Valley topological photonic crystals (TPCs), which are robust against local disorders and structural defects, have attracted great research interest, from theoretical verification to technical applications. However, previous works mostly focused on the robustness of topologically protected edge states and little attention was paid to the importance of the photonic bandgaps (PBGs), which hinders the implementation of various multifrequency functional topological photonic devices. Here, by systematically studying the relationship between the degree of symmetry breaking and the working bandwidth of the edge states, we present spoof surface plasmon polariton valley TPCs with broadband edge states and engineered PBGs, where the operation frequency is easy to adjust. Furthermore, by connecting valley TPCs operating at different frequencies, a broadband multifunctional frequency-dependent topological photonic device with selectively directional light transmission is fabricated and experimentally demonstrated, achieving the functions of wavelength division multiplexing and add–drop multiplexing. We provide an effective and insightful method for building multi-frequency topological photonic devices.

CaTiO₃是一种新兴的高温氧化物热电材料, 但多种元素掺杂对其微观结构与热电性能的影响规律尚不清晰。本研究采用水热法结合真空热压烧结分别制备了Cr、Nb、Eu、Dy、Ce与La六种不同元素掺杂的CaTiO₃多晶块体样品。Cr掺杂导致大量纳米级Cr相析出, 由于基体中施主元素含量过低, 功率因子严重损失, 其ZT仅为0.012(983 K)。Eu掺杂并未为基体提供施主载流子, 导致ZT提升不明显, 仅为0.141(1031 K)。Nb掺杂导致高热导的微米级Nb相析出, 热导率上升, 但基体中Nb含量较多为基体提供了载流子, 使其ZT有明显改善, 达到0.263(1013 K)。Dy、Ce与La掺杂则既提供载流子又作为点缺陷散射声子, 既提高了功率因子又降低了晶格热导率, 极大地提升了热电性能, ZT在1031 K分别达到0.357、0.398、0.329, 比纯CaTiO₃(0.096)分别提升了296%、342%、265%。其中, Dy掺杂的样品在整个温度测试范围内具有最低的晶格热导率和较高的功率因子, 通过调控Dy含量与晶界处富集第二相的含量, 可以解耦电和热传输性能, 有望刷新目前CaTiO₃的ZT记录。本研究揭示了多种元素掺杂条件下CaTiO₃的成分-结构-性能联系, 为其在高温热电领域的应用提供了理论支撑。

Colliding of two counter-propagating laser pulses is a widely used approach to create a laser field or intensity surge. We experimentally demonstrate broadband coherent terahertz (THz) radiation generation through the interaction of colliding laser pulses with gas plasma. The THz radiation has a dipole-like emission pattern perpendicular to the laser propagation direction with a detected peak electric field 1 order of magnitude higher than that by single pulse excitation. As a proof-of-concept demonstration, it provides a deep insight into the physical picture of laser–plasma interaction, exploits an important option to the promising plasma-based THz source, and may find more applications in THz nonlinear near-field imaging and spectroscopy.

Ultra-broadband, intense, coherent terahertz (THz) radiation can be generated, detected, and manipulated using laser-induced gas or liquid plasma as both the THz wave transmitter and detector, with a frequency coverage spanning across and beyond the whole “THz gap.” Such a research topic is termed “plasma-based THz wave photonics in gas and liquid phases.” In this paper, we review the most important experimental and theoretical works of the topic in the non-relativistic region with pump laser intensity below 1018W/cm2.

Wavelength-tunable dissipative solitons and amplifier similaritons have been obtained by inserting all-fiber Mach–Zehnder interferometer (MZI) filters with different free spectral ranges (FSRs) in a Yb-doped mode-locked fiber laser. The MZI filter is fabricated by splicing one segment of seven-core fiber (SCF) between two segments of single-mode fibers. The bandwidth of the filter depends on the FSR of the modulated interference curve and consequently depends on the tapered fiber diameter. Inserting MZI filters with bandwidths in a fiber laser and applying a tensile strain on the tapered SCF, both wavelength-tunable dissipative solitons and amplifier similaritons have been obtained.

High-performance terahertz (THz) devices with reconfigurable features are highly desirable in many promising THz applications. However, most of the existing reconfigurable THz elements are still limited to volatile responses, single functionality, and time-consuming multistep manufacturing procedures. In this paper, we report a lithography-free approach to create reconfigurable and nonvolatile THz components by exploring the reversible, nonvolatile, and continuous THz modulation capability of the phase change material Ge2Sb2Te5. As a proof of concept, THz gratings with significant Rayleigh anomalies and diffraction as well as ultrathin THz flat lenses with subwavelength and ultra-broadband focusing capabilities are designed and fabricated on ultrathin Ge2Sb2Te5 films using the presented photo-imprint strategy. Moreover, such a method can also be adopted to create more complex THz devices, such as Pancharatnam–Berry phase metasurfaces and grayscale holographic plates. With these findings, the proposed method will provide a promising solution to realize reconfigurable and nonvolatile THz elements.

Surface plasmons (SPs) are electromagnetic surface waves that propagate at the interface between a conductor and a dielectric. Due to their unique ability to concentrate light on two-dimensional platforms and produce very high local-field intensity, SPs have rapidly fueled a variety of fundamental advances and practical applications. In parallel, the development of metamaterials and metasurfaces has rapidly revolutionized the design concepts of traditional optical devices, fostering the exciting field of meta-optics. This review focuses on recent progress of meta-optics inspired SP devices, which are implemented by the careful design of subwavelength structures and the arrangement of their spatial distributions. Devices of general interest, including coupling devices, on-chip tailoring devices, and decoupling devices, as well as nascent SP applications empowered by sophisticated usage of meta-optics, are introduced and discussed.

太赫兹（THz）波由于其诸多独特的性质，有着广泛的应用前景。然而由于相关材料和器件的发展相对滞后，太赫兹技术在实际中的应用尚有诸多限制。超材料和超表面概念的提出，能够对太赫兹波的相位、振幅、偏振进行有效操控，为太赫兹技术的发展提供了许多新的思路。其重要的功能之一是依靠相位不连续将入射波反射到非镜面方向，即通称的广义斯涅尔定律。然而，此前报道的大多数异常反射装置的效率都相对较低，在实际应用中存在局限性。针对这一问题，文中提出了一种太赫兹超表面异常反射器，将法向入射光反射到 40° 方向且不改变其偏振，并从理论上阐述了提高效率的思路，且通过数值模拟展示其有效性。通过使用全介质材料构建超表面从而消除材料损耗，并利用不同布洛赫波的耦合以提供非局部响应，令器件的工作效率超过99%。此外，这一设计理念可以推广到偏振无关器件中，并且对其他类似的器件也有一定参考意义。这一工作有潜力被应用于太赫兹波激光器、太赫兹波腔谐振器等太赫兹波实际器件中。