Photonics

12 pages, 4378 KB

Open AccessArticle

Analysis of Color Fade Phenomenon in Studies on the Multi-Angle Characterization of Spectral Reflectance Standards

by Maciej Skrzetuszewski, Łukasz Litwiniuk, Maciej Zajkowski and Sylwia Górnik

Photonics 2025, 12(9), 915; https://doi.org/10.3390/photonics12090915 - 12 Sep 2025

This paper describes the new aspects to be taken into account in the calibration procedures for reflectance spectrophotometers used at the Central Office of Measures in Warsaw, Poland. The measurement set-up for the multi-angled characterization of the spectral reflectance standards is presented. The [...] Read more.

This paper describes the new aspects to be taken into account in the calibration procedures for reflectance spectrophotometers used at the Central Office of Measures in Warsaw, Poland. The measurement set-up for the multi-angled characterization of the spectral reflectance standards is presented. The main problem considered in this publication is the insufficient knowledge of the wide angular characteristics of the sample tested in reflected light, what affects accuracy and, consequently, uncertainty in the process of dissemination of the units of measurement during the calibration of reflectance spectrophotometers. The results of tests for a wider range of the angle of reflection are presented here, with particular attention paid to the study of the actual limits of the color characteristics for ceramic chromatic standards. The basic calculation formulas used in reflectance colorimetry are presented and applied to prepare extended reflectance characteristics of standards in the tested angle of incidence and angle of reflection configurations. Based on these analyses, conclusions were presented. Full article

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

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13 pages, 3349 KB

Open AccessArticle

Magnetostrictive Behavior of Metglas^® 2605SC and Acoustic Sensing Optical Fiber for Distributed Static Magnetic Field Detection

by Zach Dejneka, Daniel Homa, Logan Theis, Anbo Wang and Gary Pickrell

Photonics 2025, 12(9), 914; https://doi.org/10.3390/photonics12090914 - 12 Sep 2025

Abstract

Fiber optic technologies have strong potential to augment and improve existing areas of sensor performance across many applications. Magnetic sensing, in particular, has attracted significant interest in structural health monitoring and ferromagnetic object detection. However, current technologies such as fluxgate magnetometers and inspection [...] Read more.

Fiber optic technologies have strong potential to augment and improve existing areas of sensor performance across many applications. Magnetic sensing, in particular, has attracted significant interest in structural health monitoring and ferromagnetic object detection. However, current technologies such as fluxgate magnetometers and inspection gauges rely on measuring magnetic fields as single-point sensors. By using fiber optic distributed strain sensors in tandem with magnetically biased magnetostrictive material, static and dynamic magnetic fields can be detected across long lengths of sensing fiber. This paper investigates the relationship between Fiber Bragg Grating (FBG)-based strain sensors and the magnetostrictive alloy Metglas^® 2605SC for the distributed detection of static fields for use in a compact cable design. Sentek Instrument’s picoDAS system is used to interrogate the FBG based sensors coupled with Metglas^® that is biased with an alternating sinusoidal magnetic field. The sensing system is then exposed to varied external static magnetic field strengths, and the resultant strain responses are analyzed. A minimum magnetic field strength on the order of 300 nT was able to be resolved and a variety of sensing configurations and conditions were also tested. The sensing system is compact and can be easily cabled as both FBGs and Metglas^® are commercialized and readily acquired. In combination with the robust and distributed nature of fiber sensors, this demonstrates strong promise for new means of magnetic characterization. Full article

(This article belongs to the Special Issue Optical Fiber Sensors: Design and Application)

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23 pages, 6748 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)

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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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25 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

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

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

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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