Development Of Metasurfaces Research Articles

Acoustic reflector remotely tunable by the acoustic radiation force

Specifically structured surface can be used to control acoustic waves reflection enabling wavefront shaping tailored for desired applications such as imaging or cloaking. With the development of metasurfaces, which enable changing the reflection of an incident acoustic wave at an interface using a sub-wavelength structure, it is possible to explore new frontiers of Snell-Descartes laws. However, the control over wave propagation is pre-established when using fixed structures, directing research towards metasurfaces reconfigurable in both time and space. This work proposes a metamaterial architecture using deformations of a fluid interface between two media through the acoustic radiation pressure (ARP). An analytical and numerical study is conducted to assess the phase shift on airborne acoustic wave induced by a unit cell featuring a Helmholtz resonator tuned by the water surface elevation induced by ARP. The possibility to program in real-time the phase shift is successfully tested experimentally for an incident wave of frequency 3400 Hz. The extension to a metasurface is introduced through the juxtaposition of 15 unit cell. A retroreflection effect is then numerically demonstrated, highlighting the effectiveness of the proposed approach. This concept of real-time and non-contact reconfigurable metasurface opens new possibilities for beam deflection, acoustic holography or information encoding.

Polarization-Addressable Optical Movement of Plasmonic Nanoparticles and Hotspot Spin Vortices.

Spin-orbit coupling in nanoscale optical fields leads to the emergence of a nontrivial spin angular momentum component, transverse to the orbital momentum. In this study, we initially investigate how this spin-orbit coupling effect influences the dynamics in gold monomers. We observe that localized surface plasmon resonance induces self-generated transverse spin, affecting the trajectory of the nanoparticles as a function of the incident polarization. Furthermore, we investigate the spin-orbit coupling in gold dimers. The resonant spin momentum distribution is characterized by the unique formation of vortex and anti-vortex spin angular momentum pairs on opposite surfaces of the nanoparticles, also affecting the particle motion. These findings hold promise for various fields, particularly for the precision control in the development of plasmonic thrusters and the development of metasurfaces and other helicity-controlled system aspects. They offer a method for the development of novel systems and applications in the realm of spin optics.

Dynamic polarization-regulated metasurface with variable focal length

Polarization and focal length are both critical optical parameters with many applications in many fields, such as optical communications and imaging. The development of metasurfaces provides a new realization of optical systems. In this paper, based on metasurfaces’ powerful electromagnetic modulation capability, we integrate polarization conversion with continuous zoom function and propose a dynamic polarization-regulated metasurface with variable focal length. It realizes the reversible conversion of polarization state, which can convert linearly polarized light into elliptically polarized light and circularly polarized light and convert circularly polarized light to linearly polarized light. At the same time, it achieves a 4.4× zoom range, with a constant focal length variation from 70 µm to 309 µm. The metasurface has the advantages of small size, easy integration, and reconfigurability, providing a new design idea for complex functional optical systems.

Multi‐Channel Image Encryption Based on an All‐Dielectric Metasurface Incorporating Near‐Field Nanoprinting and Far‐Field Holography

AbstractMetasurfaces that can efficiently control the light‐field characteristics have shown many advantages in ultra‐compact, high‐resolution, and high‐concealment optical imaging such as nanoprinting and holography. The development of metasurfaces with multiple functions operating at multiple wavelengths can promote the progress of optical imaging with high information storage and encryption densities. Here, an all‐dielectric metasurface is proposed for multi‐channel image encryption in the near field by controlling the amplitude distribution based on Marius’ law and for holographic imaging in the far field by controlling the phase distribution based on the Pancharatnam–Berry phase. This metasurface can realize the pattern imaging of 12 channels by independently regulating the three‐wavelength channel and different polarization modes. The metasurface achieves independent control of the amplitude, phase, polarization, and wavelength of the incident light wave, improving the storage capacity of information and its encryption security level. The proposed multichannel metasurface provides an effective solution for high‐capacity optical encryption and information storage applications.

Designing high-performance propagation-compressing spaceplates using thin-film multilayer stacks.

The development of metasurfaces has enabled unprecedented portability and functionality in flat optical devices. Spaceplates have recently been introduced as a complementary element to reduce the space between individual metalenses, which will further miniaturize entire imaging devices. However, spaceplates necessitate an optical response which depends on the transverse spatial frequency component of a light field - therefore making it challenging both to design them and to assess their ultimate performance and potential. Here, we employ inverse-design techniques to explore the behaviour of general thin-film-based spaceplates. We observe a tradeoff between the compression factor R and the numerical aperture NA of such devices; we obtained a compression factor of R=5.5 for devices with an NA = 0.42, and up to a record R=340 with NA of 0.017. Our work illustrates that even simple designs consisting of realistic materials (i.e., silicon and glass) permit capable spaceplates for monochromatic applications.

Intelligent Omni-Surfaces: Simultaneous Refraction and Reflection for Full-Dimensional Wireless Communications

The development of metasurfaces has unlocked various use cases in wireless communication networks to improve performance by manipulating the propagation environment. Intelligent omni-surface (IOS), an innovative technique in this category, is proposed for coverage extension. In contrast to the widely studied reflective metasurfaces, i.e., intelligent reflecting surfaces (IRSs), which can only serve receivers located on the same side of the transmitter, the IOS can achieve full-dimensional wireless communications by enabling the simultaneous reflection and refraction of the surface, and thus users on both sides can be served. In this paper, we provide a comprehensive overview of the state-of-the-art in IOS from the perspective of wireless communications, with the emphasis on their design principles, channel modeling, beamforming design, experimental implementation and measurements, as well as possible applications in future cellular networks. We first describe the basic concepts of metasurfaces, and introduce the corresponding design principles for different types of metasurfaces. Moreover, we elaborate on the reflective-refractive model for each IOS element and the channel model for IOS-aided wireless communication systems. Furthermore, we show how to achieve full-dimensional wireless communications with the IOS for three different scenarios. In particular, we present the implementation of an IOS-aided wireless communication prototype and report its experimental measurement results. Finally, we outline some potential future directions and challenges in this area.

Compact Terahertz Dielectric Folded Metasurface

AbstractDespite modern terahertz (THz) systems benefit from the developments in metasurfaces with flexible wavefront manipulation capabilities, the large propagation space between the THz source/detector and metasurface component, as well as the inherent insertion loss of metasurfaces, are the two main bottlenecks that hinder metasurface‐based THz devices from becoming a practical technology. This article addresses these two problems by demonstrating a compact, high‐efficiency folded metasurface system in the THz band. The device comprises two parallel dielectric metasurfaces, between which the THz waves are confined to reduce the system volume. The bottom reflective metasurface consists of an array of anisotropic dielectric resonators, which can simultaneously manipulate THz waves’ phase and polarization properties. The upper metasurface is a dielectric Bragg polarizer that selects the desired linear polarization of THz waves to pass through. Low‐loss and nondispersive high‐resistivity silicon is used as the material for both metasurfaces in this design, which is essential to achieving high efficiency. The compact and high‐efficiency folded THz metasystem is further experimentally verified. The introduced folded device can be used in diverse applications such as high‐speed THz communications, non‐destructive detection, and imaging systems, significantly reducing their volume and increasing their radiation efficiency.

Multifunctional metasurface for broadband absorption, linear and circular polarization conversions

With the development of metasurfaces and the improvement of manufacturing technology, it is important and imperative to design novel metasurfaces that can flexibly manipulate terahertz (THz) waves. In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in THz band. For absorption mode, the MFMS can absorb above 90% energy in the frequency band of 1.74-3.52 THz with the relative bandwidth of 67.6%. For both linear-linear and circular-circular polarization conversion modes, the relative bandwidth with over 90% polarization conversion rates (PCRs) reaches 49.3% in the frequency band of 1.54-2.55 THz. The working mechanism of the MFMS is analyzed by the surface current distributions, and its properties of the absorption and polarization conversion under oblique incident angles are investigated, respectively. The proposed metasurface has promising prospects in terahertz devices such as modulators, smart switches and other terahertz devices.

Metasurfaces for quantum photonics

Rapid progress in the development of metasurfaces allowed to replace bulky optical assemblies with thin nanostructured films, often called metasurfaces, opening a broad range of novel and superior applications to the generation, manipulation, and detection of light in classical optics. Recently, these developments started making a headway in quantum photonics, where novel opportunities arose for the control of nonclassical nature of light, including photon statistics, quantum state superposition, quantum entanglement, and single-photon detection. In this Perspective, we review recent progress in the field of quantum-photonics applications of metasurfaces, focusing on innovative and promising approaches to create, manipulate, and detect nonclassical light.

Phase-change reconfigurable metasurface for broadband, wide-angle, continuously tunable and switchable cloaking.

Being invisible at will has fascinated humanity for centuries and it has become more tangible with the development of metasurfaces, which have demonstrated the extraordinary ability of wavefront manipulation. However, state-of-the-art invisibility cloaks typically work in a deterministic system with a limited bandwidth and small incident angle ranges. Here, by integrating the phase-change material of Ge2Sb2Te5 and the wavefront tailoring functionality of a reflective metasurface, we have achieved a unique carpet cloak that is endowed with broadband invisibility from 6920 to 8220 nm, fully concealing objects over a wide angular span of ±25° and a prominent radar cross-section reduction. Furthermore, the central cloaking wavelength can be continuously tuned with Ge2Sb2Te5 film under different intermediate phases by precisely controlling external stimuli, which will provide a flexible and encouraging way to achieve active features once fabricated. Simulation results also show that the cloaking bandwidth can be significantly extended by triggering Ge2Sb2Te5 from the amorphous to crystalline states. Importantly, the hybrid metasurface can realize switching of "ON" and "OFF" states in terms of cloaking features by converting Ge2Sb2Te5 from the amorphous to the crystalline state. To the best of our knowledge, this is the first metasurface carpet cloak that utilizes the phase-change material of Ge2Sb2Te5 to achieve ultra-broadband, wide-angle, continuously tunable and switchable cloaking with low profiles, light weights, and easy access. This design of a reconfigurable cloak is expected to find potential applications in various areas such as vehicle cloaking, illusions and so on.

Giant Nonlinear Circular Dichroism from Intersubband Polaritonic Metasurfaces.

Nonlinear metasurfaces are advancing into a new paradigm of "flat nonlinear optics" owing to the ability to engineer local nonlinear responses in subwavelength-thin films. Recently, attempts have been made to expand the design space of nonlinear metasurfaces through nonlinear chiral responses. However, the development of metasurfaces that display both giant nonlinear circular dichroism and significantly large nonlinear optical response is still an unresolved challenge. Herein, we propose a method that induces giant nonlinear responses with near-unity circular dichroism using polaritonic metasurfaces with optical modes in chiral plasmonic nanocavities coupled with intersubband transitions in semiconductor heterostructures designed to have giant second and third order nonlinear responses. A stark contrast between effective nonlinear susceptibility elements for the two spin states of circularly polarized pump beams was seen in the hybrid structure. Experimentally, near-unity nonlinear circular dichroism and conversion efficiencies beyond 10-4% for second- and third-harmonic generation were achieved simultaneously in a single chip.

Dual-Physics Metasurfaces for Simultaneous Manipulations of Acoustic and Electromagnetic Waves

Metasurfaces have shown unprecedented possibilities for wavefront manipulation of waves. The research efforts have been focused on the development of metasurfaces that perform a specific functionality for waves of one physical nature, for example, for electromagnetic waves. In this work, we propose the use of power-flow conformal metamirrors for creation of multiphysics devices which can simultaneously control waves of different nature. In particular, we introduce metasurface devices which perform specified operations on both electromagnetic and acoustic waves at the same time. Using a purely analytical model based on surface impedances, we introduce metasurfaces that perform the same functionality for electromagnetic and acoustic waves and, even more challenging, different functionalities for electromagnetics and acoustics. We provide realistic topologies for practical implementations of proposed metasurfaces and confirm the results with numerical simulations.

Bandwidth-enhanced carpet cloak by using a phase-gradient metasurface with a multilayer unit cell in terahertz range

The metasurfaces can effectively manipulate the phase, polarization and amplitude of electromagnetic waves. The development of metasurfaces provides a new choice for designing ultra-thin and arbitrary-shaped carpet cloak devices. Here, we firstly use the classical Snell’s law to derive the generalized Snell’s reflection law for reflective cloak devices, and explores the working principle and design method of metasurface reflection cloak. A multi-layer metasurface structure is proposed to design a broadband terahertz wave carpet cloak device with well cloak effect in the wide frequency range from 0.67 THz to 0.85 THz. Based on Snell’s law, we innovatively cover the metasurface structural unit with a high refractive index dielectric layer to achieve a wide-angle response of the metasurface. Based on the full-wave simulation analysis of the finite integral method, the results show that the designed cloak still has a good cloak effect under the wide angle from 35°to 55°.

Metantenna: When Metasurface Meets Antenna Again

Metasurfaces, composed of 2-D planar arrays of sub-wavelength metallic or dielectric scatterers, have provided unprecedented freedoms in manipulating electromagnetic (EM) waves upon interfaces. The development of metasurface has always been closely related to antennas. On the one hand, metasurface was developed from reflect arrays/transmit arrays that are used as reflectors/lens of antennas, and most fundamental theories of metasurfaces are directly borrowed from antenna array theories; on the other hand, the development of antennas was flourished and expedited by progresses in metasurfaces. Many emerging antenna configurations have been constructed based on unique functional metasurfaces. In this article, we will review briefly the development roadmap of both metasurfaces and metasurface-based antennas, including antenna-inspired metasurfaces, metasurface-assisted antennas, and metasurface antennas. In particular, the recent fusion of metasurface and antenna as metantenna will bring significant impacts on methodologies of functional metasurface, antenna design, and radio-frequency device miniaturization.

太赫兹波前调制超表面器件研究进展

太赫兹波前调制超表面器件研究进展

太赫兹波前调制超表面器件研究进展

太赫兹波前调制超表面器件研究进展

Tunable beam deflector by mutual motion of cascaded bilayer metasurfaces

Tunable metasurface devices are highly desired within the development of metasurfaces, which have superior capabilities for tailoring the wavefront of light. Inspired by the diffractive Alvarez lens and Moiré lens, we find that cascaded bilayer metasurfaces can not only realize active lenses, but also other tunable functional devices. To demonstrate, two kinds of deflectors tuned by lateral and rotational mutual motions of the double metasurface layers are designed and verified by simulations. The presented method is anticipated to realize compact tunable metasurface devices in optical communication, measurement, bio-imaging and display.

Electromagnetic metasurfaces: physics and applications

Metasurfaces are ultrathin metamaterials consisting of planar electromagnetic (EM) microstructures (e.g., meta-atoms) with pre-determined EM responses arranged in specific sequences. Based on careful structural designs on both meta-atoms and global sequences, one can realize homogenous and inhomogeneous metasurfaces that can possess exceptional capabilities to manipulate EM waves, serving as ideal candidates to realize ultracompact and highly efficient EM devices for next-generation integration-optics applications. In this paper, we present an overview on the development of metasurfaces, including both homogeneous and inhomogeneous ones, focusing particularly on their working principles, the fascinating wave-manipulation effects achieved both statically and dynamically, and the representative applications so far realized. Finally, we also present our own perspectives on possible future directions of this fast-developing research field in the conclusion.

A monolithic immersion metalens for imaging solid-state quantum emitters

Quantum emitters such as the diamond nitrogen-vacancy (NV) center are the basis for a wide range of quantum technologies. However, refraction and reflections at material interfaces impede photon collection, and the emitters’ atomic scale necessitates the use of free space optical measurement setups that prevent packaging of quantum devices. To overcome these limitations, we design and fabricate a metasurface composed of nanoscale diamond pillars that acts as an immersion lens to collect and collimate the emission of an individual NV center. The metalens exhibits a numerical aperture greater than 1.0, enabling efficient fiber-coupling of quantum emitters. This flexible design will lead to the miniaturization of quantum devices in a wide range of host materials and the development of metasurfaces that shape single-photon emission for coupling to optical cavities or route photons based on their quantum state.

Plasmonic Near‐Complete Optical Absorption and Its Applications

AbstractNear‐complete absorption of light has the potential to underpin advances in photodetection, advanced chemistry, coloration of materials, and energy. This review paper reports recent progress on the development of metasurfaces and thin film structures that produce strong absorption bands in the visible and longer wavelength regions of the electromagnetic spectrum, due in part to the excitation of plasmonic resonances. Proof‐of‐concept demonstrations are discussed for applications of these in chemical sensing, the generation of structural color, the creation of optoelectronic devices, and photocatalysis. Emerging future applications are also discussed.