Liang Wu

Conventional C ₂ ‐symmetric metasurfaces supporting symmetry‐protected bound states in the continuum (SP‐BICs) are often hindered by sensitivity to fabrication errors. Here, we demonstrate that for metasurfaces composed of resonant dimers possessing local inversion symmetry, the SP‐BIC mode remains robustly sustained at the Γ ‐point as long as in‐plane mirror symmetry is preserved, even if the dimers undergo spatial displacement within the lattice that breaks global periodic inversion symmetry. This characteristic endows the design with a unique offset‐robustness, significantly relaxing the stringent requirements for fabrication precision. Build on this, we introduce an asymmetry parameter ( α ) to break the mirror symmetry (and consequently the local inversion symmetry), enabling the transformation of the BIC into a quasi‐BIC (QBIC). Experimental and simulation results show that the radiative loss of the QBIC can be tuned via α , with the quality factor following a power‐law scaling of Q ∝ α ^−1.95 . Momentum‐space and near‐field analyses indicate that this transition is accompanied by the splitting of topological singularities and the breakdown of multipole interference equilibrium. This study demonstrates that local inversion symmetry is the physical origin of BIC formation, whereas mirror symmetry ensures the critical tolerance to displacement, providing a theoretical basis and design approach for high‐performance, process‐tolerant terahertz photonic devices.

Chiral metasurface is an important platform for engineering circular dichroism and optical activity. Thanks to the unprecedented capabilities of optical metasurfaces for light‐field control, metalenses enable the achievement of various desired functions. In this paper, we propose and experimentally demonstrate a chiral metalens based on a full‐phase modulated approach to realize subwavelength‐resolution terahertz holography. The all‐dielectric chiral metalens is composed of metamolecules consisting of two different sub‐meta‐atoms. Destructive and constructive interference are induced through phase control of the transmission amplitude and phase of two sub‐meta‐atoms under the incidence of orthogonal circularly polarized light beams, resulting in a considerable chiral effect. To achieve terahertz wavefront shaping, the geometric phase is introduced by rotating the azimuth angle of the sub‐meta‐atoms with the interference effect. Each focal point of the chiral metalens was employed as an individual hologram pixel, enabling subwavelength resolution in the chiral terahertz hologram. By independently controlling the position of each focal point, we successfully demonstrated chiral holographic imagery ranging from 2D to 3D patterns. Owing to its flexible design and ultrathin architecture, the chiral metalens holds great potential for integrated photonic systems, particularly in chiroptical spectroscopy, chiral imaging, and terahertz communications.

Terahertz holography plays an important role in modern information photonics. However, conventional methods suffer from large pixel sizes due to the wavelength diffraction limit and a complex setup to generate holograms. Thanks to the unprecedented capability of metasurfaces in light control, here a metalens holography is proposed and experimentally demonstrated that can realize a subwavelength‐resolution hologram with both an arbitrary curved trajectory and customized polarization structures in the terahertz regime. The all‐dielectric multi‐foci metalenses, with the combination of geometric and propagation phase approaches, are exploited for fine control of the cross‐polarization and co‐polarization of the incident circularly polarized beam. By separate manipulation of the two orthogonally polarized wavefronts, the spatial position and polarization state of every focal point can be controlled independently. By using every focal point of the metalens as the pixel unit, the typical terahertz holograms of 2D ring, Archimedes spiral, and 3D knot curved trajectories with various customized polarization structures are performed with good agreement between the experimental and simulations. The meta‐holographic sub‐wavelength resolution surpasses the wavelength diffraction limitation imposed by conventional holography, holding the promising application for super‐resolution terahertz imaging and high‐definition communication.

Despite significant advancements in terahertz (THz) generation and detection technologies, the practical deployment of portable THz systems remains constrained by existing modulator limitations, particularly stringent temperature requirements, inefficient thermal management, and high power consumption. Here, we demonstrate a breakthrough in magnetically controlled THz modulation using a CoFe2O4/MgO/F-Mica composite structure. The tunable optical response and dielectric properties of the composite under varying magnetic fields were systematically investigated via THz time-domain spectroscopy. Experimental results revealed a magnetic field-dependent THz transmission attenuation, with systematic suppression of transmission spectra proportional to the applied magnetic field intensity. A theoretical model accounting for external magnetic field variations was proposed, which agrees well with the experimental results regarding the imaginary component. Remarkably, the composite material realizes phase modulation simultaneously under magnetic field. This exceptional magnetic responsiveness significantly broadens the application potential of ferrites in the THz regime. These findings provide critical insights for designing tunable multifunctional THz magnetic devices in 6G communications, medical diagnostics, and nondestructive testing applications.

Terahertz vortex beams, carrying orbital angular momentum (OAM), are quite desirable for enhancing data transmission capability in telecommunication. However, it faces fundamental and technical challenges in a single metasurface to simultaneously generate orthogonal basis vortices with linear polarization ( x ‐ and y ‐polarity) and circular polarization (left‐ and right‐handed polarity) under the orthogonal polarized light incident. Here, we proposed a chip‐integrated all‐dielectric metasurface in the terahertz regime, to demonstrate the simultaneous generation of four‐channel orthogonal polarized vortex beams at various topological charges under the x ‐ and y ‐polarized light incident. The polarization multiplexed metasurface was designed only with a propagation phase strategy, consisting of polarization‐maintaining and polarization‐conversion meta‐atoms. Simultaneous control of polarization and topological charges in vortex beams was realized by properly arranging birefringent meta‐atom arrays to induce additional phases of x ‐ and y ‐polarization as customized, showing more degrees of freedom for carrying information. The experimental results are in good agreement with the simulations. Such a metasurface approach provides complete polarization bases for further synthesis of diverse polarization vortices required for huge‐capacity communication.

Advances in wireless communication systems require multifunction‐integrated optical devices to increase information capacities. However, the wavefront‐shaping metasurfaces thus far face challenges in manipulating orthogonal polarization independently and achieving versatile wavefront shaping simultaneously. Here, the scheme of chip‐integrated multi‐section metalens geometries is proposed to operate simultaneously with efficient focusing, orthogonal polarization manipulation, and vortex beam generation. Two spin decoupling metasurfaces are prepared to implement four‐channel terahertz wavefront shaping. It can independently engineer the co‐polarized and cross‐polarized components conversion under circularly polarized incidence. One metasurface realizes the polarization conversion in four independent channels under either left‐ or right‐handed circular incidence. The other achieves different spin‐to‐orbit conversions to generate vortex beams with independent polarization manipulation in four channels. The results suggest promising applications for high‐capacity and high‐security terahertz communication.

As we know, valley-Hall kink states or pseudospin helical edge states are excited by polarized-momentum-locking [left-handed circular polarization (LCP) and right-handed circular polarization (RCP)] because the valley-Hall kink modes or pseudospin polarized modes have intrinsic and local chirality, which is difficult for these states to achieve phase modulation. Here we theoretically design and study a compatible topological photonic system with coexistence of photonic quantum Hall phase and pseudospin Hall phase, which is composed of gyromagnetic photonic crystals with a deformed honeycomb lattice containing six cylinders. A typical kind of hybrid topological waveguide states with pseudospin-characteristic, magnetic field-dependent, and strong robustness against backscattering and perfect electric conductor (PEC) is realized in the present system. Furthermore, we re-design a structure with intersection-liked, achieve splitting for one-way pseudospin quantum Hall edge states by using phase modulation. Robustness of the one-way pseudospin-quantum Hall edge states in splitting has been demonstrated as well. Additionally, PEC inserted in transport channel brings optical path difference in waveguide transmission, which would influence splitting for hybrid topological waveguide states in phase difference modulation. This work not only provides a new way for manipulation (i.e., phase modulation) of hybrid topological waveguide states in compatible topological photonic system from distinct topological classes but also has potential in various applications, such as sensing, signal processing, and on-chip communications.

Recently, the rapid progress of deep learning techniques has brought unprecedented transformations and innovations across various fields. While neural network-based approaches can effectively encode data and detect underlying patterns of features, the diverse formats and compositions of data in different fields pose challenges in effectively utilizing these data, especially for certain research fields in the early stages of integrating deep learning. Therefore, it is crucial to find more efficient ways to utilize existing datasets. Here, we demonstrate that the predictive accuracy of the network can be improved dramatically by simply adding supplementary multi-frequency inputs to the existing dataset in the target spectrum predicting process. This design methodology paves the way for interdisciplinary research and applications at the interface of deep learning and other fields, such as photonics, composite material design, and biological medicine.