Photonics

23 pages, 5347 KB

Open AccessArticle

A Transformer-Based Approach to Facilitate Inverse Design of Achromatic Metasurfaces

by Xucong Bian, Xiang’ai Cheng, Jiahui Liao, Zixiao Hua, Zhongjie Xu, Jiangbin Zhang and Zhongyang Xing

Photonics 2025, 12(9), 913; https://doi.org/10.3390/photonics12090913 - 11 Sep 2025

Abstract

Accurate and efficient prediction of the spectral responses of metasurface unit cells is key to intelligent metasurface design. Here, we propose a Shape-integrated Dual-Spectrum-aware transformer (SiDSaT) for forward prediction of metasurface responses. Trained on a large-scale simulation dataset, SiDSaT achieves a phase mean [...] Read more.

Accurate and efficient prediction of the spectral responses of metasurface unit cells is key to intelligent metasurface design. Here, we propose a Shape-integrated Dual-Spectrum-aware transformer (SiDSaT) for forward prediction of metasurface responses. Trained on a large-scale simulation dataset, SiDSaT achieves a phase mean absolute error (MAE) below 0.05 across both cylindrical and cuboidal unit cells, demonstrating strong prediction accuracy and generalization. We further embedded SiDSaT into an inverse design framework and applied it to the design of single-wavelength and broadband achromatic metalenses. Results of focusing performance and dispersion control confirm the effectiveness and versatility of SiDSaT in supporting the high-precision inverse design of metasurface optical devices. This work offers a scalable and accurate approach for intelligent metasurface design across diverse shape configurations and broadband spectral ranges. Full article

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

14 pages, 2297 KB

Open AccessArticle

Mode Propagation of Elliptical Perfect Optical Vortex in Turbulent Oceanic Channel

by Xiaowan Peng, Lin Yu, Yong Zhao and Lifa Hu

Photonics 2025, 12(9), 912; https://doi.org/10.3390/photonics12090912 - 11 Sep 2025

Abstract

As extensions of circular symmetric vortex beams, elliptical vortex beams with more diverse field forms are worthy of attention. In this paper, we investigate the mode propagation characteristics of an elliptical perfect optical vortex (EPOV) beam in oceanic turbulence. The theoretical model is [...] Read more.

As extensions of circular symmetric vortex beams, elliptical vortex beams with more diverse field forms are worthy of attention. In this paper, we investigate the mode propagation characteristics of an elliptical perfect optical vortex (EPOV) beam in oceanic turbulence. The theoretical model is constructed to analyze the detection probability of orbital angular momentum mode and average capacity at the receiver. The results reveal that the self-focusing property of the EPOV beam is able to improve propagation performance. By changing the elliptical scaling factor and the ratio of ring radius to width, the self-focusing effect is adjustable. The smaller elliptical scaling factor and ring radius to width ratio are beneficial for short-range transmission, while the larger ones are better for long-range transmission. Furthermore, the impacts of oceanic temperature and salinity in wide variation ranges are analyzed by use of the oceanic turbulence optical power spectrum. Higher capacity is obtained when the EPOV beam propagates in low-temperature and low-salinity oceanic channel. The research is referable for the design of underwater communication systems. Full article

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20 pages, 15205 KB

Open AccessArticle

19 × 1 Photonic Lantern for Mode Conversion: Simulation and Adaptive Control for Enhanced Mode Output Quality

by Pengfei Liu, Yuxuan Ze, Hanwei Zhang, Baozhu Yan, Qiong Zhou, Dan Zhang, Yimin Yin and Wenguang Liu

Photonics 2025, 12(9), 911; https://doi.org/10.3390/photonics12090911 - 11 Sep 2025

Abstract

High-order linear polarization (LP) modes and vortex beams carrying orbital angular momentum (OAM) are highly useful in various fields. High-order LP modes provide higher thresholds for nonlinear effects, reduced sensitivity to distortions, and better energy extraction in high-power lasers. OAM beams are useful [...] Read more.

High-order linear polarization (LP) modes and vortex beams carrying orbital angular momentum (OAM) are highly useful in various fields. High-order LP modes provide higher thresholds for nonlinear effects, reduced sensitivity to distortions, and better energy extraction in high-power lasers. OAM beams are useful in optical communication, imaging, particle manipulation, and fiber sensing. The ability to switch between these mode outputs enhances system versatility and adaptability, supporting advanced applications both in research and industry. This paper presents the design of a 19 × 1 photonic lantern capable of outputting 19 LP modes and 16 OAM modes with low loss. Using the beam propagation method, we simulated and analyzed the mode evolution process and insertion loss, and we calculated the transmission matrix of the photonic lantern. The results indicate that the designed device can efficiently evolve into these modes with a maximum insertion loss not exceeding 0.07 dB. Furthermore, an adaptive control system was developed by introducing a mode decomposition system at the output and combining it with the Stochastic Parallel Gradient Descent (SPGD) + basin hopping algorithm. Simulation results show that this system can produce desired modes with over 90% mode content, demonstrating promising application prospects in switchable high-order mode systems. Full article

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

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26 pages, 3254 KB

Open AccessArticle

Inverse Design of Tunable Graphene-Based Terahertz Metasurfaces via Deep Neural Network and SHADE Algorithm

by Siyu Chen, Junyi Lin, Jingchun Sun and Xue-Shi Li

Photonics 2025, 12(9), 910; https://doi.org/10.3390/photonics12090910 - 10 Sep 2025

Abstract

The terahertz (THz) frequency range holds critical importance for next-generation, wireless communications and biomedical sensing applications. However, conventional metamaterial design approaches suffer from computationally intensive simulations and optimization processes that can extend over several months. This work presents an intelligent inverse design framework [...] Read more.

The terahertz (THz) frequency range holds critical importance for next-generation, wireless communications and biomedical sensing applications. However, conventional metamaterial design approaches suffer from computationally intensive simulations and optimization processes that can extend over several months. This work presents an intelligent inverse design framework integrating deep neural network (DNN) surrogate modeling with success-history-based adaptive differential evolution (SHADE) for tunable graphene-based THz metasurfaces. Our DNN surrogate model achieves an exceptional coefficient of determination (R² = 0.9984) while providing a four-order-of-magnitude acceleration compared with conventional electromagnetic solvers. The SHADE-integrated framework demonstrates 96.7% accuracy in inverse design tasks with an average convergence time of 10.2 s. The optimized configurations exhibit significant tunability through graphene Fermi level modulation, as validated by comprehensive electromagnetic field analysis. This framework represents a significant advancement in automated electromagnetic design and establishes a robust foundation for intelligent photonic systems across diverse frequency regimes. Full article

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10 pages, 2316 KB

Open AccessCommunication

Highly Sensitive Light Guide Sensor for Multilocation and Multimodal Deformation Decoupling Using Flexible OLED

by Hayoon Lee, Hyeon Seok An and Jongwook Park

Photonics 2025, 12(9), 909; https://doi.org/10.3390/photonics12090909 - 10 Sep 2025

Abstract

This work proposes a highly sensitive optical sensor system that compensates for joint fragility by combining a flexible organic light-emitting diode (FOLED) with a stretchable light guide, and its performance was systematically evaluated. The developed sensor, leveraging the high flexibility of OLEDs, was [...] Read more.

This work proposes a highly sensitive optical sensor system that compensates for joint fragility by combining a flexible organic light-emitting diode (FOLED) with a stretchable light guide, and its performance was systematically evaluated. The developed sensor, leveraging the high flexibility of OLEDs, was capable of detecting mechanical deformations in various positions and forms in real time and could distinguish up to seven independent signals without electromagnetic interference. Under repeated 50% tensile strain, the device sustained 130,000 cycles, and during the 75° bending test, all three configurations—single line, serpentine, and serpentine with bump—exhibited stable performance for a minimum of 80,000 cycles. The sensor system developed in this study holds promise for future applications in wearable electronics and robotics. Full article

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

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8 pages, 2273 KB

Open AccessCommunication

Iridescence and Luminescence from Opal Matrices for Show Business

by Nikolai V. Gaponenko, Svetlana M. Kleshcheva, Ekaterina I. Lashkovskaya, Uladzimir A. Zaitsau, Vladimir A. Labunov, Bashar Z. S. Hamadneh, Vadim D. Zhivulko, Alexander V. Mudryi, Yuriy V. Radyush, Nikolai I. Kargin and Tamara F. Raichenok

Photonics 2025, 12(9), 908; https://doi.org/10.3390/photonics12090908 - 10 Sep 2025

Abstract

The paper reports on obtaining visually appealing images from opal matrices to artificial samples comprising regular packing of monodisperse silica globules. We show the images of iridescence, photoluminescence, and both of them simultaneously, exciting upconversion luminescence of Er³⁺ ions from BaTiO₃ [...] Read more.

The paper reports on obtaining visually appealing images from opal matrices to artificial samples comprising regular packing of monodisperse silica globules. We show the images of iridescence, photoluminescence, and both of them simultaneously, exciting upconversion luminescence of Er³⁺ ions from BaTiO₃ xerogel/opal matrix. Opal matrix with BaTiO₃ xerogel doped with Er³⁺ and Yb³⁺ ions demonstrates upconversion luminescence under excitation with the wavelength 980 nm of the laser with the main bands ranging from 500 to 570 nm and 640–700 nm, corresponding to the transitions from the excited states ²H_11/2, ⁴S_3/2, ⁴F_9/2, ⁴I_9/2 to the ground state ⁴I_15/2 of trivalent Er ions. In our view, the synthesis of opal matrices along with the generation of luminescent xerogels doped, for example, with trivalent lanthanides, is a promising approach for obtaining colorful images, always very individual and often very attractive, bringing joy and pleasure at concerts and other show business events. Full article

(This article belongs to the Special Issue Photonic Crystals and Materials with Tunable Luminescence for Show Business)

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23 pages, 5665 KB

Open AccessArticle

Ultra-Broadband Solar Absorber Design Covering UV to NIR Range Based on Cr–SiO₂ Metamaterial Planar Stacked Structures

by Wei-Ling Hsu, Xin-Yu Lin, Chia-Min Ho, Cheng-Fu Yang and Kuei-Kuei Lai

Photonics 2025, 12(9), 907; https://doi.org/10.3390/photonics12090907 - 10 Sep 2025

Abstract

This paper presents the design of an ultrabroadband solar absorber, developed using a metamaterial stack composed of only two materials, consisting of alternating layers of Cr and SiO₂. Starting with a Cr layer as the substrate, multiple pairs of Cr and [...] Read more.

This paper presents the design of an ultrabroadband solar absorber, developed using a metamaterial stack composed of only two materials, consisting of alternating layers of Cr and SiO₂. Starting with a Cr layer as the substrate, multiple pairs of Cr and SiO₂ were stacked sequentially, where one Cr layer and one SiO₂ layer constitute a single pair. To further enhance performance, a cylindrical Cr structure was added to the top. A key innovation of this work lay in its material simplicity and cost efficiency, relying solely on two inexpensive materials, Cr and SiO₂. Additionally, the inclusion of the top Cr cylinder was found to significantly enhance absorptivity. Simulations demonstrate that removing this feature led to a noticeable reduction in absorptivity of approximately 10% across the 500–2000 nm wavelength range. Another important finding is the effect of the number of Cr–SiO₂ pairs on absorption behavior. When the number of pairs increases from four to five, the average absorptivity decreases slightly, but the absorption bandwidth is notably broadened. Further increasing six pairs resulted in a marginal increase in bandwidth, while maintaining the average absorptivity. Moreover, a low-absorptivity dip at 360 nm was slightly mitigated, rising to approximately 0.900. Based on these insights, a six-pair metamaterial structure was chosen for further optimization. Utilizing COMSOL Multiphysics^® simulation software (version 6.0), the absorber was successfully engineered to achieve high performance across an exceptionally broad spectral range, from 200 nm to 2160 nm. Under optimal design parameters, it exhibited an average absorptivity of 0.950, with absorptivity consistently exceeding 0.900 throughout this range. This demonstrates the absorber’s strong potential for efficient solar energy harvesting using a structurally simple and cost-effective design. Full article

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

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15 pages, 6498 KB

Open AccessArticle

A Ring-Core Anti-Resonant Photonic Crystal Fiber Supporting 90 Orbital Angular Momentum Modes

by Huimin Shi, Linghong Jiang, Chao Wang, Junjun Wu, Limian Ren and Pan Wang

Photonics 2025, 12(9), 906; https://doi.org/10.3390/photonics12090906 - 10 Sep 2025

Abstract

To address the issues of limited orbital angular momentum (OAM) mode count, poor transmission quality, and complex cladding structures in ring-core photonic crystal fibers, a novel OAM-supporting ring-core anti-resonant photonic crystal fiber is designed. This fiber features a high-index-doped ring-core surrounded by a [...] Read more.

To address the issues of limited orbital angular momentum (OAM) mode count, poor transmission quality, and complex cladding structures in ring-core photonic crystal fibers, a novel OAM-supporting ring-core anti-resonant photonic crystal fiber is designed. This fiber features a high-index-doped ring-core surrounded by a three-layer anti-resonant nested tube cladding. Numerical simulations based on the finite element method indicate that the designed fiber has the ability to reliably transmit up to 90 OAM modes within the wavelength range of 1530–1620 nm. Additionally, this fiber demonstrates outstanding performance characteristics, achieving a peak effective refractive index difference of 0.0041 while maintaining remarkably low confinement loss between 10⁻¹² dB/m and 10⁻⁸ dB/m. The minimum effective mode field area is 101.41 μm², and the maximum nonlinear coefficient is 1.05 W⁻¹·km⁻¹. The dispersion is flat, with a minimum dispersion variation of merely 0.5394 ps/(nm·km). The mode purity is greater than 98.5%, and the numerical aperture ranges from 0.0689 to 0.089. The designed OAM-supporting ring-core anti-resonant photonic crystal fiber has broad application prospects in long-haul optical communication and high-speed data transmission. Full article

(This article belongs to the Special Issue Optical Fiber Communication: Challenges and Opportunities)

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18 pages, 2185 KB

Open AccessReview

Research Progress on Aging Detection of Composite Insulators Based on Spectroscopy

by Junfei Nie, Yunpiao Cai, Jinke Chen, Furong Chen, Jiapei Cao, Quan Li and Zhenlin Hu

Photonics 2025, 12(9), 905; https://doi.org/10.3390/photonics12090905 - 10 Sep 2025

Abstract

The safety of composite insulators in high-voltage transmission lines is directly related to the stable operation of the power system, which is a fundamental condition for the normal functioning of people’s lives and industrial production. Composite insulators are exposed to outdoor conditions for [...] Read more.

The safety of composite insulators in high-voltage transmission lines is directly related to the stable operation of the power system, which is a fundamental condition for the normal functioning of people’s lives and industrial production. Composite insulators are exposed to outdoor conditions for extended periods of time, and with the increase in service life, they are subjected to aging due to external environmental factors and electrical stresses. This aging leads to a decline in their electrical insulation, mechanical properties, and other performance, which, in severe cases, may result in power system failures. Therefore, accurate assessment and detection of the aging status of composite insulators are particularly important. Traditional detection methods such as visual inspection, hardness testing, and hydrophobicity testing have limitations, including single functionality and susceptibility to environmental interference, which cannot comprehensively and accurately reflect the aging condition of the insulators. In recent years, spectroscopy-based detection technologies have been increasingly applied for the rapid detection of composite insulators due to their advantages, such as high sensitivity, non-contact measurement, and multi-dimensional information extraction. Common spectroscopic detection methods include Ultraviolet Discharge (UV Discharge), Fourier Transform Infrared (FTIR) Spectroscopy, Raman Spectroscopy (RS), Hyperspectral Imaging (HSI), Laser-Induced Breakdown Spectroscopy (LIBS), and Terahertz (THz) Spectroscopy. These methods offer non-contact, remote, and rapid capabilities, enabling detailed analysis of the insulator’s surface microstructure, chemical composition, and aging characteristics. This paper introduces = spectroscopy-based methods for detecting the aging status of composite insulators, analyzing the advantages and limitations of these methods, and discussing the challenges of their industrial application. Furthermore, the paper reviews the research progress and practical applications of spectroscopic techniques in the evaluation of insulator aging status, systematically summarizing important achievements in the field and providing an outlook for future developments. Full article

(This article belongs to the Special Issue Advanced Optical Measurement Spectroscopy and Imaging Technologies)

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30 pages, 4237 KB

Open AccessArticle

On the “Bi-Phase” of Fluorescence to Scattering with Single-Fiber Illumination and Detection: A Quasi-Analytical Photon-Transport Approach Operated with Center-Illuminated Area Detection

by Daqing Piao

Photonics 2025, 12(9), 904; https://doi.org/10.3390/photonics12090904 - 9 Sep 2025

Abstract

Bi-phasic (with a local minimum) response of fluorescence to scattering when probed by a single fiber (SF) was first observed in 2003. Subsequent experiments and Monte Carlo studies have shown the bi-phasic turning of SF fluorescence to occur at a dimensionless reduced scattering [...] Read more.

Bi-phasic (with a local minimum) response of fluorescence to scattering when probed by a single fiber (SF) was first observed in 2003. Subsequent experiments and Monte Carlo studies have shown the bi-phasic turning of SF fluorescence to occur at a dimensionless reduced scattering of ~1 and vary with absorption. The bi-phase of SF fluorescence received semi-empirical explanations; however, better understandings of the bi-phase and its dependence on absorption are necessary. This work demonstrates a quasi-analytical projection of a bi-phasic pattern comparable to that of SF fluorescence via photon-transport analyses of fluorescence in a center-illuminated-area-detection (CIAD) geometry. This model-approach is principled upon scaling of the diffuse fluorescence between CIAD and a SF of the same size of collection, which expands the scaling of diffuse reflectance between CIAD and a SF discovered for steady-state and time-domain cases. Analytical fluorescence for CIAD is then developed via radial-integration of radially resolved fluorescence. The radiance of excitation is decomposed to surface, collimated, and diffusive portions to account for the surface, near the point-of-entry, and diffuse portion of fluorescence associated with a centered illumination. Radiative or diffuse transport methods are then used to quasi-analytically deduce fluorescence excited by the three portions of radiance. The resulting model of fluorescence for CIAD, while limiting to iso-transport properties at the excitation and emission wavelengths, is compared against the semi-empirical model for SF, revealing bi-phasic turning [0.5~2.6] at various geometric sizes [0.2, 0.4, 0.6, 0.8, 1.0 mm] and a change of three orders of magnitude in the absorption of the background medium. This model projects a strong reduction in fluorescence versus strong absorption at high scattering, which differs from the semi-empirical SF model’s projection of a saturating pattern unresponsive to further increases in the absorption. This framework of modeling fluorescence may be useful to project frequency-domain and lifetime pattens of fluorescence in an SF and CIAD. Full article

(This article belongs to the Section Biophotonics and Biomedical Optics)

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13 pages, 3431 KB

Open AccessArticle

Design of Grating-Embedded Tantalum Pentoxide Microring Resonators with Piezoelectric Tunability

by Jiazhao He, Mingjian You, Zhenyu Liu, Junke Zhou, Ning Ding, Ziming Zhang, Zhengqi Li, Xingyu Tang, Weiren Cheng, Jiaxin Hou, Shangyu Wang and Qiancheng Zhao

Photonics 2025, 12(9), 903; https://doi.org/10.3390/photonics12090903 - 9 Sep 2025

Abstract

Stimulated Brillouin scattering (SBS) in microresonators offers a unique way to develop narrow-linewidth chip-scale lasers. Yet their coherence performance is hindered by the cascaded SBS process, which clamps the output power and broadens the fundamental linewidth of the first-order Stokes wave. Resonance splitting [...] Read more.

Stimulated Brillouin scattering (SBS) in microresonators offers a unique way to develop narrow-linewidth chip-scale lasers. Yet their coherence performance is hindered by the cascaded SBS process, which clamps the output power and broadens the fundamental linewidth of the first-order Stokes wave. Resonance splitting proves to be an effective approach to suppress intracavity SBS cascading. However, precisely aligning and controlling the resonance splitting behavior remains challenging. We address these issues by proposing a piezoelectrically actuated grating-embedded tantalum pentoxide (Ta₂O₅) microring resonator. This microresonator comprises a Bragg grating segment that induces a counter-propagating wave and a ring segment that is integrated with a lead zirconate titanate (PZT) actuator. The half-circumference Bragg grating has a peak reflectivity of 31% at 1549.8 nm and a bandwidth of 88.89 pm, which is narrow enough to ignite resonance splitting in only one azimuthal mode. The PZT actuator empowers the resonator with a frequency tuning rate of 0.1726 GHz/V, particularly useful for post-fabrication compensation and splitting control. The proposed architecture offers a promising solution to breaking the intracavity cascaded SBS chain with frequency tuning capability, paving the way towards highly coherent chip-scale laser sources. Full article

(This article belongs to the Special Issue Integrated Waveguide-Based Photonic Devices)

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16 pages, 3496 KB

Open AccessArticle

A CMOS Bandgap-Based VCSEL Driver for Temperature-Robust Optical Applications

by Juntong Li and Sung-Min Park

Photonics 2025, 12(9), 902; https://doi.org/10.3390/photonics12090902 - 9 Sep 2025

Abstract

This paper presents a temperature-robust current-mode vertical-cavity surface-emitting laser (VCSEL) driver (or CMVD) fabricated in a standard 180 nm CMOS process. While prior art relies on conventional current-mirror circuits for bias generation, the proposed CMVD integrates a bandgap-based biasing architecture to achieve high [...] Read more.

This paper presents a temperature-robust current-mode vertical-cavity surface-emitting laser (VCSEL) driver (or CMVD) fabricated in a standard 180 nm CMOS process. While prior art relies on conventional current-mirror circuits for bias generation, the proposed CMVD integrates a bandgap-based biasing architecture to achieve high thermal stability and process insensitivity. The bandgap core yields a temperature-compensated reference voltage and is then converted into both stable bias and modulation currents through a cascode current-mirror and switching logic. Post-layout simulations of the proposed CMVD show that the reference voltage variation remains within ±2%, and the bias current deviation is under 10% across full PVT conditions. Furthermore, the output current variation is limited to 7.4%, even under the worst-case corners (SS, 125 °C), demonstrating the reliability of the proposed architecture. The implemented chip occupies a compact core area of 0.0623 mm² and consumes an average power of 18 mW from a single 3.3 V supply, suggesting that the bandgap-stabilized CMVD is a promising candidate for compact, power-sensitive optical systems requiring reliable and temperature-stable performance. Full article

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

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16 pages, 2189 KB

Open AccessArticle

Analysis of Radiative Transfer Characteristics of a Spherical Continuous-Spectrum Light Source Under Rainfall Conditions

by Zhenfeng Li, Yinjun Gao, Xianghua Zhang, Yu Lei and Hui Yan

Photonics 2025, 12(9), 901; https://doi.org/10.3390/photonics12090901 - 9 Sep 2025

Abstract

The current research on light transmission under rainfall conditions primarily focuses on monochromatic converging light sources, and the related conclusions cannot be directly applied to spherical continuous-spectrum light sources (SCLSs). Based on the Lorenz–Mie scattering method, this study calculated the optical parameters of [...] Read more.

The current research on light transmission under rainfall conditions primarily focuses on monochromatic converging light sources, and the related conclusions cannot be directly applied to spherical continuous-spectrum light sources (SCLSs). Based on the Lorenz–Mie scattering method, this study calculated the optical parameters of Gamma-distributed rainfall across three rainfall types and four intensity levels. A numerical algorithm model for radiative transfer under rainfall conditions was established for SCLSs. The effects of rainfall type, rainfall intensity, and light wavelength on radiative transfer were analyzed. Key conclusions include the following: when rainfall intensity is below moderate, the type of rainfall can be disregarded. However, for heavy to torrential rain, distinct differences between stratiform and non-stratiform rainfall must be considered. The attenuation caused by rainfall intensity does not increase linearly. Specifically, attenuation during moderate rain is lower than that in light rain, while heavy and torrential rain exhibit greater attenuation than both light and moderate rain. Wavelength bands significantly influence radiative transfer. Efforts to optimize the attenuation of radiative energy by rainfall should focus on the primary energy bands where most energy is concentrated. These findings highlight the importance of considering rainfall classification, nonlinear attenuation mechanisms, and wavelength-specific characteristics when evaluating radiative transfer under varying rainfall conditions. Full article

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25 pages, 5513 KB

Open AccessArticle

Ptycho-LDM: A Hybrid Framework for Efficient Phase Retrieval of EUV Photomasks Using Conditional Latent Diffusion Models

by Suman Saha, Paolo Ansuinelli, Luis Barba, Iacopo Mochi and Benjamín Béjar Haro

Photonics 2025, 12(9), 900; https://doi.org/10.3390/photonics12090900 - 8 Sep 2025

Abstract

Extreme ultraviolet (EUV) photomask inspection is a critical step in semiconductor manufacturing, requiring high-resolution, high-throughput solutions to detect nanometer-scale defects. Traditional actinic imaging systems relying on complex optics have a high cost of ownership and require frequent upgrades. An alternative is lensless imaging [...] Read more.

Extreme ultraviolet (EUV) photomask inspection is a critical step in semiconductor manufacturing, requiring high-resolution, high-throughput solutions to detect nanometer-scale defects. Traditional actinic imaging systems relying on complex optics have a high cost of ownership and require frequent upgrades. An alternative is lensless imaging techniques based on ptychography, which offer high-fidelity reconstruction but suffer from slow throughput and high data demands. In particular, the ptychographic standard solver—the iterative Difference Map (DifMap) algorithm—requires many measurements and iterations to converge. We propose Ptycho-LDM, a hybrid framework integrating DifMap with a conditional Latent Diffusion Model for rapid and accurate phase retrieval. Ptycho-LDM alleviates high data acquisition demand by leveraging data-driven priors while offering improved computational efficiency. Our method performs coarse object retrieval using a resource-constrained reconstruction from DifMap and refines the result using a learned prior over photomask patterns. This prior enables high-fidelity reconstructions even in measurement-limited regimes where DifMap alone fails to converge. Experiments on actinic patterned mask inspection (APMI) show that Ptycho-LDM recovers fine structure and defect details with far fewer probe positions, surpassing the DifMap in accuracy and speed. Furthermore, evaluations on both noisy synthetic data and real APMI measurements confirm the robustness and effectiveness of Ptycho-LDM across practical scenarios. By combining generative modeling with physics-based constraints, Ptycho-LDM offers a promising scalable, high-throughput solution for next-generation photomask inspection. Full article

(This article belongs to the Special Issue Computational Imaging for Semiconductor Devices Metrology Applications)

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9 pages, 1605 KB

Open AccessArticle

Enhancement of High-Order Harmonic Generation by Suppressing Quantum Diffusion of the Electron Wavepacket

by Meiyan Qin, Xiaosong Zhu, Shaolin Ke, Xiaofan Zhang and Qing Liao

Photonics 2025, 12(9), 899; https://doi.org/10.3390/photonics12090899 - 7 Sep 2025

Viewed by 215

Abstract

High-order harmonic generation with mid-infrared laser fields has been considered the most promising method to produce soft X-rays attosecond pulses, which provides an important tool for probing the ultrafast electronic dynamics in atoms, molecules, and solids in real time. However, quantum diffusion of [...] Read more.

High-order harmonic generation with mid-infrared laser fields has been considered the most promising method to produce soft X-rays attosecond pulses, which provides an important tool for probing the ultrafast electronic dynamics in atoms, molecules, and solids in real time. However, quantum diffusion of the electron wavepacket can lead to a dramatic drop of the harmonic yield when a mid-infrared laser field is used. Here we theoretically demonstrate that a spatially structured (SS) laser field can suppress quantum diffusion of the electron wavepacket and lead to a significant enhancement of high-order harmonic generation, compared with those generated by the spatially homogeneous (SH) laser field. The SS laser field is inhomogeneous in transverse direction perpendicular to the laser polarization and homogeneous in the polarization direction of the laser field. The electric field presents a valley structure. It is found that this valley structure can confine the electron wavepacket around the parent ion, prevent the electron wavepacket spreading, and finally lead to the significant enhancement of the high-order harmonics. Our results provide a novel method for controlling the ultrafast electron wavepacket dynamics of HHG. Full article

(This article belongs to the Special Issue Advanced Photonic Sensing Technologies for Optical Fiber Devices)

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16 pages, 12711 KB

Open AccessArticle

Self-Learning-Based Fringe Domain Conversion for 3D Surface Measurement of Translucent Objects at the Mesoscopic Scale

by Wenqing Su, Tao Zou, Huankun Chen, Haipeng Niu, Zhaoshui He, Yumei Zhao, Zhuyun Chen and Ji Tan

Photonics 2025, 12(9), 898; https://doi.org/10.3390/photonics12090898 - 7 Sep 2025

Viewed by 197

Abstract

Three-dimensional measurement of translucent objects using structured light techniques remained fundamentally challenging due to severe degradation of fringe patterns caused by subsurface scattering, which inevitably introduced phase errors and compromised measurement accuracy. Although deep learning had emerged as a powerful tool for fringe [...] Read more.

Three-dimensional measurement of translucent objects using structured light techniques remained fundamentally challenging due to severe degradation of fringe patterns caused by subsurface scattering, which inevitably introduced phase errors and compromised measurement accuracy. Although deep learning had emerged as a powerful tool for fringe analysis, its practical implementation was hindered by the impractical requirement for large-scale labeled datasets, particularly in scattering-dominant measurement scenarios. To overcome these limitations, we developed a self-learning-based fringe domain conversion method inspired by image style transfer principles, where degraded and ideal fringe patterns were treated as distinct domains for cyclic translation. The proposed framework employed dual generators and discriminators to establish cycle-consistency constraints while incorporating both numerical intensity-based and physical phase-derived optimization targets, effectively suppressing phase errors and improving fringe modulation without requiring paired training data. Experimental validation demonstrated superior performance in reconstructing high-fidelity 3D morphology of translucent objects, establishing this approach as a robust solution for precision metrology of complex scattering media. Full article

(This article belongs to the Special Issue Advancements in Optical Metrology and Imaging)

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11 pages, 2289 KB

Open AccessArticle

Reconfigurable High-Efficiency Power Dividers Using Waveguide Epsilon-Near-Zero Media for On-Demand Splitting

by Lin Jiang, Qi Hu and Yijun Feng

Photonics 2025, 12(9), 897; https://doi.org/10.3390/photonics12090897 - 6 Sep 2025

Viewed by 252

Abstract

Although epsilon-near-zero (ENZ) media have emerged as a promising platform for power dividers, the majority of existing designs are confined to fixed power splitting. In this work, two dynamically tunable power dividers using waveguide ENZ media are proposed by precisely modulating the internal [...] Read more.

Although epsilon-near-zero (ENZ) media have emerged as a promising platform for power dividers, the majority of existing designs are confined to fixed power splitting. In this work, two dynamically tunable power dividers using waveguide ENZ media are proposed by precisely modulating the internal magnetic field and the widths of the output waveguides. The first approach features a mechanically reconfigurable ring-shaped ENZ waveguide. By continuously re-distributing the magnetic field within the ENZ tunneling channels utilizing rotatable copper plates, arbitrary power division among multiple output ports is constructed. The second design integrates a rectangular-loop ENZ cavity into a substrate-integrated waveguide, with four positive–intrinsic–negative diodes embedded to dynamically activate specific output ports. This configuration steers electromagnetic energy toward output ports with varying cross-sectional areas, enabling on-demand control over both the power division and the number of output ports. Both analytical and full-wave simulation results confirm dynamic power division, with transmission efficiencies exceeding 93%. Despite differences in structure and actuation mechanisms, both designs exhibit flexible field control, high reconfigurability, and excellent transmission performance, highlighting their potential in advanced applications such as real-time wireless communications, multi-input–multi-output systems, and reconfigurable antennas. Full article

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

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15 pages, 8241 KB

Open AccessArticle

Low-Loss 795 nm Electro-Optic Modulators

by Xutong Lu, Xiyao Song, Ruixiang Song, Jiaqi Cui, Shuaihong Qi, Zhangyuan Chen and Yanping Li

Photonics 2025, 12(9), 896; https://doi.org/10.3390/photonics12090896 - 6 Sep 2025

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Abstract

Electro-optic modulators in the near-infrared spectrum are finding applications in atomic clocks, quantum sensing, quantum information processing, and high-precision measurement. We developed thin-film lithium niobate electro-optic modulators operating at 795 nm for modulation around the D₁ line of ⁸⁷Rb with satisfactory [...] Read more.

Electro-optic modulators in the near-infrared spectrum are finding applications in atomic clocks, quantum sensing, quantum information processing, and high-precision measurement. We developed thin-film lithium niobate electro-optic modulators operating at 795 nm for modulation around the D₁ line of ⁸⁷Rb with satisfactory overall performance. Specifically, we made a systematic improvement to reduce the insertion loss, including widening the modulation waveguides, thickening the overcladding, polishing and coating the facets. The fabricated device possesses a low insertion loss of 7.6 dB, an extinction ratio exceeding 30 dB, a 3 dB modulation bandwidth of ~22 GHz, a half-wave voltage-length product of ~1.8 Vcm, and strong adaptability for packaging. Full article

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13 pages, 2559 KB

Open AccessArticle

Generation of an Electromagnetic Jet Using a PTFE-Loaded WR90 Waveguide: Design and Characterization

by Antoine Deubaibe, M. Podda Abouna, Mathis Granger, Bernard Bayard and Bruno Sauviac

Photonics 2025, 12(9), 895; https://doi.org/10.3390/photonics12090895 - 5 Sep 2025

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Abstract

We present a compact dielectric lens integrated at the aperture of a WR90 rectangular waveguide, achieved using polytetrafluoroethylene (PTFE). This innovative configuration enables, for the first time in the X- and Ku-bands, the direct generation of a subwavelength electromagnetic jet from a guided [...] Read more.

We present a compact dielectric lens integrated at the aperture of a WR90 rectangular waveguide, achieved using polytetrafluoroethylene (PTFE). This innovative configuration enables, for the first time in the X- and Ku-bands, the direct generation of a subwavelength electromagnetic jet from a guided structure. The beam exhibits the hallmark features of an electromagnetic jet: strong near-field focusing, a subwavelength beam width surpassing the diffraction limit, and a quasi-planar wavefront sustained over a propagation distance of about

2 λ

. The lens design was systematically optimized, and its performance was assessed through full-wave finite element simulations and experimentally validated on a fabricated prototype. Excellent agreement between the simulation and measurement confirms the robustness of the approach. Beyond its simplicity and low cost, this solution achieves state-of-the-art focusing performance compared to free-space and guided-wave alternatives. It offers strong potential for applications in high-resolution imaging, precision sensing, and material characterization, particularly in opaque or highly lossy environments. Full article

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14 pages, 4679 KB

Open AccessArticle

Rapid Dynamic Separation of Radial and Azimuthal Polarization Components in Circular Airy Vortex Beams via Linear Electro-Optic Effect in Uniaxial Crystals

by Guoliang Zheng, Tiefeng He, Zikun Xu, Jiawen Li, Xuhui Zhang, Lili Wan and Qingyang Wu

Photonics 2025, 12(9), 894; https://doi.org/10.3390/photonics12090894 - 5 Sep 2025

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Abstract

This paper presents a rapid approach for the dynamic separation of radial polarization (R-pol) and azimuthal polarization (A-pol) components in circular Airy vortex beams (CAVBs) by utilizing the linear electro-optic (EO) effect in uniaxial crystals. By applying an external electric field along the [...] Read more.

This paper presents a rapid approach for the dynamic separation of radial polarization (R-pol) and azimuthal polarization (A-pol) components in circular Airy vortex beams (CAVBs) by utilizing the linear electro-optic (EO) effect in uniaxial crystals. By applying an external electric field along the z-axis of a strontium barium niobate (SBN) crystal, tunable spatial separation of the R-pol and A-pol components is achieved. Under positive electric fields, the crystal maintains negative uniaxial properties with increased birefringence, extending the focal separation distance. Conversely, negative electric fields initially reduce the birefringence of the crystal; further increases in negative field strength will transition the crystal to a positive uniaxial state, subsequently enhancing birefringence and restoring focal separation. Experimental simulations demonstrate a focal separation of 1.4 mm at ±15 kV/mm, with R-pol focusing first at +15 kV/mm and A-pol preceding at −15 kV/mm. The polarization distributions at the foci confirm the successful separation of the two components. This approach overcomes the static limitation of conventional polarization splitters in separating R-pol and A-pol components, showing significant potential for optical manipulation, high-resolution imaging, and quantum information processing. Full article

(This article belongs to the Section Optical Interaction Science)

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13 pages, 2440 KB

Open AccessArticle

High-Fidelity Long-Haul Microwave Photonic Links with Composite OPLLs and Multi-Core Fiber for Secure Command and Control Systems in Contested Environments

by Yuanshuo Bai, Zhaochen Zhang, Weilin Xie, Yang Li, Teng Tian, Dachuan Yuan and Haokai Shen

Photonics 2025, 12(9), 893; https://doi.org/10.3390/photonics12090893 - 5 Sep 2025

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Abstract

Secure communication for critical command nodes has emerged as a pivotal challenge in modern warfare, in particular considering the vulnerability of these nodes to electronic reconnaissance. To cope with the severe interference, this paper proposes a robust solution for long-distance secure command and [...] Read more.

Secure communication for critical command nodes has emerged as a pivotal challenge in modern warfare, in particular considering the vulnerability of these nodes to electronic reconnaissance. To cope with the severe interference, this paper proposes a robust solution for long-distance secure command and control system leveraging phase-modulated microwave photonic links. Studies that analyze the impairing nonlinear distortions and phase noise stemming from different sources in optical phase demodulation during long-haul transmission has been carried out, unveiling their impairment in coherent transmission systems. To overcome these limitations, a linearized phase demodulation and noise suppression technique based on composite optical phase-locked loop and multi-core fiber is proposed and experimentally validated. Experimental results demonstrate a long-haul transmission over 100 km with an 81 dB suppression for third-order intermodulation distortion and a 27 dB improvement in noise floor at 5 MHz under closed-loop condition, verifying a significant enhancement in the fidelity in long-distance transmission. This method ensures a highly reliable secure communication for command and control systems in contested electromagnetic environments. Full article

(This article belongs to the Special Issue Photodetectors for Next-Generation Imaging and Sensing Systems)

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12 pages, 741 KB

Open AccessArticle

Implementation and Realistic Security of Unidimensional Modulation Continuous-Variable Quantum Key Distribution in Downstream Access Networks

by Pu Wang, Jianqiang Liu, Zengliang Bai, Liwei Chang and Yan Tian

Photonics 2025, 12(9), 892; https://doi.org/10.3390/photonics12090892 - 5 Sep 2025

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Abstract

To address the demand for low-cost deployment in quantum key distribution (QKD) networks, this study explores the implementation of unidimensional (UD) modulation continuous-variable quantum key distribution (CV-QKD) protocols within downstream access networks. The UD CV-QKD protocol employs a single modulator for information encoding, [...] Read more.

To address the demand for low-cost deployment in quantum key distribution (QKD) networks, this study explores the implementation of unidimensional (UD) modulation continuous-variable quantum key distribution (CV-QKD) protocols within downstream access networks. The UD CV-QKD protocol employs a single modulator for information encoding, offering benefits such as reduced implementation cost and lower random number consumption, which collectively decrease the overall setup expense of QKD systems. Through systematic performance analysis, it is demonstrated that the proposed UD modulation downstream access network scheme exhibits strong scalability and practical applicability. When supporting 32 users, the system maintains secure communication over transmission distances of up to 50 km. As the number of users increases to 64, performance declines slightly; however, the system still achieves a 35 km transmission distance, which remains suitable for many metropolitan access applications. Even in high-density access scenarios involving 128 users, the system sustains a positive key rate within a transmission range of 20 km. Furthermore, this study evaluates the protocol’s practical security under source intensity errors and finite-size effects. These results provide meaningful guidance for deploying low-cost, high-security quantum communication access networks and contribute to advancing QKD technologies toward scalable, real-world implementations. Full article

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9 pages, 1739 KB

Open AccessArticle

High-Responsivity Waveguide UTC Photodetector with 90 GHz Bandwidth for High-Speed Optical Communication

by Yu Zheng, Qin Han, Han Ye, Shuai Wang, Yimiao Chu, Liyan Geng and Junming An

Photonics 2025, 12(9), 891; https://doi.org/10.3390/photonics12090891 - 5 Sep 2025

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Abstract

A directly coupled waveguide uni-traveling carrier photodetector (UTC-PD) with high responsivity and broad bandwidth is demonstrated. The device’s epitaxial structure was carefully optimized via optical simulations to enhance quantum efficiency. Furthermore, the fabrication process was refined to introduce a vertically defined mushroom-shaped mesa [...] Read more.

A directly coupled waveguide uni-traveling carrier photodetector (UTC-PD) with high responsivity and broad bandwidth is demonstrated. The device’s epitaxial structure was carefully optimized via optical simulations to enhance quantum efficiency. Furthermore, the fabrication process was refined to introduce a vertically defined mushroom-shaped mesa structure, which effectively maintains high responsivity while facilitating further improvement in bandwidth performance. As a result, the fabricated device, without the use of an anti-reflection coating, simultaneously achieves a responsivity of 0.49 A/W and a 3 dB bandwidth of 90 GHz. Full article

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

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9 pages, 3923 KB

Open AccessArticle

High-Precision Angle Sensor Based on Angle Amplification via Double-Layer Regular Prism Structure

by Bai Zhang, Xixi Cao, Lihan Su, Zipeng Yin, Chunyan Zhou, Xueliang Kang and Yiwei Liu

Photonics 2025, 12(9), 890; https://doi.org/10.3390/photonics12090890 - 4 Sep 2025

Viewed by 246

Abstract

In this paper, a high-precision sensor for angle measurement with angle amplification based on the double-layer regular prisms structure was designed. The angle amplification was achieved by multiple reflections of the measurement laser between the inner and outer double-layer regular prism structure. The [...] Read more.

In this paper, a high-precision sensor for angle measurement with angle amplification based on the double-layer regular prisms structure was designed. The angle amplification was achieved by multiple reflections of the measurement laser between the inner and outer double-layer regular prism structure. The trajectory of the measurement laser within the double-layer regular prism structure was investigated, and a corresponding mathematical model was developed. A position-sensitive detector (PSD) measures displacement variations in the measurement laser and ultimately enables angle measurement by applying the displacement-to-angle conversion relationship derived from analysis of the reflection trajectory model. The sensor prototype achieved a measurement precision of ±0.5″. Additionally, the feasibility of the alternative measurement method using multiple measurement units was experimentally verified, while its measurement accuracy remained comparable to that of a single unit. The 360° angle measurement through proper arrangement of multiple PSDs can be achieved as well, and its feasibility has been discussed. Full article

(This article belongs to the Special Issue Optical Sensors and Devices)

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9 pages, 2158 KB

Open AccessCommunication

Ultrafast Laser Writing of In-Line Filters Based on MZI

by Longwang Xiu, Yanfei Liu, Xinyu Hu, Yuxi Pang and Xiangdong Cao

Photonics 2025, 12(9), 889; https://doi.org/10.3390/photonics12090889 - 4 Sep 2025

Viewed by 320

Abstract

In mode-locked fiber lasers and optical sensors, in-line filters are essential components. Fiber-core Mach–Zehnder interferometer (MZI) technology has garnered a lot of research interest for the several manufacturing techniques for in-line MZI filters. Although multi-line inscription is frequently needed in existing methods to [...] Read more.

In mode-locked fiber lasers and optical sensors, in-line filters are essential components. Fiber-core Mach–Zehnder interferometer (MZI) technology has garnered a lot of research interest for the several manufacturing techniques for in-line MZI filters. Although multi-line inscription is frequently needed in existing methods to attain enough waveguide width, this approach adds complexity to production and may result in compromised waveguide quality. In this work, we present an improved single-line direct-writing method that attains similar MZI filtering results to multi-line scan. Additionally, the MZI filter created with the modified single-line direct-writing technique has a smaller insertion loss and requires less direct-writing energy than the previous single-line direct-writing technique. A 516 μm long MZI-based in-line filter was successfully constructed. The results of the characterization showed a central loss dip at 1089.82 nm, a free-spectral range (FSR) of 141.36 nm, an extinction ratio of 19.69 dB, and an insertion loss of 1.122 dB. This method decreased the insertion loss by a factor of 2.7 for an identical extinction ratio and improved the direct-writing efficiency by a factor of 9 for an equivalent FSR with multi-line scan. There was consistency between the experimental and simulation results. We also took measurements of the MZI’s temperature sensitivity. This work shows notable improvements in waveguide quality and ease of manufacture. This accomplishment lays the groundwork for further advancements in integrated mode-locked fiber laser technology. Full article

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20 pages, 37629 KB

Open AccessArticle

Design of a Modified Moiré Varifocal Metalens Based on Fresnel Principles

by Di Chang, Shuiping Sun, Lieshan Zhang and Xueyan Li

Photonics 2025, 12(9), 888; https://doi.org/10.3390/photonics12090888 - 3 Sep 2025

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Abstract

This paper proposes a Fresnel-based Modified Moiré Varifocal Metalens (MMVL) addressing the inherent defocus at 0° rotation and significant focal quality degradation during varifocal operation in Traditional Moiré Varifocal Metalenses (TMVLs). The transmission function of the Fresnel-modified Moiré metalens combines a static term [...] Read more.

This paper proposes a Fresnel-based Modified Moiré Varifocal Metalens (MMVL) addressing the inherent defocus at 0° rotation and significant focal quality degradation during varifocal operation in Traditional Moiré Varifocal Metalenses (TMVLs). The transmission function of the Fresnel-modified Moiré metalens combines a static term with a dynamic term, allowing the MMVLs to effectively overcome these limitations. Meanwhile, to minimize energy losses arising from polarization conversion and diffraction between the two metalenses, the nano-units on the metalenses are optimized by Particle Swarm Optimization (PSO) with FDTD simulations, maximizing the polarization conversion efficiency and transmittance. The simulation results demonstrate superior focal quality and stability in the MMVL throughout full rotational cycles, with super-diffraction-limited focusing maintained across all varifocal states. MMVLs have advantages in robustness; under axial distance variation (d = 0–20

d_{0}

, 0–3 μm), they maintain on-axis focus without deviation; with centering error (p = 0–10

p_{0}

, 0–3 μm), they sustain a clear focus at >36% efficiency. These results confirm that MMVLs have enhanced tolerance to manufacturing/assembly errors compared to TMVLs, delivering significantly stabilized optical performance. This advancement enables new possibilities for integrated micro-optics and optical tweezer applications. Full article

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17 pages, 4501 KB

Open AccessArticle

Highly Sensitive SNS Structure Fiber Liquid-Sealed Temperature Sensor with PVA-Based Cladding for Large Range

by Si Cheng, Chuan Tian, Xiaolei Bai and Zhiyu Zhang

Photonics 2025, 12(9), 887; https://doi.org/10.3390/photonics12090887 - 3 Sep 2025

Viewed by 266

Abstract

A liquid-sealed single-mode–no-core–single-mode (SNS) structure fiber temperature sensor based on polyvinyl alcohol (PVA) partial replacement coating is proposed. Using a liquid-sealed glass capillary structure, the PVA solution is introduced into the SNS structure and avoids its influence by environmental humidity. Temperature can be [...] Read more.

A liquid-sealed single-mode–no-core–single-mode (SNS) structure fiber temperature sensor based on polyvinyl alcohol (PVA) partial replacement coating is proposed. Using a liquid-sealed glass capillary structure, the PVA solution is introduced into the SNS structure and avoids its influence by environmental humidity. Temperature can be obtained by measuring the shift of the multimode interference spectrum, which is affected by the thermal optical effect of the PVA solution. Through theoretical simulation of the sensor, the optimal NCF fiber length and coating stripped length are obtained by comprehensively considering the transmitted loss and output spectrum signal-to-noise ratio (SNR). The optimal PVA solution concentration is selected by measuring the thermo-optic coefficient (TOC) and refractive index (RI). Based on the theoretical optimization results, a PVA solution-coated SNS fiber optic temperature sensor is experimentally fabricated, and temperature-sensing characteristics are measured within −3.6 to 73.2 °C. The experimental results show that the sensor has a high sensitivity (nm/°C, maximum is 21.713 nm/°C) and has a resolution of 10⁻³ °C.

λ_{d i p}

has a stable negative linear relationship with temperature, and the correlation coefficient of the fitting curve exceeds 95%. The temperature cycling experiment and long-term stability test show that the temperature sensor has good repeatability and stability. The experimental results also show the nonlinear relationship between the temperature measurement range and sensitivity, clarify the important factors affecting the response performance of fiber temperature sensors, and provide important reference values for optical fiber temperature sensors. Full article

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

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12 pages, 5419 KB

Open AccessArticle

High-Precision Point-Ahead Angle Real-Time Prediction Algorithm for Inter-Satellite Laser Links

by Xiangnan Liu, Xiaoping Li, Zhongwen Deng and Haifeng Sun

Photonics 2025, 12(9), 886; https://doi.org/10.3390/photonics12090886 - 3 Sep 2025

Viewed by 268

Abstract

The accurate prediction of the point-ahead angle (PAA) is crucial for applications of inter-satellite laser links (ISLLs), especially laser ranging and continuous communication. Herein, a real-time and high-precision point-ahead-angle algorithm is presented; the principle of the algorithm is mathematically characterized, and its performance [...] Read more.

The accurate prediction of the point-ahead angle (PAA) is crucial for applications of inter-satellite laser links (ISLLs), especially laser ranging and continuous communication. Herein, a real-time and high-precision point-ahead-angle algorithm is presented; the principle of the algorithm is mathematically characterized, and its performance is simulated and verified using typical on-orbit scenarios. The maximum PAAs of a typical geosynchronous equatorial orbit (GEO)–GEO link and low Earth orbit (LEO)–GEO link were simulated with this algorithm, and the results are consistent with those of typical calculation methods, proving the algorithm’s accuracy. The performance of the proposed algorithm was verified using a practical engineering application of ISLLs, where it was used to calculate the point-ahead angle during stable on-orbit communication. The Pearson correlations between the curves of azimuth, elevation, and total point-ahead angles, and the actual experimental data are 99.91%, 52.32%, and 98.01%, respectively. The corresponding average deviations are −5.8510 nrad, −1.0945 nrad, and −79.5403 nrad, respectively. The maximum calculation error is 5.2103%, and the calculation accuracy exceeds 94%. The above results show that the algorithm produces results that closely match actual on-orbit experimental data with high calculation accuracy, enabling the accurate prediction of the point-ahead angle and the improvement of ISLL stability. Additionally, with this method, the measurement error of the laser ranging is smaller than 50 μm, further enhancing the accuracy of precision measurements based on ISLLs. Full article

(This article belongs to the Special Issue New Progress in Optical Precision Measurement in the Field of Space Technology)

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26 pages, 2751 KB

Open AccessArticle

Reinforcement Learning Compensatory-Based Fully Actuated Control Method for Risley Prisms

by Runqiang Xing, Meilin Xie, Haoqi Xue, Jie Wang and Fan Wang

Photonics 2025, 12(9), 885; https://doi.org/10.3390/photonics12090885 - 2 Sep 2025

Viewed by 451

Abstract

Beam pointing control based on Risley prisms is of great significance in wide-angle, high-precision application scenarios, such as laser communication, but its inherent nonlinear system characteristics seriously restrict the performance of beam pointing control, such as accuracy. For this reason, this paper combines [...] Read more.

Beam pointing control based on Risley prisms is of great significance in wide-angle, high-precision application scenarios, such as laser communication, but its inherent nonlinear system characteristics seriously restrict the performance of beam pointing control, such as accuracy. For this reason, this paper combines the theory of fully actuated control with reinforcement learning methods and designs a fully actuated control method based on reinforcement learning compensation: suppressing the influence of system nonlinearity through fully actuated control, using reinforcement learning to estimate system perturbations and nonlinearities, and then outputting a compensated control quantity using the low-dimensional output of fully actuated control as the reference input of reinforcement learning reduces the complexity of learning and realises the end-to-end uncertainty estimation. Finally, the stability of the method is theoretically analyzed, and the effectiveness of the method is verified by experimental analysis, which can further improve the beam pointing accuracy of the Risley prism system. Full article

(This article belongs to the Special Issue Laser Communication Systems and Related Technologies)

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11 pages, 4895 KB

Open AccessArticle

Narrow-Linewidth Semiconductor Laser with Hybrid Feedback

by Mingyuan Xue, Haiyang Shangguan, Hao Dong, Xinyu Wang, Zeying Lv, Lingxuan Zhang and Weiqiang Wang

Photonics 2025, 12(9), 884; https://doi.org/10.3390/photonics12090884 - 2 Sep 2025

Viewed by 280

Abstract

Narrow-linewidth semiconductor lasers have become indispensable devices in high-precision measurement and detection. Among various available technologies, self-injection locking plays a crucial role due to its significant ability to reduce linewidth and enhance coherence. Here, we demonstrate a hybrid feedback narrow-linewidth laser based on [...] Read more.

Narrow-linewidth semiconductor lasers have become indispensable devices in high-precision measurement and detection. Among various available technologies, self-injection locking plays a crucial role due to its significant ability to reduce linewidth and enhance coherence. Here, we demonstrate a hybrid feedback narrow-linewidth laser based on fixed external cavity feedback combined with self-injection locking feedback. The laser consists of a semiconductor gain chip, fiber Bragg grating, and micro-ring resonator, achieving laser mode selection and linewidth compression. Ultimately, a single longitudinal mode narrow-linewidth laser output with a Lorentzian linewidth of 149 Hz and a side-mode suppression ratio of 65 dB was obtained. The demonstrated laser can be applied in applications such as coherent optical communication and high-precision coherent detection. Full article

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

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