Metasurface Array Research Articles

An End‐Fed Programmable Metasurface Based on Substrate Integrated Waveguide for Novel Phased Array

A programmable metasurface antenna based on electrically tunable elements operating in 5G millimeter‐wave band, which has the features of low cost, easy manufacturing, low profile, easy integration with planar circuits, is proposed herein. The prototype consists of a 128‐element metasurface array, an 8‐channel beamforming chip as equal amplitude power divider networks, and a control network. Elements mounted with varactors to realize different states are controlled by DC bias signal from the back of a printed circuit board (PCB). By assigning different voltage values, array coding can be dynamically changed, thereby realizing beam steering. Both element dimensions and its location along substrate integrated waveguide (SIW) are optimized to better antenna performance. Experiment results show that the proposed metasurface can achieve not only the scanning range of ±70° for unidirectional beam in azimuth and ±40° in elevation but also ±50° for dual beam in azimuth. The whole prototype is fabricated based on PCB technologies, and good agreements among simulated and measured results are obtained. The proposed electrically tunable metasurface array is a good alternative to the traditional expensive phased array and has a great potential application prospect in radar and communication systems.

An ultra-high figure of merit refractive index sensor with Mie lattice resonance of a toroidal dipole in an all-dielectric metasurface array in the near-infrared

Recently, improvement of the sensing performance of refractive index sensors using the weak far-field radiation and strong local field enhancement properties of toroidal dipole resonances has been intensively studied. Transmission/reflection spectra with significant narrow linewidth resonance have a vital effect in improving the sensing performance. However, a narrower linewidth always leads to smaller modulation depth of the resonance, which hinders the sensing performance to be improved for experiments. In this paper, we design an ultrathin all-dielectric asymmetric X-type metasurface array, where an extremely narrow linewidth and high modulation depth of transmission resonance in the near-infrared have been demonstrated with Mie lattice resonance formed by the coupling of the toroidal dipole with Rayleigh anomalous diffraction. With optimized structure parameters, a transmission dip with a full width at half-maximum as narrow as 0.061 nm and a modulation depth as high as 99.24% are achieved at a wavelength of 943.33 nm with a corresponding Q factor of 15464. According to the analysis of the displacement current distributions and the scattered powers in the far field at the resonant and nonresonant wavelengths, it is confirmed that the narrow linewidth resonance originates from the coupling of the toroidal dipole with Rayleigh anomalous diffraction. A sensitivity and a figure of merit of 321 nm RIU−1 and 5262 RIU−1 are numerically demonstrated respectively for a refractive index sensor based on the all-dielectric asymmetric X-type metasurface array.

A reconfigurable asymmetric-transmission metasurface for dynamic manipulation of transmission, reflection, and polarization

A broadband reconfigurable metasurface consisting of perpendicular metallic gratings and a PIN diode-driven split circular ring for polarization and propagation modes control is demonstrated. The designed metasurface possesses tunable properties in two propagation modes. In the “OFF” state, it can convert incident linear-polarized waves into transmitted cross-polarized waves with full transmission. In the “ON” state, it can reflect incident linear-polarized waves into co-polarized waves with full reflection. Without the increasing number of active elements commonly utilized in chirality-type metasurface polarizers, the equivalent transformation of the split circular ring can be achieved by switching the single PIN diode, and high polarization-conversion efficiency is guaranteed. A metasurface array with 10 × 10 unit cells is fabricated and measured. The experimental results show that the tunable transmission, reflection, and polarization properties of the proposed reconfigurable metasurface can be achieved from 4.9 to 7 GHz.

Electrically programmable solid-state metasurfaces via flash localised heating

In the last decades, metasurfaces have attracted much attention because of their extraordinary light-scattering properties. However, their inherently static geometry is an obstacle to many applications where dynamic tunability in their optical behaviour is required. Currently, there is a quest to enable dynamic tuning of metasurface properties, particularly with fast tuning rate, large modulation by small electrical signals, solid state and programmable across multiple pixels. Here, we demonstrate electrically tunable metasurfaces driven by thermo-optic effect and flash-heating in silicon. We show a 9-fold change in transmission by <5 V biasing voltage and the modulation rise-time of <625 µs. Our device consists of a silicon hole array metasurface encapsulated by transparent conducting oxide as a localised heater. It allows for video frame rate optical switching over multiple pixels that can be electrically programmed. Some of the advantages of the proposed tuning method compared with other methods are the possibility to apply it for modulation in the visible and near-infrared region, large modulation depth, working at transmission regime, exhibiting low optical loss, low input voltage requirement, and operating with higher than video-rate switching speed. The device is furthermore compatible with modern electronic display technologies and could be ideal for personal electronic devices such as flat displays, virtual reality holography and light detection and ranging, where fast, solid-state and transparent optical switches are required.

A dual-band, polarization-insensitive, wide-angle metasurface array for electromagnetic energy harvesting and wireless power transfer

A dual-band, polarization-insensitive, wide-angle metasurface array is presented in this article for electromagnetic (EM) energy harvesting in the UMTS-2100 band and Wi-Fi band. The metasurface unit cell is composed of two rings (each with four splits) nested in a centrosymmetric manner. The proposed metasurface array energy harvester consists of periodic array unit cells, a single series diode rectifier, and a load. The design of interconnected unit cells to form energy flow channels enhances the power density of the array terminals, thus improving the ability of the metasurface array to capture energy. In addition, the proposed resonant structure is centrosymmetric, so that consistent and effective collection efficiency can be obtained under different polarizations as well as at wide angular incidence. Moreover, the designed rectifier circuit enables the absorber to rectify dual bands simultaneously at low input power density. The prototype of the finite array is fabricated and tested in an anechoic chamber. The results show that the collection efficiency of the proposed metasurface array can reach 64.8% and 41.1% at two frequencies when the available power density reaches 46.4 μW/cm2.

Polarization multiplexing multichannel high-Q terahertz sensing system

Terahertz functional devices with high-Q factor play an important role in spectral sensing, security imaging, and wireless communication. The reported terahertz devices based on the electromagnetic induction transparency (EIT) effect cannot meet the needs of high-Q in practical applications due to the low-Q factor. Therefore, to increase the Q-factor of resonance, researchers introduced the concept of bound state in the continuum (BIC). In the quasi-BIC state, the metasurface can be excited by the incident wave and provide resonance with a high-Q factor because the condition that the resonant state of the BIC state is orthogonal is not satisfied. The split ring resonator (SRR) is one of the most representative artificial microstructures in the metasurface field, and it shows great potential in BIC. In this paper, based on the classical single-SRR array structure, we combine the large and small SRR and change the resonance mode of the inner and outer SRR by changing the outer radius of the inner SRR. The metasurface based on parameter-tuned BIC verified that the continuous modulation of parameters in a system could make a pair of resonant states strongly coupled, and the coherent cancellation of the resonant states will cause the linewidth of one of the resonant states to disappear, thus forming BIC. Compared with the single-SRR array metasurface based on symmetry-protected BIC, the dual-SRR array metasurface designed in this paper has multiple accidental BICs and realizes multichannel multiplexing of X-polarization and Y-polarization. It provides a brilliant platform for high-sensitivity optical sensor array, low threshold laser and efficient optical harmonic generation.

Multiple symmetry protected BIC lines in two dimensional synthetic parameter space

Abstract Bound states in the continuum (BICs) have attracted significant interest in recent years due to their unique optical properties, such as infinite quality factor and wave localization. In order to improve the optical performance of BICs based devices, more degrees of freedom are required to tune BICs in high-dimension parameter space for practical applications. To effectively tune more BICs, we form a 2D synthetic parameter space based on a nanohole metasurface array. Multiple symmetry protected BIC modes with high Q factors can be achieved at high-order symmetry point. Through manipulating asymmetry parameters, BIC lines formed by a series of BIC modes can be found in the 2D synthetic parameter space. Moreover, the electric field distributions are investigated to demonstrate the generation and evolution of BICs. By measuring the absorption spectra, the tuning of multiple BICs with synthetic asymmetry parameters is experimentally explored, which agrees well with theoretical results. Therefore, our design can provide new insight for a variety of on-chip applications, such as nonlinear devices, integrated nanolasing array, and high-resolution sensors for infrared molecular detection.

Polarization-insensitive and wide-angle metasurface to harvest dual-band energy in an ISM band

This paper reports a novel dual-band metasurface structure to harvest electromagnetic energy in the environment efficiently. The unit structure comprises a novel Jerusalem cross on F4B substrate, a centrosymmetric structure which exhibits excellent stability under different polarization and incident angles of ISM bands (2.45 GHz and 5.8 GHz). Then the composite structure is designed to complete the array design of the metasurface. The harvetsed energy is guided to the back of the array through vias and collected by a dual-band differential input power combiner. Numerical simulation validates the dual-band, polarization-insensitive and wide-angle energy harvesting of the metasurface array constructed by the composite structure. The experimental results demonstrate that the metasurface array can achieve a peak energy harvesting efficiency of 91.6% and 94.9% under TE and TM polarization, respectively.

A novel design of metasurface antenna for multiple applications: Magnitude, phase, and radiation manipulation

Multifunctional metasurface triggers great interest due to their potential ability to manipulate the propagation of electromagnetic (EM) waves. Here, we propose a novel design of metasurface to realize EM wave magnitude, phase, and radiation manipulation. The metasurface unit cell consists of different structures with various functions. Double-square loops with lumped resistors can realize the absorption function to manipulate the reflected wave magnitude. Square spilt rings etched on the top and middle layers are to realize polarization conversion and phase manipulation. Finally, the radiation function is achieved through adding a feeding structure to a middle square patch of each unit. A 4 × 4 metasurface array is fabricated and tested to verify the design correctness. Both simulated and measured results indicate the sample can attain good radiation and scattering performance. The proposed metasurface offers a feasible strategy to design multifunctional metadevices and for other related practical applications.

Experimental Characterization of a Waveguide-Fed Varactor-Tuned Metamaterial Element Using the Coupled Dipole Framework

We confirm experimentally that the essential electromagnetic properties of a single, waveguide-fed, tunable metamaterial radiator can be described within a coupled dipole framework, providing a foundation for metasurface array antenna design. The metamaterial element considered here is an electrically small aperture consisting of a complementary electric-LC resonator with its resonance frequency controlled by a pair of varactor diodes. Using the dipole framework, we reduce the detailed properties of the tunable element—which is a complex composite of electrically small resonant opening and bias circuitry—to a combination of effective magnetic and electric polarizabilities, with the magnetic response modeled by a Lorentzian resonance with a dc component. Experiments reveal that the designed element scatters the excitation fields into the waveguide and free space predominantly as a polarizable magnetic dipole, with a polarizability matching that is predicted from a simulation-based polarizability retrieval. This experimental analysis validates the dipole framework, unlocking the potential for improved holographic beamforming approaches for the design and analysis of reconfigurable metasurface antennas.

Double Fano resonance and refractive index sensors based on parallel-arranged Au nanorod dimer metasurface arrays

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Compact Broadband Linearly Polarized Quincunx Metasurface Antennas Using Embedded Fractal Design

A quincunx metasurface (MTS) structure is presented and exploited to design compact broadband metasurface antennas (MTAs). The MTS patch unit is constructed by connecting five same-size quincunx-arrangement squares with strip lines. Since it is a fractal structure and structurally embedded with other units, the gap between adjacent units is prolonged, increasing the edge capacitance. Meanwhile, the surface current is adjusted to flow along the diagonal of quincunx patches, producing a large strip inductance. Hence, the resonance responding to the MTS radiator can be shifted to the low frequencies, while a compact radiating aperture can be obtained accordingly. With the help of characteristic mode analysis (CMA), the quincunx MTS array is modified for further miniaturization. Jerusalem cross aperture and four rectangle apertures are etched on the ground plane, generating aperture modes. Subsequently, the modified quincunx MTS is coupled to a U-shaped feeding network through apertures, forming a horizontally polarized MTA and realizing an operating bandwidth of 37.92% and a peak gain of 7.36 dBi with a compact radiating aperture of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.34\lambda _{0} \times 0.34\lambda _{0}$ </tex-math></inline-formula> . Ultimately, a 45° linearly polarized quincunx MTA using a double U-shaped feeding network is also proposed, obtaining a broader operating bandwidth of 44.60% and 6.43 dBi peak gain with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.34\lambda _{0} \times 0.34\lambda _{0}$ </tex-math></inline-formula> radiating aperture.

Possibility of Anapole State in Dielectric Nanohole Array Metasurfaces with Different Hole Shapes

The optical anapole resonances in nanostructures display strong field confinement and substantially suppressed scattering. In this study using three-dimensional finite-difference time-domain simulations, it is shown that high refractive index dielectric nanohole array metasurfaces having different profiles of the holes can possess the anapole state. The multipole decomposition including the dipole electric toroidal moment for the lattice elements of the arrays is provided. The anapole state in the lattice elements is illustrated by time-averaged distributions of the energy. As a result, high-index freestanding metasurfaces with anapole state can be designed.

Double-layer polarization-independent achromatic metasurface array for optical fiber bundle coupling in microendoscope

Optical fiber bundle-based microendoscope, which is significant in clinical diagnosis and industrial detection, calls for miniaturization of the probe and high-resolution observation. Here, we propose a double-layer metasurface array borrowing the structures of insect compound eyes to meet both requirements instead of traditional optical components. Each unit in the array aims for an incident field of view, focusing light at the center of the fiber end face with no chromatic aberration at the wavelengths of 470 nm, 530 nm and 630 nm. The metasurface array is composed of a series of isotropic TiO2 nanopillars which are special selected after considering resonance mode and angular dispersion characteristics, etched on both sides of a silica substrate, with the individual functions of deflecting and focusing. In image space, numerical aperture (NA) is 0.287 and the particular layout of two layers achieve zero telecentricity theoretically, which meet the requirements of optical fiber bundle coupling. A unit for incident angle of 20° is shown to validate our design approach numerically, which obtains a focused spot close to the diffraction limit. The compact and ultrathin metasurface could greatly reduce the size of the probe in optical fiber bundle based microendoscope while ensuring the imaging quality.

Static Beam Steering by Applying Metasurfaces on Photonic-Crystal Surface-Emitting Lasers

Photonic-crystal surface-emitting laser (PCSEL) holds promise for laser beam with high efficacy while retain the small divergence angle, being now all the rage as laser source in modern opto-electronic technologies to replace edge emitting lasers and vertical-cavity surface-emitting lasers (VCSELs). Arbitrary beam shaping and deflection of VCSELs with ultra-thin flat optics, aka metasurfaces, has recently demonstrated, making possibility to realize a compact system in many technologies. However, the large divergence angle and limited output power at single fundamental mode of the VCSEL limits its application. Here, we report the static steering of laser beam with high efficiency and near 1° divergence angle by shining the laser beam of the PCSEL through the metasurface array placed on top. The small divergence angle is contributed from PCSEL. On the other hand, the metasurface array offers the higher efficiency beam deflection, without considering additional collimating or focusing. This provides highly flexible platform and is capable to manipulate the laser emission through the design of the metasurfaces and the PCSELs. Moreover, the beam proprieties can be further modified for specific application through the metasurfaces. The integration of metasurface with PCSEL provides the compact and collimated laser source, promising more accurate generation of versatile laser sources on demand for automotive ultra-compact light detection and ranging (LiDAR), depth sensing, optical communication, etc.

Dual-band and dynamic regulated terahertz linear polarization converter based on graphene metasurface

In this paper, a highly efficient dual-band and dynamic regulated terahertz linear polarization converter is proposed. Based on the principle of electromagnetic (EM) wave polarization control, a periodic array metasurface composed of graphene split square ring and elliptical patches is designed to realize dual-band and high efficiency linear polarization conversion in terahertz band. The simulation results show that the polarization conversion ratio (PCR) is higher than 90% in the frequency range of 0.656–0.730 THz and 0.809–1.449 THz, and corresponding relative bandwidths are 10.7% and 56.7%, respectively. The dual-band performance is maintained within the incident angle of 50°. In addition, the dynamic regulation of dual-band terahertz linear polarization converter is obtained by modifying the Fermi level and relaxation time of graphene. The designed dual-band terahertz linear polarization converter has a broad application prospect in terahertz communication, sensing and spectrum.

Scalable, Dual-Band Metasurface Array for Electromagnetic Energy Harvesting and Wireless Power Transfer.

A dual-band metasurface array is presented in this paper for electromagnetic (EM) energy harvesting in the Wi-Fi band and Ku band. The array consists of metasurface unit cells, rectifiers, and load resistors. The metasurface units within each column are interconnected to establish two channels of energy delivery, enabling the transmission and aggregation of incident power. At the terminals of two channels, a single series diode rectifier and a voltage doubler rectifier are integrated into them to rectify the energy in the Wi-Fi band and the Ku band, respectively. A 7 × 7 prototype of the metasurface array is fabricated and tested. The measured results in the anechoic chamber show that the RF-to-dc efficiencies of the prototype at 2.4 GHz and 12.6 GHz reach 64% and 55% accordingly, when the available incident power at the surface is 3 dBm and 14 dBm, respectively.

Sub-micron embedded metasurface arrays for polarizer with improved efficiency more than 99%

Sub-micron embedded metasurface arrays for polarizer with improved efficiency more than 99%

Design of Low-RCS Broadband High-Gain Antennas Based on Transmission Array Metasurface.

In this paper, a low-RCS broadband high-gain antenna based on metasurface transmission array is proposed, consisting of two parts: a metasurface transmission array and a feed antenna. When designing the metasurface transmission array, the phase compensation method is used to achieve the beam convergence effect of metasurface in the broadband. By designing the elements and using the checkerboard arrangement, the RCS of the incident wave with fixed polarization can be reduced more than 10 dB at X band or Ku band. The feed antenna is designed as a microstrip magnetic and electric dipole antenna, which has the characteristics of small structure and wide impedance bandwidth. An antenna that can reduce RCS by more than 10 dB in Ku band is simulated and measured. The measurement and simulation results show that the −10 dB operating bandwidth of the high-gain antenna designed in this paper is 6.7~13.5 GHz, and the relative bandwidth is 67%. The designed metasurface can effectively improve the gain of the antenna in the operating frequency band. In this way, the design of high-gain antenna is realized, and the antenna has an obvious RCS reduction effect on the vertically incident y-polarized wave in the whole Ku band. The method to design an antenna in this paper realizes the regulation of radiation and scattering at the same time, which has important reference significance for expanding the function of transmission array antennae and has great application value.

Full-space beam scanning based on transmission reflection switchable quadratic phase metasurface.

Beam scanning based on metasurfaces is widely discussed in recent years owing to its high integration, lightweight, and low cost. However, most of the reported beam scanning metasurfaces operate in either transmission or reflection mode. Here, we propose a full-space beam scanning metasurface based on transmission reflection switchable meta-atom and the quadratic phase distribution. As a validation, a metasurface array with 400 units (20 × 20) was experimentally demonstrated. Beam scanning of ± 35 ° was achieved in both transmission mode and reflection mode. A larger scanning angle (± 45 °) was further verified simulatively with a 900-units (30 × 30) array. The method provides an avenue for expanding the space of electromagnetic wave manipulation and may have great potential in wireless communication and radar detection.