Metasurface-empowered spectral and spatial light modulation for disruptive holographic displays

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.

Ultracompact polarization multiplexing meta-combiner for augmented reality display

Augmented reality (AR) display, as a next-generation innovative technology, is revolutionizing the ways of perceiving and communicating by overlaying virtual images onto real-world scenes. However, the current AR devices are often bulky and cumbersome, posing challenges for long-term wearability. Metasurfaces have flexible capabilities of manipulating light waves at subwavelength scales, making them as ideal candidates for replacing traditional optical elements in AR display devices. In this work, we propose and fabricate what we believe is a novel reflective polarization multiplexing gradient metasurface based on propagation phase principle to replace the optical combiner element in traditional AR display devices. Our designed metasurface exhibits different polarization modulations for reflected and transmitted light, enabling efficient deflection of reflected light while minimizing the impact on transmitted light. This work reveals the significant potential of metasurfaces in next-generation optical display systems and provides a reliable theoretical foundation for future integrated waveguide schemes, driving the development of next-generation optical display products towards lightweight and comfortable.

Switchable optical trapping based on vortex-pair beams generated by a polarization-multiplexed dielectric metasurface

Optical trapping is a state-of-the-art methodology that plays an integral role in manipulating and investigating microscopic objects but faces formidable challenges in multiparticle trapping, flexible manipulation, and high-integration applications. In this study, we propose and demonstrate a switchable optical scheme for trapping microparticles incorporating disparate vortex-pair beams generated by a polarization-multiplexed metasurface. The miniaturized all-dielectric metasurface, which comprises an array of titanium dioxide nanoposts, was manufactured and characterized to provide polarization-tuned two-fold vortex-pair beams. The profiles of the created vortices can be flexibly tailored by adjusting the combination of topological charges and the separation among phase singularities. Under transverse electric polarized light conditions, a vortex-pair beam with opposite topological charge combinations traps a single microparticle within one beam spot, while under transverse magnetic polarization conditions, two microparticles are captured simultaneously by a vortex-pair beam with the same topological charge signs. The proposed switchable trapping scheme (incorporating a vortex-pair light beam) is expected to feature enhanced integration and flexible manipulation of multiple particles with potential applications in biophysics, nanotechnology, and photonics.

An all-dielectric metasurface based on Fano resonance with tunable dual-peak insensitive polarization for high-performance refractive index sensing

A symmetric all-dielectric metasurface based on silicon and GaAs is proposed and numerically studied. In the mid-infrared region, two Fano resonant peaks with a reflectance exceeding 90% are observed. By altering the geometric parameters of the metasurface, the wavelength location and quality factor (Q-factor) of the resonant peaks can be tuned. The highest Q-factors can be 9609.67 and 3476.33, respectively. The proposed metasurface structure for optical refractive index sensing shows high performance and is insensitive to the plane wave's polarization state. In the refractive index range of 1.00 to 1.10, the highest sensitivity and figure of merit (FoM) are 1901.34 nm RIU-1 and 2492.04 RIU-1, respectively. The highest sensitivity is 2248.57 nm RIU-1 and FoM is 977.64 RIU-1 in the refractive index range of 1.30 to 1.40. These research results will help improve and innovate related sensing technologies and devices.

Metasurfaces-Driven Hyperspectral Imaging via Multiplexed Plasmonic Resonance Energy Transfer

Obtaining single-molecular-level fingerprints of biomolecules and electron-transfer dynamic imaging in living cells are critically demanded in postgenomic life sciences and medicine. However, the possible solution called plasmonic resonance energy transfer (PRET) spectroscopy remains challenging due to the fixed scattering spectrum of a plasmonic nanoparticle and limited multiplexing. Here, multiplexed metasurfaces-driven PRET hyperspectral imaging, to probe biological light-matter interactions, is reported. Pixelated metasurfaces with engineered scattering spectra are first designed over the entire visible range by the precision nanoengineering of gap plasmon and grating effects of metasurface clusters. Pixelated metasurfaces are created and their full dark-field coloration is optically characterized with visible color palettes and high-resolution color printings of the art pieces. Furthermore, three different biomolecules (i.e., chlorophyll a, chlorophyll b, and cytochrome c) are applied on metasurfaces for color palettes to obtain selective molecular fingerprint imaging due to the unique biological light-matter interactions with application-specific biomedical metasurfaces. This metasurface-driven PRET hyperspectral imaging will open up a new path for multiplexed real-time molecular sensing and imaging methods.

Dynamic control of hybrid grafted perfect vector vortex beams

Perfect vector vortex beams (PVVBs) have attracted considerable interest due to their peculiar optical features. PVVBs are typically generated through the superposition of perfect vortex beams, which suffer from the limited number of topological charges (TCs). Furthermore, dynamic control of PVVBs is desirable and has not been reported. We propose and experimentally demonstrate hybrid grafted perfect vector vortex beams (GPVVBs) and their dynamic control. Hybrid GPVVBs are generated through the superposition of grafted perfect vortex beams with a multifunctional metasurface. The generated hybrid GPVVBs possess spatially variant rates of polarization change due to the involvement of more TCs. Each hybrid GPVVB includes different GPVVBs in the same beam, adding more design flexibility. Moreover, these beams are dynamically controlled with a rotating half waveplate. The generated dynamic GPVVBs may find applications in the fields where dynamic control is in high demand, including optical encryption, dense data communication, and multiple particle manipulation.

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

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

Bio-Inspired Nanomembranes as Building Blocks for Nanophotonics, Plasmonics and Metamaterials

Nanomembranes are the most widespread building block of life, as they encompass cell and organelle walls. Their synthetic counterparts can be described as freestanding or free-floating structures thinner than 100 nm, down to monatomic/monomolecular thickness and with giant lateral aspect ratios. The structural confinement to quasi-2D sheets causes a multitude of unexpected and often counterintuitive properties. This has resulted in synthetic nanomembranes transiting from a mere scientific curiosity to a position where novel applications are emerging at an ever-accelerating pace. Among wide fields where their use has proven itself most fruitful are nano-optics and nanophotonics. However, the authors are unaware of a review covering the nanomembrane use in these important fields. Here, we present an attempt to survey the state of the art of nanomembranes in nanophotonics, including photonic crystals, plasmonics, metasurfaces, and nanoantennas, with an accent on some advancements that appeared within the last few years. Unlimited by the Nature toolbox, we can utilize a practically infinite number of available materials and methods and reach numerous properties not met in biological membranes. Thus, nanomembranes in nano-optics can be described as real metastructures, exceeding the known materials and opening pathways to a wide variety of novel functionalities.

Single Pixel Imaging Key for Holographic Encryption Based on Spatial Multiplexing Metasurface

Compared with the traditional holographic technology, metasurface holography is a promising technology due to the large field angle and high spatial resolution. Thanks to the precise control of phase, amplitude, polarization and so on, metasurface holography provides a flexible platform for light modulation, optical encryption and so on. Besides, the process of image reconstruction by single pixel imaging is similar to a form of encoding and decoding, which is realized by calculating the correlation between a series of modulation patterns and their corresponding intensity signals. In this work, an optical encryption scheme is proposed based on spatial multiplexing metasurface, which depends on the combination of holographic technology and single pixel imaging technology. In the encryption scheme, the image transmitted by single pixel imaging based on metasurface is used as the addressing key of holography. Besides, illuminating different positions of the metasurface can generate different holographic reconstructed images, and there is 50% information overlapped between adjacent sub-holograms. This work makes use of the spatial multiplexing property of metasurface, which can complete different functions, paving the way for the application in the field of optical imaging encryption and information security.

Broad-Band Polarization-Insensitive Metasurface Holography with a Single-Phase Map

The remarkable potential of metasurface holography promises revolutionary advancements for imaging, chip-integrated augmented/virtual reality (AR/VR) technology, and flat optical displays. The choice of constituent element geometry constrains many potential applications purveyed through polarization-independent optical response. The limited capabilities and degree of freedoms in commonly used meta-atoms restrict the design flexibility to break the conventional trade-off between polarization-insensitivity and bandwidth. Here, we propose a geometric phase-enabled novel design strategy to break this conventional trade-off. The proposed strategy ensures the realization of broad-band polarization-insensitivity through a simplified design procedure. An identical output wavefront manipulation is achieved by adjusting the phase delay freedom of geometric phase engineering under different incident polarization conditions. For proof of concept, a metahologram device is fabricated by an optimized complementary metal-oxide-semiconductor (CMOS)-compatible material of hydrogenated amorphous silicon (a-Si:H). This metahologram device reproduces the required hologram with high image fidelity and efficiency under different polarization scenarios of white light incidence. Due to the simple design strategy, low computational cost, and easy fabrication, the proposed technique can be an excellent candidate for realizing polarization-insensitive metahologram devices.

Single-Step Fabricable Flexible Metadisplays for Sensitive Chemical/Biomedical Packaging Security and Beyond

Secure packaging and transportation of light-sensitive chemical and biomedical test tubes are crucial for environmental protection and public health. Benefiting from the compact form factor and high efficiency of optical metasurfaces, we propose a broad-band polarization-insensitive flexible metasurface for the security of sensitive packages in the transport industry. We employ both the propagation and the geometric phase of novel TiO₂ resin-based anisotropic nanoresonators to demonstrate a flexible and broad-band polarization-insensitive metasurface in the visible domain. The ultraviolet nanoimprint lithographic technique (UV-NIL) is used to fabricate high-index TiO₂ nanoparticle-embedded-resin (nano-PER) structures that are patterned on a flexible substrate. This novel approach provides swift single-step fabrication without secondary fabrication steps such as deposition and etching. Moreover, replicating and transforming patterns over flexible substrates make the proposed technique highly suitable for large-throughput commercial manufacturing. As the proposed metahologram manifests high transmission efficiency in the visible domain, such flexible metaholographic platforms could find several exciting applications in bendable/curved displays, wearable devices, and holographic labeling for interactive displays.