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Convolutional neural network (CNN) is recognized as state of the art of deep learning algorithm, which has a good ability on the image classification and recognition. The problems of CNN are as follows: the precision, accuracy and efficiency of CNN are expected to be improved to satisfy the requirements of high performance. The main work is as follows: Firstly, wavelet convolutional neural network (wCNN) is proposed, where wavelet transform function is added to the convolutional layers of CNN. Secondly, wavelet convolutional wavelet neural network (wCwNN) is proposed, where fully connected neural network (FCNN) of wCNN and CNN are replaced by wavelet neural network (wNN). Thirdly, image classification experiments using CNN, wCNN and wCwNN algorithms, and comparison analysis are implemented with MNIST dataset. The effect of the improved methods are as follows: (1) Both precision and accuracy are improved. (2) The mean square error and the rate of error are reduced. (3) The complexitie of the improved algorithms is increased.

A Bessel beam has the properties of propagation invariance and a self-healing effect, leading to a variety of interesting phenomena and applications. Recently, as a planar diffractive element with miniaturized size, metasurfaces are widely employed to manipulate light in the subwavelength region, including generating a Bessel beam. However, such a metasurface-generated Bessel beam allows output light with no tunable functions. Here, with the interplay of the geometric phase and the dynamic phase, we propose a method to generate and allow conversion from any orthogonal polarizations to independent Bessel beams with a single-layer dielectric metasurface. The simulation results indicate that the arbitrary conversion between different Bessel beams is related to the spin-dependent orbit motion caused by the tight-focusing effect, leading to the singularity of the spot. This physical mechanism is well studied and the theoretical model for revealing the dependence of different incident polarization on the conversion dynamics is presented. Our approach paves a way for efficient generation and multifunctional applications, ranging from high-numerical-aperture devices to compact nanophotonic platforms for spin-dependent structured beams.

Background: Esophageal squamous cell carcinoma is one of the leading aggressive malignancies with high mortality. Semaphorin 3F has been reported to be involved in lymphangiogenesis by interacting the vascular endothelial growth factor C/neuropilin 2 axis. This study aimed to assess the clinical and functional role of semaphorin 3F and preliminarily evaluate the relationship between semaphorin 3F and lymph node metastasis in esophageal squamous cell carcinoma. Methods: The messenger RNA expression of semaphorin 3F was analyzed using quantitative real-time polymerase chain reaction. The expression differences of semaphorin 3F between patients having esophageal squamous cell carcinoma with and without lymph node metastasis were assessed, and the correlation of semaphorin 3F with vascular endothelial growth factor C and neuropilin 2 was estimated. The prognostic value of semaphorin 3F was evaluated using Kaplan-Meier survival curves and Cox regression analysis. Gain- and loss-functional cell experiments were performed to explore the biological function of semaphorin 3F, vascular endothelial growth factor C, and neuropilin 2. Results: The messenger RNA expression of semaphorin 3F was reduced in esophageal squamous cell carcinoma tissues compared with normal tissues, and lower semaphorin 3F expression was observed in patients having esophageal squamous cell carcinoma with positive lymph node metastasis. Semaphorin 3F expression was associated with lymph node metastasis and negatively correlated with vascular endothelial growth factor C and neuropilin 2. Lower semaphorin 3F expression was related to a poor overall survival of esophageal squamous cell carcinoma and served as an independent prognostic indicator. In esophageal squamous cell carcinoma cells, semaphorin 3F messenger RNA expression was also decreased compared with normal cells, and the overexpression of semaphorin 3F could significantly inhibit cell proliferation, migration, and invasion. The downregulation of vascular endothelial growth factor C and neuropilin 2 could inhibit cell proliferation, migration, and invasion of esophageal squamous cell carcinoma cells. Conclusion: All data indicate that semaphorin 3F serves as a potential prognostic biomarker and tumor suppressor of esophageal squamous cell carcinoma and may be involved in the lymph node metastasis development through regulating neuropilin 2.

Metalens, a prominent application of two-dimensional metasurfaces, has demonstrated powerful abilities even beyond traditional optical lenses. By manipulating the phase distribution of metalens composed of appropriately arranged nanoscale building blocks, the wavefront of incident wave can be controlled based on Huygens principle, thus achieving the desired reflected and transmitted wave for many different purposes. Metalenses will lead a revolution in optical imaging due to its flat nature and compact size, multispectral acquisition and even off-axis focusing. Here, we review the recent progress of metalenses presenting excellent properties, with a focus on the imaging application using these metalenses. We firstly discuss the mechanism for achieving metalenses with high efficiency, large numerical aperture, controlling the chromatic dispersion or monochromatic aberrations and large area fabrication. Then, we review several important imaging applications including wide-band focusing imaging, polarization dependent imaging, light field imaging and some other significant imaging systems in different areas. Finally, we make a conclusion with an outlook on the future development and challenges of this developing research field.

Metalenses with non-trivial performance, abundant applications, and tremendous potential, have emerged as a flat optical element or configuration in recent years. The increasing concerns about how to integrate more functions into a single metalens have become a hot topic. Here, based on a genetic algorithm, we demonstrate several metalenses with more than two optical functions depending on the wavelength of light. We first design three arbitrary chromatic dispersive metalenses, whose focal planes can be determined at will at different wavelengths. Then, a metalens-based color router is presented, which is able to guide and focus the light with four wavelengths to different positions. Furthermore, we exhibit a tri-functional structured light generator to produce focused beam, focused orbital angular momentum beam, and the Bessel beam at three wavelengths, respectively. Our results may have potential applications in dispersion manipulation, optical micro-manipulation, and subwavelength resolution spectral imaging.

Optical tweezers (OTs) and optical spanners (OSs) are powerful tools of optical manipulation, which are responsible for particle trapping and rotation, respectively. Conventionally, the OT and OS are built using bulky three-dimensional devices, such as microscope objectives and spatial light modulators. Recently, metasurfaces are proposed for setting up them on a microscale platform, which greatly miniaturizes the systems. However, the realization of both OT and OS with one identical metasurface is posing a challenge. Here, we offer a metasurface-based solution to integrate the OT and OS. Using the prevailing approach based on geometric and dynamic phases, we show that it is possible to construct an output field, which promises a high-numerical-aperture focal spot, accompanied with a coaxial vortex. Optical trapping and rotation are numerically demonstrated by estimating the mechanical effects on a particle probe. Moreover, we demonstrate an on-demand control of the OT-to-OS distance and the topological charge possessed by the OS. By revealing the OT–OS metasurfaces, our results may empower advanced applications in on-chip particle manipulation.

Two organic–inorganic iodobismuthates, C5H6NBiI4 ([py][BiI4]) and C6H8NBiI4 ([mepy][BiI4]), have been prepared with their structures revealed by single-crystal X-ray diffraction. One-dimensional BiI4− anionic chains built by edge-sharing BiI6 octahedra were found in both materials; short I⋯I, I⋯C contacts and hydrogen bonding give rise to three-dimensional intermolecular interactions. Both compounds are semiconductors, with band gaps of around 2.0 eV, and the contribution from the organic moieties to the conduction band minimum has been derived by density functional theory. Solid-state optical and electrochemical studies performed on powders and thin films were carried out, and their stabilities under an ambient environment have been demonstrated. Their use as the absorber layer in printable mesoscopic solar cells without any hole transport material has led to efficiencies up to 0.9%, showing a promising new approach towards the development of lead-free third-generation photovoltaic materials.

Metasurfaces are 2D metamaterials composed of subwavelength nanoantennas according to specific design. They have been utilized to precisely manipulate various parameters of light fields, such as phase, polarization, amplitude, etc., showing promising functionalities. Among all meta-devices, the metalens can be considered as the most basic and important application, given its significant advantage in integration and miniaturization compared with traditional lenses. However, the resonant dispersion of each nanoantenna in a metalens and the intrinsic chromatic dispersion of planar devices and optical materials result in a large chromatic aberration in metalenses that severely reduces the quality of their focusing and imaging. Consequently, how to effectively suppress or manipulate the chromatic aberration of metalenses has attracted worldwide attention in the last few years, leading to variety of excellent achievements promoting the development of this field. Herein, recent progress in chromatic dispersion control based on metalenses is reviewed.

The chromatic aberration of metasurfaces limits their application. How to cancel or utilize the large chromatic dispersion of metasurfaces becomes an important issue. Here, we design Si-based metasurfaces to realize flexible chromatic dispersion manipulation in mid-infrared region. We demonstrate the broadband achromatic metalens and achromatic gradient metasurface to cancel the chromatic aberration over a continuous bandwidth (8–12 μm). In contrast, the metalens and gradient metasurface with enhanced chromatic dispersion have also been realized, where the focal length and deflection angle with different wavelengths vary more significantly than the conventional devices designed with geometric phase. These demonstrations indicate promising potential applications.

Supercapacitors are well-known as promising energy storage devices capable of bridging the gap between conventional electrolytic capacitors and batteries to deliver both high power and energy densities for applications in electric vehicles and a smart energy grid. However, many reported instances of high-capacitance pseudocapacitors employ strong Faradaic reactions that hinder fast charge–discharge cycles and long-term stability, limiting their commercial viability. In this study, we utilise an economical and solution-processable procedure to fabricate a Cs3Bi2I9-based symmetric supercapacitor employing both electric double layer capacitance and pseudocapacitance with an aqueous NaClO4 electrolyte to deliver an outstanding device areal capacitance of 2.4 F cm−2 and specific capacitance of 280 F g−1. The Cs3Bi2I9 device achieves an excellent 88% capacitance retention after 5000 charge–discharge cycles, proving its long-term cycle stability and promise as a practical supercapacitor. We characterise the time-dependent charge storage mechanisms through cyclic voltammetry and electrochemical impedance spectroscopy to find that electrostatic charge accumulation predominates at high potentials (0.3–0.6 V) whereas weak, Faradaic charge adsorption and pore penetration bolster charge storage at lower potentials (0.0–0.2 V).