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Recent Advances in C-Band High-Power and High-Speed Radio Frequency Photodiodes: Review, Theory and Applications
Singular Value Decomposition-Assisted Holographic Generation of High-Quality Cylindrical Vector Beams Through Few-Mode Fibers

Journal Description

Photonics

Photonics is an international, scientific, peer-reviewed, open access journal on the science and technology of optics and photonics, published monthly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, Ei Compendex, CAPlus / SciFinder, and other databases.
Journal Rank: CiteScore - Q2 (Instrumentation)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 14.8 days after submission; acceptance to publication is undertaken in 1.9 days (median values for papers published in this journal in the first half of 2025).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Companion journal: Lights.

Impact Factor: 1.9 (2024); 5-Year Impact Factor: 2.0 (2024)

Imprint Information Journal Flyer Open Access ISSN: 2304-6732

Latest Articles

14 pages, 3001 KB

Open AccessArticle

Investigation of Debris Mitigation in Droplet-Based Terbium Plasma Sources Produced by Laser Ablation Under Varying Buffer Gas Pressures

by Shuaichao Zhou, Tao Wu, Ziyue Wu, Junjie Tian and Peixiang Lu

Photonics 2025, 12(10), 1035; https://doi.org/10.3390/photonics12101035 (registering DOI) - 19 Oct 2025

The fragment suppression ability of terbium plasma generated by laser at different environmental pressures is investigated, with a focus on exploring the slowing effect of buffer gas on high-energy particles. Using two-dimensional radiation hydrodynamic simulations with the FLASH code, this study evaluates the [...] Read more.

The fragment suppression ability of terbium plasma generated by laser at different environmental pressures is investigated, with a focus on exploring the slowing effect of buffer gas on high-energy particles. Using two-dimensional radiation hydrodynamic simulations with the FLASH code, this study evaluates the debris mitigation efficiency of terbium plasma across a range of buffer gas pressures (50–1000 Pa). Key findings reveal that helium buffer gas exhibits a nonlinear pressure-dependent response in plasma dynamics and debris suppression. Specifically, at 1000 Pa helium, the plasma shockwave stops within stopping distance

x_{s t}

= 12.13 mm with an attenuation coefficient of b = 0.0013 ns⁻¹, reducing radial expansion by 40% compared to 50 Pa (

x_{s t}

= 23.15 mm, b = 0.0010). This pressure scaling arises from enhanced collisional dissipation, confining over 80% of debris kinetic energy below 200 eV under 1000 Pa conditions. In contrast, argon exhibits superior stopping power within ion energy domains (≤1300 eV), attaining a maximum stopping power of 2000 eV·mm⁻¹ at 1300 eV–a value associated with a 6.4-times-larger scattering cross-section compared to helium under equivalent conditions. The study uncovers a nonlinear relationship between kinetic energy and gas pressure, where the deceleration capability of buffer gases intensifies with increasing kinetic energy. This work demonstrates that by leveraging argon’s broadband stopping efficiency and helium’s confinement capacity, debris and high energy ions can be effectively suppressed, thereby securing mirror integrity and source efficiency at high repetition rates. Full article

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

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18 pages, 5635 KB

Open AccessArticle

Multi-Soliton Propagation and Interaction in Λ-Type EIT Media: An Integrable Approach

by Ramesh Kumar Vaduganathan, Prasanta K. Panigrahi and Boris A. Malomed

Photonics 2025, 12(10), 1034; https://doi.org/10.3390/photonics12101034 (registering DOI) - 19 Oct 2025

Electromagnetically induced transparency (EIT) is well known as a quantum optical phenomenon that permits a normally opaque medium to become transparent due to the quantum interference between transition pathways. This work addresses multi-soliton dynamics in an EIT system modeled by the integrable Maxwell–Bloch [...] Read more.

Electromagnetically induced transparency (EIT) is well known as a quantum optical phenomenon that permits a normally opaque medium to become transparent due to the quantum interference between transition pathways. This work addresses multi-soliton dynamics in an EIT system modeled by the integrable Maxwell–Bloch (MB) equations for a three-level

Λ

-type atomic configuration. By employing a generalized gauge transformation, we systematically construct explicit N-soliton solutions from the corresponding Lax pair. Explicit forms of one-, two-, three-, and four-soliton solutions are derived and analyzed. The resulting pulse structures reveal various nonlinear phenomena, such as temporal asymmetry, energy trapping, and soliton interactions. They also highlight coherent propagation, elastic collisions, and partial storage of pulses, which have potential implications for the design of quantum memory, slow light, and photonic data transport in EIT media. In addition, the conservation of fundamental physical quantities, such as the excitation norm and Hamiltonian, is used to provide direct evidence of the integrability and stability of the constructed soliton solutions. Full article

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

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9 pages, 2395 KB

Open AccessArticle

A Wide Field of View and Broadband Infrared Imaging System Integrating a Dispersion-Engineered Metasurface

by Bo Liu, Yunqiang Zhang, Zhu Li, Xuetao Gan and Xin Xie

Photonics 2025, 12(10), 1033; https://doi.org/10.3390/photonics12101033 (registering DOI) - 19 Oct 2025

We present a compact hybrid imaging system operating in the 3–5 μm spectral band that combines refractive optics with a dispersion-engineered metasurface to overcome the longstanding trade-off between wide field of view (FOV), system size, and thermal stability. The system achieves an ultra-wide [...] Read more.

We present a compact hybrid imaging system operating in the 3–5 μm spectral band that combines refractive optics with a dispersion-engineered metasurface to overcome the longstanding trade-off between wide field of view (FOV), system size, and thermal stability. The system achieves an ultra-wide 178° FOV within a total track length of only 28.25 mm, employing just three refractive lenses and one metasurface. Through co-optimization of material selection and system architecture, it maintains the modulation transfer function (MTF) exceeding 0.54 at 33 lp/mm and the geometric (GEO) radius below 15 μm across an extended operational temperature range from –40 °C to 60 °C. The metasurface is designed using a propagation phase approach with cylindrical unit cells to ensure polarization-insensitive behavior, and its broadband dispersion-free phase profile is optimized via a particle swarm algorithm. The results indicate that phase-matching errors remain small at all wavelengths, with a mean value of 0.11068. This design provides an environmentally resilient solution for lightweight applications, including automotive infrared night vision and unmanned aerial vehicle remote sensing. Full article

(This article belongs to the Special Issue Optical Metasurfaces: Applications and Trends)

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14 pages, 1222 KB

Open AccessArticle

Beyond Fresnel Wave Surfaces: Theory of Off-Shell Photonic Density of States and Near-Fields in Isotropy-Broken Materials with Loss or Gain

by Maxim Durach and David Keene

Photonics 2025, 12(10), 1032; https://doi.org/10.3390/photonics12101032 - 17 Oct 2025

Fresnel wave surfaces, or isofrequency light shells, provide a powerful framework for describing electromagnetic wave propagation in anisotropic media, yet their applicability is restricted to reciprocal, lossless materials and far-field radiation. This paper extends the concept by incorporating near-field effects and non-Hermitian responses [...] Read more.

Fresnel wave surfaces, or isofrequency light shells, provide a powerful framework for describing electromagnetic wave propagation in anisotropic media, yet their applicability is restricted to reciprocal, lossless materials and far-field radiation. This paper extends the concept by incorporating near-field effects and non-Hermitian responses arising in media with loss, gain, or non-reciprocity. Using the Om-potential approach to macroscopic electromagnetism, we reinterpret near fields as off-shell electromagnetic modes, in analogy with off-shell states in quantum field theory. Formally, both QFT off-shell states and electromagnetic near-field modes lie away from the dispersion shell; physically, however, wavefunctions of fundamental particles admit no external sources (virtual contributions live only inside propagators), whereas macroscopic electromagnetic near-fields are intrinsically source-generated by charges, currents, and boundaries and are therefore directly measurable—for example via near-field probes and momentum-resolved imaging—making “off-shell” language more natural and operational in our setting. We show that photonic density of states (PDOS) distributions near Fresnel surfaces acquire Lorentzian broadening in non-reciprocal media, directly linking this effect to the Beer–Bouguer–Lambert law of exponential attenuation or amplification. Furthermore, we demonstrate how Abraham and Minkowski momenta, locked to light shells in the far field, naturally shift to characterize source structures in the near-field regime. This unified treatment bridges the gap between sources and radiation, on-shell and off-shell modes, and reciprocal and non-reciprocal responses. The framework provides both fundamental insight into structured light and practical tools for the design of emitters and metamaterial platforms relevant to emerging technologies such as 6G communications, photonic density-of-states engineering, and non-Hermitian photonics. Full article

12 pages, 2251 KB

Open AccessArticle

Ultra-High Spectral Contrast Nanobeam Photonic Crystal Cavity on Bending Waveguide

by Ping Yu, Peihong Cheng, Zhuoyuan Wang, Jingrui Wang, Fangfang Ge, Huiye Qiu and Daniel Kacik

Photonics 2025, 12(10), 1031; https://doi.org/10.3390/photonics12101031 - 17 Oct 2025

In this article, one-dimensional photonic crystal cavities on bending waveguides (PCCoBW) used for achieving high-contrast spectra are proposed, analyzed, and experimentally verified on silicon on insulator (SOI). Both air and dielectric modes of the PCCoBW calculated by the finite-difference time-domain (FDTD) method show [...] Read more.

In this article, one-dimensional photonic crystal cavities on bending waveguides (PCCoBW) used for achieving high-contrast spectra are proposed, analyzed, and experimentally verified on silicon on insulator (SOI). Both air and dielectric modes of the PCCoBW calculated by the finite-difference time-domain (FDTD) method show finger-ring-like mode profiles with the achievement of high-quality factors (Q∼10

^{6}

), even when the bending radius is less than 50 times the lattice constant. Straight waveguides side-coupled to the cavity are used to access and measure mode resonances. The measured spectra show a high extinction ratio over 40 dB for dielectric modes and 20 dB for air modes, respectively. Both dielectric and air resonant modes are revealed with Q-factors over 3.3 × 10

^{4}

and 7.9 × 10

^{4}

, respectively, for the coupled PCCoBWs. The proposed PCCoBW could be implemented as high-contrast notch filtering and would benefit a broad range of applications such as optical filters, modulators, sensors, or switches. Full article

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

61 pages, 2114 KB

Open AccessReview

Roadmap for Exoplanet High-Contrast Imaging: Nulling Interferometry, Coronagraph, and Extreme Adaptive Optics

by Ziming Guo, Qichang An, Canyu Yang, Jincai Hu, Xin Li and Liang Wang

Photonics 2025, 12(10), 1030; https://doi.org/10.3390/photonics12101030 - 17 Oct 2025

The detection and characterization of exoplanets are central topics in astronomy, and high-contrast imaging techniques such nulling interferometry, coronagraphs, and extreme adaptive optics (ExAO) are key tools for the direct detection of exoplanets. This review synthesizes the pivotal role of these techniques in [...] Read more.

The detection and characterization of exoplanets are central topics in astronomy, and high-contrast imaging techniques such nulling interferometry, coronagraphs, and extreme adaptive optics (ExAO) are key tools for the direct detection of exoplanets. This review synthesizes the pivotal role of these techniques in astronomical research and critically analyzes their role as key drivers of progress in the field. Nulling interferometry suppresses stellar light through the phase control of multiple telescopes, thereby enhancing the detection of faint planetary signals. This technology has evolved from the initial Bracewell concept to the LIFE (Large Interferometer For Exoplanets) technique, which will achieve a contrast ratio of 10⁻⁷ in the mid-infrared wavelength range in the future. Coronagraphs block starlight to create a “dark region” for direct observation of exoplanets. By leveraging innovative mask designs, theoretical contrast ratios of up to 4 × 10⁻⁹ can be achieved. ExAO systems achieve precise wavefront correction to optimize the high-contrast imaging performance and mitigate atmospheric disturbances. By leveraging wavefront sensing, thousand-element deformable mirrors, and real-time control algorithms, these systems suppress the turbulence correction residuals to 80 nm RMS, enabling ground-based telescopes to achieve a Strehl ratio exceeding 0.9. This work provides a comprehensive analysis of the underlying principles, prevailing challenges, and future application prospects of these technologies in astronomy. Full article

19 pages, 13717 KB

Open AccessArticle

Vector Vortex Beams: Theory, Generation, and Detection of Laguerre–Gaussian and Bessel–Gaussian Types

by Xin Yan, Xin Tao, Minghao Guo, Chunliang Zhou, Jingzhao Chen, Guanyu Shang and Peng Li

Photonics 2025, 12(10), 1029; https://doi.org/10.3390/photonics12101029 - 17 Oct 2025

A vector vortex beam (VVB) combines the phase singularity of a vortex beam (VB) with the anisotropic polarization of a vector beam, enabling the transmission of complex optical information and offering broad application prospects in optical sensing, high-capacity communication, and high-resolution imaging. In [...] Read more.

A vector vortex beam (VVB) combines the phase singularity of a vortex beam (VB) with the anisotropic polarization of a vector beam, enabling the transmission of complex optical information and offering broad application prospects in optical sensing, high-capacity communication, and high-resolution imaging. In this work, we present a detailed theoretical analysis of the generation and detection of VVBs with Laguerre–Gaussian (LG) and Bessel–Gaussian (BG) forms. Particular emphasis is placed on the polarization characteristics of VVBs, the evolution of beam profiles after passing through polarizers with different orientations, and the interference features arising from the coaxial superposition of a VVB with a circularly polarized divergent spherical wave. To validate the theoretical analysis, LGVVBs were experimentally generated using a Mach–Zehnder interferometer by superposing two vortex beams with opposite topological charges and orthogonal circular polarizations. Furthermore, the introduction of an axicon enabled the direct conversion of LGVVBs into BGVVBs. The excellent agreement between theoretical predictions and experimental observations lays a solid foundation for beginners to systematically understand VVB characteristics and advance future research. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Vortex Beams)

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12 pages, 5562 KB

Open AccessArticle

Random Search Algorithm-Assisted Automatic Mode-Locked Fiber Lasers

by Penghui Yang, Yanrong Song, Lin Mao and Ruyue You

Photonics 2025, 12(10), 1028; https://doi.org/10.3390/photonics12101028 - 16 Oct 2025

Automatic mode-locking is a crucial approach for achieving ultrashort pulses in fiber lasers. Here, a random search algorithm was developed, and an automatic mode-locked laser was constructed. Numerical simulations of an automatic mode-locked Yb-doped fiber laser were conducted, and both continuous-wave, as well [...] Read more.

Automatic mode-locking is a crucial approach for achieving ultrashort pulses in fiber lasers. Here, a random search algorithm was developed, and an automatic mode-locked laser was constructed. Numerical simulations of an automatic mode-locked Yb-doped fiber laser were conducted, and both continuous-wave, as well as mode-locked pulse states, were successfully obtained. The laser utilized a squeezer-type electrically controlled polarization controller to adjust the mode-locking states and enabled the controllable output of 532.71 fs dissipative solitons and 23.87 ps noise-like pulses, with search times of 14.19 s and 2.37 s, respectively. The center wavelengths were 1034 nm and 1038 nm, with signal-to-noise ratios of 63.1 dBm and 51.2 dBm, respectively. This work effectively addresses the polarization state drift caused by temperature and vibration, enhancing the laser’s environmental adaptability through adaptive monitoring. Full article

(This article belongs to the Special Issue Advanced Fiber Laser Technology and Its Application: 2nd Edition)

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9 pages, 2410 KB

Open AccessArticle

High Quality Factor Unidirectional Guided Resonances in Etchless Lithium Niobate Metagratings for Polarization Modulation

by Zhidong Gu, Jiaxin Peng, Zhiyong Wu, Lei Wang, Jiajun Zhu, Ye Feng, Xinyi Sun, Zhenjuan Zhang and Guoan Zhang

Photonics 2025, 12(10), 1027; https://doi.org/10.3390/photonics12101027 - 16 Oct 2025

Unidirectional guided resonances (UGRs), as distinctive resonant eigenstates in planar photonic lattices, exhibit unique capability of emitting light in a single direction. In this work, UGRs with high-Q factor and infinite proximity to the

Γ

-point infinitely using etchless lithium niobate (LN) metagratings [...] Read more.

Unidirectional guided resonances (UGRs), as distinctive resonant eigenstates in planar photonic lattices, exhibit unique capability of emitting light in a single direction. In this work, UGRs with high-Q factor and infinite proximity to the

Γ

-point infinitely using etchless lithium niobate (LN) metagratings are proposed and investigated numerically. By adjusting the parameters of metagraings, the Q-factor and asymmetric radiation ratio of UGRs can be flexibly tuned, and the wavelength center of UGRs respect will move with respect to the wave vector along the

Γ

-X direction. Accompanied by the optimizing of asymmetric radiation ratio, the evolution of two dispersion curves from avoided crossing to crossing can be observed. Furthermore, leveraging the polarization sensitivity of UGRs, we achieve a broadband linear-to-circular polarization conversion with a high polarization extinction ratio. This work advances the fundamental understanding of UGRs while potentially offering promising applications in metagratings-based surface-emitting lasers, beam steering, and refractive index sensors. Full article

(This article belongs to the Special Issue Advanced Photonics Metamaterials and Metasurfaces: Science and Applications, 2nd Edition)

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25 pages, 6408 KB

Open AccessReview

Application Prospects of Optical Fiber Sensing Technology in Smart Campus Construction: A Review

by Huanhuan Zhang, Xinli Zhai and Jing Sun

Photonics 2025, 12(10), 1026; https://doi.org/10.3390/photonics12101026 - 16 Oct 2025

As smart campus construction continues to advance, traditional safety monitoring and environmental sensing systems are increasingly showing limitations in sensitivity, anti-interference capability, and deployment flexibility. Optical fiber sensing (OFS) technology, with its advantages of high sensitivity, passive operation, immunity to electromagnetic interference, and [...] Read more.

As smart campus construction continues to advance, traditional safety monitoring and environmental sensing systems are increasingly showing limitations in sensitivity, anti-interference capability, and deployment flexibility. Optical fiber sensing (OFS) technology, with its advantages of high sensitivity, passive operation, immunity to electromagnetic interference, and long-distance distributed sensing, provides a novel solution for real-time monitoring and early warning of critical campus infrastructure. This review systematically examines representative applications of OFS technology in smart campus scenarios, including structural health monitoring of academic buildings, laboratory environmental sensing, and intelligent campus security. By analyzing the technical characteristics of various types of optical fiber sensors, the paper explores emerging developments and future potential of OFS in supporting intelligent campus construction. Finally, the feasibility of building data acquisition, transmission, and visualization platforms based on OFS systems is discussed, highlighting their promising roles in campus safety operations, the integration of teaching and research, and intelligent equipment management. Full article

(This article belongs to the Special Issue Applications and Development of Optical Fiber Sensors)

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15 pages, 3042 KB

Open AccessArticle

Mathematical Analysis and Freeform Surface Modeling for LED Illumination Systems Incorporating Diffuse Reflection and Total Internal Reflection

by Xin Xu, Jianghua Rao, Xiaowen Liang, Zhenmin Zhu and Yuanyuan Peng

Photonics 2025, 12(10), 1025; https://doi.org/10.3390/photonics12101025 - 16 Oct 2025

Indirect lighting systems employing light-emitting diodes (LEDs) and diffuse reflective surfaces are prevalent in applications demanding stringent illumination uniformity. However, conventional diffuse reflection approaches exhibit inherent limitations (inevitable light loss from multiple diffuse reflections and trade-off between uniformity and efficiency). To overcome these [...] Read more.

Indirect lighting systems employing light-emitting diodes (LEDs) and diffuse reflective surfaces are prevalent in applications demanding stringent illumination uniformity. However, conventional diffuse reflection approaches exhibit inherent limitations (inevitable light loss from multiple diffuse reflections and trade-off between uniformity and efficiency). To overcome these constraints, we introduce a novel composite freeform surface illumination system that synergistically integrates total internal reflection (TIR) with diffuse reflection. This design leverages the inherent Lambertian radiation characteristics of LEDs and the properties of ideal diffuse reflectors. A rigorous mathematical model is derived based on the luminous intensity distribution of the LED chip, the prescribed illumination requirements on the target plane, the principle of energy conservation, and Snell’s law. The resulting system of nonlinear equations is solved to generate a series of two-dimensional profile curves, which are subsequently synthesized into an off-axis freeform surface. Simulated results demonstrate that the proposed system achieves higher optical efficiency and superior illumination uniformity compared to traditional diffuse reflector configurations. This universal and feasible methodology broadens the application potential of high-performance diffuse indirect lighting. Full article

(This article belongs to the Special Issue New Perspectives in Micro-Nano Optical Design and Manufacturing)

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14 pages, 3457 KB

Open AccessArticle

Improving the High-Pressure Sensing Characteristics of Y₂MoO₆:Eu³⁺ Using a Machine Learning Approach

by Marko G. Nikolic, Dragutin Sevic and Maja S. Rabasovic

Photonics 2025, 12(10), 1024; https://doi.org/10.3390/photonics12101024 - 16 Oct 2025

In this study, we explore the potential of applying machine learning (ML) to enhance high-pressure luminescence sensing. We investigate the luminescence behavior of Y₂MoO₆:Eu³⁺, synthesized via a self-initiated, self-sustained reaction. Emission spectra were collected under varying pressures [...] Read more.

In this study, we explore the potential of applying machine learning (ML) to enhance high-pressure luminescence sensing. We investigate the luminescence behavior of Y₂MoO₆:Eu³⁺, synthesized via a self-initiated, self-sustained reaction. Emission spectra were collected under varying pressures using a 405 nm laser diode and an AVANTES AvaSpec 2048TEC USB2 spectrometer. An analysis of the pressure-dependent curve, based on the intensities of two key peaks, indicates a possible crystal phase transition or another underlying physical phenomenon. Moreover, the non-unique relationship between pressure and peak intensity limits its effectiveness for precise sensing. To overcome this challenge, we employ an ML-based approach, combining Uniform Manifold Approximation and Projection (UMAP) for data visualization with a deep neural network to estimate pressure directly from the full luminescence spectrum. This strategy significantly extends the usable pressure range of Y₂MoO₆:Eu³⁺ up to 12 GPa, representing a marked improvement over conventional methods. Full article

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12 pages, 3199 KB

Open AccessArticle

Design Methodology of a VIS Hybrid Refractive–Metalens System with a Wide FOV

by Xingyi Li, Peixuan Wu, Yuanyuan Xing, Peng Shi, Xinjian Yao and Yaoguang Ma

Photonics 2025, 12(10), 1023; https://doi.org/10.3390/photonics12101023 - 16 Oct 2025

The emergence of metalenses has opened new possibilities for miniaturizing optical systems. However, the limited group delay provided by meta-atoms restricts their aperture size under broadband operation. This challenge has stimulated the development of hybrid refractive–metalens systems, which overcome the performance limitations of [...] Read more.

The emergence of metalenses has opened new possibilities for miniaturizing optical systems. However, the limited group delay provided by meta-atoms restricts their aperture size under broadband operation. This challenge has stimulated the development of hybrid refractive–metalens systems, which overcome the performance limitations of individual metalenses while achieving a more compact form factor than conventional refractive lens assemblies. Here, we propose a design methodology for hybrid lenses that combines ray tracing with full-wave simulation. We analyze key aspects of the metalens within the hybrid system for a wide wavelength band—specifically, dispersion and transmission efficiency. Based on this approach, we designed a high-resolution hybrid lens operating in the 435–656 nm visible band with a 35° field of view. The results demonstrate that the proposed lens achieves imaging performance equivalent to that of conventional refractive systems while reducing the total track length by 29%. This validates the effectiveness of our design method, indicating its strong potential for application in compact and lightweight optical systems. Full article

(This article belongs to the Special Issue Photonics Metamaterials: Processing and Applications)

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15 pages, 2817 KB

Open AccessArticle

Universal Phase Correction for Quantum State Transfer in One-Dimensional Topological Spin Chains

by Tian Tian, Yingnan Yan and Shizhen Wang

Photonics 2025, 12(10), 1022; https://doi.org/10.3390/photonics12101022 - 16 Oct 2025

Gap-protected topological channels are a promising way to realize robust and high-fidelity state transfer in quantum networks. Although various topological transfer protocols based on the Su-Schrieffer-Heeger (SSH) model or its variants have been proposed, the phase accumulation during the evolution, as an essential [...] Read more.

Gap-protected topological channels are a promising way to realize robust and high-fidelity state transfer in quantum networks. Although various topological transfer protocols based on the Su-Schrieffer-Heeger (SSH) model or its variants have been proposed, the phase accumulation during the evolution, as an essential aspect, is underestimated. Here, by numerically studying the phase information of quantum state transfer (QST) in one-dimensional (1D) topological spin chains, we uncover a universal phase correction

ϕ_{0} = (N - 1) π / 2

for both adiabatic and diabatic topological schemes. Interestingly, the site-number-dependent phase correction satisfies

Z_{4}

symmetry and is equally effective for perfect mirror transmission in spin chains. Our work reveals a universal phase correction in 1D topologically protected QST, which will prompt a reevaluation of the topological protection mechanism in quantum systems. Full article

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

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16 pages, 923 KB

Open AccessArticle

Photobiomodulation in Complex Female Infertility Profile: A Case Report with 12-Month Follow-Up and Review of Current Mechanism in Reproductive Photomedicine

by Ruth Phypers and Reem Hanna

Photonics 2025, 12(10), 1021; https://doi.org/10.3390/photonics12101021 - 16 Oct 2025

Female infertility from polycystic ovarian syndrome (PCOS) and endometriosis poses a challenge for both clinicians and women who are trying to conceive. The present clinical single case report aimed to evaluate the efficacy of multiple wavelengths of red and near-infrared (NIR) laser photobiomodulation [...] Read more.

Female infertility from polycystic ovarian syndrome (PCOS) and endometriosis poses a challenge for both clinicians and women who are trying to conceive. The present clinical single case report aimed to evaluate the efficacy of multiple wavelengths of red and near-infrared (NIR) laser photobiomodulation (PBM) for increasing the potential of fertility in a woman with PCOS, endometriosis and low ovarian reserve. The observations helped to inform and establish the following: (1) any adverse effects; (2) the possibility of producing an effective PBM protocol; and (3) a healthy live birth. The case report concerns a female who failed to conceive naturally beyond five years and had experienced one unsuccessful IVF cycle. Methods: Case report of one female subject with infertility issues, which included failure to conceive naturally beyond five years. Previous conditions were recorded and then compared with outcomes from after the patient received a course of PBM treatments. PBM treatments were given at weekly and/or at two-week intervals over a 5-month period during the follicular stage of the menstrual cycle, using IR and NIR wavelengths between 600 and 1000 nm. Results: After five months a spontaneous conception was achieved. The case resulted in a full-term pregnancy and the birth of a healthy baby. Improvements in reproductive health outcomes in this case give reason to suggest that PBM helped to alleviate PCOS and endometriosis which could have been associated with a low ovarian reserve. Conclusions: The case report indicates that a multiwavelength of red and NIR-PBM laser therapy could have positively contributed to a healthy live birth in a female diagnosed with PCOS, endometriosis and a low ovarian reserve. Extensive studies with large data are warranted to validate our PBM dosimetry and treatment protocols to assess the potential impact of PBM for treating endometriosis and PCOS. Subsequently, to understand the genetic and phenotype biomarkers would be an important step further to standardise a range of PBM light dosimetry. Full article

(This article belongs to the Special Issue Shining Light on Healing: Photobiomodulation Therapy)

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20 pages, 4701 KB

Open AccessArticle

FMCW LiDAR Nonlinearity Compensation Based on Deep Reinforcement Learning with Hybrid Prioritized Experience Replay

by Zhiwei Li, Ning Wang, Yao Li, Jiaji He and Yiqiang Zhao

Photonics 2025, 12(10), 1020; https://doi.org/10.3390/photonics12101020 - 15 Oct 2025

Frequency-modulated continuous-wave (FMCW) LiDAR systems are extensively utilized in industrial metrology, autonomous navigation, and geospatial sensing due to their high precision and resilience to interference. However, the intrinsic nonlinear dynamics of laser systems introduce significant distortion, adversely affecting measurement accuracy. Although conventional iterative [...] Read more.

Frequency-modulated continuous-wave (FMCW) LiDAR systems are extensively utilized in industrial metrology, autonomous navigation, and geospatial sensing due to their high precision and resilience to interference. However, the intrinsic nonlinear dynamics of laser systems introduce significant distortion, adversely affecting measurement accuracy. Although conventional iterative pre-distortion correction methods can effectively mitigate nonlinearities, their long-term reliability is compromised by factors such as temperature-induced drift and component aging, necessitating periodic recalibration. In light of recent advances in artificial intelligence, deep reinforcement learning (DRL) has emerged as a promising approach to adaptive nonlinear compensation. By continuously interacting with the environment, DRL agents can dynamically modify correction strategies to accommodate evolving system behaviors. Nonetheless, existing DRL-based methods often exhibit limited adaptability in rapidly changing nonlinear contexts and are constrained by inefficient uniform experience replay mechanisms that fail to emphasize critical learning samples. To address these limitations, this study proposes an enhanced Soft Actor-Critic (SAC) algorithm incorporating a hybrid prioritized experience replay framework. The prioritization mechanism integrates modulation frequency (MF) error and temporal difference (TD) error, enabling the algorithm to dynamically reconcile short-term nonlinear perturbations with long-term optimization goals. Furthermore, a time-varying delayed experience (TDE) injection strategy is introduced, which adaptively modulates data storage intervals based on the rate of change in modulation frequency error, thereby improving data relevance, enhancing sample diversity, and increasing training efficiency. Experimental validation demonstrates that the proposed method achieves superior convergence speed and stability in nonlinear correction tasks for FMCW LiDAR systems. The residual nonlinearity of the upward and downward frequency sweeps was reduced to

1.869 \times 10^{- 5}

and

1.9411 \times 10^{- 5}

, respectively, with a spatial resolution of 0.0203m. These results underscore the effectiveness of the proposed approach in advancing intelligent calibration methodologies for LiDAR systems and highlight its potential for broad application in high-precision measurement domains. Full article

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

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12 pages, 7227 KB

Open AccessArticle

High-Resolution Interferometric Temperature Sensor Based on Two DFB Fiber Lasers with High-Temperature Monitoring Potential

by Mikhail I. Skvortsov, Kseniya V. Kolosova, Alexander V. Dostovalov, Evgeniy V. Golikov, Alexander A. Vlasov, Sofia R. Abdullina, Andrey A. Rybaltovsky, Denis S. Lipatov, Aleksey S. Lobanov, Mikhail E. Likhachev, Olga N. Egorova and Sergey A. Babin

Photonics 2025, 12(10), 1019; https://doi.org/10.3390/photonics12101019 - 15 Oct 2025

A high-resolution temperature sensor using the beat frequency measurement between the modes of two DFB fiber lasers is presented. The laser cavities are formed by the femtosecond inscription technique in a highly Er/Yb co-doped phosphosilicate fiber with low optical losses and compact design. [...] Read more.

A high-resolution temperature sensor using the beat frequency measurement between the modes of two DFB fiber lasers is presented. The laser cavities are formed by the femtosecond inscription technique in a highly Er/Yb co-doped phosphosilicate fiber with low optical losses and compact design. The experimental results show a sensitivity of 1 GHz/°C, leading to a temperature resolution of 0.02 °C restricted by the thermistor used in the experiment. The maximum possible resolution determined by the laser linewidth is estimated as 2 × 10⁻⁶ °C. The operation of such a sensor at high temperatures (≈750 °C) with the possibility of further temperature increase is demonstrated. The combination of high resolution and broad temperature range makes the sensor attractive for various applications, especially in high-temperature monitoring. Full article

(This article belongs to the Special Issue Recent Advances in Fiber Laser Technology)

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14 pages, 7151 KB

Open AccessArticle

Design of Hollow-Core Anti-Resonant Fibers Supporting Few Weakly Coupled Polarization-Maintaining Modes

by Linxuan Zong, Jiayao Cheng and Yueyu Xiao

Photonics 2025, 12(10), 1018; https://doi.org/10.3390/photonics12101018 - 15 Oct 2025

A nested semi-tube hollow-core anti-resonant fiber (HC-ARF) that can support the high-purity transmission of a few polarization-maintaining modes is designed in this paper. By employing bi-thickness hybrid silica/silicon anti-resonant tubes, the birefringence of the orthogonal polarized modes is significantly improved, and the weak [...] Read more.

A nested semi-tube hollow-core anti-resonant fiber (HC-ARF) that can support the high-purity transmission of a few polarization-maintaining modes is designed in this paper. By employing bi-thickness hybrid silica/silicon anti-resonant tubes, the birefringence of the orthogonal polarized modes is significantly improved, and the weak coupling condition of the five lowest-order polarization maintaining modes, including the LP_{01_x}, LP_{01_y}, LP_{11a_x}, LP_{11b_x}, and LP_{11a_y}, can be met. The effective refractive index difference between each pair of the supported adjacent modes is larger than 1.0 × 10⁻⁴. With hybrid multi-layer nested semi-tubes, the confinement losses of the supported modes are all less than 1.50 × 10⁻¹ dB/m within a transmission band from 1.530 to 1.620 μm. The minimum confinement losses of the LP_{01_y}, LP_{01_x}, LP_{11a_y}, LP_{11a_x}, and LP_{11b_x} modes are 3.71 × 10⁻⁴ dB/m, 1.61 × 10⁻³ dB/m, 2.00 × 10⁻² dB/m, 1.30 × 10⁻¹ dB/m, and 4.20 × 10⁻² dB/m, respectively. Meanwhile, the unwanted higher-order modes are filtered out well to guarantee the modal purity. The minimum higher-order-mode extinction ratio of the lowest-loss LP₂₁ mode to the highest-loss LP₁₁ mode remains larger than 139 from 1.545 to 1.615 μm. The numerical results highlight the potential of the proposed polarization-maintaining few-mode hollow-core anti-resonant fibers in many application fields, such as short-range and high-capacity data transmission networks, fiber sensing systems, quantum communication systems, and so on. Full article

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

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10 pages, 3924 KB

Open AccessArticle

1970 W 1030 nm Single-Mode All-Fiber Master Oscillator Power Amplifier with ~3.2 GHz Linewidth Based on Ultra-Low NA Active Fiber

by Yang Liu, Xiaoyong Xu, Mengfan Cui, Wei Li, Chongwei Wang, Yan Peng, Junjie Zheng, Zilun Chen, Yisha Chen, Wei Liu, Hu Xiao, Zefeng Wang and Pengfei Ma

Photonics 2025, 12(10), 1017; https://doi.org/10.3390/photonics12101017 - 15 Oct 2025

A high-power narrow-linewidth fiber laser with single-mode beam quality is experimentally demonstrated. By employing a cascaded phase modulation strategy, the stimulated Brillouin scattering (SBS) threshold of the laser is effectively increased from 973 W to 1970 W. High-order modes are well suppressed during [...] Read more.

A high-power narrow-linewidth fiber laser with single-mode beam quality is experimentally demonstrated. By employing a cascaded phase modulation strategy, the stimulated Brillouin scattering (SBS) threshold of the laser is effectively increased from 973 W to 1970 W. High-order modes are well suppressed during power scaling, benefiting from the significant bending loss of a low numerical aperture (NA) ytterbium-doped fiber. A maximum output power of 1970 W is achieved, with a linewidth of 3.2 GHz and a beam quality factor M² of 1.14. To the best of our knowledge, this represents the highest reported output power for narrow-linewidth fiber lasers (linewidth < 10 GHz) operating at wavelengths below 1040 nm. Full article

(This article belongs to the Special Issue High-Power Fiber Lasers)

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11 pages, 3558 KB

Open AccessCommunication

Design and Fabrication of Thermopile Infrared Detector Based on Carbon Black Nanoparticle Absorption Layer

by Cheng Lei, Zhenyu Zhang, Boyou Shao, Xiangyang Ren, Tengteng Li, Fengchao Li and Ting Liang

Photonics 2025, 12(10), 1016; https://doi.org/10.3390/photonics12101016 - 14 Oct 2025

This study demonstrates a high-performance thermopile infrared detector that incorporates a carbon black nanoparticle (CBNP) absorption layer. To overcome the limitations associated with conventional infrared-absorbing materials—including high cost, complex fabrication, and constrained spectral response—a highly porous CBNP thin-film absorption layer was deposited onto [...] Read more.

This study demonstrates a high-performance thermopile infrared detector that incorporates a carbon black nanoparticle (CBNP) absorption layer. To overcome the limitations associated with conventional infrared-absorbing materials—including high cost, complex fabrication, and constrained spectral response—a highly porous CBNP thin-film absorption layer was deposited onto the thermopile sensing area using inkjet printing. Combined with an optimized microcavity design, this approach significantly enhances the photothermal conversion efficiency of the device. Experimental results indicate that the detector equipped with the CBNP absorption layer achieves a responsivity of 47.9 V/W and a detectivity of 1.14 × 10⁸ cm·Hz¹/²·W⁻¹. These values represent improvements of 34.55% in responsivity and 34.28% in detectivity, respectively, compared to a reference device without the CBNP layer. This work provides a promising strategy for the development of low-cost yet high-performance infrared detectors. Full article

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