Anisotropic Metasurface Research Articles

A multifunctional broadband polarization rotator based on reflective anisotropic metasurface

In this paper, both linear cross-polarization conversion (CPC) and linear-to-circular or circular-to-linear polarization conversion based on a single reflective anisotropic metasurface are realized and experimentally demonstrated. The multifunctional CPC metasurface in the frequency range of 5.9-6.4 GHz and 8.7-17.7 GHz has a fractional band of 68.2%, and the efficiency reaches almost 100% under plasma resonance. In addition, the metasurface acts as a high efficiency circular-polarizer in the range of 6.7–8.4 GHz. Moreover, the polarization transforming functionality of the structure is stable for the change of incident angle for both x-polarized or transverse-electric (TE) and y-polarized or transverse-magnetic (TM) illumination up to 45∘. It can be seen that the anticipated hypersurface has potential applications in reflector antenna, satellite communication and radar.

Gain Improvement of Vivaldi MIMO Antenna With Pattern Diversity Using Bi-Axial Anisotropic Metasurface for Millimeter-Wave Band Application

In this letter, a high gain Vivaldi multi-input–multi-output (MIMO) antenna with orthogonal pattern diversity for millimeter-wave (mm-Wave) band application is proposed with the reduction paradigm towards nonuniform phase errors (at Vivaldi aperture) through metasurface loading. The nonuniform phase error limits the endfire gain (4.9–5.9 dBi) and hence the efficacy of the system. To compensate the phase error and improve the gain, a bi-axial anisotropic metasurface unit cells have been thoroughly investigated in systematic manner and strategically loaded at Vivaldi MIMO antenna. The endfire gain improvement with metasurface loading is reflected to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 73% higher at 28 GHz with gain variation 8.2–10.2 dBi in the band of interest. Simultaneously, high pattern integrity behavior of the MIMO system is confirmed by the appreciable 1 dB gain bandwidth (33%). The standard port-to-port isolation (>15 dB) and MIMO performance parameters (ECC < 0.2 and TARC > 10 dB) confirms its suitability for mm-Wave band application.

Transmissive metasurface for multi-channel and full-polarization modulation of electromagnetic wavefronts

Metasurfaces have great potential for flexible manipulation of electromagnetic wave polarizations and wavefronts. Here, we propose a general method for achieving independent wavefront manipulation in a single polarization-multiplexing transmissive metasurface. As a proof of concept, we design a transmission-type anisotropic metasurface for independent wavefront manipulation in full-polarization channels. An x -polarized wave transmitted through such a metasurface could be converted into four outgoing beams with delicately designed polarization states that converge to specific positions for holographic imaging. The measured results are in good agreements with simulated ones, verifying the independent wavefront manipulations with arbitrary polarization conversions. Compared with the existing traditional meta-devices with single-polarization modulation, we achieve polarization-multiplexed metasurfaces with mixed polarization and phase control, which can greatly improve the functional richness of the system.

Classification of Bianisotropic Metasurfaces from Reflectance and Transmittance Measurements

Using fundamental electromagnetic properties of metasurfaces, we build a platform to classify reciprocal bianisotropic metasurfaces from typical experimental measurements and determine isotropic, anisotropic, bi-isotropic (chiral), and bianisotropic (so-called omega) properties. We provide experimental guidelines to identify each class by measuring macroscopic scattering parameters, that is, reflection and transmission coefficients upon plane wave illumination with linear and/or circular polarization. We explicitly provide a recipe of which metasurface properties can and cannot be inferred by means of the chosen polarization, reflection, and transmission properties. We also clarify common confusions in the classification of anisotropic versus chiral metasurfaces based on circular dichroism measurements presented in the recent literature.

Hexagonal boron nitride nanophotonics: a record-breaking material for the ultraviolet and visible spectral ranges.

A global trend towards miniaturization and multiwavelength performance of nanophotonic devices drives research on novel phenomena, such as bound states in the continuum and Mietronics, as well as surveys for high-refractive index and strongly anisotropic materials and metasurfaces. Hexagonal boron nitride (hBN) is one of the promising materials for future nanophotonics owing to its inherent anisotropy and prospects of high-quality monocrystal growth with an atomically flat surface. Here, we present highly accurate optical constants of hBN in the broad wavelength range of 250-1700 nm combining imaging ellipsometry measurements, scanning near-field optical microscopy and first-principles quantum mechanical computations. hBN's high refractive index, up to 2.75 in the ultraviolet (UV) and visible range, broadband birefringence of ∼0.7, and negligible optical losses make it an outstanding material for UV and visible range photonics. Based on our measurement results, we propose and design novel optical elements: handedness-preserving mirrors and subwavelength waveguides with dimensions of 40 nm operating in the visible and UV ranges, respectively. Remarkably, our results offer a unique opportunity to bridge the size gap between photonics and electronics.

Cascaded metasurface for separated information encryption [Invited

For a conventional cascaded metasurface, the combination channel and each single channel are mutually dependent because the phase modulation of a cascaded metasurface is the sum of each single one. Here we propose a cascaded metasurface that can independently encode information into multiple channels. Based on the orientation degeneracy of anisotropic metasurfaces, each single metasurface can produce a quick-response (QR) image in the near field, governed by the Malus law, while the combined channel can produce a holographic image in the far field, governed by geometric phase. The independent and physically separated trichannel design makes information encryption safer.

Ultra-wideband Linear-to-Circular and Circular-to-Linear Polarization Conversion Realized by Anisotropic Metasurface

Ultra-wideband Linear-to-Circular and Circular-to-Linear Polarization Conversion Realized by Anisotropic Metasurface

Generating High-Purity Directive Circularly Polarized Beams From Conformal Anisotropic Holographic Metasurfaces

Using anisotropic holographic metasurfaces to transform the creeping waves into circularly polarized (CP) beams has initiated the quest for tangible applications in different disciplines. However, the present designs are only limited to the planar impedance surfaces with rare studies concerning the linear-to-circular polarization converting holographic metasurface over the conformal platforms. In this article, we demonstrate the perfect transformation of linearly polarized (LP) surface waves into CP waves through cylindrical anisotropic holographic metasurfaces consisting of gradient H-shaped slits etched on the periodic circular patches. Especially, the linear-to-circular polarization conversion rate can always maintain a very high level for the beam synthesis no matter how the curvature of the metasurface changes, and such high-purity CP beams also demonstrate very good quality of steerable characteristics over conformal surfaces. Our approach, using anisotropic holographic metasurfaces to transform the creeping waves into high-purity CP beams, should pave the way for more advanced functional meta-device designs over the nonplanar impedance surfaces.

ЦИЛИНДРИЧЕСКИЕ АНИЗОТРОПНЫЕ МЕТАПОВЕРХНОСТИ С БИГРАДИЕНТНЫМ СПИРАЛЬНЫМ КОДИРОВАНИЕМ ФАЗЫ ПАНЧАРАТНАМ-БЭРРИ И АНОМАЛЬНЫМ РАССЕЯНИЕМ

Scattering characteristics of anisotropic cylindrical phase-gradient metasurfaces (MSs) with various helical Pancharatnam-Berry phase (PB-phase) coding are studied. The efficiencies of the scattering field reduction of circularly polarized (CP) waves in the forward half-space is compared for three different MS models with the same PB-phase gradient in the azimuthal direction and different phase gradients in the axial direction. The metasurfaces are conformally located on semi-cylindrical metallic polyhedral prisms. The meta-particles are of the form of triple coupled split-ring resonators. Spiral coding of the PB-phase of MS unit cells in the azimuthal and axial directions is carried out by the rotation of the meta-particles. The effect of constant phase gradients on the frequency characteristics of backscattered fields and bistatic diagrams of scattering of CP-waves in the azimuthal and meridional planes is numerically estimated. It is shown that the axial phase gradient causes more efficient anomalous scattering of co- and cross-polarized CP-waves. It leads to the deviation of intense diffraction lobes from the normal in the meridional plane by a large angle, with a shift of the lobes in the azimuthal plane. Bigradient MSs provide the scattering field reduction of CP-waves by at least 10 dB in the band from 10-12 GHz to 18.5 GHz in almost the entire forward half-space in the azimuthal plane and in the sector of angles up to ±45° in the meridional plane.

Anisotropic Complementary Metantenna for Low Sidelobe Radiation and Low In-Band Co-Polarized Scattering Using Characteristic Mode Analysis

An anisotropic complementary metantenna (ACMA) is proposed for the integration of low sidelobe radiation and low in-band co-polarized (IBCP) scattering with the aid of characteristic mode analysis (CMA). With the guidance of CMA, the proposed ACMA evolving from a conventional metantenna (MTA) not only generates a coding phase distribution for low scattering but also restores broadside radiation modes like a uniform MTA. With the IBCP conditions set to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -polarization and the band around 9 GHz, the ACMA is constructed by mixing two types of double-layer anisotropic complementary metasurface (MTS) unit cells. Two desired characteristic modes of ACMA are simultaneously excited by a substrate integrated waveguide (SIW) cavity through dual bow-tie slots. Both the simulation and experiments demonstrate that the proposed ACMA achieves both the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -polarized broadside radiation with sidelobe level below −18.9 dB and IBCP scattering levels below −17.8 dB over the frequency range from 8.87 to 9.78 GHz.

Ultracompact Polarization Splitter–Rotator Based on Shallowly Etched Subwavelength Gratings and Anisotropic Metasurfaces

Polarization splitter–rotators (PSRs) are an essential component in on-chip polarization-sensitive and polarization–division multiplexing systems. In this work, we propose an ultracompact and high-performance silicon-based polarization splitter–rotator utilizing anisotropic metasurfaces, which is the first to combine the two, to our knowledge. The tilted periodic metasurface structure has different modulation effects on different polarized light fields, such as the transverse–electric (TE) mode and the transverse–magnetic (TM) mode, which are beneficial for designing polarization management devices. According to the results, the entire length of the silicon PSR was ~13.5 μm. The TE-to-TM conversion loss and polarization conversion ratio ere −0.154 dB and 96.5% at 1.55 μm, respectively. In the meanwhile, the cross talk and reflection loss were −27.0 dB and −37.3 dB, when the fundamental TE mode was input. The insertion loss and cross talk were −0.19 dB and −25.01 dB at the central wavelength when the fundamental TM mode was input. In addition, the bandwidth reached up to ~112 nm with polarization conversion loss and insertion loss higher than −0.46 dB and −0.36 dB. The simulations also show that the designed devices had good fabrication tolerance.

Dynamic and complete terahertz wavefront manipulation via an anisotropic coding metasurface.

A reconfigurable anisotropic coding metasurface composed of a graphene layer and anisotropic Jerusalem-cross metallic layer is proposed for dynamic and complete multi-channel terahertz wavefront manipulation. By controlling the Fermi energy of graphene, continuous amplitude modulation is realized for the coding elements with certain phase responses. By arranging anisotropic phase coding elements with a specific coding sequence and changing the Fermi energy of graphene, the proposed metasurface can dynamically control multi-channel reflection beams with designed power distribution and simultaneously manipulate the scattering pattern from diffusion to mirror scattering under x- and y-polarized incidence, respectively. Compared with the dynamic phase modulation metasurface, such a tunable metasurface uses three degrees of freedom, including the polarization, phase, and amplitude responses to fully control the reflected wavefronts, which may have promising applications in tunable terahertz multi-functional holograms and multi-channel information communication.

Anisotropic mode excitations and enhanced quantum interference in quantum emitter-metasurface coupled systems

This study proposes a nanophotonic structure that supports quantum interference (QI) between orthogonal decay channels in multilevel quantum emitters within the framework of the quantum master equation. The Green functions of the electric field are obtained by applying boundary conditions in the presence of two-dimensional metasurfaces. We demonstrate distinct in-plane excitation features of the surface plasmon modes (SPMs) with the anisotropic metasurfaces tailored to conductivity components. In particular, we observed that the Purcell factor of transitions with orthogonal polarizations experiences unequal enhancements, owing to the anisotropic propagation of the SPMs. This property depends only on the anisotropy of the metasurfaces; thus, it is easily manipulated. Using this platform and considering experimentally achievable material parameters, we predict a strong interference effect in three-level quantum emitters. In principle, this enables the generation of maximum QI. Our study provides a method for realizing QI systems and has potential applications in highly integrated, tuneable quantum devices.

Tunable anisotropic metasurface by utilizing phase change material in terahertz range

Due to the capability of achieving versatile control of differently polarized electromagnetic waves, anisotropic metasurfaces have attracted extensive attentions. To manipulate terahertz waves flexibly, we propose a tunable anisotropic metasurface based on phase change material vanadium dioxide (VO2). It is composed of a gold bottom layer deposited on the back of polyimide dielectric layer and a gold patch located on the front of the polyimide dielectric substrate. When VO2 is in the insulating state, the predesigned metasurface produces diversified functions, including terahertz beam splitting, deviation focusing, and multivortex beam under different polarization terahertz wave incidence. When VO2 becomes a metallic state, the proposed metasurface changes the number of terahertz beams, the shape of vortex beams, and the focusing effect. This scheme provides an innovative idea for the dynamic regulation of the terahertz wave in future terahertz technology systems.

Equivalent circuit model for reflective polarization converter based on anisotropic metasurfaces

A simple equivalent circuit model (ECM) for a reflective polarization converter (RPC) comprising anisotropic metasurfaces is presented in this paper. The impedance matrix of an anisotropic metasurface in x and y axis is derived by the impedance matrix in a diagonal axis multiply with a rotated matrix, while the diagonal impedance matrix can be calculated by a simple LC network, which contains a series of capacitors and inductors. The presence of the dielectric substrates is considered using the transmission line theory. Some typical RPCs with different metasurface shapes are used to verify the effectiveness of the ECM. The methodology provides a simple approach for the design and optimization of RPC. Finally, we designed a polarization converter based on the proposed method, and the measured results are in good agreement with the theoretical results.

Resonance fluorescence engineering in hybrid systems consist of biexciton quantum dots and anisotropic metasurfaces.

The resonance fluorescence properties in the steady-state regime are investigated for a driven cascaded exciton-biexciton quantum dot coupled to the two-dimensional black phosphorus metasurfaces. It is shown that for the material parameters under consideration, both the elliptic and hyperbolic dispersion patterns of the surface plasmon modes are achievable according to the variation of the carrier concentration. Further study on the Purcell factor indicates unequal enhancements in the spontaneous decay of the orthogonal in-plane dipoles. Motivated by this intriguing phenomenon, we then investigate the steady-state properties of the driven quantum dot, where the populations of the dressed levels are highly tunable by engineering the anisotropy of the surfaces. As a result, the manipulation of the carrier concentration will lead to strong modifications in the resonance fluorescence. Under certain conditions, one can observe the squeezing of two-mode noise spectra with different resonances and polarizations. Although at the expense of declines in the photon-sideband detunings, it is feasible to enhance the two-mode squeezing by gate doping. Our proposal can be easily extended to other hybrid systems containing anisotropic metasurfaces, which are important for the development of quantum information science.

Anisotropic coding metasurfaces and their active manipulation based on vanadium dioxide for multifunctional applications in the terahertz region.

Various kinds of metasurfaces have been proposed because they can be tailored to achieve the desired modulations on electromagnetic wave that do not occur in nature. Compared to conventional metamaterials, coding metasurfaces integrated with information science theory possess numerous distinctive advantages - simple design, time-saving and compatibility with digital devices. Here we propose terahertz multifunctional anisotropic reflective metasurfaces with a metal-insulator-metal cavity structure whose top constructional layer consists of a pair of gold arc-rings and a gold cut-wire located between them. Two different functions of narrow-band absorption and broadband polarization conversion are realized based on different coding matrices using the binary codes '0' and '1'. Furthermore, we integrate a specific coding metasurface with vanadium dioxide (VO2) to realize a temperature-controlled active metasurface. Through the temperature change, dynamic functionalities switching between a narrow-band polarization converter with a polarization conversion ratio over 94% and an efficient low-pass filter are achieved under the phase transition of VO2, and the active metasurface is polarization independent. The proposed coding metasurfaces are verified numerically and experimentally, and have promising applications in terahertz modulation and functional devices.

Cryptography Metasurface for One‐Time‐Pad Encryption and Massive Data Storage

AbstractCompared with traditional encryption methods, one‐time‐pad encryption shows theoretically unbreakable characteristics in cryptography owing to the randomness of the generated keys which are generally the same length as the target message. Here, a novel one‐time‐pad encryption strategy is proposed for combining one‐time‐pad keys storage and associated information authentication in metasurface platform. In the concept, visual secret sharing protocol is used to generated one‐time‐pad key by encoding each pixel of secret to two shared sub‐pixels, while each share reveals no information about original image. Then instead of overlaying the two shares to retrieve the secret, the two shares are further encoded to two random polarization key sequences of horizontal and vertical polarization states in an anisotropic metasurface for encryption. In decryption, a single anisotropic metasurface is adopted as the ciphertext to reconstruct target image combined with the doubly‐encrypted polarization keys. By replacing the conventional multichannel metasurface‐based encryption methods with the digital‐based one‐time‐pad encryption, this work enables the reusability of the metasurface and paves the way toward a new methodology for massive data storage.

INFLUENCE OF UNIAXIAL PLASMON METASURFACE ON ANTIREFLECTION PROPERTIES OF DIELECTRIC LAYER

Subject and Purpose. Th e study of the eff ect of refl ectionless electromagnetic waves propagation through solid-state structures containing metasurfaces at its boundaries has a great scientifi c and practical interest for improving the performance and creating new types of nanoelectronics and optics devices. Th e aim of this work is to study the eff ect of an anisotropic uniaxial plasmon metasurface located at the boundary of the dielectric layer on the eff ect of refl ectionless propagation of electromagnetic waves. The study of the effect of refl ectionless propagation of electromagnetic waves through solid-state structures containing metasurfaces at its boundaries is of great scientific and practical interest for improving the performance and creating new types of nanoelectronics and optics devices. Methods and Methodology. Numerical simulations were used to study the effect of the refl ectionless electromagnetic waves propagation through an anisotropic uniaxial plasma metasurface lying on the dielectric layer. It is used to determine the thicknesses and permeability values of the dielectric layer, for which the effect was observed. Results. It is shown that the presence of an anisotropic uniaxial plasmon metasurface on the dielectric layer leads to a signifi cant conditions change of the eff ect of refl ectionless propagation of p-polarized electromagnetic waves along and across the main axis of anisotropy of the metasurface. It was shown that the metasurface removes the rigid restriction of the dielectric layer permeability value. To achieve the effect of refl ectionless propagation of electromagnetic waves, the permeability of the dielectric layer can be chosen within a wide range. Conclusion. Dielectric layers with anisotropic uniaxial plasmonic metasurfaces have signifi cantly better characteristics for the effect of refl ectionless propagation of electromagnetic waves. They can be used to create fundamentally new nanoelectronic and optical devices.

Multi‐Channel Metasurface for Versatile Wavefront and Polarization Manipulation

AbstractMetasurfaces are extensively studied for the flexible manipulation of wavefront and polarization of electromagnetic waves with significant merits such as ultra‐thin profiles and low insertion losses. However, conventional meta‐devices are usually limited by achieving only single polarization modulation, and it is challenging to achieve mixed polarization and wavefront manipulation in a single metasurface. Here, a single‐layer anisotropic metasurface for independent wavefront manipulation in multiple polarization channels is presented. The meta‐atom is composed of two orthogonal dumbbell‐shaped metal patches placed on the top of a dielectric layer with grounded plane on the bottom. The reflective phases of the two orthogonal linearly polarized waves can be independently manipulated by changing the dimensions of the dumbbell‐shaped resonator. As a result, not only the propagation phase but also the polarization state of the outgoing wave can be manipulated independently as desired. As proof of concept, a metasurface is designed for converging the reflection beams of four polarization states to specific positions for four‐focus holographic imaging. The measured results are in good agreements with simulated ones, verifying the independent wavefront manipulations with arbitrary polarization conversions.