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Integrating metasurfaces on‐chip provides a promising approach to modulating and extracting the in‐plane waves, which bridges the conversion between guided and free‐space waves and suggests tremendous applications, including guided‐wave‐driven holography, photonic integrated lasers, and on‐chip routers. However, despite these efforts, it remains challenging to achieve multicolor 3D holographic projections via on‐chip meta‐optics, along with switchability. Here, the multicolor 3D holography free from zero‐order diffraction and the immersion switchable display enabled by the on‐chip integrated metasurface is proposed and demonstrated. By leveraging the propagation‐accumulated phase of the guided waves and exploiting an optimization algorithm, an on‐chip meta‐hologram driven by guided waves is developed to project both multicolor and multiplane images with independent encoding freedom. Moreover, the switch between two colorful holographic images is also demonstrated via an easily accessible immersion tuning scheme. Such an on‐chip‐driven meta‐hologram exhibits low background noise or crosstalk with high information quality and is also free from sophisticated nanostructure searching or elaborate target‐image predesigning. The proposed on‐chip‐driven metasurface for multicolor 3D holography promises future applications in dynamic display, virtual/augmented reality, and liquid sensing. [ABSTRACT FROM AUTHOR]

Actively tuning quasi‐bound states in the continuum (q‐BIC) has emerged as a prominent theme in nanophotonics due to its tailored light–matter interaction. However, the practical controllable q‐BIC metadevices still exhibit critical challenges for achieving convenient tuning in the visible regime with strong reversibility and large‐area implementation. Herein, an immersion‐triggered tuning approach is demonstrated for switchable q‐BIC in the visible regime using 1.5D metagratings. Moreover, by employing the water as the trigger, active q‐BIC‐based optical information encryption is demonstrated due to the spectra alternation. In addition, the proposed q‐BIC is insensitive to incident angles regarding quality factor, resonant wavelength, and modulation depth (MD). This immersion‐triggered strategy for q‐BIC offers a practical tuning approach for achieving dynamic switchable optical functionalities, with potential applications in metasurface‐empowered active q‐BIC optical devices. [ABSTRACT FROM AUTHOR]

Heading toward real‐life applications outside the laboratory, a longstanding obstacle for meta‐optics is to achieve an easy‐accessible tuning approach with practical characteristics, including a large tuning area, low complexity, low cost, and low energy consumption. Water (H2O) stimuli, a ubiquitous substance in nature, can potentially serve as a rescue solution and has attracted broad interest. However, despite its great simplicity, water tuning still faces an unresolved but critical challenge, that is, to enable independent‐programmable functionalities transformation. Herein, a pixel‐scale programmable visualization transformation simply tuned by exhaling water vapors through constructing a hydrogel‐based reconfigurable architectural metasurface (HRAM) with its geometric sensitivity to water molecules is originally demonstrated. Due to the moisture‐induced resonant mode switch from HRAM scaling up/down, the amplitude‐programmable meta‐pixels for obtaining multi‐channel encoding freedom are successfully created. Via simply exhaling vapors to the sample pattern, it dynamically exhibits independent‐programmable visualization (nanoprinting and meta‐holography) switch in real‐time at the prior‐/post‐humid states, beyond the conventional coloring change or simply on‐and‐off style switch utilizing humidity tuning scheme. Such a tuning strategy with good programmability, repeatability, and a large tuning area would blaze new trails for meta‐display dynamics in practical applications, including display/cosmetics, information storage/encryption, and humidity sensors. [ABSTRACT FROM AUTHOR]

Hydrogel materials endow the flat optics platform with active tuning capability, owing to their remarkable humidity‐responsive swelling behavior. Despite recent advances in hydrogel‐based devices for spectral tuning, their complex patterning processing and limited functionality obstruct them from practical applications. Herein, a single‐step direct‐printing technique is originally demonstrated with an active hydrogel material platform for realizing unprecedented multi‐field full‐color display dynamics. Through exploring the dose‐induced shrinkage on polyvinyl alcohol, the stepwise hydrogel nanocavities sandwiched by ultrathin metallic films can be directly printed by grayscale e‐beam lithography. Due to the tunable structural coloration from hydrogel nanocavity scaling, multi‐functionalities are successfully created for optical concealment, dynamic coloring, and dynamic full‐color holography. By encoding the cavity‐dependent transmission phase into the direct‐printed hydrogel platform, it originally enables the projected full‐color holographic dynamics in real‐time by simply exhalation, beyond the static holographic display or monochromatic holographic switching. The proposed active displays can rapidly respond to the surrounding humidity change at a millisecond‐level (< 150 ms). Such a direct‐printing strategy for hydrogel nanocavity represents a critical advance toward the unprecedented dynamic full‐color display, and suggests promising applications in optical security, gas sensing, multispectral imaging, full‐color holography, and next‐generation display techniques. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The exploit of on‐chip metasurfaces with full optical controllability and multiplexing capability holds great promise for photonic integration circuits (PIC). Despite previous endeavors in metasurfaces controlling guided waves, it still faces critical challenges to realize practical display applications, for instance, augmented reality (AR). Here, a new type of AR based on multiplexed on‐chip meta‐holography is proposed and experimentally demonstrated by integrating judiciously engineered meta‐atoms above waveguide. Through hybridizing detour and Pancharatnam–Berry phases, on‐chip metasurfaces can independently manipulate both guided waves and free‐space light to enable a triple‐channel holography‐multiplexing with independent‐encoding freedom. Eventually, an RGB‐coloring AR hologram free from zero‐order diffraction that can project virtual images into a real‐world environment is realized, showcasing its significant potential for wearable devices (glasses or contact lens) integration. This study finds a feasible route toward multifunctional PIC devices and applications in wearable AR displays, imaging multiplexing, information storage, etc. [ABSTRACT FROM AUTHOR]

Heading towards to intelligent photonic technology, meta‐optics is in the revolutionary process of changing from passive to active controllable devices. Despite various emerging tuning mechanisms exploration and demonstration, they mainly focus on spectral amplitude alternation or near‐field imaging switch. Most tuning schemes inevitably demand quite complicated nanofabrication to incorporate nanotextured active materials, thus limiting its applicable scenarios outside the laboratory. Hence, a practically accessible solution in real life to simultaneously realize multi‐field (both near‐ and far‐field) dynamic displays remains a critical challenge. Here, a practical electric‐driven liquid‐crystal‐integrated metasurface (ELIM) is proposed and demonstrated toward advanced intelligent dynamic display. Through elaborately screening building block (α‐Si nanopillar) geometry to build up a systematic architectural dictionary, conventional spatial‐multiplexing is successfully achieved and the degeneracy for amplitude/phase selections is created and thus any arbitrary multi‐field encryptions are allowed. By leveraging ELIM anisotropic characteristics for orthogonal polarizations, an electric‐driven dynamic tuning is practically realized for the first time to enable quad‐fold dynamic exhibitions, including switchable dual‐nanoprinting (near‐field) and simultaneous dual‐holography (far‐field) images with independent‐encryption freedom. Overall, it is envisioned that meta‐optics integrated with the liquid‐crystal platform can easily find practical applications in real life for intelligent dynamic display, imaging multiplexing, information encryption/security, etc. [ABSTRACT FROM AUTHOR]

Although metasurface‐based devices exhibit great potential in optical display and storage technology, the challenges in practical nanoantenna fabrication limit their wide application. In parallel, flat optics, including planar thin‐film nanocavities, have also been extensively studied to realize various spectral engineering and imaging functionalities with large areas and simpler architecture. However, a longstanding practical challenge is to achieve multiplexing imaging functionalities with dynamic switchable ability in real‐time, which to date remains unexplored. In this study, by utilizing the typical inflation sensitivity of hydrogels to humidity change, a multiplexing imaging tunable strategy based on stepwise metal–hydrogel–metal (MHM) nanocavities is originally explored and demonstrated to exhibit dynamic switchable red–green–blue multichannel nanoprinting in real‐time. By decoupling the amplitude/phase correlation, MHM nanocavities successfully enable the hybrid encryption of simultaneous meta‐holography with independent‐encoding freedom in addition to multiplexing nanoprinting. Such an imaging approach, which employs a dynamic tuning scheme, paves a promising avenue toward various applications including state‐of‐the‐art tunable imaging display/storage/encryption, humidity optical sensors, and next‐generation dynamic augmented reality technology. [ABSTRACT FROM AUTHOR]

As metasurfaces have shown great potential for light manipulation, the majority of optical source parameters have been extensively explored and progressively realized for new degrees of freedom in optical control and multiplexing, including wavelength, polarization, and forward/backward illumination, etc. However, the incident wave vector (k) direction, namely the illumination angle, as one of the critical parameters, has not been fully explored for optical multiplexing due to the lack of angular‐encoding freedom. Here, a general strategy is proposed to realize angular‐multiplexing metasurface based on building up an independent‐encoded amplitude/phase dictionary, in which one can retrieve any arbitrary combination of optical response with different angular illuminations. A series of angular‐multiplexing designs are theoretically and experimentally demonstrated, including angular‐multiplexed meta‐holographs, nanoprintings as well as a hybridized nanoprinting with holography. These studies' numerical calculations and experiments confirm the new degree of freedom for arbitrary encoded amplitude and phase at different illumination angles. The findings establish a new platform for achieving a complexity of functions for angular resolved illumination, and expanding the manipulative capabilities for optical multiplexing. [ABSTRACT FROM AUTHOR]

Metal–insulator–metal (MIM) nanocavity, as a lossy Fabry–Pérot (FP) scheme, has been widely studied for color filter and perfect absorber functionality, which can be integrated into functional photonic devices. However, such triple‐layered MIM still lacks the ability to induce multiple intensity levels for meticulous grayscale imaging because of strong spectral sensitivity to cavity thickness variation. Moreover, the MIM stack remains unexplored to multiplex a near‐field nanoprinting and holographic imaging because it is challenging to break the mutual dependence relation between the intensity and phase shift. Herein, a new film stack of dual‐Fabry–Pérot (DFP) nanocavity is proposed to create triple‐fold freedom in light modulations: intensity, phase shift and operation wavelength, which can be respectively modulated by the top/bottom/total cavity length. By spatially arranging the stepwise nanocavities, the designed DFP pattern can show multiplexing dual‐channel imaging, which encrypts/conceals a grayscale nanoprinting image and simultaneously projects a far‐field holographic image. Such DFP strategy allows for new possibility of independent light modulation and creates new dimensional degree of freedom for thin‐film nanocavity. The proposed functional DFP strategy enriches the subwavelength building block design for metasurfaces and thin‐film stacks, which would promisingly empower advanced applications in information multiplexing, imaging encryption/concealing, and many other related fields. [ABSTRACT FROM AUTHOR]

Liquid immersion on metasurface was earlier demonstrated to realize spectral control. However, it remains a great challenge to achieve tunable phase modulation and versatile beam‐steering performance, which are critical for practical optoelectronic devices. Here, a new liquid‐immersive mechanism with metasurfaces for active beam‐steering is proposed and experimentally realized. Based on the dielectric‐on‐metal nanostructure with selective hydrophilic/hydrophobic properties, the switchable beam‐steering is initiated and successfully presented in the broadband visible regime with a large reflection angle of ≈±30°. Specifically, the beam diffraction direction is tuned between two opposite‐directional channels by water immersion or drying in a repeatable and controllable manner. The proposed straightforward tuning strategy enjoys great convenience in structural patterning and large‐area implementation, instead of requiring any complicated contact patterning or external modulation. This study provides an alternative optical platform for switchable beam‐steering functionality, which is promising for potential applications in tunable display, directional emission, sensing technologies, etc. [ABSTRACT FROM AUTHOR]

Metallic patterned metasurfaces can effectively manipulate the propagation of surface plasmonic waves in the near-field regime. Extraordinary optical phenomena such as diffraction-free propagation also have been enabled by periodic uniform metallic grating metasurfaces (UMGM). However, such metallic patterned metasurfaces usually exhibit a relatively narrow-band non-diffractive property and the realization of visible-frequency broadband diffraction-free on-chip propagation has been quite challenging due to intensive structural dispersive and sensitive wavelength selectivity. Here, we proposed a novel design of a hybrid metallic grating metasurface (HMGM) with two different ridge widths, which could display a broadband diffraction-free on-chip propagation in the visible frequency. By optimization and appropriate hybridization of the ridges of different widths, it enables effective modication of the dispersion of surface plasmons, thus forming the broadband diffraction-free characteristics. Compared to the UMGM, our proposed HMGM can facilitate enhanced propagation of the surface plasmon polaritons and strongly confine the surface plasmonic field to the deep-subwavelength scale. With such hybrid implementation, the surface plasmonic waves propagate parallel to the ridges and their wavefronts remain the original shape without diverging at the broadband wavelength of 600 nm–800 nm. Overall, such broadband diffraction-free propagation along the HMGM could find many potential applications in on-chip plasmonic devices including sub-diffraction resolution imaging, hyperlenses, and photon routing, etc. [ABSTRACT FROM AUTHOR]

As an emerging field in the discipline of optics, plasmonics and metasurfaces have been demonstrated to enable a new degree of freedom to manipulate light for arbitrary beam steering, spectral splitting as well as precise wavefront shaping. However, it has been mostly studied in parallel with the field of diffractive optics, and awaits the unveiling of how the hybridizations between plasmonic effect and diffraction effect interact and impact. Here, we have theoretically proposed a new type of polarization-insensitive meta-grating structure across the broadband visible regime. The structure design combines the width gradient (critical resonant length) from a trapezoid-nanoantenna with the height gradient from a blazed grating profile. The hybridized meta-grating creates both plasmonic effect and grating effect, which enables all the optical incident photons to be directed to the same orientation regardless of the light polarization. As we know, both metasurfaces and diffractive optical elements (such as gratings) are, more often than not, quite sensitive to the incident light polarization. Moreover, if placing our meta-grating on a flexible/stretchable substrate (such as polydimethylsiloxane), the outgoing angle can be effectively adjusted by tuning the period or density of meta-grating arrays. Such meta-grating architectures can be potentially manufactured by existing photolithography and nanoimprint techniques, and can easily find a wide range of practical polarization-insensitive applications, including broadband deflector and emitter, tunable display and imaging device, high signal-to-noise ratio spectrometer, polarization-insensitive plasmonic coupler, etc. [ABSTRACT FROM AUTHOR]

Through hybridizing detour and Pancharatnam-Berry phases, it can independently manipulate both guided waves and free-space light to enable a triple-channel holography-multiplexing, which showcases its significant potential for wearable devices (eyeglasses or contact lens) integration. Augmented Reality Enabled by On-Chip Meta-Holography Multiplexing Light (Laser Photonics Rev. 16(6)/2022) B Augmented Reality Holograms b A miniaturized augmented reality hologram free from zero-order diffraction based on multiplexed on-chip meta-holography is demonstrated by Zhongyang Li and colleagues in article number 2100638. [Extracted from the article]