Underwater dynamic polarization imaging without dependence on the background region.

Active-polarization imaging holds significant promise for achieving clear underwater vision. However, only static targets were considered in previous studies, and a background region was required for image restoration. To address these issues, this study proposes an underwater dynamic polarization imaging method based on image pyramid decomposition and reconstruction. During the decomposition process, the polarized image is downsampled to generate an image pyramid. Subsequently, the spatial distribution of the polarization characteristics of the backscattered light is reconstructed by upsampling, which recovered the clear scene. The proposed method avoids dependence on the background region and is suitable for moving targets with varying polarization properties. The experimental results demonstrate effective elimination of backscattered light while sufficiently preserving the target details. In particular, for dynamic targets, processing times that fulfill practical requirements and yield superior recovery effects are simultaneously obtained.

Duplex-Hierarchy Representation Learning for Remote Sensing Image Classification.

Remote sensing image classification (RSIC) is designed to assign specific semantic labels to aerial images, which is significant and fundamental in many applications. In recent years, substantial work has been conducted on RSIC with the help of deep learning models. Even though these models have greatly enhanced the performance of RSIC, the issues of diversity in the same class and similarity between different classes in remote sensing images remain huge challenges for RSIC. To solve these problems, a duplex-hierarchy representation learning (DHRL) method is proposed. The proposed DHRL method aims to explore duplex-hierarchy spaces, including a common space and a label space, to learn discriminative representations for RSIC. The proposed DHRL method consists of three main steps: First, paired images are fed to a pretrained ResNet network for extracting the corresponding features. Second, the extracted features are further explored and mapped into a common space for reducing the intra-class scatter and enlarging the inter-class separation. Third, the obtained representations are used to predict the categories of the input images, and the discrimination loss in the label space is minimized to further promote the learning of discriminative representations. Meanwhile, a confusion score is computed and added to the classification loss for guiding the discriminative representation learning via backpropagation. The comprehensive experimental results show that the proposed method is superior to the existing state-of-the-art methods on two challenging remote sensing image scene datasets, demonstrating that the proposed method is significantly effective.

Whole exome sequencing discloses a pathogenic MTM1 gene mutation in a continuous polyhydramnios family in China: Case report and literature review.

Polyhydramnios can be caused by genetic defects at times. However, to establish an accurate diagnosis and provide a precise prenatal consultation in a given case is still a great challenge toward obstetricians. To uncover the genetic cause of polyhydramnios in the two consecutive pregnancies, we performed whole-exome sequencing of DNA for the second suffering fetuses, their parents, and targeted sanger sequencing of other members of this family. We discovered a hemizygous truncating variant in MTM1 gene, c.438_439 del (p. H146Q fs*10) in this Chinese family. In the light of the molecular discoveries, the fetus's clinical phenotype was considered to be a good fit for X-linked myotubular myopathy (XLMTM). There is no related research to the prenatal manifestations of MTM1-related XLMTM among Chinese population, and this is the first one to present. Though the etiology of polyhydramnios is complicated, WES may provide us with a creative avenue in prenatal diagnosis.

High-efficiency dual-layer grating coupler for vertical fiber-chip coupling in two polarizations.

Efficient coupling between optical fibers and high-index-contrast silicon waveguides is essential for the development of integrated nanophotonics. Herein, a high-efficiency dual-layer grating coupler is demonstrated for vertical polarization-diversity fiber-chip coupling. The two waveguide layers are orthogonally distributed and designed for y- and x-polarized L P 01 fiber modes, respectively. Each layer consists of two 1D stacked gratings, allowing for both perfectly vertical coupling and high coupling directionality. The gratings are optimized using the particle swarm algorithm with a preset varying trend of parameters to thin out the optimization variables. The interlayer thickness is determined to ensure efficient coupling of both polarizations. The optimized results exhibit record highs of 92% (-0.38d B) and 85% (-0.72d B) 3D finite-difference time-domain simulation efficiencies for y and x polarizations, respectively. The polarization-dependent loss (PDL) is below 2 dB in a 160 nm spectral bandwidth with cross talk between the two polarizations less than -24d B. Fabrication imperfections are also investigated. Dimensional offsets of ±10n m in etching width and ±8 nm in lateral shift are tolerated for a 1 dB loss penalty. The proposed structure offers an ultimate solution for polarization diversity coupling schemes in silicon photonics with high directionality, low PDL, and a possibility to vertically couple.

Ecological risk assessment of heavy metals in riverine sediments of rural area driven by urbanization.

Rural revitalization denotes the gathering of large populations in rural areas and the subsequent gradual urbanization. Rural environments have been deteriorated by heavy metals (HMs) over the last few years. Without the existence of large-scale industries, the accumulation of HMs in sediments due to population aggregation in rural environments needs to be scientifically confirmed. Therefore, in this study we first understand the sediment pollution in rural environments in China and across the globe, and subsequently investigate HMs in sediments in rural micro water. The study area, Sichuan Province, China, was divided into two areas, namely, sparsely populated areas (SPA) and densely populated areas (DPA). Eight typical HMs (As, Zn, Ni, Hg, Cd, Cr, Cu, and Pb) were selected to target in riverine sediments, and the content and spatial distribution characteristics were analyzed. The results indicate that As, Hg, Cd, and Pb concentrations in sediments were higher than background values (BVs), with high concentration sample sites located in the DPA. In addition, the geo-accumulation index (Igeo), pollution load index (PLI) and potential ecological risk index (RI) were used to quantitatively evaluate the pollution characteristics of HMs in sediments, revealing that the sediments exhibited high As and Hg pollution in the DPA (PLI = 1.09). In general, mild (RI = 48.76) and moderate (RI = 154.92) HM pollution was observed in the sediments of the SPA and DPA, respectively, based on the high PLI (> 1.0) and RI (> 150) values. Correlation analysis and principal component analysis (PCA) indicate that the Cd in the sediment generally originated from geogenic sources, while the other elements (Zn, As, Cu, Cr, Hg, Ni and Pb) were primarily linked to anthropogenic sources. Finally, the results demonstrate that population aggregation will lead to the enrichment of HMs.

Underwater active polarization descattering based on a single polarized image.

Active polarization imaging techniques have tremendous potential for a variety of underwater applications. However, multiple polarization images as input are necessary for almost all methods, thereby limiting the range of applicable scenarios. In this paper, via taking full advantage of the polarization feature of target reflective light, the cross-polarized backscatter image is reconstructed via introducing an exponential function for the first time, only based on mapping relations of co-polarized image. Compared with rotating the polarizer, the result performs a more uniform and continuous distribution of grayscale. Furthermore, the relationship of degree of polarization (DOP) between the whole scene and backscattered light is established. This leads to an accurate estimation of backscattered noise and high-contrast restored images. Besides, single-input greatly simplifies the experimental process and upgrades efficiency. Experimental results demonstrate the advancement of the proposed method for objects with high polarization under various turbidities.

Influence mechanism of the particle size on underwater active polarization imaging of reflective targets.

Underwater active polarization imaging is a promising imaging method, however, it is ineffective in some scenarios. In this work, the influence of the particle size from isotropic (Rayleigh regime) to forward-scattering on polarization imaging is investigated by both Monte Carlo simulation and quantitative experiments. The results show the non-monotonic law of imaging contrast with the particle size of scatterers. Furthermore, through polarization-tracking program, the polarization evolution of backscattered light and target diffuse light are detailed quantitatively with Poincaré sphere. The findings indicate that the noise light's polarization and intensity scattering field change significantly with the particle size. Based on this, the influence mechanism of the particle size on underwater active polarization imaging of reflective targets is revealed for the first time. Moreover, the adapted principle of scatterer particle scale is also provided for different polarization imaging methods.

Visibility enhancement of underwater images based on polarization common-mode rejection of a highly polarized target signal.

Underwater active polarization imaging is promising due to its effect of significantly descattering. Polarization-difference is commonly used to filter out backscattered noise. However, the polarization common-mode rejection of target signal has rarely been utilized. In this paper, via taking full advantage of this feature of Stokes vectors S2 which ably avoids interference from target light, the spatial variation of the degree of polarization of backscattered light is accurately estimated, and the whole scene intensity distribution of background is reconstructed by Gaussian surface fitting based on least square. Meanwhile, the underwater image quality measure is applied as optimization feedback, through iterative computations, not only sufficiently suppresses backscattered noise but also better highlights the details of the target. Experimental results demonstrate the effectiveness of the proposed method for highly polarized target in strongly scattering water.

Low-cost and simple fabrication of hierarchical Al nanopit arrays for deep ultraviolet refractive index sensing.

Herein, we proposed a simple non-lithographic way to fabricate hierarchical Al nanopit arrays performed as deep ultraviolet (DUV, 200-300 nm) refractive index sensing. Only by adjusting the Al deposition thickness on the Al nanopit array, the hierarchical Al nanopit arrays with tunable plasmonic properties in the DUV region were obtained. The prepared hierarchical Al nanopit arrays are of very good time stability and its RI sensitivity and concentration detection limit of adenine ethanol solution reach 311 nm/RIU and5×10-6M,respectively, as the Al deposition thickness is 60 nm. Furthermore, the electric field distribution simulation results show that high RI sensing characteristic are mainly attributed to the local surface plasmon resonance. This investigation provides a facile way to develop low cost, high efficient and easily fabricated Al-based RI sensor in the DUV region.

Metal-free visible-light-driven cascade cyclization reaction to synthesize 2-oxindoles via benzoyl and phenylsulfinyl radicals with acrylamide derivatives.

A metal-free visible-light-driven cascade cyclization reaction to synthesize 3-methyl-3-acetophenone-2-oxindoles and 3-methyl-3-(methylsulfonyl)benzene-2-oxindoles in yields up to 96% and 99%, via benzoyl and phenylsulfinyl radicals with acrylamide derivatives is reported, respectively. Extensive studies, including gram-scale, radical capture and isotope experiments, were performed to indicate that the reaction may involve a radical process.

Exact optical path difference and complete performance analysis of a spectral zooming imaging spectrometer.

The optical path difference (OPD) equations of the dual Wollaston prisms (DWP) with an adjustable air gap (AG) are derived by the wave normal tracing method, which is suitable for arbitrary incidence plane and angle. The spatial distribution of the OPD for various AG is presented. The validity of the OPD equation is verified by comparing the calculated interferograms with experimentally observed one. The performance of a novel static birefringent Fourier transform imaging spectrometer (SBFTIS) based on the DWP is investigated. The spectral resolution can be adjusted by changing the AG and the field of view can reach 10.0°, which is much larger than that predicted by our previous work. The results obtained in this article provide a theoretical basis for completely describing the optical transmission characteristic of the DWP and developing the high-performance birefringent spectral zooming imaging spectrometer.

Deterministic Relation between Optical Polarization and Lattice Symmetry Revealed in Ion-Doped Single Microcrystals.

Rare-earth ion doped crystals are of great significance for microsensing and quantum information, while the ions in the crystals emit light with spontaneous partial polarization, which is, though believed to be originated from the crystal lattice structure, still lacking a deterministic explanation that can be tested with quantitative accuracy. We report experimental evidence showing the profound physical relation between the polarization degree of light emitted by the doped ion and the lattice symmetry by demonstrating, with high precision, that the lattice constant ratio c/a directly quantifies the macroscopic effective polar angle of the electric and magnetic dipoles, which essentially determines the linear polarization degree of the emission. Based on this result, we further propose a pure optical technology to identify the three-dimensional orientation of a rod-shaped single microcrystal using the polarization-resolved microspectroscopy. Our results, demonstrating the physical origin of light polarization in ion-doped crystals, allow work toward on-demand polarization control with crystallography and provide a versatile platform for polarization-based microscale sensing in dynamical systems.

Ultra-broadband Bragg concave diffraction grating designs on 220-nm SOI for wavelength demultiplexing.

The appropriate broadband design of a de/multiplexer can significantly increase the channel number and consequently the transmission capacity of a wavelength division multiplexing system. Herein, we present the first ultra-broadband Bragg concave diffraction grating (CDG) on a 220-nm silicon-on-insulator, covering most of the E, S, C, L, and U telecommunication wavebands spanning from 1.425 to 1.675 µm. A wide-band-gap Bragg mirror is employed to facilitate broadband reflection, with a low diffraction order of grating for a sufficient free spectral range. Numerical simulations show that the proposed approaching blazed concave diffraction grating (AB-CDG) for the two-material case exhibits a high integration, simple fabrication process, and promising spectral performance. We fabricate the grating for design verification with a low transmission loss of -0.6 dB and a crosstalk below -33.7 dB for the eight measured wavelength channels covering the spectral range from 1.5 to 1.61 µm that is limited by the bandwidth of the grating coupler. This design can be used for broadband wavelength demultiplexing, frontier astronomical observation, and spectroscopic imaging.

Snapshot broadband polarization imaging based on Mach-Zehnder-grating interferometer.

Full polarization imaging plays an important role in remote sensing to distinguish artificial objects from the natural environment, recognizing objects in shadows and sun glint suppression. In this paper, we propose a broadband full Stokes channeled modulated polarization imaging system based on a Mach-Zehnder-grating interferometer (MZGI) with advantages such as compact size, low cost, snapshot ability, and high optical efficiency. It uses gratings to compensate for the dispersion of the carried frequency when inputting broadband light to generate interference fringes. Two detectors are assembled to the output plane to acquire the interference fringes. Each image obtained by the detectors can be individually demodulated into different Stokes parameters individually. When the two groups are combined together, the full Stokes parameters are obtained. The simulation and optical efficiency analysis demonstrate that the interference fringes can obtain the full polarization information simultaneously with high optical efficiency in broadband wavelengths.

Effect of straw-derived dissolved organic matter on the adsorption of sulfamethoxazole to purple paddy soils.

The presence of sulfamethoxazole (SMX) in croplands has become an international concern. The environmental behavior and fate of SMX in agricultural soils are not well understood, especially when the adsorption behavior is disturbed by the dissolved organic matter (DOM) released by crop straw. As canola straw is one of the biomasses widely returned to farmlands, we characterized DOM derived from pristine and decomposed canola straw, and explored the effects and mechanisms of the DOMs on regulating SMX adsorption to purple paddy soils. The spectral analysis showed that the molecular weight, aromaticity, and hydrophobicity of canola straw-derived DOM increased as decomposition proceeded. These physicochemical properties collectively determined the effects of the DOM on SMX adsorption. The DOM derived from pristine canola straw increased SMX maximum adsorption capacity of the soils by approximately 2.6 times, but this positive effect gradually decreased to a steady state by day 90 in the straw decomposition period. Nevertheless, the SMX adsorption behavior in the soils was invariably determined by the DOM extracts. These adsorption processes of SMX were well fitted by the double-chamber kinetics model and the Langmuir and Freundlich thermodynamic models. Thermodynamic parameters indicated that SMX adsorption onto the soils was spontaneous and endothermic, and this adsorption characteristics was not significantly (p > 0.05) changed by the DOM extracts. However, the adsorption kinetics were altered by those DOMs, i.e., the fast and slow adsorption processes were both diminished. Correspondingly, co-adsorption and cumulative adsorption were identified as the main mechanisms determining SMX adsorption to the purple paddy soils in the presence of the straw-derived DOMs. These results collectively indicated that the DOMs released by straw in croplands may decrease the ecological risks of organic pollutants by inhibiting their migration processes.

Dual-input concave diffraction grating demultiplexer based on dielectric multidirectional reflectors: publisher's note.

This publisher's note corrects an affiliation in J. Opt. Soc. Am. A36, 1585 (2019)JOAOD60740-323210.1364/JOSAA.36.001585.

Dual-input concave diffraction grating demultiplexer based on dielectric multidirectional reflectors.

The conventional concave diffraction grating (CDG) is commonly operated as a coarse demultiplexer device due to significant increases in the chip size and cost for large dispersion. Compact dense wavelength multiplexing is proposed and demonstrated by utilizing a dual-input CDG integrated with dielectric multidirectional reflectors. This structure allows light beams incident from two different directions to be efficiently reflected and get diffracted into the respective output waveguides by a single grating, thus creating a doubled channel number and halved channel spacing while keeping the chip size constant. The dielectric multidirectional reflector is designed by one-dimensional photonic crystal theory and used as the grating tooth to provide high reflectivities over a wide angular range. Simulation results suggest that the dual-input CDG with incident angles of 1° and 6° exhibits efficiency of more than $-0.564 \,\,{\rm{dB}} $ and crosstalk less than $-21.2 \,\,{\rm{dB}} $.

High-Sensitivity and Long-Life Microchannel Plate Processed by Atomic Layer Deposition.

As a key component of electron multiplier device, a microchannel plate (MCP) can be applied in many scientific fields. Pure aluminum oxide (Al2O3) as secondary electron emission (SEE) layer were deposited in the pores of MCP via atomic layer deposition (ALD) to overcome problems such as high dark current and low lifetime which often occur on traditional MCP. In this paper, we systematically investigate the morphology, element distribution, and structure of samples by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS), respectively. Output current of different thickness of Al2O3 was studied and an optimal thickness was found. Experimental tests show that the average gain of ALD-MCP was nearly five times better than that of traditional MCP, and the ALD-MCP showed better sensitivity and longer lifetime.

Perfect matching of concave diffraction grating with continuously circular Bragg mirrors on SOI platform.

A concave diffraction grating (CDG), based on circular Bragg mirrors, was constructed on the 220 nm silicon-on-insulator (SOI) platform. This continuous and smooth dielectric mirror is employed to eliminate the extra scattering loss occurring at the connection with neighboring grating teeth. A perfect match between the Bragg condition and the grating condition was derived in order to determine the geometrical parameters of the grating profile. finite-difference time-domain (FDTD) simulation shows that the reflection of the designed Bragg mirror can be up to 99.7% over a broad bandwidth of 330 nm. And the grating with circular Bragg mirrors exhibits low insertion loss in a relatively high order of M=5 with some unwanted diffraction orders suppressed, thus creating a large dispersion while keeping compact structure.