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Computation of the Multi-Spheres Scattering Coefficient Using the Prime Index Method
Effects of Thickness and Grain Size on Harmonic Generation in Thin AlN Films
Exploring Changes in Ocular Aberrations for Different Fixation and Accommodation Stimuli

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, CAPlus / SciFinder, and other databases.
Journal Rank: JCR - Q2 (Optics)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 14.9 days after submission; acceptance to publication is undertaken in 1.9 days (median values for papers published in this journal in the second half of 2024).
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: 2.1 (2023); 5-Year Impact Factor: 2.1 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2304-6732

Latest Articles

10 pages, 6501 KiB

Open AccessCommunication

Phase Disturbance Compensation for Quantitative Imaging in Off-Axis Digital Holographic Microscopy

by Ying Li, Wenlong Shao, Lijie Hou and Changxi Xue

Photonics 2025, 12(4), 345; https://doi.org/10.3390/photonics12040345 (registering DOI) - 4 Apr 2025

Holographic detection technology has found extensive applications in biomedical imaging, surface profilometry, vibration monitoring, and defect inspection due to its unique phase detection capability. However, the accuracy of quantitative holographic phase imaging is significantly affected by the interference from direct current and twin [...] Read more.

Holographic detection technology has found extensive applications in biomedical imaging, surface profilometry, vibration monitoring, and defect inspection due to its unique phase detection capability. However, the accuracy of quantitative holographic phase imaging is significantly affected by the interference from direct current and twin image terms. Traditional methods, such as multi-exposure phase shifting and off-axis holography, have been employed to mitigate these interferences. While off-axis holography separates spectral components by introducing a tilted reference beam, it inevitably induces phase disturbances that compromise measurement accuracy. This study provides a computational explanation for the incomplete phase compensation issue in existing algorithms and establishes precision criteria for phase compensation based on theoretical formulations. We propose two novel phase compensation methods—the non-iterative compensation approach and the multi-iteration compensation technique. The principles and applicable conditions of these methods are thoroughly elucidated, and their superiority is demonstrated through comparative experiments. The results indicate that the proposed methods effectively compensate for phase disturbances induced by the tilted reference beam, offering enhanced precision and reliability in quantitative holographic phase measurements. Full article

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22 pages, 3342 KiB

Open AccessArticle

Ensquared Energy and Optical Centroid Efficiency in Optical Sensors, Part 3: Optical Sensors

by Marija Strojnik and Yaujen Wang

Photonics 2025, 12(4), 344; https://doi.org/10.3390/photonics12040344 (registering DOI) - 3 Apr 2025

We previously introduced the concepts of optical centroid efficiency (OCE) and enclosed energy within a rectangular pixel (EOD). We applied them to an ideal lens with and without a central obscuration for two different detector pixel sizes. Also, we [...] Read more.

We previously introduced the concepts of optical centroid efficiency (OCE) and enclosed energy within a rectangular pixel (EOD). We applied them to an ideal lens with and without a central obscuration for two different detector pixel sizes. Also, we analyzed the performance of OCE vs. EOD for the following three Seidel primary aberrations of an ideal lens: spherical, coma, and astigmatism, plus defocus. In this paper, we concentrate on three different optical remote sensing instrument configurations. We burden them with a set of aberrations to mimic realistic generalized error budgets that cover potential ground, lunch, and on-orbit environmental conditions. The shape of the OCE vs. EOD curve depends to a large degree on the dominant aberration. With the proper choice of detector pixel size, OCE increases with EOD when EOD is larger than 0.6. The increased detector pixel size is advantageous for structures that enhance diffraction effects, and for off-axis and asymmetrical configurations. Analytical and experimental tests are proposed for original critical cases. Furthermore, OCE and EOD, as functional figures of merit, may be effectively applied to instruments for monitoring tumors and their evolution to cancerous tissue, leading to timely diagnosis. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology, 2nd Edition)

9 pages, 3167 KiB

Open AccessCommunication

Filter-Assisted Self-Coherent Detection Field Recovery Scheme for Dual-Polarization Complex-Valued Double-Sideband Signals

by Jiahao Huo, Li Han, Peng Qin, Jianlong Tao, Haolin Bai and Xiaoying Zhang

Photonics 2025, 12(4), 343; https://doi.org/10.3390/photonics12040343 (registering DOI) - 3 Apr 2025

In this paper, we have proposed a filter-assisted self-coherent detection (FASCD) scheme that reconstructs the optical field of a dual-polarization complex-valued double-sideband (DP-CV-DSB) signal. At the receiver, the carrier is extracted using an optical bandpass filter (OBPF), and a pair of orthogonal carriers [...] Read more.

In this paper, we have proposed a filter-assisted self-coherent detection (FASCD) scheme that reconstructs the optical field of a dual-polarization complex-valued double-sideband (DP-CV-DSB) signal. At the receiver, the carrier is extracted using an optical bandpass filter (OBPF), and a pair of orthogonal carriers is constructed to achieve polarization-division multiplexing (PDM) by a Faraday rotator mirror (FRM). To address the issue of polarization crosstalk, channel estimation is performed using the least squares (LS) method, and the estimation results are further optimized through the intra-symbol frequency-domain averaging (ISFA) method. We demonstrate the system architecture and algorithms by simulation on a 224 Gbit/s 16-ary quadrature amplitude modulation DSB-PDM-OFDM system. The system performance is improved by 1 dB using the ISFA method. Full article

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

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23 pages, 5235 KiB

Open AccessArticle

Tunable All-Optical Pattern Recognition System Based on Nonlinear Optical Loop Mirror for Bit-Flip BPSK Targets

by Ying Tang, Ziyi Kang, Xin Li, Ningjing Liang, Jinyong Chang and Genqing Bian

Photonics 2025, 12(4), 342; https://doi.org/10.3390/photonics12040342 - 3 Apr 2025

As the basic physical infrastructure of various networks, optical networks are crucial to the advancement of information technology. Meanwhile, as new technologies emerge, the security of optical networks is facing serious threats. To improve the security of optical networks, optoelectronic firewalls primarily leverage [...] Read more.

As the basic physical infrastructure of various networks, optical networks are crucial to the advancement of information technology. Meanwhile, as new technologies emerge, the security of optical networks is facing serious threats. To improve the security of optical networks, optoelectronic firewalls primarily leverage all-optical pattern recognition to perform direct detection and analysis of data transmitted through the optical network at the optical layer. However, the current all-optical pattern recognition system still faces some problems when deployed in optical networks, including phase-lockingand relatively low recognition efficiency and scalability. In this paper, we propose a tunable all-optical pattern recognition system based on a nonlinear optical loop mirror (NOLM) for bit-flip BPSK targets. The operational principles and simulation setup of the proposed system are comprehensively described. Numerical simulations demonstrate that the system can accurately recognize and determine the position of 4-bit and 8-bit bit-flip BPSK targets in 16-bit input data with tunable frequencies of 192.8 THz and 193.4 THz at a data rate of 100 Gbps. Finally, the impact of input noise is evaluated by extinction ratio (ER), contrast ratio (CR), Q factor, bit error rate (BER), amplitude modulation (AM), and signal-to-noise ratio (SNR) under both frequencies. Full article

(This article belongs to the Special Issue Advancements in Optical Information Processing and Communication Technologies)

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13 pages, 4788 KiB

Open AccessArticle

Design of High-Efficiency Circularly Polarized Reflection Mirror Based on Chiral Dielectric Metasurface

by Bo Cheng, Yuxiao Zou, Kunpeng Zhai and Guofeng Song

Photonics 2025, 12(4), 341; https://doi.org/10.3390/photonics12040341 - 3 Apr 2025

Circularly polarized lasers can directly generate circularly polarized light without requiring complex external optics, enabling applications in biosensing, environmentally friendly antibacterial treatments, and cancer cell phototherapy. However, the circular dichroism (CD) of chiral metasurface mirrors—a core component of such lasers—typically remains below 3%, [...] Read more.

Circularly polarized lasers can directly generate circularly polarized light without requiring complex external optics, enabling applications in biosensing, environmentally friendly antibacterial treatments, and cancer cell phototherapy. However, the circular dichroism (CD) of chiral metasurface mirrors—a core component of such lasers—typically remains below 3%, limiting beam quality. Using COMSOL simulations, we broke the metasurface’s structural symmetry via displacement and rotation operations, introducing chirality to the unit cell. At 980 nm, the metasurface achieved 99.85% reflectivity and 52% CD. Multipole analysis suggests this enhancement stems from electric dipole and quadrupole coupling. Our laser design could generate micro-nano-scale chiral light, advancing applications in biophotonics, biomedicine, and life sciences. Full article

(This article belongs to the Special Issue Vertical-Cavity Surface-Emitting Laser Technology: Innovations and Future Trends)

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9 pages, 851 KiB

Open AccessArticle

Performance of Ship-Based QKD Under the Influence of Sea-Surface Atmospheric Turbulence

by Gui-Ying Jiang, Ya-Ping Li, Xiao-Han Li, Wei-Dong Zhang, Zi-Ao Wan, Qi-Ming Zhu, Peng-Fei Gong and Song Zhang

Photonics 2025, 12(4), 340; https://doi.org/10.3390/photonics12040340 - 3 Apr 2025

There are numerous studies on the effects of ocean turbulence on wireless optical communications and on satellite–ground quantum key distribution (QKD); however, there are few studies on the impact of near sea-surface turbulence on ship-based QKD performance. This study investigates the influence of [...] Read more.

There are numerous studies on the effects of ocean turbulence on wireless optical communications and on satellite–ground quantum key distribution (QKD); however, there are few studies on the impact of near sea-surface turbulence on ship-based QKD performance. This study investigates the influence of sea-surface atmospheric turbulence on laser beam propagation, atmospheric scintillation, and aiming error. It focuses on the impact of sea-surface turbulence on the performance of satellite-to-ship QKD and ship-to-ship QKD systems. The results show that strong turbulence severely degrades QKD system performance; horizontal transmission distances change from 32 km (weak turbulence) to 3 km (strong turbulence) in ship-to-ship QKD. Full article

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

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15 pages, 802 KiB

Open AccessArticle

Optical Field-to-Field Translation Under Atmospheric Turbulence: A Conditional GAN Framework with Embedded Turbulence Parameters

by Dongxiao Zhang, Junjie Zhang, Yinjun Gao and Taijiao Du

Photonics 2025, 12(4), 339; https://doi.org/10.3390/photonics12040339 - 2 Apr 2025

We propose a field mapping approach for the propagation of laser beams through atmospheric turbulence, leveraging a Generative Adversarial Network (GAN). The proposed GAN utilizes a U-Net architecture as its generator, with turbulence characteristic parameters introduced into the bottleneck layer of the U-Net [...] Read more.

We propose a field mapping approach for the propagation of laser beams through atmospheric turbulence, leveraging a Generative Adversarial Network (GAN). The proposed GAN utilizes a U-Net architecture as its generator, with turbulence characteristic parameters introduced into the bottleneck layer of the U-Net network, enabling effective control over the generator. This design allows for the flexible simulation of Gaussian beam propagation across a range of turbulence intensities and transmission distances. A comparative analysis between the neural network predictions and numerical simulation results indicates that the neural network can achieve a field mapping speedup of four orders of magnitude while maintaining a relative error within 16% for the second-order statistical moments of the light spot. Additionally, the study investigates the effect of varying turbulence intensities on prediction accuracy. The results indicate that high-frequency speckle patterns caused by beam breakup are the primary factor limiting prediction accuracy under strong or saturated turbulence conditions. Full article

(This article belongs to the Special Issue Recent Advances in Optical Turbulence)

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17 pages, 10281 KiB

Open AccessArticle

Design and Research of Large-Scale Curvature Adjustment Optical Mirror

by Kailun Zhao, Liuxing Song, Dewei Sun, Qiaolin Huang, Rongguang Guo, Guoliang Tian and Jinping He

Photonics 2025, 12(4), 338; https://doi.org/10.3390/photonics12040338 - 2 Apr 2025

This study introduces an optimization design method for large-scale curvature-adjustable optical mirrors, innovatively integrating parametric modeling with the optimized layout of actuators, targeting the achievement of extensive curvature adjustability and high-precision surface correction for segmented mirrors. The optimization objective is based on the [...] Read more.

This study introduces an optimization design method for large-scale curvature-adjustable optical mirrors, innovatively integrating parametric modeling with the optimized layout of actuators, targeting the achievement of extensive curvature adjustability and high-precision surface correction for segmented mirrors. The optimization objective is based on the surface figure residual when the curvature radius of the segmented mirror is altered by 100 mm. Through the optimization of the number, arrangement, and thickness of reinforcement ribs of the actuators on the back of the segmented mirror, a parametric model of a segmented mirror with an edge-to-edge distance of 510 mm and a radius of curvature 9100 mm is developed. Simulation outcomes reveal that a 0–15 μm variation in the actuators results in a curvature radius change of 178.45 mm in the segmented mirror, with a highly linear correlation, achieving a radius of curvature reconfiguration of the primary mirror in the optical system from 9100 mm to 9000 mm, with a residual surface figure error of less than 10 nm. The experimental results indicate that within a 0–15 μm closed-loop stroke range, the curvature radius of the segmented mirror can be adjusted by 146.89 mm, fulfilling the design objective of a lightweight mirror with a significantly adjustable curvature radius. This research is anticipated to offer technical support and serve as a reference for the assembly, adjustment, and inspection of large-aperture segmented mirrors, as well as for the curvature radius variation in multiple segmented mirrors, thereby holding substantial practical value in engineering applications. Full article

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15 pages, 4626 KiB

Open AccessArticle

A Novel Sophia-SPGD (Stochastic Parallel Gradient Descent) Optimization Method for Wavefront Correction in WFS-Less AO (Wavefront Sensorless Adaptive Optics) Systems

by Peng Chen, Wenjie Yang, Yongqi Ge, Zhiguang Zhang, Xianshuo Li, Zhengqing Qi and Huizhen Yang

Photonics 2025, 12(4), 337; https://doi.org/10.3390/photonics12040337 - 2 Apr 2025

In wavefront sensorless adaptive optics (WFS-less AO) systems, stochastic parallel gradient descent (SPGD) is the primary optimization method for correcting wavefront distortions. However, as the intensity of atmospheric turbulence interference increases, the fixed gain coefficient of the SPGD algorithm results in significant decreases [...] Read more.

In wavefront sensorless adaptive optics (WFS-less AO) systems, stochastic parallel gradient descent (SPGD) is the primary optimization method for correcting wavefront distortions. However, as the intensity of atmospheric turbulence interference increases, the fixed gain coefficient of the SPGD algorithm results in significant decreases in convergence speed and precision. Moreover, the algorithm is inclined to local optima, thus failing to satisfy the requirements for real-time wavefront distortion correction. To address these issues, this paper introduces a new optimization algorithm, Sophia optimized stochastic parallel gradient descent (Sophia-SPGD), which is based on second-order clipped stochastic optimization in deep learning. This algorithm computes the first-order and second-order moments of the performance metrics from its first and second gradients, respectively, and dynamically modulates the gain via a shearing mechanism to increase the convergence speed and diminish the probability of falling into local optima. Numerical simulations and experiments demonstrate that under strong turbulence conditions, the performance of Sophia-SPGD surpasses that of the traditional SPGD algorithm. Full article

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10 pages, 3846 KiB

Open AccessArticle

Optical Differentiation and Edge Detection Based on Birefringence of Uniaxial Crystals

by Xu Chen, Ping Huang, Xuan Tang and Xunong Yi

Photonics 2025, 12(4), 336; https://doi.org/10.3390/photonics12040336 - 2 Apr 2025

Optical differential operations can directly extract edge information from images and have significant application potential in fields such as image processing and object recognition. In this work, we propose an optical spatial differentiator based on the birefringence effect of uniaxial crystals. The system [...] Read more.

Optical differential operations can directly extract edge information from images and have significant application potential in fields such as image processing and object recognition. In this work, we propose an optical spatial differentiator based on the birefringence effect of uniaxial crystals. The system comprises two orthogonal polarizers and a uniaxial crystal, offering advantages of structural simplicity, operational stability, low cost, and seamless compatibility with conventional optical systems. Experimental results demonstrate that the proposed differentiator achieves clear edge imaging for both amplitude and phase objects, while also enabling dark-field differential imaging of transparent biological cells, thereby substantially enhancing imaging quality and contrast. This efficient and robust design provides a promising solution for advancing optical differentiation techniques in applications ranging from data processing to biomedical imaging. Full article

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17 pages, 13853 KiB

Open AccessArticle

Investigation on the Full-Aperture Diffraction Efficiency of AOTF Based on Tellurium Dioxide Crystals

by Zhiyuan Mi, Huijie Zhao, Qi Guo, Zhoujun Zhong and Chengsheng Zhou

Photonics 2025, 12(4), 335; https://doi.org/10.3390/photonics12040335 - 2 Apr 2025

The influence of acoustic field distribution and temperature variations on the full-aperture diffraction efficiency of non-collinear acousto-optic tunable filters (AOTFs) was investigated based on tellurium dioxide crystals. The strong acoustic anisotropy of the crystal induces non-uniform acoustic energy distribution, limiting the overall diffraction [...] Read more.

The influence of acoustic field distribution and temperature variations on the full-aperture diffraction efficiency of non-collinear acousto-optic tunable filters (AOTFs) was investigated based on tellurium dioxide crystals. The strong acoustic anisotropy of the crystal induces non-uniform acoustic energy distribution, limiting the overall diffraction efficiency. To analyze this effect, the acoustic field distribution within a large-aperture AOTF was simulated, and the diffraction efficiency across different aperture regions was evaluated and experimentally validated. The results demonstrate that sound beam contraction and acoustic energy non-uniformity significantly reduce the peak diffraction efficiency and increase the power required to achieve high diffraction efficiency. Additionally, temperature-induced variations in acoustic velocity alter the acoustic field structure, leading to spatially non-uniform changes in diffraction efficiency. Both simulations and experimental measurements confirm that while the overall impact of temperature on full-aperture diffraction efficiency remains relatively small, localized variations are pronounced, highlighting potential inaccuracies in single-beam-based efficiency measurements. Full article

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14 pages, 3191 KiB

Open AccessArticle

Wide-Angle, Polarization-Independent Broadband Metamaterial Absorber by Using Plasmonic Metasurface-Based Split-Circular Structure

by Thanh Son Pham, Bui Xuan Khuyen, Vu Dinh Lam, Liangyao Chen and Youngpak Lee

Photonics 2025, 12(4), 334; https://doi.org/10.3390/photonics12040334 - 2 Apr 2025

Absorption of electromagnetic waves in a broadband frequency range with polarization insensitivity and wide incidence angles is greatly needed in modern technological applications. Many methods using metamaterials have been suggested to address this requirement; they can be complex multilayer structures or use external [...] Read more.

Absorption of electromagnetic waves in a broadband frequency range with polarization insensitivity and wide incidence angles is greatly needed in modern technological applications. Many methods using metamaterials have been suggested to address this requirement; they can be complex multilayer structures or use external electronic components. In this paper, we present a plasmonic metasurface structure that was simply fabricated using the standard printed circuit board technique but provided a high absorption above 90%, also covering a broadband frequency range from 12.30 to 14.80 GHz. This plasmonic metasurface consisted of structural unit cells composed of multiple split rings connected by a copper bar. Analysis, simulation, and measurement results showed that the metasurface also showed polarization-insensitive properties and maintained an absorption above 90% at incident angles up to 45 degrees. The suggested plasmonic metasurface is a fundamental design that can also be used to design the absorber in different frequency ranges and is able to adapt well to being fabricated at various scales. Full article

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

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13 pages, 1772 KiB

Open AccessArticle

Reliability Analysis of Multi-Autonomous Underwater Vehicle Cooperative Systems Based on Fuzzy Control

by Yu Hao, Yuan Yao, Yanbo Zhang and Fang Zuo

Photonics 2025, 12(4), 333; https://doi.org/10.3390/photonics12040333 - 2 Apr 2025

Autonomous underwater vehicles (AUVs) perform a wide range of functions, since underwater circumstances are diverse and varied and resources are plentiful. However, existing prevalent theoretical computation methods for classifying underwater environments are unable to keep up with the constantly evolving and complicated undersea [...] Read more.

Autonomous underwater vehicles (AUVs) perform a wide range of functions, since underwater circumstances are diverse and varied and resources are plentiful. However, existing prevalent theoretical computation methods for classifying underwater environments are unable to keep up with the constantly evolving and complicated undersea world. Therefore, in the design process of multi-AUV cooperative systems, there is usually some uncertainty in the parameters. This uncertainty creates some challenges in the design process and affects the system’s performance. In this study, a reliability-based multidisciplinary design optimization is presented, in which some of the problem parameters are uncertain. In this regard, it is assumed that some of the problem parameters are in the form of fuzzy numbers. We develop a multi-AUV cooperative system dependability model based on fuzzy control, leveraging the membership function of fuzzy control to thoroughly evaluate the environmental effects. We propose a method to evaluate the reliability of multi-AUV cooperative systems, which is of practical value. This solution can be used to evaluate and examine the cooperative system’s dependability in an unidentified underwater environment. The factors contributing to the reliability of multi-AUV cooperative systems are obtained. The results show that these contributing factors reflect different aspects of reliability for multi-AUV cooperative systems. It is possible to determine the reliability variation in the population of underwater vehicles operating in a complex underwater environment, which establishes a solid foundation for the further optimization of multi-AUV cooperative systems. Full article

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

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12 pages, 8821 KiB

Open AccessArticle

Tunable Slow Light in Valley-Locked Topological Photonic Crystal Waveguide

by Chenyang Peng, Gang Li, Junhao Yang, Chunlin Ma and Xinyuan Qi

Photonics 2025, 12(4), 332; https://doi.org/10.3390/photonics12040332 - 2 Apr 2025

This study introduces a topological photonic slow-light waveguide based on a honeycomb unit cell, which allows for the convenient tuning of the group index and bandwidth through the valley-locked effect. The topological properties of the unit cell are initially assessed. By adjusting the [...] Read more.

This study introduces a topological photonic slow-light waveguide based on a honeycomb unit cell, which allows for the convenient tuning of the group index and bandwidth through the valley-locked effect. The topological properties of the unit cell are initially assessed. By adjusting the air gap in the topologically protected photonic crystal (PhC) waveguide, it is possible to continuously vary the group index from 47 to 6 and the normalized group index–bandwidth product (NGBP) from 0.495 to 0.573. Furthermore, the chiral propagation characteristics and propagation loss of the topologically protected PhC waveguide are evaluated. The findings indicate that the structure supports chiral propagation and maintains a high transmission rate even after passing through sharp corners. The results contribute to a deeper understanding of topological photonics and suggest potential for applications in future photonic technologies, such as dynamic topological photonic retarders and nonlinear localization enhancers. Full article

(This article belongs to the Section New Applications Enabled by Photonics Technologies and Systems)

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9 pages, 2607 KiB

Open AccessCommunication

Far-Zone Spectral Density of Light Waves Scattered by Random Anisotropic Hollow Medium

by Yue Yu, Yongtao Zhang, Jixiong Pu, Huanting Chen and Huichuan Lin

Photonics 2025, 12(4), 331; https://doi.org/10.3390/photonics12040331 - 1 Apr 2025

A random anisotropic hollow scatterer is discussed and the far-zone characteristics of scalar light waves scattered by this type of medium are theoretically analyzed. The results show that the scattered far-zone spectral density distributions have interesting patterns of “central ellipses and peripheral circles” [...] Read more.

A random anisotropic hollow scatterer is discussed and the far-zone characteristics of scalar light waves scattered by this type of medium are theoretically analyzed. The results show that the scattered far-zone spectral density distributions have interesting patterns of “central ellipses and peripheral circles” or “central circles and peripheral ellipses”, which are decided by the outer and inner correlation lengths of the scatterer. This phenomenon provides some new insights into the generation and manipulation of the scattered far field, and can be applied in the reconstruction of the scattering medium’s structure. Full article

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9 pages, 1226 KiB

Open AccessCommunication

J-Aggregate-Enhanced Hybrid Nanoporous Alumina for Resonator-Free Amplified Emission

by Evgeniia O. Soloveva, Nikita Toropov and Anton A. Starovoytov

Photonics 2025, 12(4), 330; https://doi.org/10.3390/photonics12040330 - 1 Apr 2025

This study explores the development and optical characterization of a hybrid material combining nanoporous anodic alumina with J-aggregates of pseudoisocyanine dyes, highlighting its potential for photonic applications in bright broadband sources. The hybrid material was synthesized by impregnating an alumina matrix with a [...] Read more.

This study explores the development and optical characterization of a hybrid material combining nanoporous anodic alumina with J-aggregates of pseudoisocyanine dyes, highlighting its potential for photonic applications in bright broadband sources. The hybrid material was synthesized by impregnating an alumina matrix with a dye solution, which facilitated a thermally stimulated self-assembly process for the formation of J-aggregates. The incorporation of J-aggregates within the matrix was confirmed through several independent optical measurement techniques. A distinct absorption peak and corresponding luminescence signal were attributed to J-aggregate formation, while energy transfer from the alumina’s intrinsic oxygen vacancy centers to the dye aggregates was observed under specific excitation conditions. Amplified spontaneous emission was achieved under pulsed laser excitation, characterized by spectral narrowing and a nonlinear increase in emission intensity beyond a critical pump threshold, indicative of a similarity with random lasing facilitated by scattering within the porous structure. Full article

(This article belongs to the Special Issue Advances in Micro and Nano-Photonics: Emerging Materials and Applications)

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13 pages, 10030 KiB

Open AccessArticle

Advanced Fabrication of 56 Gbaud Electro-Absorption Modulated Laser (EML) Chips Integrated with High-Speed Silicon Photonic Substrates

by Liang Li, Yifan Xiao, Weiqi Wang, Chenggang Guan, Wengang Yao, Yuming Zhang, Xuan Chen, Qiang Wan, Chaoqiang Dong and Xinyuan Xu

Photonics 2025, 12(4), 329; https://doi.org/10.3390/photonics12040329 - 1 Apr 2025

With the rapid growth of data center demand driven by AI, high-speed optical modules (such as 800G and 1.6T) have become critical components. Traditional 800G modules face issues such as complex processes and large sizes due to the separate packaging of EML chips, [...] Read more.

With the rapid growth of data center demand driven by AI, high-speed optical modules (such as 800G and 1.6T) have become critical components. Traditional 800G modules face issues such as complex processes and large sizes due to the separate packaging of EML chips, AlN substrates, and capacitors. This study proposes a high-speed EML module based on silicon integration, where resistors, capacitors, and AuSn soldering areas are integrated onto the silicon substrate, enabling the bonding of the EML chip, reducing packaging costs, and enhancing scalability. Key achievements include: the development of a 100G EML chip; the fabrication of a high-speed silicon integrated carrier; successful Chip-on-Carrier (COC) packaging and testing, with a laser output power of 10 mW, extinction ratio of 10 dB, and bandwidth greater than 40 GHz; and reliability verified through 500 h of aging tests. This study provides an expandable solution for next-generation high-speed optical interconnects. Full article

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17 pages, 841 KiB

Open AccessArticle

Theoretical and Experimental Comparison of Three Pumping Methods for Thulium Fiber Lasers for Low-Output Power (<10 W)

by Anna Mauro, Valentina Serafini, Chiara Bellezza Prinsi, Matteo Cavagnetto, Luca Maggio Tanasi, Sabina Zaimovic, José Maria Blanco Triana, Gabriella Motta and Guido Perrone

Photonics 2025, 12(4), 328; https://doi.org/10.3390/photonics12040328 - 1 Apr 2025

Over the last decade, the number of demonstrations of Tm-doped fiber lasers has increased rapidly thanks to the applications of 2

μ

m fiber laser in sensing, surgery, and polymer processing. In the literature, there is plenty of evidence that increasing the output [...] Read more.

Over the last decade, the number of demonstrations of Tm-doped fiber lasers has increased rapidly thanks to the applications of 2

μ

m fiber laser in sensing, surgery, and polymer processing. In the literature, there is plenty of evidence that increasing the output power and the efficiency of this class of fiber lasers is of interest to the scientific and industrial communities. This article presents a theoretical and experimental study on three possible pumping methods for a Tm-doped fiber laser: out-of-band pumping, using a semiconductor-based module emitting at 793 nm; in-band pumping, using an ad hoc homemade fiber laser emitting at 1600 nm; an intracavity configuration, in which in the pump light is generated within the laser cavity itself. This work demonstrates how applying alternative pumping methods does not lead to significant improvements in laser performance without first taking into account the losses introduced in the system when switching from a cladding-pumped to a core-pumped configuration. Full article

(This article belongs to the Special Issue Optical Fiber Lasers and Laser Technology)

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15 pages, 2888 KiB

Open AccessArticle

Up to 2700 km Field Trial of Novel Cross Domain Protection Mechanism Against Multi-Point Failure in Long Distance Network Based on Segmented Dual-Node Interconnection

by Liuyan Han, Xinyu Chen, Haibin Huang, Dechao Zhang and Han Li

Photonics 2025, 12(4), 327; https://doi.org/10.3390/photonics12040327 - 31 Mar 2025

With the rapid deployment of 5G networks and the increasing demand for high-reliability services across industries such as smart grids, healthcare, and unmanned aerial vehicle (UAV) trajectory tracking, the need for robust and efficient transport network protection mechanisms has become critical. Traditional protection [...] Read more.

With the rapid deployment of 5G networks and the increasing demand for high-reliability services across industries such as smart grids, healthcare, and unmanned aerial vehicle (UAV) trajectory tracking, the need for robust and efficient transport network protection mechanisms has become critical. Traditional protection schemes, such as optical layer and electrical layer linear protection, face significant challenges in handling multi-point failures and achieving fault isolation in cross domain scenarios. To address these limitations, this paper proposes a novel cross-domain protection mechanism based on segmented Dual-Node Interconnection (DNI). By constructing a DNI topology between adjacent domains and leveraging a three-point bridge mechanism, the proposed solution enables efficient fault isolation and rapid service recovery in the event of multi-point failures. The proposed protection mechanism also introduces periodic status interaction messages between nodes, ensuring coordinated protection switching across domains. We conducted the first field trial to validate the proposed protection mechanism in a multi-domain, multi-vendor network spanning over 2700 km. The results demonstrate that the proposed protection scheme achieves protection switching times of less than 50 ms under various fault scenarios, including intra-domain and inter-domain failures, significantly outperforming traditional linear protection methods. This work represents a significant advancement in cross domain protection, offering a robust solution for enhancing the reliability of long-distance transport networks. Full article

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13 pages, 3845 KiB

Open AccessArticle

Ultra-Compact Multimode Micro-Racetrack Resonator Based on Cubic Spline Curves

by Zhen Li, Chuang Cheng, Xin Fu and Lin Yang

Photonics 2025, 12(4), 326; https://doi.org/10.3390/photonics12040326 - 31 Mar 2025

Micro-racetrack resonators have become one of the key components for realizing signal processing, generation, and integration in microwave photonics, owing to their high Q factor, compact footprint, and tunability. However, most of the reported micro-racetrack resonators are confined to the single-mode regime. In [...] Read more.

Micro-racetrack resonators have become one of the key components for realizing signal processing, generation, and integration in microwave photonics, owing to their high Q factor, compact footprint, and tunability. However, most of the reported micro-racetrack resonators are confined to the single-mode regime. In this paper, we designed an ultra-compact multimode micro-racetrack resonator (MMRR) based on shape-optimized multimode waveguide bends (MWBs). Cubic spline curves were used to represent the MWB boundary and adjoint methods were utilized for inverse optimization, achieving an effective radius of 8 μm. Asymmetric directional couplers (ADCs) were designed to independently couple three modes into a multimode micro-racetrack, according to phase-matching conditions and transmission analysis. The MMRR was successfully fabricated on a commercial platform using a 193 nm dry lithography process. The device exhibited high loaded Q factors of 2.3 × 10⁵, 4.1 × 10⁴, and 2.9 × 10⁴, and large free spectral ranges (FSRs) of 5.4, 4.7, and 4.2 nm for

{TE}_{0}

,

{TE}_{1}

, and

{TE}_{2}

modes, with about a 19 × 55 μm² footprint. Full article

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

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