Search Results (50)

Bessel beams occupy an important position in optical research due to their characteristics of long focal depth, self-healing ability, and diffraction-free propagation. Traditional methods for generating Bessel beams suffer from complexity, a large size, low uniformity, and limited NA. Metasurfaces are considered to be a new technology for the miniaturization of optical devices due to their ability to regulate optical fields at subwavelength scales flexibly. Here, we generated Bessel beams by a complex-amplitude (CA) metasurface. The polarization conversion efficiency was controlled by the geometric size, while the phase value from 0 to 2π was manipulated based on the Pancharatnam–Berry (PB) phase. This approach enabled precise control over the axial intensity distribution of the optical field, which facilitated the generation of sub-millimeter-scale Bessel beams. Axial light field control based on CA metasurfaces has great potential for applications in a variety of fields, such as particle manipulation, large-depth-of-field imaging, and laser processing. Full article

Millimeter-wave signals experience substantial path loss when penetrating common building materials, hindering seamless indoor coverage from outdoor networks. To address this limitation, we present the 28-GHz “Meta-Window”, a mass-producible, visible transparent device designed to enhance millimeter-wave signal focusing. Fabricated via metal sputtering and etching on a standard soda-lime glass substrate, the meta-window incorporates subwavelength metallic structures arranged in a rotating pattern based on the Pancharatnam–Berry phase principle, enabling 0–360$°$ phase control within the 25–32 GHz frequency band. A 210 mm × 210 mm prototype operating at 28 GHz was constructed using a 69 × 69 array of metasurface unit cells, leveraging planar electromagnetic lens principles. Experimental results demonstrate that the meta-window achieves greater than 20 dB signal focusing gain between 26 and 30 GHz, consistent with full-wave electromagnetic simulations, while maintaining up to 74.93% visible transmittance. This dual transparency—for both visible light and millimeter-wave frequencies—was further validated by a communication prototype system exhibiting a greater than 20 dB signal-to-noise ratio improvement and successful demodulation of a 64-QAM single-carrier signal (1 GHz bandwidth, 28 GHz) with an error vector magnitude of 4.11%. Moreover, cascading the meta-window with a reconfigurable reflecting metasurface antenna array facilitates large-angle beam steering; stable demodulation (error vector magnitude within 6.32%) was achieved within a ±40$°$ range using the same signal parameters. Compared to conventional transmissive metasurfaces, this approach leverages established glass manufacturing techniques and offers potential for direct building integration, providing a promising solution for improving millimeter-wave indoor penetration and coverage. Full article

Vector beams (VBs) with longitudinally varying polarization states provide a new dimension for light field manipulation, and promote the advancements of related areas such as optical metrology, longitudinal depth detection, and classical and quantum communications. In this study, we propose a half-wave plate dielectric metasurface based on a spatial partitioning method, realizing the longitudinal manipulation of the polarization states of higher-order Poincaré (HOP) beams by changing the elliptical polarization state of the incident light and selecting the appropriate propagation distances. The metasurface is composed of two sub-metasurfaces, and the two sets of a-Si:H meta-atoms are uniformly arranged on concentric rings of different radii with an equal interval. The propagation and Pancharatnam–Berry phases are utilized to construct the axicon and helical phase profiles. As a result, two sub-metasurfaces, respectively, generate the first- and second-order VBs with longitudinally varying polarization states. The polarization states of generated VBs correspond to points on different meridians of nth-order HOP spheres from the south pole to the north pole. The consistency between the theoretical and simulated results demonstrates the feasibility and practicability of the proposed method. This study provides an innovative strategy to extend the modulation of light fields from two-dimensional to three-dimensional space. Full article

The manipulation of electromagnetic waves using metasurfaces is important in areas such as stealth and communication. In this paper, we reported on the use of an element-based polarizer for the first step, which enables the incident electromagnetic waves to integrate into the cross-polarized waves with a relative bandwidth of 88% within 15–37.1 GHz. Then, an eight-element coding metasurface based on the Pancharatnam–Berry phase is presented for circular polarization anomalous reflection. The simulated values show that our work can achieve a high-efficiency (94%) and wide-angle (70°) anomalous reflection under normal incidence. The simulated values present good agreement with the experimental values. Our work reveals the ability to manipulate the waves and electromagnetic stealth. Full article

Delaying an electromagnetic (EM) wave pulse on a thin screen for a significant time before releasing it is highly desired in many applications, such as optical camouflage, information storage, and wave–matter interaction boosting. However, available approaches to achieve this goal either require thick and complex systems or suffer from low efficiencies and a short delay time. This paper proposes an ultra-thin meta-platform that can significantly delay an EM-wave pulse after reflection. Specifically, our meta-platform consists of three meta-surfaces integrated together, of which two are responsible for efficiently coupling incident EM-wave pulse into surface waves (SWs) and vice versa, and the third one supports SWs exhibiting significantly reduced group velocity. We employ theoretical model analyses, full-wave simulations, and microwave experiments to validate the proposed concept. Our experiments demonstrate a 13 ns delay of an EM pulse centered at 12.975 GHz, enabled by a λ/8-thick and 38-λ-long meta-device with an efficiency of 32% (or 70%) with (or without) material loss taken into account. A larger delay time can be enabled by devices with larger sizes considering that the SWs group velocity of our device can be further reduced via dispersion engineering. These findings establish a new road for delaying an EM-wave pulse with ultra-thin screens, which may lead to many promising applications in integration optics. Full article

A wideband polarization-insensitive bistatic radar cross-section (RCS) reduction design under linear and circular polarization incidence is proposed based on spherical-chessboard metasurfaces. A new metasurface element with wideband characteristics was designed, including a double split-ring structure, single-layer media, and metal board. In the proposed RCS-reduction design, the Pancharatnam–Berry (P-B) phase theory is applied with the designed metasurface element to realize phase distribution mimicking the low-scattering sphere, and thus realizing RCS reduction. In addition, the chessboard configuration is combined with spherical phase distribution to further improve the performance of monostatic and bistatic RCS reduction. Finally, the proposed RCS reduction design can not only realize wideband RCS reduction but also exhibit polarization-insensitive characteristics. It realized 10 dB monostatic and bistatic RCS reduction in a frequency band ranging from 8.5 to 21 GHz (84.8% relative bandwidth) under linear polarization (LP) and circular polarization (CP) incidence. The straightforward and efficient design method of the hybrid spherical chessboard can effectively avoid the complex and time-consuming optimization process in RCS-reduction design. Full article

Augmented reality overlays computer-generated virtual information onto real-world scenes, enhancing user interaction and perception. However, traditional augmented reality optical systems are usually large, bulky, and have limited optical performance. In this paper, we propose a novel compact monochrome reflective dielectric metalens visor with see-through properties, engineered using a periodic structure of spin-dependent supercells. The supercell, which is composed of staggered twin nanofins, provides spin-dependent destructive or constructive interference with different circularly polarized incidences. The design combines the principles of interference with the Pancharatnam–Berry phase to enhance reflection at a working wavelength of 650 nm while maintaining good transmission. Right circularly polarized light incident from the substrate side causes destructive interference, enabling the supercell to work in reflection mode, while left circularly polarized light causes constructive interference, enabling the supercell to work in transmission mode. Furthermore, the supercell-constructed metalens can achieve near-diffraction-limited reflective focusing and a broad diagonal field of view of approximately 96°. In addition, compared to transmissive metalens visors, the reflective design eliminates the need for a beam splitter, significantly reducing the size and weight of the system. Our work could facilitate the development of compact and lightweight imaging systems and provide valuable insights for augmented reality near-eye display applications. Full article

Metasurfaces can flexibly manipulate electromagnetic waves by engineering subwavelength structures, which have attracted enormous attention in holography, cloaking, and functional multiplexing. For structures with n-fold (n > 2) rotational symmetry, they have been utilized to realize broadband and high-efficiency wavefront manipulation with generalized Pancharatnam–Berry phase, whereas spin-selective wavefront manipulation is still a challenge limited by their symmetrical spin–orbit interactions. Here, we demonstrate the spin-selective wavefront manipulations with generalized Pancharatnam–Berry phase in the range of 560–660 nm with a metal–insulator–metal metasurface consisting of the chiral C3 logarithmic spiral nanostructures. As a proof of concept, two deflectors and a bifocal metalens are designed. This configuration may provide a platform for various applications in polarimetry, polarization-selective images, and nonlinear optical responses. Full article

Conventional chiral metasurfaces are constrained by predetermined functionalities and have limited versatility. To address these constraints, we propose a novel chirality-switchable terahertz (THz) metasurface with integrated heating control circuits tailored for spin-selective anomalous reflection, leveraging the phase-change material vanadium dioxide (VO₂). The reversible and abrupt insulator-to-metal phase transition feature of VO₂ is exploited to facilitate a chiral meta-atom with spin-selectivity capabilities. By employing the Pancharatnam–Berry phase principle, complete 2$\pi$ reflection phase coverage is achieved by adjusting the orientation of the chiral structure. At the resonant frequency of 0.137 THz, the designed metasurface achieves selective absorption of a circularly polarized wave corresponding to the state of the VO₂ patches. Concurrently, it reflects the circularly polarized wave of the opposite chirality anomalously at an angle of 28.4° while maintaining its handedness. This chirality-switchable THz metasurface exhibits promising potential across various applications, including wireless communication data capacity enlargement, polarization modulation, and chirality detection. Full article

Metasurfaces can realize the flexible manipulation of electromagnetic waves, which have the advantages of a low profile and low loss. In particular, the coding metasurface can flexibly manipulate electromagnetic waves through controllable sequence encoding of the coding units to achieve different functions. In this paper, a three-layer active coding metasurface is designed based on vanadium dioxide ($V{O}_2$), which has an excellent phase transition. For the designed unit cell, the top patterned layer is composed of two split square resonant rings (SSRRs), whose gaps are in opposite directions, and each SSRR is composed of gold and $V{O}_2$. When $V{O}_2$ changes from the dielectric state to the metal state, the resonant mode changes from microstrip resonance to LC resonance, correspondingly. According to the Pancharatnam-Berry (P-B) phase, the designed metasurface can actively control terahertz circularly polarized waves in the near field. The metasurface can manipulate the order of the generated orbital angular momentum (OAM) beams: when the dielectric $V{O}_2$ changes to metal $V{O}_2$, the order l of the OAM beams generated by the metasurface changes from −1 to −2, and the purity of the generated OAM beams is relatively high. It is expected to have important application values in terahertz wireless communication, radar, and other fields. Full article

The Pancharatnam–Berry (PB)-phase liquid crystal (LC) planar optical elements, featuring large apertures and a light weight, are emerging as the new generation optics. The primary method for fabricating large-aperture LC planar optical elements is through photo-alignment, utilizing polarization laser direct writing. However, conventional polarization direct writing suffers from an inertia-induced stopping step during splicing, leading to suboptimal optical effects. Here, we propose a novel highly efficient method for arbitrary polarization patterning, significantly reducing interface splicing errors in these optical elements. (We call it dynamic polarization patterning technology). This process involves simultaneous mobile splicing and real-time generation of different polarization patterns for exposure, eliminating the inertia-related splicing interruption. As a demonstration, we fabricated a lens with an aperture of approximately 1 cm within 30 min at 633 nm. Furthermore, we developed a 100% fill-factor lens array (3 × 3) with an element lens diameter of approximately 7 mm within 1.5 h at 532 nm. Their focal lengths were uniformly set at 30 cm, demonstrating superior convergence capabilities within their designated working wavelengths, alongside commendable performance in converging light across various other wavelengths. Our measurements confirmed the good focusing performance of these samples. The convergence spot size of the lens deviated by approximately 40% from the theoretical diffraction limit, whereas the lens array exhibited a deviation of around 30%. The dynamic polarization direct writing during uniform platform movement reduced splicing errors to a mere 100–200 nm. The enhancement in imaging quality can be primarily attributed to the innovative use of mobile polarization splicing exposure technology, coupled with the inherent self-smoothing properties of LC molecules. This synergy significantly mitigates the impact of seam diffraction interference. Full article

This paper introduces an innovative approach to integral volumetric imaging employing time and polarization multiplexing techniques to present volumetric three-dimensional images. Traditional integral volumetric imaging systems with a coarse lens array often face moiré pattern issues stemming from layered panel structures. In response, our proposed system utilizes a combination of time and polarization multiplexing to achieve two focal planes using a single display panel. Full article

Topological nature in different areas of physics and electronics has often been characterized and controlled through topological invariants depending on the global properties of the material. The validity of bulk–edge correspondence and symmetry-related topological invariants has been extended to non-Hermitian systems. Correspondingly, the value of geometric phases, such as the Pancharatnam–Berry or Zak phases, under the adiabatic quantum deformation process in the presence of non-Hermitian conditions, are now of significant interest. Here, we explicitly calculate the Zak phases of one-dimensional topological nanobeams that sustain guided-mode resonances, which lead to energy leakage to a continuum state. The retrieved Zak phases show as zero for trivial and as π for nontrivial photonic crystals, respectively, which ensures bulk–edge correspondence is still valid for certain non-Hermitian conditions. Full article

In recent years, the emergence of virtual reality (VR) and augmented reality (AR) has revolutionized the way we interact with the world, leading to significant advancements in 3D display technology. However, some of the currently employed 3D display techniques rely on stereoscopic 3D display method, which may lead to visual discomfort due to the vergence-accommodation conflict. To address this issue, several true 3D technologies have been proposed as alternatives, including multi-plane displays, holographic displays, super multi-view displays, and integrated imaging displays. In this review, we focus on planar liquid crystal (LC) devices for different types of true 3D display applications. Given the excellent optical performance of the LC devices, we believe that LC devices hold great potential for true 3D displays. Full article

Currently, vortex beams are extensively utilized in the information transmission and storage of communication systems due to their additional degree of freedom. However, traditional terahertz metasurfaces only focus on the generation of narrowband vortex beams in reflection or transmission mode, which is unbeneficial for practical applications. Here, we propose and design terahertz metasurface unit cells composed of anisotropic Z-shaped metal structures, two dielectric layers, and a VO₂ film layer. By utilizing the Pancharatnam–Berry phase theory, independent control of a full 2π phase over a wide frequency range can be achieved by rotating the unit cell. Moreover, the full-space mode (transmission and reflection) can also be implemented by utilizing the phase transition of VO₂ film. Based on the convolution operation, three different terahertz metasurfaces are created to generate vortex beams with different wavefronts in full-space, such as deflected vortex beams, focused vortex beams, and non-diffraction vortex beams. Additionally, the divergences of these vortex beams are also analyzed. Therefore, our designed metasurfaces are capable of efficiently shaping the wavefronts of broadband vortex beams in full-space, making them promising applications for long-distance transmission, high integration, and large capacity in 6G terahertz communications. Full article