Optics

The optical microscope is an indispensable observation instrument that has fundamentally contributed to progress in science and technology. Dark-field microscopy and scattered light imaging techniques enable high-contrast observation of nanoparticles in water. However, the scattered light is focused by the optical lenses, resulting in a blurred image of the nanoparticle structure. Here, we developed a projection optical microscope (PROM), which directly observes the scattered light from the nanoparticles without optical lenses. In this method, the sample is placed below the focus position of the microscope’s objective lens and the projected light is detected by an image sensor. This enables direct observation of the sample with a spatial resolution of approximately 20 nm. Using this method, changes in the aggregation state of nanoparticles in solution can be observed at a speed faster than the video frame rate. Moreover, the mechanism of such high-resolution observation may be related to the quantum properties of light, making it an interesting phenomenon from the perspective of optical engineering. We expect this method to be applicable to the observation and analysis of samples in materials science, biology and applied physics, and thus to contribute to a wide range of scientific, technological and industrial fields. Full article

The Volume Bragg Grating (VBG) imaging technique provides a novel approach to gaze-type hyperspectral imaging. However, collimation constraints of the incident beam during narrow-band filtering and high-spatial-resolution imaging introduce system complexity, hindering miniaturization and modularization of the optical system. To address these limitations, this paper proposes a convex transmissive VBG structure with tunable design parameters to enhance the field of view (FOV), relax collimation requirements, improve imaging quality, narrow filter spectral bandwidth, and simplify the optical system design. For the precise analysis and optimization of convex VBG performance, we established a physical model for filtered imaging using a convex transmissive VBG with polychromatic extended sources. An evaluation metric termed the “Maximal Splitting Angle (MSA)” was introduced to quantify the dispersion extent of image spots. This approach was employed to investigate the intrinsic correlations between structural parameters (such as the radius of curvature, vector tilt angle, grating period, and thickness) and key system performance indicators (spatial resolution and spectral resolution). The necessity of optimizing these parameters was rigorously demonstrated. Theoretical analysis confirms that convex transmissive VBG achieves superior spatial and spectral resolution over planar VBG under reduced collimation constraints. The experimental results show a 58.5% enhancement in spatial resolution and a 63.6% improvement in spectral bandwidth for the convex transmissive VBG system. Crucially, while planar transmissive VBG suffers from stray fringe interference during wavelength tuning, its convex counterpart remains unaffected. This study proposes a novel device structure, offering new perspectives for optimizing VBG-filtered spectral imaging systems. Full article

Traditionally, retrieving both temperature and CO₂ concentration in atmospheric remote sensing has relied on two independent lidar systems, leading to increased system complexity and limited coordination. To address this challenge, we propose a coordinated retrieval approach using a three-wavelength differential absorption lidar (DIAL) system. A temperature-sensitive wavelength is selected to distinguish strong absorption from weak absorption, forming the tri-wavelength configuration. By exploiting the different sensitivities of absorption cross-sections to thermal and molecular variations, simultaneous retrieval of both parameters is achieved. A standard atmospheric profile under clean-air conditions is constructed. The CO₂ absorption spectrum near 1573 nm is generated using Voigt line shapes and data from the HITRAN database. Extinction and backscatter coefficients are retrieved through the Klett method. A layer-by-layer solution of the coupled differential equations is then performed to extract temperature and concentration simultaneously. Results are benchmarked against the atmospheric model, demonstrating the feasibility of the approach. This method provides a promising pathway for high-precision, multi-parameter DIAL sensing. Full article

Wireless optical communication technology offers advantages, such as high-data transmission rates, confidentiality, and robust anti-interception capabilities, making it highly promising for cross-sea–air interface communication applications. However, to our knowledge, no studies have been conducted on the spatial transmission efficiency of light after it passes through ocean waves. To address this issue, a seawater-wave–atmosphere model based on Gerstner waves was constructed. Using the Monte Carlo method, the optical power distributions of the laser light passing through the sea–air interface at the first- and second-level sea scales were simulated. The optimal positions for deploying one to three receiving optical systems were analyzed, and a laser communication receiving system was designed. Furthermore, simulations were conducted to determine the optical transmission efficiency of the designed optical receiver system. At the first-level sea scale, the optimal position for a single-point detector was (0°, ±5.61°), whereas those for the two detectors were (0°, ±5.61°) and (0°, ±5.68°). At the second-level sea scale, the optimal position for a single-point detector was (0°, ±3.17°), and the optimal positions for the two detectors were (0°, ±3.1°) and (0°, ±2.98°). Under the designed conditions, the optical transmission efficiency for a single detector at the first- and second-level sea scales was 0.74–0.88%, respectively, while it was 0.79–1.09% in the two-detector case. At the second-level sea scale, the optical transmission efficiency for a single detector was 0.37–2.09% and 0.50–1.97% in the two-detector case. Full article

The use of magnetic materials, such as ferrofluids, is of great importance in biomedical applications, and as a result, interest in studying their magneto-optical properties has grown significantly in recent years. Therefore, in this work, magnetic nanoparticles were synthesized with chitosan coating, leaving the product as a ferrofluid in aqueous solution. Structural, morphological, magnetic, and optical characterization was carried out obtaining a cubic structure centered on the faces, a spherical morphology with a size distribution of 10–14 nm according to TEM images and a magnetic saturation of 53 emu/g. In the optical properties, the effect of chitosan shell on the forbidden band was studied, showing a blue-shifting effect, due to reduction on the inner magnetic nanoparticles size. Full article

Zinc oxide (ZnO), a wide-bandgap semiconductor, has garnered significant interest for photocatalytic applications due to its excellent chemical stability, non-toxicity, and strong oxidative capability. In this study, density functional theory (DFT) calculations were employed to explore the impact of ruthenium (Ru) doping on the structural, electronic, and magnetic properties of wurtzite ZnO. The introduction of Ru leads to bandgap narrowing and the emergence of impurity states, thereby enhancing visible light absorption. Charge density analysis reveals enhanced electron delocalization, while the projected density of states (PDOS) indicates strong hybridization between the Ru 4d orbitals and the ZnO electronic states. The density of states at the Fermi level, N(EF), exhibits a notable dependence on doping concentration and magnetic configuration. For non-magnetic states, N(EF) reaches 11 states/eV and 9.5 states/eV at 12.5% and 25% Ru concentrations, respectively. In ferromagnetic configurations, these values decrease to 0.65 states/eV and 1.955 states/eV, while antiferromagnetic states yield 4.945 states/eV and 0.65 states/eV. These variations highlight Ru’s crucial role in regulating electronic density, thereby affecting electrical conductivity, magnetic properties, and photocatalytic efficiency. The results offer theoretical guidance for designing high-performance Ru-doped ZnO photocatalysts. Full article

While laser-assisted turning (LAT) improves the machinability of GH 4169 through heating-induced thermal softening, revealing the influence of the laser processing parameters on its thermal field and machining efficiency is crucial. In this study, the influence of different laser processing parameters on the thermal field during the preheating process of LAT is systematically investigated by combining finite element (FE) simulation and experimentation, from which the optimal processing parameters of the LAT of GH 4169 are obtained. Firstly, the experimental platform of LAT is established, and a 2D FE model of the LAT of GH 4169 is constructed. Secondly, the absorption coefficient of GH 4169 with a 1064 nm wavelength laser is calibrated through experimentation and FE simulation, which lay an accurate foundation for the subsequent thermal field analysis. Furthermore, the FE simulation of the preheating process of the LAT of GH 4169 is carried out, focusing on the influence of laser power, laser spot diameter, laser spot movement speed and laser spot–tool edge distance on the thermal field, in terms of the peak and final preheating temperatures. The results show that laser power, laser spot movement speed and laser spot diameter have a significant influence on both of the two temperatures, while laser spot–tool edge distance only affects the final preheating temperature. In addition, the regression equations of the peak and final preheating temperatures are obtained based on the FE simulation results, and the optimal processing parameters are determined by combining the boundary conditions (peak temperature of 650–950 °C and initial preheating temperature of ≤190 °C). Comparison experiments with conventional turning (CT) show that under the optimal processing parameters, LAT can effectively reduce the cutting force, surface roughness and tool flank wear, which indicates that a rational selection of laser processing parameters is crucial for improving the capability of LAT of GH 4169. Full article

To address the challenge of efficiently identifying and providing early warnings for typical structural damages in small and medium-sized bridges during long-term service, this paper proposes an intelligent monitoring and recognition method based on ultra-weak fiber Bragg grating (UWFBG) array sensing. By deploying UWFBG strain-sensing cables across the bridge, the system enables continuous acquisition and spatial analysis of multi-point strain data. Based on this, a series of experimental scenarios simulating typical structural damages—such as single-slab loading, eccentric loading, and bearing detachment—are designed to systematically analyze strain evolution patterns before and after damage occurrence. While strain distribution maps allow for visual identification of some typical damages, the approach remains limited by reliance on manual interpretation, low recognition efficiency, and weak detection capability for atypical damages. To overcome these limitations, machine learning algorithms are further introduced to extract features from strain data and perform pattern recognition, enabling the construction of an automated damage identification model. This approach enhances both the accuracy and robustness of damage recognition, achieving rapid classification and intelligent diagnosis of structural conditions. The results demonstrate that the integration of the monitoring system with intelligent recognition algorithms effectively distinguishes different types of damage and shows promising potential for engineering applications. Full article

Background: This narrative review aims to assess multiple strategies available to evaluate and manage corneal astigmatism in the context of cataract surgery, with a focus on the surgical techniques, intraocular lens (IOL) selection, and the integration of advanced new technologies. Methods: A narrative review based on a literature search in PubMed/MEDLINE and the Cochrane Library, covering publications from 1990 to 2025, was conducted. Eligible studies included randomized controlled trials, observational studies, prospective and retrospective analyses, and systematic reviews. Key search terms included “astigmatism”, “cataract surgery”, “keratometry”, and “refraction.” Studies were screened and selected by two independent reviewers. Results: Corneal astigmatism is the most common form of astigmatism. While the anterior corneal astigmatism plays a more important role, the posterior corneal astigmatism and the posterior-to-anterior corneal ratio (Gullstrand ratio) can impact the postoperative refractive results in a very important way. While planning the cataract surgery, surgically induced astigmatism (SIA), especially on the posterior cornea, must be taken into consideration. Various approaches, such as opposite clear corneal incisions (OCCIs), toric intraocular lens (IOLs), intraoperative aberrometry, and the integration of artificial intelligence and robotic-assisted surgery, are increasing the precision of astigmatism correction and surgical outcomes. Conclusions: Individualized surgical planning and precise measurement are key factors in reducing residual astigmatism and obtaining the best visual outcomes in patients with corneal astigmatism undergoing cataract surgery. By taking into consideration the posterior corneal data, refining IOL calculations, and embracing the rapidly developing technological innovations, patient satisfaction and visual quality can be substantially improved, and the predictability of the surgical outcome can be enhanced. Full article

This study explores the transmission characteristics between the links of UV(ultraviolet)-network communication under mobile conditions. Utilizing the prevalent UV-network communication network topology as a foundation, a UV-network communication model tailored to mobile scenarios was developed. This model includes a method for calculating the impulse response of the system, focusing specifically on three common network topology structures: two parallel links, co-address of the originating link, and co-address of the receiving link. The simulation and analysis conducted in this study examine the impact of various factors on the system’s impulse response, such as receiver movement speed, geometric parameters of the receivers, link spacing, and the angle between links. The results indicate that receiver movement speed significantly influences pulse response fading, with faster speeds resulting in more severe fading. Additionally, in parallel links, smaller link spacing results in stronger impulse response. Furthermore, a smaller angle between the originating and receiving co-addresses results in increased inter-link interference. The study findings in this paper will lay the foundation for the study of UV mobile self-organizing networks. Full article

Optical frequency domain reflectometry (OFDR) is one of the key diagnostic tools for fiber optic components and circuits built on them. A low signal-to-noise ratio, resulting from the low intensity of backscattered signals, prevents the correct quantitative description of the medium parameters. Known methods of signal denoising, such as empirical mode decomposition, frequency filtering, and activation function dynamic averaging, make the signal smoother but introduce errors into its dynamic characteristics, changing the intensity of reflection peaks and distorting the backscattering level. We propose a method to reduce OFDR trace noise using elliptical arc fitting (EAF). The obtained results indicate that this algorithm efficiently processes both areas with and without contrasting back reflections, with zero distortion of Fresnel reflection peaks, and with zero attenuation error in regions without Fresnel reflections. At the same time, other methods distort reflection peaks by 14.2–42.6% and shift the correct level of Rayleigh scattering by 27.2–67.3%. Further work will be aimed at increasing the accuracy of the method and testing it with other types of data. Full article

This paper explores the formal structure and philosophical implications of polarization-path entanglement in quantum optics, where different degrees of freedom of a single photon become entangled. We examine the mathematical conditions under which coherence is preserved or lost, emphasizing the role of distinguishability and information flow. The analysis is situated within major interpretational frameworks (including Copenhagen, Many-Worlds, QBism, and Bohmian mechanics) to evaluate whether such entanglement reflects physical reality or epistemic constraints. Finally, we discuss experimental realizations, relevance to quantum information processing, and open conceptual questions regarding the ontological status of single-particle entanglement. Full article

Deep neural networks have led to a substantial increase in multifaceted classification tasks by making use of large-scale and diverse annotated datasets. However, diverse optical coherence tomography (OCT) datasets in cardiovascular imaging remain an uphill task. This research focuses on improving the diversity and generalization ability of augmentation architectures while maintaining the baseline classification accuracy for coronary atrial plaques using a novel dual-generator and dynamically fused discriminator conditional generative adversarial network (DGDFGAN). Our method is demonstrated on an augmented OCT dataset with 6900 images. With dual generators, our network provides the diverse outputs for the same input condition, as each generator acts as a regulator for the other. In our model, this mutual regularization enhances the ability of both generators to generalize better across different features. The fusion discriminators use one discriminator for classification purposes, hence avoiding the need for a separate deep architecture. A loss function, including the SSIM loss and FID scores, confirms that perfect synthetic OCT image aliases are created. We optimize our model via the gray wolf optimizer during model training. Furthermore, an inter-comparison and recorded SSID loss of 0.9542 ± 0.008 and a FID score of 7 are suggestive of better diversity and generation characteristics that outperform the performance of leading GAN architectures. We trust that our approach is practically viable and thus assists professionals in informed decision making in clinical settings. Full article

Anti-resonant hollow-core fibers have exhibited excellent performance in applications such as high-power pulse transmission, network communication, space exploration, and precise sensing. Employing anti-resonant hollow-core fibers instead of light guiding arms for transmitting laser energy at the 2.79 μm band can significantly enhance the flexibility of medical laser handles, reduce system complexity, and increase laser transmission efficiency. Nevertheless, common anti-resonant hollow-core fibers do not have the ability to maintain the polarization state of light during laser transmission, which greatly affects their practical applications. In this paper, we propose a polarization-maintaining anti-resonant hollow-core fiber applicable for transmission at the mid-infrared 2.79 μm band. This fiber features a symmetrical geometric structure and an asymmetric refractive index cladding composed of quartz and a type of mid-infrared glass with a higher refractive index. Through optimizing the fiber structure at the wavelength scale, single-polarization transmission can be achieved at the 2.79 μm wavelength, with a polarization extinction ratio exceeding 1.01 × 10⁵, indicating its stable polarization-maintaining performance. Simultaneously, it possesses low-loss transmission characteristics, with the loss in the x-polarized fundamental mode being less than 9.8 × 10⁻³ dB/m at the 2.79 µm wavelength. This polarization-maintaining anti-resonant hollow-core fiber provides a more reliable option for the light guiding system of the 2.79 μm Er; Cr: YSGG laser therapy device. Full article

Functional Optical Balance (FOB) is a novel personalized strategy for intraocular lens (IOL) selection in cataract surgery, designed to reconcile the trade-off between optical quality and spectacle independence. FOB is a core concept aiming to maximize visual performance by treating the two eyes as a synergistic pair. One eye (often the dominant eye) is optimized for pristine optical quality (typically distance vision with a high-contrast monofocal or low-add IOL). In contrast, the fellow eye is optimized for extended depth of focus and pseudoaccommodation (using an extended depth-of-focus or multifocal/trifocal IOL) to reduce dependence on glasses. This review introduces the rationale and theoretical basis for FOB, including the interplay of depth of focus and optical aberrations, binocular summation, ocular dominance, and neuroadaptation. We discuss the clinical implementation of FOB: how the first-eye results guide the second-eye IOL choice in a tailored “mix-and-match” approach, as well as practical workflow considerations such as patient selection, ocular measurements, and decision algorithms. We also review current evidence from the literature on asymmetric IOL combinations (e.g., monofocal plus multifocal, or EDOF plus trifocal), highlighting visual outcomes, patient satisfaction, and remaining evidence gaps. Overall, FOB represents a paradigm shift toward binocular, patient-customized refractive planning. Early clinical reports suggest it can deliver a continuous range of vision without significantly compromising visual quality, though careful patient counseling and case selection are essential. Future directions include the integration of advanced diagnostics, artificial intelligence-driven IOL planning tools, and adaptive optics simulations to refine this personalized approach further. The promise of FOB is to improve cataract surgery outcomes by achieving an optimal balance: one that provides each patient with excellent visual quality and functional vision across distances, tailored to their lifestyle and expectations. Full article

Tongue cancer, the most aggressive subtype of oral cancer, presents critical challenges due to the limited number of specialists available and the time-consuming nature of conventional histopathological diagnosis. To address these issues, we developed an intelligent diagnostic system integrating Mueller matrix microscopy with deep learning to enhance diagnostic accuracy and efficiency. Through Mueller matrix polar decomposition and transformation, micro-polarization feature parameter images were extracted from tongue cancer tissues, and purity parameter images were generated by calculating the purity of the Mueller matrices. A multi-stage feature dataset of Mueller matrix parameter images was constructed using histopathological samples of tongue cancer tissues with varying stages. Based on this dataset, the clinical potential of Mueller matrix microscopy was preliminarily validated for histopathological diagnosis of tongue cancer. Four mainstream medical image classification networks—AlexNet, ResNet50, DenseNet121 and VGGNet16—were employed to quantitatively evaluate the classification performance for tongue cancer stages. DenseNet121 achieved the highest classification accuracy of 98.48%, demonstrating its potential as a robust framework for rapid and accurate intelligent diagnosis of tongue cancer. Full article

Terahertz (THz) frequencies, spanning from 0.1 to 1 THz, are poised to play a pivotal role in the development of future 6G wireless communication systems. These systems aim to utilize photonic technologies to enable ultra-high data rates—on the order of terabits per second—while maintaining low latency and high efficiency. In this work, we present a novel photonic method for generating sub-THz vector signals within the THz band, employing a semiconductor optical amplifier (SOA) and phase modulator (PM) to create an optical frequency comb, combined with in-phase and quadrature (IQ) modulation techniques. We demonstrate, both through simulation and experimental setup, the generation and successful transmission of a 0.1 THz vector. The process involves driving the PM with a 12.5 GHz radio frequency signal to produce the optical comb; then, heterodyne beating in a uni-traveling carrier photodiode (UTC-PD) generates the 0.1 THz radio frequency signal. This signal is transmitted over distances of up to 30 km using single-mode fiber. The resulting 0.1 THz electrical vector signal, modulated with quadrature phase shift keying (QPSK), achieves a bit error ratio (BER) below the hard-decision forward error correction (HD-FEC) threshold of ${3.8 \times 10}^{-3}$. To the best of our knowledge, this is the first experimental demonstration of a 0.1 THz photonic vector THz wave based on an SOA and a simple PM-driven optical frequency comb. Full article

The optical properties of a heterostructure containing GaSb/GaAs quantum dots (QDs) have been systematically investigated via photoluminescence (PL) measurements to gain insights into carrier dynamics. The QD and wetting layer (WL) emissions exhibit a complementary dependence on the excitation intensity and temperature, reflecting the interplay between carrier localization in the WL and carrier relaxation from the WL to the QDs. Carrier dynamics related to localization, injection, and recombination are further validated by time-resolved photoluminescence (TRPL). These findings highlight the necessity of carefully optimizing GaSb/GaAs QD structures to mitigate the impact of carrier localization, thereby enhancing the ultimate performance of devices utilizing these QDs as active region materials. Full article

Quadcolor cameras with conventional RGB channels were studied. The fourth channel was designed to improve the estimation of the spectral reflectance and chromaticity from the camera signals. The RGB channels of the quadcolor cameras considered were assumed to be the same as those of the Nikon D5100 camera. The fourth channel was assumed to be a silicon sensor with an optical filter (band-pass filter or notch filter). The optical filter was optimized to minimize a cost function consisting of the spectral reflectance error and the weighted chromaticity error, where the weighting factor controls the contribution of the chromaticity error. The study found that using a notch filter is more effective than a band-pass filter in reducing both the mean reflectance error and the chromaticity error. The reason is that the notch filter (1) improves the fit of the quadcolor camera sensitivities to the color matching functions and (2) provides sensitivity in the wavelength region where the sensitivities of RGB channels are small. Munsell color chips under illuminant D65 were used as samples. Compared with the case without the filter, the mean spectral reflectance rms error and the mean color difference (ΔE₀₀) using the quadcolor camera with the optimized notch filter reduced from 0.00928 and 0.3062 to 0.0078 and 0.2085, respectively; compared with the case of using the D5100 camera, these two mean metrics reduced by 56.3%. Full article