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Over the past years, nanostructured metalenses with thin form factors have been extensively studied for their potential in consumer and industrial applications. Despite significant advancements, current metalenses struggle to achieve high numerical aperture (NA), manufacturable structures, broad working bandwidth, and extended depth of focus (DOF) simultaneously. This paper introduces a comprehensive inverse design framework that facilitates the rapid development of polarization‐insensitive 3D metalenses, effective in both frequency and spatial domains. The framework employs shape‐constrained topology optimization to define horizontal ring profiles, along with discrete particle swarm optimization to manage discretized ring heights. Two immersed silicon carbide metalenses are demonstrated to showcase this framework's capability, providing near‐unity NAs for enhanced photon collection. The first design is an extended DOF metalens, exhibiting a DOF over four times the light wavelength and achieving a maximum diffraction efficiency of 23%, close to the theoretical limit. The second design achieves broadband achromaticity, suppressing chromatic aberrations across a wide 300 nm bandwidth (850–1150 nm) while maintaining an average diffraction efficiency of 10%. This methodology serves as a valuable tool for deploying functional metalenses with implications for nanophotonics, quantum optics, and quantum nanotechnology. [ABSTRACT FROM AUTHOR]

Wide‐field imaging is widely adopted due to its fast acquisition, cost‐effectiveness, and ease of use. Its extension to direct volumetric applications, however, is burdened by the trade‐off between resolution and depth of field (DOF), dictated by the numerical aperture of the system. It is demonstrated that such trade‐off is not intrinsic to wide‐field imaging, but stems from the spatial incoherence of light: images obtained through spatially coherent illumination are shown to have resolution and DOF independent of the numerical aperture. This fundamental discovery enables to demonstrate an optimal combination of coherent resolution‐DOF enhancement and incoherent tomographic sectioning for scanning‐free, wide‐field 3D microscopy on a multicolor histological section. [ABSTRACT FROM AUTHOR]

A novel high‐speed, high‐resolution 3D microscopy technique named BP‐TIDT is presented that quantifies the refractive index (RI) distribution of label‐free, transparent samples. This method combines a bi‐plane detection scheme (BP) with the transport of intensity diffraction tomography (TIDT), effectively circumventing the need for matched illumination conditions under high numerical aperture (NA) objectives, which enables 15 fps volume rates and 326 nm lateral resolution. The effectiveness and accuracy of the proposed approach are validated through high‐resolution imaging of polystyrene microspheres and HepG2 cells. Moreover, the wide‐ranging applicability of BP‐TIDT is demonstrated by investigating subcellular organelle motion, including mitochondria and lipid droplets, as well as the macroscopic apoptosis process in living COS‐7 cells. To the best of current knowledge, this is the first time that high spatial‐temporal resolution dynamic ODT results are obtained in a non‐interferometric and motion‐free manner, highlighting the potential of BP‐TIDT in advancing research on dynamic cellular processes. [ABSTRACT FROM AUTHOR]

Nanophotonic devices are optical platforms capable of unprecedented wavefront control. To push the limits of experimental device performance, scalable design methodologies that combine the simplicity and fabricability of conventional design paradigms with the extended capabilities of freeform optimization are required. A novel gradient‐based design framework for large‐area freeform metasurfaces is introduced in which nonlocal interactions between simply shaped nanostructures, placed on an irregular lattice, are tailored to produce high‐order hybridized modes that support customizable large‐angle scattering profiles. Utilizing this approach, multifunctional super‐dispersive metalenses are designed and experimentally demonstrated. The approach to high‐numerical‐aperture radial metalenses capable of diffraction limited focusing and the generation of donut‐shaped point spread functions is also extended. It is anticipated that these concepts will have utility in super‐resolution microscopy, particle trapping, additive manufacturing, and metrology applications that require ultra‐high numerical apertures. [ABSTRACT FROM AUTHOR]

Introducing super‐resolution techniques to imaging through scattering media potentially revolutionizes the technical analysis for many exotic applications, such as cell structures behind biological tissues. The main challenge is scattering media's inhomogeneous structures, which scramble the light path and create noise‐like speckle patterns, hindering object's visualization even at a low‐resolution level. Here, a computational method is proposed relying on the object's spatial and temporal fluctuation to visualize nanoscale objects through scattering media non‐invasively. Taking advantage of the optical memory effect and multiple frames, the point spreading function (PSF) of scattering media is estimated. Multiple images of fluctuating objects are obtained by deconvolution; then, the super‐resolution image is achieved by computing the higher‐order cumulants. Non‐linearity of high order cumulant significantly suppresses artifacts in the resulting images and enhances resolution by a factor of N$\sqrt N $, where N is the cumulant order. The proof‐of‐concept demonstrates a resolution of 266 nm at the 6th‐order cumulant with numerical aperture (NA) of 0.42, breaking the diffraction limit by a factor of 2.45. An adaptive approach is also demonstrated for imaging through dynamic scattering media. The non‐invasive super‐resolution speckle fluctuation imaging (NISFFI) presents a nanoscopy technique with straightforward imaging hardware configuration to visualize samples behind scattering media. [ABSTRACT FROM AUTHOR]

Metalenses have revolutionized optical technologies with their superior ability to manipulate light and the potential to replace conventional, bulky optical components. However, their commercialization is hindered by limitations in conventional manufacturing techniques, such as small patterning areas, low throughput, and high cost. In this study, two methods are introduced for scalable and wafer‐scale manufacturing of metalenses operating in the near‐infrared region, aimed at overcoming the abovementioned challenges. The first type of metalens is polarization‐independent and constructed using hydrogenated amorphous silicon cylindrical structures fabricated through direct photolithography. This metalens has a diameter of 1 cm and numerical aperture (NA) of 0.53. The focusing efficiency is confirmed at a 940 nm wavelength, and the focal spot profile approaches the diffraction limit. The second metalens is polarization‐dependent and fabricated using silicon nanoparticle‐embedded‐resin rectangular structures through a cost‐effective nanoimprinting method. This process can produce metalenses with a diameter of 5 mm and an NA of 0.53. Both types of metalenses demonstrate high‐resolution capabilities when imaging a 1951 USAF resolution test target and bioimaging. This research offers innovative pathways for the mass production and large‐scale fabrication of metalenses. It is believed that the work will accelerate the industrialization of metalenses, fostering further advances in optical technology. [ABSTRACT FROM AUTHOR]

Optical metalenses offer a compact approach for the development of nanoscale optical devices with various imaging functionalities. Realizing high‐quality images using metalenses with large numerical aperture (NA) requires eliminating unwanted optical aberrations. Existing strategies have largely focused only on correcting chromatic aberrations, and a metalens capable of simultaneously correcting chromatic and spherical aberrations has not yet been developed. Here, this issue is addresed by realizing an aplanatic phase profile for a red–green–blue (RGB) achromatic metalens, thereby demonstrating an RGB‐achromatic aplanatic metalens. This device consists of crystalline silicon nanostructures and it enables RGB‐achromatic aplanatic focusing with an NA of 0.635. The focal length of metalens remains unchanged at the three RGB wavelengths, whereas the associated focal spots are significantly smaller than those of an RGB‐achromatic metalens with spherical aberrations. An enhanced RGB imaging resolution is demonstrated, offering exciting opportunities to power up various imaging and display applications using flat metalenses. [ABSTRACT FROM AUTHOR]

Ultraviolet photoacoustic microscopy (UV‐PAM), based on the high intrinsic optical absorption of DNA/RNA, holds great promise for intraoperative label‐free histopathological imaging modalities. Although clinical histopathology requires high‐resolution images to observe individual cell structures, conventional UV‐PAM suffers from relatively low resolution compared to the clinical histological modalities. Notably, opto‐ultrasound beam combiners or ring‐shaped ultrasound transducers, which have been used as geometrically coaxial methods of conventional reflection‐mode UV‐PAMs, restrict the numerical apertures (NA) due to their long working distances and/or hollow structures. Here, an ultraviolet‐transparent ultrasound transducer (UV‐TUT) is demonstrated that enables high‐resolution reflection‐mode UV‐PAM by improving the NA (0.38) and consequent spatial resolution (0.47 ± 0.03 µm). The study has successfully demonstrated its superior performance with mouse brain tissue and performed photoacoustic histopathology with cancerous animal tissues. This work proposes the ultimate form of a label‐free reflection‐mode UV‐PAM system with the potential to boost the practical use of intraoperative photoacoustic histopathology. [ABSTRACT FROM AUTHOR]

As increasingly more demanding photonics applications are brought on‐chip, more complex design solutions are employed to deliver enhanced performance: e.g., meta‐molecules, inverse‐designed freeform structures, and multilayer metasurfaces. Instead, this study introduces anti‐reflective metasurfaces fabricated in a single nanolithography step that follows deposition of multiple dielectrics onto a substrate. Anti‐reflective metasurfaces offer fundamentally better transmission efficiencies compared to conventional equivalents. Conventional and anti‐reflective metalenses, both fabricated in the Ta2O5/SiO2 material platform for 461 nm operation, show an improvement in focusing efficiencies from ≈ 55% to ≈ 90% at low numerical apertures and from ≈ 35% to ≈ 65% at high numerical apertures. Simulations of ideal and imperfect metalenses indicate that anti‐reflective metasurfaces not only improve transmission at the design library level, but also reduce spurious diffraction and protect against higher‐order scattering. [ABSTRACT FROM AUTHOR]

Strongly confined electromagnetic (EM) fields generated by tightly focused light beams are applied widely in nano‐optics due to their vectorial characteristics. The inclusion of the longitudinal polarized component plays a crucial role in both the physical characteristics and practical uses of tightly focused vector beams. The acquisition of the distributions of the three orthogonal polarized components of these fields is advantageous for the comprehensive examination of their captivating physical phenomena and possible applications. However, this continues to pose a noteworthy obstacle, especially in the case of the fields that are generated by high numerical aperture objectives. A novel approach is proposed to quantifying the three mutually perpendicular polarizations simultaneously in the focal plane. The method utilizes a dual‐mode waveguide probe that is composed of a dielectric nanoparticle and a metal‐dielectric waveguide. This design allows for the simultaneous support of both transverse electric (TE) and transverse magnetic (TM) modes. Consequently, it enables the polarization recognition of scattering light in k‐space. Importantly, this method effectively eliminates any interference originating from the background light. The work involves an analysis of the theoretical notion of the probe and followed by experimental investigations. This approach holds promise for augmenting optical nanoscopy methodologies and their associated applications. [ABSTRACT FROM AUTHOR]

The rapidly advancing capabilities in nanophotonic design are enabling complex functionalities limited mainly by physical bounds. The efficiency of transmission is a major consideration, but its ultimate limit remains unknown for most systems. This study introduces a matrix formalism that puts a fundamental bound on the channel‐averaged transmission efficiency of any passive multi‐channel optical system based only on energy conservation and the desired functionality, independent of the interior structure and material composition. Applying this formalism to diffraction‐limited nonlocal metalenses with a wide field of view shows that the transmission efficiency must decrease with the numerical aperture for the commonly adopted designs with equal entrance and output aperture diameters. It also shows that reducing the size of the entrance aperture can raise the efficiency bound. This study reveals a fundamental limit on the transmission efficiency as well as provides guidance for the design of high‐efficiency multi‐channel optical systems. [ABSTRACT FROM AUTHOR]

Spatial frequency processing is an essential technology for extracting morphological information from an optical image. Although various Fourier-based flat optical elements have been proposed as spatial-frequency filters to realize image processing, their transfer functions are statically fixed once fabricated, thus limiting the versatile, dynamic functionalities and practical applications. Here, a novel practical tuning strategy is demonstrated to realize switchable spatial-frequency processing for edge-enhanced and bright-field imaging by employing a tunable hydrogel-scalable nanoslide. By utilizing multilayered metallic and hydrogel stacks construction, the nanoslide directly manipulates the optical spatial frequency in the wavevector domain and exhibits opposite image processing at different wavelength channels due to the cavity-induced wavelength-sensitivity. More intriguingly, via controlling the ambient humidity, the angular-dependent optical response of the nanoslide can be effectively tuned for dynamic edge-enhanced imaging due to the hydrogel's inflation from moisture. In addition, the nanoslide is readily fabricated at a large scale and integrated into compact imaging systems, such as a biomicroscope. With the advantages of a high numerical aperture -0.8, polarization-insensitive, microscopy-compatible, and facile architecture, the proposed hydrogel-based nanoslide can find potential applications in machine vision, real-time image processing, biological imaging, and analog computing. [ABSTRACT FROM AUTHOR]

Optical‐resolution photoacoustic microscopy (OR‐PAM) enables both high‐resolution and high‐contrast imaging of optical chromophores ranging from biological tissues to inorganic samples. The lateral spatial resolution of OR‐PAM depends on its optical configuration and is primarily determined by the numerical aperture of the objective lens. This study demonstrates a novel, lens‐free, shear‐force photoacoustic microscopy system using a tapered fiber, serving as a proof‐of‐concept toward the implementation of super‐resolution, near‐field scanning photoacoustic microscopy. An uncoated tapered fiber is attached to a quartz tuning fork, thereby maintaining the near‐field distance between the fiber and sample surface via a shear‐force detection mechanism. Light‐field simulation confirms an evanescent wave at the end of the uncoated, tapered fiber. Based on the photoacoustic simulation and 2D photoacoustic scanning experimental results, targets are imaged with high‐lateral resolutions of the order of 1.0 ± 0.3 µm. These results demonstrate the existence of near‐field photoacoustic signals and the potential for future development of super‐resolution, near‐field, scanning photoacoustic microscopy. [ABSTRACT FROM AUTHOR]

Optical metasurface is a 2D array of subwavelength meta‐atoms that arbitrarily manipulates amplitude, polarization, and wavefront of incident light, offering great advantages in miniaturization and integration. However, the presuppositions hidden in conventional unit‐cell‐based design approach, including discrete phase sampling, local periodicity approximation, and normal response, imply that the responses and interactions of meta‐atoms are almost impossible to be accurately modeled, thus impeding the effective design of high‐efficiency ultrahigh numerical aperture (NA) metalens. Here, based on vector diffraction theory and plane wave expansion method, theoretical limitation of metalens efficiency is comprehensively investigated. It is identified that for high‐NA metalens, theoretical focusing efficiency is limited by diffraction capability of vector field, while evanescent wave attenuation dominates theoretical efficiency decline for ultrahigh‐NA metalens. It is also shown that the efficiency of conventional metalens has a huge gap from theoretical limitation, owing to imperfect diffractive focusing and impedance mismatch reflections. To fill such efficiency gap, the high‐efficiency high‐NA freeform metalens based on topology optimization is further demonstrated. Particularly, topology geometric constraints are utilized to reduce minimum feature size while keeping high efficiency. The results could shed new light on the understanding and design of ultrahigh‐NA metalens and find promising applications in optical imaging, microscopy, and lithography. [ABSTRACT FROM AUTHOR]

Metalens research has made major advances in recent years. These advances rely on the simple design principle of arranging meta-atoms in regular arrays to create an arbitrary phase and polarization profile. Unfortunately, the concept of equally spaced meta-atoms reaches its limit for high deflection angles where the deflection efficiency decreases. The efficiency can be increased using nano-antennas with multiple elements, but their polarization sensitivity hinders their application in metalenses. Here, it is shown that by designing polarization-insensitive dimer nano-antennas and abandoning the principle of equally spaced unit cells, polarization-insensitive ultrahigh numerical aperture (NA = 1.48) oil-immersion operation with an efficiency of 42% can be demonstrated. This represents a significant improvement on other polarization-insensitive designs at visible wavelength. This single layer metalens is used to replace a conventional objective lens and demonstrates the confocal scanning microscopic imaging of a grating with a period of 300 nm at 532 nm operating wavelength. Overall, the results experimentally demonstrate a novel design concept that further improves metalens performance. [ABSTRACT FROM AUTHOR]

Femtosecond laser‐based fabrication of integrated photonic crystal waveguides inside of a transparent polymer is reported. In general, the fabrication of waveguides based on femtosecond laser‐induced positive refractive index modifications is feasible. However, in transparent polymers their performance is limited since only minor refractive index changes can be achieved with this technique. These restrictions can be circumvented by generating hexagonal "photonic lattice like" waveguides, which consist of negative refractive index modifications in the cladding, enabling light confinement in the unirradiated core. A comprehensive study on the fabrication of this new class of polymer waveguide is performed as well as a characterization of its numerical aperture, mode field diameter, and attenuation. In addition, integration of Bragg gratings based on positive and negative refractive index modulations within the waveguide's core is studied. Moreover, we highlight that polymer photonic crystal waveguides are compatible with common femtosecond laser‐based internal structuring processes, enabling the creation of monolithic optofluidic devices, which is demonstrated by the fabrication of a Fabry–Pérot interferometer. [ABSTRACT FROM AUTHOR]

Metasurface provides a powerful platform to correct the chromatic aberration of conventional lenses in a flexible, integratable, and ultra‐compact manner. Mid‐wavelength infrared has promised many exciting applications ranged from molecular fingerprint detection to low‐light‐level night vision. Developing broadband achromatic metalens in mid‐wavelength infrared becomes necessary to meet the increasingly urgent demands on high performance photonic devices. Here, we demonstrate the broadband achromatic metalenses from 3.5 to 5 µm with all‐silicon metasurfaces. Large phase dispersion control range is achieved to realize metalenses with both large numerical apertures and sample sizes while maintaining high focusing efficiency. The experimental results verify the diffraction‐limited achromatic focusing and imaging of the metalenses in mid‐wavelength infrared. Additionally, we also demonstrate the versatility by successfully implementing the generation of the broadband achromatic focusing optical vortex (L = 2). This work represents a solid step toward practical implementation of metalens and may find applications in mid‐wavelength infrared imaging and detections. [ABSTRACT FROM AUTHOR]

Focusing light into a tiny spot of high resolution is of significant importance in fields from imaging, photolithography to microwave engineering and sensing. However, most of the previous high resolution metalenses are constrained by their limited bandwidth and efficiency. In this paper, on the basis of Mikaelian lens derived from conformal transformation optics, a rectangular gradient refractive index lens with a relatively larger refractive index profile is put forward and manufactured by gradient isotropic dielectrics. Highly efficient (above 74%) broadband (7–14 GHz) achromatic high resolution focusing with full width at half maximum (FWHM) around 0.2λ as well as large numerical aperture (NA) of 2.04 has been accomplished. Measured results agree well with theoretical predictions, which makes the presented lens having a great potential to be employed in high resolution imaging systems. [ABSTRACT FROM AUTHOR]

For decades, accelerating beams have attracted considerable interest in fundamental physics and in various emerging applications. However, not only are conventional accelerating beam generators (such as spatial light modulators) bulky and diffraction‐inefficient, they also have a poorly resolved ability of phase manipulation that limits the accelerating beam's minimum size and maximum degree of curvature. In this study, a dielectric metasurface is used to generate highly focused nondiffractive Bessel‐like accelerating beams with predefined arbitrary trajectories within a broadband spectral range of 550–710 nm. In particular, a similar metasurface with a combined phase profile allows the generation of a Bessel‐like vortex beam with an ultrahigh numerical aperture of 0.79, resulting in a subwavelength beamwidth of 234 nm (≈0.43λ) down to the diffraction limit. In addition, various accelerating Bessel‐like beams and beam arrays with different predefined trajectories and characteristic beam parameters that are not otherwise achievable with conventional spatial light modulators are demonstrated with synthetic‐phase metasurfaces. This study promotes the diversity of Bessel‐like accelerating beams for practical applications in fields such as optical manipulation, optical storage, biomedical imaging, and material processing. [ABSTRACT FROM AUTHOR]

Metasurfaces are planarized and miniaturized versions of conventional optical elements. Subwavelength‐thick single‐layer metalenses have diffraction limited resolution for on‐axis imaging but relatively low resolution for off‐axis imaging due to off‐axial aberrations. The aberrations of planar single‐layer metalenses have been corrected by patterning two metasurfaces on both sides of a substrate to form metalens doublets with a thickness of hundreds of micrometers to millimeters. The multilevel diffractive lenses are demonstrated to achieve wide angle imaging with a thickness of several micrometers, however, the off‐axial aberrations are not compensated. Here, an epsilon‐greedy algorithm‐based scheme for achieving a planar wavelength‐thick single‐layer aberration‐compensated (SLAC) flat lens consisting of dielectric nanoring structures fabricated by 3D printing are proposed. The scheme is experimentally validated via a SLAC flat lens. This SLAC flat lens has a thickness of 1 µm, a numerical aperture of 0.45, a focal length of 1 mm, a full field of view (FOV) of 32° that enables aberration‐compensated imaging along the focal plane and monochromatic microscopic imaging with resolution better than 2.2 µm at a wavelength of 633 nm. This scheme can lead to ultrathin wide‐FOV flat lens designs as well as low‐cost mass production, which has various applications in miniscopes, mobile camera modules, and machine vision. [ABSTRACT FROM AUTHOR]

Inefficient and wide‐angle emission as well as low emission rate of optical nanoemitters (such as quantum dots) have been strongly limiting their practical applications in next‐generation nanophotonic devices, such as nanoscale light‐emitting diodes (LEDs) and on‐chip single photon sources. Optical nanoantennas provide a promising way to deal with these challenges. Yet, there has been no solution that can overcome these drawbacks simultaneously on a single device. Here, a hybrid plasmonic nanoantenna consisting of a silver nanocube positioned at the center of a gold concentric‐ring structure is proposed, which can simultaneously enhance the emission directionality and decay rate of quantum dots embedded in the nanogap beneath the nanocube while maintaining high quantum efficiency. Coupling quantum dots to this nanoantenna can result in 60% of the emitted photons collected by the first lens with a numerical aperture (NA) of 0.5 and 21% for a NA of 0.12. The total emission intensity and decay rate are enhanced by 121‐fold and 424‐fold, respectively, compared with quantum dots on a glass substrate. A high quantum efficiency above 50% is obtained in simulation. This novel platform can be applied to enhance various types of optical nanoemitters and to develop high‐speed directional nano‐LEDs and single photon sources. [ABSTRACT FROM AUTHOR]