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The fabrication of plasmonic metasurfaces on large surfaces is the next challenge to adapt them to augmented reality systems. The optical properties of a self‐assembled hexagonal plasmonic metasurface, realized with a large‐area compatible approach, are compared at different levels and a correlated‐disorder plasmonic metasurface fabricated by electron‐beam lithography and considered here as the reference: the contribution of plasmonic nanostructure arrangements is studied using the structure factor, physical properties are assessed by optical transmission and reflection measurements, and finally the entire metasurfaces are tested macroscopically in a head‐up display system. [ABSTRACT FROM AUTHOR]

Optical metasurfaces with pronounced spectral characteristics are promising for sensor applications. Currently, deep learning (DL) offers a rapid manner to design various metasurfaces. However, conventional DL models are usually assumed as black boxes, which is difficult to explain how a DL model learns physical features, and they usually predict optical responses of metasurfaces in a fuzzy way. This makes them incapable of capturing critical spectral features precisely, such as high quality (Q) resonances, and hinders their use in designing metasurface sensors. Here, a transformer‐based explainable DL model named Metaformer for the high‐intelligence design, which adopts a spectrum‐splitting scheme to elevate 99% prediction accuracy through reducing 99% training parameters, is established. Based on the Metaformer, all‐dielectric metasurfaces based on quasi‐bound states in the continuum (Q‐BIC) for high‐performance metasensing are designed, and fabrication experiments are guided potently. The explainable learning relies on spectral position encoding and multi‐head attention of meta‐optics features, which overwhelms traditional black‐box models dramatically. The meta‐attention mechanism provides deep physics insights on metasurface sensors, and will inspire more powerful DL design applications on other optical devices. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper presents a High Gain Metasurface (HGM) antenna design optimized for IoT applications. The antenna operates at a 5.8 GHz frequency and utilizes a quarter‐wavelength unit cell structure. The design employs a Graph Sample and Aggregate‐Attention Network (GSAAN) to enhance the transmission characteristics of the metasurface. To optimize the performance of GSAAN, the Giza Pyramids Construction Algorithm (GPCN) is applied to adjust the weight parameters, leading to significant improvements in radiation efficiency, bandwidth, gain, directivity, and return loss. The proposed HGM antenna is simulated in MATLAB 2023b, where it demonstrates substantial performance gains over existing methods. Specifically, the proposed design achieves 28.34% higher gain compared to the MSA‐RHCOA method, 24.47% improvement over HGM‐AD‐MATCS, 26.34% better gain than BR‐HGA‐PGM, and a 32.12% gain increase relative to MSA‐Hyb‐ADSA‐HMSOA. These enhancements make the proposed antenna design a competitive solution for high‐gain applications in wireless communication, satellite communication, and radar systems. The integration of GSAAN with GPCN optimization in the HGM antenna design enables the creation of highly directive radiation patterns, making it well‐suited for IoT applications that require high performance and reliability. The results of this study demonstrate the effectiveness of the proposed approach in achieving superior antenna performance, positioning it as a strong alternative to existing metasurface antenna designs. [ABSTRACT FROM AUTHOR]

Diffractive Neural Networks (DNNs) leverage the power of light to enhance computational performance in machine learning, offering a pathway to high-speed, low-energy, and large-scale neural information processing. However, most existing DNN architectures are optimized for single tasks and thus lack the flexibility required for the simultaneous execution of multiple tasks within a unified artificial intelligence platform. In this work, we utilize the polarization and wavelength degrees of freedom of light to achieve optical multi-task identification using the MNIST, FMNIST, and KMNIST datasets. Employing bilayer cascaded metasurfaces, we construct dual-channel DNNs capable of simultaneously classifying two tasks, using polarization and wavelength multiplexing schemes through a meta-atom library. Numerical evaluations demonstrate performance accuracies comparable to those of individually trained single-channel, single-task DNNs. Extending this approach to three-task parallel recognition reveals an expected performance decline yet maintains satisfactory classification accuracies of greater than 80 % for all tasks. We further introduce a novel end-to-end joint optimization framework to redesign the three-task classifier, demonstrating substantial improvements over the meta-atom library design and offering the potential for future multi-channel DNN designs. Our study could pave the way for the development of ultrathin, high-speed, and high-throughput optical neural computing systems. [ABSTRACT FROM AUTHOR]

Metasurfaces have recently gained significant attention due to the strong capacity in light field manipulation. However, most traditional metasurfaces are fabricated on rigid substrates, which fix their functionality after fabrication and limit their applications in dynamic measurement fields. In this work, we designed and fabricated a silver metasurface embedded in a stretchable substrate for sensing applications. This metasurface can generate different point cloud patterns under varying stretch ratios when illuminated by a laser beam. By collecting and analyzing the patterns, we can precisely reconstruct the deformation of the metasurface. Furthermore, the sample exhibits excellent performance under incident light of various wavelengths. These results pave the way for developing microdevices with novel capabilities based on flexible metamaterials. [ABSTRACT FROM AUTHOR]

This study presents the design, fabrication, and characterization of a wide field-of-view (FOV) metalens optimized for capsule endoscopy. The metalens achieved a 165° FOV with a high modulation transfer function (MTF) of 300 lines per millimeter (lp/mm) across the entire FOV, operating in the near-infrared (NIR) narrow-bandpass imaging at 940 nm. The performance of the metalens-based system is evaluated using two bandwidths, 12 nm and 32 nm, showing MTF values of 0.2 and 0.3 at 250 lp/mm, respectively. The metalens-based system maintains a compact form factor with a total track length of 1.4 mm and a diameter of 1.58 mm. Compared to a traditional 108° FOV endoscope, the nano-optic capsule endoscope demonstrated superior performance in terms of FOV, contrast, and resolution. This advancement represents a significant step toward enhancing diagnostic capabilities in medical imaging, offering improved performance in a more compact package compared to conventional optics. [ABSTRACT FROM AUTHOR]

Bound states in the continuum represent a captivating and significant phenomenon in the realms of photonics, materials science, and quantum mechanics. These exceptional resonant states have emerged as crucial elements in a diverse array of nanotechnology applications including chiral nanophotonics. Applying bound states in the continuum for chiral applications is a challenging problem and usually requires some additional complicated steps such as multi‐layer lithography, adding superstrate with index matching materials and geometry parameters adjusting. Nevertheless, creating a structure placed in inhomogeneous background that is capable to perfectly convert one circular polarization to the opposite one is still a challenging problem. This work presents chiral metasurface based on bound states in the continuum allowing to achieve perfect unitary circular conversion in an inhomogeneous environment. This approach is based on a coupling of two chiral but not perfect resonances which makes it possible to get one mode with chiral dichroism value of 1. A theoretical model is built, perform numerical calculation and conduct an experimental verification to prove this concept. The presented results could find many applications in sensing, optics, telecommunications, biomedical and chemical analysis. [ABSTRACT FROM AUTHOR]

In conventional optical microscopes, image contrast of objects mainly results from the differences in light intensity and/or color. Muller matrix optical microscopes (MMMs), on the other hand, can provide significantly enhanced image contrast and rich information about objects by analyzing their interactions with polarized light. However, state‐of‐the‐art MMMs are fundamentally limited by bulky and slow polarization state generators and analyzers. Here, the study demonstrates a metasurface‐based MMM, i.e., Meta‐MMM, which is equipped with a chip‐integrated, single‐shot metasurface polarization state analyzer (Meta‐PSA). The Meta‐MMM is featured with high‐speed measurement (≈2s per Muller matrix (MM) image), superior operation stability, dual‐color operation, and high measurement accuracy (measurement error 1–2%) for MM imaging. The Meta‐MMM is applied to nanostructure characterization, surface morphology analysis, and discovering birefringent structures in honeybee wings. The Meta‐MMMs hold the promise to revolutionize various applications from biological imaging, medical diagnosis, and material characterization to industry inspection and space exploration. [ABSTRACT FROM AUTHOR]

Metasurface‐based flat optics has a great potential to replace conventional bulky and heavy optical elements, consistent with the trend of miniaturizing optical elements. One of the trends is to broaden the operating area of the metasurface. The previous approaches are focused on expanding the metasurface area, which has intrinsic manufacturing and optical limitations. Here, this work presents the fabrication of wafer‐scale metalens arrays, and demonstrates the Gabor superlens composed of the metalens arrays, which behaves optically like a large lens system. A pair of fabricated 8‐inch‐sized metalens arrays are used to float the large‐area display, producing a real image in the air. This superlens is easily manufactured in a high‐throughput and cost‐effective manner using an argon fluoride dry scanner and a single reticle. Their capability for diffraction‐limited focusing and imaging is demonstrated. Considering the groundbreaking nature of imaging a large‐area display through the metalens arrays, this work shows a great potential for scaling up the optical display systems in a simple manner. [ABSTRACT FROM AUTHOR]

In this paper, a dual-frequency trifunctional metasurface (MS) consisting of three metal layers printed on two substrate layers is proposed. The low-frequency transmitted wave is regulated through a C-shaped slot etched in middle layer and C-shaped patches in top/bottom metal layers. High-frequency reflected waves can be regulate by the C-shaped slot etched in ring patch in top/bottom layers. Also, in top/bottom layers, C-shaped patches and slots operate in electric and magnetic resonant modes that the interference between transmitted and reflected waves is suppressed. This MS integrates three independent working modes, that is to say, it can reflect x-polarized waves propagating along +z/-z direction at high frequency and transmit x-polarized low-frequency waves from -z direction. Meanwhile, 360° phase coverage and continuous amplitude control from 0 to 1 can be independently achieved in three working modes. Based on this MS, an asymmetric spatial power divider is designed and measured. The measured results are consistent with the designed goals. [ABSTRACT FROM AUTHOR]

Hiding an isolated object in free space using a transmissive invisibility cloak has become a significant research area, propelled by advancements in metamaterials and transformation optics over the past decade. Despite the availability of various simplified methods for implementing transmissive cloaks, issues such as impedance mismatches and narrow working bandwidths often arise, posing challenges. Achieving a broadband transmissive cloak in free space has proven to be particularly arduous. This study presents a near‐perfect one‐directional broadband transmissive cloak constructed from multilayer metasurfaces of arbitrary shapes, showcasing superior performance across a broadband frequency range. The phase distribution of the metasurfaces and the efficacy of the transmissive cloak are assessed using the generalized Snell's law. An experimental near‐perfect broadband transmissive cloak is successfully demonstrated to operate within the frequency range of 8.5 to 11.2 GHz. This study contributes to reducing the density and mass of cloaks, thereby facilitating the expansion of cloaking capabilities in various directions and across different frequency bands. [ABSTRACT FROM AUTHOR]

3D nanolithography based on two‐photon polymerization (TPP) allows for the high‐precision fabrication of nearly arbitrary 3D micro/nanostructures, finding extensive applications in areas such as micro‐optics, micro‐mechanics, and biomedicine. However, the large size, complexity of optical systems, and high costs have significantly constrained the widespread adoption of 3D nanolithography technology in both scientific research and industry. In this study, a metasurface is introduced, for the first time, into 3D nanolithography resulting in the construction of a miniaturized and simplified TPP system that achieved efficient multi‐focus parallel processing with high uniformity. A microlens array is fabricated, showcasing the system's application capacity to generate an array of devices with high consistency and quality. It is believed that the utilization of metasurface devices will provide a novel TPP operating platform, enabling richer and more flexible printing functionalities while maintaining system miniaturization and low cost. [ABSTRACT FROM AUTHOR]

We employed a double-layer coupled diffractive optical element, based on metasurfaces and diffraction gratings, which exhibits wavefront modulation and chromatic dispersion compensation. Utilizing this double-layer coupled diffractive optical element in the optical information transmission process of a diffractive waveguide allows for the transmission of color image information using a single-layer waveguide structure. Our results demonstrate that, under the conditions of a field of view of 47° × 47°, an entrance pupil size of 2.9 × 2.9 mm2, and an exit pupil extension size of 8.9 mm, the uniformity of the brightness for each monochromatic field reached 85%, while the uniformity of color transmission efficiency exceeded 95%. [ABSTRACT FROM AUTHOR]

Decoupling of phase and polarization is significant for multidimensional light manipulation. However, this requires traditional cascaded and parallel optical elements, resulting in a bulky and complex system. Metasurfaces can potentially replace complex optical modules as novel ultrathin planar optical elements. Herein, an ultrathin single‐layer metasurface is proposed to decouple the phase and polarization based on the Pancharatnam–Berry phase. The rotation angles of the two nanofins are employed to manipulate the phase and polarization independently, significantly simplifying the design process. Diffraction‐limited focusing with a degree of linear polarization higher than 95% is achieved for wavelengths in the 405–633 nm range. Furthermore, a metasurface can arbitrarily manipulate the relative intensity between different channels. The intensity ratio is adjusted from 0.12 to 6.62. These results will pave the way for miniaturized, integrated, and multi‐channel optical elements. [ABSTRACT FROM AUTHOR]

In this paper, a metamaterial inspired meandered line loaded antenna with dual-band characteristics for wireless applications is presented. Initially, the antenna is loaded with a single meandered line structure and operates over a single band with a center frequency of 5.64 GHz and circularly polarized (CP) radiation. Further, it is loaded with two more similar meandered line structures inducing an extra band with a center frequency of 3.4 GHz and hence operating as a dual band antenna with an impedance bandwidth of 11.4% and 33.7%, respectively, exhibiting CP radiation in its second band. Moreover, the antenna is backed with a metasurface (MS) at the ground side with a separation of 18.4 mm to enhance the gain and radiation of the antenna. The antenna exhibits good radiation characteristics with peak gains of 7.66 dBi and 8.7 dBi in the first and second bands, respectively. The antenna is fabricated, and promising experimental results have been observed. [ABSTRACT FROM AUTHOR]

In this paper, a perfect absorber (PA) based on tungsten is proposed to include hexagonal‐shaped metasurface absorbers with varying hole sizes ranging from quadrangular to circular, allowing them to cover a wide wavelength spectrum. The study investigates the effects of various parameters, including the number of sides of the inner hole, on the absorber's performance and identifies the most suitable absorber by introducing an equivalent circuit. The outcomes of full‐wave numerical simulations primarily based on the finite element method (FEM) highly correspond to the final results of the circuit model. Additionally, the circuit model significantly reduces computation time and requires less storage compared with full‐wave simulations. The results show that the hexagonal‐square metasurface absorber achieves exceptional absorption rates, with an average of 99.9% in the 431 to 532 nm wavelength range and over 90% in the 300 to 915 nm range. The hexagonal‐hexagonal metasurface absorber also exhibits high absorption rates, with an average of over 99% in the 431 to 518 nm and 700 to 780 nm ranges, and over 90% in the 300 to 940 nm range. The absorption performance of the proposed hexagonal‐circle metasurface absorber is also remarkable, with an absorption value of over 99% in the 670 to 771 nm range and above 90% in the 365 to 991 nm range. These models can be utilized to design and simulate other subwavelength absorbers in a broad frequency range, including terahertz and visible light, making them suitable for various applications. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) is one of the possible solutions to overcome challenges that bring up the 6G communication networks. Unit cell design for RIS is similar in many aspects to the design of artificial magnetic conductors (AMC) because both have a common nature of changing the phase of the reflected wave. However, RIS is aimed at controlling the angle of reflection to maintain requirements for the radiation pattern similar to phased antenna arrays such as low side lobes and beamwidth. The paper reviews the criteria for optimizing RIS: unit cell dimensions, phase span, frequency bandwidth, and loss. An optimization algorithm is proposed for the proper accounting of RIS optimization criteria. A new X-band unit cell is designed using the proposed optimization algorithm. [ABSTRACT FROM AUTHOR]

Metasurfaces, consisting of arrays of subwavelength structures, are lightweight and compact while being capable of implementing the functions of traditional bulky optical components. Furthermore, they have the potential to significantly improve complex optical systems in terms of space and cost, as they can simultaneously implement multiple functions. The wafer-scale mass production method based on the CMOS (complementary metal oxide semiconductor) process plays a crucial role in the modern semiconductor industry. This approach can also be applied to the production of metasurfaces, thereby accelerating the entry of metasurfaces into industrial applications. In this study, we demonstrated the mass production of large-area meta-axicons with a diameter of 2 mm on an 8-inch wafer using DUV (Deep Ultraviolet) photolithography. The proposed meta-axicon designed here is based on PB (Pancharatnam–Berry) phase and is engineered to simultaneously modulate the phase and polarization of light. In practice, the fabricated meta-axicon generated a circularly polarized Bessel beam with a depth of focus (DoF) of approximately 2.3 mm in the vicinity of 980 nm. We anticipate that the mass production of large-area meta-axicons on this CMOS platform can offer various advantages in optical communication, laser drilling, optical trapping, and tweezing applications. [ABSTRACT FROM AUTHOR]

In the field of modern optical computing and communication, optical bistability plays a crucial role. With a weak third-order nonlinear coefficient, low switch thresholds of optical bistability from Si-based nanophotonic structures remain a challenge. In this work, a metasurface consisting of silicon nanostrip arrays placed on the optically thick silver film is proposed. The light–matter interaction is enhanced by mirror-inducing the magnetic anapole states (MASs) and asymmetrically optimizing its silicon nanostrip. Numerical results show that the average enhancement factor (EF) of an electric field can be greatly enhanced to be 1524.8. Moreover, the optical bistability of the proposed metasurface achieves the thresholds of ION-OFF and IOFF-ON of 8.5 MW/cm2 and 7.1 MW/cm2, respectively, which is the lowest threshold when compared to the previous works based on silicon nanostructures. The angular dependance of the bistability performance is also investigated. This work facilitates the proposed hybrid metasurface in the fields of miniaturized all-optical switches and modulators, which are key components in optical computing and communication. [ABSTRACT FROM AUTHOR]

Measurements of the refractive index of liquids are in high demand in numerous fields such as agriculture, food and beverages, and medicine. However, conventional ellipsometric refractive index measurements are too expensive and labor‐intensive for consumer devices, while Abbe refractometry is limited to the measurement at a single wavelength. Here, a new approach is proposed using machine learning to unlock the potential of colorimetric metasurfaces for the real‐time measurement of the dispersive refractive index of liquids over the entire visible spectrum. The platform with a proof‐of‐concept experiment for measuring the concentration of glucose is further demonstrated, which holds a profound impact in non‐invasive medical sensing. High‐index‐dielectric metasurfaces are designed and fabricated, while their experimentally measured reflectance and reflected colors, through microscopy and a standard smartphone, are used to train deep‐learning models to provide measurements of the dispersive background refractive index with a resolution of ≈10−4, which is comparable to the known index as measured with ellipsometry. These results show the potential of enabling the unique optical properties of metasurfaces with machine learning to create a platform for the quick, simple, and high‐resolution measurement of the dispersive refractive index of liquids, without the need for highly specialized experts and optical procedures. [ABSTRACT FROM AUTHOR]

The terahertz frequency region of the electromagnetic spectrum is crucial for understanding the formation and evolution of galaxies and stars throughout the universe's history, as well as the process of planet formation. Detecting the unique spectral signatures of molecules and atoms requires terahertz spectrometers, which must be operated in space observatories due to water vapor absorption in the Earth's atmosphere. However, current terahertz spectrometers face challenges such as low resolution, limited bandwidth, large volume, and complexity. In this paper, the issues of size and weight are addressed by demonstrating a concept for a centimeter‐sized, low‐weight terahertz spectrometer using a metasurface. The design of the metasurface spectrometer is first discussed for the 1.85 to 2.4 THz range, followed by its fabrication. Next, an array of quantum cascade lasers operating at slightly different frequencies around 2.1 THz is utilized to characterize the spectrometer. Finally, a spectrum inversion method is applied to analyze the measured data, confirming a resolution R (λ/Δλ) of at least 273. This concept can be extended to other application areas, such as planetary observations and various wavelengths in the far‐infrared (FIR) and near‐infrared (NIR) ranges. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) heterojunctions composed of GaN/graphene have high transmittance and excellent carrier transport properties. The combination of multidimensional hybrid heterojunctions with metasurfaces can open up many fascinating prospects for novel optical components over a broad range of the electromagnetic spectrum. This work experimentally demonstrates a multifunctional temperature‐sensitive meta‐device based on GaN/graphene vdW heterojunctions integrated with a metasurface. Notably, it is discovered that the conductivity of the vdW heterojunctions increases rapidly when it is excited by a thermal signal, resulting in a significant change in the relative phase retardation as well as amplitude modulation of an incident THz wave. Then a continuous wavelet transform is used instead of the traditional Fourier transform, and the two‐dimensional wavelet coefficient card is built to achieve fast detection over a wider range of temperature. Simultaneously, the variation of temperature dynamically controls the contributions of the multipoles, eventually determining the active switching of exotic anapoles with extreme non‐radiative confinement to highly radiative electric dipoles. This work offers the possibility of designing novel chip‐scale multifunctional thermal tuning devices and promotes the potential application of active micro‐nanophotonic devices in temperature sensors, terahertz modulators, and dynamic near‐field imaging. [ABSTRACT FROM AUTHOR]

A cutting-edge antenna system has been developed for new radio (NR) millimeter wave operating from 36.0 to 40.0 GHz frequency range 2 (FR 2) n260 band applications. This innovative system incorporates metasurface-inspired printed dual-port MIMO technology, which includes LP to CP conversion features. The positional orientation of the elements of the MIMO antenna with stacked metasurface provoked the spatial diversity. To convert linearly polarised (LP) waves to circularly polarised (CP) waves, the metasurface layer is suspended above the MIMO antenna. LP to CP polarisation conversion occurs when the conducting strip and rectangular space between strips on the substrate generate π/2 phase-shifted electric field components (Ex and Ey). The proposed stepped impedance-fed antenna elements and metasurface are fabricated on commercially available high-frequency laminates using a double-layer printed circuit board (PCB) fabrication facility. The test findings exhibit a satisfactory level of concurrence with the calculated/measured findings regarding scattering parameters, diversity performance parameters, and realized gain. The result is a highly efficient and versatile antenna system that is ideal for advanced engineering applications. [ABSTRACT FROM AUTHOR]

Naked-eye 3D micro-LED display combines the characteristics of 3D display with the advantages of micro-LED. However, the 3D micro-LED display is still at the conceptual stage, limited by its intrinsic emission properties of large divergence angle and non-coherence, as well as difficulties in achieving large viewing angles with high luminous efficiency. In this work, we propose a double-layer metasurface film integrating functions of collimation with multiple deflections, constituting a micro-LED naked-eye 3D display system. The system is characterized through numerical simulations using the 3D finite-difference time-domain method. The simulation results show that the double-layer metasurface film restricts 90% of the emitted light of the micro-LED to the vicinity of the 0° angle, improving its spatial coherence. Subsequently, a large-angle, low-crosstalk outgoing from −45° to 45° is achieved, while providing a deflection efficiency of over 80% and a pixel density of up to 605. We believe this design provides a feasible approach for realizing naked-eye 3D micro-LED displays with a large field of view, low crosstalk, and high resolution. [ABSTRACT FROM AUTHOR]

As metasurfaces are in the spotlight, research is being conducted to incorporate them into transmitarray (TA) antennas. Among these, as an attempt to create a low-profile design, a patch antenna classified as low-gain can be utilized as an appropriate source antenna. However, for high efficiency of the TA, the gain of the source antenna must be fundamentally improved. For this, a simple side metal structure was applied to a metallic cross-type slot transmitarray. This acts as a resonant element and reflector by utilizing the electromagnetic wave radiated from the source antenna. The changes in the center frequency and gain due to the application of the side metal structure to the source antenna were analyzed. The gain of the source antenna was improved by a total of 4.63 dB. This is expected to be applied to create various source waves and to conduct future research on improving the gain in transmitarray antennas. [ABSTRACT FROM AUTHOR]

We present a sensor that utilizes a modified single-frequency split beam metasurface reflector to measure the refractive index of materials ranging from one to three. Samples are placed into a cavity between a PCB-etched dielectric and a reflecting ground plane. It is illuminated using a 10.525 GHz free-space transmit horn with reflecting angles measured by sweeping a receiving horn around the setup. Predetermined changes in measured angles determined through simulations will coincide with the material's index. The sensor is designed using the Fourier transform method of array synthesis and verified with FEM simulations. The device is fabricated using PCB milling and 3D printing. The quality of the sensor is verified by characterizing 3D printed dielectric samples of various infill percentages and thicknesses. Without changing the metasurface design, the sensing performance is extended to accommodate larger sample thicknesses by including a modified 3D printed fish-eye lens mounted in front of the beam splitter; this helps to exaggerate changes in reflected angles for those samples. All the methods presented are in agreement and verified with single-frequency index measurements using Snell's law. This device may offer a viable alternative to traditional index characterization methods, which often require large sample sizes for single-frequency measurements or expensive equipment for multi-frequency parameter extraction. [ABSTRACT FROM AUTHOR]

Contact lenses have been instrumental in vision correction and are expected to be utilized in augmented reality (AR) displays through the integration of electronic and optical components. In optics, metasurfaces, an array of sub‐wavelength nanostructures, have offered optical multifunctionality in an ultra‐compact form factor, facilitating integration into various imaging, and display systems. However, transferring metasurfaces onto contact lenses remains challenging due to the non‐biocompatible materials of extant imprinting methods and the structural instability caused by the swelling and shrinking of the wetted surface. Here, a biocompatible method is presented to transfer metasurfaces onto contact lenses using hyaluronic acid (HA) as a soft mold and to allow for holographic light projection. A high‐efficiency metahologram is obtained with an all‐metallic 3D meta‐atom enhanced by the anisotropy of a rectangular structure, and a reflective background metal layer. A corrugated metal layer on the HA mold is supported with a SiO2 capping layer, to avoid unwanted wrinkles and to ensure structural stability when transferred to the surface of pliable and wettable contact lenses. Biocompatible method of transferring metasurfaces onto contact lenses promises the integration of diverse optical components, including holograms, lenses, gratings and more, to advance the visual experience for AR displays and human‐computer interfaces. [ABSTRACT FROM AUTHOR]

A conformal reflective metasurface fed by a dual-band multiple-input multiple-output (MIMO) antenna is proposed for low-cost beam steering applications in 5G Millimeter-wave frequency bands. The beam steering is accomplished by selecting a specific port of MIMO antenna. Each MIMO port is associated with a beam that points in a different direction due to a conformal reflective metasurface. This novel conformal metasurface antenna design has the advantages of higher gain, lower cost, a simpler feeding source, and a lower profile when compared to traditional reflective metasurfaces using bulky horn antennas and phased arrays with complex feeding networks and phase shifters for beam steering. The proposed beam steering antenna consists of a compact five-element dual-band MIMO and a 32 × 32 unit-cell conformal dual-band reflective metasurface placed at the top of the MIMO antenna to obtain the beam steering capability as well as gain enhancement. The proposed reflective metasurface has a stable response under oblique incidence angles of up to 60 0 at 24 GHz and 38 GHz and its symmetric, single-layer structure, ensures polarization insensitivity and stable response under conformal conditions. The presented MIMO antenna design is not only compact but also offers a wideband response effectively covering the desired 5G mm-wave frequency bands. The overall size of the MIMO antenna alone is 70 × 12 mm 2 with a maximum gain of 5.4 and 7.2 dB. It is further improved up to 13.1 and 14.2 dB at 24 and 38 GHz respectively, with a beam steering range of ś 40 0 by using a conformal reflective metasurface. Unlike the existing beam steering strategies, the suggested method is not only cost-effective but also increases the overall directivity and gain of the source MIMO antenna. The measured results agree with the simulated results, making it a potential candidate in the 5G and beyond beam steering applications. [ABSTRACT FROM AUTHOR]

Plasmonic nanostructures are frequently utilized to create metasurfaces with a large variety of optical effects. Control over shape and positioning of the nanostructures is key to the function of such plasmonic metasurfaces. Next to lithographic means, directed self‐assembly is a viable route to create plasmonic structures on surfaces with the necessary precision. Here, a combined approach of DNA origami self‐assembly and electron beam lithography is presented for determinate positioning of gold nanospheres on a SiO2 surface. First, DNA origami structures bind to the electron beam‐patterned substrate and subsequently, gold nanoparticles attach to a defined binding site on the DNA origami structure via DNA hybridization. A sol‐gel reaction is then used to grow a silica layer around the DNA, thereby increasing the stability of the self‐assembled metasurface. A mean yield of 74% of single gold nanospheres is achieved located at the determinate positions with a spatial position accuracy of 9 nm. Gold nanosphere dimers and trimers are achieved with a rate of 65% and 60%, respectively. The applicability of this structuring method is demonstrated by the fabrication of metasurfaces whose optical response can be tuned by the polarization of the incoming and the scattered light. [ABSTRACT FROM AUTHOR]

Notch filters usually involve high costs, great difficulties in processing, and very limited tunability. By coating a nematic liquid crystal (LC) layer onto a well‐designed quasi‐bound states in the continuum (quasi‐BICs) metasurface, this work designs and demonstrates a high‐Q tunable filtering system with precise tunability in the near‐infrared spectral range. Optimal structural parameters and the filtering performance are first determined by numerical simulations and then confirmed in experiments. The precise tunability is enabled by modifying the LC molecules’ principal axes with an applied voltage, where the least distinguishable central wavelength interval is smaller than 0.3 nm, and the largest Q factor extracted from experiments can be ≈256.1. Compared to most of the commercial notch filters that work in the visible region and have no tunability, this work achieves an ultra‐narrowband filtering system that features low manufacture difficulty and cost, and great control of light propagation. The proposed design also opens new avenues for developing BIC‐based high‐Q devices with enhanced signal‐to‐noise ratio and multifunctional properties. [ABSTRACT FROM AUTHOR]

The multi‐dimensional light‐field manipulation capability of metasurfaces positions them as promising candidates for displaying nanoprinting and holographic images at ultra‐short distances with subwavelength resolution. In recent years, merging nanoprinting and holographic images into a single‐layer metasurface has emerged as a research focus to enhance information storage capacity. However, existing multi‐channel metasurface designs often limit the number of polarization states available for the holographic image. Here, a scheme is proposed and demonstrated to encode both a continuous grayscale image and a vectorial hologram with a continuously varying linear polarization distribution onto a complex amplitude‐modulated metasurface. The nanoprinting and holographic images generated from dielectric metasurface exhibit broadband response for the visible light. This method paves the way for compact optical devices tailored for applications in information encoding, high‐density optical storage, and information anti‐counterfeiting. [ABSTRACT FROM AUTHOR]

Conventional approaches for designing metasurfaces with the desired scattering response are often a time‐consuming and onerous process that heavily relies on the design experience and empirical methods. In this paper, a time and resource‐efficient design method is proposed for the synthesis of multiple metasurface polarizers with an efficient automated data generation process by utilizing the structure validation surrogate model (SVSM). Moreover, a novel attention and space‐to‐depth enhanced adaptive tandem network (ASE‐ATN) is proposed which integrates symmetry‐aware space‐to‐depth (SA‐SPD) along with the attention mechanism for efficient feature extraction. Several design examples of metasurfaces with linear polarization to orthogonal linear polarization (LP‐OLP) and/or linear polarization to circular polarization (LP‐CP) conversion capabilities are provided to verify the performance of the proposed method. The feasibility of the proposed method is demonstrated through the fabrication and measurement of a dual‐band dual‐polarization converter. [ABSTRACT FROM AUTHOR]

Rayleigh wave isolation using metamaterials is a research hotspot in the engineering community, yet the development of relevant mitigation methods remains an open and challenging problem. Herein, we propose a new type of metasurface, known as an engineered metagrating, which is a special metasurface buried in soil and plays a role in shielding surface Rayleigh waves. Moreover, the total omnidirectional reflection characteristics and subwavelength properties exhibited by the proposed metasurface provide a more flexible reference for surface Rayleigh wave mitigation measures in practical engineering applications. This work can open new avenues for controlling the propagation of seismic surface waves. [ABSTRACT FROM AUTHOR]

Terahertz waves can be widely used for short‐range communication in complex indoor environments and non‐destructive object detection applications. Metasurfaces are widely used in terahertz sensing and communication devices because they can modulate terahertz waves in multiple dimensions. Metamaterial robot brain can utilize metasurfaces' powerful direct modulation ability to achieve sensing and communication functions. The metasurface devices realized based on Dynamic Heterogeneous Redundancy (DHR) architecture can improve the confidentiality and security of terahertz wave wireless communication. While the intrinsic ohmic loss and quality factor of usual metallic metamaterials are usually low, the concept of bound states in the continuum (BIC) has been proposed for stronger terahertz‐matter interactions. Among them, high‐order BICs are of interest because of their strong robustness to structural defects. Therefore, an aluminium‐graphene hybrid metasurface with high‐order BIC is proposed. We have the principle of excitation of high‐order BICs is investigated and creatively proposed with high robustness realized using the magnetical EIT effect. The robustness of the high‐order BIC is also utilized to design security hardware based on DHR architecture. The designed secure hardware can satisfy the demand for an intelligent robotic brain to the internal terahertz wave confidential wireless communication. [ABSTRACT FROM AUTHOR]

Due to nontrivial field topologies, polarization vortices carrying polarization singularities have attracted increasing interest in the fields of optics and photonics. However, the conventional methods for generation of polarization vortcies still suffer from the complexity and the heavy bulk. In this work, taking advantage of spin‐decoupled geometric phase in metasurfaces, a novel method is proposed to generate polarization vortices with customizable topological charges. By tailoring spin‐decoupled geometric phases generated by the metasurface, distinct helical phase profiles can be imparted to left‐ and right‐handed circularly polarized components. Consequently, two scalar vortices with different topological charges can be simultaneously generated in the two orthogonal circular polarization components, leading to the generation of the polarization vortices with the needed topological charges and the diverse morphologies. Both simulation and experimental results well demonstrate the method. Owing to the nondispersive feature of geometric phases, the designed metasurface works well in a wide frequency band. The proposed method contributes a reliable and feasible solution for customizing the generation of polarization vortices, which can be further transposed to other frequencies and applied to information encoding and polarization detection etc. [ABSTRACT FROM AUTHOR]

Optical computing and image processing performed by sensor front‐end metasurfaces is receiving increasing interest because of advantages such as significant reduction of latency time, energy consumption, and system complexity. Despite the rapid progress, concurrent processing, the most important feature of electronic computing, has not yet been well implemented in optical computing. Here, a metasurface‐based optical image processor that can perform optical differentiation and integration tasks simultaneously is proposed. This optical front‐end processor integrates two coherent transfer functions corresponding to differential and integral convolution kernels into a built‐in metasurface by polarization encoding, allowing concurrent processing of multiple all‐optical computational tasks. The simultaneous differentiation and integration operations on images for edge enhancement and denoising are demonstrated at multiple visible wavelengths. This concurrent processing architecture paves a promising pathway toward multifunctional and higher‐speed image processing for machine vision and biomedical imaging and shows the potential to expedite and potentially supplant certain digital neural network algorithms. [ABSTRACT FROM AUTHOR]

Dynamic wavefront shaping with optical metasurfaces has presented a major challenge and inspired a large number of highly elaborate solutions. Here, this study experimentally demonstrates thermo‐optically reconfigurable, nonlocal metasurfaces using simple device architectures and conventional CMOS‐compatible dielectric materials. These metasurfaces support quasi‐bound states in the continuum (q‐BICs) derived from symmetry breaking and encoded with a spatially varying geometric phase, such that they shape optical wavefront exclusively on spectrally narrowband resonances. Due to the enhanced light‐matter interaction enabled by the resonant q‐BICs, a slight variation of the refractive index introduced by heating and cooling the entire device leads to a substantial shift of the resonant wavelength and a subsequent change to the optical wavefront associated with the resonance. This study experimentally demonstrates a metalens modulator, the focusing capability of which can be thermally turned on and off, and reconfigurable metalenses, which can be thermo‐optically switched to produce two distinct focal patterns. The devices offer a pathway to realize reconfigurable, multifunctional meta‐optics using established manufacturing processes and widely available dielectric materials that are conventionally not considered “active” materials due to their small thermo‐optic or electro‐optic coefficients. [ABSTRACT FROM AUTHOR]

In the field of holographic imaging, high-reflectivity metasurfaces have become a crucial technology for achieving high efficiency and high-resolution image reconstruction. This study utilizes the dynamic tunability of magnesium (Mg) to numerically design an optical metasurface capable of displaying multiple holographic images in different states, achieving a reflectivity of up to 82%. In its normal state, the metasurface uses the resonance phase modulation of the metallic Mg structure to display images. Upon the introduction of hydrogen, the Mg transitions to its dielectric state, and a separate gold (Au) structure is used to modulate and display different images. The core contribution of this research lies in the application of a high-reflectivity metal layer, which enhances the imaging effects post-magnesium switching and improves the quality of image display. This work provides a new solution for dynamic optical displays and information storage technologies, thereby expanding the application scope of optical metasurfaces. [ABSTRACT FROM AUTHOR]

This paper presents an ultra-wideband polarization converting metasurface (PCM) for millimeter wave which can manipulate the linear polarized (LP) incident wave to its orthogonal counterpart in the frequency range of 49.7 to 142.2 GHz with an ultra-wide bandwidth of 92.5 GHz and a fractional bandwidth (FBW) of 96%. The proposed PCM shows outstanding results in achieving higher fractional bandwidth with overall polarization conversion ratio (PCR) > 90% in the desired band. The proposed PCM has low profile dimensions with thickness and periodicity of 0.5 mm (0.083 λo) and 1.43 mm (0.24 λo), where λo is the maximum wavelength at the lower operating frequency. Surface current distribution is studied to show the physics of polarization conversion. The design is versatile and adoptable in low-profile applications where minimum thickness is required and can be utilized in remote sensing, microwave relays, and astronomy. [ABSTRACT FROM AUTHOR]

A wideband transmitarray antenna (TA) incorporating a polarization conversion metasurface (PCM) is proposed. Four PCM elements with annular metallic polarizers are utilized to provide 2‐bit phase compensation without altering the geometric parameters of the elements, resulting in a wideband TA with a bandwidth comparable to that of the individual elements. A prototype of the proposed TA is designed, fabricated, and measured. The measured 1‐ and 3‐dB gain bandwidths of the proposed TA are found to be 10–13.6 GHz (30%) and 9.2–15 GHz (48.3%), respectively, while the effective 1‐dB transmission band of the individual elements is 7.8–14.6 GHz. The similarity between the bandwidth of the proposed TA and that of elements used in our design demonstrates less wastage of element bandwidth by the proposed approach. A measured peak gain of 27.2 dBi and a peak aperture efficiency (AE) of 48.7% highlight the promising potential of the proposed TA for long‐distance communication, point‐to‐point communication, and other applications. [ABSTRACT FROM AUTHOR]

A low-profile broadband circularly polarized (CP) dielectric resonator antenna (DRA) is proposed, utilizing DR reutilization and metasurface (MS) techniques. Two resonant frequencies and an AR minimum are achieved simultaneously, by exciting a rectangular DR with an inclined corner-truncated coupling slot, for it generates nearly degenerated TE111 modes. For significant bandwidth enhancement and low profile, a new resonator is formed by reusing the DR and loading an MS above, which works in orthogonal TM modes. To increase the axial ratio bandwidth (ARBW) further without enlarging the antenna size， two parasitic patches are printed on two adjacent side walls of the DR. To verify the rationality and feasibility, the antenna is fabricated and measured. The fabricated prototype possesses the profile of 0.06λ0 (λ0 is the free-space wavelength at the center frequency). The measured impedance bandwidth (IBW) and ARBW are 36.05% (4.23 ~ 6.09 GHz) and 22.46% (4.9 ~ 6.14 GHz), respectively. The proposed antenna has both broadband characteristics and a low profile, making it easy to integrate into space-limited wireless communication systems with high data rates. [ABSTRACT FROM AUTHOR]

In recent years, the rapid development of dynamically tunable metasurfaces has provided a new avenue for flexible control of optical properties. This paper introduces a transmission-type electrically tunable metasurface, employing a series of subwavelength-scale silicon (Si) nanoring structures with an intermediate layer of Al2O3-ITO-Al2O3. This design allows the metasurface to induce strong Mie resonance when transverse electric (TE) waves are normally incident. When a bias voltage is applied, the interaction between light and matter is enhanced due to the formation of an electron accumulation layer at the ITO-Al2O3 interface, thereby altering the resonance characteristics of the metasurface. This design not only avoids the absorption loss of metal nanostructures and has a large modulation depth, but also shows compatibility with complementary metal oxide semiconductor (CMOS) technology. [ABSTRACT FROM AUTHOR]

Optical encryption is an increasingly significant technique in the realm of information security. In the recent decade, there has been considerable interest in using planar optics elements for information encryption. However, information leakage possibly occurs due to limited encrytion channels available for single‐layer devices. To circumvent this problem, a novel encryption method is put forward using secret sharing cascaded liquid crystal (LC) elements with spatial dislocation, which can produce near‐field patterns and far‐field holographic images under different illumination conditions. Specifically, Malus's Law and its inherent one‐to‐four mapping of rotational degeneracy, along with the Pancharatnam‐Berry (PB) phase introduced by LC molecules, to achieve multi‐channel encryption are utilized. Therefore, each cascaded LC unit can manipulate the amplitude and phase imparted to output light independently, thus only by obtaining both LC devices can decryption be realized. To further enhance the encryption security, the author purposely divide each LC device into multiple regions and find that the encrypted patterns can only be recovered when the two LC elements align precisely with a specific dislocation. These experimental measurements agree well with the design, thus demonstrating the strong encryption capability and broad application prospects of the design approach in the field of optical encryption with high cost‐effectiveness. [ABSTRACT FROM AUTHOR]

For over 35 years of research, the debate about the systematic compositionality of neural networks remains unchanged, arguing that existing artificial neural networks are inadequate cognitive models. Recent advancements in deep learning have significantly shaped the landscape of popular domains, however, the systematic combination of previously trained neural networks remains an open challenge. This study presents how to dynamically synthesize a neural network for the design of broadband electromagnetic metasurfaces. The underlying mechanism relies on an assembly network to adaptively integrate pre‐trained inherited networks in a transparent manner that corresponds to the metasurface assembly in physical space. This framework is poised to curtail data requirements and augment network flexibility, promising heightened practical utility in complex composition‐based tasks. Importantly, the intricate coupling effects between different metasurface segments are accurately captured. The approach for two broadband metasurface inverse design problems is exemplified, reaching accuracies of 96.7% and 95.5%. Along the way, the importance of suitably formatting the spectral data is highlighted to capture sharp spectral features. This study marks a significant leap forward in inheriting pre‐existing knowledge in neural‐network‐based inverse design, improving its adaptability for applications involving dynamically evolving tasks. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) photodetection and imaging have sparked significant interests across a wide range of applications. While silicon photodiodes are commonly employed, the small light absorption coefficients of Si in NIR severely limit the performance, especially in the case of thin active Si layers. Although various light harvesting techniques are proposed to increase light absorption of Si, pixel‐level strategy for enhanced NIR imaging is still challenging in CMOS image sensors (CISs) with a pixel size in only a micron scale. In this paper, plasmonic metasurfaces are intimately integrated on top of 2.3 µm thick Si active regions of the pixels of a backside illumination (BI)‐CIS for NIR imaging for the first time. 200% improved photoresponsivity is obtained in experiments in such a planar Si layer rather than patterning the Si layer with potential damage to the active region. Numerical simulation results reveal highly enhanced light intensity in the thin active Si layer due to the presence of plasmonic metasurfaces. Significantly improved imaging brightness and signal‐to‐noise ratio of NIR imaging are demonstrated under both laser and LED illumination. This CMOS‐compatible technique is expected to hold promising potentials in applications including machine vision, iris certification, light detection and ranging (LiDAR), and optical communication in data centers. [ABSTRACT FROM AUTHOR]

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As the demand increases in the field of wireless communication system, the interest of researchers increases to develop and analyzes the antenna for these applications. This article present metasurface (MS) frequency reconfigurable antenna (FRA) which is optimized using neural network (NN) approach. The designed structure is a multilayer consists of three-layer patch antenna placed under the MS structure. The resonating patch is a rectangular shaped and substrate is a circular shaped show as to reduce the geometry of the antenna. The proposed structure is fabricated on FR-4 substrate of thickness 1.6 mm. The MS structure consists of split ring rectangular (SRR) strips made up of copper. The antenna reconfigured the operating frequency from 4.85 to 7 GHz having overall bandwidth of 2.15 GHz with wide range of tuning. The central frequency of rectangular patch antenna is 6.15 GHz. The MS is analyzed by using effective parameters i.e., effective permittivity (εr) & effective permeability (μr) and it is observed that the MS is behaving as a metamaterial in the desired range of frequency. The reconfigured operating frequency (ROF) is found at the anticlockwise rotation angles of 0°, 30°, 600 and 90°. The realized gain and radiation efficiency are calculated at each ROF. The validation of proposed MS based FRA is carried out first by simulating using Ansys HFSS and then measured inside the anechoic chamber. The proposed antenna is optimizes using NN model which shows minimum error during analysis and synthesis process. [ABSTRACT FROM AUTHOR]

Multi-channel holographic metasurfaces have great potential for applications in wireless communications and radar. However, geometric phase-based multichannel metasurface units often have complex phase spectra, making the design of holographic metasurfaces complex and time-consuming. To address this challenge, we propose a dynamic attention mixer-based residual network to streamline the optimization and design of a multi-channel holographic metasurface unit. We conduct validation using multi-channel metasurface units, with a training set mean squared error (MSE) of 0.003 and a validation set MSE of 0.4. Additionally, we calculate the mean absolute error (MAE) for the geometric parameters θ1 and θ2 of the backward-predicted metasurface units in the validation set, which are 0.2° and 0.6°, respectively. Compared to traditional networks, our method achieves robust learning outcomes without the need for extensive datasets and provides accurate results even in complex electromagnetic responses. It is believed that the method presented in this paper is also applicable to the design of other artificial materials or multifunctional metasurfaces. [ABSTRACT FROM AUTHOR]

Over the past few decades, metasurfaces have revolutionized conventional bulky optics by providing an effective approach to manipulate optical waves at the subwavelength scale. This advancement holds great potential for compact, multifunctional, and reconfigurable optical devices. Notably, metasurfaces constructed with anisotropic nanostructures have exhibited remarkable capability in manipulating the polarization state of optical waves. Furthermore, they can be employed to achieve independent control of the amplitude and phase of optical waves in different polarization channels. This capability has garnered significant attention from the photonics community due to its unprecedented potential for polarization-selective and -multiplexed optical wave manipulation, offering versatile applications in optical imaging, communication, and detection. This paper reviews the design principles, representative works, and recent advancements in anisotropic nanostructures for optical polarization manipulation, detection, as well as polarization-selective and -multiplexed optical wave manipulation. Personal insights into further developments in this research area are provided. [ABSTRACT FROM AUTHOR]