Tunable VO_(2) cavity enables multispectral manipulation from visible to microwave frequencies

Optical materials capable of dynamically manipulating electromagnetic waves are an emerging field in memories,optical modulators,and thermal management.Recently,their multispectral design preliminarily attracts much attention,aiming to enhance their efficiency and integration of functionalities.However,the multispectral manipulation based on these materials is challenging due to their ubiquitous wavelength dependence restricting their capacity to narrow wavelengths.In this article,we cascade multiple tunable optical cavities with selective-transparent layers,enabling a universal approach to overcoming wavelength dependence and establishing a multispectral platform with highly integrated functions.Based on it,we demonstrate the multispectral(ranging from 400 nm to 3 cm),fast response speed(0.9 s),and reversible manipulation based on a typical phase change material,vanadium dioxide.Our platform involves tandem VO_(2)-based Fabry–Pérot(F-P)cavities enabling the customization of optical responses at target bands independently.It can achieve broadband color-changing capacity in the visible region(a shift of~60 nm in resonant wavelength)and is capable of freely switching between three typical optical models(transmittance,reflectance,and absorptance)in the infrared to microwave regions with drastic amplitude tunability exceeding 0.7.This work represents a state-of-art advance in multispectral optics and material science,providing a critical approach for expanding the multispectral manipulation ability of optical systems.

Super-reflector enabled by non-interleaved spin-momentum-multiplexed metasurface

Electromagnetic wave multiplexing,especially for that occurring at different incidences(spatial-frequency multiplexing),is pivotal for ultrathin multifunctional interfaces and high-capacity information processing and communication.It is yet extremely challenging based on passive and compact wave elements,since the wave excitation and scattering channels are exclusively coupled through gradient phases and hence momentum matching condition at the interface.Here,we propose a spin-momentum multiplexed paradigm called a super-reflector enabling on-demand control of both retroreflections and anomalous reflections using a non-interleaved single-celled metasurface.By multiplexing four channels connecting two spin states excited onto each input of three spatial frequencies,a total of twelve channels are engineered,among which three are retroreflected channels and the residual are anomalous reflection ones.Our compound multiplexed super-reflector allows five degrees of freedom in circular polarization Jones'matrix,approaching the intrinsic upper limit of such planar metasurface.The concept has been experimentally verified by a proof-of-concept super-reflector at microwave frequency,showcasing twelve reflected beams and a high efficiency exceeding 90.6%defined as the ratio of reflected power to incidence for each channel beam.Our strategy opens a new avenue for angle multiplexing and angle-resolved metadevices toward the capacity limit of 2D planar Jones'matrix.

Recent advances in metasurface design and quantum optics applications with machine learning,physics-informed neural networks,and topology optimization methods

As a two-dimensional planar material with low depth profile,a metasurface can generate non-classical phase distributions for the transmitted and reflected electromagnetic waves at its interface.Thus,it offers more flexibility to control the wave front.A traditional metasurface design process mainly adopts the forward prediction algorithm,such as Finite Difference Time Domain,combined with manual parameter optimization.However,such methods are time-consuming,and it is difficult to keep the practical meta-atom spectrum being consistent with the ideal one.In addition,since the periodic boundary condition is used in the meta-atom design process,while the aperiodic condition is used in the array simulation,the coupling between neighboring meta-atoms leads to inevitable inaccuracy.In this review,representative intelligent methods for metasurface design are introduced and discussed,including machine learning,physics-information neural network,and topology optimization method.We elaborate on the principle of each approach,analyze their advantages and limitations,and discuss their potential applications.We also summarize recent advances in enabled metasurfaces for quantum optics applications.In short,this paper highlights a promising direction for intelligent metasurface designs and applications for future quantum optics research and serves as an up-to-date reference for researchers in the metasurface and metamaterial fields.

Interference-assisted kaleidoscopic meta-plexer for arbitrary spin-wavefront manipulation

Achieving simultaneous polarization and wavefront control,especially circular polarization with the auxiliary degree of freedom of light and spin angular momentum,is of fundamental importance in many optical applications.Interferences are typically undesirable in highly integrated photonic circuits and metasurfaces.Here,we propose an interference-assisted metasurface-multiplexer(meta-plexer)that counterintuitively exploits constructive and destructive interferences between hybrid meta-atoms and realizes independent spin-selective wavefront manipulation.Such kaleidoscopic meta-plexers are experimentally demonstrated via two types of single-layer spinwavefront multiplexers that are composed of spatially rotated anisotropic meta-atoms.One type generates a spinselective Bessel-beam wavefront for spin-down light and a low scattering cross-section for stealth for spin-up light.The other type demonstrates versatile control of the vortex wavefront,which is also characterized by the orbital angular momentum of light,with frequency-switchable numbers of beams under linearly polarized wave excitation.Our findings offer a distinct interference-assisted concept for realizing advanced multifunctional photonics with arbitrary and independent spin-wavefront features.A variety of applications can be readily anticipated in optical diodes,isolators,and spin-Hall meta-devices without cascading bulky optical elements.

Deterministic Approach to Achieve Full-Polarization Cloak

Achieving full-polarization(σ)invisibility on an arbitrary three-dimensional(3D)platform is a long-held knotty issue yet extremely promising in real-world stealth applications.However,state-of-the-art invisibility cloaks typically work under a specific polarization because the anisotropy and orientation-selective resonant nature of artificial materials made theσ-immune operation elusive and terribly challenging.Here,we report a deterministic approach to engineer a metasurface skin cloak working under an arbitrary polarization state by theoretically synergizing two cloaking phase patterns required,respectively,at spin-up(σ+)and spin-down(σ−)states.Therein,the wavefront of any light impinging on the cloak can be well preserved since it is a superposition ofσ+andσ−wave.To demonstrate the effectiveness and applicability,several proof-of-concept metasurface cloaks are designed to wrap over a 3D triangle platform at microwave frequency.Results show that our cloaks are essentially capable of restoring the amplitude and phase of reflected beams as if light was incident on a flat mirror or an arbitrarily predesigned shape under full polarization states with a desirable bandwidth of~17.9%,conceiving or deceiving an arbitrary object placed inside.Our approach,deterministic and robust in terms of accurate theoretical design,reconciles the milestone dilemma in stealth discipline and opens up an avenue for the extreme capability of ultrathin 3D cloaking of an arbitrary shape,paving up the road for real-world applications.

Polarization-insensitive 3D conformal-skin metasurface cloak

Electromagnetic metasurface cloaks provide an alternative paradigm toward rendering arbitrarily shaped scatterers invisible.Most transformation-optics(TO)cloaks intrinsically need wavelength-scale volume/thickness,such that the incoming waves could have enough long paths to interact with structured meta-atoms in the cloak region and consequently restore the wavefront.Other challenges of TO cloaks include the polarization-dependent operation to avoid singular parameters of composite cloaking materials and limitations of canonical geometries,e.g.,circular,elliptical,trapezoidal,and triangular shapes.Here,we report for the first time a conformal-skin metasurface carpet cloak,enabling to work under arbitrary states of polarization(SOP)at Poincarésphere for the incident light and arbitrary conformal platform of the object to be cloaked.By exploiting the foundry three-dimensional(3D)printing techniques to fabricate judiciously designed meta-atoms on the external surface of a conformal object,the spatial distributions of intensity and polarization of its scattered lights can be reconstructed exactly the same as if the scattering wavefront were deflected from a flat ground at any SOP,concealing targets under polarization-scanning detections.Two conformal-skin carpet cloaks working for partial-and full-azimuth plane operation are respectively fabricated on trapezoid and pyramid platforms via 3D printing.Experimental results are in good agreement with numerical simulations and both demonstrate the polarization-insensitive cloaking within a desirable bandwidth.Our approach paves a deterministic and robust step forward to the realization of interfacial,free-form,and full-polarization cloaking for a realistic arbitrary-shape target in real-world applications.

High-efficiency broadband polarization-independent superscatterer using conformal metasurfaces

Safe detection of an arbitrarily shaped platform is critical for survivability, rescue, or navigation safety in a remote region. Metasurfaces afford great potential due to their strong electromagnetic(EM) wave control. However,studies have mainly focused on the physics and design of metasurfaces on planar plates, which does not satisfy the current requirements of aerodynamics and aesthetics. Herein, we propose a sophisticated strategy to design a metasurface that can wrap over arbitrarily shaped objects with moderate curvature on which optical aberrations are commonly introduced. By designing each meta-atom on the basis of the required position and phase compensation, exact EM wavefronts are restored. For verification, several conformal metasurfaces were designed and numerically studied on metallic cylinders at the microwave spectrum. A proof-of-concept device is fabricated and is experimentally characterized. The results demonstrate the availability of the desirable dual-beam superscatterer with strong backscattering enhancement toward two directions, thus indicating that the distortions induced by an arbitrary platform can be efficiently corrected. Our method affords an efficient alternative for designing highperformance multifunctional optoelectronic devices equipped on a moderately curved platform.

Harmonic suppressed bandpass filter using composite right/left handed transmission line

A wideband composite right/left handed transmission line (CRLH TL) in conjunction with its corresponding equivalent circuit model is studied based on a cascaded complementary single split ring resonator (CCSSRR).The characterization is performed by theory analysis,circuit simulation,and full-wave electromagnetic (EM) simulation.The negative refractive index (NRI) and backward wave propagation performance of the CRLH TL are demonstrated.For application,a bandpass filter (BPF) with enhanced out-of-band selectivity and harmonic suppression operating at the wireless local area network (WLAN) band is designed,fabricated,and measured by combining the CRLH TL with a complementary electric inductive-capacitive resonator (CELC).Three CELC cells with wideband stopband performance in the conductor strip and ground plane,respectively,are utilized in terms of single negative permeability.The design concept has been verified by the measurement data.

Miniaturized fractal-shaped branch-line coupler for dual-band applications based on composite right/left handed transmission lines

In this paper,novel dual-band (DB) branch-line couplers (BLCs) employing a composite right/left handed transmission line (CRLH TL) and fractal geometry are presented for the first time.The CRLH TL,with specified characteristic impedance and phase shift,consists of lumped elements for the left handed (LH) part and fractal-shaped microstrip lines (MLs) for the right handed (RH) part,which can be designed separately.Two designed BLCs are involved in size reduction,one using a 3/2 fractal curve of first iteration,the other constructed based on a hybrid shape of fractal and meandered lines.A miniaturized principle for CRLH TL realization is derived and an exact design method for fractal implementation is developed.For verification,an example coupler was fabricated and measured.Consistent numerical and experimental results confirmed the design concept,showing that the BLCs obtain DB behavior centered at 0.9 GHz and 1.8 GHz respectively with good in-band performance,except for slightly larger coupled insertion loss for the hybrid-shaped BLC case.In addition,the proposed fractal-and hybrid-shaped BLCs obtained a 49.7% and 64.1% size reduction respectively relative to their conventional counterparts working in the lower band.The most important contributions of this article are the demonstration of compatibility between the fractal and CRLH TL techniques and the provision of an alternative approach and a new concept for designing devices.

Adaptable Invisibility Management Using Kirigami-Inspired Transformable Metamaterials

Many real-world applications,including adaptive radar scanning and smart stealth,require reconfigurable multifunctional devices to simultaneously manipulate multiple degrees of freedom of electromagnetic(EM)waves in an on-demand manner.Recently,kirigami technique,affording versatile and unconventional structural transformation,has been introduced to endow metamaterials with the capability of controlling EM waves in a reconfigurable manner.Here,we report for a kirigami-inspired sparse meta-architecture,with structural density of 1.5%in terms of the occupation space,for adaptive invisibility based on independent operations of frequency,bandwidth,and amplitude.Based on the general principle of dipolar management via structural reconstruction of kirigami-inspired meta-architectures,we demonstrate reconfigurable invisibility management with abundant EM functions and a wide tuning range using three enantiomers(A,B,and C)of different geometries characterized by the folding angleβ.Our strategy circumvents issues of limited abilities,narrow tuning range,extreme condition,and high cost raised by available reconfigurable metamaterials,providing a new avenue toward multifunctional smart devices.

Adaptable Invisibility Management Using Kirigami-Inspired Transformable Metamaterials

Many real-world applications,including adaptive radar scanning and smart stealth,require reconfigurable multifunctional devices to simultaneously manipulate multiple degrees of freedom of electromagnetic(EM)waves in an on-demand manner.Recently,kirigami technique,affording versatile and unconventional structural transformation,has been introduced to endow metamaterials with the capability of controlling EM waves in a reconfigurable manner.Here,we report for a kirigami-inspired sparse meta-architecture,with structural density of 1.5%in terms of the occupation space,for adaptive invisibility based on independent operations of frequency,bandwidth,and amplitude.Based on the general principle of dipolar management via structural reconstruction of kirigami-inspired meta-architectures,we demonstrate reconfigurable invisibility management with abundant EM functions and a wide tuning range using three enantiomers(A,B,and C)of different geometries characterized by the folding angleβ.Our strategy circumvents issues of limited abilities,narrow tuning range,extreme condition,and high cost raised by available reconfigurable metamaterials,providing a new avenue toward multifunctional smart devices.