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Many contemporary imaging systems seek tunable focusing components with minimal form factors and versatile functionalities; however, existing solutions are typically limited in size, efficiency, and tuning speed. Here, low-loss all-dielectric metasurfaces integrated with liquid crystals (LCs) are used to demonstrate highly compact multifunctional zoom components. The phase profiles imparted by the metalens are modulated in real time by means of field-dependent LCs, enabling electrically driven continuous focal length variation and active bifocal imaging with low applied voltages (

Metal alloy nanostructures represent a promising platform for next-generation nanophotonic devices, surpassing the limitations of pure metals by offering additional buttons for tailoring their optical properties by compositional variations. While alloyed nanoparticles hold great potential, their scalability and underexplored optical behavior still limit their application. Here, we establish a systematic approach to quantifying the unique optical behavior of the AgAuPd ternary system while providing a direct comparison with its pure constituent metals. Computationally, we analyze their electronic structure and uncover the transition of Pd d states to Pd/Ag hybridized s states in the bulk form, explaining the similar optical properties observed between Pd and AgAuPd. Experimentally, we fabricate pure metal and fully alloyed nanoparticles through solid-state dewetting, a scalable method. During the process, we trace the optical transition in the systems from the initial thin film stage to the final nanoparticle stage with in situ ellipsometry. We reveal the interplay between optical properties influenced by chemical interdiffusion and localized surface plasmon resonance arising from morphological changes with ex situ surface characterizations. Additionally, we analytically implement a metallic layer derived from the ternary system in a trilayer device, resulting in a single-time and irreversible color filter, to demonstrate an application encompassing a lithography-free and cost-effective route for nanophotonic devices.

Nanophotonic structures have shown promising routes to controlling and enhancing nonlinear optical processes at the nanoscale. However, most nonlinear nanostructures require a handling substrate, reducing their application scope. Due to the underwhelming heat dissipation, it has been a challenge to evaluate the nonlinear optical properties of free-standing nanostructures. Here, we overcome this challenge by performing shot-controlled fifth harmonic generation (FHG) measurements on a SiC meta-membrane - a free-standing transmission metasurface with pronounced optical resonances in the mid-infrared (λ res ≈ 4,000 nm). Back focal plane imaging of the FHG diffraction orders and rigorous finite-difference time-domain simulations reveal at least two orders of magnitude enhancement of the FHG from the meta-membrane, compared to the unstructured SiC film of the same thickness. Single-shot measurements of the meta-membrane with varying resonance positions reveal an unusual spectral behavior that we explain with Kerr-driven intensity-dependent resonance dynamics. This work paves the way for novel substrate-less nanophotonic architectures.

The perfect vector vortex beams (PVVBs) have played an important role in various fields due to their advantages of unique vortex features, flexible polarization distribution and multiple degrees of freedom (DoFs). The simultaneous and precise control over multiple DoFs, such as the polarization distribution, beam shape and position which greatly influence various characteristics of PVVBs, holds paramount importance. However, it is still difficult to manipulate various DoFs in a multiplexing way and the control precision of polarization distribution only reaches the half-integer level, notably hindering the further application and development of PVVBs. Here, an approach that integrates holographic technique with geometric phase metasurfaces, experimentally demonstrates the multiplexing control of PVVBs over three DoFs, i.e., enabling the independent manipulation of non-uniform polarization distributions, beam shapes and spatial positions. Furthermore, non-integer polarization order of the generated PVVBs can be arbitrary non-integer numbers with a high resolution of 0.1, largely improving the control precision. With such multiplexing manipulation of PVVBs with high precision, we can provide abundant processing dimensions for information science and technologies, exhibiting broad application potentials in fields such as information encryption, high-speed optical communication, and precise particle manipulation. [ABSTRACT FROM AUTHOR]

Simultaneous optical display and depth perception are crucial in many intelligent technologies but are usually realized by separate bulky systems unfriendly to integration. Metasurfaces, artificial two-dimensional optical surfaces with strong light–matter interaction capabilities at deep subwavelength scales, offer a promising approach for manufacturing highly integrated optical devices performing various complex functions. In this work, we report a polarization-multiplexed metasurface that can functionally switch between holographic display and Dammann gratings. By tailoring the incidence polarization, the metasurface can display high-quality holographic images in the Fresnel region or project a uniform spot cloud nearly covering the entire 180° × 180° transmissive space. For the latter, a projection and three-dimensional (3D) reconstruction experiment is conducted to elaborate the potential in retrieving 3D complex spatial information. The current results provide a prominent way to manufacture lightweight and highly-integrated comprehensive imaging systems especially vital for cutting-edge intelligent visual technologies. [ABSTRACT FROM AUTHOR]

Metasurfaces have garnered significant attention in recent years for their ability to manipulate electromagnetic (EM) wave propagation, owing to their high design flexibility, low profiles, and ease of fabrication. This study proposes the use of polarization-dependent anisotropic metasurfaces to manipulate the phase of orthogonal linearly polarized EM waves, enabling polarization multiplexing with distinct functionalities based on incident polarizations. Additionally, the proposed metasurfaces enable the generation of single pencil beams, multiple pencil beams, circularly and elliptically shaped radiation beams, offering versatile polarization manipulation capabilities. The radiation theory of planar array antennas was employed to predict the far-field patterns of the metasurfaces, demonstrating satisfactory agreement with simulated results and affirming the feasibility of the proposed method. The ability of focusing the incoming EM wave into a focal point or multi focal points and generating vortex beam carrying orbital angular momentum (OAM) under the incidence of orthogonal linearly polarized waves are also demonstrated by the proposed anisotropic metasurfaces. This proposed metasurfaces pave the way for the development of multifunctional metadevices capable of advanced EM regulation through polarization and phase modulations in free space, with potential applications in wireless communication, imaging, and radar systems. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for designing a superstrate for the Fabry Pérot antenna, to achieve beam steering over the full azimuthal plane. The superstrate of the proposed antenna consists of a linearly graded metasurface (LgMS) and a constant phase partially reflecting surface (PRS). The hybrid metasurfaces offer gradual changes in the magnitude and phase of the reflection and transmission coefficient characteristics, which causes tilting of the main lobe direction.Further, the mechanical rotation of the superstrate structure in the azimuthal plane causes the main lobe direction to steer in the same plane. The proposed antenna operates from 4.33 GHz to 5.1 GHz with a maximum directivity of about 11 dBi and offers beam steering over complete azimuthal plane for frequencies below 4.8 GHz. The proposed structure can be used as a beam steering antenna for applications like air traffic control, satellite communication, shipboard communication, etc. [ABSTRACT FROM AUTHOR]

In this paper, a new coating structure is proposed for broadband radar cross section (RCS) reduction using 1‐bit metasurfaces. The designed structure consists of two types of unit cell, arranged in concentric square rings. The substrate of unit cells is different, FR4 and Ultralum‐2000 with thicknesses of 2.4 and 0.762 mm, respectively. The proposed structure shows an ultrawideband property to reduce the RCS, less than −10 dB, in the frequency range of 14–45 GHz. This range covers part of Ku‐band (14–18 GHz), K‐band (18–27 GHz), and Ka‐band (27–40 GHz) and part of millimeter‐wave band (40–45 GHz). To validate the designed work and simulation results, a prototype with the dimension of 84 × 84 mm2 is fabricated and tested. Also, the RCS reduction is determined analytically and presented. The measured results verify well the analytical and simulation results. In short, this work includes three new points: (1) the use of two substrates with different thickness and dielectric constant to design unit cells, (2) a new arrangement of array cells in the form of concentric square rings, and (3) achieving a great bandwidth to reduce RCS. [ABSTRACT FROM AUTHOR]

With the rapid development of metasurface technology, metasurfaces have gained significant attention in optical edge detection. Owing to their precise control over the phase, amplitude, and polarization state of electromagnetic waves, metasurfaces offer a novel approach to edge detection that not only overcomes the size limitations of traditional optical devices but also significantly enhances the flexibility and efficiency of image processing. This paper reviews recent research advances in metasurfaces for optical edge detection. Firstly, the principles of phase-controlled metasurfaces in edge detection are discussed, along with an analysis of their features in different applications. Then, methods for edge detection based on polarization and dispersion modulation of metasurfaces are elaborated, highlighting the potential of these technologies for efficient image processing. In addition, the progress in multifunctional metasurfaces is presented, offering new perspectives and application prospects for future optical edge detection, along with a discussion on the limitations of metasurface-based edge detection technologies and an outlook on their future development. [ABSTRACT FROM AUTHOR]

Multifoci focusing has always been a problem that researchers continue to pay attention to and urgently needs to be solved. Metasurfaces display unprecedented capabilities and flexibilities to solve this problem. In this work, Pancharatnam–Berry (PB)‐phase‐based plasmonic metasurfaces are presented to realize wavelength‐selective directional focusing on the same focal plane. Ultrathin meta‐atoms with the half‐wave plate effect have only three layers, and 360° phase modulation is obtained by axially rotating gold strip based on PB phase. Two metasurfaces are designed to verify our strategy. Above all, a wavelength‐selective directional focusing metasurface is presented to converge right‐handed circularly polarized wave with wavelengths of 187, 271, and 355 μm at different predetermined positions at 810 μm. Next, the second metasurface exhibits the function that three vortex beams carrying orbital angular momentums with different topological charges can be produced under the irradiation of incident wave at the aforementioned wavelengths. In this research, a solid step is paved toward practical applications of flat photonics. [ABSTRACT FROM AUTHOR]

Meta‐lenses can offer potential improvements over traditional optical components in imaging, display, and detection. Initial meta‐lenses strive for uniform spectral responses over broadband for full‐color imaging. Nevertheless, enhancing wavelength selectivity remains crucial for specific applications, such as fluorescence imaging and augmented reality, requiring specific wavelengths. Current methods struggle to balance nonlocal resonance with local phase control or introduce an additional filter layer. Here, an all‐dielectric resonant meta‐lens for wavelength‐selective focusing based on the Fresnel zone plate design is experimentally demonstrated. The coupling between nonlocal lattice resonance and local Mie‐type resonance is effectively manipulated to control the reflection and bandwidth. Without considering the balance between nonlocal resonance excitation and local phase control, the resonant meta‐lens can reflectively focus at a resonant wavelength of 460 nm while allowing normal transmission at non‐resonant wavelengths, which is generally restricted in conventional metallic counterparts. Simulation (experimental) results indicate a high color purity of 90% (66%), surpassing those of meta‐lenses with filtering functions. A multi‐resonant meta‐lens is further designed for red, green, and blue colors. This work offers enhanced options for wavelength‐selective meta‐lenses, expanding their potential in optical imaging and display applications. [ABSTRACT FROM AUTHOR]

The advent of a new era of flat optics is due to the optical metasurfaces, whose large number of degrees of freedom allowed one to fabricate various optical elements on a single technological platform. The use of van der Waals (vdW) layered materials, which have a remarkable combination of a high refractive index, record optical anisotropy and bright exciton resonances, can lead to operating regimes of metasurfaces that are unattainable for their dielectric counterparts. In this work, the degree of freedom related to the optical anisotropy is used for control of the balance and competition of modes of vdW resonators, leading to the observation of both the well‐known hybrid anapole effect and recently predicted octupole quasi‐trapped mode (OQTM) regime in the same metasurface. Using far‐field and near‐field analysis of the metasurface composed of MoS2${\rm MoS}_2$ disks, both the common and significantly different features of these two effects are demonstrated and it is found that the remarkable combination of narrow spectral features and strong energy localization makes OQTM‐supported vdW metasurfaces a much more attractive alternative for creating flat nanophotonic devices, including narrowband converters, light concentrators, as well as surface‐emitting lasers and nonlinear light converters. [ABSTRACT FROM AUTHOR]

Improving light absorption is essential for the development of solar thermoelectric generators. Most efficient light absorbers require a back mirror (a thick metal film) to reduce the reflectivity by promoting the interference between the incident and the reflected light. However, the presence of thick a continuous metal film supposes a limitation for thermoelectric applications, as it behaves like a shortcut of the Seebeck voltage. In this work, a back mirror‐free selective light absorber is presented, designed for the fabrication of thermoelectric devices. The combination of a high and a low refractive index material covered by a semi‐transparent electrode is optimized. As a difference to the back mirror, the semi‐transparent electrode can be patterned to prevent the quenching of the Seebeck voltage. Thanks to this, the low refractive index material can be replaced by a transparent thermoelectric, enabling efficient heat‐to‐energy conversion with negligible loss of absorption performance. [ABSTRACT FROM AUTHOR]

Metasurfaces garner widespread attention for their remarkable ability to precisely manipulate light and construct optical multiplexing devices. However, there is still a lack of effective solutions for achieving high‐performance wavelength decoupling in the realm of wavelength multiplexing. In this work, a novel wavelength decoupling method based on minimalist metasurfaces featuring a single‐celled configuration is proposed. These metasurfaces are composed of only two types of nanobricks, each capable of modulating the phase of two different wavelengths simultaneously as desired. The proposed minimalist metasurfaces possess the advantages of flexible design, enabling wavelength decoupling with incidences at both co‐ and cross‐polarization states. Interestingly, by integrating the wavelength decoupling metasurface with liquid crystal devices, information encryption can be achieved. The proposed wavelength decoupling method holds broad application prospects in the fields of optical data storage, image display, information security, and beyond. [ABSTRACT FROM AUTHOR]

Over the past decades, metasurfaces have experienced rapid development controlling the propagation of electromagnetic waves. Seamlessly combining metasurfaces with semiconductor devices enhance the device's performance and expand functional diversity. Currently, vertical‐cavity surface‐emitting lasers integrated with metasurfaces (MS‐VCSELs) employed to generate various wavefronts. However, the existing MS‐VCSELs that use only phase modulation still face limitations and challenges in generating customized fields, especially in 3D space. Here, amplitude‐phase metasurfaces are proposed and joint amplitude‐phase modulations are employed to increase the degree of freedom in controlling laser fields. By using electron beam lithography (EBL) and inductively coupled plasma reaction ion etching (ICP‐RIE), metasurfaces are directly fabricated on the back‐emitting surface of VCSELs, enabling samples to realize diverse functions such as multi‐focus multi‐plane generation and intensity control, multi‐plane holographic images, and laser beam deflections with different intensities. Compared to traditional discrete metasurface configurations, the proposed scheme achieves on‐chip integration of amplitude‐phase metasurface with the light source, enhancing the multidimensional laser field modulation capabilities of MS‐VCSELs in the 3D space while further promoting the cross‐integration of metasurfaces with optoelectronic devices. It is believed that MS‐VCSELs with amplitude‐phase modulations hold significant promise for applications in 3D imaging, facial recognition, and laser communications. [ABSTRACT FROM AUTHOR]

Spatiotemporal vortex pulses (STVPs) with transverse orbital angular momentum (OAM) have recently stimulated great interest, influencing wide disciplines from classical to quantum optics. However, generating sophisticated STVPs in high‐efficiency and compact systems remains a challenge. This work outlines an ultra‐compact metasurface approach to efficiently generate STVPs through the coupling of free‐space plane waves with a quasi‐bound state in the continuum (quasi‐BIC). The approach leverages external excitation of the quasi‐BIC at the Γ‐point by slightly dislocating two sub‐layer gratings to break the mirror symmetries. This operation converts the incident wave into a unidirectional surface mode and induces a Fano resonance, resulting in STVPs in the frequency‐momentum domain. The method is demonstrated experimentally with a meta‐grating to produce an electromagnetic (EM) STVP with a topological charge of l = −1 with high fidelity and use the set‐up to unravel the hitherto unexplored diffraction and dispersive properties of near‐field STVPs. The present work can be extended from the microwave to the visible light regime by simply scaling the metasurface, and allowing high‐order OAM generation through cascaded elements, thereby paving a robust way to build up ultra‐compact STVP multiplexing devices for future applications. [ABSTRACT FROM AUTHOR]

Cyanide, a highly toxic chemical compound, presents severe risks to both human health and the environment. Its presence is particularly concerning in various industrial sectors, including mining, electroplating and chemical manufacturing, as well as in natural water bodies due to industrial discharge. This study introduces a graphene-based metasurface sensor designed for highly sensitive cyanide detection within the terahertz frequency range. The sensor's design was refined through comprehensive electromagnetic modelling and analysis. Performance characterization demonstrates optimal sensitivity of 929 GHz RIU−1, coupled with a figure of merit of 14.286 RIU−1 between 0.806 and 0.856 THz frequencies. The detection limit achieved is 0.053 RIU. Adjustments to graphene's chemical potential and structural dimensions demonstrated the device's adaptability. Additionally, the application of machine learning techniques, specifically 1D-CNN regression, proved effective in optimizing sensor performance. The predictive model demonstrated remarkable accuracy, with an optimal R2 score exceeding 95%, indicating that over 94.9% of the variance in the data was accounted for. This high precision enables accurate estimation of absorption values for wavelengths between measured points, underscoring the model's reliability in spectroscopic analysis. This work highlights a versatile platform for rapid, label-free cyanide detection, with significant potential for applications in environmental monitoring, industrial safety and public health protection. [ABSTRACT FROM AUTHOR]

Diffractive Optical Elements (DOEs) are indispensable tools across numerous technological domains due to their capacity to manipulate light with sophistication and versatility. Their compact dimensions, lightweight nature, and compatibility with diverse materials render DOEs as prime candidates for integration into various optical systems, spanning from consumer electronics to state‐of‐the‐art scientific devices. Thus, DOEs stand as essential catalysts in technological advancement, facilitating innovation and unlocking new applications across a broad spectrum of disciplines. In this comprehensive review paper, Numerous types of DOEs widely acknowledge for their efficacy in both free space optics and imaging applications are delved. Beyond mere enumeration, their practical applications, elucidating their transformative impact on these fields are carefully examined. Furthermore, the challenges encountered in their implementation are dissected, paving the way for insightful discussions on future trajectories and advancements. [ABSTRACT FROM AUTHOR]

Time‐varying electromagnetic materials are introducing new ways to control and transform light waves, unlocking unexplored scattering phenomena. In this paper, the wave phenomena associated with abrupt changes in the surface impedance of a metasurface introduced uniformly in space, forming a time interface are investigated. Efficient transformation of a monochromatic surface wave propagating along the metasurface into a radiated wave at a significantly higher frequency is demonstrated. This phenomenon realizes an efficient radiator for electromagnetic wireless signals at high frequencies relying on generators and modulators operated at a much lower frequency. [ABSTRACT FROM AUTHOR]

Guided waves are the perfect carriers of electromagnetic signals in planar miniaturized devices due to their high localization and controlled propagation direction. However, it is still a challenge to control the polarization of propagating guided waves. In this work, the broadband polarization TE‐TM degeneracy of highly localized guided waves propagating along an all‐dielectric metasurface and a subwavelength chain of dielectric high‐index cylinders is discovered, both theoretically and experimentally. Using the discovered near‐field polarization degree of freedom, the polarization transformation for guided waves propagating along a subwavelength chain of dielectric cylinders at any frequency within the finite spectral range is demonstrated experimentally. Namely, the simplest planar near‐field polarization device – the quarter‐wave‐retardation (linear‐to‐circular) polarization transformer of guided waves is implemented. The results obtained discover the polarization degree of freedom for guided waves paving the way toward numerous applications in flat optics and planar photonics. [ABSTRACT FROM AUTHOR]

We investigate the electromagnetic modes supported by parallel-plate waveguides created by juxtaposing two planar metasurface junctions, focusing on specific parameter ranges where each junction sustains a line wave. We explore how these waves interact as the waveguide thickness changes, considering both purely reactive and non-Hermitian scenarios (incorporating gain/loss). Our findings suggest the potential to achieve tightly confined, quasi-one-dimensional modes, as well as exceptional points and intriguing transitions between waveguiding and radiative regimes. These findings hold promise for applications in fields ranging from nonlinear optics to sensing and imaging. [ABSTRACT FROM AUTHOR]

Metasurfaces have opened doors to combining multiple photonic functionalities in a single compact device. In particular, the ability to generate short terahertz (THz) pulses with precise wavefront engineering in a single THz metasurface redefined the role metasurfaces can play in THz systems. Here, an InAs metalens emitter which generates and focuses a THz pulse beam is demonstrated using a 130 nm thick InAs metasurface designed as a binary‐phase Fresnel zone plate. The THz beam is focused to a spot of ≈430 μm at 1 THz with a short focal length of 5 mm and large numerical aperture of 0.5. Nanoscale InAs Mie resonators comprising the metasurface enable THz generation with an amplitude as high as 20 times compared to plasmonic THz emitters and several times compared to a 1 mm thick ZnTe crystal. This InAs metasurface emitter provides a new paradigm for designing THz imaging, spectroscopy, and communication systems, where THz beam generation and shaping are performed with a single device without compromising the generation efficiency, while eliminating losses and avoiding limitations of phase matching of conventional nonlinear optics approaches. [ABSTRACT FROM AUTHOR]

A metasurface composed of silver nanoflower arrays, which exhibit asymmetrical absorption and surface‐enhanced Raman scattering (SERS) due to hybrid plasmonic effects, is reported. The silver nanoflowers are fabricated by oblique deposition of silver on a polymer nanohole array on a glass substrate, forming petal‐like semicontinuous thin films on the inner walls of the holes. Depending on the deposition angle, three‐ or five‐petal nanoflowers are obtained. The nanoflower arrays show strong reflection from the air side and broadband and wide‐angle absorption from the glass side, as a result of transmission surface plasmon resonance and localized surface plasmon resonance, respectively. The three‐petal structure, which absorbs most of the incident light from the glass side, induces a localized enhancement of electric field in the center of each nanohole, providing a high‐sensitivity SERS substrate. The SERS performance of the metasurface by direct measurement and near‐field simulation is demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents a detailed design, simulation, measurement, and validation of an Inductive Intertwined Frequency Selective Surface (IIFSS) employing a 2.5D configuration (2.5DIIFSS). The proposed unit cell achieves high miniaturization, with dimensions as small as $0.0096\lambda _{0} \times 0.0096\lambda _{0}$ at 0.268 GHz, using 4 vias per unit cell. The compact design delivers a fractional bandwidth of 87% for the passband associated with the fundamental harmonic. Additionally, the unique 2.5D configuration introduces extra inductance and capacitance, effectively shifting higher harmonics to higher frequencies, thus maintaining a stable stop band beyond the fundamental harmonic. The angular stability analysis reveals minimal variation up to an incidence angle of 60° for both TE and TM modes across the fundamental harmonic. To elucidate the underlying physics, an equivalent circuit model was developed, accurately capturing the fundamental harmonic behavior of the structure. To further validate the design and demonstrate its scalability, a prototype was designed and fabricated for operation at 2.4 GHz, addressing the measurement challenges associated with the original 0.268 GHz design. This prototype was rigorously tested in a transmission regime, with measurement results showing good agreement with simulation data, thereby confirming the efficacy and practicality of the proposed design.

This study introduces a reflective polarization converter based on metasurface, designed to offer both Linear-to-Linear polarization (LLP) and Linear-to-Circular polarization (LCP). The design comprises two periodically arranged split ring resonators with a slotted stripe that operate in the X, Ku, and K bands. The three discrete frequency bands demonstrate over 90% Polarization Conversion Rate for LLP for oblique incidence waves up to 45°. Additionally, the proposed converter achieves Left-Hand Circular Polarization (LHCP) in two sub-bands and Right-Hand Circular Polarization (RHCP) in two sub-bands for oblique incidence waves up to 45°. The metasurface design introduced in this study exhibits significant potential for satellite applications in 6G networks, owing to its versatile LLP and LCP conversion properties in the X, Ku, and K bands.

We present a 1-bit reconfigurable intelligent surface (RIS) operating at millimeter-wave frequencies that suppresses the undesired grating lobes encountered in binary phase modulation schemes and achieves high resolution beam steering. We incorporate fixed, random phase delays at each unit cell of the surface which breaks the periodicity of the phase quantization error and suppresses side lobes. Additionally, the random phase delays reduce the beam pointing error – a limitation of binary RISs - which can be beneficial in applications that require high resolution beam steering. The proposed topology allows for scalable RIS apertures that are compatible with printed circuit board (PCB) fabrication technology. It consists of four metasurface tiles of 256 radiating elements ( $16\times 16$ ) connected on a separate control board that houses the control unit and power supply. The prototype is designed to operate at 27.2 GHz and perform electronic beam steering in ±60° in both azimuth and elevations planes. A quantization lobe reduction of more than 10 dB is achieved with the proposed technique and the surface is well suited for mmWave 5G communication scenarios to enhance signal coverage and signal-to-noise ratio.

Line-waves are one-dimensional modes propagating at the interface between two planar complementary surfaces, characterized by tight transversal confinement of the field. Despite their unique guiding properties, their use in real microwave devices is still in the early stages, lacking a comprehensive design procedure and comparative analysis with conventional guiding structures. To fill this gap, here we report a simple and straightforward workflow for designing waveguides supporting 1D modes propagation. The design is based on the analytical relations existing between the surface impedance of the propagating modes and the sheet impedance of the metasurfaces, which allow quick retrieval of the geometrical parameters of the complementary metasurfaces sustaining the line-wave propagation. This approach is used to design several waveguiding layouts and compare their transmission performance through full-wave simulations accounting for dielectric and ohmic losses. Finally, experimental results for some selected designs in the microwave regime are provided, and a thoughtful comparison between a line-wave waveguide and an equivalent microstrip transmission line is carried out to assess the suitability of these devices for efficient high-frequency waveguiding.

This paper proposes miniaturized, lightweight and ultrasensitive planar metamaterial sensor for relative permittivity measurement of nondispersive materials. The proposed sensor is designed using a thin-substrate microstrip line loaded with tapered sectorial Complementary Split Ring Resonator (CSRR). Compared to similar state-of-the-art sensors, the proposed one is at least (25)% more sensitive with a wide dynamic range of the sensing related frequency. Moreover, unlike previously proposed sensors, the relative permittivity of a dielectric sample can be estimated using the variation of the minimum transmission frequency as well as the variation of the 10-dB sensor’s bandwidth which increases the integrity and accuracy of the obtained results. The minimum transmission frequency of the proposed sensor shifts by almost 7.6 GHz with a percentage change of 61% when the relative permittivity of the material under test (MUT) changes from 1 to 10. In addition, the 10-dB bandwidth is reduced by almost 7.7 GHz for the same MUT relative permittivity changes. Experimental measurements are in good agreement with the numerical findings. The paper includes a comprehensive sensitivity analysis that investigates the effect of resonator’s split length as well as its path width on the sensitivity and dynamic range of CSRR based sensors. Finally, the proposed sensor was used for microfluidic sensing to further demonstrate its practicality using different samples with different electrical properties. The sensor was able to provide distinct features for three different eye drops. The proposed sensor can be utilized as an effective permittivity sensor for various sensing applications such as displacement, nondestructive and biomedical sensing.

Abstract This paper presents a novel design approach for an anomalous reflector metasurface for communication systems operating at 8 GHz band. The main contribution of this work is the development of a general analytical method that accurately calculates the electromagnetic response of realistic metasurfaces with periodic impedance profiles. The modulated surface impedance is achieved by incorporating appropriately sized conductive patches on a grounded dielectric substrate. The proposed design utilizes a genetic algorithm (GA) optimization technique to optimize the surface impedance that achieving efficient reflection of incident waves towards a specific angle of 45˚. The optimization process targets a specific impedance profile derived from the analytical model, leading to the desired anomalous reflection behavior. Then by using periodic boundary conditions, dimensions of an elliptical unit cells can be obtained. To evaluate the anomalous reflection performance, the bistatic radar cross section (BRCS) are simulated at different frequencies. A reflector metasurface sheet is fabricated and measured for verification. The proposed approach provides a foundation for implementing intelligent metasurfaces in various communication applications.

An optical response (reflection, transmission, and absorption spectra) of a photonic crystal layer with a square lattice of chiral holes with rotation axis C2 to circularly polarized light is theoretically investigated. The geometrical parameters of the structure are selected to achieve the maximum possible circular dichroism response under the condition of complete absence of optical losses in the system. It is shown that the account of losses in thin near-surface layers of the structure, for example, due to scattering on surface roughness or absorption due to metallization of near-surface layers, leads to rapid degradation of the degree of chirality of the optical response, increasing the absorption value. Calculations are carried out for a chiral photonic crystal layer made of diamond for a wavelength range of λ=10–12 um (wave number, 830 – 1000 cm–1).

The next generation of infrared (IR) sensors may enable unprecedented applications in fields like spectroscopy, health monitoring, and communication systems. For instance, metasurface-enhanced micro-electromechanical system (MEMS)-based IR sensors have demonstrated excellent performance in terms of responsivity and spectral-selectivity. However, it is burdensome to experimentally determine the performance limits of this and other IR sensing technologies as it requires time-consuming and expensive systematic testing not always feasible in research settings. To address this challenge, an automated solution for characterizing miniaturized sensing devices is presented in this paper and applied to experimentally determine the performance limits of MEMS-based IR sensors. The system offers low-cost, rapid, and automated characterization of on-chip IR sensors, determining key performance metrics such as noise, responsivity, and noise-equivalent power. The platform is flexible, easily adapted to different types of devices, chip layouts, and light sources, and is designed to test a large number of sensors within the same wafer -spending ~ 20 seconds per device- using a combination of optical and radiofrequency interrogation techniques. The system has been applied to test over 1500 MEMS-based IR sensors. Collected data revealed hidden trade-offs between responsivity and noise with respect to the device thickness and allowed a statistical analysis of sensing response versus device geometrical dimensions. The best-performing devices exhibit a quality factor, responsivity, fluctuation induced noise, and noise-equivalent power of 2391, 164 Hz/nW 0.257 H z / H z , and 5.01 p W / H z respectively. The proposed automated platform provides an efficient and cost-effective solution for characterizing the next generation of IR sensing devices.

Design of multiple-feed lens antennas requires multivariate and multi-objective optimization processes, which can be accelerated by PSO algorithms. However, the PSO algorithm often fails to achieve optimal results with limited computation resources since spaces of candidate solutions are quite large for lens antenna designs. This paper presents a design paradigm for multiple-feed lens antennas based on a physics-assisted particle swarm optimization (PA-PSO) algorithm, which guides the swarm of particles based on laws of physics. As a proof of concept, a design of compact metalens antenna is proposed, which measures unprecedented performances, such as a field of view at ±55°, a 21.7 dBi gain with a flatness within 4 dB, a 3-dB bandwidth >12°, and a compact design with a f-number of 0.2. The proposed PA-PSO algorithm reaches the optimal results 6 times faster than the ordinary PSO algorithm, which endows promising applications in the multivariate and multi-objective optimization processes, including but not limited to metalens antenna designs.

Abstract The telecommunication wavelengths are crucial for developing a photonic integrated circuit (PIC). The absorption fingerprints of many gases lie within these spectral ranges, offering the potential to create a miniaturized gas sensor for PIC. This work presents novel double Fano resonances within the telecommunication band, based on silicon metasurfaces for selective gas sensing applications. Our proposed design comprises periodically coupled nanodisk and nanobar resonators mounted on a quartz substrate. Fano resonances can be engineered across the range from λ = 1.52 μm to λ = 1.7 μm by adjusting various geometrical parameters. A double detection sensor of carbon monoxide (CO) at λ = 1.566 μm and nitrous oxide (N2O) at λ = 1.674 μm is developed. The sensor exhibits exceptional refractometric sensitivity to CO of 1,735 nm/RIU with an outstanding FOM of 11,570 at the first Fano resonance (FR1). In addition, the sensor shows a sensitivity to N2O of 194 nm/RIU accompanied by an FOM of 510 at the second Fano resonance (FR2). The structure reveals absorption losses of 6.3% for CO at the FR1, indicating the sensor selectivity to CO. The sensor is less selective at FR2 and limited to spectral shifts induced by each gas type. Our proposed design holds significant promise for the development of a highly sensitive double-sensing refractometric photonic integrated gas sensor.

Electromagnetic waves carrying orbital angular momentum (OAM), namely OAM beams, are important in various fields including optics, communications, and quantum information. However, most current schemes can only generate single or several simple OAM modes. Multi-mode OAM beams are rarely seen. This paper proposes a scheme to design metasurfaces that can generate multiple polarization-multiplexed OAM modes with equal intervals and intensities (i.e., OAM combs) working in the terahertz (THz) range. As a proof of concept, we first design a metasurface to generate a pair of polarization-multiplexed OAM combs with arbitrary mode numbers. Furthermore, another metasurface is proposed to realize a pair of polarization-multiplexed OAM combs with arbitrary locations and intervals in the OAM spectrum. Experimental results agree well with full-wave simulations, verifying a great performance of OAM combs generation. Our method may provide a new solution to designing high-capacity THz devices used in multi-mode communication systems.