Highly Wavelength-Selective Self-Powered Solar-Blind Ultraviolet Photodetector Based on Colloidal Aluminum Nitride Quantum Dots.

Colloidal quantum dots are semiconductor nanocrystals endowed with unique optoelectronic properties. A major challenge to the field is the lack of methods for synthesizing quantum dots exhibit strong photo-response in the deep-ultraviolet (DUV) band. Here, a facile solution-processed method is presented for synthesizing ultrawide bandgap aluminium nitride quantum dots (AlN QDs) showing distinguished UV-B photoluminescence. Combined with the strong optical response in solar blind band, a solution-processed, self-powered AlN-QDs/ß-Ga2O3 solar-blind photodetector is demonstrated. The photodetector is characterized with a high responsivity of 1.6 mA W-1 under 0 V bias and specific detectivity 7.60 × 10-11 Jones under 5 V bias voltage with good solar blind selectivity. Given the solution-processed capability of the devices and extraordinary properties of AlN QDs, this study anticipates the utilization of AlN QDs will open up unique opportunities for cost-effective industrial production of high-performance DUV optoelectronics for large-scale applications.

Half-spectrum OFDM to quadruple the spectral efficiency of underwater wireless optical communication with digital power division multiplexing.

Improving the spectrum efficiency (SE) is an effective method to further enhance the data rate of bandwidth-limited underwater wireless optical communication (UWOC) systems. Non-orthogonal frequency-division multiplexing (NOFDM) with a compression factor of 0.5 can save half of the bandwidth without introducing any inter-carrier-interference (ICI) only if the total number of subcarriers is large enough, and we termed it as half-spectrum OFDM (HS-OFDM). To the best of our knowledge, this is the first reported work on a closed-form HS-OFDM signal in the discrete domain from the perspective of a correlation matrix. Due to the special mathematical property, no extra complex decoding algorithm is required at the HS-OFDM receiver, making it as simple as the conventional OFDM receiver. Compared with traditional OFDM, HS-OFDM can realize the same data rate, but with a larger signal-to-noise ratio (SNR) margin. To fully use the SNR resource of the communication system, we further propose a digital power division multiplexed HS-OFDM (DPDM-HS-OFDM) scheme to quadruple the SE of conventional OFDM for the bandwidth-starved UWOCs. The experimental results show that HS-OFDM can improve the receiver sensitivity by around 4 dB as opposed to conventional 4QAM-OFDM with the same data rate and SE. With the help of the DPDM-HS-OFDM scheme, the data rate of multi-user UWOC can reach up to 4.5 Gbps under the hard-decision forward error correction (HD-FEC) limit of a bit error rate (BER) of 3.8×10-3. Although there is some performance degradation in comparison with single-user HS-OFDM, the BER performance of multi-user DPDM-HS-OFDM is still superior to that of conventional single-user 4QAM-OFDM. Both single-user HS-OFDM and multi-user DPDM-HS-OFDM successfully achieve 2 Gbps/75 m data transmission, indicating that the DPDM-HS-OFDM scheme is of great importance in bandwidth-limited UWOC systems and has guiding significance to underwater wireless optical multiple access.

An aberration-free line scan confocal Raman imager and type classification and distribution detection of microplastics.

An aberration-free line scanning confocal Raman imager (named AFLSCRI) is developed to achieve rapid Raman imaging. As an application example, various types and sizes of MPs are identified through Raman imaging combined with a machine learning algorithm. The system has excellent performance with a spatial resolution of 2 µm and spectral resolution of 4 cm-1. Compared to traditional point-scanning Raman imaging systems, the detection speed is improved by 2 orders of magnitude. The pervasive nature of MPs results in their infiltration into the food chain, raising concerns for human health due to the potential for chemical leaching and the introduction of persistent organic pollutants. We conducted a series of experiments on various types and sizes of MPs. The system can give a classification accuracy of 98% for seven different types of plastics, and Raman imaging and species identification for MPs as small as 1 µm in diameter were achieved. We also identified toxic and harmful substances remaining in plastics, such as Dioctyl Phthalate (DOP) residues. This demonstrates a strong performance in microplastic species identification, size recognition and identification of hazardous substance contamination in microplastics.

S2DA-Net: Spatial and spectral-learning double-branch aggregation network for liver tumor segmentation in CT images.

Accurate liver tumor segmentation is crucial for aiding radiologists in hepatocellular carcinoma evaluation and surgical planning. While convolutional neural networks (CNNs) have been successful in medical image segmentation, they face challenges in capturing long-term dependencies among pixels. On the other hand, Transformer-based models demand a high number of parameters and involve significant computational costs. To address these issues, we propose the Spatial and Spectral-learning Double-branched Aggregation Network (S2DA-Net) for liver tumor segmentation. S2DA-Net consists of a double-branched encoder and a decoder with a Group Multi-Head Cross-Attention Aggregation (GMCA) module, Two branches in the encoder consist of a Fourier Spectral-learning Multi-scale Fusion (FSMF) branch and a Multi-axis Aggregation Hadamard Attention (MAHA) branch. The FSMF branch employs a Fourier-based network to learn amplitude and phase information, capturing richer features and detailed information without introducing an excessive number of parameters. The FSMF branch utilizes a Fourier-based network to capture amplitude and phase information, enriching features without introducing excessive parameters. The MAHA branch incorporates spatial information, enhancing discriminative features while minimizing computational costs. In the decoding path, a GMCA module extracts local information and establishes long-term dependencies, improving localization capabilities by amalgamating features from diverse branches. Experimental results on the public LiTS2017 liver tumor datasets show that the proposed segmentation model achieves significant improvements compared to the state-of-the-art methods, obtaining dice per case (DPC) 69.4 % and global dice (DG) 80.0 % for liver tumor segmentation on the LiTS2017 dataset. Meanwhile, the pre-trained model based on the LiTS2017 datasets obtain, DPC 73.4 % and an DG 82.2 % on the 3DIRCADb dataset.

One-pot in situ synthesis of an NS-ligand co-doped metal-organic framework for the enhanced adsorption-assisted photocatalytic decontamination of metronidazole.

Doping active agents into metal-organic frameworks (MOFs) is widely sought after owing to its potential to enhance adsorption and photocatalytic efficiency, surpassing the potential of bare frameworks. This study incorporated a catalytically active NS-ligand (1,2-benzisothiazolin-3-one) into a very stable and porous PCN-600 MOF via an in situ synthesis approach. The NS-ligand, which matched with the host ligands of PCN-600, enabled the highly efficient synthesis of NS-co-doped MOFs. The pristine PCN-600 framework and morphology were retained in the MOF altered with the NS-ligand, as demonstrated by XRD, FTIR, and SEM characterizations. A high electron density was generated due to the synergistic effect between the defects in the NS-co-doped photocatalyst and engineered active sites. This facilitated the adsorption-assisted photocatalytic decontamination of metronidazole with an 87% removal by PCN-600-NS-10 compared to 43% by pristine PCN-600 within a total time of 150 min. The MOF doped with the NS-ligand exhibited a reduced band gap and enhanced adsorption and photocatalytic capabilities compared to pristine PCN-600. The impact of operational parameters, such as catalyst dosage, initial solution pH, and MNZ concentration, was also explored. Pseudo-second and pseudo-first order models were found to describe the adsorption and degradation kinetics of metronidazole and the Dubinin-Radushkevich model was found to fit the equilibrium adsorption results. The thermodynamic characteristics of adsorption processes (ΔGads, ΔHads, and ΔSads) demonstrated that adsorption was physical, spontaneous, and exothermic and resulted in increased entropy.

Label-free analysis of the ß-hydroxybutyricacid drug on mitochondrial redox states repairment in type 2 diabetic mice by resonance raman scattering.

BACKGROUND: Mitochondrial redox imbalance underlies the pathophysiology of type2 diabetes mellitus (T2DM), and is closely related to tissue damage and dysfunction. Studies have shown the beneficial effects of dietary strategies that elevate ß-hydroxybutyrate (BHB) levels in alleviating T2DM. Nevertheless, the role of BHB has not been clearly elucidated. METHODS: We performed a spectral study to visualize the preventive effects of BHB on blood and multiorgan mitochondrial redox imbalance in T2DM mice via using label-free resonance Raman spectroscopy (RRS), and further explored the impact of BHB therapy on the pathology of T2DM mice by histological and biochemical analyses. FINDINGS: Our data revealed that RRS-based mitochondrial redox states assay enabled clear and reliable identification of the improvement of mitochondrial redox imbalance by BHB, evidenced by the reduction of Raman peak intensity at 750 cm-1, 1128 cm-1 and 1585 cm-1 in blood, tissue as well as purified mitochondria of db/db mice and the increase of tissue mitochondrial succinic dehydrogenase (SDH) staining after BHB treatment. Exogenous supplementation of BHB was also found to attenuate T2DM pathology related to mitochondrial redox states, involving organ injury, blood glucose control, insulin resistance and systemic inflammation. INTERPRETATION: Our findings provide strong evidence for BHB as a potential therapeutic strategy targeting mitochondria for T2DM.

Single-Molecule Protein Analysis by Centrifugal Droplet Immuno-PCR with Magnetic Nanoparticles.

Detecting proteins in ultralow concentrations in complex media is important for many applications but often relies on complicated techniques. Herein, a single-molecule protein analyzer with the potential for high-throughput applications is reported. Gold-coated magnetic nanoparticles with DNA-labeled antibodies were used for target recognition and separation. The immunocomplex was loaded into microdroplets generated with centrifugation. Immuno-PCR amplification of the DNA enabled the quantification of proteins at the level of single molecules. As an example, ultrasensitive detection of α-synuclein, a biomarker for neurodegenerative diseases, is achieved. The limit of detection was determined to be ∼50 aM in buffer and ∼170 aM in serum. The method exhibited high specificity and could be used to analyze post-translational modifications such as protein phosphorylation. This study will inspire wider studies on single-molecule protein detection, especially in disease diagnostics, biomarker discovery, and drug development.

A high-precision and wide-range pH monitoring system based on broadband cavity-enhanced absorption spectrum.

A high-precision pH monitoring system over a wide pH range is introduced. The system comprises a cavity-enhancement module constructed by two high-reflectivity mirrors, a microfluidic pH sensing chip based on a binary-indicator membrane of Congo red and m-cresol purple, and a hyperspectral transmission module. This structure extends the effective absorption optical path of the sensing chip, significantly amplifying the spectral differences at various pH values. The spectrum of the transmitted light is recorded by a self-developed hyperspectral module and then converted to broadband cavity-enhanced absorption spectrum (BBCEAS) via the Beer-Lambert law. An artificial neural network (ANN) is employed to predict pH values of the solution. With such a design, this system exhibits a wide detecting range of 2 M [H+] - 2 M [OH-] (corresponding to pH -0.3-14.3) with a response time of about 120 s. The system can achieve a higher detection accuracy with root mean square error (RMSE) of 0.073, as compared to 0.137 without the cavity enhancement. The system also possesses good properties of repeatability, long-term stability, ion resistance, and organic corrosion resistance. These excellent properties make the proposed system a promising candidate technology for harsh environments, such as seawater acidification warning, chemical plant sewage monitoring, and biological sample detection.

4D hyperspectral surface topography measurement system based on the Scheimpflug principle and hyperspectral imaging.

A four-dimensional (4D) hyperspectral surface topography measurement (HSTM) system that can acquire uniform inelastic signals [three-dimensional (3D) spatial data] and reflection/fluorescence spectra of an object is proposed. The key components of the system are a light-sheet profilometer based on the Scheimpflug principle and a hyperspectral imager. Based on the mapping relationships among the image coordinate systems of the two imaging subsystems and the coordinate system of the real space, the spectral data can be assigned to the corresponding 3D point cloud, forming a 4D model. The spectral resolution is better than 4 nm. 700 nm, 546 nm, and 436 nm are selected as the three primary colors of red, green, and blue to restore the color. The 4D hyperspectral surface reconstruction experiments of philodendron and chlorophytum have shown the good performance of the proposed HSTM system and the great application potential for plant phenotype and growth analysis in agriculture.

Low-cross-talk and thermo-insensitive CWDM (de)multiplexer assisted with compact MZIs and slot waveguides.

A low-cross-talk and thermo-insensitive 1×4 coarse wavelength-division multiplexing device is proposed on the silicon-on-insulator platform with the help of compact Mach-Zehnder interferometers (MZIs) and slot waveguides. The compact MZIs are used to achieve wavelength-insensitive power splitting. In the phase shifters, the trade-off between the opposite thermo-optical coefficients of the Si core and SU8 cladding in the slot waveguide is used to overcome the strong thermo-optic effect of silicon. The simulated results show that the cross talk is less than -20d B at central wavelengths and the temperature-dependent wavelength shift is reduced to ∼4.7p m/∘ C. For the four channels, the 1-dB and 3-dB bandwidths are ∼14n m and ∼18n m, respectively.

Low-cost, high-speed multispectral imager via spatiotemporal modulation based on a color camera.

Spectral imaging is a powerful tool in industrial processes, medical imaging, and fundamental scientific research. However, for the commonly used spatial/spectral-scanning spectral imager, the slow response time has posed a big challenge for its employment in dynamic scenes. In this paper, we propose a spatiotemporal modulation concept and build a simple, low-cost spectral imager by combining a liquid crystal (LC) cell with a commercial color camera. By the synergic effect of temporal modulation of the LC materials and spatial modulation of the Bayer filter in a color camera, high-quality multispectral imaging is successfully demonstrated with a high rate of 8 Hz, far beyond the counterparts. Experimental results show that even with three tuning states of the LC material, optical signals with a 10-nm band can be resolved in the range between 410 and 700 nm by this method, overcoming the tradeoff between spectral resolution and time resolution. As a proof of demonstration, we present its potential usage for metamerism recognition, showing superiority over traditional color cameras with more spectral details. Considering its low cost, miniaturization and monolithic-integration ability on color sensors, this simple approach may bring the spectral imaging technology closer to the consumer market and even to ubiquitous smartphones for health care, food inspection and other applications.

Utilizing Mixed Training and Multi-Head Attention to Address Data Shift in AI-Based Electromagnetic Solvers for Nano-Structured Metamaterials.

When designing nano-structured metamaterials with an iterative optimization method, a fast deep learning solver is desirable to replace a time-consuming numerical solver, and the related issue of data shift is a subtle yet easily overlooked challenge. In this work, we explore the data shift challenge in an AI-based electromagnetic solver and present innovative solutions. Using a one-dimensional grating coupler as a case study, we demonstrate the presence of data shift through the probability density method and principal component analysis, and show the degradation of neural network performance through experiments dealing with data affected by data shift. We propose three effective strategies to mitigate the effects of data shift: mixed training, adding multi-head attention, and a comprehensive approach that combines both. The experimental results validate the efficacy of these approaches in addressing data shift. Specifically, the combination of mixed training and multi-head attention significantly reduces the mean absolute error, by approximately 36%, when applied to data affected by data shift. Our work provides crucial insights and guidance for AI-based electromagnetic solvers in the optimal design of nano-structured metamaterials.

Wide-field-of-view auto-coupling optical antenna system for high-speed bidirectional optical wireless communications in C band.

Due to a great many superior features of infrared light communication (ILC), like high capacity and strong privacy, ILC is considered a potential candidate for serving the high demands of beyond fifth-generation/sixth-generation (B5G/6 G) communication systems. However, the terminal's limited field-of-view (FOV) induces great difficulty in establishing line-of-sight (LoS) link between the transceiver and the terminal. In this paper, we propose a wide-FOV auto-coupling optical antenna system that utilizes a wide-FOV telecentric lens to collect incident infrared beams and automatically couple them into a specific single-mode-fiber (SMF) channel of fiber array and optical switch. The performance of this optical antenna system is assessed through simulation and manual alignment operation, and validated by automatic alignment results. A coupling loss of less than 10.6 dB within a FOV of 100° for both downstream and upstream beams in C band is demonstrated by the designed system. Furthermore, we establish a bidirectional optical wireless communications (OWC) system employing this antenna and a fiber-type modulating retro-reflector (MRR) system in the terminal. Both 10-Gbps on-off keying (OOK) downstream and upstream transmissions are successfully realized with the FOV of up to 100° in C band where the measured bit-error-rate (BER) is lower than 3.8 × 10-3. To the best of our knowledge, this is a brand-new auto-coupling optical antenna system with the largest FOV in ILC automatic alignment works in terminals that have ever been reported.

Phase Interrogation Sensor Based on All-Dielectric BIC Metasurface.

The low performance of sensors based on an all-dielectric metasurface limits their application compared to metallic counterparts. Here, for the first time, an all-dielectric BIC (bound states in the continuum) metasurface is employed for highly sensitive phase interrogation refractive index sensing. The proposed sensor is well analyzed, fabricated, and characterized. Experimentally, a high-performance BIC-based microfluidic sensing chip with a Q factor of 1200 is achieved by introducing symmetry breaking. A refractive index sensor with high figure of merit of 418 RIU-1 is demonstrated, which is beneficial to the phase interrogation. Notably, we measure a record phase interrogation sensitivity of 2.7 × 104 deg/RIU to the refractive index, thus enabling the all-dielectric BIC to rival the refractive index detection capabilities of metal-based sensors such as surface plasmon resonance. This scheme establishes a pivotal role of the all-dielectric metasurface in the field of ultrahigh sensitivity sensors and opens possibilities for trace detection in biochemical analysis and environment monitoring.

Ppb-level methane detection sensitivity based on a homemade Raman fiber amplifier and differential photoacoustic technology.

A high-power near-infrared wavelength-modulated differential photoacoustic spectroscopy sensor for parts-per-billion (ppb) level methane detection is reported by using a homemade Raman fiber optical amplifier. A commercial 1653.7 nm continuous wave distributed feedback laser is employed as a seed source to excite a high light power of ∼550m W, which greatly improves sensor performance. Wavelength modulation spectroscopy and differential techniques are applied to further improve the signal-to-noise ratio of the photoacoustic signal. A 1σ minimum detection limit of ∼10p p b for methane detection is achieved with an integration time of 10 s.

Elimination of the fundamental mode hybridization on an x-cut lithium-niobate-on-insulator by using a densely packed bent waveguide array.

Lithium niobate (L i N b O 3, LN) is a promising material for integrated photonics due to its natural advantages. The commercialization of thin-film LN technology has revitalized this platform, enabling low-loss waveguides, micro-rings, and compact electro-optical modulators. However, the anisotropic birefringent nature of X-cut LN leads to mode hybridization of TE and TM modes, which is detrimental to most polarization-sensitive integrated optical waveguide devices. A novel structure, to the best of our knowldege, utilizing a densely packed bent waveguide array is presented in this paper to eliminate mode hybridization. The refractive index is modulated in a manner that eliminates the avoided crossing of the refractive index curves of the TE and TM fundamental modes; thus, mode hybridization is prevented. The structures are readily accessible in the full range of commercially available LN film thicknesses from 400 to 720 nm and in any etching depth. The proposed structures give a polarization extinction ratio of -30d B across all bend radii, while simultaneously maintaining low excess loss of less than -1d B after reaching a 100 µm bend radius.

Line laser scanning microscopy based on the Scheimpflug principle for high-resolution topography restoration and quantitative measurement.

A line laser scanning microscopy system with a larger depth of field based on the Scheimpflug principle is proposed for high-resolution surface topography restoration and quantitative measurement on miniature non-transparent samples. An imaging model based on the Scheimpflug principle is established, and a calibration method without system parameters is derived, which is further extended to a microscopic system. The measuring range of the system is 5m m×4m m×x m m, where x is the movement distance of the displacement stage. In the z-axis direction, the relative error of measurement is about 1% when z is of the millimeter level and less than 7% when z is of the micron level, and the spatial resolution is better than 3.8 µm. In the y-axis direction, the relative error of measurement is less than 5%. Finally, three-dimensional scanning of two samples with different surfaces is carried out to verify the feasibility of the system. The experimental results show that our system has the capability of high-resolution topography restoration and can be applied in industrial production scenarios such as automatic measurement and intelligent identification.

Polished hollow core Bragg fiber sensor for simultaneous measurement of cortisol concentration and temperature.

Disturbance of surrounding temperature inevitably affects the accuracy of fiber biosensors. To that end, we propose a compact label-free optofluidic sensor based on a polished hollow core Bragg fiber (HCBF) that can simultaneously measure the cortisol concentration and surrounding temperature in real-time. The sensor is comprised of fusion splicing single mode fiber (SMF), multimode fiber (MMF) and HCBF. HCBF is side polished to remove part of the cladding that the suspended inner surface of the fiber can contact the external environment. After the incident light passes through the MMF from the SMF, it enters the hollow area, high refractive index (RI) layers, respectively, where the anti-resonant reflecting optical waveguide (ARROW) guiding mechanism and Mach-Zehnder interferometer (MZI) are simultaneously excited. Taking advantage of the high RI layers of HCBF, compared to the fiber with uniform cladding, the light can be more confined in the cladding and more sensitive to inner surface medium. The inner surface of sensor is immobilized with cortisol aptamer for the sake of achieving high sensitivity and specific sensing of cortisol with the limit of detection (LOD) to be 4.303 pM. The proposed sensor has a compact structure, enables temperature compensation, and can be fabricated at low cost making it highly suitable for in-situ monitoring and high-precision sensing of cortisol and other biological analytes.

High-Performance Low-Voltage Transparent Metal-Semiconductor-Metal Ultraviolet Photodetectors Based on Ultrathin Gold Asymmetric Interdigitated Electrodes.

A high-performance, low-voltage, transparent, metal-semiconductor-metal ultraviolet (UV) photodetector (PD) is proposed and experimentally demonstrated, based on gold (Au) asymmetric interdigitated (aIDT) electrodes with thicknesses well below 10 nm. A 7-nm-thick Au film, with a visible transmittance of 80.4% and a sheet resistance of 11.55 Ω/sq, is patterned into aIDT electrodes on a ZnO active layer, whose average visible transmittance is up to 74.3%. Meshing the pads further improves the overall transmittance of the device. Among all fabricated devices, the PD with the aIDT finger width ratio of 1:4 performs the best. Very low dark currents are achieved at 0, 0.5 and 1 V, allowing for high responsivities and specific detectivities to the UV light. It is also a fast device, especially under the biases of 0.5 and 1 V. The comprehensive performances are comparable and even superior to those of the reported devices. The asymmetric Schottky junctions induced by the aIDT electrodes under UV illumination are the main mechanism for the low-voltage operation of our transparent PD, which is promising to be applied widely.

Optical Fiber Fabry-Pérot Microfluidic Sensor Based on Capillary Fiber and Side Illumination Method.

In this paper, an optical fiber Fabry-Pérot (FP) microfluidic sensor based on the capillary fiber (CF) and side illumination method is designed. The hybrid FP cavity (HFP) is naturally formed by the inner air hole and silica wall of CF which is side illuminated by another single mode fiber (SMF). The CF acts as a naturally microfluidic channel, which can be served as a potential microfluidic solution concentration sensor. Moreover, the FP cavity formed by silica wall is insensitive to ambient solution refractive index but sensitive to the temperature. Thus, the HFP sensor can simultaneously measure microfluidic refractive index (RI) and temperature by cross-sensitivity matrix method. Three sensors with different inner air hole diameters were selected to fabricate and characterize the sensing performance. The interference spectra corresponding to each cavity length can be separated from each amplitude peak in the FFT spectra with a proper bandpass filter. Experimental results indicate that the proposed sensor with excellent sensing performance of temperature compensation is low-cost and easy to build, which is suitable for in situ monitoring and high-precision sensing of drug concentration and the optical constants of micro-specimens in the biomedical and biochemical fields.