Photonics

11 pages, 2734 KB

Open AccessArticle

Coaxial LiDAR System Utilizing a Double-Clad Fiber Receiver

by Hao Chen, Zhenquan Su, Zhuolun Li, Hanfeng Ding and Jun Zhang

Photonics 2025, 12(11), 1080; https://doi.org/10.3390/photonics12111080 (registering DOI) - 1 Nov 2025

LiDAR technology has undergone significant advancement in recent years, establishing itself as a technique for long-range, high-precision detection. As its use expands into more intricate scenarios, the need to overcome blind spots in the scanning field and enhance system stability has become increasingly [...] Read more.

LiDAR technology has undergone significant advancement in recent years, establishing itself as a technique for long-range, high-precision detection. As its use expands into more intricate scenarios, the need to overcome blind spots in the scanning field and enhance system stability has become increasingly critical. This paper introduces a novel coaxial LiDAR system featuring a double-clad optical fiber-based receiver which consists of a single-mode fiber core for the emission of the laser beam and a multimode inner cladding for the collection and transmission of the back-reflected beam. The real-time system is specifically engineered to measure distances in both near and far fields, eliminating blind spots. Experimental evaluations demonstrate that our system achieves a detection range of 0.2–70.7 m, with a distance accuracy of 3.4 cm and an angular resolution of 0.018°. Compared with conventional LiDAR systems, our approach eliminates the need for complex optical pathway designs and algorithmic compensation. It offers a simplified structure, enhanced stability, and high accuracy. Full article

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14 pages, 3863 KB

Open AccessArticle

PN Junction Optimization for High-Speed Silicon Photonic Modulators

by Mahmoud Hamouda, Carine Mankarious, Aser El-Dahshan, Alaa Fathy, Eslam El-Fiky and Diaa Khalil

Photonics 2025, 12(11), 1079; https://doi.org/10.3390/photonics12111079 (registering DOI) - 31 Oct 2025

Abstract

PN-junction-based modulators are widely used in silicon photonic transceivers for different applications. Different junction shapes have been proposed in the literature. This work studies the optimization of the PN junction by tailoring the doping profile to achieve a high-efficiency modulator with sufficient bandwidth. [...] Read more.

PN-junction-based modulators are widely used in silicon photonic transceivers for different applications. Different junction shapes have been proposed in the literature. This work studies the optimization of the PN junction by tailoring the doping profile to achieve a high-efficiency modulator with sufficient bandwidth. For this purpose, a new N-shaped junction is proposed, which achieves superior performance compared to other junction shapes. The proposed junction has an efficiency that is 60% better than that of the lateral PN junction for the same doping condition, while maintaining a high bandwidth similar to other junctions such as the L-shaped and S-shaped designs. A junction design with an estimated RC bandwidth between 70 GHz and 94 GHz is also proposed. The impact of using the proposed junction in micro-ring modulators (MRMs) is also studied. N-shaped junctions in MRM demonstrated a 112% increase in electro-optic bandwidth over the vertical PN junction, with 60% and 140% improvements in extinction ratio (ER) and optical modulation amplitude (OMA), respectively, compared to the lateral PN junction. Full article

(This article belongs to the Special Issue Recent Advancement in Microwave Photonics)

21 pages, 4096 KB

Open AccessArticle

Highly Sensitive Dual-Polished Dual-Core PCF-Based SPR Sensor for Hemoglobin Detection Using FEM and Machine Learning

by Abrar Adib, Anik Chowdhury, Aditta Chowdhury, Md Abu Huraiya, Abu Farzan Mitul and Mohammad Istiaque Reja

Photonics 2025, 12(11), 1078; https://doi.org/10.3390/photonics12111078 (registering DOI) - 31 Oct 2025

Abstract

This research investigates a dual-polished surface plasmon resonance sensor based on dual-core photonic crystal fiber, featuring an innovative design aimed at enhancing hemoglobin concentration detection in blood, providing a valuable tool for diagnosing numerous health issues, such as chronic obstructive pulmonary disease. The [...] Read more.

This research investigates a dual-polished surface plasmon resonance sensor based on dual-core photonic crystal fiber, featuring an innovative design aimed at enhancing hemoglobin concentration detection in blood, providing a valuable tool for diagnosing numerous health issues, such as chronic obstructive pulmonary disease. The sensor makes use of an external sensing mechanism and utilizes gold (Au) coating as the plasmonic material, chosen for its strong plasmonic response and excellent chemical stability, ensuring robust performance across the 1.31–1.42 refractive index range. The electromagnetic characteristics and efficacy of the designed sensor were thoroughly investigated using the finite element method. Our proposed sensor demonstrates outstanding performance metrics, attaining peak amplitude sensitivity of about 734 RIU⁻¹, and wavelength sensitivity of 74,000 nm/RIU along with 1.35 × 10⁻⁶ RIU wavelength resolution. It also exhibits a notable Figure of Merit value of 667 for a corresponding Full width at Half Maximum value of 111 nm. Finally, a machine learning model based on linear regression was employed that enables the prediction of any hemoglobin concentration levels corresponding to analyte RI values. These exceptional performance metrics highlight the potential of our sensor as a reliable, cost-effective and highly sensitive solution for real-time biosensing applications. Full article

(This article belongs to the Special Issue Advances in Optical Sensors and Applications)

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17 pages, 5143 KB

Open AccessArticle

Hybrid Physical-Data Modeling Approach for Surface Scattering Characteristics of Low-Gloss Black Paint

by Zhen Mao, Zhaohui Li, Wei Liu, Yunfei Yin, Limin Gao and Jianke Zhao

Photonics 2025, 12(11), 1077; https://doi.org/10.3390/photonics12111077 (registering DOI) - 31 Oct 2025

Abstract

This study presents a hybrid BRDF modeling framework combining a five-parameter physical model with a (20,20,20) Multilayer Perceptron (MLP) model network to address the critical challenge of accurate grazing-angle prediction for low-gloss black coatings (SB-3A, Z306, PNC). While the baseline parametric model achieves [...] Read more.

This study presents a hybrid BRDF modeling framework combining a five-parameter physical model with a (20,20,20) Multilayer Perceptron (MLP) model network to address the critical challenge of accurate grazing-angle prediction for low-gloss black coatings (SB-3A, Z306, PNC). While the baseline parametric model achieves <5% RMSE at θ_i ≤ 60°, its inability to capture shadowing effects leads to >1.2 RMSE at 80° incidence. The proposed MLP model-enhanced solution reduces these high-angle errors to <0.012 RMSE while maintaining <5-min computational efficiency. Comprehensive validation shows the framework’s universality across materials with apparent anisotropy indices (ASI) of 0.465–30.26. The work demonstrates that neural networks can optimally compensate for missing physics in traditional models without sacrificing interpretability, offering immediate industrial value for aerospace coating analysis. Full article

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12 pages, 4256 KB

Open AccessArticle

Tunable-Charge Optical Vortices Through Edge Diffraction of a High-Order Hermit-Gaussian Mode Laser

by Shuaichen Li, Yiyang Zhang, Ying Li, Linge Mao, Pengfan Zhao and Zhen Qiao

Photonics 2025, 12(11), 1076; https://doi.org/10.3390/photonics12111076 - 30 Oct 2025

Abstract

An optical vortex is a typical structured light field characterized by a helical wavefront and a central phase singularity. With its expanding applications in modern information technology, the demand for generating vortex beams with diverse topological charges continues to grow. Existing methods for [...] Read more.

An optical vortex is a typical structured light field characterized by a helical wavefront and a central phase singularity. With its expanding applications in modern information technology, the demand for generating vortex beams with diverse topological charges continues to grow. Existing methods for modulating the topological charges of vortex beams involve complex operations and high costs. This study proposes a novel approach to modulate the topological charges of optical vortices through edge diffraction of a high-order Hermit–Gaussian (HG) mode laser. First, a high-order HG mode laser is built using off-axis pumping configuration. By selectively obscuring specific lobes of the high-order HG beam, various optical vortices are generated using a cylindrical lens mode converter. The topological charge can be continuously tuned by controlling the number of obscured lobes. This method substantially improves the efficiency of topological charge modulation, while also enabling the generation of fractional vortex states. These advancements show potential in mode-division-multiplexed optical communications and encryption. Full article

(This article belongs to the Special Issue Advances in Solid-State Laser Technology and Applications)

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19 pages, 2671 KB

Open AccessReview

The Transition of Luminescent Materials and Conductive Electrodes in Upconversion Devices to Flexible Architectures

by Huijuan Chen, Weibo Feng and Tianling Qin

Photonics 2025, 12(11), 1075; https://doi.org/10.3390/photonics12111075 - 30 Oct 2025

Abstract

Flexible upconversion (UC) devices, owing to their unique combination of high–efficiency optical energy conversion and mechanical flexibility, have attracted increasing attention in the fields of optoelectronics, wearable devices, flexible displays, and biomedical applications. However, significant challenges remain in balancing optical performance, mechanical adaptability, [...] Read more.

Flexible upconversion (UC) devices, owing to their unique combination of high–efficiency optical energy conversion and mechanical flexibility, have attracted increasing attention in the fields of optoelectronics, wearable devices, flexible displays, and biomedical applications. However, significant challenges remain in balancing optical performance, mechanical adaptability, long–term stability, and scalable fabrication, which limit their practical deployment. This review systematically introduces five representative upconversion mechanisms—excited–state absorption (ESA), energy transfer upconversion (ETU), energy migration upconversion (EMU), triplet–triplet annihilation upconversion (TTA–UC), and photon avalanche (PA)—highlighting their energy conversion principles, performance characteristics, and applicable scenarios. The article further delves into the flexible transition of upconversion devices, detailing not only the evolution of the luminescent layer from bulk crystals and nanoparticles to polymer composites and hybrid systems, but also the optimization of electrodes from rigid metal films to metal grids, carbon–based materials, and stretchable polymers. These developments significantly enhance the stability and reliability of flexible upconversion devices under bending, stretching, and complex mechanical deformation. Finally, emerging research directions are outlined, including multi–mechanism synergistic design, precise nanostructure engineering, interface optimization, and the construction of high–performance composite systems, emphasizing the broad potential of flexible UC devices in flexible displays, wearable health monitoring, solar energy harvesting, flexible optical communications, and biomedical photonic applications. This work provides critical insights for the design and application of high–performance flexible optoelectronic devices. Full article

(This article belongs to the Special Issue Organic Photodetectors, Displays, and Upconverters)

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14 pages, 2622 KB

Open AccessArticle

Enhancing the Solar-Blind UV Detection Performance of β-Ga₂O₃ Films Through Oxygen Plasma Treatment

by Rongxin Duan, Guodong Wang, Lanlan Guo, Yuechao Wang, Yumeng Zhai, Xiaolian Liu, Junjun Wang, Yingli Yang and Xiaojie Yang

Photonics 2025, 12(11), 1074; https://doi.org/10.3390/photonics12111074 - 30 Oct 2025

Abstract

This study systematically investigated the effects of oxygen plasma treatment on oxygen vacancy defects in sputtered β-gallium oxide (β-Ga₂O₃) films and their corresponding ultraviolet (UV) detection performance. The sputtered β-Ga₂O₃ film subjected [...] Read more.

This study systematically investigated the effects of oxygen plasma treatment on oxygen vacancy defects in sputtered β-gallium oxide (β-Ga₂O₃) films and their corresponding ultraviolet (UV) detection performance. The sputtered β-Ga₂O₃ film subjected to 1 min of oxygen plasma treatment exhibited optimal photodetection properties. Compared to the untreated sample, the dark current was reduced by approximately one order of magnitude to 0.378 pA at 10 V bias. It exhibited an 86% (from 2.92 s to 0.41 s) decrease in response time, a 41.6% increase in photocurrent, a very high photo-to-dark current ratio of 9.18 × 10⁵, and a specific detectivity of 2.62 × 10¹⁰ cm·Hz^1/2W⁻¹ under 254 nm UV illumination intensity of 799 μW/cm² at 10 V bias. Notably, appropriate oxygen plasma treatment minimizes electron capture, enhances the separation and collection of photogenerated carriers, and suppresses the persistent photoconductivity (PPC) effect, thus ultimately shortening the response time. Oxygen plasma processing thus provides an effective approach to fabricating high-performance β-Ga₂O₃ solar-blind photodetectors (SBPDs). Full article

(This article belongs to the Special Issue New Advances in Semiconductor Optoelectronic Materials and Devices)

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9 pages, 2178 KB

Open AccessArticle

High-Bandwidth Intensity-Difference Squeezed State at 895 nm Based on Four-Wave Mixing

by Rong Ma, Wen Zhang, Xiaowei Wu, Xiaoqin Qu and Xiaolong Su

Photonics 2025, 12(11), 1073; https://doi.org/10.3390/photonics12111073 - 30 Oct 2025

Abstract

As an essential quantum resource, the intensity-difference squeezed state based on four-wave mixing (FWM) in atomic vapor is widely applied in quantum information processing. In particular, a high intensity-difference squeezing bandwidth is vital for the realization of high-speed information processing. However, limited by [...] Read more.

As an essential quantum resource, the intensity-difference squeezed state based on four-wave mixing (FWM) in atomic vapor is widely applied in quantum information processing. In particular, a high intensity-difference squeezing bandwidth is vital for the realization of high-speed information processing. However, limited by the bandwidth of photodetectors, broadband intensity-difference squeezed state based on this system has not yet been reported. Here, we developed a transimpedance broadband balanced homodyne detector at 895 nm, achieving a bandwidth greater than 100 MHz and a maximum signal-to-noise ratio of 15 dB with 4 mW optical power. Utilizing this detector in a nondegenerate FWM process based on cesium vapor, we experimentally achieved broadband intensity-difference squeezing with a bandwidth of 100 MHz, which yielded a maximum squeezing of −7.17 ± 0.8 dB between 20 and 40 MHz. Meanwhile, using this detector, we experimentally investigated the cavity-enhanced FWM process, achieving a squeezing level of −6.07 ± 0.5 dB within a 4 MHz frequency range, which is limited by the cavity bandwidth. This work provides a reliable detection tool and experimental foundation for the research and application of broadband squeezed light sources based on FWM. Full article

(This article belongs to the Special Issue Advanced Research in Quantum Optics)

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15 pages, 1414 KB

Open AccessArticle

Compact Six-Degree-of-Freedom Displacement Sensing Based on Laser Reflection and Position-Sensitive Detectors

by Jingyu Chen, Junjie Li, Yuan Diao, Ke Wang, Wenbo Dong, Mengxi Yu and Zongfeng Li

Photonics 2025, 12(11), 1072; https://doi.org/10.3390/photonics12111072 - 29 Oct 2025

Abstract

To meet pose-control and vibration-suppression requirements in confined spaces, a compact, noncontact six-degree-of-freedom (6-DoF) displacement-sensing method is proposed. The method is based on laser reflection and a position-sensitive detector (PSD) and features an adjustable incidence angle. An adjustable-incidence-angle PSD–corner-cube retro-reflector (CCR) configuration is [...] Read more.

To meet pose-control and vibration-suppression requirements in confined spaces, a compact, noncontact six-degree-of-freedom (6-DoF) displacement-sensing method is proposed. The method is based on laser reflection and a position-sensitive detector (PSD) and features an adjustable incidence angle. An adjustable-incidence-angle PSD–corner-cube retro-reflector (CCR) configuration is devised, which reduces the PSD’s spatial footprint to 10.4% of that of a conventional layout. Building on this configuration, an analytical model is derived that maps the target’s 6-DoF displacement to the PSD spot motion as a function of the fixed relative pose between the PSD and the CCR mounted on the target. The model is linearized under the small-angle assumption. Experiments show an accuracy of 5.89 μm for translation within ±1.5 mm and 0.0027° for rotation within ±0.5°. The method couples a compact architecture with high precision and provides both a theoretical basis and an engineering-ready pathway for high-bandwidth pose sensing in confined spaces. Full article

(This article belongs to the Special Issue New Progress in Optical Precision Measurement in the Field of Space Technology)

21 pages, 8124 KB

Open AccessArticle

Design of Miniaturized Cooled Medium-Wave Infrared Curved Bionic Compound-Eye Optical System

by Fu Wang, Yinghao Chi, Linhan Li, Nengbin Cai, Yimin Zhang, Yang Yu, Sili Gao and Kaijun Ma

Photonics 2025, 12(11), 1071; https://doi.org/10.3390/photonics12111071 - 29 Oct 2025

Abstract

To address the issues of insufficient detector target size and high system complexity in infrared bionic compound-eye systems, this paper designs a miniaturized cooled medium-wave infrared curved bionic compound-eye optical system specifically for large target surface detectors and develops a proof-of-concept prototype for [...] Read more.

To address the issues of insufficient detector target size and high system complexity in infrared bionic compound-eye systems, this paper designs a miniaturized cooled medium-wave infrared curved bionic compound-eye optical system specifically for large target surface detectors and develops a proof-of-concept prototype for verification. The system comprises three components: (1) a curved multi-aperture array, which consists of 61 sub-apertures with an entrance pupil diameter of 5 mm and a focal length of 10 mm; (2) a cooled planar detector; and (3) a relay imaging system, which adopts secondary imaging technology and achieves the matching between the array and detector with only six infrared lenses. The fill factor is introduced to analyze light energy utilization efficiency, providing a theoretical basis for improving the system’s signal-to-noise ratio and spatial information collection capability; meanwhile, the focal length distribution and pupil matching are analyzed to ensure the system’s optical performance. The system operates within the 3.7–4.8 μm wavelength band, with a total focal length of 3.08 mm, F-number of 2, and field of view reaching 108°. Simulations demonstrate that all sub-aperture imaging channels have MTF values greater than 0.47 at 33.3 lp/mm, with distortion less than 3%. Imaging test results verify that the system possesses excellent imaging performance. Full article

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21 pages, 4970 KB

Open AccessArticle

Measuring Phase–Amplitude Coupling Effect with OPM-MEG

by Yong Li, Hao Lu, Chunhui Wang, Fuzhi Cao, Jianzhi Yang, Binyi Su, Ying Liu and Xiaolin Ning

Photonics 2025, 12(11), 1070; https://doi.org/10.3390/photonics12111070 - 29 Oct 2025

Abstract

Optically pumped magnetometers (OPMs) present a promising opportunity to advance magnetoencephalography (MEG), enhancing the accuracy of neuronal activity recordings due to their high spatiotemporal resolution. However, to fully realize the potential of OPM-MEG as an emerging brain functional imaging technology, it is essential [...] Read more.

Optically pumped magnetometers (OPMs) present a promising opportunity to advance magnetoencephalography (MEG), enhancing the accuracy of neuronal activity recordings due to their high spatiotemporal resolution. However, to fully realize the potential of OPM-MEG as an emerging brain functional imaging technology, it is essential to measure key indicators of neural dynamics, particularly phase–amplitude coupling (PAC). PAC is a fundamental mechanism for integrating information across different frequency bands and plays an important role in various cognitive functions and neurological disorders. Therefore, measuring PAC with OPM-MEG is a crucial step toward expanding its applications. In this study, brain signals under pitch sequence stimulation were recorded using OPM-MEG to analyze the PAC effect in the primary auditory cortex (Aud) and the inferior frontal gyrus (IFG), as well as the functional connectivity between brain regions. The findings were validated through EEG control experiments. The results indicated that the PAC effect measured by OPM-MEG was largely consistent with that measured by EEG, with OPM-MEG appearing to detect PAC more prominently under the current experimental conditions. The PAC of Aud exhibited a trend of initially increasing and then decreasing centered on the target pitch, showing hemispheric symmetry. The PAC of IFG showed variations under different pitch conditions and displayed right hemisphere lateralization. Functional connectivity analysis provided convergent evidence for the mechanisms underlying the PAC effect and suggested the reliability of the OPM-MEG system in capturing cross-frequency neural dynamics. To our knowledge, this study provides the first task-based evidence that OPM-MEG can measure PAC effects in cortical regions, offering an initial foundation for future investigations of brain dynamics using this technology. Full article

(This article belongs to the Section Quantum Photonics and Technologies)

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14 pages, 2288 KB

Open AccessArticle

Design and Modeling of Compact Tunable Lens Driven by Bilateral Dielectric Elastomer

by Zhuoqun Hu, Meng Zhang, Zihao Gan, Jianming Lv, Zhaoyang Liu and Huajie Hong

Photonics 2025, 12(11), 1069; https://doi.org/10.3390/photonics12111069 - 29 Oct 2025

Abstract

Compared to traditional mechanical zoom lenses, tunable lenses driven by dielectric elastomers provide clear advantages in zoom range, response speed, and lightweight design. However, these lenses generally employ planar dielectroelastomer actuation, resulting in redundant structures. Additionally, the viscoelastic properties of dielectroelastomer materials often [...] Read more.

Compared to traditional mechanical zoom lenses, tunable lenses driven by dielectric elastomers provide clear advantages in zoom range, response speed, and lightweight design. However, these lenses generally employ planar dielectroelastomer actuation, resulting in redundant structures. Additionally, the viscoelastic properties of dielectroelastomer materials often make precise control of focal length difficult. To overcome this issue, this paper introduces a compact, spherical dielectroelastomer-driven tunable lens with a radial size of 20 mm and an effective aperture of 8 mm. A dual-sided actuation structure allows for a 55% adjustment in focal length. Using thermodynamic principles and a spring–viscoelastic rheological model, static and dynamic models of the system have been developed. Experimental results demonstrate that the proposed model accurately predicts the lens’s dynamic response, with a root-mean-square error of less than 0.135, thereby providing a reliable theoretical basis for achieving high-precision focal length control. Full article

(This article belongs to the Section Optoelectronics and Optical Materials)

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13 pages, 2074 KB

Open AccessArticle

Research on Diabetes Analysis Based on Deep Learning-Enhanced Data

by Yin Zhang, Shaolong Chen, Jiawei Nie, Hang Zhao, Jun Song and Yuanlong Deng

Photonics 2025, 12(11), 1068; https://doi.org/10.3390/photonics12111068 - 29 Oct 2025

Abstract

Diabetes poses a global health challenge, with accurate classification and blood glucose prediction being crucial for effective management and treatment. However, traditional methods are hindered by data scarcity. This study aims to use deep learning to complete data expansion to improve the accuracy [...] Read more.

Diabetes poses a global health challenge, with accurate classification and blood glucose prediction being crucial for effective management and treatment. However, traditional methods are hindered by data scarcity. This study aims to use deep learning to complete data expansion to improve the accuracy of diabetes classification and blood glucose prediction. Raman spectroscopy, Conditional Generative Adversarial Networks (CGAN), and a suite of optimized regression models were employed, with the best hyperparameter combinations for each model on the current dataset determined through grid search and cross-validation. The introduction of CGAN for data augmentation effectively addressed the issue of data scarcity, resulting in a significant improvement in overall performance. The top-performing model achieved a diabetes classification accuracy of over 99% and a blood glucose prediction error of 0.28 mg/dL. The application of CGAN notably enhanced both classification and prediction accuracy, a trend further supported by performance improvements illustrated through comparative graphs. This integrated approach provides a robust solution for accurate diabetes diagnosis and blood glucose prediction, demonstrating potential advancements in non-invasive diabetes management. Full article

(This article belongs to the Special Issue Optical Sensors for Advanced Biomedical Applications)

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13 pages, 1686 KB

Open AccessArticle

The Influence of Ultrashort Laser Pulse Duration on Shock Wave Generation in Water Under Tight Focusing Conditions

by Nikita Rishkov, Nika Asharchuk, Vladimir Yusupov and Evgenii Mareev

Photonics 2025, 12(11), 1067; https://doi.org/10.3390/photonics12111067 - 28 Oct 2025

Abstract

The control of mechanical effects, such as shock waves, induced by ultrashort laser pulses in water is crucial for applications in biomedicine and material processing. However, optimizing these effects requires a detailed understanding of how laser parameters, particularly pulse duration, influence the underlying [...] Read more.

The control of mechanical effects, such as shock waves, induced by ultrashort laser pulses in water is crucial for applications in biomedicine and material processing. However, optimizing these effects requires a detailed understanding of how laser parameters, particularly pulse duration, influence the underlying energy deposition mechanisms. This study systematically investigates the dependence of shock wave amplitude on fluence (up to 10 J/cm²) and pulse duration (200 fs to 10 ps) of near-infrared laser pulses under tight focusing conditions (Numerical aperture NA = 0.42), using a combined experimental and numerical approach based on the dynamical rate equation model. Our key finding is that the shock wave amplitude is governed by the total kinetic energy of the electrons in the laser-induced plasma, leading to a distinct maximum at approximately 5 ps (confidence interval: 4.5–5.5 ps) and saturation at fluences ~7 J/cm². This optimum arises from a balance between the increasing effectiveness of avalanche ionization for longer pulses and the competing effects of electron recombination and reduced photoionization efficiency. Consequently, these results identify a practical parameter window—pulse durations of 4–6 ps at moderate fluences—for optimizing laser-induced mechanical effects in applications such as laser surgery in aqueous media. Full article

(This article belongs to the Section Optical Interaction Science)

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11 pages, 3094 KB

Open AccessArticle

Fresnel Coherent Diffraction Imaging Without Wavefront Priors

by Ling Bai, Wen Cao, Yueshu Xu, Cuifang Kuang and Xu Liu

Photonics 2025, 12(11), 1066; https://doi.org/10.3390/photonics12111066 - 28 Oct 2025

Abstract

Fresnel diffraction plays a critical role in coherent diffraction imaging and holography. Experimental setups for these techniques are often designed based on plane-wave illumination. However, two key issues arise in practical applications: on the one hand, it is difficult to obtain an ideal [...] Read more.

Fresnel diffraction plays a critical role in coherent diffraction imaging and holography. Experimental setups for these techniques are often designed based on plane-wave illumination. However, two key issues arise in practical applications: on the one hand, it is difficult to obtain an ideal plane wave in experiments, which inevitably introduces wavefront curvature; on the other hand, the use of spherical waves enhances the quality of reconstruction results, while it also imposes additional requirements for the calibration of both the illumination wavefront and experimental parameters. To address these issues, we introduce a diffraction-adapted propagation model that integrates both the spherical wavefront effects and sampling variations within the diffraction model. The parameters of this model can be estimated through prior-free optimization, thereby eliminating the need for prior knowledge of system parameters or specific experimental setups. Our approach enables robust reconstruction across a wide range of Fresnel diffraction patterns. It also allows for the automatic calibration of experimental parameters using only the measured data. The effectiveness of the proposed method has been validated through both theoretical analysis and experimental results. Full article

(This article belongs to the Special Issue Computational Optical Imaging: Theories, Algorithms, and Applications)

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15 pages, 3641 KB

Open AccessArticle

Asymmetric Nano-Sensor Based on Inverted Trapezoidal U-Shaped Circular Cavity Structure

by Mengqi Zhao, Shubin Yan, Zhaokun Yan, Weijie Yang, Hongfu Chen, Guang Liu, Yang Cui and Taiquan Wu

Photonics 2025, 12(11), 1065; https://doi.org/10.3390/photonics12111065 - 28 Oct 2025

Abstract

This paper presents a novel asymmetric U-shaped refractive index sensor, which is based on a MIM waveguide and coupled with a U-shaped resonator, which integrates a ring, a circular cavity, and two rectangular cavities (URRCTR), in addition to an inverted rectangular nanostructure. The [...] Read more.

This paper presents a novel asymmetric U-shaped refractive index sensor, which is based on a MIM waveguide and coupled with a U-shaped resonator, which integrates a ring, a circular cavity, and two rectangular cavities (URRCTR), in addition to an inverted rectangular nanostructure. The efficiency of the proposed sensor was investigated and optimized through the FEM. Simulation results indicate that the interaction between the broadband mode supported by the inverted square-shaped structure on the primary waveguide and the confined narrowband mode of the URRCTR resonator generates a distinct asymmetric feature in the transmission profile, a characteristic indicative of Fano resonance. The geometric parameters of the structure are crucial for tuning the Fano resonance features. Through systematic optimization, the sensor achieves a sensitivity of 3480 nm/RIU and a figure of merit (FOM) of 55.23. Due to its high sensitivity, compact footprint, and favorable temperature-dependent properties, the presented sensor reveals considerable promise for various applications in integrated photonic sensing. Full article

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8 pages, 5376 KB

Open AccessArticle

Efficient Loading of an Yb MOT on the ¹S₀ → ¹P₁ Transition

by Zhufang Zhao, Shunxiang Wang, Jun Jian, Quanxin Zhang, Wenliang Liu, Jizhou Wu, Yuqing Li and Jie Ma

Photonics 2025, 12(11), 1064; https://doi.org/10.3390/photonics12111064 - 28 Oct 2025

Abstract

We demonstrate efficient loading of an Yb three-dimensional magneto-optical trap (3D MOT) on the ¹S₀ → ¹P₁ transition. The experiment employs a two-dimensional magneto-optical trap (2D MOT) as an efficient cold atom source. Through optimization of the 2D MOT, [...] Read more.

We demonstrate efficient loading of an Yb three-dimensional magneto-optical trap (3D MOT) on the ¹S₀ → ¹P₁ transition. The experiment employs a two-dimensional magneto-optical trap (2D MOT) as an efficient cold atom source. Through optimization of the 2D MOT, auxiliary Zeeman slower, and push beam parameters that govern atomic capture, we achieve an atomic loading rate of 5 ×

10^{6}

atoms/s in the 3D MOT, with approximately ∼10⁷ trapped atoms. Our experimental results confirm the successful transfer of a substantial number of atoms from the 2D region to the science chamber via the push beam, providing an experimental foundation for subsequent implementation of narrow-line MOT and two-color MOT. Full article

(This article belongs to the Special Issue Advanced Research in Quantum Optics)

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16 pages, 4465 KB

Open AccessArticle

Genetic Algorithm Optimization for Designing Polarization-Maintaining Few-Mode Fibers with Uniform Doping Profiles

by Hao Gu, Jian Wang, Zhiyu Chang, Kun Li, Xingcheng Han and Bin Liu

Photonics 2025, 12(11), 1063; https://doi.org/10.3390/photonics12111063 - 28 Oct 2025

Abstract

To support mode-division multiplexing with reduced inter-modal crosstalk, we propose a novel polarization-maintaining few-mode fiber design with a uniform doping profile and no air holes. The fiber employs two placed low-index inclusions to lift modal degeneracy and achieve strong birefringence while maintaining compatibility [...] Read more.

To support mode-division multiplexing with reduced inter-modal crosstalk, we propose a novel polarization-maintaining few-mode fiber design with a uniform doping profile and no air holes. The fiber employs two placed low-index inclusions to lift modal degeneracy and achieve strong birefringence while maintaining compatibility with standard MCVD and OVD fabrication processes. A genetic algorithm is used to optimize the geometrical and refractive index parameters. Finite element simulations show that the optimized design supports ten guided modes with a minimum effective index difference exceeding

3.8 \times 10^{- 4}

across the C+L band. The fiber exhibits moderate dispersion and strong modal isolation. Tolerance analysis confirms good robustness against index fluctuations and moderate sensitivity to dimensional variations. These features suggest that the proposed PM-FMF is a promising candidate for short-reach spatial-division multiplexing applications where intrinsic polarization and mode separation are desired. Full article

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11 pages, 3010 KB

Open AccessArticle

Optimization of Tungsten Anode Target Design for High-Energy Microfocus X-Ray Sources via Geant4 Monte Carlo Simulation

by Yuetian Liu, Lili Li, Yiheng Liu, Xue Zhang, Liwei Xin, Zhengkun Fu, Jinshou Tian, Wei Zhao and Duan Luo

Photonics 2025, 12(11), 1062; https://doi.org/10.3390/photonics12111062 - 27 Oct 2025

Abstract

High-energy microfocus X-ray sources are increasingly applied in non-destructive testing, high-resolution imaging, and additive manufacturing. The design and optimization of the anode target critically determine source efficiency, spectral characteristics, and imaging performance. In this study, Monte Carlo simulations using the Geant4 toolkit were [...] Read more.

High-energy microfocus X-ray sources are increasingly applied in non-destructive testing, high-resolution imaging, and additive manufacturing. The design and optimization of the anode target critically determine source efficiency, spectral characteristics, and imaging performance. In this study, Monte Carlo simulations using the Geant4 toolkit were conducted to systematically evaluate transmission and reflection tungsten targets with varied thicknesses and incidence angles under electron beam energies ranging from 100 to 300 keV. The results reveal that, for a microfocus X-ray source operating at a maximum tube voltage of 225 kV, the optimal transmission tungsten target exhibits a thickness of 18 μm, whereas the optimal reflection tungsten target achieves maximum efficiency at a 30 μm thickness with a 25° incidence angle. A nearly linear relationship between electron energy and optimal transmission target thickness is established within the 100–300 keV range. Additionally, the influence of beryllium window thickness and filter materials on the emergent X-ray spectrum is analyzed, demonstrating pathways for spectral hardening and transmission optimization. This study further elucidates the angular–intensity distribution of emitted X-rays, providing critical insights into beam spatial characteristics. Collectively, these findings establish a theoretical foundation for target optimization, enabling enhanced X-ray source performance in high-resolution imaging and supporting applications in detector calibration, flatness correction, beam hardening correction, and radiation shielding design. Full article

(This article belongs to the Special Issue Ultrafast Dynamics Probed by Photonics and Electron-Based Techniques)

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