Photonics

10 pages, 2733 KB

Open AccessArticle

Phase Noise Suppression in Fiber Interferometers over the Hz–kHz Range Using Solid-Core and Hollow-Core Photonic Crystal Fibers

by Yibin Liang, Kejian Li and Kunhua Wen

Photonics 2026, 13(4), 361; https://doi.org/10.3390/photonics13040361 (registering DOI) - 9 Apr 2026

Abstract

Fiber interferometers are widely used in precision measurement fields such as seismic observation, gravitational-wave detection, and aerospace guidance. However, phase noise in the Hz–kHz range has become an important factor limiting further improvement in measurement accuracy. In this work, a solid-core photonic crystal [...] Read more.

Fiber interferometers are widely used in precision measurement fields such as seismic observation, gravitational-wave detection, and aerospace guidance. However, phase noise in the Hz–kHz range has become an important factor limiting further improvement in measurement accuracy. In this work, a solid-core photonic crystal fiber (PCF) and a hollow-core photonic bandgap fiber (HC-PBGF) were introduced into the sensing arms of a fiber interferometer to reduce phase noise in this frequency range. Theoretical analysis showed that, compared with a conventional solid-core fiber, the PCF and the 19-cell HC-PBGF used in this study could reduce the phase noise by approximately 3 dB and 7 dB, respectively. The experimental results agreed well with the theoretical predictions, confirming that both fibers can effectively suppress high-frequency phase noise, with HC-PBGF showing superior noise reduction performance. This work provides a feasible approach for improving the performance of fiber interferometers in precision measurement. Full article

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

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50 pages, 5839 KB

Open AccessReview

Wavefront Coherence Stabilization for Large Segmented Telescope: Measurement and Control

by Wuyang Wang, Qichang An and Xiaoxia Wu

Photonics 2026, 13(4), 360; https://doi.org/10.3390/photonics13040360 (registering DOI) - 9 Apr 2026

Abstract

Large-aperture optical synthetic aperture technology, by combining multiple aperture units, breaks through the limitations of a single reflector and has become the preferred system for extending the resolution and diffraction limit of imaging systems. In particular, segmented telescopes have accumulated extensive engineering practice [...] Read more.

Large-aperture optical synthetic aperture technology, by combining multiple aperture units, breaks through the limitations of a single reflector and has become the preferred system for extending the resolution and diffraction limit of imaging systems. In particular, segmented telescopes have accumulated extensive engineering practice experience, such as the 30 m TMT and the 39 m ELT. However, the stable maintenance of wavefront coherence between multiple sub-apertures requires strict phase synchronization and group delay matching accuracy, which hinders the further development of sparse aperture telescopes and distributed interferometric telescopes (Long-Baseline Interferometers). This review systematically summarizes the research progress on synthetic aperture systems in wavefront coherence detection and stable maintenance control, focusing on two main physical architectures (Michelson and Fizeau types) and the related control algorithms. Furthermore, based on the basic logic from “measurement” to “modulation”, it prospects the development trends driven by interdisciplinary technologies such as embodied intelligent dynamic prediction, photonic integration, and real-time sensing based on deep learning. The aim is to provide a reference for wavefront-stabilization solutions in the next-generation ultra-large-aperture optical synthetic aperture systems. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Systems for Astronomy)

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11 pages, 237 KB

Open AccessArticle

Classical Correspondence of Squeezing Operators and the Extension of Bohr’s Correspondence Principle

by Ke Zhang and Hongyi Fan

Photonics 2026, 13(4), 359; https://doi.org/10.3390/photonics13040359 - 9 Apr 2026

Abstract

Bohr’s correspondence principle acts as a link between quantum physics and classical physics theory, while squeezed light, as a special nonclassical quantum state in quantum physics, achieves precision measurements and gravitational wave detection by minimizing quantum noise in one quadrature component of the [...] Read more.

Bohr’s correspondence principle acts as a link between quantum physics and classical physics theory, while squeezed light, as a special nonclassical quantum state in quantum physics, achieves precision measurements and gravitational wave detection by minimizing quantum noise in one quadrature component of the optical field. Consequently, determining whether the classical counterpart of the squeezing operator reflects classical spatial scaling transformations is of significant theoretical importance. This paper establishes a universal integral formula that transforms any operator into its Weyl ordering form using the method of integration within the ordered product of operators, combined with the coherent state representation and integration theory within Weyl ordering. By transforming both single-mode and two-mode squeezing operators into their corresponding Weyl ordering forms, their classical counterpart functions are derived. This elucidates the classical correspondence of the squeezed light field density operator and demonstrates that this correspondence fundamentally represents a classical scaling transformation. As a practical application of the classical counterpart of the single-mode squeezing operator, the photon number distribution characteristics in a single-mode squeezed light field are obtained, confirming its noise-squeezing effect. This study not only deepens the theoretical implications of Bohr’s correspondence principle from the perspective of “transformation correspondence” but also introduces novel insights into the establishment of the mathematical foundations of quantum optics and quantum statistical theory. Full article

22 pages, 5062 KB

Open AccessArticle

A Tunable Hydrogen-Bond-Mediated Polymer-Based Mechanical Approach for Non-Destructive Cleaning of Silver Films

by Yuhang Zhang, Yun Du, Tao Shen, Xingyue Gao, Kaipeng Liu, Yunfei Luo, Chengwei Zhao, Zeyu Zhao, Changtao Wang and Ling Liu

Photonics 2026, 13(4), 358; https://doi.org/10.3390/photonics13040358 - 8 Apr 2026

Abstract

Silver films are key building blocks for plasmonic and nanophotonic devices, whose optical performance and device reliability are highly sensitive to particulate contamination introduced during fabrication and operation. Herein, a non-destructive surface cleaning strategy specifically applicable to silver film systems is proposed, based [...] Read more.

Silver films are key building blocks for plasmonic and nanophotonic devices, whose optical performance and device reliability are highly sensitive to particulate contamination introduced during fabrication and operation. Herein, a non-destructive surface cleaning strategy specifically applicable to silver film systems is proposed, based on the synergistic regulation of the mechanical properties of a polymer layer and its interfacial adhesion to the silver film. Such regulation is achieved by tuning hydrogen-bond-mediated interactions within a modified poly(vinyl alcohol) (PVA) layer, enabling effective control over the locus of fracture during peeling, such that fracture preferentially occurs at the polymer/silver interface. Unlike conventional polymer-assisted cleaning methods that suffer from an inherent trade-off between bulk cohesion and interfacial adhesion, this approach decouples the two properties through molecular-level hydrogen-bond redistribution. As a result, particulate contaminants can be efficiently removed from the silver surface while preserving the structural integrity of the silver film. The proposed method achieves a particle removal efficiency of up to 98% for contaminants larger than 30 nm and can be stably applied to silver films with lateral dimensions ranging from 1 inch to 12 inches, demonstrating excellent scalability. By further adjusting the processing parameters and compositional ratios of the polymer layer, this strategy is expected to be adaptable to silver films with different thicknesses and structural configurations, providing a reliable surface cleaning solution for improving the performance and reliability of plasmonic and optoelectronic thin-film devices. Full article

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

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14 pages, 2897 KB

Open AccessArticle

High-Power, Low-Divergence, Single Cross-Sectional-Mode 795 nm Semiconductor Laser Based on Photonic Crystal Epitaxy

by Bingqi Hou, Yufei Wang, Aiyi Qi, Yang Chen, Ziyuan Liao, Xuyan Zhou and Wanhua Zheng

Photonics 2026, 13(4), 357; https://doi.org/10.3390/photonics13040357 - 8 Apr 2026

Abstract

The 795 nm wavelength corresponds to the D1 transition of rubidium atoms and is widely used in atomic optical pumping, atomic clocks, magnetometers, and precision spectroscopy. For compact free-space collimation, beam shaping, and efficient fiber coupling, edge-emitting semiconductor lasers with reduced fast-axis (vertical) [...] Read more.

The 795 nm wavelength corresponds to the D1 transition of rubidium atoms and is widely used in atomic optical pumping, atomic clocks, magnetometers, and precision spectroscopy. For compact free-space collimation, beam shaping, and efficient fiber coupling, edge-emitting semiconductor lasers with reduced fast-axis (vertical) divergence are highly desirable, yet low-divergence designs at 795 nm remain limited. Here, we propose and demonstrate low-divergence photonic-crystal epitaxy (LD–PC) for 795 nm edge-emitting lasers. By engineering a periodic n-side photonic-crystal stack to place the fundamental vertical mode near the photonic band edge, the vertical mode is expanded while maintaining effective modal discrimination. Narrow-ridge Fabry–Pérot lasers based on GaAsP/AlGaAs single-quantum-well epitaxy were fabricated and characterized. The optimized LD–PC device (3 μm ridge width, 1 mm cavity length) delivers 227 mW at 200 mA with a threshold current of 23 mA, a slope efficiency of 1.28 W/A, and a peak wall-plug efficiency of 55% under continuous-wave operation at 25 °C. The measured far-field divergences (FWHMs) are 7.16° and 18.83° in the lateral and vertical directions, respectively, corresponding to a reduction in the vertical divergence from >40° in the reference structure to <20° with LD–PC. These results validate photonic-crystal epitaxy as an effective route toward compact, high-performance, low-divergence 795 nm semiconductor laser sources for rubidium-based atomic systems. Full article

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

24 pages, 2013 KB

Open AccessArticle

Capacity-Enhanced Li-Fi Transmission Using Autoencoder-Based Latent Representation: Performance Analysis Under Practical Optical Links

by Serin Kim, Yong-Yuk Won and Jiwon Park

Photonics 2026, 13(4), 356; https://doi.org/10.3390/photonics13040356 - 8 Apr 2026

Abstract

Visible light communication (VLC)-based Li-Fi systems suffer from limitations in transmission capacity expansion due to the restricted modulation bandwidth of LEDs. In this study, a latent representation-based NRZ-OOK Li-Fi transmission framework that exploits the statistical feature distribution of the latent space is proposed [...] Read more.

Visible light communication (VLC)-based Li-Fi systems suffer from limitations in transmission capacity expansion due to the restricted modulation bandwidth of LEDs. In this study, a latent representation-based NRZ-OOK Li-Fi transmission framework that exploits the statistical feature distribution of the latent space is proposed to improve transmission efficiency without expanding the physical bandwidth. An autoencoder is employed to transform input images into low-dimensional latent vectors, which are then quantized and modulated for transmission. At the receiver, hard decision and inverse quantization are performed, and the image is reconstructed through a trained decoder by leveraging the distribution characteristics of the latent representation. The effective transmission capacity gain

G_{c a p}

is defined to quantify the amount of representable information relative to the original data under the same physical link resources according to the latent dimension, achieving up to a 49-fold data representation efficiency. The experimental results over practical optical links (0.5–1.5 m) showed that, in short-range conditions, larger latent dimensions maintained higher reconstruction PSNR, whereas under channel degradation conditions, smaller latent dimensions exhibited higher robustness, demonstrating a performance inversion phenomenon. Furthermore, it was confirmed that the dominant factor governing reconstruction performance shifts from the representational capability of the data to error accumulation characteristics depending on the channel condition. These results suggest that the latent representation-based transmission framework is an effective Li-Fi strategy that can simultaneously consider transmission efficiency and channel robustness through information representation optimization in bandwidth-limited environments. Full article

(This article belongs to the Special Issue Neural Networks in Optical Communications and Optical Computing: Implementation, Applications, and Prospects)

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11 pages, 1503 KB

Open AccessArticle

Semiconductor Optoelectronic Polarization Imaging Approach for Enhanced Daytime Space Target Detection

by Guanyu Wen, Shuang Wang, Yukun Zeng, Shuzhuo Miao and Mingliang Zhang

Photonics 2026, 13(4), 355; https://doi.org/10.3390/photonics13040355 - 8 Apr 2026

Abstract

Daytime detection of space targets is challenging due to the strong skylight background and the limited resolution of conventional polarization imaging systems. In this work, we present a semiconductor-based polarization detection method that integrates a CMOS polarization imaging sensor with a Schmidt–Cassegrain telescope. [...] Read more.

Daytime detection of space targets is challenging due to the strong skylight background and the limited resolution of conventional polarization imaging systems. In this work, we present a semiconductor-based polarization detection method that integrates a CMOS polarization imaging sensor with a Schmidt–Cassegrain telescope. To compensate for the spatial resolution loss inherent in division-of-focal-plane semiconductor polarization detectors, a bicubic interpolation algorithm is applied to reconstruct the degree and angle of polarization images. Furthermore, a spectral filtering strategy is introduced to suppress skylight-induced stray radiation, improving image contrast and reducing the risk of detector saturation. The developed system combines semiconductor optoelectronic detection, optical filtering, and computational reconstruction into a compact experimental platform. Validation experiments on Polaris and low-Earth-orbit space targets under daytime conditions demonstrate that the proposed approach achieves clearer and sharper polarization images compared with traditional intensity-based methods. Objective evaluation metrics, including gradient, contrast, brightness, and spatial frequency, confirm significant improvements in image quality. These results highlight the potential of semiconductor optoelectronic devices for polarization-based imaging and provide an effective framework for enhancing daytime space target detection. Full article

(This article belongs to the Special Issue Semiconductor Optoelectronic Devices: Characterizations, Design and Fabrication)

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16 pages, 4253 KB

Open AccessArticle

Concentric-Ring-Assisted Multimode Fiber Supports Numerous High-Order LP Beams

by Chengyang Zhu, Xi Zhang, Haixuan Xu, Jingwen Zhang, Shuqi Ma and Yize Liang

Photonics 2026, 13(4), 354; https://doi.org/10.3390/photonics13040354 - 8 Apr 2026

Abstract

This study proposes and numerically investigates the design and characterization of a ring-assisted (RA) fiber supporting 11 LP mode groups and a concentric-ring-assisted (CRA) fiber supporting 13 LP mode groups. Based on the relationship between the normalized frequency and the number of LP [...] Read more.

This study proposes and numerically investigates the design and characterization of a ring-assisted (RA) fiber supporting 11 LP mode groups and a concentric-ring-assisted (CRA) fiber supporting 13 LP mode groups. Based on the relationship between the normalized frequency and the number of LP modes, a step-index (SI) fiber capable of supporting 13 LP mode groups is first designed. By leveraging the overlap between the high-index ring-assisted structure and the LP₂₂ mode, the effective index difference (Δn_eff) between the LP₂₂ and LP₀₃ modes is enhanced. The resulting RA 11-LP mode fiber achieves a minimum effective index difference Min|Δn_eff| of 0.78 × 10⁻³, comparable to that of a standard SI 4-mode fiber, and a minimum effective area Min|A_eff| of 164 μm², which effectively suppresses nonlinear effects. Furthermore, by introducing a second ring structure to form a CRA design, we realize a 13-LP mode fiber. This structure selectively increases the effective index of the LP₆₁ mode through overlap with its power distribution, while leaving the effective index of the LP₁₃ mode unaffected. The CRA 13-LP mode fiber exhibits highly stable effective indices across the C band. It demonstrates a Min|Δn_eff | of 0.55 × 10⁻³, which ensures effective mode separation and reduced inter-mode crosstalk. The Min|A_eff| is 131 μm²—still above 100 μm²—thereby mitigating nonlinear impairments. With support for 46 spatial modes in total, this fiber significantly enhances transmission capacity. Full article

(This article belongs to the Special Issue Advanced Optical Fiber Communication)

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11 pages, 2683 KB

Open AccessArticle

High-Bandwidth 940 nm VCSEL with Zn-Diffusion for Optical Communications

by Fu-He Hsiao, Yu-Jie Lin, Chia-Jung Tsai, Chia-Chen Li, Yun-Han Chang, Chih-Ting Chang, Jr-Hau He, Chun-Liang Lin, Yu-Heng Hong and Hao-Chung Kuo

Photonics 2026, 13(4), 353; https://doi.org/10.3390/photonics13040353 - 8 Apr 2026

Abstract

We present the simulation-guided design and experimental demonstration of high-speed 940 nm vertical-cavity surface-emitting lasers (VCSELs). Utilizing established device optimization principles, a simulation study was conducted focusing on the number of oxide layers and the aperture size, which predicted a maximum modulation bandwidth [...] Read more.

We present the simulation-guided design and experimental demonstration of high-speed 940 nm vertical-cavity surface-emitting lasers (VCSELs). Utilizing established device optimization principles, a simulation study was conducted focusing on the number of oxide layers and the aperture size, which predicted a maximum modulation bandwidth of over 35 GHz. To validate the simulation, a device with a 4-μm double-oxide aperture was fabricated and characterized. Additionally, a Zn-diffusion process was incorporated during fabrication to reduce p-DBR resistance and suppress higher-order transverse modes. The fabricated device achieved an experimental modulation bandwidth of 34 GHz and demonstrated successful 100 Gbit/s PAM-4 data transmission. The close agreement between the simulated and measured performance highlights the successful practical integration of these techniques for developing high-speed optical interconnects. Full article

(This article belongs to the Special Issue Optical Communication: Technologies and Applications)

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19 pages, 4085 KB

Open AccessArticle

A Bidirectionally Tunable Infrared Absorber via Phase-Transition-Modulated Fabry–Perot Resonance

by Yiqun Zhou, Qi Wang, Tianrong Ouyang, Chen Wang, Ruijin Hong and Dawei Zhang

Photonics 2026, 13(4), 352; https://doi.org/10.3390/photonics13040352 - 7 Apr 2026

Abstract

A bidirectional infrared absorber leveraging the Fabry–Perot resonance within a cascaded metal-dielectric nano-film structure is proposed. The absorber integrates a top Ag–VO₂–SiO₂ film stack, an intermediate thin Ag metal layer, and a bottom Al₂O₃–Ti–Al₂O [...] Read more.

A bidirectional infrared absorber leveraging the Fabry–Perot resonance within a cascaded metal-dielectric nano-film structure is proposed. The absorber integrates a top Ag–VO₂–SiO₂ film stack, an intermediate thin Ag metal layer, and a bottom Al₂O₃–Ti–Al₂O₃ layer, enabling switchable narrowband and broadband absorption under forward and backward illumination, respectively. Under front illumination, the structure exhibits a high narrowband absorption peak of 98% at a wavelength of 1110 nm when VO₂ is in its metallic state. In contrast, when VO₂ transitions to its insulating state, the absorption peak shifts to 1165 nm. Additionally, under back illumination, ultra-broadband absorption is achieved, covering a wavelength range of 1000–2760 nm with an average absorption of 98%. The proposed absorber demonstrates excellent absorption performance with structural simplicity and low manufacturing cost, offering great potential for applications in solar photovoltaic devices, photodetectors, and related fields. Full article

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10 pages, 1720 KB

Open AccessArticle

Generation of Soliton Molecules in an All-Normal Dispersion Yb-Doped Fiber Laser with a Lyot Filter

by Yanshu Wu, Guangyi Wu, Zichen Zhao, Jiaxin Xie, Abdul Qayyum Khan, Muhammad Shahid Rafiqued, Dongyun Yin and Shuai Yuan

Photonics 2026, 13(4), 351; https://doi.org/10.3390/photonics13040351 - 7 Apr 2026

Abstract

Soliton molecules offer practical advantages in high-speed optical communication, precision spectroscopy, and micromachining. In all-normal dispersion fiber lasers, group velocity dispersion broadens the pulse duration, hindering the attainment of the nonlinearity dispersion balance essential for soliton molecule formation. Consequently, the generation of soliton [...] Read more.

Soliton molecules offer practical advantages in high-speed optical communication, precision spectroscopy, and micromachining. In all-normal dispersion fiber lasers, group velocity dispersion broadens the pulse duration, hindering the attainment of the nonlinearity dispersion balance essential for soliton molecule formation. Consequently, the generation of soliton molecules in such lasers is a technically demanding task. Here, we report an all-normal dispersion fiber laser, mode-locked via nonlinear polarization evolution (NPE) and Lyot filtering. By adjusting the intracavity polarization, this setup allows direct control over pulse interactions, enabling the generation of stable soliton molecules, soliton bound states, and multipulse states. A spectral modulation period of up to 0.95 nm is achieved. In addition, different types of solitons, such as soliton singlets and soliton molecules in tightly and loosely bound states, are observed. Full article

(This article belongs to the Special Issue Advanced Photonic Technologies: From Light Sources and Nonlinear Optics to Sensing Applications)

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14 pages, 2611 KB

Open AccessArticle

Brillouin Zone Folding-Induced Magnetic Toroidal Dipole Metasurfaces for Tunable Mid-Infrared Upconversion

by Wanghao Zhu, Congfu Zhang, Wenjuan Shi, Di Ma and Hongjun Liu

Photonics 2026, 13(4), 350; https://doi.org/10.3390/photonics13040350 - 7 Apr 2026

Abstract

High quality factor (Q factor) resonant metasurfaces enable efficient mid-infrared (MIR) upconversion, yet their narrow operating bandwidths severely limit practical broadband detection and imaging applications. Although high Q magnetic toroidal dipole (MTD) modes exhibit outstanding momentum space (

k

-space) stability in linear [...] Read more.

High quality factor (Q factor) resonant metasurfaces enable efficient mid-infrared (MIR) upconversion, yet their narrow operating bandwidths severely limit practical broadband detection and imaging applications. Although high Q magnetic toroidal dipole (MTD) modes exhibit outstanding momentum space (

k

-space) stability in linear optics, their application in nonlinear processes has primarily been confined to degenerate second-harmonic generation (SHG), leaving complex non-degenerate processes such as sum-frequency generation (SFG) largely unexplored. Here, we propose a tunable MIR upconversion platform based on an all-dielectric gallium phosphide (GaP) dimer metasurface. Breaking the in-plane symmetry to trigger Brillouin zone folding excites robust MTD quasi-guided modes (MTD-QGM), tightly confining the locally enhanced optical fields within the highly nonlinear GaP nanostructure. Synchronizing this high Q resonance with a spatially overlapping pump mode yields an exceptional SFG conversion efficiency of

7.9 \times 10^{- 4}

, successfully translating a 3101.8 nm MIR signal to the 903 nm near-infrared band. Crucially, the intrinsic

k

-space stability of the MTD-QGM enables continuous, broadband upconversion through simple angle tuning. This mechanism effectively overcomes the narrow-band limitations characteristic of typical symmetry-protected resonators, establishing a robust paradigm for room-temperature MIR detection. Full article

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18 pages, 10375 KB

Open AccessArticle

Extended Coherent Modulation Imaging for Object Reconstruction with Single Diffraction Pattern

by Yue Wang, Yafang Zou, Ye Wu, Xinke Li, Xibao Gao, Long Jin, Weiyou Zeng, Qinglan Wang and Xi He

Photonics 2026, 13(4), 349; https://doi.org/10.3390/photonics13040349 - 7 Apr 2026

Abstract

Coherent diffraction imaging (CDI) is a fast-growing imaging technique. Among all CDI methods, coherent modulation imaging (CMI) has strong potential for dynamic imaging because of its ability to form an image from a single diffraction pattern. However, current CMI methods mostly reconstruct the [...] Read more.

Coherent diffraction imaging (CDI) is a fast-growing imaging technique. Among all CDI methods, coherent modulation imaging (CMI) has strong potential for dynamic imaging because of its ability to form an image from a single diffraction pattern. However, current CMI methods mostly reconstruct the exit wave distribution behind the object plane, which is seriously affected by the illumination artifact. Recently, some improved CMI methods have been developed to resolve the problem. However, many of these methods still need two diffraction patterns—one empty-sample diffraction pattern and another snapshot measurement. Recent advances in randomized probe imaging have shown that a single diffraction pattern suffices for quantitative reconstruction when the probe is pre-calibrated. Herein, we propose a modified CMI algorithm to reconstruct pure object function with single diffraction pattern, thereby simplifying the experimental process. Moreover, the proposed method can also work in the situation where the modulation effect is weak. Both numerical simulations and optical experiments have been conducted to verify the proposed method. Full article

(This article belongs to the Special Issue Steady-State and Ultrafast Time-Resolved Optical Spectroscopy and Laser Applications in Biology, Chemistry, Physics, Biomedical Optics and High-Resolution Imaging)

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12 pages, 2913 KB

Open AccessArticle

Molecular Histology for Azoospermia by Submicron-Resolution Mid-IR Photothermal Spectroscopy

by Zhengyan Wu, Zhicong Chen, Pengcheng Fu, Delong Zhang, Geng An and Hyeon Jeong Lee

Photonics 2026, 13(4), 348; https://doi.org/10.3390/photonics13040348 - 3 Apr 2026

Viewed by 223

Abstract

Non-obstructive azoospermia (NOA), a severe male infertility condition with impaired or absent sperm production, is treated by microsurgical testicular sperm extraction (micro-TESE), whose success depends on identifying seminiferous tubules with active spermatogenesis. To address this challenge, we demonstrate that mid-infrared photothermal (MIP) microscopy [...] Read more.

Non-obstructive azoospermia (NOA), a severe male infertility condition with impaired or absent sperm production, is treated by microsurgical testicular sperm extraction (micro-TESE), whose success depends on identifying seminiferous tubules with active spermatogenesis. To address this challenge, we demonstrate that mid-infrared photothermal (MIP) microscopy can provide label-free molecular signatures to distinguish different NOA subtypes in patient tissues. We applied MIP microscopy and MIP-guided IR spectroscopy to testicular tissues from obstructive azoospermia (normal spermatogenesis) and idiopathic NOA (abnormal spermatogenesis) patients. Tissue classification was performed using a Singular Value Decomposition–Random Forest (SVD-RF) pipeline. MIP imaging revealed distinct lipid distribution and reduced lipid content in NOA tissues compared to normal spermatogenic tissues. Using SVD to extract spectroscopic features and RF for classification, we achieved 94.03% accuracy in distinguishing testicular tissues as normal spermatogenesis or three pathological subtypes of idiopathic NOA. These findings demonstrate MIP microscopy as an effective tool for characterizing the spermatogenic potential of seminiferous tubules based on their molecular composition, potentially facilitating improved sperm retrieval strategies. Full article

(This article belongs to the Special Issue Artificial Intelligence for Label-Free Imaging and Spectroscopy in the Life Sciences)

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4 pages, 165 KB

Open AccessEditorial

Closing Editorial: Emerging Trends in Metamaterials and Metasurfaces Research

by David E. Fernandes and Tiago A. Morgado

Photonics 2026, 13(4), 347; https://doi.org/10.3390/photonics13040347 - 3 Apr 2026

Viewed by 206

Abstract

Over the past two decades, metamaterials and metasurfaces [...] Full article

(This article belongs to the Special Issue Emerging Trends in Metamaterials and Metasurfaces Research)

3 pages, 135 KB

Open AccessEditorial

Editorial for the Special Issue “Coherence Properties of Light: From Theory to Applications”

by Yongtao Zhang, Jiayi Yu and Yahong Chen

Photonics 2026, 13(4), 346; https://doi.org/10.3390/photonics13040346 - 2 Apr 2026

Viewed by 280

Abstract

Optical coherence, encompassing both spatial and temporal coherence, describes the correlations among the components of a fluctuating electric field at two or more points in space and time [...] Full article

(This article belongs to the Special Issue Coherence Properties of Light: From Theory to Applications)

17 pages, 4621 KB

Open AccessArticle

Perfectly Nonreciprocal Diffraction of 1D Atomic Lattices with Geometrical and Structural Disorders

by Yao-Long Xie, Tao Shui, Xuan-Xue Luo, Qiu-Ping Lu, Xu Deng and Wen-Xing Yang

Photonics 2026, 13(4), 345; https://doi.org/10.3390/photonics13040345 - 2 Apr 2026

Viewed by 182

Abstract

Geometrical and structural disorders are inevitable in fabricated photonic structures and can significantly impact their optical performance. Here, we investigate the robustness of perfectly nonreciprocal diffraction (PND) against these two types of disorder in one-dimensional (1D) atomic lattices. The significantly distinct diffraction phenomenon [...] Read more.

Geometrical and structural disorders are inevitable in fabricated photonic structures and can significantly impact their optical performance. Here, we investigate the robustness of perfectly nonreciprocal diffraction (PND) against these two types of disorder in one-dimensional (1D) atomic lattices. The significantly distinct diffraction phenomenon can be uncovered when the optical lattices introduce controlled random perturbations into the geometrical and structural parameters of each lattice site. Our results demonstrate that the forward diffraction spectrum exhibits remarkable resilience to both disorder types. Conversely, the backward diffraction spectrum is highly sensitive, displaying distinct responses to uncorrelated and correlated disorders. Specifically, PND persists only below a critical strength for uncorrelated geometrical disorder but is well preserved under correlated geometrical disorder. In stark contrast, PND shows strong robustness against uncorrelated structural disorder yet is significantly degraded by its correlated counterpart. These contrasting phenomena are attributed to whether the disorder introduces random spatial phase shifts that disrupt the destructive interference underlying PND. Our findings provide fundamental insights into wave transport in disordered potentials and offer a pathway for designing robust nonreciprocal devices resilient to fabrication imperfections. Full article

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

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18 pages, 3889 KB

Open AccessArticle

Proposal of Difference-Frequency Wave Generation Induced by Dual-Wavelength Free-Electron Laser Oscillations

by Norihiro Sei, Takeshi Sakai, Heishun Zen and Hideaki Ohgaki

Photonics 2026, 13(4), 344; https://doi.org/10.3390/photonics13040344 - 1 Apr 2026

Viewed by 320

Abstract

Optical klystrons have been developed in storage ring free-electron lasers (FELs) as insertion devices to increase the FEL gain in a straight section with limited length. By adjusting the magnetic field in the dispersion section of the optical klystron to shift the relative [...] Read more.

Optical klystrons have been developed in storage ring free-electron lasers (FELs) as insertion devices to increase the FEL gain in a straight section with limited length. By adjusting the magnetic field in the dispersion section of the optical klystron to shift the relative delay between the electron bunch and FEL pulse from an integer multiple of the FEL wavelength, FELs can oscillate at two wavelengths. The electron density of the electron bunch that interacts with the FEL pulse in a small-signal regime is modulated at the FEL wavelength period. When the FEL oscillates simultaneously at two wavelengths, the electron density of the electron bunch beats through the modulation with two periods. This beat generates long-wavelength coherent edge radiation at a bending magnet located in the straight section containing the optical klystron. Difference-frequency waves induced by dual-wavelength ultraviolet free-electron lasers generate a high-intensity mid-infrared monochromatic beam. Our findings will lay the foundation for the development of the difference-frequency waves of soft X-rays and extreme ultraviolet light using hard X-ray FELs. Full article

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

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11 pages, 5672 KB

Open AccessArticle

Metasurface-Assisted Rydberg-Atom Sensor with Wavefront Shaping and Enhanced Sensitivity

by Hao Zhang, Zhen Chen, Jun Huang, Jianjun Chen, Wenguang Yang, Mingyong Jing, Zongkai Liu, Junyao Xie, Liantuan Xiao, Suotang Jia and Linjie Zhang

Photonics 2026, 13(4), 343; https://doi.org/10.3390/photonics13040343 - 1 Apr 2026

Viewed by 355

Abstract

Rydberg-atom electric-field sensors have emerged as an important research direction in quantum precision measurement, owing to their intrinsic SI traceability, noninvasive measurement capability, and wide frequency tunability. However, under free-space conditions, the geometric divergence of microwaves (MWs) limits the practical detection performance of [...] Read more.

Rydberg-atom electric-field sensors have emerged as an important research direction in quantum precision measurement, owing to their intrinsic SI traceability, noninvasive measurement capability, and wide frequency tunability. However, under free-space conditions, the geometric divergence of microwaves (MWs) limits the practical detection performance of the system. In this work, we propose and experimentally demonstrate a metasurface-assisted Rydberg-atom hybrid sensor. Through introducing wavefront shaping of the incident microwave field with a metasurface (MS), electric-field enhancement in the atomic sensing region is achieved. Without altering the intrinsic sensitivity of the Rydberg-atom sensor, the equivalent sensitivity of the hybrid sensor is improved to

57.3 nV {cm}^{- 1} {Hz}^{- 1 / 2}

. This scheme provides a new route toward high-sensitivity, integrated quantum sensing of the microwave electric field. Full article

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

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16 pages, 5847 KB

Open AccessArticle

Reshaping Optical Speckles and Random Light Beam

by Yi Cui and Jun Xiong

Photonics 2026, 13(4), 342; https://doi.org/10.3390/photonics13040342 - 31 Mar 2026

Viewed by 248

Abstract

Speckle patterns generated by coherent illumination of random media are ubiquitous in optical imaging and information processing. However, most existing studies have primarily focused on isotropic or homogeneous speckle fields, while controlled manipulation of speckle patterns with customized geometric morphologies has received comparatively [...] Read more.

Speckle patterns generated by coherent illumination of random media are ubiquitous in optical imaging and information processing. However, most existing studies have primarily focused on isotropic or homogeneous speckle fields, while controlled manipulation of speckle patterns with customized geometric morphologies has received comparatively little attention. Here, we propose a random phase-coded array (RPA) as a general framework for generating geometrically reshaped speckle, enabling the formation of nonconventional random light fields whose ensemble-averaged intensity distributions follow prescribed geometric shapes. In this framework, the speckle geometry is determined by the unit-cell structure of the RPA, the unit-cell size governs the overall spatial extent of the speckle pattern, and the illuminating beam size sets the characteristic speckle grain size. These relationships are rigorously validated through theoretical derivations and numerical simulations. As a result, the global statistical envelope of the random light field can be intuitively and flexibly controlled without compromising the fully developed speckle characteristics. Our experimental framework offers a straightforward, scalable, and versatile approach for generating customized random light fields, with potential applications in optical information processing, secure optical communication, computational imaging, and speckle-based metrology. Full article

(This article belongs to the Special Issue Ghost Imaging and Quantum-Inspired Classical Optics)

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13 pages, 2830 KB

Open AccessArticle

Additive Manufacturing Based Polymer Compounded Refractive Lenses for X-Ray Focusing at Synchrotron Light Sources

by Boyong Wang, Rongcheng Yang, Pingping Wen, Zhihao Guan, Yajun Tong, Zhi Qiao and Huaidong Jiang

Photonics 2026, 13(4), 341; https://doi.org/10.3390/photonics13040341 - 31 Mar 2026

Viewed by 262

Abstract

Additive manufacturing offers a promising route to low-cost, rapidly deployable X-ray focusing optics with geometries that are difficult to realize by conventional machining. Here, we report polymer compound refractive lenses (CRLs) for hard X-ray focusing fabricated by projection micro-stereolithography (PµSL, DLP-based) and by [...] Read more.

Additive manufacturing offers a promising route to low-cost, rapidly deployable X-ray focusing optics with geometries that are difficult to realize by conventional machining. Here, we report polymer compound refractive lenses (CRLs) for hard X-ray focusing fabricated by projection micro-stereolithography (PµSL, DLP-based) and by two-photon polymerization (2PP). Two-dimensional bi-parabolic CRL elements were produced in multiple photopolymer resins (HTL, Tough, ST1400 for PμSL; IP-S for 2PP) and evaluated by at-wavelength metrology at the Shanghai Synchrotron Radiation Facility. The single-lens residual phase errors (RMS) less than 0.1

λ

were measured for PµSL-fabricated HTL, and Toughlenses, respectively, while 2PP-fabricated IP-S lenses achieved 0.008

λ

. And the analysis indicates that PµSL lenses are primarily limited by systematic mid-order aberrations, whereas 2PP substantially suppresses coma but shows residual spherical aberration attributable to process calibration and shrinkage. Leveraging the higher fidelity of 2PP, a 65-element parabolic CRL array (radius of curvature of 100 µm) was fabricated and demonstrated hard X-ray focusing at 15 keV with focal spot sizes of 6.4 ± 1 µm (H) and 6.8 ± 1 µm (V), and a flux gain of 220. The measured performance agrees with theoretical expectations when accounting for X-ray source properties, detector resolution and chromatic aberration. These results establish a practical pathway for additively manufactured polymer CRLs with DLP and 2PP techniques as compact, customization focusing optics for synchrotron beamlines. Full article

(This article belongs to the Special Issue Next-Generation X-Ray Optical Technologies and Applications)

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16 pages, 14432 KB

Open AccessArticle

Polarization Tailored Photonic Jets via Janus Microcylinders

by Qingyu Wang, Zhenya Wang and Gangyin Luo

Photonics 2026, 13(4), 340; https://doi.org/10.3390/photonics13040340 - 31 Mar 2026

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Abstract

Photonic jets (PJs) generated from mesoscale dielectric particles can achieve sub-diffraction-scale light field constraints and significant near-field intensity enhancement, which have important application value in the fields of nanoimaging, optical sensing, and laser processing. Recent studies show that the axial-extension and transverse-focus characteristics [...] Read more.

Photonic jets (PJs) generated from mesoscale dielectric particles can achieve sub-diffraction-scale light field constraints and significant near-field intensity enhancement, which have important application value in the fields of nanoimaging, optical sensing, and laser processing. Recent studies show that the axial-extension and transverse-focus characteristics of PJs can be effectively regulated through interface engineering methods, such as using double-layer structures and truncated geometries. Such structures can be referred to as Janus microstructures separated by surface refracted interfaces. However, systematic research on the effect of incident light polarization on the formation and regulation of PJs on the surface interfaces of Janus systems is lacking. In this study, the PJ characteristics under polarization regulation in curved-interface Janus microcylinders are systematically investigated by performing full-wave numerical simulations. The results show that polarization modulation introduces a new degree of freedom for regulating the energy flow distribution and morphology of PJs. An appropriate polarization state can be selected to effectively regulate key characteristic parameters, such as the length, peak intensity, and full width at half maximum of the nanojet, without changing the particle geometry or material composition. This study reveals the synergy between the surface-interface Janus structures and polarization engineering, providing a new physical method for the flexible regulation of PJs in near-field optics. Full article

(This article belongs to the Special Issue Nanophotonics and Metasurfaces for Optical Manipulation)

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13 pages, 2381 KB

Open AccessArticle

Low-Frequency Time-Domain Response of Thin-Film Lithium Niobate Electro-Optic Modulator

by Run Li, Jinye Li, Zongyu Lu, Jiayu Huang, Qianqian Jia, Zichuan Xiang, Jinlong Xiao and Jianguo Liu

Photonics 2026, 13(4), 339; https://doi.org/10.3390/photonics13040339 - 31 Mar 2026

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Abstract

Thin-film lithium niobate electro-optic modulators exhibit outstanding advantages such as large bandwidth, low insertion loss, and low half-wave voltage, demonstrating broad application prospects. However, due to internal defects in lithium niobate crystals, modulators exhibit electro-optic relaxation phenomena, with the relaxation time of thin-film [...] Read more.

Thin-film lithium niobate electro-optic modulators exhibit outstanding advantages such as large bandwidth, low insertion loss, and low half-wave voltage, demonstrating broad application prospects. However, due to internal defects in lithium niobate crystals, modulators exhibit electro-optic relaxation phenomena, with the relaxation time of thin-film structures being reduced by more than two orders of magnitude compared to bulk materials. In this study, we fitted and simulated the electro-optic relaxation behavior of thin-film lithium niobate modulators based on RC circuit model, effectively explaining their time-domain response characteristics under low-frequency conditions. By comparing thin-film modulators with and without silica cladding structures, the fitting results indicate that the relaxation time of modulators with cladding is approximately 11.9 ms, showing positive DC drift, whereas the relaxation time of modulators without cladding is significantly shortened to about 88.6 μs and exhibits negative DC drift. Additionally, the enhancement of optical intensity alters the photoconductivity of the material, thereby affecting its low-frequency electro-optic response behavior. This research provides important ideas for the design and optimization of next-generation integrated lithium niobate photonic modulators with high stability and controllability. Full article

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16 pages, 2143 KB

Open AccessArticle

Numerical Simulation of a Compact Dual-Window In-Fiber Polarization Filter Using Gold-Deposited Square-Lattice Photonic Crystal Fiber

by Shuangjie Bai, Nan Chen, Jianing Zhang, Xiaoming Hu, Zhiwen Shan, Chenxun Liu, Fan Yang and Cheng Lu

Photonics 2026, 13(4), 338; https://doi.org/10.3390/photonics13040338 - 31 Mar 2026

Viewed by 276

Abstract

This work presents a compact broadband in-fiber polarization filter using gold-deposited square-lattice photonic crystal fiber (PCF) numerically. The finite element method (FEM) is utilized to analyze the transmission characteristics of this PCF. The simulation results indicate that when the cladding hole diameter is [...] Read more.

This work presents a compact broadband in-fiber polarization filter using gold-deposited square-lattice photonic crystal fiber (PCF) numerically. The finite element method (FEM) is utilized to analyze the transmission characteristics of this PCF. The simulation results indicate that when the cladding hole diameter is 1.5 μm, the large hole diameter is 2.1 μm, the long axis of elliptical holes is 1.96 μm, the short axis of elliptical holes is 0.98 μm, the pitch is 2 μm, and the gold layer thickness is 50 nm, the x-polarized mode can interact with two plasmonic modes, and two surface plasmon resonance (SPR) processes at two common communication windows can be achieved. The length of this PCF filter is set as 0.5 mm, exhibiting the maximum extinction ratio (ER) of −51.4 dB at 1.31 μm and −47.3 dB at 1.55 μm, and the operating bandwidth of >860 nm. Additionally, the estimated splice losses are ~2.22 dB at 1.31 μm and ~1.42 dB at 1.55 μm. It is expected that this small-size PCF-SPR filter, characterized by its efficient filtering performance and wide bandwidth, will serve as a promising candidate for building integrated networks that combine optical fiber communication, sensing, and computing capabilities. Full article

(This article belongs to the Special Issue Plasmonics for Advanced Photonic Applications)

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18 pages, 9267 KB

Open AccessArticle

Differentiable Automated Design of Automotive Freeform AR-HUD Optical Systems

by Chengxiang Fan, Jihong Zheng, Xinjun Wan, Xiaoxiao Wei and Yunfeng Nie

Photonics 2026, 13(4), 337; https://doi.org/10.3390/photonics13040337 - 30 Mar 2026

Viewed by 330

Abstract

The automotive augmented reality head-up display (AR-HUD) system projects critical driving information directly into the driver’s line of sight, enhancing driving safety, user experience, and navigation efficiency. However, due to the intrinsic asymmetry of vehicle windshields, existing optical configurations are difficult to use [...] Read more.

The automotive augmented reality head-up display (AR-HUD) system projects critical driving information directly into the driver’s line of sight, enhancing driving safety, user experience, and navigation efficiency. However, due to the intrinsic asymmetry of vehicle windshields, existing optical configurations are difficult to use as effective design starting points. The asymmetric transmission region of the windshield causes the AR-HUD optical system to deviate significantly from the YOZ plane, increasing the complexity of system design and optimization. To address these challenges, this paper proposes an automated design method for automotive AR-HUD optical systems. Given the windshield geometry and system design specifications, a normal-guided iterative construction method is first employed to generate a high-performance initial optical structure with low distortion. Subsequently, differentiable ray tracing combined with optimization algorithms is employed to further improve system performance. Based on the proposed method, an AR-HUD optical system with a 130 mm × 50 mm eye-box and a 13° × 4° field of view was designed. The design results indicate that the maximum optical distortion is 0.51%. At five sampled eye positions within the eye-box, the MTF exceeds 0.5 at the spatial frequency of 6 lp/mm, and the dynamic distortion remains below 5.36′. Finally, a complete experimental prototype was established, and the experimental results verified the feasibility and effectiveness of the proposed automated design method. Full article

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

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13 pages, 871 KB

Open AccessArticle

Trough-Shift Pointer for Weak Measurement with Large Range and High Spectral Resolution

by Wenzhao Huang, Zifu Su, Weiqian Zhao, Yafei Yu, Jindong Wang and Zhengjun Wei

Photonics 2026, 13(4), 336; https://doi.org/10.3390/photonics13040336 - 30 Mar 2026

Viewed by 294

Abstract

Weak measurement enables the amplification of weak physical effects via post-selection and has become an important tool in precision optical metrology; however, conventional schemes based on mean-pointer shifts suffer from response saturation, limited linear range, and stringent stability requirements. Here, we propose and [...] Read more.

Weak measurement enables the amplification of weak physical effects via post-selection and has become an important tool in precision optical metrology; however, conventional schemes based on mean-pointer shifts suffer from response saturation, limited linear range, and stringent stability requirements. Here, we propose and experimentally demonstrate a weak-measurement scheme based on spectral-interference trough shifts, where the zero-intensity points of the post-selected spectrum act as the measurement pointer, establishing an analytical mapping between the trough displacement and the target phase or time delay. Theoretical analysis shows that, under detector resolution limits, the measurement resolution depends solely on the frequency of extinction point and is independent of weak-value singular amplification or bias-phase modulation, thereby maintaining high sensitivity while avoiding pointer saturation. Experiments demonstrate that the trough-shift scheme achieves significantly better agreement between measured and theoretical sensitivities than biased weak measurement and provides a stable linear response without additional bias-compensation structures, reaching a minimum resolvable phase variation at the

10^{- 7}

level. Moreover, the approach intrinsically supports multi-period traceable measurements and exhibits strong robustness against intensity fluctuations and spectral distortions, offering a promising route toward high-sensitivity, large-dynamic-range, and stable weak measurement-based optical sensing. Full article

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

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5 pages, 147 KB

Open AccessEditorial

Editorial for the Special Issue “Liquid Crystals in Photonics” in Photonics

by Yannanqi Li

Photonics 2026, 13(4), 335; https://doi.org/10.3390/photonics13040335 - 30 Mar 2026

Viewed by 326

Abstract

Liquid crystals (LCs) occupy a distinctive position among functional optical materials, combining the fluidity of liquids with the long-range molecular order characteristic of crystalline solids [...] Full article

(This article belongs to the Special Issue Liquid Crystals in Photonics)

24 pages, 1545 KB

Open AccessArticle

PMSDA: Progressive Multi-Strategy Domain Alignment for Cross-Scene Vibration Recognition in Distributed Optical Fiber Sensing

by Yuxiang Ni, Jing Cheng, Di Wu, Qianqian Duan, Linhua Jiang, Xing Hu and Dawei Zhang

Photonics 2026, 13(4), 334; https://doi.org/10.3390/photonics13040334 - 29 Mar 2026

Viewed by 393

Abstract

Distributed optical fiber vibration sensing (DVS) has shown strong potential in perimeter security, pipeline leakage monitoring, transportation safety, and structural health diagnostics owing to its high sensitivity, long-range coverage, and immunity to electromagnetic interference. However, severe cross-scene distribution mismatch is often encountered in [...] Read more.

Distributed optical fiber vibration sensing (DVS) has shown strong potential in perimeter security, pipeline leakage monitoring, transportation safety, and structural health diagnostics owing to its high sensitivity, long-range coverage, and immunity to electromagnetic interference. However, severe cross-scene distribution mismatch is often encountered in real-world deployments: indoor, outdoor, and pipeline environments exhibit markedly different noise patterns and time–frequency characteristics, thereby degrading the generalization ability of models trained in a single scene. To address this challenge, we propose a Progressive Multi-Strategy Domain Alignment (PMSDA) framework for label-disjoint cross-scene vibration recognition. PMSDA uses a compact expansion–compression encoder together with complementary alignment mechanisms—maximum mean discrepancy (MMD), correlation alignment (CORAL), and adversarial domain discrimination—to learn a scene-robust latent space from a labeled indoor source and two unlabeled target domains (outdoor and pipeline) within a single alternating-training model. Because the fine-grained source and target label spaces are disjoint, PMSDA is formulated as a representation-transfer framework rather than a standard label-shared unsupervised domain adaptation method; target-domain recognition is therefore performed through domain-specific prototype clustering in the aligned latent space. On three representative scenes with nine event classes in total, PMSDA achieved 89.5% accuracy, 86.7% macro-F1, and 0.93 AUC for Indoor→Outdoor, and 85.8%, 84.7%, and 0.87, respectively, for Indoor→Pipeline, outperforming traditional feature+SVM/RF pipelines, CNN/ResNet baselines, and representation-transfer baselines adapted from DANN/CDAN/SHOT under the same evaluation protocol. These results indicate that PMSDA is a promising and effective framework for offline cross-scene DVS evaluation under disjoint target event sets. Full article

(This article belongs to the Special Issue Machine Learning and Artificial Intelligence for Optical Networks)

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15 pages, 2187 KB

Open AccessArticle

Tunable Hybrid Antiresonance and Mach–Zehnder Interferometer Based on Silica Capillary for Dual-Parameter Sensing

by Mariline M. Costa, Ana I. Freitas, Jörg Bierlich and Marta S. Ferreira

Photonics 2026, 13(4), 333; https://doi.org/10.3390/photonics13040333 - 29 Mar 2026

Viewed by 291

Abstract

An all-silica-based sensor comprising a section of capillary fiber spliced between two singlemode fibers (SMFs) is proposed for the simultaneous measurement of strain and temperature. By intentionally introducing a controlled transversal offset at one of the fusion splice points, core and cladding modes [...] Read more.

An all-silica-based sensor comprising a section of capillary fiber spliced between two singlemode fibers (SMFs) is proposed for the simultaneous measurement of strain and temperature. By intentionally introducing a controlled transversal offset at one of the fusion splice points, core and cladding modes are simultaneously excited in the capillary, enabling the coexistence of two distinct guiding mechanisms within the sensor. The resulting spectral response exhibits two superimposed modulations associated with antiresonance (AR) guidance and a Mach–Zehnder interferometer (MZI). A comprehensive numerical model is developed to describe the interaction between the two mechanisms as a function of the offset. The model is experimentally validated through characterization of the spectral response for increasing offsets, confirming the coexistence and evolution of the AR and MZI components through free spectral range and visibility analysis. The two interference components allow for independent tracking of their wavelength shifts, enabling simultaneous strain and temperature measurements with estimated resolutions of 11.9 με and 0.45 °C, respectively. Owing to the single-element, one-step fabrication process, and the entirely silica-based configuration, the proposed sensor offers a compact and cost-effective solution for localized multiparameter monitoring. Full article

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

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27 pages, 7505 KB

Open AccessArticle

Zoom Long-Wave Infrared Constant Ground Resolution Imaging Optical System Design

by Zhiqiang Yang, Wenna Zhang, Bohan Wu, Liguo Wang, Yao Li, Lihong Yang and Lei Gong

Photonics 2026, 13(4), 332; https://doi.org/10.3390/photonics13040332 - 29 Mar 2026

Viewed by 231

Abstract

Long-wave infrared (LWIR) airborne optical systems for ground imaging are widely utilized in applications such as ground reconnaissance, agricultural monitoring, counterterrorism, and other fields. Traditional oblique-view ground-imaging optical systems suffer from a critical drawback compared to nadir-view systems: the significant variation in object [...] Read more.

Long-wave infrared (LWIR) airborne optical systems for ground imaging are widely utilized in applications such as ground reconnaissance, agricultural monitoring, counterterrorism, and other fields. Traditional oblique-view ground-imaging optical systems suffer from a critical drawback compared to nadir-view systems: the significant variation in object distances between distant and nearby targets. This disparity leads to inconsistent ground resolution (GR), manifesting in images where distant targets exhibit significantly lower resolution than nearby ones. This characteristic is highly detrimental to information acquisition and three-dimensional modeling of the system. Furthermore, the limited field of view of fixed focal length systems prevents the unmanned aerial vehicle (UAV) from acquiring target information effectively across varying flight altitudes. To address this issue, this paper designs an oblique imaging optical system capable of achieving both constant GR and zoom functionality in the LWIR band. By controlling the ground resolution, a LWIR continuous zoom optical system was designed. The system maintains constant GR over the entire field of view. Its modulation transfer function (MTF) approaches the diffraction limit across the full field of view, and the spot diagram remains within Airy’s disk at each view angle. The radius of the spot diagram is smaller than that of the Airy disk, indicating that the geometric aberrations of the system are well corrected. The imaging performance is primarily determined by the wavelength and the F-number. In the case of LWIR, the longer wavelength results in a larger Airy disk radius. The system meets imaging quality requirements and is suitable for air-to-ground target reconnaissance imaging. Full article

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Photonics, Volume 13, Issue 4 (April 2026) – 52 articles

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