Reflective Metasurface Research Articles

Electrically controllable optical switch metasurface based on vanadium dioxide.

We report a voltage-tunable reflective gold wire grid metasurface on vanadium dioxide thin film, which consists of a metal-insulator-metal (MIM) structure. We excite surface plasmon polariton (SPP) modes on the gold surface by fabricating a one-dimensional structured gold wire grid. Joule heating of laser-induced graphene (LIG) can be controlled by the voltage at the bottom, allowing vanadium dioxide in the structure to complete the transition from the insulating state to the metallic state. The phase transition of vanadium dioxide strongly disrupts the plasmon modes excited by the gold wire grid above, thereby realizing a huge change in the reflection spectrum. This acts as a tunable metasurface optical switch with a maximum modulation depth (MD) of over 20 dB. We provide a more effective and simple method for creating tunable metasurfaces in the near-infrared band, which can allow metasurfaces to have wider applications in optical signal processing, optical storage, and holography.

A wide-incidence-angle insensitive multi-polarization converter based on reflective metasurface

In this paper, we propose a wide-incidence-angle insensitive reflective metasurface multi-polarization converter, using split-ring-resonators and cross oscillators structure. The simulated results indicate that the polarization conversion ratio for linear to linear (LTL) polarization conversion is greater than 90% in three frequency bands of 5.03–5.19 GHz (3.13%), 6.38–6.82 GHz (6.67%) and 7.38–7.44 GHz (0.81%). Meanwhile, the axial ratio for linear to circular (LTC) polarization conversion is less than 3 dB in four frequency bands of 4.79–5 GHz (4.29%), 5.24–6.27 GHz (17.90%), 6.94–7.35 GHz (5.74%) and 7.45–7.48 GHz (0.40%). LTL or LTC polarization conversion will not be affected when the incidence angle is tilted by 45° under both transverse electric and transverse magnetic modes. To verify the polarization conversion performance, a sample consisting of 18 × 18 unit cells is fabricated and measured. The measured results are found to be in reasonable agreement with the simulated results, demonstrating the potential application of this design for future microwave polarization state manipulation.

Dispersion study of a broadband terahertz focusing reflecting metasurface for 6G wireless communication

In 6G wireless communications, functional terahertz reflecting metasurfaces are expected to play increasingly important roles such as beamforming and beamsteering. However, their performance optimization as a function of multiple competing design parameters remains a significant challenge. This paper demonstrates a multi-dimensionally optimized design of a functional and efficient focusing metasurface reflector in the burgeoning D-band (0.11-0.17 THz). In addition to achieving 20% fractional bandwidth (0.135-0.165 THz), this design is polarization-maintaining, diffraction limited, simple in design, and exhibits 64.1% broadband power efficiency (1.9 dB insertion loss). We perform a unique study of the magnitude of temporal (group-delay) dispersion introduced by this design to the broadband signal at the focus. Despite being formed by an array of highly dispersive resonators, the metasurface exhibits very low dispersion, which avoids pulse reshaping and its consequent limitations on achievable data rate. The low dispersion characteristic of the metasurface is a consequence of its optimized design. The design and performance of the focusing reflector are presented followed by a dispersion analysis revealing that only 2.83% temporal broadening of the pulse is observed at the focus.

High-performance full-Stokes polarization detection at exceptional point in a non-Hermitian metasurface

Polarization and its detection have attracted tremendous attention due to the rich information it provides and the practical applications it enables. Here, we propose a high-performance reflective pixelated metasurface with full-Stokes detection in the visible wavelength, which integrates both linear polarization (LP) and circular polarization (CP) filters on one platform. The system achieves a high extinction ratio for CP incidence in a non-Hermitian system, generated from the exceptional point (EP) effect. With integrated LP filters, full-Stokes detection can be obtained with accuracy and efficiency in real time. The EP-based innovation also promises other practical applications, such as polarization imaging technologies and optical computing.

Implementation of a Low-Cost Chipless RFID System With Paper-Based Substrates Printed Tags for Traceability Applications in the Packaging Sector

Increasing competitiveness as well as levels of sustainability are some of the main challenges that the packaging sector is facing. The introduction of information and communication technologies provides new functionalities, such as traceability within logistic processes. In this context, RFID technologies can play a key role but can also pose hurdles, owing to increased cost, as well as to difficulties in relation with recycling and complying with product circularity. In this sense chipless RFID opens new possibilities, by avoiding the use of information coded chips, reducing costs in material and placement, as well by improving recyclability. In this work, a frequency based chipless RFID solution is presented, in which 2D geometrical patterns printed with conductive ink, resembling transmitive or reflective metasurfaces, are designed and integrated within paper-based substrates. An in-house reader system is implemented based on conventional Software Defined Radio platforms in the 0-6GHz and in the 0-12GHz range, in which received signal post-processing is performed to increase reader sensitivity, without the need of using Vector Network Analyzer equipment. Moreover, in order to reduce material waste, an automatic fault detection system based on artificial vision coupled to a robot arm is designed and tested. Different prototypes in paper substrates as well as in reference printed circuit boards have been fabricated and measured, showing good agreement. The proposed solution provides a feasible chipless RFID system with a portable low-cost reader which can be embedded in paper/cardboard materials in packaging applications.

A Broadband Multifunctional Reconfigurable Polarization Conversion Metasurface

In this work, a reflective polarization conversion metasurface (PCM) with symmetrical L-shaped patches is proposed which enables to switch between different polarization modes by PIN diodes, i.e., linear-to-linear (LTL) cross-polarization and linear-to-circular (LTC) polarization. Because of multimodes activated in the structure, the PCM shows an ultrawide bandwidth both for LTL and LTC polarization conversion. A microstrip line-based DC biasing network composed of radial stubs is introduced to isolate RF currents, which can resolve problems raised by RF lumped choke inductors in the ultrawide bandwidth. A prototype with 15 × 15 units is fabricated. The simulated and measured results show that when the PIN diodes are forward biased, the PCM achieves LTC polarization conversion in the range of 5.96–15.34 GHz (relative bandwidth of 88.4%) with the axial ratio (AR) less than 3 dB; when the PIN diodes are reverse biased, the PCM achieves LTL polarization conversion in the range of 6.05–14.76 GHz (relative bandwidth of 83.75%) with the polarization conversion ratio (PCR) higher than 90%. The proposed PCM is expected to be potentially applied to a broad scanning range array, intelligent reflecting surfaces (IRS), and remote sensing.

Multifunctional Reflective Metasurface to Independently and Simultaneously Control Amplitude and Phase with Frequency Tunability (Advanced Optical Materials 14/2023)

Multifunctional Reflective Metasurface to Independently and Simultaneously Control Amplitude and Phase with Frequency Tunability (Advanced Optical Materials 14/2023)

Design of Reflective Tunable Structural Color Metasurface Based on Guided-Mode Resonance Filter and Sb2S3

In recent years, dynamically tunable structural color has attracted great interest. Here, we introduce the guided-mode resonance (GMR) filter and the phase-change material Sb2S3 to design a reflective optical metasurface to produce tunable structural color, in which the combination of the GMR filter, with narrow resonant wavelength, and the Sb2S3, with a much larger bandgap and higher refractive index, helps to produce high-quality tunable structural color. The simulation results indicate that through the phase transition between the amorphous and crystalline states of Sb2S3, the proposed metasurface can generate tunable structural color that can be perceived by the naked eye. Furthermore, the metasurface can sensitively sense environmental changes through changes in structural color. This work provides a new method for realizing dynamically tunable structural color, and paves the way for the application of controllable structural color in dynamic displays, optical stealth, colorimetric sensing, and other fields.

Generation of Terahertz OAM Waves with Six Modes Based on Three-Layer Z-Shaped Reflective Metasurface

In this paper, a broadband and efficient three-layer Z-shaped reflective metasurface for linear polarization conversion is designed and six different modes of orbital angular momentum (OAM) waves are generated in the terahertz band. The designed metasurface consisted of several units, and it is divided into twelve regions. The phase difference is achieved by changing the structural parameters of the units, and then different modes of OAM waves are generated. The terahertz OAM waves with the modes of ±1, ±2, and ±3 are generated by metasurface with high efficiency and wide bandwidth. The results show that the designed metasurface could produce high purity terahertz OAM waves with six different modes, and the reflection amplitude of the metasurface unit is more than 0.9 in the frequency range of 1.0 THz to 1.8 THz. The generated OAM waves with the modes of ±1 and ±2 have a mode purity more than 90%. The designed metasurface has good wavefront control ability, which provides an effective method to generate multimode OAM waves.

Taming Fabry–Pérot resonances in a dual-metasurface multiband antenna with beam steering in one of the bands

Metasurfaces are artificial materials that can provide properties not readily available in nature for the interaction with acoustic, elastodynamic, or electromagnetic waves. In Electromagnetics, metasurfaces allow particular functionalities to antennas, which in turn lately have been increasingly pushed to a multiband operation. To fully exploit metasurfaces’ capabilities, the use of a metasurface reflector and a metasurface superstrate surrounding a radiating element in multiband antennas is interesting. However, such topology generally creates multiple reflections inside the formed cavity, known as Fabry–Pérot resonances. Here we show that one should tame this phenomenon to use two parallel metasurfaces surrounding a planar radiating element. We present the conditions to obtain directive, multiband antennas under such circumstances. The concepts are validated with a compact device for 5G/4G/Wi-Fi 2.4/5/6E performing a beam steering in the 5G without disturbing the radiation patterns of the other bands. This device demonstrates that the functionalities of two metasurfaces may be exploited in a single design if the presented conditions are respected. We also anticipate our work to be a starting point for other studies in the wave domain. For example, compact, multiband, beam-steerable microphones or sonar transducers with two parallel metasurfaces could be investigated in the future.

Design of a 3-bit encoded THz ultra-wideband vortex beam generator based on a metasurface

With the rapid development of high-speed THz communications, there has been a growing interest in exploring the potential of the orbital angular momentum (OAM) of electromagnetic waves. In this study, we propose a cross-polarized reflective broadband metasurface operating in the THz band to harness the benefits of OAM in the optical field. We quantitatively analyze the reflection amplitude and phase characteristics of the metasurface elements, which supports the design of a reflective broadband element surface array with an ordered arrangement of 3-bit elements. By combining the 3-bit metasurface elements in an array, linearly polarized waves can effectively be converted into vortex beams in the operating frequency range of 0.6THz-1.3THz. The simulation results demonstrate that the designed metasurface element structure can achieve not only efficient cross-polarization reflection amplitude but also effective phase control by adjusting the size parameters. Our proposed metasurface is able to convert linearly polarized waves into vortex beams with an efficiency exceeding 85% and can achieve high-purity OAM beam acquisition. Furthermore, the metasurface structure is simple to implement and can be easily integrated with photoelectric circuits, making it ideal for use in ultrahigh-speed THz communications.

An analytical design for a metasurface with polarization conversion based on the transmission-line model

In this paper, an analytical design method for reflective polarization conversion metasurface (RPCM) is proposed. Specifically, two transmission-line models corresponding to two orthogonal incident electric fields are established, and the equivalent parallel impedance of the periodic dipole array is calculated by the variational method. Thereby, the polarization conversion coefficient of the metasurface is analytically related to the geometrical parameters of the periodic dipole array. Two RPCMs with different operation frequencies are theoretically designed, whose results agree well with the software simulation. Thus, the method provides an analytical approach to synthesize the polarization conversion metasurface, greatly facilitating the design and giving insight into the physical mechanism.

Bottom‐Up Tunable Broadband Semi‐Reflective Chiral Mirrors

AbstractConventional mirrors flip the handedness of circularly polarized light upon reflection. However, there is an increasing demand for the design and fabrication of handedness‐preserving mirrors as well as chiral reflective metasurfaces with tunable spin states of reflected photons that work in a broad wavelength range in the UV and visible domain. Most chiral mirrors fabricated up to now are prepared by top‐down techniques, such as e‐beam lithography, which are very costly and difficult to scale up to macroscopic devices. Here, an efficient bottom‐up strategy is introduced for fabricating chiral mirrors by using Layer‐by‐Layer assembly of oriented silver nanowire layers prepared by grazing incidence spraying on a semi‐reflective silver layer. The resulting chiral metasurfaces display structure‐dependent differential reflectance for circularly polarized light in a broad wavelength range in the UV, visible, and near infrared domains, reaching an extremely high figure of merit. Their differential reflectance reaches up to 95% of the maximum polarization efficiency, with the handedness of the reflected light being partially preserved. These large‐area chiral mirrors with tunable chiral reflectance open perspectives in various fields, such as in optics, sensing, and chiral light‐matter interactions.

Broadband cross circularly polarized carpet invisibility cloak based on Pancharatnam–Berry phase reflective metasurface

We present a broadband circularly polarized reflective metasurface carpet cloak. The metasurface unit cell is composed of two crossed H-shaped metal patterns. When the incident wave is left-handed circularly polarization (LCP), the metasurface can achieve high-efficiency cross-polarization conversion in the wide frequency range. The cross-polarization reflection efficiency is higher than 94%. By using the proposed cross-polarized reflection unit cell structure, the phase gradient metasurfaces based on the Pancharatnam–Berry phase principle is proposed, and a broadband reflective metasurface invisibility cloak is constructed. The simulation results show that when the LCP light is incident vertically, the proposed carpet cloak can significantly suppress the scattering and reconstruct the wavefront in the broadband frequency range.

Broadband and high-efficiency thermal switchable InSb metasurface for terahertz wave anomalous reflection and focusing effect

In this paper, a reflective metasurface composed of a dielectric substrate sandwiched with a double-split-ring (DSR) structure InSb and a metal ground plane was proposed in terahertz (THz) region, which can realize a high-efficient thermal switchability of circular-polarization (CP) conversion, anomalous reflection, and planar reflective focusing effect in a broadband manner. Simulation results demonstrated that the designed InSb metasurface structure can achieve high-efficient reflective CP conversion, with the magnitude of the reflected orthogonal CP wave being over 0.8 on average from 0.7 THz to 1.55 THz under the external higher thermal (T = 320 K, “On” state). Conversely, the magnitude of the reflected orthogonal CP wave is nearly zero under external lower thermal conditions (T = 240 K, “Off” state). Furthermore, the proposed InSb metasurface structure can achieve a high-efficient reflective CP conversion with an efficiency of about 0.7 under the “On” state, and a 2π phase full coverage by adjusting the oriented rotation angle (α) of the DSR structure InSb. As evidences of the concept, two InSb metasurfaces have been constructed to achieve the broadband switchable anomalous reflection phenomenon and reflective focusing effect based on Pancharatnam-Berry (PB) phase principle. The proposed metasurface has great potential in developing a dynamically tunable device for THz wavefront modulation applications in the future.

Terahertz Bessel beam generator.

The Bessel beam has broad application prospects in wireless energy transmission and high-speed communications. The traditional Bessel beam generation method has the problems of large volume, low efficiency, and complex manufacturing. To solve the above problems, we present a terahertz Bessel beam generator based on the reflective metasurface, which is composed of a metal pattern, dielectric layer, and bottom metal plate. Under the incidence of right circularly polarized (RCP) wave, the zero-order Bessel beam and zero-order symmetric double Bessel beam are generated. It can be found that the bottom angle of the axicon of the first-order Bessel beam is inversely proportional to the propagation distance of the Bessel beam. Comparing the electric field intensity distribution, phase distribution, and mode purity of the second-order Bessel beam and the second-order vortex beam in different observation planes, it can be seen that the energy of the higher-order Bessel beam is more concentrated and the field distribution is more stable than those of the ordinary vortex beam. The reflective terahertz Bessel beam generator has potential application value in terahertz wireless communications, measurement, radar detection, and imaging.

Wideband reflective half- and quarter-wave plate metasurface based on multi-plasmon resonances

In this article, a single-layer reflective anisotropic metasurface (MS) is proposed, which presents both half- and quarter-wave plate operation in different microwave frequency regimes. The unit cell of the proposed metasurface consists of a tilted rectangular plane with triangular ends accompanied by an equidistant-filled triangle on both sides. The unit cell is printed on a dielectric substrate backed by a metallic plane. The proposed meta-plate transforms horizontal polarization into vertical and vice versa in two wide frequency bands, 7.1-15.3 GHz and 19.8-21.7 GHz. Similarly, a linearly polarized (LP) wave is transformed into a circularly polarized (CP) wave and vice versa at 7.9 GHz and 21.8 GHz. The wide bandwidth is acquired through three plasmonic resonances occurring at 8.2 GHz, 12.7 GHz and 20.8 GHz, where the cross-polarization conversion ratio reaches almost 100%. Moreover, quarter and half-wave plate operations occurring at 7.9 GHz and 7.1-15.3 GHz, respectively, are robust to changes in oblique incidence angle (up to 45°) both for transverse-electric (TE) and transverse-magnetic (TM) polarizations. The physical mechanism behind polarization conversion is also explained through surface current distribution. The proposed meta-plate structure is fabricated and validated through experimental measurements. The wide bandwidth, high efficiency, angular stability, and simple structure make the proposed metastructure incredible for numerous microwave applications such as antennas, radars, and satellite communication.

Wideband OAM Generator Design Using a Low Q-Factor and C-Shaped Element

Reflective metasurfaces have been widely explored for generating orbital angular momentum (OAM) carried by vortex beams. However, the most OAM generators have narrow bandwidth or major for circular polarization waves, which are caused by the propagation phase and Pancharatnam–Berry (PB) phase. In this letter, by combining the propagation phase and reflection polarization conversion metasurface, a novel OAM generator operating at microwave band is proposed, which is based on a low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factor C-shaped element. A proof-of-concept prototype is fabricated and measured. This generator not only covers a broad bandwidth from 12 to 18 GHz (40%) but can also be used for dual-linear and dual-circular polarized waves.

Enhanced ultrathin ultraviolet detector based on a diamond metasurface and aluminum reflector.

Metasurface is a kind of sub-wavelength artificial electromagnetic structure, which can resonate with the electric field and magnetic field of the incident light, promote the interaction between light and matter, and has great application value and potential in the fields of sensing, imaging, and photoelectric detection. Most of the metasurface-enhanced ultraviolet detectors reported so far are metal metasurfaces, which have serious ohmic losses, and studies on the use of all-dielectric metasurface-enhanced ultraviolet detectors are rare. The multilayer structure of the diamond metasurface-gallium oxide active layer-silica insulating layer-aluminum reflective layer was theoretically designed and numerically simulated. In the case of gallium oxide thickness of 20 nm, the absorption rate of more than 95% at the working wavelength of 200-220 nm is realized, and the working wavelength can be adjusted by changing the structural parameters. The proposed structure has the characteristics of polarization insensitivity and incidence angle insensitivity. This work has great potential in the fields of ultraviolet detection, imaging, and communications.

The extreme bulk-modulus contrast of bubbly soft matter for underwater acoustic modulation

Bubbles in liquid and soft matter are excellent acoustic resonators with extremely low resonant frequencies. We find that bubbly soft matter (BSM) can enable full-phase (2π) modulation of incident acoustic waves just through changing the bubble size. Compared with the conventional solid–solid binary locally resonant metamaterial (SSM), due to the extreme bulk-modulus ratio of the bubbles and the soft matrix, the BSM has two distinguished merits. First, the size of the bubbly inclusions for the full-phase modulation is only about a third of the solid inclusions in the SSM; second, the range of variation of the bubbly inclusions to cover the full-phase modulation is two orders of magnitude wider than that of the solid inclusions. These features, combined with the salient advantage of wave-impedance match between soft matter and water, can realize compact and light-weight reflective and transmissive underwater bubble metasurfaces. At the lower limit 3 kHz of the active sonar operating frequency, an ultrathin reflective metasurface with a thickness of 1/50 the wavelength can redirect the incident waves at a given angle. Bubble resonance in soft matter opens a new avenue for underwater acoustic modulation at the deepest subwavelength.