Inhomogeneous Metasurface Research Articles

Ultrafast near-infrared pyroelectric detector based on inhomogeneous plasmonic metasurface

Pyroelectric (PE) detection technologies have attracted extensive attention due to the cooling-free, bias-free, and broadband properties. However, the PE signals are generated by the continuous energy conversion processes from light, heat, to electricity, normally leading to very slow response speeds. Herein, we design and fabricate a PE detector which shows extremely fast response in near-infrared (NIR) band by combining with the inhomogeneous plasmonic metasurface. The plasmonic effect dramatically accelerates the light-heat conversion process, unprecedentedly improving the NIR response speed by 2−4 orders of magnitude to 22 μs, faster than any reported infrared (IR) PE detector. We also innovatively introduce the concept of time resolution into the field of PE detection, which represents the detector’s ability to distinguish multiple fast-moving targets. Furthermore, the spatially inhomogeneous design overcomes the traditional narrowband constraint of plasmonic systems and thus ensures a wideband response from visible to NIR. This study provides a promising approach to develop next-generation IR PE detectors with ultrafast and broadband responses.

Perfectly matched inhomogeneous receiving metasurface for line source incidence

This paper presents a perfectly matched inhomogeneous receiving metasurface for line source incidence, based on the effective medium equivalency. Each building block of the inhomogeneous metasurface has effective constitutive parameters that satisfy a specific relationship dependent on the location of the line source. By doing so, the reflection from the receiving metasurface for the cylindrical wave incidence can be significantly suppressed, improving the total reception efficiency greatly. Theoretical analysis, numerical calculation, full-wave simulations and experimental results are consistent with each other, showing promising applications in some short-range wireless power transmission systems, where the incident wave is non-planar.

Coherent retroreflective metasurfaces

Inhomogeneous metasurfaces have shown possibilities for unprecedented control of wave propagation and scattering. While it is conventional to shine a single incident plane wave from one side of these metastructures, illuminating by several waves simultaneously from both sides may enhance possibilities to control scattered waves, which results in additional functionalities and novel applications. Here, we unveil how by using coherent plane-wave illumination of a properly designed inhomogeneous metasurface sheet it is possible to realize controllable retroreflection. We call these metasurfaces “coherent retroreflectors” and explain the method for realizing them both in theory and in practice. We show that coherent retroreflectors can be used for filtering undesired modes and creation of field-localization regions in waveguides. The latter application is in resemblance to bound states in the radiation continuum.Received 22 December 2020Accepted 28 June 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.L032025Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetismPhysical SystemsMetamaterialsTechniquesElectromagnetic wave theoryGeneral Physics

Azimuthally Inhomogeneous Metasurface Cloak for Cylindrical Objects

An analytical formula to define an azimuthally inhomogeneous metasurface (AIM) cloak for cylindrical objects is presented. The inhomogeneity of the metasurface is modeled by Fourier decomposing the azimuthally varying susceptibility distribution. The AIM cloak provides weighted control on each scattering mode to enhance the scattering reduction capability for prescribed incident angles of interest. With an AIM cloaking layer, the scattering reduction of a 0.15-wavelength radius metallic cylinder can be enhanced by more than 6 dB compared to a conventional homogenous metasurface cloak. Accuracy of the formulation is proven with full-wave simulations. The design of the AIM cloak is experimentally validated at four bistatic angles.

Generating dual-polarization beams carrying dual orbital angular momentum modes based on anisotropic holographic metasurfaces

Through this study, we demonstrate the generation of linear dual-polarization beams with different orbital angular momentum (OAM) modes by designing, manufacturing, and experimentally measuring an anisotropic holographic metasurface. A combination of the leaky-wave theory and the microwave holographic method is proposed as a way to effectively construct the metasurface based on the interferogram obtained by the interference between the surface waves excited by a monopole and our predesigned OAM beams. In addition, the inhomogeneous holographic metasurface is composed of massive square metallic patches of different dimensions on a grounded substrate, and the anisotropy of the different particles is characterized by the different orientation angles of the rectangular slots that are etched on the upper metallic layer. The close agreement between the numerical simulations and experimental measurements verify the good performance of the metasurface. This finding creates a new opportunity to generate dual-polarization dual-OAM modes for radio vortex beams and lays a solid foundation for multiple OAM modes in wireless communication systems.

Manipulation of acoustic wavefront by transmissive metasurface based on pentamode metamaterials**Project supported by the National Natural Science Foundation of China (Grant Nos. 61571222 and 11474160), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20161009), and the Six-Talent Peaks Project of Jiangsu Province, China.

An underwater acoustic metasurface with sub-wavelength thickness is designed for acoustic wavefront manipulation. In this paper, a pentamode lattice and a frequency-independent generalized acoustic Snellʼs law are introduced to overcome the limitations of narrow bandwidth and low transmittance. The bulk modulus and effective density of each unit cell can be tuned simultaneously, which are modulated to guarantee the achievement of refractive index profile and high transmission. Here, we actualize anomalous refraction, generation of non-diffracting Bessel beam, sub-wavelength flat focusing, and surface wave conversion by constructing inhomogeneous acoustic metasurface. This design approach has potential applications in medical ultrasound imaging and underwater acoustic communications.

Helicity Multiplexed Spin‐Orbit Interaction in Metasurface for Colorized and Encrypted Holographic Display

AbstractThe photonic spin‐orbit interaction (PSOI) in inhomogeneous anisotropic metasurface has drawn much attentions recently due to its superior ability to manipulate light wave in the deep‐subwavelength scale. Traditional methods involving PSOI are limited to operational spectral bandwidth owing to the intrinsic dispersion of the constitutive materials. In this paper, a helicity‐multiplexing scheme is proposed to achieve independent control of the PSOI in both the spectral and spatial domains by combining the broadband characteristic with polarization dependence of the metasurface. Two simultaneous functions of multicolor holographic display and polarization encryption are experimentally demonstrated with a single metasurface perforated with nanoholes. Although the optical response of the nanoholes themselves are almost independent of the light wavelength, the obtained image can have abundant spectral information. The approach proposed here is promising for realizing multifunction optical device, multicolor display, optical storage and information encryption.

Focusing metasurface quantum-cascade laser with a near diffraction-limited beam.

A terahertz vertical-external-cavity surface-emitting-laser (VECSEL) is demonstrated using an active focusing reflectarray metasurface based on quantum-cascade gain material. The focusing effect enables a hemispherical cavity with flat optics, which exhibits higher geometric stability than a plano-plano cavity and a directive and circular near-diffraction limited Gaussian beam with M2 beam parameter as low as 1.3 and brightness of 1.86 × 106 Wsr-1m-2. This work initiates the potential of leveraging inhomogeneous metasurface and reflectarray designs to achieve high-power and high-brightness terahertz quantum-cascade VECSELs.

Shaping the spatial and spectral emissivity at the diffraction limit

Metasurfaces have attracted a growing interest for their ability to artificially tailor an electromagnetic response on various spectral ranges. In particular, thermal sources with unprecedented abilities, such as directionality or monochromaticity, have been achieved. However, these metasurfaces exhibit homogeneous optical properties whereas the spatial modulation of the emissivity up to the wavelength scale is at the crux of the design of original emitters. In this letter, we study an inhomogeneous metasurface made of a nonperiodic set of optical nano-antennas that spatially and spectrally control the emitted light up to the diffraction limit. Each antenna acts as an independent deep subwavelength emitter for given polarization and wavelength. Their juxtaposition at the subwavelength scale encodes far field multispectral and polarized images. This opens up promising breakthroughs for applications such as optical storage, anti-counterfeit devices, and multispectral emitters for biochemical sensing.

Dual-channel near-field control by polarizations using isotropic and inhomogeneous metasurface.

We propose a method for dual-channel near-field manipulations by designing isotropic but inhomogeneous metasurfaces. As example, we present a dual-channel near-field focusing metasurface device. When the device is driven by surface waves from different channels on the metasurface, the near fields will be focused at the same spatial point with different polarizations. Conversely, if a linearly polarized source is radiated at the spatial focal point, different channels will be evoked on the metasurface controlled by polarization. We fabricated and measured the metasurface device in the microwave frequency. Well agreements between the simulation and measurement results are observed. The proposed method exhibits great flexibility in controlling the surface waves and spatial waves simultaneously. It is expected that the proposed method and dual-channel device will facilitate the manipulation of near electromagnetic or optical waves in different frequency regimes.

Spin-orbit interaction of light in metasuface

Spin-orbit interaction of light in metasurface is investigated in this paper. We theoretically analyze the transfromation of circularly and linearly polarized light by metasurface with Jones matrix. The results indicate that the interaction of light with spatially inhomogeneous and anisotropic metasurface leads to a coupling of spin-orbital angular momentum. The nanostructrues of metasurfaces are arranged at a definite rate of rotation, which induces an additional space-variant geometrical phase (i.e., Pancharatnam-Berry phase). The Pancharatnam-Berry phase is dependent on the polarization handedness of the incident wave. This characteristic can result in spin-dependent split. A left/right-circular polarized beam is transfromed into a right/left-circular polarized vortex beam by the metasurfaces. In the convertion process, the sign of spin angular momentum of photons is inversed. At the same time, each photon can acquire orbital angular momentum from the inhomogeneous and anisotropic media. The case that a linearly polarized beam inputs the metasurfaces also is considered. A linearly polarized wave can be regarded as the linear superposition of left-circular and right-circular polarized wave. The two circularly plarized components are respectively converted into circularly polarized vortex beam with reverse polarization handedness. The coherent superposition of the two output components forms a cylindrical vector beam. Finally, we adopt the combination of a metasurface and spiral phase plate to verify the theoretical results. The vortex phase can be eliminated by the spiral phase plate when a left-circular polarized light is input, while topological charge of vortex phase will increase when a right-circular polarized light is input. For the case of inputting linearly polarized beam, one of the two outputing circularly polarized components can be eliminated by the helical phase through using the spiral phase plate, while the topological charge of another component increases. It results in the fact that the intensity pattern splits into two parts. The central part does not have helical phase, while the ambient ring-shaped intensity has helical phase. In order to judge the polarization handedness of output wave, the Stokes parameter S3 is measured by inserting a Glan laser polarizer and a quarter wave plate behind the spiral phase plate. The experimental results are in good agreement with theoretical analyses. These results are helpful for understanding the manipulation of light with metasurface.

Realization of polarization evolution on higher-order Poincaré sphere with metasurface

We present a simple and convenient method to yield cylindrical vector (CV) beams and realize its polarization evolution on higher-order Poincaré sphere based on inhomogeneous birefringent metasurface. By means of local polarization transformation of the metasurface, it is possible to convert a light beam with homogeneous elliptical polarization into a vector beam with any desired polarization distribution. The Stokes parameters of the output light are measured to verify our scheme, which show well agreement with the theoretical prediction. Our method may provide a convenient way to generate CV beams, which is expected to have potential applications in encoding information and quantum computation.

Metasurfing: Addressing Waves on Impenetrable Metasurfaces

Metasurfaces constitute a class of thin metamaterials, which are used from microwave to optical frequencies to create new antennas and microwave devices. Here, we propose the use of variable-impedance metasurfaces for transforming surface or guided waves into different wavefield configurations with desirable properties. We will shortly refer to this metasurface-driven wavefield transformation as “metasurfing.” Metasurfing can be obtained by an appropriate synthesis of inhomogeneous metasurface reactance that allows a local modification of the dispersion equation and, at constant operating frequency, of the local wave vector. The general effects of metasurface modulation are similar to those obtained in solid (volumetric) inhomogeneous metamaterial as predicted by the transformation optics-namely, readdressing the propagation path of an incident wave. However, significant technological simplicity is gained. Several examples are shown as a proof of concept.