From Single-Dimensional to Multidimensional Manipulation of Optical Waves with Metasurfaces

Hybrid strategy in compact tailoring of multiple degrees-of-freedom toward high-dimensional photonics

Tailoring multiple degrees-of-freedom (DoFs) to achieve high-dimensional laser field is crucial for advancing optical technologies. While recent advancements have demonstrated the ability to manipulate a limited number of DoFs, most existing methods rely on bulky optical components or intricate systems that employ time-consuming iterative methods and, most critically, the on-demand tailoring of multiple DoFs simultaneously through a compact, single element-remains underexplored. In this study, we propose an intelligent hybrid strategy that enables the simultaneous and customizable manipulation of six DoFs: wave vector, initial phase, spatial mode, amplitude, orbital angular momentum (OAM) and spin angular momentum (SAM). Our approach advances in phase-only property, which facilitates tailoring strategy experimentally demonstrated on a compact metasurface. A fabricated sample is tailored to realize arbitrary manipulation across six DoFs, constructing a 288-dimensional space. Notably, since the OAM eigenstates constitute an infinite dimensional Hilbert space, this proposal can be further extended to even higher dimensions. Proof-of-principle experiments confirm the effectiveness in manipulation capability and dimensionality. We envision that this powerful tailoring ability offers immense potential for multifunctional photonic devices across both classical and quantum scenarios and such compactness extending the dimensional capabilities for integration on-chip requirements.

Novel Octa-Structure Metamaterial Architecture for High Q-Factor and High Sensitivity in THz Impedance Spectroscopy

Terahertz (THz) electric inductive-capacitive (ELC) resonant metamaterials (MMs) are well established tools that can be used to detect the presence of dielectric material (e.g., nanoparticles, bioparticles, etc.) spread on their surfaces within the gap of the capacitive plates of a nanoantenna array. In THz spectroscopy, the amount of the red shift in the resonance frequency (ΔF) plays an important role in the detection of nanoparticles and their concentration. We introduce a new LC resonant MM architecture in the ELC category that maximizes dielectric sensitivity. The newly proposed architecture has an octahedral structure with uniform capacitive gaps at each forty-five-degree interval, making the structure super-symmetric and polarization independent. The inductor core is condensed into a central solid circle connecting all the eight lobes of the octahedron, thereby completing the LC circuit. This ELC resonator has very large active areas (capacitor-gaps), with hotspots at the periphery of each unit cell. The MM structure is repeated in a clustered fashion, so that the peripheral hotspots are also utilized in dielectric sensing. This results in enhancing the quality factor of MM resonance, as well as in increasing ΔF. The research comprises a combination of rigorous system-level simulations along with THz impedance spectroscopy laboratory experiments. We achieved a highly sensitive MM sensor with sensitivity reaching 1600 GHz/RIU. This sensor is fully CMOS compatible and has promising potential applications in high-sensitivity bio-sensing, characterization of nanoparticles, and ultra-low-concentration dielectrics detection, as well as in sensing differential changes in the composition of substances deposited on the metasurface.

Acoustography by Beam Engineering and Acoustic Control Node: BEACON

Acoustic manipulation has emerged as a valuable tool for precision controls and dynamic programming of cells and particles. However, conventional acoustic manipulation approaches lack the finesse necessary to form intricate, configurable, continuous, and 3D patterning of particles. Here, this study reports acoustography by Beam Engineering and Acoustic Control Node (BEACON), which delivers intricate, configurable patterns by guiding particles along custom paths with independent phase modulation. Leveraging analytical methods of orbital angular momentum beam via iterative Wirtinger hologram algorithm, this study accomplish acoustography by facilitating orbital angular momentum traps, enabling continuous 2D and 3D acoustic manipulation of microparticles in any desired geometry, with phase modulation independent of intensity. Utilizing on-chip acoustography, the BEACON platform markedly increases the space-bandwidth product to 31 000 while attaining an enhanced resolution with a pixel size of ≈25 µm, surpassing the typical resolution of over 200 µm in previous holographic particle manipulation methods. The capabilities of BEACON are demonstrated in creating intricate triple helical tracing structures using microdroplets (20 µm in diameter) and those carrying DNA to validate the effectiveness of the acoustography and phase control methods. This study offers new particle manipulation opportunities, paving the way for next-generation biomedical systems and the future of contact-free precision manufacturing.

Multifunctional Intelligent Reconfigurable Metasurface

The emergent reconfigurable metasurfaces (RMs) have attracted a lot of attention due to their potential in broad applications. As a general platform, RMs are able to control the reflection (or refraction) of incident waves with predefined functionalities. Nevertheless, the operation of RMs is highly dependent on the arrival direction of incidence. The self-adaptive design of an RM, so that it can respond to varied incident waves automatically, is highly requested in practical implementation, which is actually challenging. This study reports the realization of an intelligent RM (IRM) system, which can detect the arrival direction of impinging waves and respond to the incidence with a predefined functionality accordingly. This IRM system is constructed by integrating a direction of the arrival estimation module, a frontend by the varactor-based metasurface, and a central control unit. In experiments, an IRM system designed for TM polarization is demonstrated to perform various functions, i.e., retroreflection, directional reflection, and fixed-point energy focusing, which are highly requested by edge communication and sensing. The measured results imply that this IRM system responds quite well within a wide incident range from -60° to 60° in a frequency range from 9 to 9.5 GHz. The proposed IRM can be a good candidate for boosting 5G communication and Internet of Things applications, including beam shaping/steering, RCS manipulation, object imaging, and sensor recharging.

THz Metamaterial Sensitivity Enhancement by Reduction of Substrate's Fabry-Pérot Oscillations Using Back Plates as an Optical De-Coupler

This work presents a new method for the enhancement of sensitivity in Terahertz (THz) spectroscopy on metamaterial (MM) in terms of its resonance frequency shift (ΔF), by attaching the dielectric back plate to the MM's silicon (Si) wafer. The dielectric back plates are designed to minimize the Fresnel reflections at the backside of the substrate, identical to a broadband antireflective (AR) plate tailored for THz. Utilizing broadband AR technology, we demonstrate the concept of decoupling MM resonance from the substrate's Fabry-Pérot (FP) oscillations. This is done by effectively coupling the THz light out of the high-permittivity substrate, resulting in the improved quality factor of the MM resonance and overall plasmonic enhancement on the metasurface. The back plate acts as a surface plasmonic enhancer to the THz MM by increasing the field intensity on the front metasurface, leading to enhancement of dielectric response (MM's ΔF). This makes the MM resonance ultrasensitive to the minor changes of particle size/concentration under test spread on the metasurface, contributing to enhanced resonance ΔF. The plate also makes the Si substrate optically lossless, enabling the full effect of MM resonance shift and increasing the resonance ΔF by 8-fold compared with MM's fabricated on conventional Si substrates. This research is backed-up with system-level CST simulations and experimental THz impedance spectroscopy of the MM. This method and chip structure is CMOS compatible having potential applications for any resonant MM fabricated on a substrate aimed to maximize dielectric sensitivity for biosensing and nanoparticle THz spectroscopy.

Laser-induced microbubble as an in vivo valve for optofluidic manipulation in living Mice's microvessels

Optofluidic regulation of blood microflow in vivo represents a significant method for investigating illnesses linked to abnormal changes in blood circulation. Currently, non-invasive strategies are limited to regulation within capillaries of approximately 10 μm in diameter because the adaption to blood pressure levels in the order of several hundred pascals poses a significant challenge in larger microvessels. In this study, using laser-induced microbubble formation within microvessels of the mouse auricle, we regulate blood microflow in small vessels with diameters in the tens of micrometers. By controlling the laser power, we can control the growth and stability of microbubbles in vivo. This controlled approach enables the achievement of prolonged ischemia and subsequent reperfusion of blood flow, and it can also regulate the microbubbles to function as micro-pumps for reverse blood pumping. Furthermore, by controlling the microbubble, narrow microflow channels can be formed between the microbubbles and microvessels for assessing the apparent viscosity of leukocytes, which is 76.9 ± 11.8 Pa·s in the in vivo blood environment. The proposed design of in vivo microbubble valves opens new avenues for constructing real-time blood regulation and exploring cellular mechanics within living organisms.

Ultra-robust informational metasurfaces based on spatial coherence structures engineering

Optical information transmission is vital in modern optics and photonics due to its concurrent and multi-dimensional nature, leading to tremendous applications such as optical microscopy, holography, and optical sensing. Conventional optical information transmission technologies suffer from bulky optical setup and information loss/crosstalk when meeting scatterers or obstacles in the light path. Here, we theoretically propose and experimentally realize the simultaneous manipulation of the coherence lengths and coherence structures of the light beams with the disordered metasurfaces. The ultra-robust optical information transmission and self-reconstruction can be realized by the generated partially coherent beam with modulated coherence structure even 93% of light is recklessly obstructed during light transmission, which brings new light to robust optical information transmission with a single metasurface. Our method provides a generic principle for the generalized coherence manipulation on the photonic platform and displays a variety of functionalities advancing capabilities in optical information transmission such as meta-holography and imaging in disordered and perturbative media.

Complex-Amplitude Programmable Versatile Metasurface Platform Driven by Guided Wave

Metasurfaces have shown unparalleled controllability of electromagnetic (EM) waves. However, most of the metasurfaces need external spatial feeding sources, which renders practical implementation quite challenging. Here, a low-profile programmable metasurface with 0.05λ0 thickness driven by guided waves is proposed to achieve dynamic control of both amplitude and phase simultaneously. The metasurface is fed by a guided wave traveling in a substrate-integrated waveguide, avoiding external spatial sources and complex power divider networks. By manipulating the state of the p-i-n diodes embedded in each meta-atom, the proposed metasurface enables 1-bit amplitude switching between radiating and nonradiating states, as well as a 1-bit phase switching between 0° and 180°. As a proof of concept, two advanced functionalities, namely, low sidelobe-level beam scanning and Airy beam generation, are experimentally demonstrated with a single platform operating in the far- and near-field respectively. Such complex-amplitude, programmable, and low-profile metasurfaces can overcome integration limitations of traditional metasurfaces, and open up new avenues for more accurate and advanced EM wave control within an unprecedented degree of freedom.

Programmable optical meta-holograms

The metaverse has captured significant attention as it provides a virtual realm that cannot be experienced in the physical world. Programmable optical holograms, integral components of the metaverse, allow users to access diverse information without needing external equipment. Meta-devices composed of artificially customized nano-antennas are excellent candidates for programmable optical holograms due to their compact footprint and flexible electromagnetic manipulation. Programmable optical meta-holograms can dynamically alter reconstructed images in real-time by directly modulating the optical properties of the metasurface or by modifying the incident light. Information can be encoded across multiple channels and freely selected through switchable functionality. These advantages will broaden the range of virtual scenarios in the metaverse, facilitating further development and practical applications. This review concentrates on recent advancements in the fundamentals and applications of programmable optical meta-holograms. We aim to provide readers with general knowledge and potential inspiration for applying programmable optical meta-holograms, both intrinsic and external ways, into the metaverse for better performance. An outlook and perspective on the challenges and prospects in these rapidly growing research areas are provided.

Optical computing metasurfaces: applications and advances

Integrated photonic devices and artificial intelligence have presented a significant opportunity for the advancement of optical computing in practical applications. Optical computing technology is a unique computing system based on optical devices and computing functions, which significantly differs from the traditional electronic computing technology. On the other hand, optical computing technology offers the advantages such as fast speed, low energy consumption, and high parallelism. Yet there are still challenges such as device integration and portability. In the burgeoning development of micro-nano optics technology, especially the deeply ingrained concept of metasurface technique, it provides an advanced platform for optical computing applications, including edge detection, image or motion recognition, logic computation, and on-chip optical computing. With the aim of providing a comprehensive introduction and perspective for optical computing metasurface applications, we review the recent research advances of optical computing, from nanostructure and computing methods to practical applications. In this work, we review the challenges and analysis of optical computing metasurfaces in engineering field and look forward to the future development trends of optical computing.

Three-fold information encryption based on polarization- and wavelength-multiplexed metasurfaces

Metasurface has garnered significant attention in the field of optical encryption as it allows the integration and occultation of multiple grayscale nanoprinting images on a single platform. However, in most cases, polarization serves as the only key for encryption/decryption, and the risk of being cracked is relatively high. In this study, we propose a three-fold information encryption strategy based on a dielectric metasurface, in which a colorful nanoprinting image and two grayscale images are integrated on such a single platform. Unlike previous works based on the orientation-angle degenerated light intensity, the proposed image encryptions are realized by customizing nanobricks with polarization-mediated similar/different transmission characteristics in either broadband or at discrete wavelengths. Different combinations of polarization and monochromatic wavelengths can form three keys with different levels of decryption complexity as compared to the previous counterpart based merely on polarization. Once illuminated by non-designed wavelengths or polarized light, messy images with false information will be witnessed. Most importantly, all images are safely secured by the designated incidence polarization and cannot be decrypted via an additional analyzer as commonly happens in conventional metasurface-based nanoprinting. The proposed metasurface provides an easy-to-design and easy-to-disguise scheme for multi-channel display and optical information encryption.

Integrated metasurfaces for re-envisioning a near-future disruptive optical platform

Metasurfaces have been continuously garnering attention in both scientific and industrial fields, owing to their unprecedented wavefront manipulation capabilities using arranged subwavelength artificial structures. To date, research has mainly focused on the full control of electromagnetic characteristics, including polarization, phase, amplitude, and even frequencies. Consequently, versatile possibilities of electromagnetic wave control have been achieved, yielding practical optical components such as metalenses, beam-steerers, metaholograms, and sensors. Current research is now focused on integrating the aforementioned metasurfaces with other standard optical components (e.g., light-emitting diodes, charged-coupled devices, micro-electro-mechanical systems, liquid crystals, heaters, refractive optical elements, planar waveguides, optical fibers, etc.) for commercialization with miniaturization trends of optical devices. Herein, this review describes and classifies metasurface-integrated optical components, and subsequently discusses their promising applications with metasurface-integrated optical platforms including those of augmented/virtual reality, light detection and ranging, and sensors. In conclusion, this review presents several challenges and prospects that are prevalent in the field in order to accelerate the commercialization of metasurfaces-integrated optical platforms.

Silicon metasurface-based infrared polarizing beam splitter with on-demand deflection angles

Polarizing beam splitters (PBSs) play an important role in applications requiring polarization multiplexing or high polarization purity. Traditional prism-based PBSs usually have large volumes, which hampers their further applications in ultracompact integrated optical systems. Here, we demonstrate a single-layer silicon metasurface-based PBS with the ability to deflect two orthogonally linearly polarized infrared light beams to on-demand angles. The metasurface consists of silicon anisotropic microstructures, which can provide different phase profiles for the two orthogonal polarization states. In experiments, two metasurfaces designed with arbitrary deflection angles for x- and y-polarized light exhibit good splitting performance at an infrared wavelength of 10 μm. We envision that this type of planar and thin PBS can be used in a series of compact thermal infrared systems.

Rapid Cellular-Resolution Skin Imaging with Optical Coherence Tomography Using All-Glass Multifocal Metasurfaces

Cellular-resolution optical coherence tomography (OCT) is a powerful tool offering noninvasive histology-like imaging. However, like other optical microscopy tools, a high numerical aperture (N.A.) lens is required to generate a tight focus, generating a narrow depth of field, which necessitates dynamic focusing and limiting the imaging speed. To overcome this limitation, we developed a metasurface platform that generates multiple axial foci, which multiplies the volumetric OCT imaging speed by offering several focal planes. This platform offers accurate and flexible control over the number, positions, and intensities of axial foci generated. All-glass metasurface optical elements 8 mm in diameter are fabricated from fused-silica wafers and implemented into our scanning OCT system. With a constant lateral resolution of 1.1 μm over all depths, the multifocal OCT triples the volumetric acquisition speed for dermatological imaging, while still clearly revealing features of stratum corneum, epidermal cells, and dermal-epidermal junctions and offering morphological information as diagnostic criteria for basal cell carcinoma. The imaging speed can be further improved in a sparse sample, e.g., 7-fold with a seven-foci beam. In summary, this work demonstrates the concept of metasurface-based multifocal OCT for rapid virtual biopsy, further providing insights for developing rapid volumetric imaging systems with high resolution and compact volume.

Structural Colors on Al Surface via Capped Cu-Si3N4 Bilayer Structure

Tunable structural colors have a multitude of applications in the beautification of mobile devices, in the decoration of artwork, and in the creation of color filters. In this paper, we describe a Metal-Insulator-Metal (MIM) design that can be used to systematically tune structural colors by altering the thickness of the top metal and intermediate insulator. Cu and Si₃N₄ were selected as the top metal and intermediate insulator layers, respectively, and various reflection colors were printed on Al. To protect the Cu surface from scratchiness and oxidation, a number of capping layers, including SiO₂, LPSQ, PMMA, and the commercially available clear coat ProtectaClear, were applied. In addition to their ability to protect Cu from a humid environment without deteriorating color quality, ProtectaClear and LPSQ coatings have minimal angle dependency. Furthermore, a bilayer of PMMA/SiO₂ can protect the Cu surface from the effects of humidity. In addition, the PMMA/SiO₂ and ProtectaClear/SiO₂ bilayers can also protect against corrosion on the Cu surface. The colors can be tuned by controlling the thickness of either the metal layer or intermediate insulator layer, and vivid structural colors including brown, dark orange, blue, violet, magenta, cyan, green-yellow, and yellow colors can be printed. The measured dielectric functions of Cu thin films do not provide any evidence of the plasmonic effect, and therefore, it is expected that the obtained colors are attributed to thin-film interference.

Monolithic MOF-Based Metal-Insulator-Metal Resonator for Filtering and Sensing

Metal-insulator-metal (MIM) configurations based on Fabry-Pérot resonators have advanced the development of color filtering through interactions between light and matter. However, dynamic color changes without breaking the structure of the MIM resonator upon environmental stimuli are still challenging. Here, we report monolithic metal-organic framework (MOF)-based MIM resonators with tunable bandwidth that can boost both dynamic optical filtering and active chemical sensing by laser-processing microwell arrays on the top metal layer. Programmable tuning of the reflection color of the MOF-based MIM resonator is achieved by controlling the MOF layer thicknesses, which is demonstrated by simulation of light-matter interactions on subwavelength scales. Laser-processed microwell arrays are used to boost sensing performance by extending the pathway for diffusion of external chemicals into nanopores of the MOFs. Both experiments and molecular dynamics simulations demonstrate that tailoring the period and height of the microwell array on the MIM resonator can advance the high detection sensitivity of chemicals.

Breaking the limitation of polarization multiplexing in optical metasurfaces with engineered noise

Noise is usually undesired yet inevitable in science and engineering. However, by introducing the engineered noise to the precise solution of Jones matrix elements, we break the fundamental limit of polarization multiplexing capacity of metasurfaces that roots from the dimension constraints of the Jones matrix. We experimentally demonstrate up to 11 independent holographic images using a single metasurface illuminated by visible light with different polarizations. To the best of our knowledge, it is the highest capacity reported for polarization multiplexing. Combining the position multiplexing scheme, the metasurface can generate 36 distinct images, forming a holographic keyboard pattern. This discovery implies a new paradigm for high-capacity optical display, information encryption, and data storage.

Tunable Light Field Modulations with Chip- and Fiber-Compatible Monolithic Dielectric Metasurfaces

Metasurfaces with a high engineering degree of freedom are promising building blocks for applications in metalenses, beam deflectors, metaholograms, sensing, and many others. Though the fundamental and technological challenges, proposing tunable metasurfaces is still possible. Previous efforts in this field are mainly taken on designing sophisticated structures with active materials introduced. Here, we present a generic kind of monolithic dielectric metasurfaces for tunable light field modulations. Changes in the period number and surrounding refractive index enable discrete and continuous modulations of spatial light fields, respectively. We exemplify this concept in monolithic Lithium Niobate metasurfaces for tunable metalenses and beam deflectors. The utilization of monolithic dielectric materials facilitates the ready integration of the metasurfaces with both chip and optical fiber platforms. This concept is not limited by the availability of active materials or expensive and time-consuming fabrication techniques, which can be applied to any transparent dielectric materials and various optical platforms.

To realize a variety of structural color adjustments via lossy-dielectric-based Fabry-Perot cavity structure

Structural colors with tunable properties have extensive applications in surface decoration, arts, absorbers, and optical filters. Planar structures have more advantages over other forms studied to date due to their easy manufacturability. Metal-insulator-metal-based structures are one of the known methods to fabricate structural colors where colors can be tuned mainly by the thickness of the intermediate lossless insulator layer. However, generating colors by MIM structure requires a thin metallic layer on top, and the top metals' abrasiveness and/or oxidation may degrade the colors quickly. Thus, we propose a lossy dielectric layer to replace the top metallic layer as a solution to ensure the structure's durability by preventing scratches and oxidation. Herein, CrON/Si3N4/Metal structures have been studied where theoretical investigations suggest that highly saturated colors can be generated in the lossy-lossless dielectric structures. Experimental data validated such simulations by revealing a range of vivid colors. Furthermore, these structures can easily achieve strong light absorption (SLA) even for a thick top layer of ∼100 nm. The colors realized by these structures are appeared due to a combination of the interference effect of the asymmetric Fabry-Perot cavity structure and the absorption rate in the CrO x N1-x layer.

Spin-Decoupled Interference Metasurfaces for Complete Complex-Vectorial-Field Control and Five-Channel Imaging

Light is a complex vectorial field characterized by its amplitude, phase, and polarization properties, which can be further represented by four basic parameters, that is, amplitudes and phases of two orthogonally polarized components. Controlling these parameters simultaneously and independently at will using metasurfaces are essential in arbitrarily manipulating the light propagation. However, most of the studies so far commonly require a great number of different meta-atoms or rely on diffraction under oblique incidence, which lack convenience and flexibility in design and implementation. Here, a new metasurface paradigm is proposed that can completely manipulate the amplitudes and phases of two spin components based on the interference effect, where only two different meta-atoms are applied. For proof-of-concept demonstration, two five-channel meta-holograms for imaging and information encryption are designed and experimentally characterized. The interference method provides a simple route toward compact complex and multifunctional meta-devices.

Stokes meta-hologram toward optical cryptography

Optical cryptography manifests itself a powerful platform for information security, which involves encrypting secret images into visual patterns. Recently, encryption schemes demonstrated on metasurface platform have revolutionized optical cryptography, as the versatile design concept allows for unrestrained creativity. Despite rapid progresses, most efforts focus on the functionalities of cryptography rather than addressing performance issues, such as deep security, information capacity, and reconstruction quality. Here, we develop an optical encryption scheme by integrating visual cryptography with metasurface-assisted pattern masking, referred to as Stokes meta-hologram. Based on spatially structured polarization pattern masking, Stokes meta-hologram allows multichannel vectorial encryption to mask multiple secret images into unrecognizable visual patterns, and retrieve them following Stokes vector analysis. Further, an asymmetric encryption scheme based on Stokes vector rotation transformation is proposed to settle the inherent problem of the need to share the key in symmetric encryption. Our results show that Stokes meta-hologram can achieve optical cryptography with effectively improved security, and thereby paves a promising pathway toward optical and quantum security, optical communications, and anticounterfeiting.

Achieving optical cryptography scheme with both high capacity and security is highly desirable. Here, authors report a Stokes meta-hologram with a hierarchical encryption strategy that allows vector encryptions to produce depth-masked ciphertexts.

Sub-wavelength patterned pulse laser lithography for efficient fabrication of large-area metasurfaces

Rigorously designed sub-micrometer structure arrays are widely used in metasurfaces for light modulation. One of the glaring restrictions is the unavailability of easily accessible fabrication methods to efficiently produce large-area and freely designed structure arrays with nanoscale resolution. We develop a patterned pulse laser lithography (PPLL) approach to create structure arrays with sub-wavelength feature resolution and periods from less than 1 μm to over 15 μm on large-area thin films with substrates under ambient conditions. Separated ultrafast laser pulses with patterned wavefront by quasi-binary phase masks rapidly create periodic ablated/modified structures by high-speed scanning. The gradient intensity boundary and circular polarization of the wavefront weaken diffraction and polarization-dependent asymmetricity effects during light propagation for high uniformity. Structural units of metasurfaces are obtained on metal and inorganic photoresist films, such as antennas, catenaries, and nanogratings. We demonstrate a large-area metasurface (10 × 10 mm²) revealing excellent infrared absorption (3–7 μm), which comprises 250,000 concentric rings and takes only 5 minutes to produce.

Fabrication of metasurfaces with nanoscale structures is inefficient for large areas. Here, the authors introduce patterned pulse laser lithography for creating structured arrays with sub-wavelength feature on large-area thin films under ambient conditions.

Reflective metalens with an enhanced off-axis focusing performance

Metalenses are one of the most promising metasurface applications. However, all-dielectric reflective metalenses are rarely studied, especially regarding their off-axis focusing performance. After experimentally studying the material optical properties in this work, we propose reflective metalens based on titanium dioxide (TiO₂) and silicon dioxide (SiO₂), which operate at a visible wavelength of 0.633 µm. Unlike conventional reflective metalenses based on metallic mirrors, the proposed device was designed based on a modified parabolic phase profile and was integrated onto a dielectric distributed Bragg reflector periodic structure to achieve high reflectivity with five dielectric pairs. The focusing efficiency characteristics of the metalens were experimentally studied for beam angles of incidence between 0^∘ and 30^∘. The results reveal that the focusing efficiency for the modified metalens design remains higher than 54%, which is higher than 50%, making it promising for photonic miniaturization and integration.

Spatial Coherence Manipulation on the Disorder-Engineered Statistical Photonic Platform

Coherence, similar to amplitude, polarization, and phase, is a fundamental characteristic of the light fields and is dominated by the statistical optical property. Although spatial coherence is one of the pivotal optical dimensions, it has not been significantly manipulated on the photonic platform. Here, we theoretically and experimentally manipulate the spatial coherence of light fields by loading different random phase distributions onto the wavefront with a metasurface. We achieve the generation of partially coherent light with a predefined degree of coherence and continuously modulate it from coherent to incoherent by controlling the phase fluctuation ranges or the beam sizes. This design strategy can be easily extended to manipulate arbitrary phase-only special beams with the same degree of coherence. Our approach provides straightforward rules to manipulate the coherence of light fields in an extra-cavity-based manner and paves the way for further applications in ghost imaging and information transmission in turbulent media.

Multi-freedom metasurface empowered vectorial holography

Optical holography capable of the complete recording and reconstruction of light's wavefront, plays significant roles on interferometry, microscopy, imaging, data storage, and three-dimensional displaying. Conventional holography treats light as scalar field with only phase and intensity dimensions, leaving the polarization information entirely neglected. Benefiting from the multiple degrees of freedom (DOFs) for optical field manipulation provided by the metasurface, vectorial holography with further versatile control in both polarization states and spatial distributions, greatly extended the scope of holography. As full vectorial nature of light field has been considered, the information carried out by light has dramatically increased, promising for novel photonic applications with high performance and multifarious functionalities. This review will focus on recent advances on vectorial holography empowered by multiple DOFs metasurfaces. Interleaved multi-atom approach is first introduced to construct vectorial holograms with spatially discrete polarization distributions, followed by the versatile vectorial holograms with continuous polarizations that are designed usually by modified iterative algorithms. We next discuss advances with further spectral response, leading to vivid full-color vectorial holography; and the combination between the far-field vectorial wavefront shaping enabled by vectorial holography and the near-field nano-printing functionalities by further exploiting local polarization and structure color responses of the meta-atom. The development of vectorial holography provides new avenues for compact multi-functional photonic devices, potentially useful in optical encryption, anticounterfeiting, and data storage applications.

Generating ultraviolet perfect vortex beams using a high-efficiency broadband dielectric metasurface

Due to the topological charge-independent doughnut spatial structure as well as the association of orbital angular momentums, perfect vortex beams promise significant advances in fiber communication, optical manipulation and quantum optics. Inspired by the development of planar photonics, several plasmonic and dielectric metasurfaces have been constructed to generate perfect vortex beams, instead of conventional bulky configuration. However, owing to the intrinsic Ohmic losses and interband electron transitions in materials, these metasurface-based vortex beam generators only work at optical frequencies up to the visible range. Herein, using silicon nitride nanopillars as high-efficiency half-wave plates, broadband and high-performance metasurfaces are designed and demonstrated numerically to directly produce perfect vortex beams in the ultraviolet region, by combining the phase profiles of spiral phase plate, axicon and Fourier transformation lens based on geometric phase. The conversion efficiency of the metasurface is up to 86.6% at the design wavelength. Moreover, the influence of several control parameters on perfect vortex beam structures is discussed. We believe that this ultraviolet dielectric generator of perfect vortex beams will find many significant applications, such as high-resolution spectroscopy, optical tweezer and on-chip communication.

Optical metasurfaces for generating and manipulating optical vortex beams

Optical vortices (OVs) carrying orbital angular momentum (OAM) have attracted considerable interest in the field of optics and photonics owing to their peculiar optical features and extra degree of freedom for carrying information. Although there have been significant efforts to realize OVs using conventional optics, it is limited by large volume, high cost, and lack of design flexibility. Optical metasurfaces have recently attracted tremendous interest due to their unprecedented capability in the manipulation of the amplitude, phase, polarization, and frequency of light at a subwavelength scale. Optical metasurfaces have revolutionized design concepts in photonics, providing a new platform to develop ultrathin optical devices for the realization of OVs at subwavelength resolution. In this article, we will review the recent progress in optical metasurface-based OVs. We provide a comprehensive discussion on the optical manipulation of OVs, including OAM superposition, OAM sorting, OAM multiplexing, OAM holography, and nonlinear metasurfaces for OAM generation and manipulation. The rapid development of metasurface for OVs generation and manipulation will play an important role in many relevant research fields. We expect that metasurface will fuel the continuous progress of wearable and portable consumer electronics and optics where low-cost and miniaturized OAM related systems are in high demand.

Recent Progress in Improving the Performance of Infrared Photodetectors via Optical Field Manipulations

Benefiting from the inherent capacity for detecting longer wavelengths inaccessible to human eyes, infrared photodetectors have found numerous applications in both military and daily life, such as individual combat weapons, automatic driving sensors and night-vision devices. However, the imperfect material growth and incomplete device manufacturing impose an inevitable restriction on the further improvement of infrared photodetectors. The advent of artificial microstructures, especially metasurfaces, featuring with strong light field enhancement and multifunctional properties in manipulating the light-matter interactions on subwavelength scale, have promised great potential in overcoming the bottlenecks faced by conventional infrared detectors. Additionally, metasurfaces exhibit versatile and flexible integration with existing detection semiconductors. In this paper, we start with a review of conventionally bulky and recently emerging two-dimensional material-based infrared photodetectors, i.e., InGaAs, HgCdTe, graphene, transition metal dichalcogenides and black phosphorus devices. As to the challenges the detectors are facing, we further discuss the recent progress on the metasurfaces integrated on the photodetectors and demonstrate their role in improving device performance. All information provided in this paper aims to open a new way to boost high-performance infrared photodetectors.

Metasurface-assisted multidimensional manipulation of a light wave based on spin-decoupled complex amplitude modulation

Achieving arbitrary manipulation of the fundamental properties of a light wave with a metasurface is highly desirable and has been extensively developed in recent years. However, common approaches are typically targeted to manipulate only one dimension of light wave (amplitude, phase, or polarization), which is not quite sufficient for the acquisition of integrated multifunctional devices. Here, we propose a strategy to design single-layer dielectric metasurfaces that can achieve multidimensional modulation of a light wave. The critical point of this strategy is spin-decoupled complex amplitude modulation, which is realized by combining propagation and geometric phases with polarization-dependent interference. As proofs of concept, perfect vector vortex beams and polarization-switchable stereoscopic holographic scenes are experimentally demonstrated to exhibit the capability of multidimensional light wave manipulation, which unlocks a flexible approach for the multidimensional manipulation of a light wave such as complex light-wave control and vectorial holography in integrated optics and polarization-oriented applications.

Dual-Stimulus Control for Ultra-Wideband and Multidimensional Modulation in Terahertz Metasurfaces Comprising Graphene and Metal Halide Perovskites

Perovskites and graphene are receiving a meteoric rise in popularity in the field of active photonics because they exhibit excellent optoelectronic properties for dynamic manipulation of light-matter interactions. However, challenges still exist, such as the instability of perovskites under ambient conditions and the low Fermi level of graphene in experiments. These shortcomings limit the scope of applications when they are used alone in advanced optical devices. However, the combination of graphene and perovskites is still a promising route for efficient control of light-matter interactions. Here, we report a dual-optoelectronic metadevice fabricated by integrating terahertz metasurfaces with a sandwich complex composed of graphene, polyimide, and perovskites for ultra-wideband and multidimensional manipulation of higher-order Fano resonances. Owing to the photogenerated carriers and electrostatic doping effect, the dual optoelectronic metadevice showed different manipulation behavior at thermal imbalance (electrostatic doping state of the system). The modulation depth of the transmission amplitude reached 200%, the total resonant frequency shift was 800 GHz, and the tunable range of the resonant frequency was 68.8%. In addition, modulation of the maximum phase reached 346°. This work will inspire a new generation of metasurface-based optical devices that combine two active materials.

Accurate and broadband manipulations of harmonic amplitudes and phases to reach 256 QAM millimeter-wave wireless communications by time-domain digital coding metasurface

We propose a theoretical mechanism and new coding strategy to realize extremely accurate manipulations of nonlinear electromagnetic harmonics in ultrawide frequency band based on a time-domain digital coding metasurface (TDCM). Using the proposed mechanism and coding strategy, we design and fabricate a millimeter-wave (mmWave) TDCM, which is composed of reprogrammable meta-atoms embedded with positive-intrinsic-negative diodes. By controlling the duty ratios and time delays of the digital coding sequences loaded on a TDCM, experimental results show that both amplitudes and phases of different harmonics can be engineered at will simultaneously and precisely in broad frequency band from 22 to 33 GHz, even when the coding states are imperfect, which is in good agreement with theoretical calculations. Based on the fabricated high-performance TDCM, we further propose and experimentally realize a large-capacity mmWave wireless communication system, where 256 quadrature amplitude modulation, along with other schemes, is demonstrated. The new wireless communication system has a much simpler architecture than the currently used mmWave wireless systems, and hence can significantly reduce the hardware cost. We believe that the proposed method and system architecture can find vast application in future mmWave and terahertz-wave wireless communication and radar systems.

Full-Color Holographic Display and Encryption with Full-Polarization Degree of Freedom

Metasurfaces provide a compact and powerful platform for manipulating the fundamental properties of light, and have shown unprecedented capabilities in both optical holographic display and information encryption. For increasing information display/storage capacity, metasurfaces with more polarization manipulation channel and full-color holographic functionality are now an urgent requirement. Here, a minimalist dielectric metasurface with the capability of full-color holography encoded with arbitrary polarization is proposed and experimentally demonstrated. Without the daunting exploratory and computational problem in nanostructure searching, full-color holographic images can be multiplexed into arbitrary polarization channels through vectorial ptychography and k-space ptychography based on tetratomic macropixel geometric phase metasurfaces. Thanks to the full degree of freedom tuning in polarization and color spaces, the application scenarios such as holographic 3D imaging and information encryption are realized. The strategy exhibits promising potential in applications of 3Dl display, augmented/virtual reality, high-density data storage, and encryption.

Realization of Structural Colors via Capped Cu-based F-P Cavity Structure

Structural colors with tunable properties have several applications in the beautification of mobile devices, surface decoration, art and color filters. Herein, we propose an asymmetric F-P cavity design to systematically tune structural colors by changing the thickness of the top metal and intermediate insulator. In this study, Cu and Si₃N₄ were chosen as the top metal and intermediate insulator layers, respectively, various reflection colors being realized on the Cu surface. Various capping layers-that is, SiO₂, polymethyl methacrylate (PMMA), and a commercially available clear coat named ProtectaClear-were used to protect the Cu surface from scratching and oxidation. PMMA coatings can protect Cu from corrosive environments without degradation of the color quality. The colors can be tuned by controlling the thickness of either the metal or intermediate insulator layers, and vivid structural colors-including orange, bright orange, red, purple, violet, light blue, green-yellow, and yellow-green-can be printed. The colors obtained can be attributed to thin-film interference.

Multi-band on-chip photonic spin Hall effect and selective excitation of whispering gallery modes with metasurface-integrated microcavity

We propose an approach to realize a multi-band on-chip photonic spin Hall effect and selective excitation of whispering gallery modes (WGMs) by integrating metasurfaces with microcavities. Free-space circularly polarized light with opposite spin angular momentum can effectively excite WGMs with opposite propagation directions at fixed wavelengths. Moreover, the different WGMs with different propagation directions and polarizations can be selectively excited by manipulating the number of antennas. We demonstrate that the optical properties (i.e., coupling efficiency, peak positions, and peak widths) of the proposed metasurface-integrated microcavities can be easily tailored by adjusting different geometric parameters. This study enables the realization of chiral microcavities with exciting novel functionalities, which may provide a further step in the development of photonic integrated circuits, optical sensing, and chiral optics.

Smart Doppler Cloak Operating in Broad Band and Full Polarizations

Invisibility cloaks, a class of attractive devices that can hide objects from external observers, have become practical reality owing to the advent of metamaterials. In previous cloaking schemes, almost all demonstrated cloaks are time-invariant and are investigated in the system that is motionless, and hence they are limited to hide stationary objects. In addition, the current cloaks are typically static or require manual operation to achieve dynamic cloaking. Here, a smart Doppler cloak operating in broadband and full polarizations is reported, which consists of a time-modulated reflective metasurface and a sensing-feedback time-varying electronic control system. Experimental results show that the smart Doppler cloak is able to respond self-adaptively and rapidly to the ever-changing velocity of moving objects and then cancel different Doppler shifts in real time, without any human intervention. Moreover, the wideband and polarization-insensitive features enable the cloak to be more robust and practical. To illustrate the capabilities of the proposed approach, the smart Doppler cloak is measured in three scenarios with two different groups of linearly-polarized incidences at 3.3 and 4.9 GHz, and one group circularly-polarized incidences at 6.0 GHz, respectively.

From Lingering to Rift: Metasurface Decoupling for Near- and Far-Field Functionalization

Metasurfaces, simultaneously operating in near- and far-fields, can be employed as a promising candidate to implement different functions, thus significantly improving the information density, security, and system integration. Recent works have showcased some approaches for decoupling-at-large between near- and far-field functionalities, but unfortunately, their coupling effects are just reduced and mitigated to some extent rather than eradicated, which in turn leads to the performance limitation of metadevices. Herein, we propose a general platform for the complete rift between near- and far-field functionalities, enabled by strictly decoupled manipulation of optical amplitude and phase, leading to their distinct functions in the near- and far-fields, respectively. This concept is experimentally demonstrated by integrating the functions of a phase-only metalens and an amplitude-only grayscale-imaging nanoprint into a single-cell metasurface. Because of their completely decoupled functions, both meta-elements show high-performance characteristics, i.e., imaging quality close to the diffraction limit and high-definition grayscale-imaging with resolution as high as 63 500 dots per inch (dpi). The validated recipe may empower advanced explorations and applications in highly integrated nano-optoelectronics requiring high performance and less crosstalk.

Efficient All-Dielectric Diatomic Metasurface for Linear Polarization Generation and 1-Bit Phase Control

Optical metasurface has exhibited unprecedented capabilities in the regulation of light properties at a subwavelength scale. In particular, a multifunctional polarization metasurface making use of light polarization to integrate distinct functionalities on a single platform can be greatly helpful in the miniaturization of photonic systems and has become a hot research topic in recent years. Here, we propose and demonstrate an efficient all-dielectric diatomic metasurface, the unit cell of which is composed of a pair of a-Si:H-based nanodisks and nanopillars that play the roles as polarization-maintaining and polarization-converting meta-atoms, respectively. Through rigorous theoretical analyses and numerical simulations, we show that a properly designed diatomic metasurface can work as a nanoscale linear polarizer for generating linearly polarized light with a controllable polarization angle and superior performances including a maximum transmission efficiency of 96.2% and an extinction ratio of 32.8 dB at an operation wavelength of 690 nm. Three metasurface samples are fabricated and experimentally characterized to verify our claims and their potential applications. Furthermore, unlike previously reported dielectric diatomic metasurfaces which merely manipulate the polarization state, the proposed diatomic metasurface can be easily modified to empower 1-bit phase modulation without altering the polarization angle and sacrificing the transmission efficiency. This salient feature further leads to the demonstration of a metasurface beam splitter that can be equivalently seen as the integration of a nonpolarizing beam splitter and a linear polarizer, which has never been reported before. We envision that various metadevices equipping with distinct wavefront shaping functionalities can be realized by further optimizing the diatomic metasurface to achieve an entire 2π phase control.

Bubbles in microfluidics: an all-purpose tool for micromanipulation

In recent decades, the integration of microfluidic devices and multiple actuation technologies at the microscale has greatly contributed to the progress of related fields. In particular, microbubbles are playing an increasingly important role in microfluidics because of their unique characteristics that lead to specific responses to different energy sources and gas-liquid interactions. Many effective and functional bubble-based micromanipulation strategies have been developed and improved, enabling various non-invasive, selective, and precise operations at the microscale. This review begins with a brief introduction of the morphological characteristics and formation of microbubbles. The theoretical foundations and working mechanisms of typical micromanipulations based on acoustic, thermodynamic, and chemical microbubbles in fluids are described. We critically review the extensive applications and the frontline advances of bubbles in microfluidics, including microflow patterns, position and orientation control, biomedical applications, and development of bubble-based microrobots. We lastly present an outlook to provide directions for the design and application of microbubble-based micromanipulation tools and attract the attention of relevant researchers to the enormous potential of microbubbles in microfluidics.

Coupling Plasmonic System for Efficient Wavefront Control

Efficient and flexible manipulation of electromagnetic waves using metasurfaces has attracted continuous attention in recent years. However, previous studies mainly apply sole resonance effect to accomplish the task. Here, we show that introducing a meta-coupling effect would reveal further physical insights in the electromagnetic wave control. To demonstrate this, a reflection-type coupling system composed by two identical linear resonances in a metal-insulator-metal configuration is theoretically proposed using the coupled-mode theory, whose phase diagram can be well controlled upon the coupling changes. Such intriguing optical property is verified by a double C-shaped resonator in the terahertz regime, where the coupling effect can be tuned by changing their either relative distance or rotation. More importantly, the reflection phase shift around the working frequency can be efficiently engineered without having to change the dimensions of the resonators. Two efficient anomalous metasurface deflectors are designed and experimentally characterized, whose maximum measured efficiency is more than 70%. The proposed controlling strategy further enriches the designing freedoms of metasurfaces and may find broad applications in realizing efficient and tunable functional devices.

Polarization-dependent and tunable absorption of terahertz waves based on anisotropic metasurfaces

Metamaterial absorbers can achieve high-efficiency electromagnetic absorption in a specific band, which have been used in biochemical sensing, photoelectric detection, imaging and other fields. Tunable metamaterial absorbers provide more possibilities for the development of multifunctional electromagnetic absorption devices. Here we propose a tunable and polarization-dependent terahertz metamaterial absorber which can work for both linearly and circularly polarized waves. By introducing single layer graphene and vanadium dioxide (VO₂), switching between the two working states and wide-range tuning of the absorption efficiency are realized. When VO₂ is in insulating state, the absorber shows different tunable absorption performance for the x- or y-polarized terahertz waves, in which the maximum absorption rate is close to 100%. When VO₂ is in metallic state, the metasurface behaves as a chiral absorber, and the maximum absorption difference between the two circular polarizations is about 0.45, while the tuning efficiency reaches 86.3%. Under the two working conditions, the absorber can maintain efficient absorption with a large incident angle. In addition, as an application exploration of the absorber, we demonstrated its application in tunable and polarization multiplexed near-field image display.

Full-space metasurface holograms in the visible range

Conventional metasurface holography is usually implemented in either transmission space or reflection space. Herein, we show a dielectric metasurface that can simultaneously project two independent holographic images in the transmission and reflection spaces, respectively, merely with a single-layer design approach. Specifically, two types of dielectric nanobricks in a nanostructured metasurface are employed to act as half-wave plates for geometric phase modulation. One type of nanobrick is designed to reflect most of incident circularly-polarized light into reflection space, enabled with magnetic resonance, while another type of nanobrick transmits it into transmission space, without resonance involved. By controlling the orientation angles and randomly interleaving the two types of nanobricks to form a metasurface, a full-space metasurface hologram can be established. We experimentally demonstrate this trans-reflective meta-holography by encoding the geometric phase information of two independent images into a single metasurface, and all observed holographic images agree well with our predictions. Our research expands the field-of-view of metasurface holography from half- to full-space, which can find its markets in optical sensing, image displays, optical storages and many other potential applications.

All-dielectric metasurface with multi-function in the near-infrared band

This paper presents an approach to design the all-dielectric metasurface with multi-function in the near-infrared range of 1.5-1.6 µm. Based on the geometric phase principle, the all-dielectric metasurface is composed of the Si nanopillar and the SiO₂ substrate as an emitter unit distributed in a 21×21 array. Under the incidence of the circularly polarized light at 1550 nm, the metasurface works as a vortex-beam generator with high performance which generates the vortex beam with topological charges of ±1, and the mode purity of the vortex beam is 90.66%. Under the incidence of the linearly polarized light at 1550 nm, the metasurface also works as the azimuthally/radially polarized beam generator with high performance, and the purities of the azimuthally and the radially polarized beams are 92.52% and 91.02%, respectively. Moreover, the metasurface generates different output spots under the different incident lights which can be applied to optical encryption, and the metasurface with the phase gradient also can be used as the dual-channel encoder/decoder in optical communication. The simulated results are in good agreement with the theoretical derivation. The designed metasurface may become a potential candidate as a multi-function photon device in the integrated optical system in the future.

Mid-infrared polarization-controlled broadband achromatic metadevice

Metasurfaces provide a compact, flexible, and efficient platform to manipulate the electromagnetic waves. However, chromatic aberration imposes severe restrictions on their applications in broadband polarization control. Here, we propose a broadband achromatic methodology to implement polarization-controlled multifunctional metadevices in mid-wavelength infrared with birefringent meta-atoms. We demonstrate the generation of polarization-controlled and achromatically on-axis focused optical vortex beams with diffraction-limited focal spots and switchable topological charge (L ^∥ = 0 and L ^⊥ = 2). Besides, we further implement broadband achromatic polarization beamsplitter with high polarization isolation (extinction ratio up to 21). The adoption of all-silicon configuration not only facilitates the integration with CMOS technology but also endows the polarization multiplexing meta-atoms with broad phase dispersion coverage, ensuring the large size and high performance of the metadevices. Compared with the state-of-the-art chromatic aberration-restricted polarization-controlled metadevices, our work represents a substantial advance and a step toward practical applications.

Silicon-on-insulator based multifunctional metasurface with simultaneous polarization and geometric phase controls

Enabled with both magnetic resonance and geometric phase, dielectric nanobrick based metasurfaces have shown their unusual abilities to produce high-definition and high-efficiency holographic images. Herein, we further show that such a metasurface can not only project a holographic image in far field but also record a grayscale image right at the metasurface plane simultaneously, merely with a single-celled nanostructure design approach. Specifically, each nanobrick in a unit-cell of the metasurface acts as a half-wave plate and it can continuously rotate the polarization direction of incident linearly polarized light. Governed by Malus law, light intensity modulation is available with the help of a bulk-optic analyzer and a continuous grayscale image appears right at the metasurface plane. At the same time, the concept of orientation degeneracy of nanostructures can be utilized to generate a 4-step geometric phase, with which a holographic image is reconstructed in far field. We experimentally demonstrate this multifunctional meta-device by employing the widely used silicon-on-insulator (SOI) material and all results agree well with our theoretical prediction. With the novel features of easiness in design, high efficiency, broadband spectrum response, strong robustness, high security and high information density, the proposed SOI-based metasurfaces will have extensive applications in optical information security and multiplexing.

Graphene-bridged topological network metamaterials with perfect modulation applied to dynamic cloaking and meta-sensing

Perfect state transfer of the bus topological system enables the sharing of information or excitation between nodes. Herein we report groundbreaking research on the transfer of the graphene-bridged bus topological network structure to an electromagnetic metamaterial setting, named "bus topological network metamaterials (TNMMs)." Correspondingly, the electromagnetic response imprints onto the topological excitation. We find that the bus-TNMMs display a perfect modulation of the terahertz response. The blue-shift of resonance frequency could increase to as large as 1075 GHz. The modulation sensitivity of the bus-TNMMs reaches 1027 GHz/Fermi level unit (FLU). Meanwhile, with the enhancement of modulation, the line shape of the reflection keeps underformed. Parabola, ExpDec1, and Asymptotic models are used to estimate the modulation of the resonance frequency. Besides, the bus-TNMMs system provides a fascinating platform for dynamic cloaking. By governing the Fermi level of graphene, the bus-TNMMs can decide whether it is cloaking or not in a bandwidth of 500 GHz. Also, the bus-TNMMs exhibit the immense potential for dynamically detecting the vibrational fingerprinting of an analyte. These results give a far-reaching outlook for steering dynamically the terahertz response with the bus-TNMMs. Therefore, we believe that the discovery of bus-TNMMs will revolutionize our understanding of the modulation of the electromagnetic response.

Spin-Selective Full-Dimensional Manipulation of Optical Waves with Chiral Mirror

Realizing arbitrary manipulation of optical waves, which still remains a challenge, plays a key role in the implementation of optical devices with on-demand functionalities. However, it is hard to independently manipulate multiple dimensions of optical waves because the optical dimensions are basically associated with each other when adjusting the optical response of the devices. Here, the concise design principle of a chiral mirror is utilized to realize the full-dimensional independent manipulation of circular-polarized waves. By simply changing three structural variables of the chiral mirror, the proposed design principle can arbitrarily and independently empower the spin-selective manipulation of amplitude, phase, and operation wavelength of circular-polarized waves with a large modulation depth. This approach provides a simple solution for the realization of spin-selective full-dimensional manipulation of optical waves and shows ample application possibilities in the areas of optical encryption, imaging, and detection.

Low-Loss Organic Hyperbolic Materials in the Visible Spectral Range: A Joint Experimental and First-Principles Study

Hyperbolic media strengthen numerous attractive applications in optics such as super-resolution imaging, enhanced spontaneous emission, and nanoscale waveguiding. Natural hyperbolic materials exist at visible frequencies; however, implementations of these materials suffer substantial compromises resulting from the high loss in the currently available candidates. Here, the first experimental and theoretical investigation of regioregular poly(3-alkylthiophenes) (rr-P3ATs), a naturally low-loss organic hyperbolic material (OHM) in the visible frequency range, is shown. These hyperbolic properties arise from a highly ordered structure of layered electron-rich conjugated thiophene ring backbones separated by insulating alkyl side chains. The optical and electronic properties of the rr-P3AT can be tuned by controlling the degree of crystallinity and alkyl side chain length. First-principles calculations support the experimental observations, which result from the rr-P3AT's structural and optical anisotropy. Conveniently, rr-P3AT-based OHMs are facile to fabricate, flexible, and biocompatible, which may lead to tremendous new opportunities in a wide range of applications.

Liquid-Crystal-Mediated Geometric Phase: From Transmissive to Broadband Reflective Planar Optics

Planar optical elements that can manipulate the multidimensional physical parameters of light efficiently and compactly are highly sought after in modern optics and nanophotonics. In recent years, the geometric phase, induced by the photonic spin-orbit interaction, has attracted extensive attention for planar optics due to its powerful beam shaping capability. The geometric phase can usually be generated via inhomogeneous anisotropic materials, among which liquid crystals (LCs) have been a focus. Their pronounced optical properties and controllable and stimuli-responsive self-assembly behavior introduce new possibilities for LCs beyond traditional panel displays. Recent advances in LC-mediated geometric phase planar optics are briefly reviewed. First, several recently developed photopatterning techniques are presented, enabling the accurate fabrication of complicated LC microstructures. Subsequently, nematic LC-based transmissive planar optical elements and chiral LC-based broadband reflective elements are reviewed systematically. Versatile functionalities are revealed, from conventional beam steering and focusing, to advanced structuring. Combining the geometric phase with structured LC materials offers a satisfactory platform for planar optics with desired functionalities and drastically extends exceptional applications of ordered soft matter. Some prospects on this rapidly advancing field are also provided.

Polarization-Controlled Dual-Programmable Metasurfaces

Programmable metasurfaces allow dynamic and real-time control of electromagnetic (EM) waves in subwavelength resolution, holding extraordinary potentials to establish meta-systems. Achieving independent and real-time controls of orthogonally-polarized EM waves via the programmable metasurface is attractive for many applications, but remains considerably challenging. Here, a polarization-controlled dual-programmable metasurface (PDPM) with modular control circuits is proposed, which enables a dibit encoding capability in modifying the phase profiles of x- and y-polarized waves individually. The constructed extended interface circuit is able to extend the number of control interfaces from a field programmable gate array by orders of magnitude and also possesses memory function, which enhance hugely the rewritability, scalability, reliability, and stability of PDPM. As a proof-of-concept, a wave-based exclusive-OR logic gate platform for spin control of circularly-polarized waves, a fixed-frequency wide-angle dual-beam scanning system, and a dual-polarized shared-aperture antenna are demonstrated using a single PDPM. The proposed PDPM opens up avenues for realizing more advanced and integrated multifunctional devices and systems that have two independent polarization-controlled signal channels, which may find many applications in future-oriented intelligent communication, imaging, and computing technologies.

Simulate Deutsch-Jozsa algorithm with metamaterials

During the past few years, a lot of efforts have been devoted in studying optical analog computing with artificial structures. Up to now, much of them are primarily focused on classical mathematical operations. How to use artificial structures to simulate quantum algorithm is still to be explored. In this work, an all-dielectric metamaterial-based model is proposed and realized to demonstrate the quantum Deutsch-Jozsa algorithm. The model is comprised of two cascaded functional metamaterial subblocks. The oracle subblock encodes the detecting functions (constant or balanced), onto the phase distribution of the incident wave. Then, the original Hadamard transformation is performed with a graded-index subblock. Both the numerical and experimental results indicate that the proposed metamaterials are able to simulate the Deutsch-Jozsa problem with one round operation and a single measurement of the output eletric field, where the zero (maximum) intensity at the central position results from the destructive (constructive) interference accompanying with the balance (constant) function marked by the oracle subblock. The proposed computational metamaterial is miniaturized and easy-integration for potential applications in communication, wave-based analog computing, and signal processing systems.