Multifunctional Metasurface Research Articles

Multifunctional Metasurface Inverse Design Based on Ultra‐Wideband Spectrum Prediction Neural Network

AbstractMultifunctional metasurfaces have demonstrated extensive potential in various fields. During the design of metasurfaces, optimization of components for polarization, amplitude distribution, phase distribution, and other factors is necessary. This process typically demands expert involvement and is time‐consuming. In this paper, a metasurface inverse design method is introduced that combines a high‐precision ultra‐wideband spectrum forward prediction utilizing a neural network and a genetic algorithm. A neural network is constructed and trained to accurately predict the amplitude and phase of a 16 × 16 discrete grid structure with high degrees of freedom in the frequency range of 0.5–2 THz. Leveraging the neural network's ultra‐fast spectrum prediction capabilities (producing approximately 1000 spectra per second), the average optimization time for a single component is reduced to 1.5 min. Finally, the effectiveness of this inverse design method is validated through the design and simulation of multifunctional reflective deflection metasurfaces with two sets of 3‐bit frequency multiplexing and polarization multiplexing. The proposed metasurface inverse design method offers a new approach for the rapid design of components in complex application scenarios and holds significant reference value for metasurface designers.

Switchable multifunctional metasurface with broadband absorption and polarization conversion in the terahertz frequency band

Switchable multifunctional metasurface with broadband absorption and polarization conversion in the terahertz frequency band

Metasurface-Based Optical Logic Operators Driven by Diffractive Neural Networks.

In this paper, a novel optical logic operator based on the multifunctional metasurface driven by all-optical diffractive neural network is reported, which can perform four principal quantum logic operations (Pauli-X, Pauli-Y, Pauli-Z, and Hadamard gates). The two ground states and are characterized by two orthogonal linear polarization states. The proposed spatial- and polarization-multiplexed all-optical diffractive neural network only contains a hidden layer physically mapped as a metasurface with simple and compact unit cells, which dramatically reduces the volume and computing resources required for the system. The designed optical quantum operator is proven to achieve high fidelities for all four quantum logical gates, up to 99.96% numerically and 99.88% experimentally. The solution will facilitate the construction of large-scale optical quantum computing systems and scalable optical quantum devices.

Multifunctional comb-like acoustic metasurface for transmissive wavefront manipulation

Precise and highly efficient wavefront modulation is greatly appreciated in acoustic engineering. Here, a comb-like acoustic metasurface is developed to efficiently manipulate the transmitted wavefront. The comb-like unit consists of an array of rigid rectangular partitions supported by a base. By adjusting the height of these rectangular elements, the entire 2π transmission phase shift can be achieved. The controllability of the phase shifts is demonstrated through theoretical and numerical analysis. A particle swarm optimization algorithm is employed to determine the height of the rectangular elements to achieve accurate target phase shift while maintaining high transmission efficiency. As a case study, highly efficient acoustic focusing and waveform conversion are achieved by comb-like metasurfaces, and the effect of unit deficiency on focusing performance is discussed. Furthermore, the application of comb-like metasurfaces to generate a self-bending beam and Airy beam is verified, and the acoustic beam of self-repair performance and robustness are demonstrated. In addition, acoustic focusing is realized using two symmetric Airy beams generated from the comb-like metasurface. Experiments are conducted to verify the effectiveness of the designed metasurfaces. This work presents an effective and feasible design solution for flexible wavefront modulation.

Dielectric Metasurface Enabled Compact, Single-Shot Digital Holography for Quantitative Phase Imaging.

Quantitative phase imaging (QPI) enables nondestructive, real-time, label-free imaging of transparent specimens and can reveal information about their fundamental properties such as cell size and morphology, mass density, particle dynamics, and cellular fluctuations. Development of high-performance and low-cost quantitative phase imaging systems is thus required in many fields, including on-site biomedical imaging and industrial inspection. Here, we propose an ultracompact, highly stable interferometer based on a single-layer dielectric metasurface for common path off-axis digital holography and experimentally demonstrate quantitative phase imaging. The interferometric imaging system leveraging an ultrathin multifunctional metasurface captures image plane holograms in a single shot and provides quantitative phase information on the test samples for extraction of its physical properties. With the benefits of planar engineering and high integrability, the proposed metasurface-based method establishes a stable miniaturized QPI system for reliable and cost-effective point-of-care devices, live cell imaging, 3D topography, and edge detection for optical computing.

Information multiplexing from optical holography to multi-channel metaholography

Abstract Holography offers a vital platform for optical information storage and processing, which has a profound impact on many photonic applications, including 3D displays, LiDAR, optical encryption, and artificial intelligence. In this review, we provide a comprehensive overview of optical holography, moving from volume holography based on optically thick holograms to digital holography using ultrathin metasurface holograms in nanophotonics. We review the use of volume holograms for holographic multiplexing through the linear momentum selectivity and other approaches and highlight the emerging use of digital holograms that can be implemented by ultrathin metasurfaces. We will summarize the fabrication of different holographic recording media and digital holograms based on recent advances in flat meta-optics and nanotechnology. We highlight the rapidly developing field of metasurface holography, presenting the use of multi-functional metasurfaces for multiplexing holography in the use of polarization, wavelength, and incident angle of light. In the scope of holographic applications, we will focus on high bandwidth metasurface holograms that offer the strong sensitivity to the orbital angular momentum of light. At the end, we will provide a short summary of this review article and our perspectives on the future development of the vivid holography field.

Multifunctional optical meta-tweezers with polarization-based modulation

The use of optical trapping has become increasingly prevalent in scientific domains such as biology and physics. However, the realization of various trapping effects often requires the switching of equipment components. To address this challenge, we propose a novel approach that combines the dynamic and geometric phases with polarization multiplexing to create a monolayer multifunctional metasurface optical tweezer based on polarization modulation. Our method utilizes different circular polarizations of light to produce a both focused Gaussian field and a focused optical vortex (OV) field. Numerical simulations demonstrate that the focused Gaussian fields can effectively trap high refractive index (RI) particles, while the focused OV fields can be used as an optically controlled spanner to rotate and manipulate particles or trap low RI particles. Additionally, we present an array of polarization modulation metasurface tweezers that have the potential to trap and manipulate particles of varying radii and diverse motion behaviors. Overall, our work highlights the efficacy of polarization-modulation multifunctional metasurface tweezers in combining several trapping tasks into one device. These tweezers have promising potential for integration into future lab-on-chip technologies.

High Q-factor multifunctional plasmonic metasurfaces in the mid-infrared

As application scenarios grow in complexity, multifunctional integrated metasurfaces have been proposed as a potential development direction. We propose a multifunctional high Q-factor metasurface-based platform composed by size-scaled metasurface polarization selective absorbers (MPSAs) capable of polarization selective absorption, refractive index sensing and chiral response. By designing a gold step-shaped unit structure that can break the in-plane and out-of-plane symmetry, bound states in the continuums (BICs) with chiral response and a surface lattice resonance (SLR) are realized. The overall absorption amplitude of the quasi-BIC can reach a maximum value of 0.87 and a Q-factor of 153 while the SLR possesses a high Q-factor exceeding 1274 and a maximum absorption amplitude of 0.93. High extinction ratio up to 13 dB between the transverse magnetic and transverse electric polarization can be achieved. For refractive index (RI) sensing, the bulk RI sensitivities of the proposed MPSA for quasi-BIC and SLR are SBIC = 4000 nm/RIU and SSLR = 3740 nm/RIU, which leads to a high figure of merit (FOM) of FOMBIC = 161 /RIU and FOMSLR = 1247 /RIU, respectively. For chiral response, the maximum circular dichroism (CD) for the proposed MPSA is 0.88 by oblique incidence still maintaining a Q-factor exceeding 120, which indicates that it has potential application for chiral sensing. The proposed multifunctional metasurfaces-based platform possesses the potential to promising future applications for polarization manipulation, chiral biosensing, chiral drug analysis and quantum optics.

Tunable circular dichroism in all-dielectric metasurface with efficient wavefront manipulation

In this paper, an all-dielectric metasurface based on phase-change material Ge2Sb2Se4Te1 (GSST) working in the mid-infrared band is designed, and combined with Pancharatnam-Berry (PB) phase to realize multifunctional metasurfaces. The metasurface can convert incident circularly polarized waves to transmitted or reflected waves of opposite chirality, regardless of GSST is in amorphous or crystalline state. Due to constructive interference and destructive interference, the metasurface obtains giant circular dichroism (CD). The maximum CD value reaches 0.997 at f = 64 THz when GSST is in amorphous state and 0.97 at f = 45 THz when GSST is in crystalline state. According to the principle of PB phase, three optical devices are realized by the rational arrangement of all-dielectric meta-atoms with different rotation angles, which are beam deflectors, lenses and vortex beam generators.

A One-Bit Programmable Multi-Functional Metasurface for Microwave Beam Shaping.

In this paper, we demonstrate a multi-functional metasurface for microwave beam-shaping application. The metasurface consists of an array of programmable unit cells, and each unit cell is integrated with one varactor diode. By turning the electrical bias on the diode on and off, the phase delay of the microwave reflected by the metasurface can be switched between 0 and π at a 6.2 GHz frequency, which makes the metasurface 1-bit-coded. By programming the 1-bit-coded metasurface, the generation of a single-focus beam, a double-focus beam and a focused vortex beam was experimentally demonstrated. Furthermore, the single-focus beam with tunable focal lengths of 54 mm, 103 mm and 152 mm was experimentally observed at 5.7 GHz. The proposed programmable metasurface manifests robust and flexible beam-shaping ability which allows its application to microwave imaging, information transmission and sensing applications.

Highly efficient broadband spin-multiplexed metadevices for futuristic imaging applications

Achieving broadband and multifunctional response through a single optical device is a highly sought-after capability for various applications like microscopy and optical imaging, which provide detailed morphological information of a targeted object. Traditional optical systems require a chain of elements to achieve such functionality, resulting in bulky systems hindering integration with modern photonics devices. Metasurfaces are exquisitely designed and exhibit unprecedented light-manipulation capability at the nanoscale, thus creating easy-to-integrate miniaturized photonic devices. Recently, broadband multifunctional metasurfaces with polarization’s degree of freedom have attracted considerable interest due to their exceptional ability of wavefront shaping, which may find their applications in imaging and data communication. However, realizing single-cell driven, highly efficient multifunctional metasurfaces operating over broadband wavelengths remains challenging. This study presents a unique helicity-dependent broadband multifunctional metasurface platform to manipulate visible light for futuristic imaging applications. The proposed platform can integrate multiple optical phenomena into a single-layered metadevice to generate several uncorrelated, spin-dependent responses across the targeted visible spectrum (470–650 nm). For proof of concept, we demonstrated several all-dielectric transmissive metadevices carrying various spin-multiplexed phase profiles, efficiently generating diffraction-limited focusing and structured light beams with different characteristics. Each designed metasurface was studied under selected visible wavelengths, and the diffracted light exhibited excellent and stable broadband performance. With the advantages of broadband multifunctional platform and miniaturized metadevices, the presented strategy may open new vistas for various applications, including biomedical imaging, optical interconnects, and microscopy.

Multifunctional Metasurface Tuning by Liquid Crystals in Three Dimensions.

Optical metasurfaces present remarkable opportunities for manipulating wave propagation in unconventional ways, surpassing the capabilities of traditional optical devices. In this work, we introduce and demonstrate a multifunctional dynamic tuning of dielectric metasurfaces containing liquid crystals (LCs) through an effective three-dimensional (3D) control of the molecular orientation. We theoretically and experimentally study the spectral tuning of the electric and magnetic resonances of dielectric metasurfaces, which was enabled by rotating an external magnetic field in 3D. Our approach allows for the independent control of the electric and magnetic resonances of a metasurface, enabling multifunctional operation. The magnetic field tuning approach eliminates the need for the pre-alignment of LCs and is not limited by a finite set of directions in which the LC molecules can be oriented. Our results open new pathways for realizing dynamically reconfigurable metadevices and observing novel physical effects without the usual limitations imposed by the boundary conditions of LC cells and the external voltage.

An ultra-thin multifunctional chiral metasurface with asymmetric transmission, cross-polarization conversion, and circular dichroism for Ku- and K-band applications

In this paper, a bi-layered ultra-thin multifunctional chiral metasurface is proposed to obtain asymmetric transmission (AT), cross-polarization conversion (CPC), and circular dichroism (CD). The multifunctional chiral metasurface realizes an AT with more than 70% efficiency over a Ku-band frequency range from 14.3 to 15.8 GHz, while in the operating frequency band from 13.5 to 16.2 GHz, the CPC ratio is above 90%. In addition, the metasurface exhibits CD in the K-band with a CD parameter of 0.6 at 24 GHz. Furthermore, the functionalities of AT and CPC are stable with changes in the incident angle of up to 60° for both transverse-electric and transverse-magnetic electromagnetic waves. For verification of the anticipated concept, the proposed chiral metasurface is fabricated and measured. The proposed design can be used for potential applications in the Ku- and K-bands for satellite communication and radar.

Tunable terahertz multi-functional hybrid-patterned metasurface arrays based on vanadium dioxide

This study investigates a nine-layer multi-functional periodic array with active broadband tuning in the terahertz (THz) band. The device comprises symmetrical vanadium dioxide (VO2) films and polypropylene (PP) layers, along with silicon dioxide (SiO2) layers, hybrid-patterned metasurfaces, and a central VO2 layer. Through detailed analyses of the electric field distribution, equivalent circuit, and effective impedance, we have performed a thorough investigation of the resonance modes present in the device and meticulously optimized various parameters. Leveraging the insulator-to-metal transition of VO2, a remarkable device capable of seamlessly switching between extraordinary terahertz transmission and bi-directional perfect absorption was obtained. These characters exhibit limited susceptibility to incident angle of the incoming wave. By incorporating bow-tie apertures within the “vacuum region” of the hybrid-patterned metasurfaces, a significant improvement in field enhancement has been achieved, all while effectively eliminating any adverse effects on transmission and absorption performance. This device presents a novel and effective approach in the development of adjustable and multifunctional THz metasurface devices.

Design and analysis of terahertz multifunctional tunable metasurfaces based on single-layer square split ring

Aiming at the problems of single function, limited application range and complex structure of most metasurfaces, we propose a terahertz multifunctional tunable metasurface based on VO2-metal hybrid structure. The metasurface consists of three layers, from top to bottom, VO2-metal resonance layer, Topas dielectric layer and bottom gold film reflective layer. When circularly polarized light is incident, the metasurface can achieve broadband circular dichroism (CD) function, and the CD intensity generated at 3.19–6.24 THz is greater than 0.8, and the relative bandwidth is as high as 64.69%. When linearly polarized light is incident, the dual-band reversible linear dichroism (LD) function, broadband linear-to-circular polarized conversion function, and high-efficiency linear cross-polarization conversion function can be achieved by adjusting the polarization state of the incident light. Moreover, by adjusting the conductivity of VO2 and the state of the incident light, the adjustment of each functional intensity can be achieved. Finally, we believe that the proposed multifunctional metasurface has significant reference value in the terahertz range for constructing chiral photodetectors, CD metamirrors, intelligent switches, and polarization digital imaging systems.

Programmable multifunctional metasurface for polarization, phase, and amplitude manipulation.

Metasurfaces have shown extraordinary capability in individually manipulating various electromagnetic (EM) properties, including polarization, phase, and amplitude. However, it is still a challenge to manipulate these EM properties in one metasurface simultaneously. In this paper, a programmable multifunctional metasurface (PMFMS) is demonstrated with polarization, phase, and amplitude manipulation abilities. By controlling tunable coding states and changing the direction of incident waves, the PMFMS can operate as a transmission cross-polarization converter, spatial wave manipulator, and low-RCS radome. Besides, the PMFMS possesses an ultra-wideband property, which can operate from 6.5 to 10.2 GHz with 44.3% relative bandwidth. More importantly, multiple functionalities can also be achieved in reflection operating mode by reassembling the PMFMS. As a proof of concept, the PMFMS is fabricated and experimentally verified. Measured results are in good agreement with simulated results. Benefiting from multifunctional EM manipulations in an ultra-wideband, such a design can be applied in wireless communication systems, radar detection, and EM stealth platform.

Switchable terahertz orbital angular momentum Bessel beams based on spin-decoupled multifunctional reflective metasurfaces.

In this study, switchable terahertz (THz) multi-orbital angular momentum (OAM) Bessel beams (BBs) were developed based on a spin-decoupled reflective multifunctional metasurface (MTS). Switchability was achieved by switching the feed between left-hand circular polarization (LCP), right-hand circular polarization (RCP), and linear polarization (LP) incidences. A switchable physical model was established for calculating the beam direction, OAM mode, polarization, and non-diffractive distance of the outgoing BBs. As an example, a spin-decoupled MTS was designed to generate dual BBs under LCP incidence, which was subsequently switched to RCP or LP for switchability. The outgoing BBs could be switched among three types of beams: Type-1 under LCP incidence (LCP, θL = 40°, φL = 0°, lL = 1, dL = 18 cm) and (RCP, θR = -40°, φR = 0°, lR = -1, dR = 20 cm); Type-2 under RCP incidence (RCP, θR = 40°, φR = 0°, lR = 1, dR = 18 cm) and (LCP, θL = -19°, φL = 0°, lL = 3, dL = 16.4 cm); and Type-3 under LP incidence (LP, θ = 40°, φ = 0°, l = 1, d = 18 cm), (RCP, θR = -40°, φR = 0°, lR = -1, dR = 20 cm) and (LCP, θL = -19°, φL = 0°, lL = 3, dL = 16.4 cm). Compared with previous MTSs, the proposed spin-decoupled MTS has the advantages of switchability among BBs, high non-diffractive distance/aperture size ratio of 15, large beam deflection angle of up to 40°, and high BB conversion efficiency of up to 96%. The simulated results were consistent with those calculated using the physical model, thus validating the physical model. The designed switchable BBs have potential THz near-field applications, such as high-capacity near-field wireless communications, wireless power transfer, high-resolution imaging, non-destructive testing, and speed detection of high-speed rotating objects.

Broadband terahertz metasurface with three switchable functions based on complementary structure

In this work, we propose a switchable multifunctional metasurface based on complementary VO2-graphene structure. Tuning the state of VO2 and the Fermi level of graphene, the metasurface can act as broadband half-wave plate (HWP), quarter-wave plate (QWP) or absorber in the same frequency range of 0.65–1.27THz, respectively. In the V1G0 state, the metasurface behaves as a broadband HWP to realize linear-to-linear polarization conversion with the polarization conversion ratio >0.9 in the range of 0.64–1.37THz. In the V0G1 state, the metasurface acts as a broadband QWP achieving linear-to-circular polarization conversion with the ellipticity below −0.9 in the range of 0.65–1.27THz. In the V1G1 state, the metasurface is a broadband absorber with the absorption over 0.9 in the 0.63–1.32THz range. In addition, the physical mechanisms of the metasurface in different states are analyzed through the field and current distributions. Such a switchable multi-functional metasurface can simultaneously achieve high efficiency polarization conversion and absorption, which has potential applications in the integrated terahertz devices.

Multifunctional active terahertz metasurface with electromagnetically induced transparency, perfect absorption, and circular dichroism

Navigated by the continued demand for design integration and miniaturization, incorporating multiple diversified operations into a single metasurface hybridized with the tunable metasurface is highly demanding at the terahertz (THz) range. However, up to now, because of the limitation of the reconfigurable metasurface at the terahertz range, most metasurfaces only feature a single function or process similar functionalities at a single frequency. A multi-functional terahertz metasurface based on vanadium dioxide (VO2) is proposed in this paper, which consists of a gold layer, a VO2 bridge, a SiO2 spacer, and a VO2 layer on the back of the spacer. Under different conductivity of different VO2 layers, the proposed metasurface achieves various terahertz device functions, including single-band perfect terahertz absorption, circular dichroism (CD) for the reflected and transmitted fields, and electromagnetically induced transparency (EIT) effect. Furthermore, the proposed metasurface exhibits robust response against oblique incidences. The mechanisms of perfect absorption, chiral-selective absorption and EIT are illustrated by impedance matching theory, surface current and electric field distributions, respectively. The function-switching ability of proposed metasurface provides more options for the design of terahertz devices in the future.

Transmitted Electromagnetic Beam Steering of Pyramid All‐Dielectric Encoding Surface Microstructure

AbstractA transmission‐type all‐medium element is proposed to construct a coded metasurface. Due to the single‐layer metasurface unit structure, large reflection loss will be caused when the base plane is incident. In order to improve the efficiency of the coded metasurface device and reduce the reflection loss, the authors propose a double‐sided metasurface digital unit structure and introduces a wideband anti‐reflection pyramid microstructure to achieve significantly improved transmission characteristics. The optimized unit structure is coded and the coded metasurface is constructed. Different coding metasurface sequences are constructed based on 1‐bit, 2‐bit, and 3‐bit digital coding units. According to generalized Snell's law, the number of transmitted beams can be controlled. The authors introduce complex code addition theory to construct multifunctional beam control metasurface. Based on the far field scattering theory of metasurface, the addition theory of different sequences of transmission‐coded metasurface is analyzed. The addition operation of the superposition of two sets of symmetric double beams and two sets of ordinary double beams can be realized. Based on the analysis of far‐field scattering characteristics, the multifunctional coded metasurface is demonstrated, that is, multiple functions are simultaneously superimposed in one array without interference.