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On‐chip integrated meta‐optics hold tremendous potential for optical imaging and display applications compatible with integrated photonic devices. Despite recent endeavors in multi‐dimensional image display, it remains a challenge to realize dynamic holography applications with on‐chip integration scheme and facile accessible tuning approach. Herein, an on‐chip hydrogel‐waveguiding platform with single‐step fabrication is demonstrated for dynamic colorful holography. By exploiting the optical tunable property of the waveguiding hydrogel, the on‐chip hydrogel metasurface enables optical concealment ON/OFF and dynamic dual‐channel holographic switch within 310 ms through a simple exhalation process. Furthermore, utilizing the waveguiding hydrogel dispersion and the correlation between extraction efficiency and relative humidity, a color‐mixed holographic image is encrypted and successfully exhibited at specific humidity condition. Beyond the conventional static on‐chip monochromatic holography, such a dynamic on‐chip hydrogel platform enjoys satisfactory humidity‐responsivity, high integration capability, full‐color potential, and zero‐order diffraction interference‐free, which suggests potential applications in active optical information concealment/encryption, full‐color holography, and next‐generation wearable AR devices. [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]

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]

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]

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]

The advent of intelligent display devices has given rise to diverse and complex demands for miniature light-emitting devices. Light-emitting metasurfaces have emerged as a practical and efficient means of achieving precise light modulation. However, their practicality is limited by certain constraints. First, there is a need for further exploration of the ability to manipulate both pumping and emitting light simultaneously. Second, there is currently no encoding freedom in multi-dimensional emitting light. To address these concerns, using meta-atoms is proposed to encode both fluorescence and pumping light independently, and expand the encoding freedom with different incident wavevector directions. A light-emitting metasurface with quad-fold multiplex encoding meta-displays, including dual scattering images and dual fluorescence images, is further demonstrated. This design strategy not only manipulates both pumping and fluorescence light but also broadens encoding freedom for comprehensive multi-functionality. This can pave the way for multiplexing optical displays, information storage, and next-generation wearable displays., (© 2023 Wiley-VCH GmbH.)

Directional emission of photoluminescence despite its incoherence is an attractive technique for light-emitting fields and nanophotonics. Optical metasurfaces provide a promising route for wavefront engineering at the subwavelength scale, enabling the feasibility of unidirectional emission. However, current directional emission strategies are mostly based on static metasurfaces, and it remains a challenge to achieve unidirectional emissions tuning with high performance. Here, we demonstrate quantum dots-hydrogel integrated gratings for actively switchable unidirectional emission with simultaneously a narrow divergence angle less than 1.5° and a large diffraction angle greater than 45°. We further demonstrate that the grating efficiency alteration leads to a more than 7-fold tuning of emission intensity at diffraction order due to the variation of hydrogel morphology subject to change in ambient humidity. Our proposed switchable emission strategy can promote technologies of active light-emitting devices for radiation control and optical imaging., (© 2024. The Author(s).)