Dynamic Bifunctional Metasurfaces for Holography and Color Display

Electrically Driven PANI-Based Multilayer Nanocomposite Coatings for Dynamic Color Modulation

Reconfigurable precision regulation of structural color devices is a critical step toward versatile advanced functionality and broadening application scenarios. In this work, we demonstrate the precise manipulation of red, green, and blue, three primary colors generated by the five-layer nanocomposite coatings composed of polyaniline/indium tin oxide/titanium/titanium dioxide/titanium (PANI/ITO/Ti/TiO2/Ti). The modulation of dynamic structural colors of the proposed multilayer coatings originates from a cooperative interaction between the top PANI conductive polymer and the bottom traditional four-layer structural color consisting of ITO/Ti/TiO2/Ti. Specifically, the three primitive colors are first achieved by three different combinations of both TiO2 and ITO thicknesses, and then each color is modulated precisely by an intrinsic color change of the top PANI conductive layer at various voltages. As a result, the nanocomposite coatings demonstrate millisecond response time, excellent durability over 100 cycles, driving voltages below 1 V, and a wide temperature tolerance range from 5 to 60 °C. Additionally, centimeter-scale R, G, and B letter-shaped samples are fabricated using a mask plate coating technique, showcasing color modulation in patterned samples. Our work offers a straightforward strategy to realize the dynamic manipulation of the three primary colors within a certain range, which lays a solid foundation for the development of dynamic display technologies, such as dynamic paintings and e-books.

Gesture-Interactive Dynamic Holo-Display via Topography Flexible Metasurfaces

Heading toward the next-generation intelligent optical device, the meta-optics active tunability is one of the most desirable properties to expand its versatility beyond the traditional optical devices. Despite its advances via various tunable approaches, the encoding freedom of tuning capability still critically restricts its widespread engagement and dynamics in real-life applications. Here, we present a gesture-interactive scheme by topography flexible metasurfaces (TFMs) to expand the encoding freedom for the tuning capability. Through regulating different surface topographies, the potential tuning degree of freedom (DoF) has been fully explored to dynamically display/encrypt up to 16 independent holographic images, exceeding the state-of-the-art tuning DoF. Such topography flexibility is interactively tuned with gesture triggers, manual bending, and other large-area repeatable controlling methods to extract and display the respective holographic images. We envision that this research stimulates active meta-device innovation and suggests potential applications in next-generation interactive displays, information storage and encryption, and wearable optical devices.

Scalable Multistep Imprinting of Multiplexed Optical Anti-counterfeiting Patterns with Hierarchical Structures

Multiplexed optical techniques with multichannel patterns provide powerful strategies for high-capacity anti-counterfeiting. However, it is still a big challenge to meet the demands of achieving high encryption levels, excellent readability, and simple preparation simultaneously. Herein, we use a multistep imprinting technique, leveraging surface work-hardening to massively produce multiplexed encrypted patterns with hierarchical structures. These patterns with coupled nano- and microstructures can be instantaneously decoded into different pieces of information at different view angles under white light illumination. By incorporating perpendicular nano- and microgratings, we achieve four-channel encoded patterns, enhancing anti-counterfeiting capacity. This versatile method works on various metal/polymer materials, offering high-density information storage, direct visibility, broad material compatibility, and low-cost mass production. Our high-performance anti-counterfeiting patterns show significant potential in real-world applications.

Directional Phase and Polarization Manipulation Using Janus Metasurfaces

Janus metasurfaces, exemplifying two-faced 2D metamaterials, have shown unprecedented capabilities in asymmetrically manipulating the wavefront of electromagnetic waves in both forward and backward propagating directions, enabling novel applications in asymmetric information processing, security, and signal multiplexing. However, current Janus metasurfaces only allow for directional phase manipulation, hindering their broader application potential. Here, the study proposes a versatile Janus metasurface platform that can directionally control the phase and polarization of terahertz waves by integrating functionalities of half-wave plates, quarter-wave plates, and metallic gratings within a cascaded metasurface structure. As a proof-of-principle, the study experimentally demonstrates Janus metasurfaces capable of independent and simultaneous control over phase and polarization, showcasing propagation direction-encoded focusing and polarization conversion. Moreover, the directionally focused points are utilized with distinct polarization states for advanced applications in direction- and polarization-sensitive detection and imaging. This unique strategy for simultaneous phase and polarization control with direction-dependent versatility opens new avenues for designing ultra-compact devices with significant implications in imaging, encryption, and data storage.

Creating Anti-Chiral Exceptional Points in Non-Hermitian Metasurfaces for Efficient Terahertz Switching

Non-Hermitian degeneracies, also known as exceptional points (EPs), have presented remarkable singular characteristics such as the degeneracy of eigenvalues and eigenstates and enable limitless opportunities for achieving fascinating phenomena in EP photonic systems. Here, the general theoretical framework and experimental verification of a non-Hermitian metasurface that holds a pair of anti-chiral EPs are proposed as a novel approach for efficient terahertz (THz) switching. First, based on the Pancharatnam-Berry (PB) phase and unitary transformation, it is discovered that the coupling variation of ±1 spin eigenstates will lead to asymmetric modulation in two orthogonal linear polarizations (LP). Through loss-induced merging of a pair of anti-chiral EPs, the decoupling of ±1 spin eigenstates are then successfully realized in a non-Hermitian metasurface. Final, the efficient THz modulation is experimentally demonstrated, which exhibits modulation depth exceeding 70% and Off-On-Off switching cycle less than 9 ps in one LP while remains unaffected in another one. Compared with conventional THz modulation devices, the metadevice shows several figures of merits, such as a single frequency operation, high modulation depth, and ultrafast switching speed. The proposed theory and loss-induced non-Hermitian device are general and can be extended to numerous photonic systems varying from microwave, THz, infrared, to visible light.

Nanostructure-based orbital angular momentum encryption and multiplexing

The orthogonality among the OAM modes provides a new degree of freedom for optical multiplexing communications. So far, traditional Dammann gratings and spatial light modulators (SLMs) have been widely used to generate OAM beams by modulating electromagnetic waves at each pixel. However, such architectures suffer from limitations in terms of having a resolution of only a few microns and the bulkiness of the entire optical system. With the rapid development of the electromagnetic theory and advanced nanofabrication methods, artificial nanostructures, especially optical metasurfaces, have been introduced which greatly shrink the size of OAM multiplexing devices while increasing the level of integration. This review focuses on the study of encryption, multiplexing and demultiplexing of OAM beams based on nanostructure platforms. After introducing the focusing characteristics of OAM beams, the interaction mechanism between OAM beams and nanostructures is discussed. The physical phenomena of helical dichroism response and spatial separation of OAM beams achieved through nanostructures, setting the stage for OAM encryption and multiplexing, are reviewed. Afterward, the further advancements and potential applications of nanophotonics-based OAM multiplexing are deliberated. Finally, the challenges of conventional design methods and dynamic tunable techniques for nanostructure-based OAM multiplexing technology are addressed.

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.

Antielectric Potential Synthesis of Plasmonic Au-Ag Multidimensional Dimers Array for High-Resolution Encrypted Information

Plasmonic superstructures hold great potential in encrypted information chips but are still unsatisfactory in terms of resolution and maneuverability because of the limited fabrication strategies. Here, we develop an antielectric potential method in which the interfacial energy from the modification of 5-amino-2-mercapto benzimidazole (AMBI) ligand is used to overcome the electric resistance between the Au nanospheres (NSs) and substrate, thereby realizing the in situ growth of a Au-Ag heterodimers array in large scale. The morphology, number, and size of Ag domains on Au units can be controlled well by modulating the reaction kinetics and thermodynamics. Experiments and theoretical simulations reveal that patterned 3D Au-2D Ag and 3D Au-3D Ag dimer arrays with line widths of 400 nm exhibit cerulean and cyan colors, respectively, and achieve fine color modulation and ultrahigh information resolution. This work not only develops a facile strategy for fabricating patterned plasmonic superstructures but also pushes the plasmon-based high-resolution encrypted information chip into more complex applications.

Configurable swellability of hydrogel microstructure for structural-color-based imaging concealment/encryption

Optical information concealment/encryption technologies are of great importance to structural color applications. Although a series of responsive materials have been developed for dynamic structural color, the shortcomings of the high-quality synthesis process, the complex controlling method, and the low-resolution capability limit their practical use. Herein, we proposed a novel strategy of humidity-driven structural-color-based imaging concealment/encryption by utilizing metal-hydrogel-metal (MHM) nanocavities with configurable swellablity response to humidity change. With varied exposure doses, multi-stage MHM nanocavities with swellable hydrogel interlayers are achieved, generating dynamic structural color covering the visible spectrum. We revealed that the swelling ratio of hydrogel microstructures can be gradually adjusted between 1.05 and 2.08 by varying the exposure dose. We demonstrated that a hydrogel-based structural color image can be concealed with humidity changes by configurating swellable and non-swellable hydrogel pixels together. Furthermore, we developed the double exposure method in which the first exposure can generate pixel arrays for the deceptive image and the second exposure can locally suppress the swellablity of certain pixels. This method can highlight hidden images in a moist state, demonstrating a powerful strategy for high-density optical information encryption.

Compact angle-resolved metasurface spectrometer

Light scattered or radiated from a material carries valuable information on the said material. Such information can be uncovered by measuring the light field at different angles and frequencies. However, this technique typically requires a large optical apparatus, hampering the widespread use of angle-resolved spectroscopy beyond the lab. Here we demonstrate compact angle-resolved spectral imaging by combining a tunable metasurface-based spectrometer array and a metalens. With this approach, even with a miniaturized spectrometer footprint of only 4 × 4 μm2, we demonstrate a wavelength accuracy of 0.17 nm, spectral resolution of 0.4 nm and a linear dynamic range of 149 dB. Moreover, our spectrometer has a detection limit of 1.2 fJ, and can be patterned to an array for spectral imaging. Placing such a spectrometer array directly at the back focal plane of a metalens, we achieve an angular resolution of 4.88 × 10-3 rad. Our angle-resolved spectrometers empowered by metalenses can be employed towards enhancing advanced optical imaging and spectral analysis applications.

Perovskite single-pixel detector for dual-color metasurface imaging recognition in complex environment

Highly efficient multi-dimensional data storage and extraction are two primary ends for the design and fabrication of emerging optical materials. Although metasurfaces show great potential in information storage due to their modulation for different degrees of freedom of light, a compact and efficient detector for relevant multi-dimensional data retrieval is still a challenge, especially in complex environments. Here, we demonstrate a multi-dimensional image storage and retrieval process by using a dual-color metasurface and a double-layer integrated perovskite single-pixel detector (DIP-SPD). Benefitting from the photoelectric response characteristics of the FAPbBr2.4I0.6 and FAPbI3 films and their stacked structure, our filter-free DIP-SPD can accurately reconstruct different colorful images stored in a metasurface within a single-round measurement, even in complex environments with scattering media or strong background noise. Our work not only provides a compact, filter-free, and noise-robust detector for colorful image extraction in a metasurface, but also paves the way for color imaging application of perovskite-like bandgap tunable materials.

Orbital angular momentum multiplexing holography based on multiple polarization channel metasurface

As a high-degree-of-freedom approach to manipulate the electromagnetic wave, metasurfaces are widely used in high-capacity information technology. Extensive investigations have explored multiplexing techniques using polarization, incident angle, wavelength, and infinite-dimensional multiplexing through Orbital Angular Momentum (OAM). However, due to the limited spatial resolution and array size of the metasurface, the number of multiplexing channels that can be actually realized is limited. Therefore, research on the combination of OAM multiplexing and polarization degrees of freedom is of great significance. Here, we propose and experimentally demonstrate a metasurface holography multiplexing scheme based on multiple polarization channels combined with OAM. Taking advantage of the orthogonal independence of spin angular momentum and orbital angular momentum, multiple OAM multiplexing holograms are constructed in multiple different spin-polarization channels. Utilizing the well-established compatibility between OAM multiplexing and polarization multiplexing, we successfully integrated two multiplane holograms and 15 OAM multiplexing holograms on a single metasurface. Subsequently, we introduced an optical nested encryption framework designed for parallel communication. This work facilitates high-capacity and high-security holography by employing multiplexing metasurfaces, thereby providing innovative design concepts for optical communication, information encryption, and related domains.

Sb2S3-Based Dynamically Tuned Color Filter Array via Genetic Algorithm

Color displays have become increasingly attractive, with dielectric optical nanoantennas demonstrating especially promising applications due to the high refractive index of the material, enabling devices to support geometry-dependent Mie resonance in the visible band. Although many structural color designs based on dielectric nanoantennas employ the method of artificial positive adjustment, the design cycle is too lengthy and the approach is non-intelligent. The commonly used phase change material Ge₂Sb₂Te₅ (GST) is characterized by high absorption and a small contrast to the real part of the refractive index in the visible light band, thereby restricting its application in this range. The Sb₂S₃ phase change material is endowed with a wide band gap of 1.7 to 2 eV, demonstrating two orders of magnitude lower propagation loss compared to GST, when integrated onto a silicon waveguide, and exhibiting a maximum refractive index contrast close to 1 at 614 nm. Thus, Sb₂S₃ is a more suitable phase change material than GST for tuning visible light. In this paper, genetic algorithms and finite-difference time-domain (FDTD) solutions are combined and introduced as Sb₂S₃ phase change material to design nanoantennas. Structural color is generated in the reflection mode through the Mie resonance inside the structure, and the properties of Sb₂S₃ in different phase states are utilized to achieve tunability. Compared to traditional methods, genetic algorithms are superior-optimization algorithms that require low computational effort and a high population performance. Furthermore, Sb₂S₃ material can be laser-induced to switch the transitions of the crystallized and amorphous states, achieving reversible color. The large chromatic aberration ∆E modulation of 64.8, 28.1, and 44.1 was, respectively, achieved by the Sb₂S₃ phase transition in this paper. Moreover, based on the sensitivity of the structure to the incident angle, it can also be used in fields such as angle-sensitive detectors.

Polarization-Insensitive Metasurface Cloak for Dynamic Illusions with an Electromagnetic Transparent Window

Artificial camouflage has garnered long-standing interest in both academia and industry. The metasurface-based cloak has attracted much attention due to the powerful capability of manipulating the electromagnetic wave, convenient multifunctional integration design, and easy fabrication. However, existing metasurface-based cloaks tend to be passive and of single function and monopolarization, which cannot meet the requirement of applications in ever-changing environments. So far, it is still challenging to realize a reconfigurable full-polarization metasurface cloak with multifunctional integration. Herein, we proposed an innovative metasurface cloak, which can simultaneously realize dynamic illusion effects at lower frequencies (e.g., 4.35 GHz) and specific microwave transparency at higher frequencies (e.g., X band) for communication with the outside environment. These electromagnetic functionalities are demonstrated by both numerical simulations and experimental measurements. The simulation and measurement results agree well with each other, indicating that our metasurface cloak can generate various electromagnetic illusions for full polarizations as well as a polarization-insensitive transparent window for the signal transmission to enable the communication between the cloaked device and the outside environment. It is believed that our design can offer powerful camouflage tactics to address the stealth problem in ever-changing environments.

Toward Water-Immersion Programmable Meta-Display

Heading toward next-generation intelligent display, dynamic control capability for meta-devices is critical for real world applications. Beyond the conventional electrical/optical/mechanical/thermal tuning methods, liquid immersion recently has emerged as a facile tuning mechanism which is easily accessible (especially water) and practically implementable for large tuning area. However, due to the longstanding and critical drawback of lacking independent-encoding capability, the state-of-art immersion approach remains incapable of pixel-level programmable switching. Here a water-immersion tuning scheme with pixel-scale programmability for dynamic meta-displays is proposed. Tunable meta-pixels can be engineered to construct spectral selective patterns at prior-/post- immersion states, such that a metasurface enables pixel-level transforming animations for dynamic multifield meta-displays, including near-field dual-nanoprints and far-field dual-holographic displays. The proposed water-immersion programmable approach for meta-display, benefitting from its large tuning area, facile operation and strong repeatability, may find a revolutionary path toward next-generation intelligent display with practical applications in dynamic display/encryption, information anticounterfeit/storage, and optical sensors.

UV-Nanoimprint and Deep Reactive Ion Etching of High Efficiency Silicon Metalenses: High Throughput at Low Cost with Excellent Resolution and Repeatability

As metasurfaces begin to find industrial applications there is a need to develop scalable and cost-effective fabrication techniques which offer sub-100 nm resolution while providing high throughput and large area patterning. Here we demonstrate the use of UV-Nanoimprint Lithography and Deep Reactive Ion Etching (Bosch and Cryogenic) towards this goal. Robust processes are described for the fabrication of silicon rectangular pillars of high pattern fidelity. To demonstrate the quality of the structures, metasurface lenses, which demonstrate diffraction limited focusing and close to theoretical efficiency for NIR wavelengths λ ∈ (1.3 μm, 1.6 μm), are fabricated. We demonstrate a process which removes the characteristic sidewall surface roughness of the Bosch process, allowing for smooth 90-degree vertical sidewalls. We also demonstrate that the optical performance of the metasurface lenses is not affected adversely in the case of Bosch sidewall surface roughness with 45 nm indentations (or scallops). Next steps of development are defined for achieving full wafer coverage.

Three-Channel Metasurfaces for Multi-Wavelength Holography and Nanoprinting

Metasurfaces, employed to simultaneously generate nanoprinting and holographic images, have been extensively explored recently. Among them, multi-wavelength multiplexing in a single metasurface is often accompanied by dispersion and crosstalk, which hinder the display of multicolor patterns. Here, we propose an efficient phase method to decouple the wavelength and realize a three-channel display operating at different wavelengths. Holographic images appear in the far field with the illumination of two different circularly polarized lights while a nanoprinting image is reconstructed by inserting an orthogonal optical path with the illumination of linear polarization light. The proposed metasurface is only composed of four types of unit cells, which significantly decreases the complexity of fabrication and improves the information capacity. Benefiting from its different decoding strategies and capability of multi-wavelength control, this approach may develop broad applications in information encryption, security, and color display.

Scalable Hydrogel-Based Nanocavities for Switchable Meta-Holography with Dynamic Color Printing

Devices used for meta-optics display are currently undergoing a revolutionary transition from static to dynamic. Despite various tuning strategy demonstrations such as mechanical, electrical, optical, and thermal tunings, a longstanding challenge for their practical application has been the achievement of a conveniently accessible real-life tuning scheme for realizing versatile functionality dynamics outside the laboratory. In this study, we demonstrate a practical tuning strategy to realize a dynamic color printing with a switchable meta-holography exhibition based on hydrogel-based nanocavities. On the basis of the inflation sensitivity of a hydrogel to humidity alteration, its transmissive color was notably tuned from 450 to 750 nm. More intriguingly, by controlling the sample dry/immersed states in real time, we successfully enabled dual-channel switchable meta-holography. With the advantages of facile architecture, daily stimulus with large-area modulation, and high chromaticity, our proposed hydrogel-based nanocavities provide a promising path toward tunable display/encryption, optical sensors, and next-generation display technology.

Metalens for generating multi-channel polarization-wavelength multiplexing metasurface holograms

We demonstrate multi-channel metasurface holograms, where the pixels of holographic images are represented by the focal points of metalens, leading to the nanoscale resolution. The required phase profiles are implemented by elaborately arranging the hybrid all-dielectric meta-atoms with specific orientation angles. For verification, two-channel single-color images are reconstructed on the focal plane of the metalens by polarization control. Alternatively, three-channel color holograms are exhibited by manipulating the incident wavelengths. More uniquely, the metalens can be further engineered to generate polarization-wavelength multiplexing color holograms in six channels. Our work provides an effective approach to reconstructing holographic images and enables potential applications including color display, information engineering, and optical encryption.

Smart Metasurface for Active and Passive Cooperative Manipulation of Electromagnetic Waves

Integrating active and passive manipulation of electromagnetic (EM) waves has significant advantages for the caliber synthesis of microwave and optical integrated devices. In previous schemes, most reported designs focus only on active ways of manipulating self-radiating EM waves, such as antennas and lasers, or passive ways of manipulating external incident EM waves, such as lenses and photonic crystals. Here, we proposed a paradigm that integrates active and passive manipulation of EM waves in a reconfigurable way. As demonstrated, circularly polarized, linearly polarized, and elliptically polarized waves with customized beams are achieved in passive operation by merging Pancharatnam-Berry phases and dynamic phases, while the radiating EM waves with a customized gain are achieved by coupling the coding elements with the radiation structure in the active manipulation. Either active or passive manipulation is determined by the sensed signals and operating state to reduce detectability. Encouragingly, the proposed strategy will excite new sensing and communication opportunities, enabling advanced conceptions for next-generation compact EM devices.

Immersion-Triggered Active Switch for Spin-Decoupled Meta-Optics Multi-Display

Meta-optics exhibits many promising applications in various fields of optical displays, imaging, and information encryption. However, heading towards next-generation intelligent displays, its broad implementation is critically restricted by the lack of practical active tuning capability. Beyond the conventional electrical/optical/mechanical/thermal tuning methods, liquid immersion has recently emerged as a facile mechanism for active spectral tuning. To further conquer the challenge in achieving active complicated optical-field manipulation, here, an environment-compliant switch for meta-optics multi-display is originally proposed and experimentally realized via the liquid immersion tuning scheme. By designing the spin-decoupled phase array for left-/right-handed circular polarizations, it flexibly presents quad-fold independent-encoded phase distributions for different medium-relevant and polarization-controlled channels, thus enabling four switchable holographic images through immersion tuning. Such a proposed immersion tuning design is quite a straightforward approach for meta-optics holographic displays, enjoying full-spatial usage, design flexibility, and large-scale facile implementation. Overall, the proposed liquid immersion tuning strategy for a meta-optics multi-display would strongly benefit the practical applications in biochemical sensing, environment-adaptive displays, and information encryption.

Miniaturizing color-sensitive photodetectors via hybrid nanoantennas toward submicrometer dimensions

Digital camera sensors use color filters on photodiodes to achieve color selectivity. As the color filters and photosensitive silicon layers are separate elements, these sensors suffer from optical cross-talk, which sets limits to the minimum pixel size. Here, we report hybrid silicon-aluminum nanostructures in the extreme limit of zero distance between color filters and sensors. This design could essentially achieve submicrometer pixel dimensions and minimize the optical cross-talk arising from tilt illuminations. The designed hybrid silicon-aluminum nanostructure has dual functionalities. Crucially, it supports a hybrid Mie-plasmon resonance of magnetic dipole to achieve color-selective light absorption, generating electron hole pairs. Simultaneously, the silicon-aluminum interface forms a Schottky barrier for charge separation and photodetection. This design potentially replaces the traditional dye-based filters for camera sensors at ultrahigh pixel densities with advanced functionalities in sensing polarization and directionality, and UV selectivity via interband plasmons of silicon.

Single-sized multifunctional metasurfaces for simultaneous nanoprinting and holography inspired by tri-redundancy

Multifunctional metasurfaces, where multiple functions can be integrated into a piece of metasurface, are preferably desired for compact systems with higher integration and subwavelength footprint. Particularly, metasurfaces for simultaneous nanoprinting and holography are one of the promising directions of development image display and information hiding in meta-devices. Here, inspired by tri-redundancy, a new, to the best of our knowledge, approach is proposed for generating a nanoprinting image in the near field and holographic image in the far field simultaneously, which can solve the extremum-mapping problem existing in single-sized scheme without increasing the complexity of the nanostructures. The tri-redundancy of image recognition, hologram designing and intensity modulation introduce an extra degree of freedom, which helps to find a balance between the two types of meta-images generated by utilizing the simulated annealing algorithm. A multifunctional metasurface composed of single-sized silver nanobricks with in-plane orientation has been fabricated to demonstrate the feasibility of encoding a binary image in the near field while reconstructing a 16-steps holographic image without twin-image in the far field. This multifunctional metasurface has flexible working modes, broadband working window and large robustness for fabrication errors, and it provides a simple design scheme for multifunctional integration. We expect it can empower advanced research and applications in high-end optical anticounterfeiting, image hiding and so on.

Recent Progress in Responsive Structural Color

Structural color has been regarded as an ideal alternative to pigments because of the advantages of environmental friendliness, resistance to fading, and dynamic regulation. Responsive structural color can give real-time visible feedback to external stimuli and thus has great prospects in many applications, such as displays, sensing, anticounterfeiting, information storage, and healthcare monitoring. In this Perspective, we elucidate basic concepts, controllable fabrications, and promising applications of responsive structural colors. In particular, we systematically summarize the general regulation mode of all kinds of responsive structural color systems. First, we introduce the basic chromogenic structures as well as the regulation modes of responsive structural color. Second, we present the fabrication methods of patterned structural color. Then, the promising applications of responsive structural color systems are highlighted in detail. Finally, we present the existing challenges and future perspectives on responsive structural colors.

Optical metasurfaces towards multifunctionality and tunability

Optical metasurfaces is a rapidly developing research field driven by its exceptional applications for creating easy-to-integrate ultrathin planar optical devices. The tight confinement of the local electromagnetic fields in resonant photonic nanostructures can boost many optical effects and offer novel opportunities for the nanoscale control of light-matter interactions. However, once the structure-only metasurfaces are fabricated, their functions will be fixed, which limits it to make breakthroughs in practical applications. Recently, persistent efforts have led to functional multiplexing. Besides, dynamic light manipulation based on metasurfaces has been demonstrated, providing a footing ground for arbitrary light control in full space-time dimensions. Here, we review the latest research progress in multifunctional and tunable metasurfaces. Firstly, we introduce the evolution of metasurfaces and then present the concepts, the basic principles, and the design methods of multifunctional metasurface. Then with more details, we discuss how to realize metasurfaces with both multifunctionality and tunability. Finally, we also foresee various future research directions and applications of metasurfaces including innovative design methods, new material platforms, and tunable metasurfaces based metadevices.

All-Dielectric Metasurface-Enabled Multiple Vortex Emissions

On-chip integrated micro- and nanoscale vortex lasers are key elements for addressing the exponentially growing demand for information capacity. Although tunable vortex microlasers have been reported, each laser pulse still possesses one particular topological charge and requires additional multiplexing. In this study, the simultaneous generation of coherent laser arrays with different topological charges by combining metalenses with semiconductor microlasers is demonstrated. A TiO₂ vortex metalens converts two orbital angular momentum beams into the same diffraction-limit spot with opposite circular polarizations through spin-to-orbital conversion. Consequently, the microlaser emission at the focal spot, which can be decomposed into two circularly polarized beams, is collimated into vortex microlaser beams with two different topological charges through a time-reversal process. This concept is extended to a 2 × 2 metalens array by introducing off-axis terms, and eight topological charges are produced simultaneously. This research is a significant step toward the on-chip integration of micro- and nanolasers.