Spatial Information Lasing Enabled by Full-k-Space Bound States in the Continuum.

Optical amplification and massive information transfer in modern physics depend on stimulated radiation. However, regardless of traditional macroscopic lasers or emerging micro- and nanolasers, the information modulations are generally outside the lasing cavities. On the other hand, bound states in the continuum (BICs) with inherently enormous Q factors are limited to zero-dimensional singularities in momentum space. Here, we propose the concept of spatial information lasing, whose lasing information entropy can be correspondingly controlled by near-field Bragg coupling of guided modes. This concept is verified in gain-loss metamaterials supporting full-k-space BICs with both flexible manipulations and strong confinement of light fields. The counterintuitive high-dimensional BICs exist in a continuous energy band, which provide a versatile platform to precisely control each lasing Fourier component and, thus, can directly convey rich spatial information on the compact size. Single-mode operation achieved in our scheme ensures consistent and stable lasing information. Our findings can be expanded to different wave systems and open new scenarios in informational coherent amplification and high-Q physical frameworks for both classical and quantum applications.

Strain-Prompted Giant Flexo-Photovoltaic Effect in Two-Dimensional Violet Phosphorene Nanosheets.

As a second-order nonlinear optical phenomenon, the bulk photovoltaic (BPV) effect is expected to break through the Shockley-Queisser limit of thermodynamic photoelectron conversion and improve the energy conversion efficiency of photovoltaic cells. Here, we have successfully induced a strong flexo-photovoltaic (FPV) effect, a form of BPV effect, in strained violet phosphorene nanosheets (VPNS) by utilizing strain engineering at the h-BN nanoedge, which was first observed in nontransition metal dichalcogenide (TMD) systems. This BPV effect was found to originate from the disruption of inversion symmetry induced by uniaxial strain applied to VPNS at the h-BN nanoedge. We have revealed the intricate relationship between the bulk photovoltaic effect and strain gradients in VPNS through thickness-dependent photovoltaic response experiments. A bulk photovoltaic coefficient of up to 1.3 × 10-3 V-1 and a polarization extinction ratio of 21.6 have been achieved by systematically optimizing the height of the h-BN nanoedge and the thickness of VPNS, surpassing those of reported TMD materials (typically less than 3). Our results have revealed the fundamental relationship between the FPV effect and the strain gradients in low-dimensional materials and inspired further exploration of optoelectronic phenomena in strain-gradient engineered materials.

Polarization-insensitive high-numerical-aperture metalens for wide-field super-resolution imaging.

The development of super-oscillatory lens (SOL) offers opportunities to realize far-field label-free super-resolution microscopy. Most microscopes based on a high numerical aperture (NA) SOL operate in the point-by-point scanning mode, resulting in a slow imaging speed. Here, we propose a high-NA metalens operating in the single-shot wide-field mode to achieve real-time super-resolution imaging. An optimization model based on the exhaustion algorithm and angular spectrum (AS) theory is developed for metalens design. We numerically demonstrate that the optimized metalens with an NA of 0.8 realizes the imaging resolution (imaging pixel size) about 0.85 times the Rayleigh criterion. The metalens can achieve super-resolution imaging of an object with over 200 pixels, which is one order of magnitude higher than the unoptimized metalens. Our method provides an avenue toward single-shot far-field label-free super-resolution imaging for applications such as real-time imaging of living cells and temporally moving particles.

Electrical Transport and Dynamics of Confined DNA through Highly Conductive 2D Graphene Nanochannels.

Confining DNA in nanochannels is an important approach to studying its structure and transportation dynamics. Graphene nanochannels are particularly attractive for studying DNA confinement due to their atomic flatness, precise height control, and excellent mechanical strength. Here, using femtosecond laser etching and wetting transfer, we fabricate graphene nanochannels down to less than 4.3 nm in height, with the length-to-height ratios up to 103. These channels exhibit high stability, low noise, and self-cleaning ability during the long-term ionic current recording. We report a clear linear relationship between DNA length and the residence time in the channel and further utilize this relationship to differentiate DNA fragments based on their lengths, ranging widely from 200 bps to 48.5 kbps. The graphene nanochannel presented here provides a potential platform for label-free analyses and reveals fundamental insights into the conformational dynamics of DNA and proteins in confined space.

Broadband sensory networks with locally stored responsivities for neuromorphic machine vision.

As the most promising candidates for the implementation of in-sensor computing, retinomorphic vision sensors can constitute built-in neural networks and directly implement multiply-and-accumulation operations using responsivities as the weights. However, existing retinomorphic vision sensors mainly use a sustained gate bias to maintain the responsivity due to its volatile nature. Here, we propose an ion-induced localized-field strategy to develop retinomorphic vision sensors with nonvolatile tunable responsivity in both positive and negative regimes and construct a broadband and reconfigurable sensory network with locally stored weights to implement in-sensor convolutional processing in spectral range of 400 to 1800 nanometers. In addition to in-sensor computing, this retinomorphic device can implement in-memory computing benefiting from the nonvolatile tunable conductance, and a complete neuromorphic visual system involving front-end in-sensor computing and back-end in-memory computing architectures has been constructed, executing supervised and unsupervised learning tasks as demonstrations. This work paves the way for the development of high-speed and low-power neuromorphic machine vision for time-critical and data-intensive applications.

An Image-Based High-Throughput and High-Content Drug Screening Method Based on Microarray and Expansion Microscopy.

A high-efficiency drug screening method is urgently needed due to the expanding number of potential targets and the extremely long time required to assess them. To date, high throughput and high content have not been successfully combined in image-based drug screening, which is the main obstacle to improve the efficiency. Here, we establish a high-throughput and high-content drug screening method by preparing a superhydrophobic microwell array plate (SMAP) and combining it with protein-retention expansion microscopy (proExM). Primarily, we described a flexible method to prepare the SMAP based on photolithography. Cells were cultured in the SMAP and treated with different drugs using a microcolumn-microwell sandwiching technology. After drug treatment, proExM was applied to realize super-resolution imaging. As a demonstration, a 7 × 7 image array of microtubules was successfully collected within 3 h with 68 nm resolution using this method. Qualitative and quantitative analyses of microtubule and mitochondria morphological changes after drug treatment suggested that more details were revealed after applying proExM, demonstrating the successful combination of high throughput and high content.

Tunable Optical Activity in Twisted Anisotropic Two-Dimensional Materials.

Twisted van der Waals structures exhibit a variety of unusual electrical and optical phenomena and could provide a powerful means for designing nanodevices with tunable chiral properties. However, programming intrinsic chiral properties of the film on the atomic scale remains a great challenge due to the limitations of fabrication and measurement techniques. Here, we report a highly tunable large optical activity of twisted anisotropic two-dimensional (2D) materials, including black phosphorus (BP), ReS2, PdSe2, and α-MoO3, by varying the twist angle between the stacked layers. The chirality can be deliberately tailored through the engineering of the symmetry, band structure, and anisotropy of 2D materials, demonstrating the high tunability of the chirality. The results show the highest thickness-normalized ellipticity value (13.8 deg µm-1, twisted ReS2) and ellipticity value (1581 mdeg, twisted BP) among the systems based on 2D materials. It is also shown that the chiroptical response exists in an extremely large spectral range from the visible to the infrared. Furthermore, the twisted ReS2 enabled spin-selective control of the information transformation. These results show that highly controllable chirality in twisted 2D anisotropic materials has considerable potential in on-chip polarization optics, nano-optoelectronics, and biology.

3D bioprinting of corneal decellularized extracellular matrix: GelMA composite hydrogel for corneal stroma engineering.

Millions of individuals across the world suffer from corneal stromal diseases that impair vision. Fortunately, three-dimensional (3D) bioprinting technology which has revolutionized the field of regenerative tissue engineering makes it feasible to create personalized corneas. In this study, an artificial cornea with a high degree of precision, smoothness, and programmable curvature was prepared by using digital light processing (DLP) 3D bioprinting in one piece with no support structure, and the construct was then confirmed by optical coherence tomography (OCT). On the basis of this approach, we developed a novel corneal decellularized extracellular matrix/gelatin methacryloyl (CECM-GelMA) bioink that can produce complex microenvironments with highly tunable mechanical properties while retaining high optical transmittance. Furthermore, the composite hydrogel was loaded with human corneal fibroblasts (hCFs), and in vitro experiments showed that the hydrogel maintained high cell viability and expressed core proteins. In vivo tests revealed that the hydrogel might promote epithelial regeneration, keep the matrix aligned, and restore clarity. This demonstrates how crucial a role CECM plays in establishing a favorable environment that encourages the transformation of cell function. Therefore, artificial corneas that can be rapidly customized have a huge potential in the development of in vitro corneal matrix analogs.

Nonlinear and Anisotropic Ion Transport in Black Phosphorus Nanochannels.

Two-dimensional material nanochannels with molecular-scale confinement can be constructed by Van der Waals assembly and show unexpected fluid transport phenomena. The crystal structure of the channel surface plays a key role in controlling fluid transportation, and many strange properties are explored in these confined channels. Here, we use black phosphorus as the channel surface to enable ion transport along a specific crystal orientation. We observed a significant nonlinear and anisotropic ion transport phenomenon in the black phosphorus nanochannels. Theoretical results revealed an anisotropy of ion transport energy barrier on the black phosphorus surface, with the minimum energy barrier along the armchair direction approximately ten times larger than that along the zigzag direction. This difference in energy barrier affects the electrophoretic and electroosmotic transport of ions in the channel. This anisotropic transport, which depends on the orientation of the crystal, may provide new approaches to controlling the transport of fluids.

Design Strategies and Applications of Dimensional Optical Field Manipulation Based on Metasurfaces.

Recent rapid progress in metasurfaces is underpinned by the physics of local and nonlocal resonances and the modes coupling among them, leading to tremendous applications such as optical switching, information transmission, and sensing. In this review paper, an overview of the recent advances in a broad range of dimensional optical field manipulation based on metasurfaces categorized into different classes based on design strategies is provided. This review starts from the near-field optical resonances of artificial nanostructures and discusses the far-field optical wave manipulation based on fundamental mechanisms such as mode generation and mode coupling. The recent advances in optical field manipulation based on metasurfaces in different optical dimensions such as phase and polarization are summarized, and newly-developed dimensions such as the orbital angular momentum and the coherence dimensions resulting from phase modulation are discussed. Then, the recent achievements of multiplexing and multifunctional metasurfaces empowered by multidimensional optical field manipulation for optical information transmission and integrated applications are reviewed. Finally, the paper concludes with a few perspectives on emerging trends, possible directions, and existing challenges in this fast-developing field.

Characterization of Orbital Angular Momentum Quantum States Empowered by Metasurfaces.

Twisted photons can in principle carry a discrete unbounded amount of orbital angular momentum (OAM), which are of great significance for quantum communication and fundamental tests of quantum theory. However, the methods for characterization of the OAM quantum states present a fundamental limit for miniaturization. Metasurfaces can exploit new degrees of freedom to manipulate optical fields beyond the capabilities of bulk optics, opening a broad range of novel and superior applications in quantum photonics. Here we present a scheme to reconstruct the density matrix of the OAM quantum states of single photons with all-dielectric metasurfaces composed of birefringent meta-atoms. We have also measured the Schmidt number of the OAM entanglement by the multiplexing of multiple degrees of freedom. Our work represents a step toward the practical application of quantum metadevices for the measurement of OAM quantum states in free-space quantum imaging and communications.

Parallel Fourier ptychographic microscopy reconstruction method based on FPGA.

Fourier ptychographic microscopy (FPM) can bypass the limitation of spatial bandwidth product to get images with large field-of-view and high resolution. The complicated sequential iterative calculation in the FPM reconstruction process reduces the reconstruction efficiency of the FPM. Therefore, we propose a parallel FPM reconstruction method based on field programmable gate array (FPGA) to accelerate the FPM reconstruction process. Using this method, multiple sub-regions in the Fourier domain can be computed in parallel and we customize a dedicated high-performance computational architecture for this approach. We deploy 4 FPM reconstruct computing architectures with a parallelism of 4 in a FPGA to compute the FPM reconstruction process, achieving the speed nearly 180 times faster than traditional methods. The proposed method provides a new perspective of parallel computing for FPM reconstruction.

Preparation, properties and applications of two-dimensional superlattices.

As a combination concept of a 2D material and a superlattice, two-dimensional superlattices (2DSs) have attracted increasing attention recently. The natural advantages of 2D materials in their properties, dimension, diversity and compatibility, and their gradually improved technologies for preparation and device fabrication serve as solid foundations for the development of 2DSs. Compared with the existing 2D materials and even their heterostructures, 2DSs relate to more materials and elaborate architectures, leading to novel systems with more degrees of freedom to modulate material properties at the nanoscale. Here, three typical types of 2DSs, including the component, strain-induced and moiré superlattices, are reviewed. The preparation methods, properties and state-of-the-art applications of each type are summarized. An outlook of the challenges and future developments is also presented. We hope that this work can provide a reference for the development of 2DS-related research.

Realization of maximum optical intrinsic chirality with bilayer polyatomic metasurfaces.

Optical chirality plays a key role in optical biosensing and spin-selective optical field manipulation. However, the maximum optical intrinsic chirality, which is represented by near-unity circular dichroism (CD), is yet to be achieved in a wide bandwidth range based on nanostructures. Here, we utilize dielectric bilayer polyatomic metasurfaces to realize the maximum optical intrinsic chirality over a wide bandwidth range. The CD efficiency of the two designed metasurfaces with opposite chirality is 99.9% at 1350 nm and over 98% from 1340 nm to 1361 nm. Our work provides a straightforward and powerful method for the realization of maximum optical intrinsic chirality, which has great potential in spin-selective optical wave manipulation.

Automated Calculation of Liquid Crystal Sensing Images Based on Deep Learning.

Liquid crystal (LC)-based sensors have been extensively applied in the detection of chemical and biological events. However, the calculation of the optical images of the LC-based sensors is usually time-consuming and also might bring some errors due to the use of different judgment criteria by different users. In the present study, an automated calculation method for LC sensing images based on deep learning is provided. A convolutional network is trained with the prepared LC sensing images and their corresponding segmentation annotations to predict the positive responses. The ratio is calculated from the area of positive response to the total area selected by our image processing method. The robustness of the proposed algorithm is validated on both the test set and the label-free Cd2+ detection. The results show that the method based on deep learning can detect the positive response area in real time and the speed is much faster than the manual processing method. In addition, deep learning method can be directly applied to other label-free molecular detection assays.

Spatial Coherence Manipulation on the Disorder-Engineered Statistical Photonic Platform.

Coherence, similar to amplitude, polarization, and phase, is a fundamental characteristic of the light fields and is dominated by the statistical optical property. Although spatial coherence is one of the pivotal optical dimensions, it has not been significantly manipulated on the photonic platform. Here, we theoretically and experimentally manipulate the spatial coherence of light fields by loading different random phase distributions onto the wavefront with a metasurface. We achieve the generation of partially coherent light with a predefined degree of coherence and continuously modulate it from coherent to incoherent by controlling the phase fluctuation ranges or the beam sizes. This design strategy can be easily extended to manipulate arbitrary phase-only special beams with the same degree of coherence. Our approach provides straightforward rules to manipulate the coherence of light fields in an extra-cavity-based manner and paves the way for further applications in ghost imaging and information transmission in turbulent media.

A sliver deposition signal-enhanced optical biomolecular detection device based on reduced graphene oxide.

The development of high-sensitive biomolecular detection system is of great significance for diseases early diagnosis. The novel optical sensor based on the polarization-sensitive absorption of graphene has a great potential in biological detection. However, the detection sensitivity of the device can hardly meet the needs of clinical analysis currently. This study applies sliver deposition signal amplification to the optical biomolecular detection device based on reduced graphene oxide for the sensitive immunoassay. In redox cycling enzymatic silver deposition reaction, the more alkaline phosphatase label bound on chip surface will cause a faster silver deposition rate. The specific antibody detection confirms that the sliver deposition can enhance the detection signal significantly. In cardiac biomarker Creatine Kinase-MB measurement, the minimum detection concentration is 0.1 ng/mL. To be more important, within the range from detection limit to 10 ng/mL, the signal intensity is highly correlated with target protein concentration, so the biomolecular detection device can meet clinical assay requirements. The signal-enhanced optical biomolecular detection device based on reduced graphene oxide shows excellent sensitivity and selectivity, and provides a new strategy for biomolecules detection, which can be applied in diseases accurate prediction and diagnosis.

Tuning the Thermal Transport of Hexagonal Boron Nitride/Reduced Graphene Oxide Heterostructures.

Tuning the thermal properties of materials is considered to be of crucial significance for improving the performance of electronic devices. Along these lines, the development of van der Waals (vdW) heterostructures becomes an effective solution to affect the thermal transport mechanisms. However, vdW interactions usually block phonon transport, which leads to a reduction in thermal conductivity. In this work, we experimentally demonstrate a large enhancement in the thermal conductivity of a vdW heterostructure composed of few-layer hexagonal boron nitride (h-BN) and reduced graphene oxide (RGO). By controlling the reduction temperature of RGO and changing the thickness of h-BN, the thermal conductivity of the RGO is increased by nearly 18 times, namely, from 91 to 1685 W m-1 K-1. Photothermal scanning imaging is used to reveal the changes in the heat transfer and temperature distribution of the h-BN/RGO heterostructure. Both photothermal scanning and Raman spectroscopy experiments show that the vdW interaction between h-BN and RGO can greatly increase the thermal conductivity of RGO, which is in contrast to the conventional understanding that vdW interaction reduces thermal conductivity. Our work paves the way for the manipulation of the thermal conductivity of two-dimensional (2D) heterostructures, which could be of great significance for future nanoelectronic circuits.

A high-performance GelMA-GelMA homogeneous double-network hydrogel assisted by 3D printing.

Gelatin methacryloyl (GelMA) is a popular photocrosslinkable hydrogel that has been widely utilized in tissue engineering and regenerative medicine fields due to its excellent biocompatibility, biodegradability and cell response. However, the lack of mechanical properties limits its application. In the present study, a method for the preparation of a GelMA-GelMA (G-G) homogeneous double-network (DN) hydrogel to improve mechanical strength based on DLP 3D printing is proposed. The G-G DN hydrogel was fabricated and characterized in terms of microstructure, mechanical properties and rheological behavior. By modifying the degree of substitution (DS), the polymer concentration of double network crosslinking and the soak time, the novel G-G DN hydrogel could significantly improve the properties of strength, self-recovery and fatigue resistance. After all, the novel porous composite hydrogel (G-G DN hydrogel) could achieve more than twice that of the pure GelMA hydrogel, better fatigue resistance and printable ability. Therefore, it can be a potential choice of applications attracting great attention for its mechanical properties, great transmittance and biocompatibility.

High-performance heterogeneous FPGA data-flow architecture for Fourier ptychographic microscopy.

Fourier ptychographic microscopy (FPM) is a recently developed computational imaging technique that can achieve both high-resolution and a wide field-of-view via a sequence of low-resolution images. FPM is a complex iterative process, and it is difficult to meet the needs of rapid reconstruction imaging with the conventional FPM deployed on general purpose processors. In this paper, we propose a high-performance heterogeneous field-programmable gate array (FPGA) architecture based on the principle of full pipeline and the data-flow structure for the iterative reconstruction procedure of FPM. By optimizing the architecture network at gate-level logic circuits, the running time of the FPGA-based FPM reconstruction procedure is nearly 20 times faster than conventional methods. Our proposed architecture can be used to develop FPM imaging equipment that meets resource and performance requirements.