Bright-Field and Edge-Enhanced Imaging Using an Electrically Tunable Dual-Mode Metalens

Full-Color Quasi-Achromatic Imaging with a Dual-Functional Metasurface

Achieving broadband achromaticity in the visible spectrum is critical for enhancing the imaging performance of metalenses. However, many previous studies remain constrained by small device sizes or small numerical aperture. In this study, we propose a polarization-multiplexed metalens capable of generating zero- and high-order Bessel beams to achieve quasi-achromatic correction without size limitations. An image subtraction method with the two polarization channels is developed to mitigate the Bessel beam sidelobes to improve imaging quality. Our results demonstrate an effective quasi-achromatic focusing and imaging over a continuous wavelength range of 450-700 nm with long focus depth. The image subtraction method significantly enhances the image clarity and contrast, providing new insights for full-color imaging and detection.

Nanofabrication for Nanophotonics

Nanofabrication, a pivotal technology at the intersection of nanoscale engineering and high-resolution patterning, has substantially advanced over recent decades. This technology enables the creation of nanopatterns on substrates crucial for developing nanophotonic devices and other applications in diverse fields including electronics and biosciences. Here, this mega-review comprehensively explores various facets of nanofabrication focusing on its application in nanophotonics. It delves into high-resolution techniques like focused ion beam and electron beam lithography, methods for 3D complex structure fabrication, scalable manufacturing approaches, and material compatibility considerations. Special attention is given to emerging trends such as the utilization of two-photon lithography for 3D structures and advanced materials like phase change substances and 2D materials with excitonic properties. By highlighting these advancements, the review aims to provide insights into the ongoing evolution of nanofabrication, encouraging further research and application in creating functional nanostructures. This work encapsulates critical developments and future perspectives, offering a detailed narrative on the state-of-the-art in nanofabrication tailored for both new researchers and seasoned experts in the field.

All-optical analog differential operation and information processing empowered by meta-devices

The burgeoning demand for high-performance computing, robust data processing, and rapid growth of big data necessitates the emergence of novel optical devices to efficiently execute demanding computational processes. The field of meta-devices, such as metamaterial or metasurface, has experienced unprecedented growth over the past two decades. By manipulating the amplitude, phase, polarization, and dispersion of light wavefronts in spatial, spectral, and temporal domains, viable solutions for the implementation of all-optical analog computation and information processing have been provided. In this review, we summarize the latest developments and emerging trends of computational meta-devices as innovative platforms for spatial optical analog differentiators and information processing. Based on the general concepts of spatial Fourier transform and Green's function, we analyze the physical mechanisms of meta-devices in the application of amplitude differentiation, phase differentiation, and temporal differentiation and summarize their applications in image edge detection, image edge enhancement, and beam shaping. Finally, we explore the current challenges and potential solutions in optical analog differentiators and provide perspectives on future research directions and possible developments.

Polarization-multiplexing metafiber for dual-mode bright-field and dark-field microscopy

Bright-field and dark-field microscopy are typically used together as complementary techniques to provide comprehensive information about biological specimens with different optical absorption properties. However, switching between these two modes usually involves replacing several bulk optical components, which inevitably increases system complexity, introduces alignment challenges, and results in longer switching times. Herein, we propose a new, to the best of our knowledge, polarization-multiplexing metafiber device for dual-mode bright-field and dark-field microscopy. Utilizing a polarization-multiplexing metalens, two tailored beams (i.e., Gaussian and OAM beam) can be generated, simply by changing the handedness of the incident circularly polarized light. By integrating such metalens onto the tip of a large-mode-area photonic crystal fiber, we experimentally demonstrated that this compact and flexible metafiber can realize the dual-mode bright-field and dark-field microscopy using raspberry trichomes and pine stem, without the need to replace any optical components. The ultra-compact and flexibility features of the proposed metafiber-based dual-mode microscopy pave the way for promising applications in portable and in vivo biological imaging.

Meta-Device for Field-of-View Tunability via Adaptive Optical Spatial Differentiation

Optical edge detection is a crucial optical analog computing method in fundamental artificial intelligence, machine vision, and image recognition, owing to its advantages of parallel processing, high computing speed, and low energy consumption. Field-of-view-tunable edge detection is particularly significant for detecting a broader range of objects, enhancing both practicality and flexibility. In this work, a novel approach-adaptive optical spatial differentiation is proposed for field-of-view-tunable edge detection. This method improves the ability to acquire spatial information and facilitates edge detection over a wider angular range. The adaptive optical spatial differentiation meta-device relies on two core components: the spatial differentiation dielectric metasurface and the adaptive liquid prism. The meta-device is shown to function as a highly efficient (≈85%) isotropic spatial differentiator, operating across the entire visible spectrum (400 to 700 nm) within a wide-angle object space, expanding up to 4.5 times the original field of view. The proposed scheme presents new opportunities for efficient, flexible, high-capacity integrated data processing and imaging devices. And simultaneously provides a novel optical analog computing architecture for the next generation of wide field-of-view phase contrast microscopy.

Advanced Quantitative Phase Microscopy Achieved with Spatial Multiplexing and a Metasurface

Quantitative optical phase information provides an alternative method to observe biomedical properties, where conventional phase imaging fails. Phase retrieval typically requires multiple intensity measurements and iterative computations to ensure uniqueness and robustness against detection noise. To increase the measurement speed, we propose a single-shot quantitative phase imaging method with metasurface optics that can be conveniently integrated into conventional imaging systems with minimal modification. The improvement of the measurement speed is simultaneously made possible by combining deep learning with the transport-of-intensity equation. As a proof-of-concept, we demonstrate phase retrieval on both calibrated phase objects and biological specimens by using an imaging system integrated with our metasurface. When combined with the matched neural network, the system yields result with errors as low as 5% and increased space-bandwidth-product. A multitude of commercial applications can benefit from the compactness and rapid implementation of our proposed method.

Nonlocal Huygens' meta-lens for high-quality-factor spin-multiplexing imaging

Combining bright-field and edge-enhanced imaging affords an effective avenue for extracting complex morphological information from objects, which is particularly beneficial for biological imaging. Multiplexing meta-lenses present promising candidates for achieving this functionality. However, current multiplexing meta-lenses lack spectral modulation, and crosstalk between different wavelengths hampers the imaging quality, especially for biological samples requiring precise wavelength specificity. Here, we experimentally demonstrate the nonlocal Huygens' meta-lens for high-quality-factor spin-multiplexing imaging. Quasi-bound states in the continuum (q-BICs) are excited to provide a high quality factor of 90 and incident-angle dependence. The generalized Kerker condition, driven by Fano-like interactions between q-BIC and in-plane Mie resonances, breaks the radiation symmetry, resulting in a transmission peak with a geometric phase for polarization-converted light, while unconverted light exhibits a transmission dip without a geometric phase. Enhanced polarization conversion efficiency of 65% is achieved, accompanied by a minimal unconverted value, surpassing the theoretical limit of traditional thin nonlocal metasurfaces. Leveraging these effects, the output polarization-converted state exhibits an efficient wavelength-selective focusing phase profile. The unconverted counterpart serves as an effective spatial frequency filter based on incident-angular dispersion, passing high-frequency edge details. Bright-field imaging and edge detection are thus presented under two output spin states. This work provides a versatile framework for nonlocal metasurfaces, boosting biomedical imaging and sensing applications.

Optical Metasurfaces for Biomedical Imaging and Sensing

Optical metasurfaces, arrays of nanostructures engineered to manipulate light, have emerged as a transformative technology in both research and industry due to their compact design and exceptional light control capabilities. Their strong light-matter interactions enable precise wavefront modulation, polarization control, and significant near-field enhancements. These unique properties have recently driven their application in biomedical fields. In particular, metasurfaces have led to breakthroughs in biomedical imaging technologies, such as achromatic imaging, phase imaging, and extended depth-of-focus imaging. They have also advanced cutting-edge biosensing technologies, featuring high-quality factor resonators and near-field enhancements. As the demand for device miniaturization and system integration increases, metasurfaces are expected to play a pivotal role in the development of next-generation biomedical devices. In this review, we explore the latest advancements in the use of metasurfaces for biomedical applications, with a particular focus on imaging and sensing. Additionally, we discuss future directions aimed at transforming the biomedical field by leveraging the full potential of metasurfaces to provide compact, high-performance solutions for a wide range of applications.

The Road to Commercializing Optical Metasurfaces: Current Challenges and Future Directions

Optical metasurfaces, components composed of artificial nanostructures, are recognized for pushing boundaries of wavefront manipulation while maintaining a lightweight, compact design that surpasses conventional optics. Such advantages align with the current trends in optical systems, which demand compact communication devices and immersive holographic projectors, driving significant investment from the industry. Although interest in commercialization of optical metasurfaces has steadily grown since the initial breakthrough with diffraction-limited focusing, their practical applications have remained limited by challenges such as, massive-production yield, absence of standardized evaluation methods, and constrained design methodology. Here, this Perspective addresses the challenges in commercialization of optical metasurfaces, particularly focused on mass production, fabrication tolerance, performance evaluation, and integration into commercial systems. Additionally, we select the fields where metasurfaces may soon play significant roles and provide a perspective on their potentials. By addressing the challenges and exploring the solutions, this Perspective aims to foster discussions that will accelerate the utilization of optical metasurfaces and further build near-future metaphotonics platforms.

Axially multifocal metalens for 3D volumetric photoacoustic imaging of neuromelanin in live brain organoid

Optical resolution photoacoustic imaging of uneven samples without z-scanning is transformative for the fast analysis and diagnosis of diseases. However, current approaches to elongate the depth of field (DOF) typically imply cumbersome postprocessing procedures, bulky optical element ensembles, or substantial excitation beam side lobes. Metasurface technology allows for the phase modulation of light and the miniaturization of imaging systems to wavelength-size thickness. Here, we propose a metalens composed of submicrometer-thick titanium oxide nanopillars, which generates an elongated beam of diffraction-limited diameter with an aspect ratio of 286 and a uniform intensity throughout the DOF. The metalens enhances visualization of phantom samples with tilted surfaces compared to conventional lenses. Moreover, the volumetric imaging of neuromelanin is facilitated for depths of up to 500 micrometers within the human midbrain and forebrain organoids that are 3D biological models of human brain regions. This approach provides a miniaturized platform for neurodegenerative disease diagnosis and drug discovery.

Mid-infrared edge-enhanced imaging via angle-selective nonlinear filtering

We propose a novel, to the best of our knowledge, scheme for mid-infrared upconversion imaging with high tunability between bright-field and edge-enhanced modalities. The involved engineering of the nonlinear process favors shaping the optical transfer function of the imaging system. Consequently, a nonlinear angle-selective filter can be configured to perform an all-optical Fourier processing of the image, which highly depends on phase-matching parameters. We numerically demonstrate the ability to switch modalities between the bright-field and edge-enhanced imaging by tuning the crystal temperature and simultaneously acquiring both information by dichromatic illumination. Notably, the achieved reconfigurability is realized without changing the imaging settings, which contrasts with previous instantiations based on pump adaptation. Therefore, the proposed architecture of upconversion imagers would pave a novel way to implement layout-compact and all-optical processing for infrared images.

Fast selective edge-enhanced imaging with topological chiral lamellar superstructures

Edge detection is a fundamental operation for feature extraction in image processing. The all-optical method has aroused growing interest owing to its ultra-fast speed, low energy consumption and parallel computation. However, current optical edge detection methods are generally limited to static devices and fixed functionality. Herein, we propose a fast-switchable scheme based on a ferroelectric liquid crystal topological structure. The self-assembled chiral lamellar superstructure, directed by the azimuthally variant photo-alignment agent, can be dynamically controlled by the polarity of the external electric field and respectively generates the vector beams with nearly orthogonal polarization distribution. Even after thousands of cycles, the horizontal and vertical edges of the object are selectively enhanced with an ultra-fast switching time of ∼57 μs. Broadband edge-enhanced imaging is efficiently demonstrated. This work extends the ingenious building of topological heliconical superstructures and offers an important glimpse into their potential in the emerging frontiers of optical computing for artificial intelligence.

Single-Shot 3D Imaging Meta-Microscope

Three-dimensional (3D) imaging enables high-precision and high-resolution axial positioning, which is crucial for biological imaging, semiconductor defect monitoring, and other applications. Conventional implementations rely on bulky optical elements or scanning mechanisms, resulting in low speed and complicated setups. Here, we generate the double-helix (DH) point spread function with an all-dielectric metasurface and thus innovate the 3D imaging microscope (hence dubbed meta-microscope), both in 4f and 2f imaging systems. The 4f-meta-microscope with a numerical aperture of 0.7 achieves an axial localization accuracy below 0.12 μm within a 15.47 μm detection range, while the 2f-DH meta-microscope with a numerical aperture of 0.3 shows a 1.12 μm accuracy within a 227.33 μm range. We also demonstrate single-shot and accurate 3D biological imaging of the mouse kidney tissue and peach anther, providing a comprehensive and efficient approach for 3D bioimaging and other applications through a single-shot 3D meta-microscope.

Artificial Intelligence-Enhanced Metasurfaces for Instantaneous Measurements of Dispersive Refractive Index

Measurements of the refractive index of liquids are in high demand in numerous fields such as agriculture, food and beverages, and medicine. However, conventional ellipsometric refractive index measurements are too expensive and labor-intensive for consumer devices, while Abbe refractometry is limited to the measurement at a single wavelength. Here, a new approach is proposed using machine learning to unlock the potential of colorimetric metasurfaces for the real-time measurement of the dispersive refractive index of liquids over the entire visible spectrum. The platform with a proof-of-concept experiment for measuring the concentration of glucose is further demonstrated, which holds a profound impact in non-invasive medical sensing. High-index-dielectric metasurfaces are designed and fabricated, while their experimentally measured reflectance and reflected colors, through microscopy and a standard smartphone, are used to train deep-learning models to provide measurements of the dispersive background refractive index with a resolution of ≈10-4, which is comparable to the known index as measured with ellipsometry. These results show the potential of enabling the unique optical properties of metasurfaces with machine learning to create a platform for the quick, simple, and high-resolution measurement of the dispersive refractive index of liquids, without the need for highly specialized experts and optical procedures.

Electrically tunable planar liquid-crystal singlets for simultaneous spectrometry and imaging

Conventional hyperspectral cameras cascade lenses and spectrometers to acquire the spectral datacube, which forms the fundamental framework for hyperspectral imaging. However, this cascading framework involves tradeoffs among spectral and imaging performances when the system is driven toward miniaturization. Here, we propose a spectral singlet lens that unifies optical imaging and computational spectrometry functions, enabling the creation of minimalist, miniaturized and high-performance hyperspectral cameras. As a paradigm, we capitalize on planar liquid crystal optics to implement the proposed framework, with each liquid-crystal unit cell acting as both phase modulator and electrically tunable spectral filter. Experiments with various targets show that the resulting millimeter-scale hyperspectral camera exhibits both high spectral fidelity ( > 95%) and high spatial resolutions ( ~1.7 times the diffraction limit). The proposed "two-in-one" framework can resolve the conflicts between spectral and imaging resolutions, which paves a practical pathway for advancing hyperspectral imaging systems toward miniaturization and portable applications.

Multifaceted control of focal points along an arbitrary 3D curved trajectory

Metalenses can integrate the functionalities of multiple optical components thanks to the unprecedented capability of optical metasurfaces in light control. With the rapid development of optical metasurfaces, metalenses continue to evolve. Polarization and color play a very important role in understanding optics and serve as valuable tools for gaining insights into our world. Benefiting from the design flexibility of metasurfaces, we propose and experimentally demonstrate a super metalens that can realize multifaceted control of focal points along any 3D curved trajectory. The wavelengths and polarization states of all focal points are engineered in a desirable manner. The super metalens can simultaneously realize customized 3D positioning, polarization states, and wavelengths of focal points, which are experimentally demonstrated with incident wavelengths ranging from 501 to 700 nm. We further showcase the application of the developed super metalenses in 3D optical distance measurement. The compact nature of metasurfaces and unique properties of the proposed super metalenses hold promise to dramatically miniaturize and simplify the optical architecture for applications in optical metrology, imaging, detection, and security.

Monocular Metasurface for Structured Light Generation and 3D Imaging with a Large Field-of-View

Structured light three-dimensional (3D) imaging technology captures the geometric information on 3D objects by recording waves reflected from the objects' surface. The projection angle and point number of the laser dots directly determine the field-of-view (FOV) and the resolution of the reconstructed image. Conventionally, diffractive optical elements with micrometer-scale pixel size have been used to generate laser dot arrays, leading to limited FOV and point number within the projection optical path. Here, we theoretically put forward and experimentally demonstrate a monocular geometric phase metasurface composed of deep subwavelength meta-atoms to generate a 10 798 dot array within an FOV of 163°. Attributed to the vast number and high-density point cloud generated by the metasurface, the 3D reconstructed results showcase a maximum relative error in depth of 5.3 mm and a reconstruction error of 6.07%. Additionally, we propose a spin-multiplexed metasurface design method capable of doubling the number of lattice points. We demonstrate its application in the field of 3D imaging through experiments, where the 3D reconstructed results show a maximum relative depth error of 0.44 cm and a reconstruction error of 2.78%. Our proposed metasurface featuring advanced point cloud generation holds substantial potential for various applications such as facial recognition, autonomous driving, virtual reality, and beyond.

Functionality Expansion of Guided Mode Radiation via On-Chip Metasurfaces

On-chip metasurfaces play a crucial role in bridging the guided mode and free-space light, enabling full control over the wavefront of scattered free-space light in an optimally compact manner. Recently, researchers have introduced various methods and on-chip metasurfaces to engineer the radiation of guided modes, but the total functions that a single metasurface can achieve are still relatively limited. In this work, we propose a novel on-chip metasurface design that can multiplex up to four distinct functions. We can efficiently control the polarization state, phase, angular momentum, and beam profile of the radiated waves by tailoring the geometry of V-shaped nanoantennas integrated on a slab waveguide. We demonstrate several innovative on-chip metasurfaces for switchable focusing/defocusing and for multifunctional generators of orbital angular momentum beams. Our on-chip metasurface design is expected to advance modern integrated photonics, offering applications in optical data storage, optical interconnection, augmented reality, and virtual reality.

Minimalist design of multifunctional metasurfaces for helicity multiplexed holography and nanoprinting

Recently, polarization multiplexing has become a common strategy to enhance the information capacity of metasurfaces. Nevertheless, the intricate design of anisotropic nanostructures forming a polarization multiplexed metasurface poses a significant challenge, increasing the requirements for manufacturing processes and diminishing overall robustness. Herein, we present a minimalist metasurface comprised of only two kinds of nanostructures to achieve the integration of continuous-amplitude modulated nanoprinting and eight-step phase-only helicity-multiplexed holography. Specifically, the nanoprinting image governed by Malus's law can be observed in the orthogonally polarized light path, while holographic images can be switched by changing the chirality of the incident circularly polarized light. More importantly, the geometric phase and the propagation phase of the metasurface are optimized simultaneously according to the target images. Thus, the metasurface does not require optimizing many kinds of nanostructures to achieve the phase but only needs two kinds of nanostructures, forming a minimalist metasurface that significantly relieves the design and fabrication burden. Moreover, the proposed methodology is universal and applicable not only in polarization multiplexing but also in other multi-channel multiplexing technologies. Consequently, the proposed scheme holds promising applications in image display, information encryption, data storage, anti-counterfeiting, and more.

Stretchable Dual-Axis Terahertz Bifocal Metalens with Flexibly Polarization-Dependent Focal Position and Direction

Varifocal lenses are essential components in any optical system, while traditional lenses suffer from bulky volume, fixed focal position, and limited working spectra. As well-arranged subwavelength structures, metalenses overcome the abovementioned obstacles and exhibit merits of ultrathin thickness, flexible focal length, and multifocus. The electromagnetic responses of metasurfaces, including metalens, rely on the phase distributions of phase-shifting elements. The steerable focal direction is investigated to obtain the combinations of focusing and anomalous refraction phase distribution. To fully explore the flexibility of focal length and direction, seven designs of double layers of terahertz (THz) bifocal metalenses are proposed and investigated in this study. They exhibit dependent and independent relationships of tunable focal length and direction with flexible tuning mechanisms. Along with polarization multiplexing, two different focuses can be obtained when the incident waves are x-linear and y-linear polarization states, respectively. The simulation results agreed well with the theoretical predictions. These designs provide a new method to modulate the focal position precisely with promising applications in wireless communication, imaging, and on-chip optical integration systems.

Acoustic Assembly and Scanning of Superlens Arrays for High-Resolution and Large Field-of-View Bioimaging

High-resolution and dynamic bioimaging is essential in life sciences and biomedical applications. In recent years, microspheres combined with optical microscopes have offered a low cost but promising solution for super-resolution imaging, by breaking the diffraction barrier. However, challenges still exist in precisely and parallelly superlens controlling using a noncontact manner, to meet the demands of large-area scanning imaging for desired targets. This study proposes an acoustic wavefield-based strategy for assembling and manipulating micrometer-scale superlens arrays, in addition to achieving on-demand scanning imaging through phase modulation. In experiments, acoustic pressure nodes are designed to be comparable in size to microspheres, allowing spatially dispersed microspheres to be arranged into arrays with one unit per node. Droplet microlenses with various diameters can be adapted in the array, allowing for a wide range of spacing periods by applying different frequencies. In addition, through the continuous phase shifting in the x and y directions, this acoustic superlens array achieves on-demand moving for the parallel high-resolution virtual image capturing and scanning of nanostructures and biological cell samples. As a comparison, this noncontact and cost-effective acoustic manner can obtain more than ∼100 times the acquisition efficiency of a single lens, holding promise in advancing super-resolution microscopy and subcellular-level bioimaging.

Polarization-independent edge detection based on the spin-orbit interaction of light

In previous edge detection schemes based on the spin-orbit interaction of light, the direction and intensity of the edge-enhanced images are influenced by the incident polarization state. In this study, we develop an edge detection strategy that is insensitive to changes in both the incident polarization and the incident angle. The output intensity and transfer function remain entirely impervious to changes in incident polarization, being explicitly formulated as functions of the incident angle, specifically in terms of cot 2⁡θ i and cot⁡θ i , respectively. This behavior is attributed to the opposing nature of the polarization components E~r H-H and E~r V-V in the x-direction after undergoing mapping through the Glan polarizer, while the sum of polarization components E~r H-V and E~r V-H in the y-direction can be simplified to terms independent of incident polarization. Furthermore, we propose a metasurface design to achieve the required optical properties in order to realize the derived edge detection scheme.

Exploring plasmonic gradient metasurfaces for enhanced optical sensing in the visible spectrum

While conventional optical sensors hold historical significance, they face inherent limitations in sensitivity, operational intricacies, and bulky size. A breakthrough in this realm comes from the advent of metasurface sensors, which leverage nanoscale optical effects, thereby expanding the horizons of optical sensing applications. However, past methods employed in metasurface sensors predominantly rely on wavelength shifts or intensity changes with high-Q resonances, thereby significantly restricting the detection bandwidth. In response to these challenges, this study introduces a plasmonic gradient metasurface-based sensor (PGMS) designed for refractive index detection across a wide wavelength spectrum. Through the utilization of the Pancharatnam-Berry phase method, the PGMS achieves a distinctive 2π phase shift, facilitating the simultaneous generation of specular and deflected beams. The introduction of a far-field intensity ratio (I* = I +1/I 0) amplifies the change in optical response by maximizing the deflected beam's intensity while minimizing specular reflection. Experimental validation attests to the PGMS's consistent performance across diverse media and wavelengths, successfully overcoming challenges associated with oxidation issues. Furthermore, the incorporation of a normalization factor enhances the PGMS's sensing performance and versatility for broadband optical sensing, accommodating variations in the refractive index. Particularly sensitive in green wavelengths, the PGMS demonstrates its potential in visible spectrum applications, such as biomedical diagnostics and environmental monitoring. This research not only addresses challenges posed by conventional sensors but also propels optical sensing technologies into a realm of heightened sensitivity and adaptability.

Optical computing metasurfaces: applications and advances

Integrated photonic devices and artificial intelligence have presented a significant opportunity for the advancement of optical computing in practical applications. Optical computing technology is a unique computing system based on optical devices and computing functions, which significantly differs from the traditional electronic computing technology. On the other hand, optical computing technology offers the advantages such as fast speed, low energy consumption, and high parallelism. Yet there are still challenges such as device integration and portability. In the burgeoning development of micro-nano optics technology, especially the deeply ingrained concept of metasurface technique, it provides an advanced platform for optical computing applications, including edge detection, image or motion recognition, logic computation, and on-chip optical computing. With the aim of providing a comprehensive introduction and perspective for optical computing metasurface applications, we review the recent research advances of optical computing, from nanostructure and computing methods to practical applications. In this work, we review the challenges and analysis of optical computing metasurfaces in engineering field and look forward to the future development trends of optical computing.

Spin-Selective Angular Dispersion Control in Dielectric Metasurfaces for Multichannel Meta-Holographic Displays

Angle-dependent next-generation displays have potential applications in 3D stereoscopic and head-mounted displays, image combiners, and encryption for augmented reality (AR) and security. Metasurfaces enable such exceptional functionalities with groundbreaking achievements in efficient displays over the past decades. However, limitations in angular dispersion control make them unfit for numerous nanophotonic applications. Here, we propose a spin-selective angle-dependent all-dielectric metasurface with a unique design strategy to manifest distinct phase information at different incident angles of light. As a proof of concept, the phase masks of two images are encoded into the metasurface and projected at the desired focal plane under different angles of left circularly polarized (LCP) light. Specifically, the proposed multifunctional metasurface generates two distinct holographic images under LCP illumination at angles of +35 and -35°. The presented holographic displays may provide a feasible route toward multifunctional meta-devices for potential AR displays, encrypted imaging, and information storage applications.

Polychromatic Dual-Mode Imaging with Structured Chiral Photonic Crystals

Optical spatial differentiation is a typical operation of optical analog computing and can single out the edge to accelerate the subsequent image processing, but in some cases, overall information about the object needs to be presented synchronously. Here, we propose a multifunctional optical device based on structured chiral photonic crystals for the simultaneous realization of real-time dual-mode imaging. This optical differentiator is realized by self-organized large-birefringence cholesteric liquid crystals, which are photopatterned to encode with a special integrated geometric phase. Two highly spin-selective modes of second-order spatial differentiation and bright-field imaging are exhibited in the reflected and transmitted directions, respectively. Two-dimensional edges of both amplitude and phase objects have been efficiently enhanced in high contrast and the broadband spectrum. This work extends the ingenious building of hierarchical chiral nanostructures, enriches their applications in the emerging frontiers of optical computing, and boasts considerable potential in machine vision and microscopy.

Varifocal Metalenses: Harnessing Polarization-Dependent Superposition for Continuous Focal Length Control

Traditional varifocal lenses are bulky and mechanically complex. Emerging active metalenses promise compactness and design flexibility but face issues like mechanical tuning reliability and nonlinear focal length tuning due to additional medium requirements. In this work, we propose a varifocal metalens design based on superimposing light intensity distributions from two orthogonal polarization states. This approach enables continuous and precise focal length control within the visible spectrum, while maintaining relatively high focusing efficiencies (∼41% in simulation and ∼28% in measurement) and quality. In experimental validation, the metalens exhibited flexible tunability, with the focal length continuously adjustable between two spatial positions upon variation of the incident polarization angle. The MTF results showed high contrast reproduction and sharp imaging, with a Strehl ratio of >0.7 for all polarization angles. With compactness, design flexibility, and high focusing quality, the proposed varifocal metalens holds potential for diverse applications, advancing adaptive and versatile optical devices.