Chiral nanostructures can enhance the weak inherent chiral effects of biomolecules and highlight the important roles in chiral detection. However, the design of the chiral nanostructures is challenged by extensive theoretical simulations and explorative experiments. Recently, Zheyu Fang’s group proposed a chiral nanostructure design method based on reinforcement learning, which can find out metallic chiral nanostructures with a sharp peak in circular dichroism spectra and enhance the chiral detection signals. This work envisions the powerful roles of artificial intelligence in nanophotonic designs.

Simultaneous wireless information and power transfer (SWIPT) architecture is commonly applied in wireless sensors or Internet of Things (IoT) devices, providing both wireless power sources and communication channels. However, the traditional SWIPT transmitter usually suffers from cross-talk distortion caused by the high peak-to-average power ratio of the input signal and the reduction of power amplifier efficiency. This paper proposes a SWIPT transmitting architecture based on an asynchronous space-time-coding digital metasurface (ASTCM). High-efficiency simultaneous transfer of information and power is achieved via energy distribution and information processing of the wireless monophonic signal reflected from the metasurface. We demonstrate the feasibility of the proposed method through theoretical derivations and experimental verification, which is therefore believed to have great potential in wireless communications and the IoT devices.

In this work, we apply the group representation theory to systematically study polarization singularities in the in-plane components of the electric fields supported by a planar electromagnetic (EM) resonator with generic rotation and reflection symmetries. We reveal the intrinsic connections between the symmetries and the topological features, i.e., the spatial configuration of the in-plane fields and the associated polarization singularities. The connections are substantiated by a simple relation that links the topological charges of the singularities and the symmetries of the resonator. To verify, a microwave planar resonator with the D8 group symmetries is designed and numerically simulated, which demonstrates the theoretical findings well. Our discussions can be applied to generic EM resonators working in a wide EM spectrum, such as circular antenna arrays, microring resonators, and photonic quasi-crystals, and provide a unique symmetry perspective on many effects in singular optics and topological photonics.

Metasurfaces are subwavelength structured thin films consisting of arrays of units that allow the control of polarization, phase, and amplitude of light over a subwavelength thickness. Recent developments in topological photonics have greatly broadened the horizon in designing metasurfaces for novel functional applications. In this review, we summarize recent progress in the research field of topological metasurfaces, first from the perspectives of passive and active in the classical regime, and then in the quantum regime. More specifically, we begin by examining the passive topological phenomena in two-dimensional photonic systems, including both time-reversal broken systems and time-reversal preserved systems. Subsequently, we discuss the cutting-edge studies of active topological metasurfaces, including nonlinear topological metasurfaces and reconfigurable topological metasurfaces. After overviewing topological metasurfaces in the classical regime, we show how they could provide a new platform for quantum information and quantum many-body physics. Finally, we conclude and describe some challenges and future directions of this fast-evolving field.

Although tremendous efforts have been devoted to investigating planar single-conductor circuits, it remains challenging to provide tight confinement of electromagnetic field and compatibility with active semi-conductor components such as amplifier, harmonic generator and mixers. Single-conductor spoof surface plasmon polariton (SSPP) structure, which is one of the most promising planar single-conductor transmission media due to the outstanding field confinement, still suffers from the difficulty in integrating with the active semi-conductor components. In this paper, a new kind of odd-mode-metachannel (OMM) that can support odd-mode SSPPs is proposed to perform as the fundamental transmission channel of the single-conductor systems. By introducing zigzag decoration, the OMM can strengthen the field confinement and broaden the bandwidth of odd-mode SSPPs simultaneously. More importantly, the active semi-conductor amplifier chip integration is achieved by utilizing the intrinsic potential difference on OMM, which breaks the major obstacle in implementing the single-conductor systems. As an instance, an amplifier is successfully integrated on the single-conductor OMM, which can realize both loss compensation and signal amplification. Meanwhile, the merits of OMM including crosstalk suppression, low radar cross section (RCS), and flexibility are comprehensively demonstrated. Hence, the proposed OMM and its capability to integrate with the active semi-conductor components may provide a new avenue to future single-conductor conformal systems and smart skins.Although tremendous efforts have been devoted to investigating planar single-conductor circuits, it remains challenging to provide tight confinement of electromagnetic field and compatibility with active semi-conductor components such as amplifier, harmonic generator and mixers. Single-conductor spoof surface plasmon polariton (SSPP) structure, which is one of the most promising planar single-conductor transmission media due to the outstanding field confinement, still suffers from the difficulty in integrating with the active semi-conductor components. In this paper, a new kind of odd-mode-metachannel (OMM) that can support odd-mode SSPPs is proposed to perform as the fundamental transmission channel of the single-conductor systems. By introducing zigzag decoration, the OMM can strengthen the field confinement and broaden the bandwidth of odd-mode SSPPs simultaneously. More importantly, the active semi-conductor amplifier chip integration is achieved by utilizing the intrinsic potential difference on OMM, which breaks the major obstacle in implementing the single-conductor systems. As an instance, an amplifier is successfully integrated on the single-conductor OMM, which can realize both loss compensation and signal amplification. Meanwhile, the merits of OMM including crosstalk suppression, low radar cross section (RCS), and flexibility are comprehensively demonstrated. Hence, the proposed OMM and its capability to integrate with the active semi-conductor components may provide a new avenue to future single-conductor conformal systems and smart skins.

Controlling energy flow in waveguides has attractive potential in integrated devices from radio frequencies to optical bands. Due to the spin-orbit coupling, the mirror symmetry will be broken, and the handedness of the near-field source will determine the direction of energy transport. Compared with well-established theories about spin-momentum locking, experimental visualization of unidirectional coupling is usually challenging due to the lack of generic chiral sources and the strict environmental requirement. In this work, we design a broadband near-field chiral source in the microwave band and discuss experimental details to visualize spin-momentum locking in three different metamaterial waveguides, including spoof surface plasmon polaritons, line waves, and valley topological insulators. The similarity of these edge waves relies on the abrupt sign change of intrinsic characteristics of two media across the interface. In addition to the development of experimental technology, the advantages and research status of interface waveguides are summarized, and perspectives on future research are presented to explore an avenue for designing controllable spin-sorting devices in the microwave band.

Programmable metasurfaces enable real-time control of electromagnetic waves in a digital coding manner, which are suitable for implementing time-domain metasurfaces with strong harmonic manipulation capabilities. However, the time-domain metasurfaces are usually realized by adopting the wired electrical control method, which is effective and robust, but there are still some limitations. Here, we propose a light-controllable time-domain digital coding metasurface consisting of a full-polarization dynamic metasurface and a high-speed photoelectric detection circuit, from which the microwave reflection spectra are manipulated by time-varying light signals with periodic phase modulations. As demonstrated, the light-controllable time-domain digital coding metasurface is illuminated by the light signals with two designed time-coding sequences. The measured results show that the metasurface can well generate symmetrical harmonics and white-noise-like spectra, respectively, under such cases in the reflected wave. The proposed light-controllable time-varying metasurface offers a planar interface to tailor and link microwaves with lights in the time domain, which could promote the development of photoelectric hybrid metasurfaces and related multiphysics applications.

For camouflage applications, the performance requirements for metamaterials in different electromagnetic spectra are usually contradictory, which makes it difficult to develop satisfactory design schemes with multispectral compatibility. Fortunately, empowered by machine learning, metamaterial design is no longer limited to directly solving Maxwell’s equations. The design schemes and experiences of metamaterials can be analyzed, summarized, and learned by computers, which will significantly improve the design efficiency for the sake of practical engineering applications. Here, we resort to the machine learning to solve the multispectral compatibility problem of metamaterials and demonstrate the design of a new metafilm with multiple mechanisms that can realize small microwave scattering, low infrared emissivity, and visible transparency simultaneously using a multilayer backpropagation neural network. The rapid evolution of structural design is realized by establishing a mapping between spectral curves and structural parameters. By training the network with different materials, the designed network is more adaptable. Through simulations and experimental verifications, the designed architecture has good accuracy and robustness. This paper provides a facile method for fast designs of multispectral metafilms that can find wide applications in satellite solar panels, aircraft windows, and others.