaging device, security, and data storage.

An angle-insensitive bifunctional resonator composed of a compound silver grating is proposed. The resonator exhibits different response characteristics for TE and TM polarization, thus enabling two functions, corresponding to high-sensitivity sensor and low Q-factor absorber. For TE polarization, the Q-factor, refractive index sensitivity, and figure of merit of the resonator can reach 283.4, 2577.6 nm/RIU, and 181.5 RIU-1, respectively, due to the excitation of cavity mode resonance. For TM polarization, the resonator can be regarded as an absorber with high absorptivity (> 97%) based on magnetic resonance. This simple structure provides a good paradigm for designing high-performance multi-functional devices.

We theoretically investigate the hybrid coupling among graphene surface plasmons (GSP) and magnetic polaritons (MP) in a coupled three-mode system. Numerical results reveal that the superposition of the resonance peaks generated by plasmonic hybridization can achieve multispectral perfect absorption, and these results are verified by coupled oscillator model. The electromagnetic energy at different resonance frequencies can be selectively localized at different positions of the nanostructure. The GSP mode can interact with two MP modes by dynamically tuning the chemical potential of graphene, resulting in two distinct Rabi splitting phenomena with mode splitting energies of 10.3 meV and 16.5 meV, respectively. In particular, additional MP modes can be introduced by etching more slits with different depths in silver grating, which also leads to more spectral splitting and complicated mode coupling. The presented results should be useful for multimode interaction studies, and have potential applications in highly tunable graphene-based plasmonic devices.

We theoretically and numerically investigate the ligh-matter interaction in a classic topological photonic crystal (PhC) heterostructure, which consists of two opposite-facing 4-period PhCs spaced by a dielectric layer. Due to the excitation of topological edge mode (TEM) at the interface of the two PhCs, the strong coupling between incident light and TEM produces a high quality resonance peak, which can be applied to many optical devices. As a refractive index sensor, it achieves a sensitivity of 254.5 nm/RIU and a high figure of merit (> 250), which is superior to many previously reported sensors. We further study the coupling between photons and excitons by replacing the pure dielectric layer with the J-aggregates doped layer. By tuning the thickness of the doped layer and the angle of incident light, the dispersive TEM can efficiently interact with the molecular excitons to form a hybrid mode with TEM-like or exciton-like components, showing interesting energy transfer characteristics and flexible modulation characteristics. This work may be helpful for a better understanding of light-matter interactions in a topological PhC heterostructure, and achieve potential applications in related optical devices.

In this paper, a transmissive spin-decoupled metasurface to completely achieve independent phase control for two orthogonal helicities is proposed in the microwave region by incorporating propagation phase and geometric phase. The proposed metasurface breaks the inherent limitation encountered by conventional Pancharatnam-Berry (PB) metasurfaces, whose phase responses are locked to be opposite values for different circular-polarized (CP) wavefronts. One typical application for independently generating orbital angular momentum (OAM) vortices with different topological charges for different helicities is designed and simulated.

Vortex beams carrying orbital angular momentum (OAM) have recently attracted great interest due to their capability for providing a new method to increase the communication channels in wireless communications. It is expected that the unbounded eigenstates of OAM can bring a large number of channels to enhance the transmission capacity. Here, we propose an effective strategy to generate vortex beams by using spoof surface plasmon polaritons (SSPPs) in the microwave region. A periodically modulated SSPP ring resonator is applied to convert near-field SSPP waves into radiating a vector vortex beam. The emitted beam can possess different OAM modes at different frequencies through rational design. In addition, circularly polarized vortex beams are demonstrated. Both numerical simulations and experimental characterizations confirm the theoretical predictions. Owing to the deep subwavelength characteristic of SSPP, the proposed device can be readily integrated into miniaturized circuits and systems. We anticipate that our design will enable a wide range of applications for future wireless communication technologies.

We proposed a promising method to achieve phase modulation utilizing photonic crystal (PC). The broken parity and time-reversal symmetries induce intrinsic nonreciprocity. The supported one-way phase velocity which has a close relationship with biased magnetic field (BMF). Different from the most metasurfaces, only one structure is required to realize electromagnetic wave spatial distributions by adjusting each cell’s BMF. As an application, a deflector with only one column shows obviously nonreciprocity accompanied with magnetically tunable deflection angle. We further designed a flat lens and an axicon under different applied BMF distributions. Such phase modulation by PC provides a new flexible way to realize phase modulation, which can reduce difficulties in design and fabrication.

Strong interaction between electromagnetic radiation and matter leads to the formation of hybrid light-matter states, making a system’s absorption and emission properties distinctively different from that at the uncoupled states. For instance, strong coupling between cavity photons and quantum emitters results in the emergence of Rabi splitting andnew polaritonic eigenmodes, exhibiting characteristic spectral anticrossing and ultrafast energy exchange. There has recnetly been a rapidly increasing number of studies focusing on strong coupling between photonic nanostructures and two-dimensional materials (2DMs), demonstrating exceptional nanoscale optical properties and applications. Here, we review the recent advances and important developments of strong light-matter interactions in hybrid photonic systems based on 2DMs, including graphene, black phosphorus, and transition-metal dichalcogenides. We adopt the coupled oscillator model to describe the strong coupling phenomena and give an overview of three classes of 2DMs-based nanostructures realizing this regime. Following this, we discuss potential applications that can benefit from strong coupling induced effects and conclude our review with a perspective on the future of this rapidly emerging field.

We propose an active metasurface whose functionalities can be dynamically switched among linear-to-linear, linear-to-elliptical, and linear-to-circular polarization conversions in a wideband. The active metasurface is composed of butterfly-shaped unit cells embedded with voltage-controlled varactor diodes. By controlling the bias voltage of the varactor diodes, the electromagnetic responses of the proposed metasurface can be tailored, leading to reconfigurable polarization conversions. The simulation results reveal that with no bias voltage, the proposed metasurface is able to reflect linear-polarization waves to cross-polarization waves in the frequency range from 3.9 to 7.9 GHz, with a polarization conversion ratio of over 80%; however, at the bias voltage of −19 V, the metasurface is tuned to be a circular polarization converter in a wideband from 4.9 to 8.2 GHz. Moreover, two equivalent circuits along the $x$ - and $y$ -directions are developed to elucidate the tunable mechanism. The experimental results are in a good agreement with the simulation results obtained from commercial software and from the equivalent circuit model.