Photonics

32 pages, 10452 KB

Open AccessArticle

Physics-Guided LLM Prompt Engineering for Distributed Acoustic Sensing Data Augmentation in Pipeline Intrusion Detection

by Bingcai Sun, Xingcheng Zhao, Mosong Li, Zhaoheng Liu and Quan Li

Photonics 2026, 13(7), 693; https://doi.org/10.3390/photonics13070693 - 22 Jul 2026

Viewed by 428

Abstract

Distributed acoustic sensing (DAS) is increasingly used for third-party intrusion (TPI) detection in oil and gas pipeline monitoring, but labeled DAS data are often scarce, leading to overfitting, poor generalization, and increased false alarms and missed detections. Conventional data augmentation, GAN-based synthesis, and [...] Read more.

Distributed acoustic sensing (DAS) is increasingly used for third-party intrusion (TPI) detection in oil and gas pipeline monitoring, but labeled DAS data are often scarce, leading to overfitting, poor generalization, and increased false alarms and missed detections. Conventional data augmentation, GAN-based synthesis, and transfer learning may generate physically implausible samples or fail to cover the event feature space. To address this, we propose a physics-guided large language model (LLM) prompt-engineering framework for DAS data augmentation and pipeline intrusion detection. The framework establishes a physically grounded feature-indicator framework for DAS disturbance-event classification by mapping primary event mechanisms to measurable signal indicators, and then uses a standardized four-module prompt template to guide LLM-based synthesis-script generation. A two-stage iterative verification procedure is further introduced to constrain the generated samples in terms of physical-mechanism compliance and feature-parameter consistency. Synthetic data are combined with real data to train a lightweight PatchTransformer model for TPI detection, while an additional CNN is used to assess cross-architecture applicability. Using the public DAS1K benchmark with five-fold stratified cross-validation and a univariate controlled experiment (0–800 synthetic samples per category), the results show that the use of synthetic data improves detection performance overall. The configuration with 600 synthetic samples per category achieves 92.27% accuracy and 92.38% macro-F1, outperforming the conventional augmentation baseline by 4.74 and 4.86 percentage points, respectively. An additional CNN experiment also showed consistent performance gains across the tested augmentation settings, indicating that the benefit of the proposed synthetic data was not restricted to the PatchTransformer architecture. These findings indicate that LLM-assisted data augmentation can effectively improve the generalization of DAS-based pipeline intrusion detection when field-labeled samples are scarce. Full article

(This article belongs to the Special Issue Emerging Technologies and Applications in Fiber Optic Sensing)

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25 pages, 4257 KB

Open AccessReview

Research Advances in Side-Pumped Solid-State Lasers in the 2 µm Region

by Anyi Jiao, Jiaze Wu, Yu Ding, Xiaotao Yang and Xiaoming Duan

Photonics 2026, 13(7), 692; https://doi.org/10.3390/photonics13070692 - 22 Jul 2026

Viewed by 476

Abstract

Lasers operating in the 2 µm spectral region have significant application value and development potential in fields such as lidar, medical surgery, and mid-infrared nonlinear optics because they are located in the atmospheric absorption window and coincide with a strong absorption peak of [...] Read more.

Lasers operating in the 2 µm spectral region have significant application value and development potential in fields such as lidar, medical surgery, and mid-infrared nonlinear optics because they are located in the atmospheric absorption window and coincide with a strong absorption peak of water molecules. This article first briefly introduces the energy level characteristics and commonly used crystal matrices of Tm³⁺, Ho³⁺ and Tm³⁺/Ho³⁺ codoped systems, and then reviews the research progress of 2 µm side-pumped solid-state lasers based on these ions and matrices. This review summarizes the research progress of 2 µm side-pumped solid-state lasers, categorized by operating mode and gain medium. Particular attention is given to the mature advantages of Tm-doped garnet lasers in high average power output and the potential of Tm/Ho-codoped fluoride lasers in high-energy, high-beam-quality pulse output. Finally, this paper further reviews the development of side-pumped laser structures and offers a prospective outlook on the future development of 2 µm region side-pumped lasers. Full article

(This article belongs to the Special Issue Recent Advances in Infrared Lasers and Applications)

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25 pages, 1246 KB

Open AccessReview

Mid-Infrared Laser Spectroscopy for Stand-Off Bioaerosol Detection: Emerging Technologies and Remote Sensing Applications

by Silvia Paukovčeková and Peter Tatar

Photonics 2026, 13(7), 691; https://doi.org/10.3390/photonics13070691 - 22 Jul 2026

Viewed by 655

Abstract

Biological aerosols represent a significant challenge for modern CBRN defense due to their potential for long-range dispersion and the need for rapid threat assessment. Current stand-off detection systems are effective in recognizing anomalous aerosol clouds but often lack the molecular specificity required for [...] Read more.

Biological aerosols represent a significant challenge for modern CBRN defense due to their potential for long-range dispersion and the need for rapid threat assessment. Current stand-off detection systems are effective in recognizing anomalous aerosol clouds but often lack the molecular specificity required for reliable agent identification. This review examines the role of mid-infrared (MIR) spectroscopy as an emerging approach for chemically resolved stand-off bioaerosol sensing. The physical principles of MIR detection are discussed, including molecular vibrational fingerprints, differential scattering (DISC), and circular intensity differential scattering (CIDS), together with their relationship to aerosol optical properties and Mie resonance effects. Existing and emerging sensing architectures are reviewed, ranging from operational CO₂ laser-based DISC systems to semiconductor-based platforms utilizing tunable differential absorption lidar (DIAL), Quantum Cascade Lasers (QCLs), and dual-comb spectroscopy. The analysis highlights the ability of MIR sensing to access biomolecular signatures associated with proteins, lipids, nucleic acids, and bacterial spores, while also addressing challenges related to atmospheric attenuation, biological variability, and signal interpretation. The reviewed literature indicates that MIR spectroscopy offers a promising pathway toward improved stand-off identification of hazardous bioaerosols, supporting early threat detection and enhanced situational awareness in applications including CBRN defense, critical infrastructure protection, environmental monitoring, public health surveillance, and emergency response. Full article

(This article belongs to the Special Issue Laser as a Detection: From Spectral Imaging to LiDAR for Remote Sensing Applications (2nd Edition))

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16 pages, 1583 KB

Open AccessArticle

Exceptional-Point-Enhanced Magnetic Field Sensing in a Cavity-QED System

by Zhi-Chao Han, Yu-Bo Liang, Ming-Jie Liao, Zi-Jian Lin, Shuai-Ling Wang, Jing-Ping Xu, Jabir Hakami and Ya-Ping Yang

Photonics 2026, 13(7), 690; https://doi.org/10.3390/photonics13070690 - 22 Jul 2026

Viewed by 381

Abstract

In this study, we design a new magnetic field measurement model. Specifically, we use a single two-level atom coupled to two cavities to construct a parity–time-symmetric system supporting a third-order exceptional point. If a perturbation is applied to the atomic transition frequency, the [...] Read more.

In this study, we design a new magnetic field measurement model. Specifically, we use a single two-level atom coupled to two cavities to construct a parity–time-symmetric system supporting a third-order exceptional point. If a perturbation is applied to the atomic transition frequency, the eigenvalue of the system will change, and the eigenvalue change is proportional to the cubic root of the perturbation. If the perturbation comes from the magnetic field, a sensitive magnetic field measurement device is formed. By introducing gain and loss via the input–output field, we realize a third-order EP in the non-Hermitian Hamiltonian. Our analysis shows that the system exhibits a nonlinear response to magnetic field perturbations, leading to enhanced spectral sensitivity compared to conventional linear detectors. This equivalent EP based on a cavity-QED sensing scheme breaks the limitation of passive EP sensors and provides a new theoretical idea for the design of sensitive magnetic field measurement devices. Full article

(This article belongs to the Special Issue Non-Hermitian Photonics for Enhanced Light Control and Sensing)

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24 pages, 2990 KB

Open AccessArticle

AQFS-Net: An Adaptive Quality-Aware Fusion and Saliency-Guided Network for Visible-Infrared Object Detection

by Weijun Wu and Xufei Zhuang

Photonics 2026, 13(7), 689; https://doi.org/10.3390/photonics13070689 - 21 Jul 2026

Viewed by 326

Abstract

Object detection in real-world scenarios is often challenged by adverse visual conditions, such as low illumination, strong glare, and dense fog, which severely degrade visible-spectrum features and lead to missed detections, inaccurate localization, and reduced detection accuracy. To address these issues, this paper [...] Read more.

Object detection in real-world scenarios is often challenged by adverse visual conditions, such as low illumination, strong glare, and dense fog, which severely degrade visible-spectrum features and lead to missed detections, inaccurate localization, and reduced detection accuracy. To address these issues, this paper proposes AQFS-Net, a dual-modal fusion detection network for visible-infrared object detection. Built upon YOLOv13, AQFS-Net adopts a symmetric dual-branch backbone by incorporating infrared images, thereby exploiting the complementary information between the visible and infrared modalities. To alleviate the negative transfer caused by conventional static fusion strategies, an Adaptive Quality-Aware Fusion Module (AQFM) is designed to dynamically enhance informative features and suppress degraded information according to the modality-specific reliability of different regions. In addition, a Foreground-Aware Saliency Guidance (FASG) branch is introduced to guide the network to focus on target regions through foreground supervision, reducing interference from complex backgrounds. Experimental results on the public LLVIP and M3FD datasets show that the proposed method improves mAP@0.5 by 6.8 and 3.1 percentage points, respectively, compared with the baseline using only visible images. These results demonstrate the effectiveness of AQFS-Net in improving dual-modal fusion quality and detection performance under challenging visual conditions, providing a practical reference for visible-infrared object detection in complex illumination scenarios. Full article

(This article belongs to the Special Issue Computational Imaging: Photonics and Optical Applications)

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16 pages, 21821 KB

Open AccessArticle

Four-Channel Holographic Multiplexing via Riemann–Silberstein Geometric Phase in Bianisotropic Metasurfaces

by Yunfei Niu, Luning Qian and Chunchun Bei

Photonics 2026, 13(7), 688; https://doi.org/10.3390/photonics13070688 - 21 Jul 2026

Viewed by 315

Abstract

Conventional Pancharatnam–Berry (PB) phase metasurfaces operate within the two-dimensional SU(2) polarization space of the electric field, fundamentally limiting holographic multiplexing to two independent channels. Here, we propose and numerically demonstrate a four-channel holographic metasurface exploiting the recently discovered Riemann–Silberstein (RS) geometric phase arising [...] Read more.

Conventional Pancharatnam–Berry (PB) phase metasurfaces operate within the two-dimensional SU(2) polarization space of the electric field, fundamentally limiting holographic multiplexing to two independent channels. Here, we propose and numerically demonstrate a four-channel holographic metasurface exploiting the recently discovered Riemann–Silberstein (RS) geometric phase arising from SU(4) polarization evolution in the full electromagnetic field space. The RS vector Ψ = E + icB unifies electric and magnetic fields into a four-dimensional polarization state space. By engineering bianisotropic Huygens meta-atoms with independently controllable electric-dipole orientation angle α and magnetic-dipole orientation angle ψ, four geometric-phase channels—labeled by the joint spin eigenstates |σ,κ⟩∈{|+,+⟩,|+,−⟩,|−,+⟩,|−,−⟩}—are simultaneously addressed from a single aperture. We develop the complete SU(4) transfer-matrix formalism and optimize four quasi-independent phase profiles using an extended Gerchberg–Saxton algorithm with a three-parameter (α,ψ,h) design library, where the pillar height h serves as a third degree of freedom to overcome the linear phase constraint inherent to the two-angle parameterization. Numerical simulations at 0.8 THz demonstrate simultaneous projection of four independent holographic images with mean diffraction efficiency 60.4% and inter-channel crosstalk below 3.2%, doubling the information capacity of conventional dual-channel PB holograms. An intrinsic ~24× common-mode noise suppression arising from electromagnetic duality symmetry is also demonstrated. This work establishes a direct link between fundamental electromagnetic symmetry and high-capacity wavefront engineering. Full article

(This article belongs to the Special Issue Principle and Application of Optical Metasurfaces)

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20 pages, 3730 KB

Open AccessArticle

Physics-Verified Spectral Dreaming Enables Interpretable and Manufacturable Inverse Design of Multilayer Radiative Coolers

by Jiajun Wang and Xiuye Liu

Photonics 2026, 13(7), 687; https://doi.org/10.3390/photonics13070687 - 21 Jul 2026

Viewed by 356

Abstract

Optical inverse design faces a dilemma: neural surrogates enable fast, differentiable search but can yield physically unreliable pseudo-optima, whereas solver-in-the-loop optimization is reliable yet costly. Most surrogate methods also trust the surrogate throughout the search, train separate models for performance prediction and structure [...] Read more.

Optical inverse design faces a dilemma: neural surrogates enable fast, differentiable search but can yield physically unreliable pseudo-optima, whereas solver-in-the-loop optimization is reliable yet costly. Most surrogate methods also trust the surrogate throughout the search, train separate models for performance prediction and structure optimization, and remain largely black-box. We propose Physics-Verified Spectral Dreaming (PVSD), a unified framework for forward prediction, inverse design, and physical interpretability: a frozen differentiable spectral surrogate “dreams” structural mutations by input-gradient ascent to explore the design space, while a physical solver adjudicates every accepted update—the surrogate proposes, physics decides. We instantiate it as PVSD-TMM for one-dimensional multilayer radiative coolers. The forward predictor attains

R^{2} = 0.9936 / 0.9964 / 0.9828

for net cooling power, solar reflectance, and primary-window emissivity; neural dreaming lifts the population-mean net cooling power of 1000 random seeds from

- 466.7

to

65.8

W m⁻² (

91.4 %

reaching net cooling), and continuous-thickness refinement with 5 nm rounding yields a 14-layer manufacturable final design. Independent COMSOL finite-element and analytic TMM cross-validation converge to

P_{cool} \approx 172

W m⁻²,

R_{solar} \approx 0.970

, and

ε_{win} = 0.9252

. This is a full-spectrum radiative-balance result for an idealized radiative-only case (

h_{conv} = 0

), not a window-emittance-only metric; PVSD thus achieves high simulated broadband radiative-cooling performance under the stated assumptions, without claiming global optimality. Full article

(This article belongs to the Section Data-Science Based Techniques in Photonics)

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16 pages, 2860 KB

Open AccessArticle

Thermal Image-to-LiDAR Depth Transformation via Pretrained Visual Model and Two-Stage Depth Refinement

by HeeJeong Yoo and Hoon Yoo

Photonics 2026, 13(7), 686; https://doi.org/10.3390/photonics13070686 - 21 Jul 2026

Viewed by 330

Abstract

LiDAR sensors provide reliable physical distance measurements using laser signals, enabling accurate acquisition of 3D information for various optical systems. However, they are costly, require significant weight and space, and their reliability and accuracy degrade under adverse environmental and weather conditions. In contrast, [...] Read more.

LiDAR sensors provide reliable physical distance measurements using laser signals, enabling accurate acquisition of 3D information for various optical systems. However, they are costly, require significant weight and space, and their reliability and accuracy degrade under adverse environmental and weather conditions. In contrast, thermal cameras operating in the infrared spectrum can capture stable visual information even in challenging scenarios such as nighttime, low-light, and rain. However, they cannot directly provide the physical 3D depth information that LiDAR offers. To design efficient optical systems, there is a growing need for techniques that transform thermal image data into LiDAR-like depth information. While deep learning models can theoretically learn direct mappings between thermal and LiDAR modalities, the scarcity of acquiring paired thermal–LiDAR datasets and the difficulty of acquiring them make this task challenging. In this paper, we propose a thermal image-to-LiDAR depth transformation framework. Our method leverages large-scale pretrained visual models for depth estimation to generate initial depth predictions from thermal inputs. Since pretrained RGB-based models face a modality gap when applied to thermal data, we introduce a two-stage depth refinement. Stage 1 corrects global scale inconsistencies, and Stage 2 refines local structural details. Experiments on the MS2 dataset demonstrate that the proposed framework consistently improves the initial DepthPro outputs across day, night, and rainy conditions. Both quantitative metrics and qualitative comparisons show that RGB-pretrained depth predictions can provide useful structural cues for thermal depth estimation when their global scale and local structural errors are explicitly refined. Full article

(This article belongs to the Special Issue Diffractive Optics: From Fundamentals to Applications)

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13 pages, 14929 KB

Open AccessArticle

Nanoimprinted Dielectric Metasurface for Enhanced Light Extraction in AlGaN-Based Deep-Ultraviolet LEDs

by Yingmeng Wang, Wei Jiang, Yashu Zang, Shilin Liu, Wenyu Kang, Jun Yin and Junyong Kang

Photonics 2026, 13(7), 685; https://doi.org/10.3390/photonics13070685 - 20 Jul 2026

Viewed by 386

Abstract

Total internal reflection (TIR) loss is a critical bottleneck limiting light extraction in AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs), primarily due to the large refractive-index contrast at the light-emitting interface. Here, pyramid-shaped dielectric metasurfaces are designed and fabricated at the sapphire/air interface of [...] Read more.

Total internal reflection (TIR) loss is a critical bottleneck limiting light extraction in AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs), primarily due to the large refractive-index contrast at the light-emitting interface. Here, pyramid-shaped dielectric metasurfaces are designed and fabricated at the sapphire/air interface of flip-chip AlGaN-based DUV LEDs using a scalable nanoimprinting process. The metasurface functions as a light outcoupling layer that modifies the interfacial momentum-matching condition and redistributes photon propagation directions. Experimental results and theoretical simulations show that metasurfaces with different feature sizes enhance light extraction through distinct mechanisms. The subwavelength pyramid nanoarray perturbs the local optical field and provides additional in-plane momentum components, facilitating the coupling of high-angle photons into radiative channels, whereas the larger pyramid void structure mainly promotes photon extraction through geometrical redirection, tilted output interfaces, and dry-etching-induced rough surface scattering. As a result, an average light output power (LOP) enhancement of over 8% is achieved for AlGaN-based DUV LEDs emitting at approximately 275 nm. This work demonstrates a low-cost, scalable, and effective strategy for enhancing the LEE of DUV LEDs, with promising potential for high-efficiency ultraviolet optoelectronic application. Full article

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21 pages, 4464 KB

Open AccessArticle

Stabilization of Two-Dimensional Optical Continuous-Wave States by a Potential Trough

by Thawatchai Mayteevarunyoo and Boris A. Malomed

Photonics 2026, 13(7), 684; https://doi.org/10.3390/photonics13070684 - 20 Jul 2026

Viewed by 269

Abstract

We consider quasi-one-dimensional (Q1D) continuous waves (CWs) in the two-dimensional (2D) optical system with the cubic–quintic (CQ) nonlinearity and a Q1D potential trough. In the case of a smooth trough profile, we confirm the known modulational instability (MI) of Q1D CWs with the [...] Read more.

We consider quasi-one-dimensional (Q1D) continuous waves (CWs) in the two-dimensional (2D) optical system with the cubic–quintic (CQ) nonlinearity and a Q1D potential trough. In the case of a smooth trough profile, we confirm the known modulational instability (MI) of Q1D CWs with the transverse structure corresponding to the 1D ground state (GS) in the potential trough, and demonstrate the MI of CWs with the dipole mode (DM) transverse structure, corresponding to the lowest 1D excited state in the potential trough. The CWs of both GS and DM types remain nearly stable close to the edges of their existence regions. Stable stationary states in the form of periodic chains of 2D solitons, trapped in the potential trough, are produced in a numerical form. The dynamics of the soliton chains excited by a localized kick is studied too. For the potential trough with the singular delta-functional profile, we find two species of exact analytical solutions for CWs. One of them, composed of the free-space CQ solitons, remains unstable, while the other solution, which is composed of solutions that are singular in the free space, is completely stable. Full article

(This article belongs to the Special Issue New Perspectives in Laser Nonlinearity: Phenomena, Theory, and Breakthroughs)

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14 pages, 4169 KB

Open AccessArticle

Cost-Effective, Contactless Optical Vibration Sensor for Rotating Machinery Based on Fiber-Optic Telecommunication Components and a Cross-Correlation Method

by Nino Rozić, Petar Bašić, Zvonimir Šipuš and Elis Sutlović

Photonics 2026, 13(7), 683; https://doi.org/10.3390/photonics13070683 - 17 Jul 2026

Viewed by 475

Abstract

Vibration measurements are essential for the early detection of faults in rotating machinery and are particularly important for hydrogenerators in hydro power plants. Industrial applications of vibration measurements typically rely on displacement, velocity, and acceleration sensors, each offering distinct advantages and limitations. This [...] Read more.

Vibration measurements are essential for the early detection of faults in rotating machinery and are particularly important for hydrogenerators in hydro power plants. Industrial applications of vibration measurements typically rely on displacement, velocity, and acceleration sensors, each offering distinct advantages and limitations. This paper discusses and proposes a cost-effective, contactless optical vibration sensing system based on standard fiber-optic telecommunication components, enabling its integration into existing fiber-optic networks. The proposed system utilizes interferometric sensing principles, providing inherent immunity to electromagnetic interference and galvanic effects while achieving micrometer-scale resolution. The key advancement of the proposed sensor lies in the relatively simple and cost-effective configuration—the realization of the Michelson interferometer. It facilitates a combination of standard optical communication hardware, including a 3 × 3 fiber-optic coupler and two photodetectors for reliable discrimination of vibration displacement directions. The associated signal processing platform is based on a cross-correlation algorithm by which both the direction and the magnitude of displacement are determined. The optical sensor was experimentally validated using a realistic-scenario laboratory setup, which demonstrates the feasibility and performance of the proposed approach. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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16 pages, 2750 KB

Open AccessArticle

Speckle Noise Reduction in OCT Retinal Images Based on a Multi-Scale Self-Attention Generative Adversarial Network

by Haiyi Bian, Yingzhou Zhu, Yeman Liu, Lei Liu, Xiaoteng Yan, Zhongjie Cheng and Yanrong Wang

Photonics 2026, 13(7), 682; https://doi.org/10.3390/photonics13070682 - 17 Jul 2026

Viewed by 433

Abstract

Optical coherence tomography (OCT) is widely used in biomedical imaging and ophthalmology. However, OCT images are frequently corrupted by speckle noise from coherent light interference. This degradation hampers clinical diagnosis of retinal lesions and identification of tissue layers. We propose a speckle noise [...] Read more.

Optical coherence tomography (OCT) is widely used in biomedical imaging and ophthalmology. However, OCT images are frequently corrupted by speckle noise from coherent light interference. This degradation hampers clinical diagnosis of retinal lesions and identification of tissue layers. We propose a speckle noise reduction algorithm based on a Multi-Scale Self-Attention Generative Adversarial Network combined with a Siamese network (SA-Siamese-GAN). To address the limited receptive fields of traditional convolutional neural networks (CNNs), which can cause broken or blurred retinal layers, a self-attention mechanism is integrated into the bottleneck layer of the generator to capture global pixel dependencies. A Siamese network enforces structural consistency, and a joint loss function combining Wasserstein distance, perceptual loss, and structural similarity (SSIM) is used. Experiments on 11,103 pairs of clinical OCT retinal images show that SA-Siamese-GAN outperforms BM3D, NLM, Wavelet, and GAN-ResNet. It removes speckle noise while preserving retinal layer structure and fine textures, and achieves the highest Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index (SSIM). Full article

(This article belongs to the Special Issue Optical Imaging and Optical Image Processing: Advances in Systems, Algorithms, and Applications)

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9 pages, 1317 KB

Open AccessCommunication

Reference-Free Terahertz Time-Domain Spectroscopy for Direct Measurement of Birefringence and Linear Dichroism

by Maoto Suzuki, Tetsuo Sasaki and Saroj R. Tripathi

Photonics 2026, 13(7), 681; https://doi.org/10.3390/photonics13070681 - 17 Jul 2026

Viewed by 420

Abstract

Terahertz time-domain spectroscopy (THz-TDS) is a widely used technique for characterizing a broad range of materials in the terahertz frequency region. Conventional THz-TDS requires both reference and sample signals to extract optical parameters such as refractive index and absorption coefficient. Determining optical anisotropy, [...] Read more.

Terahertz time-domain spectroscopy (THz-TDS) is a widely used technique for characterizing a broad range of materials in the terahertz frequency region. Conventional THz-TDS requires both reference and sample signals to extract optical parameters such as refractive index and absorption coefficient. Determining optical anisotropy, specifically birefringence and linear dichroism, typically requires separate measurements of the optical parameters of the sample parallel and perpendicular to the terahertz electric field. This process increases measurement time and depends heavily on a stable reference scan. In this work, we present a simple and accurate method to directly obtain birefringence and linear dichroism without the need for a reference measurement. The proposed approach extracts anisotropic parameters solely from the sample signals by analyzing the differential phase delay and amplitude attenuation between orthogonally polarized terahertz electric field components. We validate this method experimentally using optically anisotropic materials such as TiO₂ and bamboo samples and confirm that the results agree closely with those from conventional reference-based THz-TDS. This technique offers a practical route to measure the optical anisotropy of materials, particularly in situations where acquiring a reference signal is challenging. Full article

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15 pages, 1752 KB

Open AccessArticle

Polarization-Guided Blind Unmixing for Multi-Target Scattering Imaging Beyond the Optical Memory Effect

by Jingbo Duan, Tong Zhang, Xue Dong, Pingli Han and Fei Liu

Photonics 2026, 13(7), 680; https://doi.org/10.3390/photonics13070680 - 16 Jul 2026

Viewed by 352

Abstract

Multi-target imaging beyond the optical memory effect (OME) is fundamentally challenged by the incoherent superposition of speckles originating from different OME regions, which renders object separation highly ill-posed. To address this challenge, we introduce a polarization-guided blind unmixing framework that exploits the distinct [...] Read more.

Multi-target imaging beyond the optical memory effect (OME) is fundamentally challenged by the incoherent superposition of speckles originating from different OME regions, which renders object separation highly ill-posed. To address this challenge, we introduce a polarization-guided blind unmixing framework that exploits the distinct polarization responses of different targets as an additional discrimination cue for speckle separation. Polarized speckles are first used to construct a dense polarization-response representation through Stokes-based synthesis. The resulting polarization diversity is leveraged to estimate the number of targets without prior knowledge and to identify structurally representative autocorrelation endmembers associated with different objects. An energy-constrained non-negative matrix factorization is then developed to separate individual target autocorrelations, followed by phase retrieval for object reconstruction. Experimental results demonstrate the reconstruction of up to five targets located beyond the OME range, achieving target separations of up to 2.6× the measured OME limit and peak signal-to-noise ratio (PSNR) values above 25 dB, without requiring prior knowledge of target locations, structures, polarization states, or target number. Full article

(This article belongs to the Special Issue Advances in Computational Imaging: Algorithms, Technologies, and Applications)

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21 pages, 6758 KB

Open AccessArticle

An Improved Scheme for FY-3E/HIRAS-II Radiance Simulation at Large Scan Angles

by Qi Zhang, Congming Dai and Heli Wei

Photonics 2026, 13(7), 679; https://doi.org/10.3390/photonics13070679 - 16 Jul 2026

Viewed by 407

Abstract

To address the bias in radiative simulation caused by the horizontal inhomogeneity of atmospheric parameters under large scan angles for the HIRAS-II (Hyperspectral Infrared Atmospheric Sounder-II) onboard the Fengyun-3E satellite, this study proposes a method for constructing slant-path atmospheric parameter profiles along the [...] Read more.

To address the bias in radiative simulation caused by the horizontal inhomogeneity of atmospheric parameters under large scan angles for the HIRAS-II (Hyperspectral Infrared Atmospheric Sounder-II) onboard the Fengyun-3E satellite, this study proposes a method for constructing slant-path atmospheric parameter profiles along the satellite’s line-of-sight (Exp.2). In contrast to the conventional method (Exp.1) based on the assumption of horizontally homogeneous vertical atmospheric profiles, this method accurately calculates the intersection points between the satellite’s line-of-sight and the various altitude layers of the ECMWF reanalysis data version-5 (ERA5). It employs a hybrid interpolation algorithm combining inverse distance weighting and spline interpolation to obtain a continuous distribution of atmospheric parameters along the slant path, thereby accounting for the actual observation geometry of the satellite. The results show that when the satellite zenith angle exceeds 30°, the simulation differences between Exp.2 and Exp.1 increase significantly. Specifically, in the CO₂ absorption band, the differences between the two methods are mainly concentrated between −0.1 K and 0.1 K, whereas in the water vapor absorption band, this range expands to between −0.5 K and 0.5 K. Notably, biases are concentrated near the scan edges and exhibit a strong latitudinal dependence, with high-latitude areas showing more prominent deviations due to steeper atmospheric parameter gradients and asymmetric orbital geometry. Moreover, a comparison with the measured satellite-observed brightness temperature further demonstrates that Exp.2 effectively reduces simulation biases near the scan edge. The mean bias is reduced by up to 0.1 K in water vapor absorption channels, a more significant improvement compared to the 0.03 K reduction in CO₂ absorption channels. These results indicate that the proposed slant-path profile construction method significantly enhances the accuracy and reliability of infrared hyperspectral radiative transfer forward simulations under complex observation geometries by providing a more realistic representation of the three-dimensional slant-path radiative transfer process. This advancement holds important implications for improving the atmospheric correction of remote sensing data. Full article

(This article belongs to the Special Issue Emerging Topics in Atmospheric Optics)

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12 pages, 2783 KB

Open AccessArticle

DirectDemodNet: An End-to-End Neural Demodulator for Polarization-Diverse Underwater Visible Light Communication

by Shengyao Yan, Bokai Hou, Zhe Feng, Zhiwu Chen, Zengyi Xu, Zijian Zhou, Suning Guan and Nan Chi

Photonics 2026, 13(7), 678; https://doi.org/10.3390/photonics13070678 - 16 Jul 2026

Viewed by 308

Abstract

We demonstrate an underwater visible light communication system using a circularly polarized 520 nm laser transmitter, 32APSK modulation, and a polarization-diverse dual-aperture receiver. An end-to-end post-equalization network, DirectDemodNet, directly maps dual-polarization received waveforms to 32APSK symbol logits, replacing conventional Least Mean Square (LMS) [...] Read more.

We demonstrate an underwater visible light communication system using a circularly polarized 520 nm laser transmitter, 32APSK modulation, and a polarization-diverse dual-aperture receiver. An end-to-end post-equalization network, DirectDemodNet, directly maps dual-polarization received waveforms to 32APSK symbol logits, replacing conventional Least Mean Square (LMS) + Volterra equalization. By combining waveform-difference features, dual-scale dilated temporal convolutions, and multi-period positional encoding, DirectDemodNet improves nonlinear compensation and branch fusion. Extensive evaluations are conducted across data rates from 7.5 to 13.75 Gbps over a 1.2 m static underwater channel. Experiments show that DirectDemodNet broadens the forward error correction compliant operating range and provides a maximum net transmission rate gain of 4.095 Gbps over LMS + Volterra at the 7% Hard-decision Forward Error Correction (HD-FEC) threshold. Full article

(This article belongs to the Section Optical Communication and Network)

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12 pages, 1586 KB

Open AccessArticle

Narrow-Linewidth and High Side-Mode-Suppression-Ratio 1064 nm Distributed Feedback Semiconductor Laser Enabled by Fiber Bragg Grating External Feedback

by Runqi Guan and Kexin Li

Photonics 2026, 13(7), 677; https://doi.org/10.3390/photonics13070677 - 15 Jul 2026

Viewed by 365

Abstract

To narrow spectral linewidth, stabilize longitudinal mode and improve output performance of a 1064 nm distributed feedback (DFB) semiconductor laser, we design and fabricate a laser module adopting fiber Bragg grating (FBG) external-cavity feedback and a butterfly packaging structure. The butterfly package effectively [...] Read more.

To narrow spectral linewidth, stabilize longitudinal mode and improve output performance of a 1064 nm distributed feedback (DFB) semiconductor laser, we design and fabricate a laser module adopting fiber Bragg grating (FBG) external-cavity feedback and a butterfly packaging structure. The butterfly package effectively enhances heat dissipation and optical coupling reliability. Based on the classic Schawlow–Townes theory, we elaborate on how the narrowband filtering of FBG and the extended external cavity suppress mode hopping and reduce laser linewidth. A delayed self-heterodyne testing system is built to evaluate the photoelectric characteristics, spectral features and linewidth performance under varying driving currents and ambient temperatures. Experimental results show that the laser has a threshold current of 22.54 mA and a slope efficiency of 0.18 W/A, and its maximum output power reaches 80.8 mW at 480 mA. The side-mode suppression ratio (SMSR) reaches 58.2 dB at a temperature of 25 °C and driving current of 150 mA. Benefiting from FBG feedback, the laser linewidth is compressed from 485 kHz to 115 kHz, with lower noise and excellent wavelength stability. This compact all-fiber laser is well-suited for fiber sensing, coherent detection and LiDAR systems. Full article

(This article belongs to the Special Issue Advanced Lasers and Their Applications, 3rd Edition)

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14 pages, 8806 KB

Open AccessArticle

VO₂-Driven Current-Loop-Mediated Switching for BIC Modulation in Terahertz Metasurfaces

by Lincheng Guo, Xiaodan Zhao, Dong Li, Min Wu and Yibiao Yang

Photonics 2026, 13(7), 676; https://doi.org/10.3390/photonics13070676 - 15 Jul 2026

Viewed by 362

Abstract

Terahertz metasurfaces capable of dynamic modulation face a fundamental trade-off: high-quality-factor resonances require structural symmetry, but active tuning typically relies on symmetry-breaking that inevitably introduces radiative losses. This study presents a theoretical analysis of tunable terahertz metasurfaces utilizing vanadium dioxide (VO₂) [...] Read more.

Terahertz metasurfaces capable of dynamic modulation face a fundamental trade-off: high-quality-factor resonances require structural symmetry, but active tuning typically relies on symmetry-breaking that inevitably introduces radiative losses. This study presents a theoretical analysis of tunable terahertz metasurfaces utilizing vanadium dioxide (VO₂) as an active component that circumvents this trade-off through current-loop-mediated symmetry control. Based on the current-loop-mediated coupled-mode theory, we establish a quantitative relationship between VO₂’s conductivity and resonant mode characteristics through the symmetry-breaking parameter

α (σ) \propto \oint (r \times K (σ)) \cdot d l

. The proposed theoretical framework describes the conversion mechanism between non-radiative bound states in the continuum (BIC) and radiative quasi-BIC (qBIC), where VO₂’s metal–insulator phase transition modulates surface current distributions and activates radiation channels. Through systematic analysis of multiple metasurface designs, we demonstrate that conductivity-dependent current-loop formation governs the switching between high-Q dark modes and radiative states, achieving modulation depths up to 243%—providing a robust approach for dynamic terahertz wave manipulation with explicit physical linkage between materials parameters and modal properties. Full article

(This article belongs to the Special Issue Invisibility Cloaking: Methods, Principles, Materials, and Extended Applications)

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19 pages, 12590 KB

Open AccessReview

Structured Light Enables High-Precision Quantum Metrology

by Xu-Li Yan, Rui-Ping Jia, Zhou-Xiang Wang, Miao Yan and Jia-Qi Lü

Photonics 2026, 13(7), 675; https://doi.org/10.3390/photonics13070675 - 15 Jul 2026

Viewed by 395

Abstract

The high-precision estimation of spatial parameters, such as transverse displacement, beam tilt and angular rotation, is of great importance in precision measurement, optical imaging and quantum sensing. Structured light, with controllable spatial modes and special momentum degrees of freedom, provides new opportunities to [...] Read more.

The high-precision estimation of spatial parameters, such as transverse displacement, beam tilt and angular rotation, is of great importance in precision measurement, optical imaging and quantum sensing. Structured light, with controllable spatial modes and special momentum degrees of freedom, provides new opportunities to promote the encoding and readout of quantum metrology for spatial parameters. Here, we review recent progress in structured-light-enabled quantum metrology for spatial parameter estimation. The theoretical foundations of parameter estimation are introduced, based on which the modal-encoding mechanisms of higher-order structured light modes in spatial parameter measurements are summarized. Representative studies in which structured light is combined with nonclassical resources and the mode-matched readout strategies to achieve quantum enhancement are also demonstrated. In addition, current technical bottlenecks and future directions are discussed. Full article

(This article belongs to the Special Issue Innovations in Structured Optical Field: From Fundamentals to Applications)

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11 pages, 2333 KB

Open AccessArticle

An Enhanced Genetic Algorithm for Optimization of Seven-Tube Single-Ring Anti-Resonant Hollow-Core Fiber with Record-Low Loss and Single Mode

by Wei Gao, Ang Liu, Shuqin Lou, Yuying Guo, Xin Wang and Zhenggang Lian

Photonics 2026, 13(7), 674; https://doi.org/10.3390/photonics13070674 - 15 Jul 2026

Viewed by 415

Abstract

An enhanced genetic algorithm (EGA) is proposed to optimize our previously reported seven-tube single-ring anti-resonant hollow-core fiber (SR-ARF) with a record-low loss of 4.30 dB/km at 1080 nm. Taking advantage of an improved roulette wheel selection and a threshold elimination mechanism, the EGA [...] Read more.

An enhanced genetic algorithm (EGA) is proposed to optimize our previously reported seven-tube single-ring anti-resonant hollow-core fiber (SR-ARF) with a record-low loss of 4.30 dB/km at 1080 nm. Taking advantage of an improved roulette wheel selection and a threshold elimination mechanism, the EGA effectively prevents premature convergence and enhances optimization efficiency. By adopting the proposed EGA to optimize fiber structural parameters, the confinement loss of the seven-tube SR-ARF is further reduced to 2.79 dB/km, and the higher-order mode extinction ratio reaches 204 at 1080 nm, confirming robust single-mode operation. The single-mode operation bandwidth reaches up to 240 nm, covering 920 to 1160 nm. According to the optimized structural parameters, we experimentally fabricated a seven-tube SR-ARF, of which the transmission loss is reduced to 3.29 dB/km at 1052 nm and 3.90 dB/km at 1080 nm, while maintaining near-diffraction-limited single-mode guidance with an M² of 1.07/1.05. The proposed EGA model is of great significance for the structural parameter optimization of hollow-core fibers. Full article

(This article belongs to the Special Issue The Architecture of Specialty Optical Fibers: From Design to Application)

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15 pages, 5380 KB

Open AccessArticle

Simulation-Assisted Image Analysis for High-Sensitivity Detection of 30 nm Particles in Non-Patterned Wafer Inspection Systems

by Hyoseop Shin and Dongkun Shin

Photonics 2026, 13(7), 673; https://doi.org/10.3390/photonics13070673 - 15 Jul 2026

Viewed by 401

Abstract

As semiconductor design rules continue to shrink, random nanoscale particle contamination on non-patterned wafers has become a critical source of yield loss and process instability. This study presents a simulation-guided workflow for improving the practical detectability of 30 nm particles in an optical [...] Read more.

As semiconductor design rules continue to shrink, random nanoscale particle contamination on non-patterned wafers has become a critical source of yield loss and process instability. This study presents a simulation-guided workflow for improving the practical detectability of 30 nm particles in an optical wafer inspection system without replacing the installed platform. Three controllable optical parameters—illumination polarization, wavelength, and incidence angle—were investigated through defect simulation and then validated on a production-relevant non-pattern inspection tool. The simulation and experimental results showed that p-polarized illumination generated stronger defect-relevant scattering contrast than S-polarization, 266 nm illumination provided the best practical detection performance among the evaluated wavelength conditions, and oblique illumination produced more favorable defect visibility than vertical incidence. Guided by these findings, an integrated inspection recipe using P-polarization, 266 nm illumination, and an oblique incidence angle of 20–25° was implemented on the inspection tool. Under the optimized condition, 30 nm particles were detected, whereas the legacy condition failed to provide equivalent sensitivity. The results demonstrate that defect simulation can be used as a practical engineering instrument for recipe screening, sensitivity enhancement, and faster deployment of inspection improvements in high-volume semiconductor manufacturing. Full article

(This article belongs to the Section Optical Interaction Science)

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13 pages, 1867 KB

Open AccessArticle

Nonlinear Refractive Index of Warm Rubidium Vapor

by Lovre Kardum, Grgur Premec, Neven Šantić and Damir Aumiler

Photonics 2026, 13(7), 672; https://doi.org/10.3390/photonics13070672 - 14 Jul 2026

Viewed by 350

Abstract

The potential to precisely control both the linear and nonlinear index of refraction through optical manipulation of the atomic states has recently pushed warm alkali vapors to the forefront of research in the field of quantum sensors, quantum memories, and quantum fluids of [...] Read more.

The potential to precisely control both the linear and nonlinear index of refraction through optical manipulation of the atomic states has recently pushed warm alkali vapors to the forefront of research in the field of quantum sensors, quantum memories, and quantum fluids of light. Rubidium (Rb) vapor in centimeter-scale glass cells or millimeter-scale micro-electro-mechanical system (MEMS) cells has proven to be a very promising platform for these applications, yet only a handful of research works have been dedicated to the investigation of the (non)linear refractive index of Rb vapor. We present results of theoretical calculations of the (non)linear refractive index of warm Rb vapor, based on the optical Bloch equations for 6-level Rb atoms interacting with a probe laser. They are compared to the experimental results obtained using an interferometric technique, showing very good quantitative agreement. A Kerr nonlinear refractive index

n_{2}

of up to

- 1.2 \times 10^{- 4}

cm²/W is obtained. Python scripts for all theoretical calculations presented in this work are provided, including the refractive index calculation, that can readily be used in practical implementations for simulating the (non)linear refractive index of Rb vapor including the effects of Doppler broadening, transit time broadening, pressure broadening, saturation, optical pumping, and spin-exchange collisions. Full article

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

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33 pages, 15128 KB

Open AccessArticle

EndoDGS: Degradation-Decoupled Gaussian Splatting for Endoscopic Novel-View Reconstruction

by Jiahong Dong, Hongshuai Qin, Xingru Huang, Zhiwen Zheng, Lihuan Shao, Huiyu Qi, Xiaoshuai Zhang and Jin Liu

Photonics 2026, 13(7), 671; https://doi.org/10.3390/photonics13070671 - 14 Jul 2026

Viewed by 283

Abstract

Reliable three-dimensional (3D) reconstruction from endoscopic video is essential for endoscopic digital twins, scene review, and minimally invasive visual analysis. However, endoscopic images are not clean observations of intrinsic tissue appearance. Depth-dependent blur, shallow mucosal color diffusion, wet-surface specular reflection, and frame-wise color [...] Read more.

Reliable three-dimensional (3D) reconstruction from endoscopic video is essential for endoscopic digital twins, scene review, and minimally invasive visual analysis. However, endoscopic images are not clean observations of intrinsic tissue appearance. Depth-dependent blur, shallow mucosal color diffusion, wet-surface specular reflection, and frame-wise color variation are often coupled with the captured signal. When such observation-dependent effects are directly optimized as Gaussian colors, conventional 3D Gaussian Splatting may encode transient imaging artifacts as persistent tissue appearance, leading to blurred textures, color drift, specular residues, and unstable novel-view synthesis. This paper presents EndoDGS (Endoscopic Degradation-Decoupled Gaussian Splatting), a degradation-decoupled Gaussian Splatting framework for endoscopic novel-view reconstruction. The core idea is to keep stable geometry and base tissue appearance in the Gaussian representation, while modeling endoscope-induced degradations separately in a bounded render-space compensation pipeline. EndoDGS combines lightweight appearance modulation for frame-wise color stabilization with sequential degradation compensation for optical blur, mucosal color transport, and wet-surface specular response. This design reduces the entanglement between persistent tissue appearance and transient imaging degradations without changing the underlying Gaussian geometry and visibility ordering. Experiments on synthetic colonoscopy and real endoscopic/laparoscopic datasets covering 38 scenes show that EndoDGS consistently improves reconstruction quality over representative implicit and explicit reconstruction baselines. The results demonstrate that separating stable tissue representation from observation-dependent endoscopic degradations provides a more faithful, stable, and interpretable foundation for endoscopic 3D reconstruction. Full article

(This article belongs to the Special Issue Biomedical Imaging and Its Translation and Application)

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19 pages, 690 KB

Open AccessPerspective

Beyond Silica Assumptions: Optical Network Design in the Hollow-Core Era

by Md Ghulam Saber and Zhiping Jiang

Photonics 2026, 13(7), 670; https://doi.org/10.3390/photonics13070670 - 14 Jul 2026

Viewed by 490

Abstract

Hollow-core fiber (HCF) is often presented as an incrementally better transmission medium that can be slotted into networks designed around solid-core silica. We argue instead that recent progress—most visibly reported as attenuations below 0.1 dB/km and now approaching 0.05 dB/km, together with a [...] Read more.

Hollow-core fiber (HCF) is often presented as an incrementally better transmission medium that can be slotted into networks designed around solid-core silica. We argue instead that recent progress—most visibly reported as attenuations below 0.1 dB/km and now approaching 0.05 dB/km, together with a broad low-loss window, reduced propagation delay and very low optical nonlinearity—makes it worth asking which long-standing design conventions are intrinsic to optical communication and which are artifacts of silica. Reviewing physical-layer, transceiver and network architecture implications, we suggest that the most durable gains may come not from treating HCF as a drop-in replacement, but from cross-layer co-design, and we outline the studies and demonstrations needed to test where that advantage is real. Full article

(This article belongs to the Special Issue Specialty Optical Fibers: Emerging Designs, Functionalities, and Applications)

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12 pages, 4869 KB

Open AccessArticle

Coupled Spectral–Spatial Fusion-Enabled Multi-Scale Panoramic Imaging

by Ke Yin, Zheng Wen, Yuan Liao, Shubin Liu, Xiyang Zhi and Guangzhen Bao

Photonics 2026, 13(7), 669; https://doi.org/10.3390/photonics13070669 - 14 Jul 2026

Viewed by 319

Abstract

Conventional imaging systems often suffer from a coupled limitation of narrow field of view, single modality, and insufficient effective resolution. Wide-angle imaging preserves scene context but compresses distant or small-scale targets into limited pixels, while narrow-field imaging improves details at the cost of [...] Read more.

Conventional imaging systems often suffer from a coupled limitation of narrow field of view, single modality, and insufficient effective resolution. Wide-angle imaging preserves scene context but compresses distant or small-scale targets into limited pixels, while narrow-field imaging improves details at the cost of global perception. Moreover, single-modal visible imaging is sensitive to illumination and contrast variations, whereas infrared imaging lacks fine spatial texture. To increase information at the imaging source, we propose coupled spectral–spatial fusion-enabled multi-scale panoramic imaging, a dual-field-of-view (FOV) visible–infrared framework for wide-field high-resolution perception. Two imaging units acquire paired visible and infrared images from adjacent overlapping views. For each view, a visible–infrared fusion super-resolution model integrates visible structural details with infrared radiative cues to reconstruct a high-resolution fused image. A multi-scale stitching algorithm then extracts robust features, estimates cross-view correspondences, and merges the two fused images into a large-FOV panoramic result. Outdoor experiments demonstrate that the proposed method improves local contrast, suppresses pixelation artifacts, enhances readable fine details, and expands the observable field of view, providing an effective route toward multimodal panoramic imaging. Full article

(This article belongs to the Special Issue Computational Imaging)

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15 pages, 2188 KB

Open AccessArticle

Research on the Influence of Polygonal Scanner Reflection Point Drift on Measurement Accuracy in a Laser Scanning System

by Li Wang, Ke Chen, Xueliang Kang, Bai Zhang and Hongmei Zheng

Photonics 2026, 13(7), 668; https://doi.org/10.3390/photonics13070668 - 14 Jul 2026

Viewed by 357

Abstract

The polygonal scanner is a key component of a laser scanning system. The reflection point drift of a polygonal scanner is one of the primary sources of error that limits improvements in system measurement accuracy, significantly affecting the application of laser scanning systems [...] Read more.

The polygonal scanner is a key component of a laser scanning system. The reflection point drift of a polygonal scanner is one of the primary sources of error that limits improvements in system measurement accuracy, significantly affecting the application of laser scanning systems in high-precision scenarios. Based on a geometric optics model, this article quantitatively analyzes the magnitude of the reflection point drift and the direction of the reflected ray caused by the rotation of the polygonal scanner, as well as the impact of this drift on measurement accuracy. The research shows that, compared to the ideal state, the reflection point drift causes the system’s absolute distortion to increase by nearly 20 times and relative distortion by nearly 5 times, indicating a great effect on measurement accuracy. Future research can directly incorporate this quantitative analysis model into the design of the relevant f-theta lens, effectively and conveniently improving lens design accuracy and thereby enhancing the overall measurement accuracy of the system. This study holds significant theoretical importance and engineering value in advancing the application of laser scanning technology in high-precision scenarios. Full article

(This article belongs to the Special Issue Optical Measurement Systems, 2nd Edition)

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20 pages, 20779 KB

Open AccessArticle

Numerical Demonstration of High-Energy Dissipative Soliton Resonance in a Net-Normal-Dispersion Er³⁺: ZBLAN Fiber Laser at 2.8 µm

by Jing Li, Fanjiang Xu, Si Chen, Shudan Tan, Lei Duan and Xiongxin Tang

Photonics 2026, 13(7), 667; https://doi.org/10.3390/photonics13070667 - 13 Jul 2026

Viewed by 361

Abstract

High-energy, ultrafast pulse generation from mid-infrared (MIR) fiber lasers is often limited by pulse splitting caused by excessive nonlinear phase accumulation, especially in anomalous-dispersion cavities. Dissipative soliton resonance (DSR) offers a route to energy scaling by accommodating additional gain through temporal pulse broadening [...] Read more.

High-energy, ultrafast pulse generation from mid-infrared (MIR) fiber lasers is often limited by pulse splitting caused by excessive nonlinear phase accumulation, especially in anomalous-dispersion cavities. Dissipative soliton resonance (DSR) offers a route to energy scaling by accommodating additional gain through temporal pulse broadening under peak-power clamping. Here, we numerically demonstrate DSR operation in a net-normal-dispersion Er³⁺: ZBLAN mode-locked fiber laser at 2.8 µm, using an As₂S₃ fiber for dispersion and nonlinear management. Systematic parameter sweeps show that the gain saturation energy primarily governs pulse-energy scaling, whereas the output-coupling ratio controls peak-power extraction and the operation regime. The spectral filter bandwidth and saturable absorber parameters define the stability window and mediate transitions among dissipative solitons, DSR pulses, noise-like pulses, multi-pulse states, and unstable operation. After coordinated cavity optimization, a stable rectangular DSR pulse with a maximum energy of 408.52 nJ is obtained under a 55 nm filter bandwidth, relaxing the narrow-filtering requirement reported in previous MIR DSR designs. A high-peak-power DSR state with 3112.1 W peak power and 316.58 nJ energy is also achieved at a 95% output-coupling ratio. By tuning the As₂S₃ fiber length, DSR dynamics are also accessed near the zero-dispersion boundary and in the anomalous-dispersion regime, where spike-on-pedestal temporal profiles and dual-peak spectra emerge. This work advances the understanding of MIR DSR dynamics and offers design guidance for compact, high-energy ultrafast sources at 2.8 µm. Full article

(This article belongs to the Special Issue Optical Fiber Lasers: Advances in Design, Fabrication and Applications)

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13 pages, 3537 KB

Open AccessArticle

Diffraction of Partially Coherent Light as a Nonlinear Operation

by Igor Glukhov, Sergey Moiseev and Sergey Sukhov

Photonics 2026, 13(7), 666; https://doi.org/10.3390/photonics13070666 - 12 Jul 2026

Viewed by 395

Abstract

The linear transformation of optical fields during propagation poses a fundamental limitation for neuromorphic computing applications. In this paper, a realization of a nonlinear operator based on the diffraction of partially coherent light by an aperture partially covered with a binary phase grating [...] Read more.

The linear transformation of optical fields during propagation poses a fundamental limitation for neuromorphic computing applications. In this paper, a realization of a nonlinear operator based on the diffraction of partially coherent light by an aperture partially covered with a binary phase grating is proposed. The dependence of the effective aperture width on the spatial coherence of the incident light produces a nonlinear behavior that formally introduces a nonlinear integration kernel into the propagation integral. The proposed concept is validated through numerical experiments performed using the PyWolf framework for partially coherent light propagation modeling. This coherence-induced nonlinearity, which effectively implements a nonlinear propagation kernel with an input-dependent transfer function, offers a viable pathway to overcome the limitations of purely linear diffractive networks and can be leveraged for constructing multilayer architectures. Full article

(This article belongs to the Special Issue Recent Developments in Fringe Pattern Analysis for Optics and Photonics)

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24 pages, 11385 KB

Open AccessArticle

Switchable Dissipative Ising Coupling Based on Three-Body Coupling in Magnon Systems

by Xiwen Dou, Zhengyang Zhou and Aixi Chen

Photonics 2026, 13(7), 665; https://doi.org/10.3390/photonics13070665 - 12 Jul 2026

Viewed by 425

Abstract

Magnonic systems present a compelling platform for quantum technology, owing to their strong capacity to form hybrid quantum systems via diverse couplings. To unlock the full potential of these systems, the engineering of flexible coupling between multiple magnon modes is essential. Here, we [...] Read more.

Magnonic systems present a compelling platform for quantum technology, owing to their strong capacity to form hybrid quantum systems via diverse couplings. To unlock the full potential of these systems, the engineering of flexible coupling between multiple magnon modes is essential. Here, we propose a method to realize switchable dissipative Ising coupling in magnon systems, leveraging the three-body coupling among photon, phonon, and magnon. This type of dissipative coupling is a critical component for constructing Ising machines designed to solve complex combinatorial optimization problems. By dynamically tuning the phase of a nonlinear mechanical pump, we demonstrate the realization of both ferromagnetic and antiferromagnetic dissipative interactions. The validity of the scheme is confirmed by numerical simulations, which also demonstrate its robustness against a strong uncontrollable part of dissipation. Our work provides a versatile tool that can facilitate the implementation of magnon-based quantum computing and the exploration of many-body magnon physics. Full article

(This article belongs to the Special Issue Quantum Optics: Communication, Sensing, Computing, and Simulation)

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17 pages, 1693 KB

Open AccessArticle

Self-Prompting Segment Anything Model for Esophageal OCT Images

by Cong Wang and Meng Gan

Photonics 2026, 13(7), 664; https://doi.org/10.3390/photonics13070664 - 11 Jul 2026

Viewed by 483

Abstract

Optical coherence tomography (OCT) is an established imaging modality for esophageal disease assessment, enabling high-resolution visualization of tissue layers. However, automated segmentation of esophageal OCT images remains challenging due to low contrast, complex tissue structures, in vivo confounders, and scarce labeled clinical data. [...] Read more.

Optical coherence tomography (OCT) is an established imaging modality for esophageal disease assessment, enabling high-resolution visualization of tissue layers. However, automated segmentation of esophageal OCT images remains challenging due to low contrast, complex tissue structures, in vivo confounders, and scarce labeled clinical data. To address these issues, we propose a self-prompting segment anything model (SAM)-based one-shot segmentation framework tailored for esophageal OCT images. The framework integrates a pre-trained SAM encoder for general feature extraction and a self-pretrained prompt encoder to capture domain-specific features from unlabeled OCT data. Experiments on a self-collected mouse dataset and a public human dataset yielded Dice similarity coefficient (DSC) values exceeding 85%, with the highest mean DSC among the evaluated methods under the one-shot protocol, although greater performance dispersion was observed in the heterogeneous human cohort. These findings demonstrate the potential of combining unlabeled OCT pretraining with one labeled B-scan for annotation-efficient esophageal OCT segmentation. Full article

(This article belongs to the Special Issue Optical Imaging and Optical Image Processing: Advances in Systems, Algorithms, and Applications)

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