In this paper, a beam-scanning seven-element microstrip quasi-Yagi-Uda antenna working at terahertz (THz) frequencies is presented. This antenna is printed on the surface of a silicon dioxide substrate. The directing elements are made from metal and extended to the length of the reflecting element by graphene. Metal and graphene strips are printed on the bottom of the dielectric substrate. The H-plane radiation pattern of the quasi-Yagi-Uda antenna can be deflected from −70° to 70° by controlling the bias voltage of graphene on the upper and lower substrate surfaces. The proposed antenna configuration has potential applications in THz beam scanning antennas.

Topological photonics has become a new and fascinating area in recent years, which enables electromagnetic waves to propagate with negligible backscattering and excellent robustness even when encountering sharp corners or defects. But the flexible tunability of edge and corner states is challenging once the topological photonic crystals (PhCs) have been fabricated. In this paper, we propose a new all-dielectric PhC with C₃ symmetry constructed by hexagonal array of petal-like aperture embedded in silicon background. The proposed configuration has much wider energy gap than its triangular counterpart, and hence is suitable for wideband and high-capacity applications. When the apertures are filled with liquid crystals (LCs), the topologically-protected edge and corner states can be regulated through changing the refractive index of the LCs under different bias voltages. Moreover, the robustness of topological protection of edge and corner states is further demonstrated. This is the first demonstration of LC based tunable valley higher-order photonic topological insulator. The tunability of the proposed topological PhCs may be beneficial for development of tunable optical waveguides, reconfigurable topological microcavities, and other intelligent topological optical/terahertz devices.

A wideband, low‐profile, and high‐gain antenna loaded with a dual‐layer metasurface is proposed in this study. The metasurface consists of two metallic layers printed on two dielectric layers, in which each metallic layer contains an array of square patch cells. The proposed antenna is fed by an aperture coupled layer under the metasurface. This design makes the antenna work at two different modes with different resonant frequencies close to each other, to enhance the bandwidth. To achieve the best bandwidth performance, a genetic algorithm is adopted to optimise the geometrical parameters of this antenna. This metasurface‐based antenna maintains a low profile of at 5 GHz, meanwhile yields wideband characteristics for both the impedance and gain bandwidth. The −10 dB impedance bandwidth of the proposed antenna is about 44% (4.08–6.38 GHz) and the 3 dB gain bandwidth reaches 45% (4.16–6.56 GHz) with a peak realised gain of 11.6 dBi. A prototype of the antenna is fabricated and the measured results demonstrate the authors’ design.

Topological valley transport in photonic crystals (PCs) has attracted great attention owing to its edge modes immune to backscattering. However, flexibly dynamically controlling and reconfiguring the pathway of the topological one-way propagation is still challenging. Here, we propose a tunable and programmable valley PC structure based on nematic liquid crystals (LCs). Inversion symmetry breaking and topological transition are implemented through controlling the relative permittivity of the LC cells. Topological protection of valley edge states and valley-locked beam splitting are demonstrated. Moreover, the LC-based PC can be discretized to a number of supercells, each of which can be coded with ‘0’ or ‘1’. The wave propagation pathway can be dynamically reconfigured by programming different coding patterns.

We constructed a uniaxial “form birefringence” metal that exhibits different dielectric polarizabilities along different optical axes as well as its supported optical anisotropy of surface plasmon polariton waves. The generated plasmonic index ellipsoid that exists in reciprocal space has been directly mapped and characterized in our experiment. The discovery of this anisotropic plasmonic metamaterial further completes analogy between artificial plasmonic metamaterials and conventional optical crystals, thereby providing opportunities to miniaturize myriad existing optical devices on-a-chip with plasmonics into nanometers scale.

Valley kink states and valley-polarized chiral edge states, whose topologically protected properties have great application potential in high-speed information processing and communication, have recently become important frontiers in topological photonics. However, valley photonic topological insulators mainly support single-type topological states through breaking lattice spatial symmetry. It remains difficult for different types of topological states to coexist in a specific photonic system. In this paper, we propose judiciously designed substrate-integrated topological photonic crystals (but without metal vias) with $C_3$ symmetry that can support valley kink states and valley-polarized chiral edge states in different waveguide channels. Via numerical simulations and measurements, we demonstrate the robust transmission of both valley kink states and valley-polarized chiral edge states through sharp corners and we show high-efficiency coupling between classical guided waves and topological waves. More importantly, we achieve smooth transitions between chiral and trivial edge states, trivial edge states and valley kink states, as well as valley kink states and valley-polarized chiral edge states by bridging different waveguide channels. Our proposed design is beneficial for interfacing with existing functional photonic waveguides or devices and opens up an alternative pathway for advanced planar integrated topological photonic systems with subwavelength thicknesses.