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.

On-Chip Meta-Optics for Engineering Arbitrary Trajectories with Longitudinal Polarization Variation.

On-chip integrated meta-optics promise to achieve high-performance and compact integrated photonic devices. To arbitrarily engineer the optical trajectory along the propagation path in an on-chip integrated scheme is of significance in fundamental physics and various emerging applications. Here, we experimentally demonstrate an on-chip metasurface integrated on a waveguide to enable predefined arbitrary optical trajectories in the visible regime. By transformation of the transverse phase to generate longitudinal mapping, the guided waves are extracted and molded into any different optical trajectories (parabola, hyperbola, and cosine). More intriguingly, predefined polarization states with longitudinal variation are also successfully imparted along the trajectory. Owing to the on-chip propagation scheme, the trajectories are uniquely free from zero-order diffraction interference, naturally having a higher signal-to-noise ratio beyond conventional free-space forms. Overall, such on-chip optical trajectory engineering allows for miniaturized integration and can find paths in potential applications of complex optical manipulation, advanced laser fabrication, and microscopic imaging.

Switchable unidirectional emissions from hydrogel gratings with integrated carbon quantum dots.

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.

Multi-Dimensional Light-Emitting Meta-Display: Photoluminescence and Pumping Light Multiplexing.

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.

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.

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.

Hydrogel-Based, Dynamically Tunable Plasmonic Metasurfaces with Nanoscale Resolution.

Flat metasurfaces with subwavelength meta-atoms can be designed to manipulate the electromagnetic parameters of incident light and enable unusual light-matter interactions. Although hydrogel-based metasurfaces have the potential to control optical properties dynamically in response to environmental conditions, the pattern resolution of these surfaces has been limited to microscale features or larger, limiting capabilities at the nanoscale, and precluding effective use in metamaterials. This paper reports a general approach to developing tunable plasmonic metasurfaces with hydrogel meta-atoms at the subwavelength scale. Periodic arrays of hydrogel nanodots with continuously tunable diameters are fabricated on silver substrates, resulting in humidity-responsive surface plasmon polaritons (SPPs) at the nanostructure-metal interfaces. The peaks of the SPPs are controlled reversibly by absorbing or releasing water within the hydrogel matrix, the matrix-generated plasmonic color rendering in the visible spectrum. This work demonstrates that metasurfaces designed with these spatially patterned nanodots of varying sizes benefit applications in anti-counterfeiting and generate multicolored displays with single-nanodot resolution. Furthermore, this work shows system versatility exhibited by broadband beam-steering on a phase modulator consisting of hydrogel supercell units in which the size variations of constituent hydrogel nanostructures engineer the wavefront of reflected light from the metasurface.

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.

Free-Space Optical Merging via Meta-Grating Inverse-Design.

Despite various advances in achieving arbitrary optics steering, one of the longstanding challenges is to achieve optical merging for combining multidirectional beams through single-time reflection/transmission in free space. Typically, dual-directional beam merging is conducted by combining half-transmission and half-reflection using beam splitters; however, it leads to a bulky system with stray light and low merging efficiency. The difficulty of free-space beam merging lies in imparting respective distinct wavevectors to different directional beams. Herein, we originally proposed and successfully demonstrated the free-space optical merging (FOM) functionality based on the inverse-designed meta-grating architecture in the visible regime. By utilizing the inverse problem solver, two proposed meta-grating schemes experimentally enable merging of dual-directional beams into the same outgoing angle for the first time merely through single-time reflection. We envision that the creation of free-space merging performance can be widely applicable to the future optical system and facilitate the miniature optical devices and integration.

On-chip asymmetric beam-steering for broadband visible light.

Artificial optical nanostructures including three-dimensional (3D) metamaterials and two-dimensional (2D) metasurfaces have shown overwhelming capability to control electromagnetic waves in desirable manners. However, the challenges of manufacturing a complex 3D bulk architecture or achieving nanoscale alignment between multilayers limit their practical applications, and they are unable to be used in on-chip integrated photonic devices. Therefore, the emerging dimensionality-reduction to on-chip metadevices would be of promising research value. Here, we propose a visible-frequency on-chip dual-layer design by cascading one-dimensional (1D) plasmonic metawires with metagratings, which can effectively manipulate surface plasmon polariton (SPP) wavefronts and exhibit on-chip asymmetric beam-steering functionality. Our 1D metawires consist of trapezoidal plasmonic nanoantennas and can enable broadband (460-700 nm) on-chip beam-deflection with a high conversion efficiency. The cascading plasmonic coupling between metawires/metagrating is further demonstrated with broadband asymmetric propagation performance, which is crucial for on-chip plasmonic device development. Finally, we study and theoretically verify a cascade system that integrates a dual-functional (convergent/divergent) lens for the forward/backward propagation, respectively. Compared with conventional free-space multilayer metasurfaces, on-chip 1D metawires enjoy single-time lithography processing and no alignment requirement for implementation in multifunctional devices. We believe that the proof-of-concept on-chip metawires study will pave a new, to the best of our knowledge, way for creating multifunctional photonic integrated devices and hold tremendous potential in realizing on-chip transformation optics, information processing, spectrometers, as well as optical sensors.

Dual-encryption freedom via a monolayer-nanotextured Janus metasurface in the broadband visible.

As an emerging category of two-faced 2D architecture, the Janus metasurface aims to explore another universal optical property, that is, the wavevector direction (k-direction), and to enable the asymmetric transmission between the opposite directional incidences. It exhibits significant potential in creating versatile multiplexing metasurfaces and an optical isolator in optical communication applications. However, most previous asymmetric functionality shows merely one-way functionality with the other-way simply muted or demands multilayered nanostructure fabrication and alignment. Hence, it remains a great challenge to make a monolayer-nanotextured Janus metasurface with dual-encryption freedom and conquering the difficulty for multilayer alignment and practical operation bandwidth. In this work, we have proposed and experimentally demonstrated a new strategy of a dual-encryption Janus metasurface design with a simple monolayer-nanotextured metasurface coupled with a commercialized film of the half-wave plate. Utilizing the hybridization from two independent geometrical dimensions of rectangular-antennas, our approach ingeniously transforms the polarization-multiplexing into the dual-directional channels. A series of calculations and experimental results demonstrate that our asymmetric approach simultaneously constructs completely independent imaging encryptions for both forward and backward directions. Additionally, our proposed approach becomes a practical scheme with broadband visible-frequency operation and great simplicity in design and nanofabrication. We believe the universal scheme could facilitate to increase the information encoding capacity and holographic multiplexing channels by expanding the illumination wavevector to the full-space (+/-), and it paves the route toward the potential applications in on-chip integration, telecommunications, encryption, information processing, and communication.

Angular Multiplexing Nanoprinting with Independent Amplitude Encryption Based on Visible-Frequency Metasurfaces.

Two-dimensional (2D) metasurfaces hold great promise to enable multiplexing and multifunctional optical devices due to their artificial freedom in design, device miniaturization, etc. Various multiplexing and multifunctional metasurfaces have been extensively studied, including polarization multiplexing, wavelength multiplexing, and orbit angular momentum (OAM) multiplexing. However, due to the lack of angular encoding freedom, angular multiplexing switchable nanoprinting has rarely been studied or demonstrated yet to the best of our knowledge. Here, we realize angular multiplexing switchable nanoprinting functionality with independent amplitude encryption based on visible-frequency metasurfaces. By screening a large number of structural designs and breaking the angular correlation, we eventually obtain optimal metasurface designs to realize dual-channel arbitrary image encryption. Furthermore, we illustrate that the proposed scheme would serve as an optical information concealment/retrieval strategy by combining the structural color and amplitude modulation. Overall, we believe that angular multiplexing metasurfaces would easily find promising applications, including optical information encryption/concealment, multifunctional switchable devices, and advanced eyeglass-free three-dimensional (3D) stereoscopic displays.

3D Meta-Prisms for Versatile Beam Steering by Hybridizing Plasmonic and Diffractive Effect in the Broadband Visible Regime.

As two independent optical sub-fields, diffraction optics and plasmonics both have been used for wavefront shaping and beam steering. However, the two separate concepts have always been developing as two parallel directions, which have not met for studying their structural hybridization to discover new potentials. For instance of the flat metasurfaces, even though the geometric parameters including shape, size, and periodicity have been studied, it remains mostly unexplored for the 3D spatial height variation. Here, a new type of all-metallic 3D meta-prism is proposed and experimentally demonstrated by hybridizing the localized surface plasmonic resonances (LSPR) and the blazed grating diffraction, which enables strong polarization-dependent behaviors to steer broadband visible light to drastically inverse directions. The nanofabrication of 3D meta-prism is achieved by nanostencil lithography with electron-beam evaporation. Such meta-prism could also enable to split different visible light (green, blue, and red) with high-efficiency contrast (≈10). By the mirror-symmetry arrangement, a multifunctional surface is demonstrated with polarization-/wavelength-multiplexing wavefront-shaping functions (concave, convex, or flat mirror). This unique 3D meta-prism enjoys great simplicity and versatility in broadband beam steering through the incorporation of plasmonic and diffractive effects and can be utilized in various applications including dichroic-prism splitters, multifunctional meta-mirrors, etc.

Asymmetric angular dependence for multicolor display based on plasmonic inclined-nanopillar array.

Asymmetric multicolor displays have unique and fascinating applications in the field of artificial color engineering. However, the realization of such multicolor displays still faces challenges, due to limitations associated with nanofabrication techniques. In this work, asymmetric photonic structures were realized through inclined 2D aluminum nanopillar arrays, which demonstrate asymmetric angle-dependence as multicolor displays. It was numerically and experimentally demonstrated that the distinctive symmetry breaking leads to the plasmonic coupling effect with angle-dependence and reflection differences with the opposite observing angle. Based on this concept, several color printings were designed as prototypes, which prove the utility of the controlled asymmetric color display with varied observing angles. Our results demonstrate a simple and efficient platform for asymmetric plasmonic nanostructures, which paves the way for further study and designation in artificial color engineering.

Polarization-insensitive broadband visible-light steering with tunable direction enabled by scalable plasmonics meta-gratings.

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.

On-chip metalenses based on one-dimensional gradient trench in the broadband visible.

Metasurfaces are composed of flat, ultrathin subwavelength nanoantennas with strong capability in manipulating light propagation by modulations on its phase, amplitude, and polarization. For instance, the invention of two-dimensional (2D) metalenses has enabled light focusing and imaging in three-dimensional (3D) free space with miniaturized thickness and device size at a planar surface. However, such inherent form of 2D arrays and focusing functionality at 3D optical free-space limits the degree of freedom for light propagation and manipulation along a 2D planar surface and eventually the possibility of on-chip photonic system integration. Here, we theoretically study and demonstrate a new type of planar on-chip metalens, which enables light focusing and strong localization at a 2D surface. The planar on-chip architecture design is based on the one-dimensional (1D) length or width gradient trench metalens (GTM), which could yield the elaborately engineered phase shift for propagating light within the on-chip waveguide at the visible wavelength of 500 nm. By generating 1D phase arrangement at the nanoscale, a miniature on-chip metalens with ∼3×0.5µm dimension could achieve light focusing on a 2D waveguide surface with the flexibility to design scalable focal lengths and ultra-high numerical aperture of up to ∼0.99. Additionally, GTM metalens designs could also exhibit overlapped high depth-of-focus, which consequently could behave as achromatic-like lensing at the selected focal plane. Furthermore, we manifest that the focusing functionality can also be subject to dynamically tuning and switching on-and-off with TE/TM polarization change or waveguide index alteration. We believe this new form of on-chip 1D metalens holds potential applications including on-chip light manipulation functionality of focusing and diverging, optical on-chip sensing, next-generation on-chip optical communication, signal processing as well as imaging devices, etc.

Myricanol 5-fluorobenzyloxy ether regulation of survivin pathway inhibits human lung adenocarcinoma A549 cells growth in vitro.

BACKGROUND: This study aimed to explore the growth inhibitory effect of myricanol 5-fluorobenzyloxy ether (5FEM) and its underlying mechanisms in human lung adenocarcinoma A549 cells in vitro. METHODS: 5FEM was obtained by the chemical modification of myricanol with fluorobenzyloxy ether at the OH(5) position. The cytotoxicity, cell apoptosis, cell cycle, mitochondrial membrane potential (ΔΨm), scratch test, colony formation, and the expression levels of the key survivin pathway-related genes in A549 were evaluated. RESULTS: 5FEM could significantly inhibit A549 cell growth; induce cell apoptosis; increase G0/G1 population; reduce ΔΨm; inhibit cell migration and colony formation; upregulate caspase-9, P21, and Bax expression levels; and downregulate PARP, survivin, and Bcl-2 expression level. CONCLUSION: These results enhanced our understanding of 5FEM and aid the discovery of novel myricanol derivatives as potential antitumor agents.

High-NA achromatic diffractive lensing for arbitrary dual-wavelengths enabled by hybridized metal-insulator-metal cavities.

A new type of diffractive lens based on hybridized Fabry-Perot (FP) cavities with high-NA and achromatic features for arbitrary dual-wavelengths is theoretically proposed and demonstrated. We utilize the subwavelength-scale metal-insulator-metal nanocavity to form a Fresnel zone plate (MIM-FZP) that benefits from both spectral selectivity and high numerical aperture (NA > 0.9) to enable lensing functionality. By taking advantage of the different transmission orders from MIM, any arbitrary dual-wavelength achromatic focusing design is achieved. Using this approach, we merge two independent MIM-FZP designs and realize achromatic focusing performance at the selected dual-wavelength of 400/600 nm. Furthermore, the achromatic lens also exhibits a crucial potential for dynamically tuning of the operation wavelengths and focusing lengths as actively scaling the core layer thickness of MIM. The unique MIM-FZP design can be practically fabricated using a grayscale lithography technique. We believe such high-NA and achromatic optical devices enjoy great simplicity for structural design and can easily find applications including high-resolution imaging, new-generation integrated optoelectronic devices, confocal collimation, and achromatic lens, etc.