Single-layer Metasurface Research Articles

Ultrabroadband and >93% Microwave Absorption Enabled by "Doped" Water Meta-Atom Lattice with Subwavelength Thickness.

Perfect microwave absorbers, which absorb electromagnetic waves completely, play pivotal roles in electromagnetic shielding, and stealth technologies. Existing microwave absorber technologies rely on either electromagnetic properties of absorptive materials, the resonance behavior of meta-atoms, or a combination of both. So far, achieving simultaneous broadband absorption, high efficiency, and compact sizes remains a great challenge. Inspired by atomic doping techniques employed in conventional optical materials to broaden spectral bandwidths, a single-layer microfluidic metasurface microwave absorber is proposed with the assembly of two distinct types of water meta-atoms. By manipulating electromagnetic resonances of these water meta-atoms, the metasurface maintains impedance matching over a broad working range. A microwave absorber design with a thickness equivalent to 0.2 times the central wavelength is showcased, measuring over 93% absorption across both K and Ka bands (17.5-40.0GHz). The results highlight unprecedented superiorities of microwave absorbers based on a 2D doped water meta-atom lattice when compared to previously reported metasurface absorbers utilizing identical meta-atoms. This absorber has advantages including small thickness, broad bandwidth, and cost-effectiveness, making it promising for applications in electromagnetic shielding, camouflage, and multi-spectral stealth.

Design of a Single-Layer Ultrawideband Cross-Polarization Conversion Metasurface With High Efficiency

Design of a Single-Layer Ultrawideband Cross-Polarization Conversion Metasurface With High Efficiency

An ultra-broadband low profile modified chessboard metasurface with improved backscattering reduction

Building upon the concepts of polarization conversion and the mechanism of destructive interference, a single-layered ultra-broadband metasurface for radar cross-section (RCS) or backscattering reduction is proposed in this work. A diffusion-assisted checkerboard metasurface with re-tailored unit cells at the center leads to a significant improvement in the stealth characteristics. For this, a low profile and less complex unit cell is proposed, comprising a long metallic strip along the diagonal and two thin horizontal stubs at the edges. This unique arrangement exhibits more than 90% polarization conversion efficiency from 13.2 to 38.2 GHz. Modifying the geometry of central elements in a conventional checkerboard metasurface achieves a minimum of 15 dB RCS reduction from 10 to 38 GHz. Also, as we ascend the frequency spectrum, the beams are scattered in unintended directions with reduced signal strength. Notably, there is no beam in the boresight direction, as opposed to the conventional chessboard configurations. For off-normal incidences, the metasurface exhibits good angular stability, and a minimum of 10 dB backscattering reduction is maintained up to an incidence angle variation of 60°. The final optimized fabricated prototype exhibits measurement results that agree with the simulation results for normal and wide-angle incidences.

Design of short-focus near-eye optical system for virtual reality using polarization-insensitive metasurface

Near-eye optical systems, as an important component of virtual reality displays, have attracted great research interest recently. However, current systems have complex structures and face the design challenge of combining compact, short-focus design with wide field of view and high angular resolution. In this paper, we propose a short-focus near-eye optical system with wide field of view and high angular resolution, referred to as a meta-eyepiece, by patterning a single-layer polarization-insensitive metasurface on a substrate. The metasurface, featuring a quasi-periodic nanopillar arrangement, enables precise phase modulation and enhances design flexibility. The desired metaform phase can be obtained by modeling the light propagation of the meta-eyepiece to determine key design parameters, utilizing metaform phase polynomials, customizing the objective merit function and employing advanced optimization algorithms. Our system achieves a short focal length of approximately 22 mm with an 80° field of view, offering compactness superior to conventional virtual reality optics and a minimum resolvable angle less than 1.25 arcminutes, ensuring high angular resolution. It also exhibits excellent imaging performance with full-field modulation transfer function values exceeding 0.5 at 62.5 lp/mm. Although the initial system utilizes ray optics, the scaled version is validated for its feasibility and scalability through full-wave simulations. Our meta-eyepiece structure and design method show the potential of metasurfaces for applications in virtual reality, offering valuable support for technological development in this field.

Wavelength and spin-decoupled metasurface based on single-parameter modulation.

Metasurfaces provide an unprecedented platform for precise and subwavelength-scale modulation of optical phases, leading to innovative advancements in wavefront shaping and holography devices. This study presents a single-layer umbrella-like metasurface capable of multichannel holography, encoded with both polarization and wavelength. By leveraging a unique chiral-assisted strategy, we achieve simultaneous decoupling of wavelength and spin states through single-parameter modulation. This approach circumvents the complex structure designs and multi-parameter adjustments typically required in previous methods. Numerical simulations confirm the effectiveness of this metasurface, demonstrating wavelength- and spin-decoupled phase modulation at 1550 and 980 nm. Furthermore, we successfully demonstrate a four-channel hologram operable in both transmission and reflection modes, showcasing the potential applications of this metasurface in compact functional integration, information encryption, and 3D displays. This work paves the way for the development of multifunctional optical devices with enhanced integration and performance.

Metasurface-enabled non-orthogonal four-output polarization splitter for non-redundant full-Stokes imaging

Imaging polarimetry plays an essential role in various fields since it imparts rich information that cannot be obtained through mere intensity and spectral measurements. To retrieve full Stokes parameters, at least four sensor pixels are required, each of which projects incident light to a different polarization state in the Stokes space. Conventional full-Stokes division-of-focal-plane (DoFP) cameras realize this function by integrating angled polarizers and retarders on top of image sensors. Due to the inevitable absorption at the polarizers, however, the maximum efficiency of these schemes is limited to 50% in theory. Instead of polarizers, three sets of lossless polarization beam splitters can be used to achieve higher-efficiency polarimetry, however, at the cost of reduced spatial resolution due to the need for six redundant sensor pixels. In this paper, we reveal that low-loss four-output polarization splitting (without filtering) is possible using a single-layer dielectric metasurface. Although these four states are not orthogonal to each other, our metasurface enables simultaneous sorting and focusing onto four sensor pixels with an efficiency exceeding 50%. The designed metasurface composed of silicon nanoposts is fabricated to experimentally demonstrate complete retrieval of full Stokes parameters at a near-infrared wavelength range from 1500 to 1600 nm with −0.67-dB (85.8%) transmission and −2.28-dB (59.2%) overall efficiency. Finally, multi-pixel polarimetry is demonstrated using a 3×4 superpixel array.

Multiwavelength Achromatic Deflector in the Visible Using a Single-Layer Freeform Metasurface.

Deflectors are essential for modulating beam direction in optical systems but often face form factor issues or chromatic aberration with conventional optical elements, such as prisms, mirrors, and diffractive/holographic optical elements. Despite recent efforts to address such issues using metasurfaces, their practicality remains limited due to operation wavelengths in the near-infrared or the fabrication difficulties inherent in the multilayer scheme. Here, we propose a novel single-layer metasurface achieving multiwavelength chromatic aberration-free deflection across the visible spectrum by employing the robust freeform design strategy to simplify the fabrication process. By properly selecting diffraction orders for red, green, and blue wavelengths to achieve identical wavelength-diffraction-order products, the metasurface deflects light at a consistent angle of 41.3° with a high efficiency. The coupled Bloch mode analysis explains the physical properties, and experimental fabrication and characterization confirm its effectiveness. This approach holds potential for various applications such as AR/VR, digital cameras, and high-quality optical systems.

Local control of polarization and geometric phase in thermal metasurfaces.

Thermal emission from a hot body is inherently challenging to control due to its incoherent nature. Recent advances have shown that patterned surfaces can transform thermal emission into partially coherent beams with tailored directionality and frequency selectivity. Here we experimentally demonstrate polarization-selective, unidirectional and narrowband thermal emission using single-layer metasurfaces. By implementing polarization gradients across the surface, we unveil a generalization of the photonic Rashba effect from circular polarizations to any pair of orthogonal polarizations and apply it to thermal emission. Leveraging pointwise specification of arbitrary elliptical polarization, we implement a thermal geometric phase and leverage it to prove previous theoretical predictions that asymmetric chiral emission is possible without violating reciprocity. This general platform can be extended to other frequency regimes in efforts to compactify metasurface optics technologies without the need for external coherent sources.

Perfect vortex beams generation based on reflective geometric phase metasurfaces

Perfect vortex beam (PVB) is a propagating light field with radial intensity distribution independent of topological charge and carrying orbital angular momentum (OAM). PVBs can be generated through the Fourier transformation of a Bessel-Gaussian (BG) beam, which traditionally requires a precisely aligned optical setup consisting of a spiral phase plate, a conical lens, and a Fourier lens. However, such traditional schemes are usually bulky and unstable. Here, we have utilized a method that differs from conventional approaches, employing metasurfaces designed as planar Pancharatnam-Berry (PB) phase elements to substitute for all the required components. Unlike traditional methods based on reflective or refractive elements, metasurface elements can significantly reduce the system's footprint. Because the use of metallic metasurfaces allows for a more flattened design plane, in this paper, we have demonstrated the generation of PVB within the 8 GHz microwave frequency band based on a single-layer metallic metasurface. The metasurface is composed of a square ring metal structure, which can serve as a half wave plate to provide the required geometric phase distribution for incident circularly polarized light to generate PVB. By rigorously optimizing the parameters of the square-ring structures, we have generated vortex beams carrying OAM with different topological charges. These vortex beams exhibit a constant radial intensity distribution, which validates their "perfect" characteristics. In addition, we also extracted the mode purity of different vortex beams, so that the mode states of different vortex beams can be distinguished. These results provide broader value for the application of perfect vortex beams in communication.

High Q ultra-thin nona-band polarization insensitive homogeneous single layer metasurface for electronics and space industry with electromagnetic interference and antenna radar cross section reduction

In this article, a nona-band metasurface with unit cell dimensions of 0.038λo×0.038λo×0.019λo (20×20×1.0 mm3) is designed on a FR-4 substrate (Dielectric constant εr = 4.4 and loss tangent = 0.02) of 1.0 mm thickness with 35 µm copper (Conductivity = 5.8×107 S/m) cladding with unit cell periodicity is 20 mm. 10×10 metasurface array size is 200×200×1.0 mm3. In TE/TM mode, the absorbance is greater than 99 % at the intended frequency bands (i.e., 5.76, 8.6, 12.68, 14.38, 17.05, 17.94, 19.20, 20.88, 22.62, and 23.62 GHz), and its reflectivity is almost zero. Results indicated that the metasurface is found to extremely independent on the angles of polarization of the incident wave and the absorber is almost insensitive to the incident angle (0° – 90°) for TE/TM modes. The unit cell of metasurface is having negative permittivity, near zero permeability and negative refractive index at all intended bands which confirm exotic properties of the metasurface. The metasurface is having high quality-factor (Q = 72) at 5.76 GHz frequency therefore, this metasurface is also useful for dielectric sensing application in intended bands. The metasurfaces unparalleled properties make it suitable for EMI shielding, sensing applications in the C, X, and Ku-bands, the reduction of mono-static RCS, the improvement of isolation in MIMO antennas, and the reduction of unintended noise produced by copper components used in satellite and RADAR communication.

Design and implementation of multi-band reflectarray metasurface for 5G millimeter wave coverage enhancement

A compact low-profile multi-band millimeter-wave (mm-wave) reflectarray metasurface design is presented for coverage enhancement in 5G and beyond cellular communication. The proposed single-layer metasurface exhibits a stable reflection response under oblique incidence angles of up to 60∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document} at 24 and 38 GHz, and transmission response at 30 GHz, effectively covering the desired 5G mm-wave frequency bands. The proposed reflectarray metasurface is polarization insensitive and performs equally well under TE and TM polarized incident waves due to the symmetric pattern. In addition, the low profile of the proposed metasurface makes it appropriate for conformal applications. In comparison to the state-of-the-art, the proposed reflectarray metasurface unit cell design is not only compact (3.3 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 3.3 mm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document}) but also offers two reflections and one transmission band based on a single-layer structure. It is easy to reconfigure the proposed metasurface unit cell for any other frequency band by adjusting a few design parameters. To validate the concept of coverage enhancement, a 32 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} x32 unit-cell prototype of the proposed reflectarray metasurface is fabricated and measured under different scenarios. The experimental results demonstrate that a promising signal enhancement of 20–25 dB is obtained over the entire 5G mm-wave n258, n259, and n260 frequency bands. The proposed reflectarray metasurface has a high potential for application in mm-wave 5G networks to improve coverage in dead zones or to overcome obstacles that prevent direct communication linkages.

Wide-field full-Stokes polarimetry for conical light based on all-dielectric metasurface

Polarization camera based on CMOS sensor and nano wire-grid technology have found widespread applications in medical diagnostics, remote sensing and industrial inspection. However, the limited filtering properties of wire-grid polarizers and the small field-of-view provided by conventional microlens restrict the energy efficiency of these systems while also increasing their cost, size and weight. In this study, we propose an innovative approach that integrates focusing and splitting of polarization states into a single-layer all-dielectric metasurface. This metasurface enables full-Stokes polarization imaging for a wide field-of-view conical light. The design of the metasurface utilizes a phase compensation method to effectively focus orthogonal polarized conical light onto the central pixel of the CMOS sensor. Theoretical analysis demonstrates that this metasurface can accurately detect full-Stokes parameters within ±20° incident cone angles with an average efficiency reaching 83.0%. The angle can be extended to ±90° with an average efficiency exceeding 80%. We fabricated a three super-pixel metasurface prototype, and experimental measurements reveal its ability to efficiently focus and split three pairs of orthogonal polarization states under ±11° conical angle incidence with an average focusing efficiency of 68.1%. This study presents a promising solution for achieving wide field-of-view and high-efficiency polarization detection in integrated CMOS systems.

Reflective Polarization Conversion with Multi-Functional, Ultrathin Metasurface for Ku- and K-Band Applications

Reflective polarization conversions with a simplistic design of an ultrathin, single-layered, and multi-functional anisotropic metasurface as a polarization converter is utilized for Ku- and K-band applications. The designs with two substrate thicknesses (0.095λ0 and 0.069λ0, respectively) are capable of a cross-polarization converter (CPC) and a linear-to-circular (LTC) polarization conversion. The design with 0.095λ0 thickness achieves a CPC between 17.96 and 26.90GHz with the efficiency of more than 90% and a relative bandwidth of 40% under normal incidence. It maintains angular stability by altering the oblique incidence angles up to 300 with greater than 80% of the PCR in the K-band. Meanwhile, an LTC in two frequency bands, 10.30-10.53GHz and 28.65-29.70GHz, is also numerically demonstrated. The second design with 0.069 λ0 thickness provides a CPC above the PCR value of 87% in the frequency range from 10.46-23.05GHz (covering the entire Ku- and part of the K-band) with angular stability of 40 above the PCR value of 80%. In the meantime, an LTC with relative bandwidth of 75% in the frequency range from 9.53-9.79&24.74-25.27GHz is numerically revealed. These polarization converters exhibit relatively good performances of facile structure and multi-functional properties, which can be useful in Ku- and K-band applications.

Giant circular dichroism in all-dielectric planar chiral Meta-GMR

In this paper, we introduce a simplified approach involving a single-layer dielectric meta-surface on top of planar waveguide that can achieve a high circular dichroism (CD) value of 0.95 under normal incidence. Within this intrinsic chiral structure, we harness the distinctive characteristics of guided mode resonance (GMR) [1] to induce out-of-plane electric/magnetic field vectors during lateral light propagation, thereby enhancing its optical chirality. Notably, the enhanced CD value becomes prominent at a half-wave plate thickness. This meta-GMR design enables giant CD in both of reflection and transmission, offering promising applications in biosensing, especially for chiral molecules.

Noninvasive inset-integrated meta-atom for achieving single-layer metasurface simultaneously with coded microwave reflectivity and digitalized infrared emissivity

Abstract With the rapid improvement of equipment integration technology, multi-spectrum detectors are integrated into compact volumes and widely used for object detection. Confront with this challenge, it is essential to propose a strategy to design a single-layer metasurface with multi-spectrum responses in microwave and infrared ranges. In this work, we proposed a method of designing meta-atoms, which is capable of achieving functional electromagnetic response at microwave and infrared individually. As a demonstration, a metasurface with four different occupation ratios and coding permutation features is designed, fabricated, and tested. In the microwave band, the pixel meta-atom is designed to realize highly efficient cross-polarization conversion between 5.0 and 10.0 GHz, which shows the metasurface can behave as ultra-low Radar Cross Section (RCS) reflectors in the working band; In the infrared band, different occupation ratio of meta-atoms are designed to realize the infrared emissivity from 0.60 to 0.80 in 3–14 μm, which can be used to exhibit digital infrared camouflage pattern. This work promotes the ability to use single-layer design to achieve digital infrared camouflage and microwave RCS reduction simultaneously. The one-layer design is simple in geometry, simplified in process, low cost in economy, and large scale in fabrication, which can promote practical use in compatible microwave stealth and infrared camouflage.

Monolayer directional metasurface for all-optical image classifier doublet.

Diffractive deep neural networks, known for their passivity, high scalability, and high efficiency, offer great potential in holographic imaging, target recognition, and object classification. However, previous endeavors have been hampered by spatial size and alignment. To address these issues, this study introduces a monolayer directional metasurface, aimed at reducing spatial constraints and mitigating alignment issues. Utilizing this methodology, we use MNIST datasets to train diffractive deep neural networks and realize digital classification, revealing that the metasurface can achieve excellent digital image classification results, and the classification accuracy of ideal phase mask plates and metasurface for phase-only modulation can reach 84.73% and 84.85%, respectively. Despite a certain loss of degrees of freedom compared to multi-layer phase mask plates, the single-layer metasurface is easier to fabricate and align, thereby improving spatial utilization efficiency.

Tunable on-chip optical traps for levitating particles based on single-layer metasurface

Abstract Optically levitated multiple nanoparticles have emerged as a platform for studying complex fundamental physics such as non-equilibrium phenomena, quantum entanglement, and light–matter interaction, which could be applied for sensing weak forces and torques with high sensitivity and accuracy. An optical trapping landscape of increased complexity is needed to engineer the interaction between levitated particles beyond the single harmonic trap. However, existing platforms based on spatial light modulators for studying interactions between levitated particles suffered from low efficiency, instability at focal points, the complexity of optical systems, and the scalability for sensing applications. Here, we experimentally demonstrated that a metasurface which forms two diffraction-limited focal points with a high numerical aperture (∼0.9) and high efficiency (31 %) can generate tunable optical potential wells without any intensity fluctuations. A bistable potential and double potential wells were observed in the experiment by varying the focal points’ distance, and two nanoparticles were levitated in double potential wells for hours, which could be used for investigating the levitated particles’ nonlinear dynamics, thermal dynamics and optical binding. This would pave the way for scaling the number of levitated optomechanical devices or realizing paralleled levitated sensors.

Hybrid ultrathin metasurface for broadband sound absorption

To this day, achieving broadband low-frequency sound absorption remains a challenge even with the possibilities promised by the advent of metamaterials and metasurfaces, especially when size and structural restrictions exist. Solving this engineering challenge relies on stringent impedance matching and coupling of the multiple independent local resonators in metasurface absorbers. In this Letter, we present an innovative design approach to broaden the sound absorption bandwidth at low-frequency regime. A hybrid metasurface design is proposed where four coupled planar coiled resonators are also coupled to a well-designed thin planar cavity. This hybrid metasurface creates a broad sound absorption band (130–200 Hz) that is twice as wide as that of the traditional single layer metasurface utilizing four coiled cavities at a deep subwavelength thickness (∼λ/51). This design strategy opens routes toward engineering a class of high-performance thin metasurfaces for ultra-broadband sound absorption, while keeping the planar size unchanged.

A single-layer multimode high gain circularly polarized metasurface antenna using CMA for C-band applications

Abstract This article presents an innovative design for a low-profile, high-gain circularly polarized (CP) antenna using a single-layer metasurface (MTS). The proposed design incorporates an MTS layer, comprising a 4 × 4 array of hexagonal-shaped patches, printed on the top layer of the substrate. The bottom layer features a coplanar waveguide-fed slotted ground. Circular polarization and broadside radiation are achieved through the application of characteristic mode analysis (CMA). CMA is employed to simultaneously excite desired modes, aiming for wideband circular polarization and gain enhancement. Experimental results validate the effectiveness of the design, with compact dimensions of 0.67λ0 × 0.67λ0 × 0.04λ0. The measurements demonstrate an impressive impedance bandwidth of 84.3% within the 3.7–9.1 GHz. Additionally, a 3-dB axial ratio bandwidth of 18.6% is observed between 4.96 and 5.98 GHz and 3.74% between 8.38 and 8.7 GHz. The antenna exhibits excellent radiation pattern characteristics, featuring a maximum gain of 10.08 dBi at 7.1 GHz. The radiation pattern is symmetrical with broadside directionality, making the antenna well-suited for sensing applications.

Вычислительные диэлектрические метаповерхности в фотонных топологических устройствах обработки многомерных сигналов

A single-layer computational dielectric broadband metasurface (MS) with silicon nanodiscs is proposed to implement spatial differentiation and contour recognition operations. The variety of physical mechanisms of dielectric MSs for performing similar mathematical operations is considered. The necessity of such computational nanostructures for improving the numerous methods of topological texture-fractal processing of signals and fields in modern radio physics and radio electronics is revealed.