Liqiao Jing

Full‐Polarization 3D Metasurface Cloak with Preserved Amplitude and Phase

A full-polarization arbitrary-shaped 3D metasurface cloak with preserved amplitude and phase in microwave frequencies is experimentally demonstrated. By taking the unique feature of metasurfaces, it is shown that the cloak can completely restore the polarization, amplitude, and phase of light for full polarization as if light was incident on a flat mirror.

Hyperbolic spoof plasmonic metasurfaces

Hyperbolic metasurfaces have recently emerged as a new research frontier because of the unprecedented capabilities to manipulate surface plasmon polaritons (SPPs) and many potential applications. However, thus far, the existence of hyperbolic metasurfaces has neither been observed nor predicted at low frequencies because noble metals cannot support SPPs at longer wavelengths. Here, we propose and experimentally demonstrate spoof plasmonic metasurfaces with a hyperbolic dispersion, where the spoof SPPs propagate on complementary H-shaped, perfectly conducting surfaces at low frequencies. Thus, non-divergent diffractions, negative refraction and dispersion-dependent spin-momentum locking are observed as the spoof SPPs travel over the hyperbolic spoof plasmonic metasurfaces (HSPMs). The HSPMs provide fundamental new platforms to explore the propagation and spin of spoof SPPs. They show great capabilities for designing advanced surface wave devices such as spatial multiplexers, focusing and imaging devices, planar hyperlenses, and dispersion-dependent directional couplers, at both microwave and terahertz frequencies. An artificial optical material known as a hyperbolic metasurface that operates at low frequencies has been made. Metamaterials can be designed to have optical properties not found in nature. One example is the hyperbolic metasurface, so called because the strongly anisotropic electric or magnetic response of the material creates a hyperbolic dispersion in the photons momemtum space. So far, only hyperbolic metasurfaces that operate at relatively high frequencies have been created. Now, Hongsheng Chen from Zhejiang University in China and co-workers has created a spoof plasmonic metasurface with exotic optical properties and that have low-frequency operation. They achieved this by using so-called spoof surface-plasmon polaritons that arise as light interacts with capacitances and inductances created by an array of H-shaped perfectly conducting surfaces. We propose and experimentally demonstrate spoof plasmonic metasurfaces with a hyperbolic dispersion, where the spoof SPPs propagate on complementary H-shaped perfectly conducting surfaces at low frequencies. In this way, non-divergent diffractions, negative refraction, and dispersion-dependent spin-momentum locking are observed as the spoof SPPs travel over the hyperbolic spoof plasmonic metasurfaces. They show great capabilities to design advanced surface wave devices such as spatial multiplexers, focusing and imaging devices, planar hyperlenses, and dispersion-dependent directional couplers, at both microwave and terahertz frequencies.Metasurfaces, with intrinsically planar nature and subwavelength thickness, provide us unconventional methodologies to not only mold the flow of propagating waves but also manipulate near-field waves. Plasmonic metasurfaces with topological transition for controlling surface plasmon polaritons (SPPs) recently have been experimentally demonstrated, which, however, are limited to optical frequencies. In this work, we proposed and experimentally characterized an ultrathin metasurface with the topological transition for manipulating spoof SPPs at low frequency. We demonstrated rich interesting phenomena based on this metasurface, including frequency-dependent spatial localization, non-diffraction propagation, negative refraction, and dispersion-dependent spin-momentum locking of spoof SPPs. Comparing with traditional three-dimensional metamaterials, our metasurface exhibits low propagation loss and compatibility with the photonic integrated circuit, which may find plenty of applications in spatial multiplexers, focusing and imaging devices, planar hyperlens, and dispersion-dependent directional couplers, in microwave and terahertz frequencies.

Origami-Based Reconfigurable Metamaterials for Tunable Chirality

Origami is the art of folding two-dimensional (2D) materials, such as a flat sheet of paper, into complex and elaborate three-dimensional (3D) objects. This study reports origami-based metamaterials whose electromagnetic responses are dynamically controllable via switching the folding state of Miura-ori split-ring resonators. The deformation of the Miura-ori unit along the third dimension induces net electric and magnetic dipoles of split-ring resonators parallel or anti-parallel to each other, leading to the strong chiral responses. Circular dichroism as high as 0.6 is experimentally observed while the chirality switching is realized by controlling the deformation direction and kinematics. In addition, the relative density of the origami metamaterials can be dramatically reduced to only 2% of that of the unfolded structure. These results open a new avenue toward lightweight, reconfigurable, and deployable metadevices with simultaneously customized electromagnetic and mechanical properties.

Bifunctional acoustic metamaterial lens designed with coordinate transformation

We propose a method to design bifunctional acoustic lens using acoustic metamaterials that possess separate functions at different directions. The proposed bifunctional acoustic lens can be implemented in practice with subwavelength unit cells exhibiting effective anisotropic parameters. With this methodology, we experimentally demonstrate an acoustic Luneburg-fisheye lens at operational frequencies from 6300 Hz to 7300 Hz. Additionally, a bifunctional acoustic square lens is proposed with different focal lengths for multi directions. This method paves the way to manipulating acoustic energy flows with functional lenses.

Chiral metamirrors for broadband spin-selective absorption

Chiral metamirrors are recently proposed metadevices that have the ability of selective reflection for the designated circularly polarized waves. However, previous chiral metamirrors only work in a narrow band, which would limit their potential applications in engineering. Here, we propose an approach towards broadband spin-selective absorption. By combining the chiral resonant modes of two asymmetric split-ring resonators, we design and construct a chiral metamirror that absorbs only the left-handed circularly waves over a broad frequency range. The measured results show a bandwidth of 5.1%, almost 96% larger than that of the narrowband metamirror. Furthermore, the proposed chiral metamirror exhibits prominent performance at oblique incidence, even when high-order diffraction appears. The total thickness of the metamirror is only one-ninth of the wavelength, highly suitable for on-chip integration. Our findings may provide an efficient approach to boost the working bandwidth of the chiral metamirror and ...

Kirigami metamaterials for reconfigurable toroidal circular dichroism

The ancient paper craft of kirigami has recently emerged as a potential tool for the design of functional materials. Inspired by the kirigami concept, we propose a class of kirigami-based metamaterials whose electromagnetic functionalities can be switched between nonchiral and chiral states by stretching the predesigned split-ring resonator array. Single-band, dual-band, and broadband circular polarizers with reconfigurable performance are experimentally demonstrated with maximum circular dichroism of 0.88, 0.94, and 0.92, respectively. The underlying mechanism is explained and calculated via detailed analysis of the excited multipoles, including the electric, magnetic, and toroidal dipoles and quadrupole. Our approach enables tailoring the electromagnetic functionalities in kirigami patterns and provides an alternate avenue for reconfigurable optical metadevices with exceptional mechanical properties.Metamaterials: A fold and a snip yields an optical switchA new twist on the Japanese art of origami has helped researchers achieve dynamic optical polarization switching for applications including lasers and biosensors. Metamaterials, substances engineered to manipulate radiation in non-natural ways—bending light around objects to make them appear invisible, for example—are normally impossible to re-configure after being fabricated. Liqiao Jing from Zhejiang University in Hangzhou, China, and colleagues have overcome this limitation by depositing periodic arrays of copper rings onto thin, foldable polymer sheets. By introducing small cuts and then stretching the sheets, the team created buckled, 3D surfaces with different symmetries to the original flat film. The rearranged atoms in the new structures enabled filtering of circularly polarized light, an effect which could be expanded to broadband frequencies by stacking two folded films on top of one another.An approach towards kirigami metamaterials with reconfigurable toroidal circular dichroism is presented. Inspired by the kirigami concept, kirigami-based chiral metamaterials are proposed to switch the electromagnetic performance between non-chiral and chiral states. When transforming the 2D metasurface to 3D kirigami patterns, the resonant modes exhibit gradually enhanced chiroptical response, from single-band, dual-band to broad-band functionalities.

3D Visible-Light Invisibility Cloak

Abstract The concept of an invisibility cloak is a fixture of science fiction, fantasy, and the collective imagination. However, a real device that can hide an object from sight in visible light from absolutely any viewpoint would be extremely challenging to build. The main obstacle to creating such a cloak is the coupling of the electromagnetic components of light, which would necessitate the use of complex materials with specific permittivity and permeability tensors. Previous cloaking solutions have involved circumventing this obstacle by functioning either in static (or quasistatic) fields where these electromagnetic components are uncoupled or in diffusive light scattering media where complex materials are not required. In this paper, concealing a large‐scale spherical object from human sight from three orthogonal directions is reported. This result is achieved by developing a 3D homogeneous polyhedral transformation and a spatially invariant refractive index discretization that considerably reduce the coupling of the electromagnetic components of visible light. This approach allows for a major simplification in the design of 3D invisibility cloaks, which can now be created at a large scale using homogeneous and isotropic materials.

Broadband chiral metamirrors

Chiral metamirrors can reflect one circularly polarized light without changing its handedness, while almost completely absorb the other, which would have many potential applications in engineering. In this paper, recent progresses of our group on the chiral metamirrors are reviewed. Firstly, we discuss the general method to design the chiral metamirrors under the framework of Jones calculus. The structural requirement of such chiral metamirrors is the breaking in both the n-fold rotational (n ≥ 2) symmetry and mirror symmetry. According to the general design methodology, we propose and design some chiral metamirrors that absorb only one circularly polarized light. Our design includes a bi-layer chiral metamirror in the mid-infrared region, a single-layer chiral metamirror in microwave and a broadband chiral metamirror. Our findings may provide an efficient approach to boost the working bandwidth of the chiral metamirror and a variety of applications, including molecular spectroscopy and polarization-sensitive detector.

Magnetic Fano resonances by design in symmetry broken THz meta-foils

Magnetic Fano resonances in there-dimensional symmetry broken meta-foils at THz frequencies are theoretically and experimentally studied. Sharp Fano resonances occur due to the interference between different resonances and can be designed by choosing geometric parameters of the meta-foil. At the Fano resonances, the meta-foil supports antisymmetric modes, whereas, at the main resonance, only a symmetric mode exists. The meta-foil is left-handed at the Fano resonances and shows sharp peaks of the real part of the refractive index in transmission with small effective losses opening a way to very sensitive high-speed sensing of dielectric changes in the surrounding media and of mechanical configuration.

Dynamically switchable metasurfaces based on graphene and origami

Metasurfaces, two-dimensional metamaterials consisting of engineered structures, have recently emerged as an exciting “flat” platform to manipulate electromagnetic waves in a prescribed manner. The tunability and reconfigurability are urgently needed for of metasurfaces in order to perform distinctive functionalities and miniaturize the device footprint. In this talk, I will first discuss tunable metasurfaces based on graphene nanoribbons for infrared beam steering. It is shown that the phase of the infrared light reflected from a simple graphene ribbon metasurface can span over almost the entire 2π range by changing the width of the graphene ribbons, while the amplitude of the reflection can be maintained at high values without significant variations. We successfully realize anomalous reflection, reflective focusing lenses, and non-diffracting Airy beams based on graphene metasurfaces, which are readily tunable by changing the Fermi energy of graphene. In the second part of my talk, I will discuss origami-based, dual-band chiral metasurfaces at microwave frequencies. The flexibility by folding the metasurface provides another degree of freedom for geometry control in the third dimension, which induces strong chirality from the initial, 2D achiral structure. The experimental results are in good agreement with numerical simulations and analyses. These findings open up a new paradigm of lightweight, multifunctional, and tunable devices for adaptive control over electromagnetic waves.