Photonics

13 pages, 9146 KB

Open AccessArticle

Liquid–Liquid Interfacial Self-Assembly of Au-Ag Nanoparticles for High-Performance SERS Detection of Thiram in Environmental Water Samples

by Jiali Liu, Jiafan Liu, Lianxiu Yu, Yeqi Fang, Li Jiang, Zheng Ma and Jie Hu

Photonics 2026, 13(5), 507; https://doi.org/10.3390/photonics13050507 - 21 May 2026

Viewed by 283

Abstract

Gold and silver nanoparticles have attracted extensive attention in SERS detection due to their excellent plasmonic properties. In this study, a high-performance SERS substrate was successfully prepared by a liquid–liquid self-assembly strategy. Driven by the Marangoni effect, Au-Ag nanoparticles spontaneously form a uniform [...] Read more.

Gold and silver nanoparticles have attracted extensive attention in SERS detection due to their excellent plasmonic properties. In this study, a high-performance SERS substrate was successfully prepared by a liquid–liquid self-assembly strategy. Driven by the Marangoni effect, Au-Ag nanoparticles spontaneously form a uniform and dense monolayer structure on the silicon wafer, constructing an efficient plasmon “hotspot” region, which significantly improves the detection sensitivity of the substrate. The performance of the SERS substrate was systematically evaluated using CV and Me B as Raman probe molecules. The results show that the substrate exhibits an excellent enhancement effect and good SERS sensitivity for both probe molecules. The characteristic vibration peak can be clearly identified, and the detection limit (LOD) of crystal violet is 6.76 × 10⁻¹¹ M. The substrate was applied to detect thiram residues in lake water with a LOD of 1.084 × 10⁻⁷ M, achieving highly sensitive detection. This study shows that Au-Ag nanoparticles deposited on silicon wafers by liquid–liquid self-assembly strategy can be used as a high-performance SERS substrate. It can be used for rapid and sensitive detection of thiram pesticide residues in water, and provides an efficient and feasible analysis tool for water environment safety monitoring. Full article

(This article belongs to the Special Issue Novel Developments in Optoelectronic Materials and Devices)

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11 pages, 2575 KB

Open AccessArticle

Wavelet-Fused Deep Learning for Computational Phase Correction in Dual-Comb Ranging

by Yao Li, Yuwei Cai, Zhongjian Gao, Wen Ren and Zili Zhang

Photonics 2026, 13(5), 506; https://doi.org/10.3390/photonics13050506 - 21 May 2026

Viewed by 236

Abstract

Dual-comb ranging enables rapid, high-precision absolute distance measurements, but its performance is constrained by intrinsic phase noise, which induces temporal jitter and degrades pulse-to-pulse mutual coherence. Here, we propose a deep learning network Wavelet-Fused DenseNet (WFDNet) for hardware-free computational phase correction in dual-comb [...] Read more.

Dual-comb ranging enables rapid, high-precision absolute distance measurements, but its performance is constrained by intrinsic phase noise, which induces temporal jitter and degrades pulse-to-pulse mutual coherence. Here, we propose a deep learning network Wavelet-Fused DenseNet (WFDNet) for hardware-free computational phase correction in dual-comb ranging. Through integration of complex wavelet decomposition and physics-guided feature encoding, the network, trained on model-generated data, can directly extract multi-scale time–frequency features to correct phase distortions and recover temporal coherence of the signals. Results from both simulated and experimental scenarios reveal that the approach can effectively suppress spectral noise and retrieve robust and unambiguous phases information, achieving high ranging accuracy with a standard deviation of 0.6 μm. Full article

(This article belongs to the Special Issue AI for Photonics: Intelligent Imaging, Learning-Driven Optics, and Photonic Computing)

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8 pages, 1518 KB

Open AccessArticle

High-Extinction-Ratio Electro-Optic Modulator on Thin-Film Lithium Niobate Operating at 1064 nm

by Zimiao Su and Lutong Cai

Photonics 2026, 13(5), 505; https://doi.org/10.3390/photonics13050505 - 21 May 2026

Viewed by 389

Abstract

Laser sources emitting light at 1064 nm enable key applications in lidar, quantum photonics, and remote sensing, where high-extinction-ratio intensity modulation is desired to suppress the leakage light at the “off” states during modulation. Here we demonstrate a 1064 nm thin-film lithium niobate [...] Read more.

Laser sources emitting light at 1064 nm enable key applications in lidar, quantum photonics, and remote sensing, where high-extinction-ratio intensity modulation is desired to suppress the leakage light at the “off” states during modulation. Here we demonstrate a 1064 nm thin-film lithium niobate (TFLN) Mach–Zehnder electro-optic modulator featuring a half-wave voltage–length product of 2.1 V·cm and a measured electro-optic 3 dB bandwidth exceeding 10 GHz. By optimizing the waveguide and MMI-based interferometer design to improve device balance, we achieve an extinction ratio exceeding 30 dB without thermal tuning. This high extinction ratio enables high-contrast optical modulation at 1064 nm, which is essential for optical switching and other photonic applications requiring high on–off contrast. Full article

(This article belongs to the Special Issue Microwave Photonics: Advances and Applications)

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10 pages, 1558 KB

Open AccessArticle

Polarization Characteristics of AlO Molecular Spectra in Femtosecond Laser-Induced Aluminum Plasma

by Xuefeng Chu, Qiuyun Wang and Xun Gao

Photonics 2026, 13(5), 504; https://doi.org/10.3390/photonics13050504 - 20 May 2026

Viewed by 304

Abstract

To investigate the polarization characteristics of AlO molecular emission in femtosecond laser-induced aluminum plasma, AlO molecular spectra were generated by irradiating an aluminum target with a femtosecond laser. The experimental results revealed a pronounced polarization response in the AlO emission. After a polarizer [...] Read more.

To investigate the polarization characteristics of AlO molecular emission in femtosecond laser-induced aluminum plasma, AlO molecular spectra were generated by irradiating an aluminum target with a femtosecond laser. The experimental results revealed a pronounced polarization response in the AlO emission. After a polarizer was introduced into the collection path, the signal-to-background ratio (SBR) increased from 8.30 to 10.80, while the relative standard deviation (RSD) decreased from 0.043 to 0.036, indicating improved spectral quality and stability. By modulating the laser polarization state using a half-wave plate and a quarter-wave plate, the AlO spectral intensity increased by a factor of 1.26 when the laser polarization was changed from horizontal to vertical, and by a factor of 1.75 when it was changed from linear to circular. Under circular, horizontal, and vertical polarization conditions, the SBR values obtained with a polarizer were consistently higher than those obtained without a polarizer, with the maximum value of 12.46 achieved under vertical polarization. These results demonstrate that both plasma polarization detection and laser polarization modulation can effectively achieve better-quality AlO molecular spectra. This work provides a useful reference for improving molecular spectral quality in femtosecond laser-induced spectroscopy. Full article

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14 pages, 1976 KB

Open AccessArticle

On-Chip Metasurface Multi-Channel Multiplexed Holography Based on Detour Phase

by Ceyun Zheng, Haoxiang Chen, Yang Yang, Siyu Yin, Baohui Zhang, Anxin Luo, Yu Wang, Yubin Gong and Fei Shen

Photonics 2026, 13(5), 503; https://doi.org/10.3390/photonics13050503 - 20 May 2026

Viewed by 359

Abstract

While spatially transmissive or reflective metasurfaces have achieved unprecedented wavefront control in free space, the paradigm shift toward on-chip waveguide-integrated architectures presents novel challenges for constructing compact and scalable photonic systems. Existing on-chip holographic schemes are typically constrained by the complexity of meta-atom [...] Read more.

While spatially transmissive or reflective metasurfaces have achieved unprecedented wavefront control in free space, the paradigm shift toward on-chip waveguide-integrated architectures presents novel challenges for constructing compact and scalable photonic systems. Existing on-chip holographic schemes are typically constrained by the complexity of meta-atom structures, limited multiplexing capacity, and strict dependence on specific polarization states. This report comprehensively elucidates a novel on-chip metasurface architecture that relies exclusively on a unified detour phase modulation mechanism to achieve high-capacity, multi-channel holographic multiplexing. By deeply integrating a phase-displacement-joint displacement algorithmic framework with the simulated annealing global optimization algorithm, this design highly circumvents the necessity for complex anisotropic meta-atom geometries and the physical superposition of multiple phase mechanisms. Within an ultra-compact physical footprint of 55.55 × 55.55 μm², the architecture successfully achieves customized holographic reconstruction at specific far-field planes. When discrete TE modes in the visible spectrum are injected from orthogonal lateral directions, distinctly different target holograms are reconstructed in the far field without crosstalk. This mechanism establishes a robust four-wavelength, four-channel independent coding framework. The findings not only elucidate a simplified and highly scalable methodology for ultra-high-density on-chip displays but also provide profound theoretical guidance and technical support for cutting-edge applications such as augmented reality, secure optical communications, and high-density optical data storage. Full article

(This article belongs to the Special Issue Metasurface-Based Photonic Devices and Their Applications)

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23 pages, 3698 KB

Open AccessArticle

Design of a Thin-Film Lithium Niobate Electro-Optic Modulator with Three-Dimensional L-Shaped Traveling-Wave Electrodes

by Yingbo Liu, Haiou Li, Yue Li, Yuxiang Hao and Liangpeng Qin

Photonics 2026, 13(5), 502; https://doi.org/10.3390/photonics13050502 - 19 May 2026

Viewed by 521

Abstract

The systematic influence of signal electrode width on electro-optic bandwidth and insertion loss in L-type traveling-wave lithium niobate modulators has not yet been comprehensively quantified, limiting the parametric engineering design of this device configuration. This study presents a full-band systematic simulation sweep of [...] Read more.

The systematic influence of signal electrode width on electro-optic bandwidth and insertion loss in L-type traveling-wave lithium niobate modulators has not yet been comprehensively quantified, limiting the parametric engineering design of this device configuration. This study presents a full-band systematic simulation sweep of signal electrode width and three auxiliary geometric parameters in an L-type traveling-wave lithium niobate Mach–Zehnder modulator, combined with optical mode simulation to establish joint microwave–optical optimization constraints. The study reveals the coupled modulating effect of signal electrode width on characteristic impedance, velocity mismatch, and transmission loss; it elucidates the competition mechanism underlying non-monotonic high-frequency loss behavior; and it identifies the complete impedance-neutral characteristic of the electrode–waveguide contact width as an independent loss-tuning degree of freedom decoupled from the impedance constraint. Full-system validation confirms that the final design simultaneously satisfies broadband impedance matching, low insertion loss, and high electro-optic bandwidth. The results are distilled into four quantitative design rules that provide simulation-driven guidance directly applicable to the engineering design of L-type thin-film lithium niobate modulators, advancing the systematic establishment of a parametric design methodology for this device configuration. Full article

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32 pages, 19989 KB

Open AccessArticle

Design and Fabrication of Volume Phase Holographic Gratings for CO₂ Detection: A Multi-Objective Optimization Approach

by Lei Dai, Chao Lin, Zhenhua Ji, Yang Fu, Shuo Wang and Yuquan Zheng

Photonics 2026, 13(5), 501; https://doi.org/10.3390/photonics13050501 - 18 May 2026

Viewed by 235

Abstract

Volume phase holographic gratings (VPHGs) are high-performance dispersive elements characterized by high diffraction efficiency and low noise. When used as dispersive components in imaging spectrometers for CO₂ detection, they can significantly enhance instrument performance, detection capability, and measurement accuracy. However, for short-wave [...] Read more.

Volume phase holographic gratings (VPHGs) are high-performance dispersive elements characterized by high diffraction efficiency and low noise. When used as dispersive components in imaging spectrometers for CO₂ detection, they can significantly enhance instrument performance, detection capability, and measurement accuracy. However, for short-wave infrared (SWIR) applications requiring high dispersion and operational efficiency, traditional design approaches struggle to effectively balance the trade-offs among multidimensional diffraction performance metrics, resulting in low optimization efficiency. Furthermore, as spectrometers require dispersive elements, established fabrication methods lack robust methodologies for producing large-area VPHGs. To address these gaps, we developed both a design approach and a fabrication process for VPH gratings tailored to CO₂ detection. On the design front, we propose a novel method that integrates a multi-objective simulated annealing optimization algorithm with Kogelnik’s coupled-wave theory. The optimized gratings achieve diffraction efficiencies of 95.35% (TE polarization) and 82.21% (TM polarization) across the target spectral range, with polarization sensitivity maintained below 6.57%. For fabrication, we developed holographic plate fabrication via a blade-coating technique coupled with an optimized aging protocol. A medium-to-large aperture holographic recording and exposure system with a wavefront error better than λ/25 RMS was developed. Post-processing conditions were systematically optimized based on experimental diffraction efficiency measurements, enabling the successful fabrication of VPHGs. It is explicitly noted that the experimental validation of the fabricated VPHGs is limited to the 1.620–1.630 μm wavelength range, while the full target design range of 1.620–1.650 μm has not been experimentally verified in this work. This work provides a valuable reference for the selection of dispersive elements for next-generation CO₂ detection satellites. The designed gratings fully meet application requirements, while the established fabrication process lays a solid foundation for the production of high-performance VPHGs. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

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18 pages, 13804 KB

Open AccessArticle

Automated Inverse Design Framework for Traveling-Wave Electrode Electro-Optic Modulators with Discrete Fabrication Constraints

by Qi You, Pingrang Hua, Yifei Chen, Xingshan Chen and Tong Ye

Photonics 2026, 13(5), 500; https://doi.org/10.3390/photonics13050500 - 18 May 2026

Viewed by 272

Abstract

The utilization of electro-optic modulators in engineering is progressively expanding. In this paper, an automated inverse design framework is proposed for traveling-wave electrode electro-optic modulators (EOM). It addresses key challenges in modulator design, such as multi-parameter coupling and discrete fabrication constraints. Applied to [...] Read more.

The utilization of electro-optic modulators in engineering is progressively expanding. In this paper, an automated inverse design framework is proposed for traveling-wave electrode electro-optic modulators (EOM). It addresses key challenges in modulator design, such as multi-parameter coupling and discrete fabrication constraints. Applied to a segmented electrode lithium niobate modulator, the framework achieves a 100 GHz electro-optic (EO) bandwidth and a half-wave voltage-length product of

V π \cdot L = 1 V \cdot c m

at 5 mm length, with all 20 independent runs converging successfully under the tested conditions. The framework is further validated on four modulator structures and six engineering conditions, consistently yielding EO bandwidth > 40 GHz and

V π \cdot L < 5 V \cdot c m

. This work offers a practical and adaptable solution for the automated design of high-performance electro-optic modulators under realistic fabrication constraints. Full article

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

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12 pages, 3275 KB

Open AccessArticle

Improving the Sensitivity of the Sensing Interrogation System Based on an Optoelectronic Oscillator Incorporating a Dual-Passband Microwave Photonic Filter

by Hua Wang, Gang Huang, Tongtong Xie, Zhiyi Li, Qiang Liu, Shuai Yuan, Dian Zuo and Hongyan Fu

Photonics 2026, 13(5), 499; https://doi.org/10.3390/photonics13050499 - 16 May 2026

Viewed by 334

Abstract

In this paper, we propose and demonstrate a sensitivity-enhanced sensing interrogation scheme based on an Optoelectronic oscillator (OEO), in which a switchable dual-passband microwave photonic filter (MPF) is introduced into the loop. The switchable dual-passband MPF is a combination of a modified fiber [...] Read more.

In this paper, we propose and demonstrate a sensitivity-enhanced sensing interrogation scheme based on an Optoelectronic oscillator (OEO), in which a switchable dual-passband microwave photonic filter (MPF) is introduced into the loop. The switchable dual-passband MPF is a combination of a modified fiber Mach–Zehnder interferometer (FMZI), an electro-optical modulator (EOM), a roll of dispersion compensating fiber (DCF), and a photodetector (PD). The dual-passband switching of the MPF can be achieved by simply adjusting the polarization state via rotating a polarization controller (PC) in the FMZI. The sensitivity can be improved by a factor of two by tracking the frequency corresponding to the central frequency of the high-frequency passband relative to the low-frequency passband. Temperature-sensing experiments were conducted to verify the concept of enhanced sensitivity. Experimental results on temperature sensing show that tracking low- and high-frequency OEO signals yields sensitivities of 5.23 MHz/°C and 10.84 MHz/°C, respectively, and temperature resolutions of 0.009 °C and 0.004 °C, thereby increasing sensitivity and resolution. Full article

(This article belongs to the Special Issue Advanced Optical Fiber Sensors for Harsh Environment Applications)

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17 pages, 2965 KB

Open AccessArticle

Polarization Calibration and Analysis of Solar-Induced Chlorophyll Fluorescence Wide-Swath Ultraspectral Imaging Spectrometer

by Yiwei Li, Kaiqin Cao, Zongcun Zhang, Xiaowei Jia, Xuefei Feng, Lu Liu and Yinnian Liu

Photonics 2026, 13(5), 498; https://doi.org/10.3390/photonics13050498 - 16 May 2026

Viewed by 310

Abstract

Spaceborne detection of solar-induced chlorophyll fluorescence (SIF) requires extremely high radiometric accuracy, and the polarization characteristics of an ultra-wide swath spaceborne fluorescence ultraspectral camera directly affect the accuracy of SIF retrieval. This study takes an ultra-wide swath camera based on an off-axis three-mirror [...] Read more.

Spaceborne detection of solar-induced chlorophyll fluorescence (SIF) requires extremely high radiometric accuracy, and the polarization characteristics of an ultra-wide swath spaceborne fluorescence ultraspectral camera directly affect the accuracy of SIF retrieval. This study takes an ultra-wide swath camera based on an off-axis three-mirror anastigmat telescope combined with a Littrow–Offner spectrometer as the research object. A full-field-of-view (FOV), full-spectral, pixel-by-pixel polarization testing system was established based on the Stokes–Muller formalism, achieving for the first time fine characterization and calibration of the pixel-level polarization properties of such a payload. The results show that: (1) polarization sensitivity (LPS) exhibits a strong linear positive correlation with wavelength (R² > 0.97), with good uniformity (fluctuation < 1%) across the full ±15° FOV; (2) the polarization sensitive axis (PSA) shows a symmetric distribution across the FOV and gradually approaches 90° as the wavelength increases, with a clear deviation in the short-wavelength bands and stabilization in the mid-to-long wavelength bands; (3) through multiple sets of cross-validation and Monte Carlo statistics, the calibration accuracy reaches 0.1%, and the system uncertainty is better than 0.05%. This study can provide data support and a reference basis for high-accuracy spaceborne SIF retrieval, payload polarization correction, and optical design optimization. Full article

(This article belongs to the Special Issue Nonlinear Optics and Hyperspectral Polarization Imaging)

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20 pages, 3012 KB

Open AccessArticle

Design and Simulation of a Compact Remote Raman–LIBS Spectrometer Based on Liquid Lens Focusing for Long-Range Surface Analysis

by Zhicong Li, Xiaolong Ma, Jiawei Liu, Yinghong He, Juan Lv and Jianfeng Yang

Photonics 2026, 13(5), 497; https://doi.org/10.3390/photonics13050497 - 16 May 2026

Viewed by 374

Abstract

In response to the demands for planetary material detection, in this study, we propose an optical system for a compact remote Raman–LIBS (CRBS, Laser-Induced Breakdown Spectroscopy) combined spectrometer based on liquid lens focusing. This system adopts a design approach incorporating liquid lens focusing, [...] Read more.

In response to the demands for planetary material detection, in this study, we propose an optical system for a compact remote Raman–LIBS (CRBS, Laser-Induced Breakdown Spectroscopy) combined spectrometer based on liquid lens focusing. This system adopts a design approach incorporating liquid lens focusing, a shared pulsed excitation source, and a common optical path for both transmission and reception. Compared to existing international combined Raman–LIBS spectrometer systems, the proposed optical system is more compact and achieves integrated Raman and LIBS detection capabilities, thereby facilitating system miniaturization and enhancing detection efficiency. This system represents a promising approach for compact, robust remote surface analysis instruments for terrestrial and planetary science. This study provides a theoretical foundation for achieving stable in-orbit detection in lunar material exploration and other long-distance signal detection missions. Full article

(This article belongs to the Special Issue Laser Spectroscopy: From Fundamentals to Advanced Applications)

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26 pages, 11735 KB

Open AccessArticle

Neural Network-Driven Transmission Characteristics Modeling and Manufacturing Error Detection for Photonic Lanterns

by Zhuruixiang Sun, Xiang Li, Yao Lu, Tong Liu, Zilun Chen and Zongfu Jiang

Photonics 2026, 13(5), 496; https://doi.org/10.3390/photonics13050496 - 16 May 2026

Viewed by 315

Abstract

Traditional numerical simulation methods struggle to accurately characterize the transmission characteristics of finished photonic lanterns that contain manufacturing errors. This paper proposes a method for characterizing photonic lantern devices using neural networks. In an ideal

1 \times 6

photonic lantern, the Mean Squared [...] Read more.

Traditional numerical simulation methods struggle to accurately characterize the transmission characteristics of finished photonic lanterns that contain manufacturing errors. This paper proposes a method for characterizing photonic lantern devices using neural networks. In an ideal

1 \times 6

photonic lantern, the Mean Squared Error (MSE) for predicting intensity from the multimode to the single-mode end was reduced to

10^{- 5}

, and the neural network model can identify manufacturing error patterns, providing a new approach to addressing the precise characterization and product screening of novel irregular waveguides such as photonic lanterns. Full article

(This article belongs to the Special Issue Deep Learning in Optical Engineering: Applications in Design, Simulation, and Performance)

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31 pages, 3241 KB

Open AccessArticle

A Two-Point Propagation Field of a Single Photon: A Way to X-Ray Picometer Displacement Detection and Nanometer Resolution 3D X-Ray Micro-Tomography

by Lihua Yu

Photonics 2026, 13(5), 495; https://doi.org/10.3390/photonics13050495 - 16 May 2026

Viewed by 257

Abstract

We introduce the two-point propagation field (TPPF)—a real-valued, phase-sensitive quantity defined as the functional derivative of the single-photon detection probability with respect to an infinitesimal opaque perturbation placed between the source and detection slits. The TPPF is analytically derived and shown to exhibit [...] Read more.

We introduce the two-point propagation field (TPPF)—a real-valued, phase-sensitive quantity defined as the functional derivative of the single-photon detection probability with respect to an infinitesimal opaque perturbation placed between the source and detection slits. The TPPF is analytically derived and shown to exhibit a stable, high-frequency sinusoidal structure with periods of 4~7 nm near the X-ray detection slit. This structure enables shot-noise-limited displacement detection with ∼200 pm precision for 6 keV X-rays using total photon counts on the order of 1 ×

10^{7}

and detector photon counting as low as 287. Beyond displacement detection, the TPPF physically performs a Fourier–Radon transformation of the projection data, providing a pathway to non-iterative frequency-domain tomography. Two conceptual strategies—a central blocker and off-axis multi-slit arrays—are estimated to lower the required incident photon budget by more than one order of magnitude each, yielding combined reductions of two to three orders of magnitude with near-term detector development. The TPPF concept, originally developed in a perturbative study of single-particle propagation, bridges quantum measurement questions with practical high-resolution X-ray physics. This work provides the foundational physics required for future discrete sampling and 3D numerical reconstruction algorithms. Full article

(This article belongs to the Special Issue Recent Progress in Single-Photon Generation and Detection)

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24 pages, 1734 KB

Open AccessReview

Recent Progress in Development of Hollow-Core Fibers for Telecommunications and Data Transmission Applications

by Krzysztof Borzycki

Photonics 2026, 13(5), 494; https://doi.org/10.3390/photonics13050494 - 15 May 2026

Viewed by 634

Abstract

The progress made in several fields after 2023 is rather significant. Attenuation achieved by the best HCFs was reduced to 0.05–0.10 dB/km at 1550 nm, while the lowest attenuation achieved in a single-mode fiber with a pure silica core equals 0.14 dB/km. Polarization [...] Read more.

The progress made in several fields after 2023 is rather significant. Attenuation achieved by the best HCFs was reduced to 0.05–0.10 dB/km at 1550 nm, while the lowest attenuation achieved in a single-mode fiber with a pure silica core equals 0.14 dB/km. Polarization mode dispersion (PMD) has been reduced to a level typical of SMFs, through fiber spinning. In November 2024, Microsoft announced a 2-year plan to install 15,000 km of HCF cables between and within data centers processing data for Microsoft Azure cloud services. Furthermore, several HCF manufacturers have emerged: UK-based Microsoft Azure Fiber and two Microsoft subcontractors, namely Corning Inc. and Heraeus Covantics, plus two major HCF manufacturers in China, YOFC and Linfiber. Additionally, extensive work was carried out on optical amplifiers to enable new transmission bands in HCFs, both at short wavelengths (≈1300–1500 nm), with bismuth-doped active fibers, and long wavelengths (≈1700–2100 nm), with thulium- and holmium-doped fibers. On the other hand, progress in HCF standardization, splicing and elimination of loss bands introduced by contaminants, has been marginal. Standardization is blocked by multiple fiber designs being tried, with no clear winner emerging yet. Despite this, hollow-core fibers have been successfully debuted in large-scale commercial data centers and are also used in low-latency data links. Full article

(This article belongs to the Special Issue Advances in Hollow-Core Optical Fibers: From Fundamentals to Applications)

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9 pages, 3746 KB

Open AccessArticle

Ultrafast Physical Random Bit Generation Based on an Integrated Mutual Injection DFB Laser

by Jianyu Yu, Pai Peng, Qi Zhou, Pan Dai, Xiangfei Chen and Yi Yang

Photonics 2026, 13(5), 493; https://doi.org/10.3390/photonics13050493 - 15 May 2026

Viewed by 307

Abstract

Ultrafast physical random bit generators (PRBGs) are essential components for modern applications in secure communication, quantum cryptography, encrypted optical fiber sensing and artificial intelligence. While optical chaos-based PRBGs offer high-speed capabilities, conventional systems often rely on discrete components that suffer from system complexity [...] Read more.

Ultrafast physical random bit generators (PRBGs) are essential components for modern applications in secure communication, quantum cryptography, encrypted optical fiber sensing and artificial intelligence. While optical chaos-based PRBGs offer high-speed capabilities, conventional systems often rely on discrete components that suffer from system complexity and environmental instability. This paper proposes and experimentally demonstrates a robust, integrated solution using a two-section mutual injection DFB laser. The device was fabricated using the reconstruction equivalent chirp (REC) technique, which provides precise control over grating phase variation while utilizing low-cost, high-volume fabrication methods. The laser sections, each measuring 450 μm in length, were designed with a free-running wavelength difference of 0.3 nm to ensure a flat optical spectrum and enhanced chaotic dynamics. By optimizing the bias currents, we achieved a chaos RF bandwidth of 20.1 GHz. Notably, the resulting chaotic signal lacks time-delayed signatures, which simplifies the randomness extraction process. To generate random bits, the chaotic waveform was sampled by an 8-bit analog-to-digital converter at 100 GSa/s. Following post-processing through delay-subtracting and the extraction of the four least significant bits (4-LSBs), we realized a total physical random bit rate of 400 Gb/s. The randomness of the generated sequence was successfully verified using the NIST SP 800-22 statistical test suite. This approach offers a compact, energy-efficient, and high-performance integrated chaotic source suitable for secure communication and high-performance computation. Full article

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

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13 pages, 2878 KB

Open AccessArticle

Propagation Properties of Non-Diffracting Tricomi Beam in Atmospheric Turbulence

by Lin Ma, Haibo Niu, Xingxing Han, Youzhang Zhu and Jing Shi

Photonics 2026, 13(5), 492; https://doi.org/10.3390/photonics13050492 - 15 May 2026

Viewed by 258

Abstract

Non-diffracting beams play crucial roles in the field of free-space optical communication due to their robust resistance to distortion in atmospheric turbulence. As a non-diffracting beam characterized by multiple parameters, the Tricomi beam exhibits great versatility and adjustability, attracting considerable interest recently. In [...] Read more.

Non-diffracting beams play crucial roles in the field of free-space optical communication due to their robust resistance to distortion in atmospheric turbulence. As a non-diffracting beam characterized by multiple parameters, the Tricomi beam exhibits great versatility and adjustability, attracting considerable interest recently. In this paper, we study the propagation properties of Tricomi beam in atmospheric turbulence based on the theory of random phase screen. It is found that the performance of Tricomi beam in atmospheric turbulence shows strong dependence on its asymmetric constants, topological charge, and half-cone angle. Meanwhile, the Tricomi beam manifests superior resistance to distortion and spatial mode stability in contrast to the conventional non-diffracting Bessel beam. Our work provides a valuable theoretical foundation for the design and performance optimization of next-generation free-space optical communication systems, potentially enabling enhanced data transmission fidelity over long atmospheric paths. Full article

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11 pages, 3234 KB

Open AccessArticle

A Transmission-Type High-Efficiency Chiral Filter with Three Discrete Wavelength Responses Based on Oracle Bone Structure Metasurfaces

by Bo Cheng, Tiancheng Xian, Longfeng Lv, Yuxiao Zou, Guofeng Song, Kunpeng Zhai and Hanxiao Shao

Photonics 2026, 13(5), 491; https://doi.org/10.3390/photonics13050491 - 15 May 2026

Viewed by 409

Abstract

Conventional chiral metasurfaces are typically restricted to a single resonant wavelength, which limits their ability to satisfy the requirements of broadband detection and multi-channel polarization manipulation. To overcome this limitation, this study numerically proposes a chiral metasurface based on an oracle-bone-inspired geometry. By [...] Read more.

Conventional chiral metasurfaces are typically restricted to a single resonant wavelength, which limits their ability to satisfy the requirements of broadband detection and multi-channel polarization manipulation. To overcome this limitation, this study numerically proposes a chiral metasurface based on an oracle-bone-inspired geometry. By combining dislocation with rotational symmetry breaking, the proposed structure enables pronounced circular dichroism responses at three wavelengths in the long-wave infrared region, reaching 0.68@λ₁ = 10.43 μm, 0.79@λ₂ = 10.8 μm, and 0.6@λ₃ = 10.9 μm. This design overcomes the single-wavelength limitation of conventional chiral metasurfaces and establishes a new paradigm for multi-wavelength chiral light-field manipulation. This research not only broadens the design scope of chiral photonics, but also provides a promising technical path for the development of highly integrated infrared polarization devices and multi-wavelength chiral sensing systems. Full article

(This article belongs to the Special Issue Photonic Metasurfaces: Advances and Applications)

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10 pages, 3028 KB

Open AccessArticle

Preliminary Evidence of Circadian Rhythms in the Twelve Meridians Using Infrared Thermal Imaging: A Case Series

by Jih-Huah Wu, Fu-Chien Chiu, Yi-Chia Shan and Chuan-Tsung Su

Photonics 2026, 13(5), 490; https://doi.org/10.3390/photonics13050490 - 15 May 2026

Viewed by 451

Abstract

This preliminary study explored circadian variations in meridian-associated skin temperature using infrared thermal imaging (IRTI). Four healthy adults receive a two-hour IRTI measurement alternately over a 24 h period, with thermal images acquired every 15 min. Within the 24 h monitoring period, two-hour [...] Read more.

This preliminary study explored circadian variations in meridian-associated skin temperature using infrared thermal imaging (IRTI). Four healthy adults receive a two-hour IRTI measurement alternately over a 24 h period, with thermal images acquired every 15 min. Within the 24 h monitoring period, two-hour intervals corresponding to the predicted peak activity of each meridian according to the ziwu-liuzhu theory were selected for detailed analysis. Specifically, jing-well acupoints exhibited an early increase in temperature at the onset of their predicted active intervals, whereas terminal acupoints showed a decline in temperature, suggesting the initiation and completion of meridian activity. A progressive increase followed by a decrease was observed along both the spleen meridian (9:00–11:00 a.m.) and heart meridian (11:00–1:00 p.m.), suggesting a temporal trend that may be consistent with traditional Chinese medicine (TCM) predictions. These preliminary results indicate that IRTI may provide a non-invasive approach for visualizing circadian features of meridian function, offering potential to bridge TCM concepts with modern biomedical approaches. Full article

(This article belongs to the Special Issue Light as a Cure: Photobiomodulation and Photodynamic Therapy)

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15 pages, 2015 KB

Open AccessCommunication

Pixelated Angle-Multiplexed Guided-Mode Resonance Metasurfaces for Broadband Terahertz Fingerprint Biosensing

by Weiqi Xu, Mengya Pan, Qiankai Hong, Shengyuan Shen, Conghui Guo, Yanpeng Shi and Yifei Zhang

Photonics 2026, 13(5), 489; https://doi.org/10.3390/photonics13050489 - 14 May 2026

Viewed by 498

Abstract

Terahertz (THz) fingerprint detection is central to identifying characteristic absorption fingerprints of biomolecules derived from their intrinsic rotational and vibrational modes. The development of guided-mode resonance (GMR) technology together with pixelated design offers a new approach to enhance the recognition capability of such [...] Read more.

Terahertz (THz) fingerprint detection is central to identifying characteristic absorption fingerprints of biomolecules derived from their intrinsic rotational and vibrational modes. The development of guided-mode resonance (GMR) technology together with pixelated design offers a new approach to enhance the recognition capability of such fingerprint spectra. Here, a novel secondary grating metasurface based on cycloolefin polymer (COP) is proposed, which adopts an ultra-minimalist dual-pixel complementary architecture to excite high-quality (Q)-factor GMR. Its spectral resolution does not exceed 50 GHz, enabling precise capture of target molecular characteristic information and meeting the requirements of broadband fingerprint sensing. More importantly, the design regulates the dual-pixel grating units through parameter gradient optimization and incorporates a dual regulation mode of static pixel-targeted coverage and dynamic angle fine tuning. By adjusting geometric parameters and incident angles, broadband coverage from 1.15 THz to 2.20 THz is achieved, which can accurately match the multi-fingerprint detection requirements of glutamic acid (Glu) and glutamine (Gln). This metasurface sensor, integrating the advantages of pixelation and high-Q-factor GMR characteristics, provides an effective strategy for enhanced broadband THz fingerprint sensing and shows broad application potential in the field of biochemical trace detection. Full article

(This article belongs to the Special Issue Photonic Metasurfaces: Advances and Applications)

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67 pages, 3773 KB

Open AccessSystematic Review

Photobiomodulation Therapy and Central Nervous System Disorders: A Systematic Review of Delivery Routes, Mechanisms, Parameters and Clinical Evidence

by Mark Cronshaw, Steven Parker, Edward Lynch, Will Dixon, Alan Kwong Hing and Martin Grootveld

Photonics 2026, 13(5), 488; https://doi.org/10.3390/photonics13050488 - 14 May 2026

Viewed by 547

Abstract

Photobiomodulation (PBM), the therapeutic application of red to near-infrared light, has demonstrated neuroprotective effects in preclinical CNS models, yet clinical translation remains inconsistent. This systematic review synthesises evidence for PBM across CNS applications to identify factors associated with therapeutic response. We searched five [...] Read more.

Photobiomodulation (PBM), the therapeutic application of red to near-infrared light, has demonstrated neuroprotective effects in preclinical CNS models, yet clinical translation remains inconsistent. This systematic review synthesises evidence for PBM across CNS applications to identify factors associated with therapeutic response. We searched five databases (MEDLINE, Embase, CENTRAL, Web of Science, Scopus) through January 2025 following PRISMA 2020 guidelines. Included studies employed PBM for CNS conditions with quantified neurological, cognitive, or functional outcomes; evidence quality was assessed using RoB 2, ROBINS-I, SYRCLE, and the GRADE framework. Thirty studies met inclusion criteria: 27 human studies (n ≈ 2244 participants) and 3 animal studies spanning Alzheimer’s disease, Parkinson’s disease, stroke, traumatic brain injury, and other CNS conditions. Dosimetry—particularly irradiance and light source type (laser vs. LED)—appears to be the primary factor associated with efficacy for Alzheimer’s disease (GRADE: Moderate); trans-cranial LED shows promise for Parkinson’s disease (GRADE: Low); trans-cranial 808 nm laser demonstrates no benefit for acute ischaemic stroke (GRADE: High). Systemic abscopal mechanisms may offer additional therapeutic pathways warranting investigation. These findings provide a condition-specific framework for rational PBM protocol development, supporting adequate irradiance via laser or intra-nasal delivery for Alzheimer’s disease, LED-based trans-cranial protocols for Parkinson’s disease, and integration of artificial intelligence for personalised optimisation. Full article

(This article belongs to the Special Issue Light as a Cure: Photobiomodulation and Photodynamic Therapy)

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21 pages, 1787 KB

Open AccessArticle

Distributed Twice-Extended State Kalman Filter for Multi-Photoelectric Tracking System over Sensor Networks

by Yikun Li, Chang Qin, Zhihao Xiao, Jiayi Kang, Tong Guo, Xi Zhou, Jinying Li and Yao Mao

Photonics 2026, 13(5), 487; https://doi.org/10.3390/photonics13050487 - 14 May 2026

Viewed by 362

Abstract

Multi-photoelectric tracking systems (MPTSs) provide high-precision line-of-sight (LOS) angles for long-range passive tracking, with each photoelectric tracking system (PTS) delivering bearing-only measurements. In practice, image-based target extraction and optical–mechanical pointing may suffer from intermittent errors when highly maneuverable targets are observed, thereby degrading [...] Read more.

Multi-photoelectric tracking systems (MPTSs) provide high-precision line-of-sight (LOS) angles for long-range passive tracking, with each photoelectric tracking system (PTS) delivering bearing-only measurements. In practice, image-based target extraction and optical–mechanical pointing may suffer from intermittent errors when highly maneuverable targets are observed, thereby degrading tracking accuracy. To address this issue, we consider a time-varying uncertain dynamics model with a lumped uncertainty and its temporal difference. A centralized twice-extended state Kalman filter (CTESKF) is proposed to augment the kinematic state with the lumped uncertainty and its temporal difference, yielding a Kalman-type recursion with a computable covariance upper bound. Building on this, a diffusion-based twice-extended state Kalman filter (DTESKF), which combines local updates with single-round covariance-intersection diffusion fusion, is proposed to achieve distributed filtering with limited communication cost. Simulation results show that CTESKF and DTESKF achieve competitive accuracy–efficiency trade-offs in a weakly nonlinear setting and a 3D bearing-only MPTS scenario. Full article

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15 pages, 2191 KB

Open AccessArticle

Optimization of Coronary Artery Calcium Scoring Accuracy in Low-Dose Chest Computed Tomography Using Fast Non-Local Means Denoising with High-Pitch Acquisition and Tin Filtration

by Jina Shim, Ji-Youn Kim and Kyuseok Kim

Photonics 2026, 13(5), 486; https://doi.org/10.3390/photonics13050486 - 14 May 2026

Viewed by 341

Abstract

This study evaluated quantitative accuracy of the coronary artery calcium score (CACS) and the associated radiation dose reduction achieved by applying the fast non-local means (FNLM) algorithm to non-electrocardiography (ECG)-gated, low-dose chest computed tomography (CT) images acquired with a high-pitch scan and tin [...] Read more.

This study evaluated quantitative accuracy of the coronary artery calcium score (CACS) and the associated radiation dose reduction achieved by applying the fast non-local means (FNLM) algorithm to non-electrocardiography (ECG)-gated, low-dose chest computed tomography (CT) images acquired with a high-pitch scan and tin filter. Thirty patients underwent standard-dose CACS and low-dose chest CT were retrospectively analyzed. The processed low-dose images using the FNLM algorithm demonstrated a 4.2–5.0% mean CACS decrease and ≤16.4% median value increase relative to the standard-dose CACS CT but without statistical significance (p > 0.05). Notably, the quantitative error progressively decreased with increasing algorithm strength. The Pearson correlation coefficient reached 0.949 at Stage 3, indicating robust agreement with the standard-dose CACS CT. When stratified by patient heart rate, the high heart rate cohort exhibited the largest scoring errors but without statistical significance (p > 0.05). Importantly, the FNLM-processed protocol substantially reduced radiation dose, decreasing the mean volume CT dose index by 71.2% and dose-length product by 56.5% (p < 0.05). FNLM proves to be an effective post-processing technique that preserves CACS accuracy in non-ECG-gated, low-dose chest CT, thereby offering a clinically viable alternative imaging protocol for patients requiring routine screening. Full article

(This article belongs to the Special Issue Advances in X-Ray Imaging Technology)

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27 pages, 2172 KB

Open AccessArticle

Long-Term QoT Forecasting in Dynamic Optical Networks via Decomposition-Driven Parallel Temporal Modeling

by Yihao Zhong, Changsheng Yin, Yuantao Yang, Ruopeng Yang, Yongqi Wen, Yu Jiang, Yu Tao, Yongqi Shi and Bo Huang

Photonics 2026, 13(5), 485; https://doi.org/10.3390/photonics13050485 - 14 May 2026

Viewed by 393

Abstract

Accurate long-term forecasting of Quality of Transmission (QoT) is critical for the proactive operation and condition-aware management of dynamic elastic optical networks. However, the evolution of QoT is governed by multi-scale dynamics, including slow equipment aging, periodic operating variations, and short-term channel fluctuations, [...] Read more.

Accurate long-term forecasting of Quality of Transmission (QoT) is critical for the proactive operation and condition-aware management of dynamic elastic optical networks. However, the evolution of QoT is governed by multi-scale dynamics, including slow equipment aging, periodic operating variations, and short-term channel fluctuations, which a single temporal model struggles to capture jointly. To address this issue, we propose PA-TCN-Informer, a decomposition-driven parallel forecasting framework for long-horizon QoT prediction. The proposed framework first applies Seasonal-Trend decomposition using Loess (STL) to separate the Q-factor sequence into trend, seasonal, and residual components, and then employs Variational Mode Decomposition (VMD) to further resolve the residual into short-term fluctuation modes. The decomposed components, together with physical-layer monitoring features, are fed into a parallel TCN–Informer architecture, in which the TCN branch captures local temporal patterns while the Informer branch models long-range dependencies; the two streams are subsequently fused. We evaluate the proposed framework through Optuna-based hyperparameter optimization, STL/VMD sensitivity analysis, decomposition-method comparison, multi-seed baseline comparison with statistical testing, and zero-shot leave-one-dataset-out cross-domain evaluation. On the primary dataset, PA-TCN-Informer achieves the best overall forecasting accuracy among the compared models and reduces MAE by 2.2% relative to the serial TCN–Informer. In addition, the staged STL-VMD preprocessing alone yields a 60.8% reduction in MAE compared with raw inputs, confirming the value of physically interpretable multi-scale decomposition. In the zero-shot cross-domain setting, PA-TCN-Informer remains competitive across target domains. These results demonstrate that the proposed framework provides an effective and interpretable approach to QoT forecasting, and they further indicate that topology-aware modeling is a promising direction for improving cross-domain generalization. Full article

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14 pages, 5181 KB

Open AccessArticle

Slotted Nanocircuit-Enhanced Dual-Band Chiral Metasurface for Tunable Mid-Infrared Circular Dichroism

by Xintao Gao, Fengji Wu, Shifeng Dai, Musheng Chen, Yongxi Zeng, Yanzhong Yu and Pinghui Wu

Photonics 2026, 13(5), 484; https://doi.org/10.3390/photonics13050484 - 14 May 2026

Viewed by 455

Abstract

Multi-band circular dichroism (CD) with spectral tunability is highly desirable for chiral metasurface-based sensing and polarization control. In this work, we propose a mid-infrared (MIR) metal–insulator–metal (MIM) chiral metasurface absorber composed of gold-alumina-gold (Au-Al₂O₃-Au) layers, where chirality is introduced [...] Read more.

Multi-band circular dichroism (CD) with spectral tunability is highly desirable for chiral metasurface-based sensing and polarization control. In this work, we propose a mid-infrared (MIR) metal–insulator–metal (MIM) chiral metasurface absorber composed of gold-alumina-gold (Au-Al₂O₃-Au) layers, where chirality is introduced by symmetry breaking between two gold elliptical bars in the top layer. Finite element calculations show that the structure operates over 3.5–6.5 µm and produces dual-band CD responses with values of 0.83 and −0.81. The CD magnitude in each band can be independently tuned by adjusting the semi-major or semi-minor axis of the elliptical bars. In addition, rectangular slots inserted into the bars enable continuous redshift of the resonance wavelengths, and the tunability can be further enhanced by optimizing the slot dimensions. These results provide a practical strategy for designing tunable dual-band chiral absorbers and may be useful for future chiral sensing and polarization imaging applications. Full article

(This article belongs to the Special Issue Photonics Enabled by Plasmonic Metamaterials: Recent Developments and Future Directions)

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13 pages, 8190 KB

Open AccessArticle

Divergence of Long-Range Bessel-Gaussian Beams with Truncated Coaxial Rings

by Nikolay Dimitrov, Maya Zhekova and Alexander Dreischuh

Photonics 2026, 13(5), 483; https://doi.org/10.3390/photonics13050483 - 13 May 2026

Viewed by 313

Abstract

Bessel beams, one of the four known types of beams that are exact solutions of the Helmholtz equation, are remarkable with their non-diffracting nature. In reality, generated with real (Gaussian) laser beams with finite transverse profiles, Bessel-Gaussian beams (BGBs) are quasi-non-diffracting and remarkably [...] Read more.

Bessel beams, one of the four known types of beams that are exact solutions of the Helmholtz equation, are remarkable with their non-diffracting nature. In reality, generated with real (Gaussian) laser beams with finite transverse profiles, Bessel-Gaussian beams (BGBs) are quasi-non-diffracting and remarkably stable against spatial perturbations. Quasi-non-diffracting means that the central peaks of the BGBs typically have divergences of the order of microradians. Here, we present experimental evidence that the truncation of the concentric rings surrounding the central peak of the long-range BGBs has a pronounced and controllable effect on the divergence of their peaks. The method is well suited for microradian divergences and has a minimal effect when the divergence of the BGB approaches one milliradian. The truncation of the rings of the BGBs could be applied, for example, in free-space communications, in locating a receiver station with a more divergent beam, after which the spreading of the central peak in space could be reduced to ensure a more secure data transfer. Full article

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

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13 pages, 1346 KB

Open AccessArticle

High-Stability Thulium-Doped All-Fiber Laser at 2050 nm

by Hanchuang Peng, Zhipeng Ding, Di Xin, Fengxin Dong, Xuyan Zhou, Hongbo Zhang and Wanhua Zheng

Photonics 2026, 13(5), 482; https://doi.org/10.3390/photonics13050482 - 13 May 2026

Viewed by 536

Abstract

High-power thulium-doped fiber lasers (TDFLs) operating near 2050 nm are of great interest for applications including atmospheric gas sensing and free-space optical communication owing to the favorable atmospheric transmission and the strong absorption bands of carbon dioxide (CO₂). Here, we report [...] Read more.

High-power thulium-doped fiber lasers (TDFLs) operating near 2050 nm are of great interest for applications including atmospheric gas sensing and free-space optical communication owing to the favorable atmospheric transmission and the strong absorption bands of carbon dioxide (CO₂). Here, we report an all-fiber high-power TDFL based on a 793 nm-pumped master oscillator power amplifier (MOPA) architecture. The system comprises a custom-built linear-cavity seed laser and two amplification stages. With a maximum pump power of 818 W, the final amplifier delivers 501 W at 2050 nm with a slope efficiency of 51%. Stable operation is confirmed over two hours at full power, with an RMS power fluctuation of only 0.47%. The measured beam quality factors

M^{2}

are 1.31 and 1.27 in the horizontal and vertical directions, respectively, indicating near-diffraction-limited performance. The demonstrated system combines high output power, excellent stability, and good beam quality, and thus provides a promising laser source for 2 μm high-performance applications. Full article

(This article belongs to the Special Issue Progress in Ultra-Stable Laser Source and Future Prospects)

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24 pages, 5498 KB

Open AccessArticle

Dual-Wavelength Optical Triangulation System for Focus Metrology in 350 nm Lithography

by Hengrui Guan, Xuefeng Lei, Yuheng Chu, Xinxin Zhao, Dapeng Kuang, Maoxin Song, Mingchun Ling and Jin Hong

Photonics 2026, 13(5), 481; https://doi.org/10.3390/photonics13050481 - 12 May 2026

Viewed by 308

Abstract

Thin-film interference in photoresist stacks can become a significant source of uncertainty in lithographic focus metrology, particularly when high measurement stability is required. To evaluate this effect, a Fresnel-based multilayer reflection model is used to analyze the optical response of the resist stack [...] Read more.

Thin-film interference in photoresist stacks can become a significant source of uncertainty in lithographic focus metrology, particularly when high measurement stability is required. To evaluate this effect, a Fresnel-based multilayer reflection model is used to analyze the optical response of the resist stack and to guide the selection of dual-wavelength illumination. On this basis, a dual-wavelength optical triangulation system is developed for focus metrology in 350 nm lithography, with signal acquisition performed by a linear charge-coupled device (LCCD). Rather than improving precision by reducing detector pitch, the system employs a two-stage sub-pixel localization strategy in which template matching provides coarse spot localization and weighted centroid interpolation refines the final position within localized calculation windows, keeping the computational cost manageable. A covariance-based uncertainty analysis predicts a total root-mean-square uncertainty of 27.23 nm. Prototype experiments were performed on a bare silicon wafer to establish the intrinsic performance of the instrument before introducing process-dependent optical effects. Under these conditions, the system achieved a vertical resolution of 10 nm, a repeatability of 35 nm, and a stability of 13.16 nm. The additional uncertainty expected under resist-coated-wafer conditions was assessed separately through the thin-film model. These results verify the baseline capability of the proposed system and support the feasibility of the dual-wavelength strategy for focus metrology in 350 nm lithography. Full article

(This article belongs to the Special Issue Advancements in Optical Measurement Techniques and Applications)

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19 pages, 599 KB

Open AccessArticle

Surface Phonon Polariton-Quantum Dot Coupling in One-Dimensional Periodic Microstructures for Batch Quantum State Manipulation

by Xinhua Zhang, Yuchun Liu, Xinyue Zhang, Lingchen Kong, Cuihong Jin, Yajuan Han, Mengqing Jiang, Shiying Qiao and Xinyan Gong

Photonics 2026, 13(5), 480; https://doi.org/10.3390/photonics13050480 - 12 May 2026

Viewed by 330

Abstract

To explore the strong coupling between surface phonon polaritons (SPhPs) and quantum dots in one-dimensional periodic microstructures for quantum information processing, we establish a comprehensive theoretical model for SPhPs at air–polar dielectric interfaces. By rigorously deriving the dispersion relations, we reveal the decisive [...] Read more.

To explore the strong coupling between surface phonon polaritons (SPhPs) and quantum dots in one-dimensional periodic microstructures for quantum information processing, we establish a comprehensive theoretical model for SPhPs at air–polar dielectric interfaces. By rigorously deriving the dispersion relations, we reveal the decisive role of scale effects on bandgap formation: continuous spectra without bandgaps emerge at the nanoscale (

d \sim 10

–100 nm), whereas periodic modulation induces significant Bloch mode folding and tunable bandgaps (0.5–5

μ m

width) at the microscale (

d \sim 1

–10

μ m

). Based on Fourier bandwidth limitations, we determine optimal channel widths (

L_{y} \geq 10 μ m

) for maintaining low-loss modes with energy deviations below 1%. Through electromagnetic field quantization, we obtain analytical expressions for SPhP mode amplitudes and quantum dot transition rates. Calculations demonstrate that in micrometer-scale CsI structures, spontaneous emission rates can be modulated significantly: suppressed to <0.1 times the free-space values within bandgaps (excited-state lifetimes extended to ∼10 ns) and enhanced 5–8 times at conduction band edges. Leveraging these characteristics, we propose a scheme for batch quantum state manipulation of

10^{2}

–

10^{3}

arrayed quantum dots via selective excitation of specific Bloch modes using controlled laser frequency and angle, enabling parallel single-qubit gates with theoretical fidelity > 99%. Compared with surface plasmon polariton schemes, our approach utilizes the low-loss infrared characteristics of SPhPs (

Q \sim 100

–1000, 1–2 orders higher) to reduce decoherence rates, offering a new pathway for room-temperature solid-state quantum computing and on-chip multi-node entanglement distribution. Full article

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15 pages, 4511 KB

Open AccessArticle

Design of Terahertz Polarization-Multiplexed Structured Light Metasurface Based on Particle Swarm Optimization

by Siyuan Cheng, Guangyi Zhang and Tao Ju

Photonics 2026, 13(5), 479; https://doi.org/10.3390/photonics13050479 - 11 May 2026

Viewed by 365

Abstract

We propose a terahertz achromatic polarization-multiplexed structured light metasurface based on the particle swarm optimization (PSO) algorithm, operating from 0.8 to 0.95 THz. A dielectric silicon meta-atom array combined with propagation phase modulation is employed to achieve broadband wavefront control under two orthogonal [...] Read more.

We propose a terahertz achromatic polarization-multiplexed structured light metasurface based on the particle swarm optimization (PSO) algorithm, operating from 0.8 to 0.95 THz. A dielectric silicon meta-atom array combined with propagation phase modulation is employed to achieve broadband wavefront control under two orthogonal linear polarizations. By constructing a phase-response database and using PSO for global optimization of phase compensation factors at multiple frequencies, the metasurface simultaneously satisfies different target phase profiles while suppressing chromatic aberration. Two multifunctional devices are designed. The first generates a conventional focused spot under x-polarized incidence and a first-order Bessel beam under y-polarized incidence. The second produces a focused vortex beam with topological charge l = 1 under x polarization and a focused vortex beam with l = 2 under y polarization. Full-wave simulations demonstrate stable focal positions, low inter-channel crosstalk, and good achromatic performance across the operating band. The Bessel beam preserves its nondiffracting core, while both vortex channels exhibit clear phase singularities and well-defined orbital angular momentum states. Most operating frequencies maintain relatively high focusing efficiency. Compared with conventional cascaded optical components, our design provides a compact and stable platform for terahertz structured light generation, orbital angular momentum multiplexing, nondiffracting imaging, and multidimensional polarization information processing. Full article

(This article belongs to the Special Issue Advanced Photonics Metamaterials and Metasurfaces: Science and Applications, 3rd Edition)

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12 pages, 1947 KB

Open AccessCommunication

The Spreading and Wander of a Gaussian Schell-Model Beam Through Oceanic Turbulence

by Ningjing Xiang

Photonics 2026, 13(5), 478; https://doi.org/10.3390/photonics13050478 - 11 May 2026

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Abstract

In this paper, we investigate the propagation properties of a partially coherent Gaussian Schell-model (GSM) beam by effective beam parameters in oceanic turbulence. We provide detailed analytical derivations based on the extended Huygens–Fresnel integral and the cross-spectral density function. It is found that [...] Read more.

In this paper, we investigate the propagation properties of a partially coherent Gaussian Schell-model (GSM) beam by effective beam parameters in oceanic turbulence. We provide detailed analytical derivations based on the extended Huygens–Fresnel integral and the cross-spectral density function. It is found that the angle-of-arrival fluctuation, spreading, and wander of the partially coherent GSM beam decrease with increasing source coherence parameter and turbulent kinetic energy dissipation rate, and with decreasing temperature fluctuations and mean-square temperature dissipation rate. At 200 m propagation distance, the relative mean-squared width under salinity-dominated conditions (ω = −2) is approximately 0.02% larger than that under temperature-dominated conditions (ω = −5), indicating that salinity fluctuations cause more obvious beam spreading. Full article

(This article belongs to the Special Issue Next-Generation Optical Transmission Systems: Breakthroughs, Technologies, and Emerging Frontiers)

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