Dielectric Metasurface for Synchronously Spiral Phase Contrast and Bright-Field Imaging

Computing Metasurface Enabled Quantum Phase Distillation

Quantum image distillation aims to extract the signal image from a mixture of the signal and noise images that are indistinguishable in terms of spectrum and polarization, a process that is unachievable with classical methods. However, in contrast to the amplitude image, phase distillation is challenging via direct spatial or temporal correlation of photon pairs. Incorporating with the polarization entanglement of photon pairs, it is demonstrated here that the phase signal can be quickly distilled by using an integrated computing metasurface to solve the Poisson equation. The proposed technique remains robust even with noise levels two orders higher than the signal, with potential applications in quantum communication and cryptography. Based on the present scheme, it also enables the measurement of photon wave function and the achievement of noninterferometric quantum-enhanced quantitative phase imaging. Our work involving the integrated-metasurface analogue computing paves the way for advancing efficient and rapid quantum information and image processing.

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.

Multifunctional Meta-optic Azimuthal Shear Interferometer

Azimuthal shear interferometry is a versatile tool for analyzing wavefront asymmetries. However, conventional systems are bulky, alignment-sensitive, and prone to nonuniform shear. We present a broadband, compact, and robust meta-optics-based azimuthal shear interferometer in a common-path configuration, reducing the system size to the millimeter scale. Unlike conventional designs, the meta-optic azimuthal shear interferometer utilizes the localized wavefront modulation capabilities of meta-optics to achieve uniform azimuthal shear displacement independent of the radial position, significantly enhancing accuracy and stability. Our approach eliminates the need for bulky optical components and precise multipath alignment, making it more resilient to environmental disturbances. Its multifunctionality is demonstrated through applications in all-optical edge detection, differential interference contrast microscopy, and aberrated wavefront sensing. These results underscore its potential for real-time analog image processing, advanced optical imaging, and optical testing.

Quantitative Phase Imaging with a Meta-Based Interferometric System

Optical phase imaging has become a pivotal tool in biomedical research, enabling label-free visualization of transparent specimens. Traditional optical phase imaging techniques, such as Zernike phase contrast and differential interference contrast microscopy, fall short of providing quantitative phase information. Digital holographic microscopy (DHM) addresses this limitation by offering precise phase measurements; however, off-axis configurations, particularly Mach-Zehnder and Michelson-based setups, are often hindered by environmental susceptibility and bulky optical components due to their separate reference and object beam paths. In this work, we have developed a meta-based interferometric quantitative phase imaging system using a common-path off-axis DHM configuration. A meta-biprism, featuring two opposite gradient phases created using GaN nanopillars selected for their low loss and durability, serves as a compact and efficient beam splitter. Our system effectively captures the complex wavefronts of samples, enabling the retrieval of quantitative phase information, which we demonstrate using standard resolution phase targets and human lung cell lines. Additionally, our system exhibits enhanced temporal phase stability compared to conventional off-axis DHM configurations, reducing phase fluctuations over extended measurement periods. These results not only underline the potential of metasurfaces in advancing the capabilities of quantitative phase imaging but also promise significant advancements in biomedical imaging and diagnostics.

Broadband and polarization-independent complex amplitude modulation using a single layer dielectric metasurface

Precise control over amplitude and phase across the entire space is crucial for generating user-defined wavefronts and has significant value for designing flexible optical systems. Metasurfaces have emerged as compact and effective platforms for such control, offering high spatial resolution and continuity. However, traditional methods only work at specific wavelengths or polarization states, and the demonstration of full space complex amplitude control for broadband and unpolarized light remains limited. In this study, we leverage the principle of dual meta-atom interference to simultaneously modulate amplitude and phase using a single layer metasurface. Using a randomly polarized light source, nanoprinting and Fourier holography displays of complex patterns are achieved within the wavelength range of 480-640 nm, and the results are consistent with simulations. This approach presents several key advantages: continuous, precise and robust modulation of complex amplitude as well as polarization-independent and broadband response, which significantly reduce constraints on the light source's property and fabrication and make it well-suited for a variety of practical applications, including holographic displays, high-capacity communications, computational imaging, and laser beam processing.

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.

Optical edge detection with adjustable resolution using the planar liquid crystal Alvarez lens

In this Letter, we propose an optical edge detection method with adjustable resolution using a planar liquid crystal Alvarez lens (LCAL). A planar liquid crystal Alvarez lens was fabricated by laser direct writing. When the focal length of the liquid crystal Alvarez lens changes and linearly polarized light (LP) passes through the liquid crystal Alvarez lens, the angle between the emitted left-handed circularly polarized light and right-handed circularly polarized light can be controlled, enabling adjustable resolution edge detection. The lens can adjust an edge width from 32.5 μm to 73.7 μm without requiring any rotation or axial displacement. Moreover, it can accomplish comprehensive edge detection across a broadband spectral range. This edge detection method could offer a potential application value for compact optical devices such as high-contrast microscopes and smart cameras.

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.

MEMS-metasurface-enabled mode-switchable vortex lasers

Compared to conventional lasers limited to generating static modes, mode-switchable lasers equipped with adjustable optics significantly enhance the flexibility and versatility of coherent light sources. However, most current approaches to achieving mode-switchable lasers depend on conventional, i.e., inherently bulky and slow, optical components. Here, we demonstrate fiber lasers empowered by electrically actuated intracavity microelectromechanical system (MEMS)-based optical metasurface (MEMS-OMS) enabling mode switching between fundamental Gaussian and vortex modes at ~1030 nm. By finely adjusting the voltage applied to the MEMS mirror, high-contrast switching between Gaussian (l = 0) and vortex (l = 1, 2, 3, and 5, depending on the OMS arrangement) laser modes is achieved, featuring high mode purities (>95%) and fast responses (~100 microseconds). The proposed intracavity MEMS-OMS-enabled laser configuration provides an at-source solution for generating high-purity fast-switchable laser modes, with potential applications ranging from advanced optical imaging to optical tweezers, optical machining, and intelligent photonics.

Dielectric Metasurfaces for Broadband Phase-Contrast Relief-Like Imaging

The visualization of transparent specimens in traditional light microscopy is impeded by insufficient intrinsic contrast, prompting the development of advanced contrast-enhancement methodologies to transmute minute phase discrepancies into detectable amplitude alterations. While existing methods excel in either phase-contrast imaging (contrast-enhanced image of whole objects) or relief-like imaging (deceptive three-dimensional images), it would be of great significance to seamlessly integrate both capabilities in the same device. Here, we propose a novel metasurface-assisted half-side phase-contrast technique capable of simultaneous phase-contrast and relief-like imaging across the visible spectrum, which is realized by introducing a ±π/2 phase shift to a half-side diffracted wave emitted by the objects. Our method showcases successful application to diverse specimens, including a transparent silica disk and a frog egg cell. Our work substantiates high-quality microscopic imaging of various transparent specimens, which has profound implications in cellular biology, materials science, and medical diagnostics.

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.

Broadband and parallel multiple-order optical spatial differentiation enabled by Bessel vortex modulated metalens

Optical analog image processing technology is expected to provide an effective solution for high-throughput and real-time data processing with low power consumption. In various operations, optical spatial differential operations are essential in edge extraction, data compression, and feature classification. Unfortunately, existing methods can only perform low-order or selectively perform a particular high-order differential operation. Here, we propose and experimentally demonstrate a Bessel vortex modulated metalens composed of a single complex amplitude metasurface, which can perform multiple-order radial differential operations over a wide band by presetting the order of the corresponding Bessel vortex. This architecture further enables angle multiplexing to create multiple information channels that synchronously perform multi-order spatial differential operations, indicating the superiority of the proposed devices in parallel processing. Our approach may find various applications in artificial intelligence, machine vision, autonomous driving, and advanced biomedical imaging.

Full-space metasurfaces for independent manipulation of transmission and reflection

In recent years, beam manipulation using metasurfaces has evolved from being limited to either a transmission or reflection space to encompassing a full space. However, existing methods still inevitably require complex systems and are unable to achieve continuous and arbitrary phase manipulation. Here, one type of a bilayer metasurface is proposed to simultaneously manipulate reflection and transmission phases continuously and independently, which also makes the optical system more compact without requiring any analyzers and enhances the degree of freedom for full-space beam manipulation. As a proof-of-concept demonstration, one device is designed to show different holograms in transmission and reflection spaces. Additionally, the Dammann grating designed in the reflection hologram increases the information capacity. The proposed method may pave the way toward achieving a variety of applications such as multi-channel beam manipulation and multifunctional optical devices.

All-optical complex field imaging using diffractive processors

Complex field imaging, which captures both the amplitude and phase information of input optical fields or objects, can offer rich structural insights into samples, such as their absorption and refractive index distributions. However, conventional image sensors are intensity-based and inherently lack the capability to directly measure the phase distribution of a field. This limitation can be overcome using interferometric or holographic methods, often supplemented by iterative phase retrieval algorithms, leading to a considerable increase in hardware complexity and computational demand. Here, we present a complex field imager design that enables snapshot imaging of both the amplitude and quantitative phase information of input fields using an intensity-based sensor array without any digital processing. Our design utilizes successive deep learning-optimized diffractive surfaces that are structured to collectively modulate the input complex field, forming two independent imaging channels that perform amplitude-to-amplitude and phase-to-intensity transformations between the input and output planes within a compact optical design, axially spanning ~100 wavelengths. The intensity distributions of the output fields at these two channels on the sensor plane directly correspond to the amplitude and quantitative phase profiles of the input complex field, eliminating the need for any digital image reconstruction algorithms. We experimentally validated the efficacy of our complex field diffractive imager designs through 3D-printed prototypes operating at the terahertz spectrum, with the output amplitude and phase channel images closely aligning with our numerical simulations. We envision that this complex field imager will have various applications in security, biomedical imaging, sensing and material science, among others.

Metalens for Accelerated Optoelectronic Edge Detection under Ambient Illumination

Analog systems may allow image processing, such as edge detection, with low computational power. However, most demonstrated analog systems, based on either conventional 4-f imaging systems or nanophotonic structures, rely on coherent laser sources for illumination, which significantly restricts their use in routine imaging tasks with ambient, incoherent illumination. Here, we demonstrated a metalens-assisted imaging system that can allow optoelectronic edge detection under ambient illumination conditions. The metalens was designed to generate polarization-dependent optical transfer functions (OTFs), resulting in a synthetic OTF with an isotropic high-pass frequency response after digital subtraction. We integrated the polarization-multiplexed metalens with a polarization camera and experimentally demonstrated single-shot edge detection of indoor and outdoor scenes, including a flying airplane, under ambient sunlight illumination. The proposed system showcased the potential of using polarization multiplexing for the construction of complex optical convolution kernels toward accelerated machine vision tasks such as object detection and classification under ambient illumination.

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.

Single-shot deterministic complex amplitude imaging with a single-layer metalens

Conventional imaging systems can only capture light intensity. Meanwhile, the lost phase information may be critical for a variety of applications such as label-free microscopy and optical metrology. Existing phase retrieval techniques typically require a bulky setup, multiframe measurements, or prior information of the target scene. Here, we proposed an extremely compact system for complex amplitude imaging, leveraging the extreme versatility of a single-layer metalens to generate spatially multiplexed and polarization phase-shifted point spread functions. Combining the metalens with a polarization camera, the system can simultaneously record four polarization shearing interference patterns along both in-plane directions, thus allowing the deterministic reconstruction of the complex amplitude light field in a single shot. Using an incoherent light-emitting diode as the illumination, we experimentally demonstrated speckle-noise-free complex amplitude imaging for both static and moving objects with tailored magnification ratio and field of view. The miniaturized and robust system may open the door for complex amplitude imaging in portable devices for point-of-care applications.

Intelligent Phase Contrast Meta-Microscope System

Phase contrast imaging techniques enable the visualization of disparities in the refractive index among various materials. However, these techniques usually come with a cost: the need for bulky, inflexible, and complicated configurations. Here, we propose and experimentally demonstrate an ultracompact meta-microscope, a novel imaging platform designed to accomplish both optical and digital phase contrast imaging. The optical phase contrast imaging system is composed of a pair of metalenses and an intermediate spiral phase metasurface located at the Fourier plane. The performance of the system in generating edge-enhanced images is validated by imaging a variety of human cells, including lung cell lines BEAS-2B, CLY1, and H1299 and other types. Additionally, we integrate the ResNet deep learning model into the meta-microscope to transform bright-field images into edge-enhanced images with high contrast accuracy. This technology promises to aid in the development of innovative miniature optical systems for biomedical and clinical applications.

Dielectric Metasurface Enabled Compact, Single-Shot Digital Holography for Quantitative Phase Imaging

Quantitative phase imaging (QPI) enables nondestructive, real-time, label-free imaging of transparent specimens and can reveal information about their fundamental properties such as cell size and morphology, mass density, particle dynamics, and cellular fluctuations. Development of high-performance and low-cost quantitative phase imaging systems is thus required in many fields, including on-site biomedical imaging and industrial inspection. Here, we propose an ultracompact, highly stable interferometer based on a single-layer dielectric metasurface for common path off-axis digital holography and experimentally demonstrate quantitative phase imaging. The interferometric imaging system leveraging an ultrathin multifunctional metasurface captures image plane holograms in a single shot and provides quantitative phase information on the test samples for extraction of its physical properties. With the benefits of planar engineering and high integrability, the proposed metasurface-based method establishes a stable miniaturized QPI system for reliable and cost-effective point-of-care devices, live cell imaging, 3D topography, and edge detection for optical computing.

Polarization-multiplexed metasurface enabled tri-functional imaging

Diffraction-limited focusing imaging, edge-enhanced imaging, and long depth of focus imaging offer crucial technical capabilities for applications such as biological microscopy and surface topography detection. To conveniently and quickly realize the microscopy imaging of different functions, the multifunctional integrated system of microscopy imaging has become an increasingly important research direction. However, conventional microscopes necessitate bulky optical components to switch between these functionalities, suffering from the system's complexity and unstability. Hence, solving the problem of integrating multiple functions within an optical system is a pressing need. In this work, we present an approach using a polarization-multiplexed tri-functional metasurface, capable of realizing the aforementioned imaging functions simply by changing the polarization state of the input and output light, enhancing the system structure's compactness and flexibility. This work offers a new avenue for multifunctional imaging, with potential applications in biomedicine and microscopy imaging.

Spiral-phase-objective for a compact spiral-phase-contrast microscopy

Spiral-phase-contrast imaging, which utilizes a spiral phase optical element, has proven to be effective in enhancing various aspects of imaging, such as edge contrast and shadow imaging. Typically, the implementation of spiral-phase-contrast imaging requires the formation of a Fourier plane through a 4f optical configuration in addition to an existing optical microscope. In this study, we present what we believe to be a novel single spiral-phase-objective, integrating a spiral phase plate, which can be easily and simply applied to a standard microscope, such as a conventional objective. Using a new hybrid design approach that combines ray-tracing and field-tracing simulations, we theoretically realized a well-defined and high-quality vortex beam through the spiral-phase-objective. The spiral-phase-objective was designed to have conditions that are practically manufacturable while providing predictable performance. To evaluate its capabilities, we utilized the designed spiral-phase-objective to investigate isotropic spiral phase contrast and anisotropic shadow imaging through field-tracing simulations, and explored the variation of edge contrast caused by changes in the thickness of the imaging object.

Simultaneous chiral polarization and edge enhancement imaging enabled by a single geometric-phase-based element

In this Letter, we propose a multifunctional imaging system enabled by a single geometric-phase-based liquid crystal (LC) element, which integrates chiral polarization and edge enhancement imaging. The element is located at the frequency domain plane in a 4F imaging system, and the phase profile of the element consists of a fork grating in the x direction and a grating in the y direction, which provide edge enhancement and chiral polarization imaging capabilities. Benefiting from the tunable property of the LC, the system can be switched from a polarization and edge imaging mode to the normal conventional imaging mode which is capable of conveniently acquiring the needed image information. Experiments demonstrate that the system can easily achieve multifunctional and switchable imaging, which agrees well with our design, and our LC element can work in the broadband spectrum because of the geometric phase modulation. The multifunctional strategy used here can effectively avoid the need to increase the size of the original microscopic system and the need for additional mechanical rotation of components. We believe that the proposed system with the additional advantages of electric control and tunability can find applications in biological imaging, medical detection, and optical computing.