Search Results (971)

In this paper, we demonstrate a receiver-side lookup table (Rx-side LUT) equalization method for high-speed short-reach intensity modulation and direct detection (IM/DD) transmission systems, which alleviates the computational complexity of neural network-based equalization algorithms. Compared to conventional pre-equalization techniques applied at the transmitter side, which utilize distortion correction values stored in LUTs derived from the transmitted symbols and their corresponding recovered counterparts, the Rx-side LUT relies solely on receiver-side data. The received data to be equalized serves as the index of the LUT, with a nearest-neighbor algorithm employed to find the element closest to the index and then return the corresponding equalization result from the table. With a lightweight lookup process, the proposed method releases the computation complexity of neural network-based equalization algorithms by replacing the computationally intensive operations performed during the inference phase. Experimental results indicate that compared to baseline fully connected neural network (FCNN) and gated recurrent unit (GRU) equalization, the Rx-side LUT could decrease the algorithm execution time by 25.5% and 34.6% for 100 GBaud and 22.8% and 36.9% for 112 GBaud PAM4 signals, respectively, while maintaining comparable system performance. The proposed scheme provides a low-complexity solution for high-speed, low-cost IM/DD optical interconnects. Full article

The ring-assisted Mach–Zehnder interferometer (RA-MZI) has high sensitivity and fast optical response time, and it has been used as a label-free nanophotonic biosensor. Most RA-MZI-based biosensors, however, require chemical modification of the ring surface to immobilize biomolecules that can interact with target molecules for sensing. Here, we report a novel microfluidic-integrated RA-MZI (μFRA-MZI) where a microfluidic channel was fabricated right above the photonic ring resonator. μFRA-MZI allows for direct sample delivery to the RA-MZI without chemical modification of the ring surface and measures shifts in the resonance wavelength induced by the presence of target molecules, enabling label-free detection. In order to optimize the sensitivity of μFRA-MZI, seven devices were fabricated with varied design parameters, including the gap distance between the ring and the bus waveguide (G_ring), the length of the multi-mode interferometer (L_MMI), and the length of the directional coupler (L_DC). Photonic characterization showed that the device with G_ring = 1.2 μm, L_MMI = 15.5 μm, and L_DC = 13.5 μm exhibited the highest extinction ratio (ER) compared to the other six devices, consistent with the simulation-optimized design. Testing with NaCl solutions of varying concentrations yielded a bulk sensitivity of 11.48 nm/refractive index unit (RIU) and an ER of 0.41. With the potential to further improve the device’s sensitivity and the ability to detect samples directly in flow without chemical modifications of the ring resonator, μFRA-MZI will provide a robust and effective approach for label-free biosensing. Full article

All-inorganic halide perovskites have attracted significant interest in photodetector applications due to their remarkable photoresponse properties. However, the toxicity and instability of lead-based perovskites hinder their commercialization. In this work, we propose cubic Ba₃SbI₃ as a promising, environmentally friendly, lead-free material for next-generation photodetector applications. Ba₃SbI₃ shows good light absorption, low effective masses, and favorable elemental abundance and cost, making it a promising candidate compound for device applications. Its structural, mechanical, electronic, and optical properties were systematically investigated using density functional theory (DFT) with the Perdew–Burke–Ernzerhof (PBE) and hybrid HSE06 functionals. The material was found to be dynamically and mechanically stable, with a direct bandgap of 0.78 eV (PBE) and 1.602 eV (HSE06). Photodetector performance was then simulated in an Al/FTO/In₂S₃/Ba₃SbI₃/Sb₂S₃/Ni configuration using SCAPS-1D. To optimize device efficiency, the width, dopant level, and bulk concentration for each layer of the gadgets were systematically modified, while the effects of interface defects, operating temperature, and series and shunt resistances were also evaluated. The optimized device achieved an open-circuit voltage (Voc) of 1.047 V, short-circuit current density (Jsc) of 31.65 mA/cm², responsivity of 0.605 A W⁻¹, and detectivity of 1.05 × 10¹⁷ Jones. In contrast, in the absence of the Sb₂S₃ layer, the performance was reduced to a Voc of 0.83 V, Jsc of 26.8 mA/cm², responsivity of 0.51 A W⁻¹, and detectivity of 1.5 × 10¹⁵ Jones. These results highlight Ba₃SbI₃ as a promising platform for high-performance, cost-effective, and environmentally benign photodetectors. Full article

Carbon dots (CDs) have emerged as promising nanomaterials for optical sensing due to their outstanding photoluminescence, chemical stability, and biocompatibility. In recent years, the development of sustainable CDs derived from biomass—particularly cellulose—has attracted increasing interest as a green alternative to conventional synthetic routes. This review offers a comprehensive overview of recent advances in synthesis, functionalization, and application of cellulose-based carbon dots for environmental sensing. We examine key synthetic approaches—including hydrothermal, microwave-assisted, and pyrolytic methods—and discuss how the structure and origin of cellulose influence the physicochemical properties of the resulting CDs. The mechanisms underlying their sensing performance are analyzed in detail, with a focus on the detection of heavy metals, organic pollutants, and other environmental contaminants. Challenges related to reproducibility, scalability, and long-term stability are critically addressed. Finally, we outline future directions involving hybrid nanomaterials, real-time sensing platforms, and strategies aligned with circular economy principles. This review aims to serve as a valuable resource for researchers in the fields of sustainable nanomaterials, green chemistry, and environmental sensor development. Full article

Space-based optical imaging detection serves as a crucial means for acquiring characteristic information of space objects, with the quality and resolution of images directly influencing the accuracy of subsequent missions. Addressing the scarcity of datasets in space-based optical imaging, this study introduces a method that combines an improved Phong model and higher-order spherical harmonics (HOSH) for the optical imaging computation of space objects. Utilizing HOSH to fit the light field distribution, this approach comprehensively considers direct sunlight, earthshine, reflected light from other extremely distant celestial bodies, and multiple scattering from object surfaces. Through spectral reflectance experiments, an improved Phong model is developed to calculate the optical scattering characteristics of space objects and to retrieve common material properties such as metallicity, roughness, index of refraction (IOR), and Alpha for four types of satellite surfaces. Additionally, this study designs two sampling methods: a random sampling based on the spherical Fibonacci function (RSSF) and a sequential frame sampling based on predefined trajectories (SSPT). Through numerical analysis of the geometric and radiative rendering pipeline, this method simulates multiple scenarios under both high-resolution and wide-field-of-view operational modes across a range of relative distances. Simulation results validate the effectiveness of the proposed approach, with average rendering speeds of 2.86 s per frame and 1.67 s per frame for the two methods, respectively, demonstrating the capability for real-time rapid imaging while maintaining low computational resource consumption. The data simulation process spans six distinct relative distance intervals, ensuring that multi-scale images retain substantial textural features and are accompanied by attitude labels, thereby providing robust support for algorithms aimed at space object attitude estimation, and 3D reconstruction. Full article

The analysis of cationic surfactants with high selectivity is a source of great research interest. In this study, the absorption spectra of tetra-sulphonated metal phthalocyanine (coordinated by iron, zinc, cobalt, and nickel) in the presence of cationic surfactants in complete aqueous solutions were investigated. Interestingly, the absorption spectra of tetra-sulphonated nickel phthalocyanine (NiS₄Pc) exhibits a remarkable response to the cationic surfactants compared with other water-soluble metal phthalocyanines. Further investigation has yielded important findings that cationic surfactants with carbon chains containing twelve or more carbons cause distinct spectral responses, and the response behaviors are highly similar, showing a typical structure–activity relationship. Studies on the mechanism of response indicate that the spectral behavior could be attributed to the dramatic binding effects of structure-matched cationic surfactants on the self-association equilibrium of nickel phthalocyanine. Based on the above findings, we applied NiS₄Pc as a directly responsive optical probe for the quantitative analysis of long carbon chain cationic surfactants. Due to the high degree of similarity in optical responding, this method can be used to determine the single cationic surfactant and the total cationic surfactants. It is worth mentioning that NiS₄Pc is a water-soluble optical probe that can be used in a complete aqueous phase. Therefore, this method is not only selective but also easy and fast to operate, without the need for organic solvents. Under optimized conditions, the average calibration curve equation of the method is y = 1.66 − 0.0173 x, r = 0.9987, with a limit of detection of 3 × 10⁻⁶ mol L⁻¹. This method has been applied to the determination of real samples, for which we obtained satisfactory results. We not only describe the establishment of a new method for the direct quantitative analysis of cationic surfactants but also propose a new strategy for obtaining phthalocyanine-based optical probes in this study, which explored the novel application of phthalocyanine compounds in analytical sciences. Full article

ZnO nanostructures have attracted attention as transducer materials in optical biosensing platforms due to their wide bandgap, defect-mediated photoluminescence, high surface-to-volume ratio, and tunable morphology. This review examines how the dimensionality of ZnO nanostructures affects biosensor performance, particularly in terms of charge transport, signal transduction, and biomolecule immobilization. The synthesis approaches are discussed, highlighting how they influence crystallinity, defect density, and surface functionalization potential. The impact of immobilization strategies on sensor stability and sensitivity is also assessed. The role of ZnO in various optical detection schemes, including photoluminescence, surface plasmon resonance (SPR), localized (LSPR), fluorescence, and surface-enhanced Raman scattering (SERS), is reviewed, with emphasis on label-free and real-time detection. Representative case studies demonstrate the detection of clinically and environmentally relevant targets, such as glucose, dopamine, cancer biomarkers, and SARS-CoV-2 antigens, with limits of detection in the pico- to femtomolar range. Recent developments in ZnO-based hybrid systems and their integration into fiber-optic and microfluidic platforms are explored as scalable solutions for portable, multiplexed diagnostics. The review concludes by outlining current challenges related to reproducibility, long-term operational stability, and surface modification standardization. This work provides a framework for understanding structure–function relationships in ZnO-based biosensors and highlights future directions for their development in biomedical and environmental monitoring applications. Full article

Methane (CH₄) emissions are a major contributor to greenhouse gases and pose significant challenges to global climate mitigation efforts. The accurate determination of CH₄ concentrations via remote sensing is crucial for emission monitoring but remains impeded by surface spectral heterogeneity—notably albedo variations and land cover diversity. This study systematically assessed the sensitivity of three mainstream algorithms, namely, matched filter (MF), albedo-corrected reweighted-L1-matched filter (ACRWL1MF), and differential optical absorption spectroscopy (DOAS), to surface type, albedo, and emission rate through high-fidelity simulation experiments, and proposed a dynamic regularized adaptive matched filter (DRAMF) algorithm. The experiments simulated airborne hyperspectral imagery from the Airborne Visible/InfraRed Imaging Spectrometer-Next Generation (AVIRIS-NG) with known CH₄ concentrations over diverse surfaces (including vegetation, soil, and water) and controlled variations in albedo through the large-eddy simulation (LES) mode of the Weather Research and Forecasting (WRF) model and the MODTRAN radiative transfer model. The results show the following: (1) MF and DOAS have higher true positive rates (TP > 90%) in high-reflectivity scenarios, but the problem of false positives is prominent (TN < 52%); ACRWL1MF significantly improves the true negative rate (TN = 95.9%) through albedo correction but lacks the ability to detect low concentrations of CH₄ (TP = 63.8%). (2) All algorithms perform better at high emission rates (1000 kg/h) than at low emission rates (500 kg/h), but ACRWL1MF performs more robustly in low-albedo scenarios. (3) The proposed DRAMF algorithm improves the F1 score (0.129) by about 180% compared to the MF and DOAS algorithms and improves TP value (81.4%) by about 128% compared to the ACRWL1MF algorithm through dynamic background updates and an iterative reweighting mechanism. In practical applications, the DRAMF algorithm can also effectively monitor plumes. This research indicates that algorithms should be selected considering the specific application scenario and provides a direction for technical improvements (e.g., deep learning model) for monitoring gas emission. Full article

Vector hydrophones play an extremely important role in marine exploration. How to reduce the size of vector hydrophones while improving their directional detection capability is a critical issue that needs to be addressed. The auditory organ of the fly Ormia ochracea represents a prime example of achieving high-resolution directional detection within a compact size range. This paper proposes a vector hydrophone that integrates an Ormia ochracea fly-inspired mechanically coupled structure with an optical fiber vibration sensing structure, offering advantages of small size and strong electromagnetic interference immunity. The hydrophone demonstrates a good response to acoustic pulse trains and can accurately demodulate acoustic waves from 1 kHz to 10 kHz. Directional response experiments show that this hydrophone can significantly amplify the time delay differences of incoming acoustic waves. At an acoustic frequency of 9.25 kHz, the time delay amplification factor reaches approximately 50 times within the range of −90° to +90°, exhibiting good cosine directionality. Full article

Nondestructive quality detection of characteristic fruits is essential for ensuring nutritional value, economic viability, and consumer safety in global supply chains, yet traditional destructive methods compromise sample integrity and scalability. Visible and near-infrared (Vis/NIR) spectroscopy offers a transformative solution by enabling rapid, non-invasive multi-attribute quantification through molecular overtone vibrations. This review examines recent advancements in Vis/NIR-based fruit quality detection, encompassing fundamental principles, system configurations, and detection strategies calibrated to fruit biophysical properties. Firstly, optical mechanisms and system architectures (portable, online, vehicle-mounted) are compared, emphasizing their compatibility with fruit structural complexity. Then, critical challenges arising from fruit-specific characteristics—such as rind thickness, pit interference, and spatial heterogeneity—are analyzed, highlighting their impact on spectral accuracy. Applications across diverse fruit categories (pitted, thin-rinded, and thick-rinded) are systematically reviewed, with case studies demonstrating the robust prediction of key quality indices. Subsequently, considerations in model development and validation are presented. Finally, persistent limitations in model transferability and environmental adaptability are discussed, proposing future research directions centered on integrating hyperspectral imaging, AI-driven calibration transfer, standardized spectral databases, and miniaturized, field-deployable sensors. Collectively, these methodological breakthroughs will pave the way for autonomous, next-generation quality assessment platforms, revolutionizing postharvest management for characteristic fruits. Full article

Smart polyester materials with embedded near-infrared (NIR) functionalities offer a promising pathway for low-cost, covert tagging, and object identification. In this study we present the development and characterization of polyester packaging surfaces printed with spectrally matched twin dyes that are invisible under visible light but selectively absorbed in the NIR region. The dye patterns were applied using a Direct-to-Film transfer (DTF) method onto polyester substrates. To validate their optical behavior, we applied a dual measurement approach. Laboratory grade NIR absorbance spectroscopy was used to characterize the spectral profiles of the twin dyes in the 400–900 nm range. A custom photodiode-based detection system was constructed to evaluate the feasibility of low-cost, embedded NIR absorbance sensing. Results from both methods show correlation in absorbance contrast between the dye pairs, confirming their suitability for spectral tagging. The developed materials were evaluated in a real-world detection scenario using commercially available NIR cameras. Under dark field conditions with edge illuminated planar lighting, the twin dye patterns were successfully recognized through custom software, enabling non-contact identification and spatial localization of the NIR codes. This work presents a low-cost, scalable approach for smart packaging applications based on optical detection of actively illuminated twin dyes using accessible NIR imaging systems. Full article

The detection and characterization of exoplanets are central topics in astronomy, and high-contrast imaging techniques such nulling interferometry, coronagraphs, and extreme adaptive optics (ExAO) are key tools for the direct detection of exoplanets. This review synthesizes the pivotal role of these techniques in astronomical research and critically analyzes their role as key drivers of progress in the field. Nulling interferometry suppresses stellar light through the phase control of multiple telescopes, thereby enhancing the detection of faint planetary signals. This technology has evolved from the initial Bracewell concept to the LIFE (Large Interferometer For Exoplanets) technique, which will achieve a contrast ratio of 10⁻⁷ in the mid-infrared wavelength range in the future. Coronagraphs block starlight to create a “dark region” for direct observation of exoplanets. By leveraging innovative mask designs, theoretical contrast ratios of up to 4 × 10⁻⁹ can be achieved. ExAO systems achieve precise wavefront correction to optimize the high-contrast imaging performance and mitigate atmospheric disturbances. By leveraging wavefront sensing, thousand-element deformable mirrors, and real-time control algorithms, these systems suppress the turbulence correction residuals to 80 nm RMS, enabling ground-based telescopes to achieve a Strehl ratio exceeding 0.9. This work provides a comprehensive analysis of the underlying principles, prevailing challenges, and future application prospects of these technologies in astronomy. Full article

Optical imaging technologies expand gastrointestinal endoscopy beyond white-light endoscopy (WLE), improving visualization of mucosal, vascular, and subsurface features. They are applied to the detection of neoplastic and premalignant lesions, inflammatory diseases, and small bowel and pancreatic disorders, though their validation and readiness for routine practice vary. This review critically evaluates both guideline-endorsed and investigational optical imaging techniques across major gastrointestinal indications, highlighting diagnostic performance, level of validation, current guideline recommendations, and practical challenges to adoption. In Barrett’s esophagus, narrow-band imaging (NBI) is guideline-endorsed, while acetic acid chromoendoscopy is validated in expert centers. For gastric intestinal metaplasia and early gastric cancer, magnifying NBI achieves diagnostic accuracies exceeding 90% and is guideline-recommended, with acetic acid chromoendoscopy aiding in margin delineation. In inflammatory bowel disease, dye-spray chromoendoscopy is the reference standard for dysplasia surveillance, with virtual methods such as NBI, FICE, and i-SCAN serving as practical alternatives when dye application is not feasible. In the colorectum, NBI supports validated optical diagnosis strategies (resect-and-discard, diagnose-and-leave), while dye-based chromoendoscopy improves detection of flat and serrated lesions. Capsule endoscopy remains the standard for small bowel evaluation of bleeding, Crohn’s disease, and tumors, with virtual enhancement, intelligent chromo capsule endoscopy, and AI-assisted interpretation emerging as promising adjuncts. Pancreaticobiliary applications of optical imaging are also advancing, though current evidence is still preliminary. Investigational modalities including confocal laser endomicroscopy, optical coherence tomography, autofluorescence, Raman spectroscopy, and fluorescence molecular imaging show potential but remain largely restricted to research or expert settings. Guideline-backed modalities such as NBI and dye-based chromoendoscopy are established for clinical practice and supported by robust evidence, whereas advanced techniques remain investigational. Future directions will rely on broader validation, integration of artificial intelligence, and adoption of molecularly targeted probes and next-generation capsule technologies, which together may enhance accuracy, efficiency, and standardization in gastrointestinal endoscopy. Full article

A vector vortex beam (VVB) combines the phase singularity of a vortex beam (VB) with the anisotropic polarization of a vector beam, enabling the transmission of complex optical information and offering broad application prospects in optical sensing, high-capacity communication, and high-resolution imaging. In this work, we present a detailed theoretical analysis of the generation and detection of VVBs with Laguerre–Gaussian (LG) and Bessel–Gaussian (BG) forms. Particular emphasis is placed on the polarization characteristics of VVBs, the evolution of beam profiles after passing through polarizers with different orientations, and the interference features arising from the coaxial superposition of a VVB with a circularly polarized divergent spherical wave. To validate the theoretical analysis, LGVVBs were experimentally generated using a Mach–Zehnder interferometer by superposing two vortex beams with opposite topological charges and orthogonal circular polarizations. Furthermore, the introduction of an axicon enabled the direct conversion of LGVVBs into BGVVBs. The excellent agreement between theoretical predictions and experimental observations lays a solid foundation for beginners to systematically understand VVB characteristics and advance future research. Full article

A novel airborne pathogen detection method, based on Flashing Ratchet Potential (FRP) and Electric Current Spectroscopy (ECS), is presented. The system employs a precisely engineered asymmetric electrode array to generate controlled directional transport of oxygen ions (O₂⁻•), produced via thermionic emission and three-body electron attachment. As these ions interact with airborne particles in the detection zone, measurable perturbations in the ECS profile emerge, yielding distinct spectral signatures that indicate particle presence. Proof-of-concept experiments, using standardized talcum powder aerosols as surrogates for viral-scale particles, established optimal operating parameters of 6 V potential and 600 kHz modulation frequency, with reproducible detection signals showing a relative shift of 4.5–13.4% compared to filtered-air controls. The system’s design concept incorporates humidity-resilient features, intended to maintain stability under varying environmental conditions. Together with the proposed size selectivity (50–150 nm), this highlights its potential robustness for real-world applications. To the best of our knowledge, this is the first demonstration of an open-air electro-ratchet transport system coupled with electric current spectroscopy for bioaerosol monitoring, distinct from prior optical or electrochemical airborne biosensors, highlighting its promise as a tool for continuous environmental surveillance in high-risk settings such as hospitals, airports, and public transit systems. Full article