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Photonics
Volume 12
Issue 9
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Photonics, Volume 12, Issue 9 (September 2025) – 113 articles

Cover Story (view full-size image): Mueller matrix (MM) polarimetry is increasingly valued for its diagnostic potentials. However, for a prevalently used division of time MM polarimeter based on a dual-rotating retarder scheme, beam drift induced by rotating polarizers and waveplates introduces spatial misalignment and pseudo-edge artifacts in imaging results, hindering following accurate microstructural features characterization. In this paper, we quantitatively analyze the beam drift phenomenon in MM microscopy and its impact on linear retardance measurement. The findings highlight beam drift as a dominant error source for quantifying linear retardance, necessitating careful optical design alignment and a reliable registration algorithm to obtain highly accurate polarization data for training machine learning models of pathological diagnosis using MM microscopy. View this paper
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23 pages, 3209 KB  
Article
Research on Power Laser Inspection Technology Based on High-Precision Servo Control System
by Zhe An and Yuesheng Pei
Photonics 2025, 12(9), 944; https://doi.org/10.3390/photonics12090944 - 22 Sep 2025
Viewed by 471
Abstract
With the expansion of the scale of ultra-high-voltage transmission lines and the complexity of the corridor environment, the traditional manual inspection method faces serious challenges in terms of efficiency, cost, and safety. In this study, based on power laser inspection technology with a [...] Read more.
With the expansion of the scale of ultra-high-voltage transmission lines and the complexity of the corridor environment, the traditional manual inspection method faces serious challenges in terms of efficiency, cost, and safety. In this study, based on power laser inspection technology with a high-precision servo control system, a complete set of laser point cloud processing technology is proposed, covering three core aspects: transmission line extraction, scene recovery, and operation status monitoring. In transmission line extraction, combining the traditional clustering algorithm with the improved PointNet++ deep learning model, a classification accuracy of 92.3% is achieved in complex scenes; in scene recovery, 95.9% and 94.4% of the internal point retention rate of transmission lines and towers, respectively, and a vegetation denoising rate of 7.27% are achieved by RANSAC linear fitting and density filtering algorithms; in the condition monitoring segment, the risk detection of tree obstacles based on KD-Tree acceleration and the arc sag calculation of the hanging chain line model realize centimetre-level accuracy of hidden danger localisation and keep the arc sag error within 5%. Experiments show that this technology significantly improves the automation level and decision-making accuracy of transmission line inspection and provides effective support for intelligent operation and maintenance of the power grid. Full article
(This article belongs to the Special Issue Stable Control Technology and Image Perception Technology in Optoelectronic Servo Systems)
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14 pages, 1791 KB  
Article
Rigorous Coupled-Wave Analysis Algorithm for Stratified Two-Dimensional Gratings with Unconditionally Stable H-Matrix Methods
by Kaixuan Song, Jiyong Wang and Gaofeng Wang
Photonics 2025, 12(9), 943; https://doi.org/10.3390/photonics12090943 - 22 Sep 2025
Viewed by 531
Abstract
Nanostructures with the two-dimensional (2D) periodicity are attracting increasing attention due to their promising applications in planar optical devices and their potential for scalable industrial production. While Rigorous Coupled-Wave Analysis (RCWA) has proven to be an efficient electromagnetic solver for simulating the diffraction [...] Read more.
Nanostructures with the two-dimensional (2D) periodicity are attracting increasing attention due to their promising applications in planar optical devices and their potential for scalable industrial production. While Rigorous Coupled-Wave Analysis (RCWA) has proven to be an efficient electromagnetic solver for simulating the diffraction of large-scale periodic nanostructures, it has been largely applied in nanostructures with one-dimensional (1D) periodicity and suffers from potentially low computational stability. In this study, we present a step-by-step formulation of the RCWA algorithm for 2D stratified grating structures. Through dimensionality reduction, we show that the boundary conditions in 2D gratings can be transformed into forms analogous to those of 1D gratings. Additionally, we implement a hybrid matrix algorithm to enhance the computational stability of the RCWA. The stability and accuracy of the hybrid matrix-enhanced RCWA algorithm are compared with other recursive methods. An exemplary application in metalens demonstrates the effectiveness of our algorithms. Full article
(This article belongs to the Topic Nanomaterials for Photonics and Optoelectronics: Practical Applications and Advances)
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9 pages, 790 KB  
Article
Development of a Table-Top High-Power, High-Stability, High-Harmonic-Generation Extreme-Ultraviolet Laser Source
by Ruixuan Li, Hao Xu, Kui Li, Guangyin Zhang, Jin Niu, Jiyue Tang, Zhengkang Xu, Yuwei Xiao, Xiran Guo, Jinze Hu, Yutong Wang, Yongjun Ma, Guangyan Guo, Lifen Liao, Changjun Ke, Jie Li and Zhongwei Fan
Photonics 2025, 12(9), 942; https://doi.org/10.3390/photonics12090942 - 22 Sep 2025
Viewed by 712
Abstract
In this study, we present the development of a high-average-power, exceptionally stable extreme-ultraviolet (EUV) laser source based on a high-order harmonic generation (HHG) technique. The spectrum of an ytterbium-doped laser is broadened through self-phase modulation (SPM) in a gas-filled hollow fiber and compressed [...] Read more.
In this study, we present the development of a high-average-power, exceptionally stable extreme-ultraviolet (EUV) laser source based on a high-order harmonic generation (HHG) technique. The spectrum of an ytterbium-doped laser is broadened through self-phase modulation (SPM) in a gas-filled hollow fiber and compressed down to 25.3 fs for efficient harmonic generation. The high harmonics are generated in a krypton (Kr) gas cell, delivering a total power of 241 μW within the 30–60 nm spectral range, corresponding to a single harmonic output of 166 μW at a central wavelength of 46.8 nm. Notably, the system demonstrates good power stability with a root-mean-square (RMS) deviation of only 1.95% over 12 h of continuous operation. This advanced light source holds great potential for applications in nano- and quantum-material development and in semiconductor wafer defect detection. Future work aims to further enhance the output power in the 30–60 nm band to the milliwatt level, which would significantly bolster scientific research and technological development in related fields. Full article
(This article belongs to the Special Issue Ultrafast Lasers and Nonlinear Optics)
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9 pages, 1407 KB  
Article
Improved the Diffracting Optical Waveguides Imaging by Photonic Crystal Film
by Junyu He, Caili Tong, Chaoyang Han, Chang Liu, Miaoqing Yang, Jun Wang and Bo Wang
Photonics 2025, 12(9), 941; https://doi.org/10.3390/photonics12090941 - 21 Sep 2025
Viewed by 640
Abstract
In recent years, with the continuous advancement of technology and the expansion of application scenarios, AR has become a highly regarded field. However, AR still faces several challenges in practical usage. Notable shortcomings include inadequate image uniformity, low diffraction efficiency. Among these, the [...] Read more.
In recent years, with the continuous advancement of technology and the expansion of application scenarios, AR has become a highly regarded field. However, AR still faces several challenges in practical usage. Notable shortcomings include inadequate image uniformity, low diffraction efficiency. Among these, the insufficient image uniformity stands out as a significant issue directly affecting user experience. The analysis of uniformity improvement in this study is limited to the simulated scenario of monochromatic blue light (LED light source), aiming to optimize the insufficient uniformity of the image output of the diffractive optical waveguide-based AR technology scheme. We improve the details of the input grating in the waveguide, such as the morphological characteristics of the grating, the detail parameter, etc. In addition, we propose to incorporate a photonic crystal film in the waveguide as an innovative study and find that the incorporation of the photonic crystal thin film significantly improves the uniformity of the output image in the diffractive optical waveguide scheme. In order to further verify the effect of the photonic crystal film on the uniformity of its image output, we also compare different types of coupled gratings and find that they all have a positive effect. Thus, the photonic crystal film demonstrated effective control over the diffraction optical waveguide scheme. This research offers new insights and design approaches for enhancing the output image uniformity based on diffraction optical waveguide technology, providing a new path for improving image uniformity in AR displays. Full article
(This article belongs to the Special Issue Optical Technology for Challenging Conditions：Methods and Applications)
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8 pages, 3096 KB  
Communication
Infrared Optical Vortices Generation with Holographic Optical Elements Recorded in Bayfol HX200 Photopolymer
by Álvaro Paredes-Amorín, Julia Marín-Sáez, María-Victoria Collados and Jesús Atencia
Photonics 2025, 12(9), 940; https://doi.org/10.3390/photonics12090940 - 20 Sep 2025
Viewed by 509
Abstract
Infrared optical vortices are used in the field of optical communications at wavelengths around 1550 nm. A versatile method to generate them is with a Spatial Light Modulator (SLM); however, they are expensive devices and cannot be easily integrated into compact systems, as [...] Read more.
Infrared optical vortices are used in the field of optical communications at wavelengths around 1550 nm. A versatile method to generate them is with a Spatial Light Modulator (SLM); however, they are expensive devices and cannot be easily integrated into compact systems, as opposed to Holographic Optical Elements (HOEs), which are lightweight, smaller and thinner, and easier to align and combine with other optical systems. In this work, volume transmission HOEs have been recorded in a commercial photopolymer, Bayfol HX200, by exposing it to the interference pattern obtained with an optical vortex (obtained with an SLM) and a plane wave in the visible range. When illuminated with a plane wave at 1534 nm, the diffracted beam carried an optical vortex. An experimental efficiency of approximately 45% at that wavelength has been obtained, proving the viability of the method. Full article
(This article belongs to the Special Issue Advances in Holography and Its Applications)
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14 pages, 3214 KB  
Article
On the Feasibility of Localizing Transformer Winding Deformations Using Optical Sensing and Machine Learning
by Najmeh Seifaddini, Meysam Beheshti Asl, Sekongo Bekibenan, Simplice Akre, Issouf Fofana, Mohand Ouhrouche and Abdellah Chehri
Photonics 2025, 12(9), 939; https://doi.org/10.3390/photonics12090939 - 19 Sep 2025
Viewed by 442
Abstract
Mechanical vibrations induced by electromagnetic forces during transformer operation can lead to winding deformation or failure, an issue responsible for over 12% of all transformer faults. While previous studies have predominantly relied on accelerometers for vibration monitoring, this study explores the use of [...] Read more.
Mechanical vibrations induced by electromagnetic forces during transformer operation can lead to winding deformation or failure, an issue responsible for over 12% of all transformer faults. While previous studies have predominantly relied on accelerometers for vibration monitoring, this study explores the use of an optical sensor for real-time vibration measurement in a dry-type transformer. Experiments were conducted using a custom-designed single-phase transformer model specifically developed for laboratory testing. This experimental setup offers a unique advantage: it allows for the interchangeable simulation of healthy and deformed winding sections without causing permanent damage, enabling controlled and repeatable testing scenarios. The transformer’s secondary winding was short-circuited, and three levels of current (low, intermediate, and high) were applied to simulate varying stress conditions. Vibration displacement data were collected under load to assess mechanical responses. The primary goal was to classify this vibration data to localize potential winding deformation faults. Five supervised learning algorithms were evaluated: Random Forest, Support Vector Machine, K-Nearest Neighbors, Logistic Regression, and Decision Tree classifiers. Hyperparameter tuning was applied, and a comparative analysis among the top four models yielded average prediction accuracies of approximately 60%. These results, achieved under controlled laboratory conditions, highlight the promise of this approach for further development and future real-world applications. Overall, the combination of optical sensing and machine learning classification offers a promising pathway for proactive monitoring and localization of winding deformations, supporting early fault detection and enhanced reliability in power transformers. Full article
(This article belongs to the Special Issue Science and Applications of Optical Fiber Sensors: Recent Advances and Future Trends)
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12 pages, 10672 KB  
Article
Optical Trapping by Aperiodic Kinoform Lenses Based on the Baum–Sweet Sequence
by Arlen B. Pérez-Hernández, Adrián Garmendía-Martínez, Vicente Ferrando, Vanesa P. Cuenca-Gotor, Walter D. Furlan, Juan A. Monsoriu and Francisco M. Muñoz-Pérez
Photonics 2025, 12(9), 938; https://doi.org/10.3390/photonics12090938 - 19 Sep 2025
Viewed by 464
Abstract
This work presents a new family of aperiodic diffractive lenses based on the Baum–Sweet sequence. To the best of our knowledge, this is the first report of a diffractive lens derived from this sequence. The study of their focusing properties reveals two focal [...] Read more.
This work presents a new family of aperiodic diffractive lenses based on the Baum–Sweet sequence. To the best of our knowledge, this is the first report of a diffractive lens derived from this sequence. The study of their focusing properties reveals two focal points with similar intensities along the optical axis. Both the main focal distances and the axial irradiance distribution are correlated with the aperiodic Baum–Sweet sequence. An approximate 60% increase in diffraction efficiency is observed when employing kinoform profiles instead of binary phase lenses. The integration of the Baum–Sweet-based kinoform lens into an optical tweezers system demonstrates its ability to simultaneously trap multiple particles at two distinct focal planes, highlighting its potential for applications in more advanced optical devices. Full article
(This article belongs to the Special Issue Advances in Optical Imaging)
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11 pages, 3920 KB  
Article
Dynamic Behaviors of Pulsating Noise-like Pulses in an Ultrafast Fiber Laser
by Lei Zhang, Pinghua Tang, Jinhai Zhu, Zexin Zhou, Haitao Wu and Zhenhong Wang
Photonics 2025, 12(9), 937; https://doi.org/10.3390/photonics12090937 - 19 Sep 2025
Viewed by 516
Abstract
In this study, we demonstrate the generation and observation of noise-like pulses (NLPs) with unique pulsating characteristics in an ultrafast fiber laser. Furthermore, these NLPs display distinct periodic intensity modulation during temporal evolution, and the corresponding shot-to-shot spectra based on the dispersive Fourier [...] Read more.
In this study, we demonstrate the generation and observation of noise-like pulses (NLPs) with unique pulsating characteristics in an ultrafast fiber laser. Furthermore, these NLPs display distinct periodic intensity modulation during temporal evolution, and the corresponding shot-to-shot spectra based on the dispersive Fourier transform (DFT) method exhibit chaotic characteristics with random variable envelopes in each period. Notably, the pulsating period of these NLPs decreases with the increment of pump power. Moreover, both the average output power and pulse energy show a clear linear growth trend as the pump power is raised. Numerical simulations are further conducted to validate these experimental findings. This work will enrich the study of NLPs and pulsation dynamics and provide valuable insights for the development of ultrafast fiber lasers. Full article
(This article belongs to the Special Issue Ultrafast Fiber Lasers: Nonlinear Dynamics and Novel Phenomena)
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20 pages, 10176 KB  
Article
Theoretical Analysis of Vernier-Effect-Induced Sensitivity Enhancement of Dual Fiber Fabry-Pérot Cavities in OFDRs
by Mingxin Wang and Yueyu Xiao
Photonics 2025, 12(9), 936; https://doi.org/10.3390/photonics12090936 - 19 Sep 2025
Viewed by 434
Abstract
The vernier-effect-based sensitivity enhancement of two kinds of sensing units consisting of dual fiber Fabry-Pérot (FP) cavities in the Optical Frequency Domain Reflectometry (OFDR) is analyzed in this paper. Theoretical analysis reveals that significant differences exist in the sensitivity enhancement between the cascaded [...] Read more.
The vernier-effect-based sensitivity enhancement of two kinds of sensing units consisting of dual fiber Fabry-Pérot (FP) cavities in the Optical Frequency Domain Reflectometry (OFDR) is analyzed in this paper. Theoretical analysis reveals that significant differences exist in the sensitivity enhancement between the cascaded and parallel dual fiber FP cavties when demodulated by an OFDR system. When the conditions of the vernier effect are satisfied, the sensing unit with cascaded FP cavities does not exhibit a sensitivity enhancement compared to a single FP sensor, whereas the sensing unit with parallel FP cavities can achieve an enhanced sensitivity. This phenomenon differs from that observed in direct wavelength interrogation systems. The results are further verified with numerical simulations on the temperature sensing. When the vernier-effect conditions are met, the sensitivity of the sensing unit with cascaded FP sensors is 9.99 pm/°C, while the sensitivity of the sensing unit with parallel FP sensors can reach up to 128.97 pm/°C. The findings of this paper provide valuable insights for the design of high-sensitive distributed optical fiber sensing systems. Full article
(This article belongs to the Special Issue Emerging Trends in Fiber Optic Sensing)
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11 pages, 3892 KB  
Article
High-Speed Structured Polarized Light Imaging of Bovine Heart Valve Leaflet Dynamics
by Bin Yang
Photonics 2025, 12(9), 935; https://doi.org/10.3390/photonics12090935 - 19 Sep 2025
Viewed by 457
Abstract
Collagen is the primary load-bearing component in connective tissues, and its organization dictates the biomechanical properties and functions of the tissue. Polarized light imaging has been an effective tool for characterizing collagen organization. Recently, with the integration of structured light illumination (SLI), structured [...] Read more.
Collagen is the primary load-bearing component in connective tissues, and its organization dictates the biomechanical properties and functions of the tissue. Polarized light imaging has been an effective tool for characterizing collagen organization. Recently, with the integration of structured light illumination (SLI), structured polarized light imaging (SPLI) has enabled quantification of collagen fiber orientation in the superficial layers of thick tissues with higher specificity and accuracy. However, SPLI typically requires 12 images to perform depth discrimination and collagen quantification, limiting its application in imaging tissue dynamics. To overcome this limitation, we developed a high-speed SPLI system that can perform continuous tracking and quantification of tissue deformation at 75 frames per second (FPS). High-speed SPLI was achieved by pairing a polarization camera with a rolling image processing technique. We evaluated the performance of high-speed SPLI on a bovine heart valve leaflet under uniaxial deformation. We were able to continuously track and quantify collagen fiber orientation at 75 FPS, with improved accuracy due to effective depth discrimination using SLI. Additionally, we demonstrated that reflectance with SLI is more sensitive to local collagen deformation compared to imaging without SLI, offering a complementary perspective for studying the dynamics of collagenous tissues. Full article
(This article belongs to the Special Issue Photonics for Biomedical Applications: Design and Integration of Optical Imaging Systems)
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11 pages, 3388 KB  
Communication
On-Chip Etchless and Tunable Silicon Nitride Waveguide Mode Converter Based on Low-Loss Phase Change Material
by Tianman Shu, Yuexiang Guo, Shengxiong Lai, Lun Zhang, Yin Xu and Hualong Bao
Photonics 2025, 12(9), 934; https://doi.org/10.3390/photonics12090934 - 19 Sep 2025
Viewed by 575
Abstract
The development of reconfigurable photonic integrated circuits (PICs) demands photonic devices with high-efficiency tuning capabilities, yet conventional thermo-optic and electro-optic methods suffer from limited index modulation and excessive power consumption. To overcome these limitations, we propose an etchless and tunable silicon nitride waveguide [...] Read more.
The development of reconfigurable photonic integrated circuits (PICs) demands photonic devices with high-efficiency tuning capabilities, yet conventional thermo-optic and electro-optic methods suffer from limited index modulation and excessive power consumption. To overcome these limitations, we propose an etchless and tunable silicon nitride waveguide mode converter based on low-loss phase change material, antimony triselenide (Sb2Se3). By depositing an Sb2Se3 layer on the silicon nitride wafer and using a laser-induced phase transition technique, we can write and erase the waveguide structure in the phase change wafer without waveguide etching, where the input/output waveguide is a strip waveguide and the conversion region is built using a tilted subwavelength grating structure. From the results, the obtained TE0-TE1 mode conversion efficiency, crosstalk, and insertion loss are higher than 96%, lower than −16 dB, and lower than 0.4 dB at a wavelength of 1.55 µm, respectively. The proposed device enables post-fabrication tuning of the grating duty cycle, allowing working wavelength adjustment for the same device. Furthermore, the device exhibits scalability to other higher-order mode conversions (e.g., TE0-TE2). Consequently, we expect that such devices could have important uses in programmable and multifunctional PICs. Full article
(This article belongs to the Special Issue Emerging Technologies for Silicon Photonics and Integrated Circuits)
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19 pages, 4698 KB  
Article
Numerical Analysis of an Ultra-Sensitive Optical Fiber for Hemoglobin Concentration Detection
by Aryan Abbaszadeh, Somayeh Makouei, Samrand Rash-Ahmadi and Sebelan Danishvar
Photonics 2025, 12(9), 933; https://doi.org/10.3390/photonics12090933 - 19 Sep 2025
Viewed by 481
Abstract
Hemoglobin is a vital protein in the human body, and its deficiency leads to anemia. This condition reduces oxygen levels in red blood cells, which can be life-threatening. This paper presents the design of a novel optical fiber (OF) sensor for label-free detection [...] Read more.
Hemoglobin is a vital protein in the human body, and its deficiency leads to anemia. This condition reduces oxygen levels in red blood cells, which can be life-threatening. This paper presents the design of a novel optical fiber (OF) sensor for label-free detection of hemoglobin concentration. The sensor features concentric layers of gold and silica arranged sequentially. Finite element method (FEM) simulations were used to analyze its performance. The results indicate that for a refractive index (RI) range of 1.34 to 1.41, the sensor achieves a wavelength sensitivity (Sw) of up to 38,000 nm/RIU and an amplitude sensitivity (SA) of 11,280 RIU−1. The sensor exhibits a resolution of 1.85 × 10−6 RIU and a figure of merit (FOM) of 736.56 RIU−1. Its simple construction and high sensitivity make it a promising candidate for hemoglobin detection applications. Full article
(This article belongs to the Special Issue Optical Fiber Sensors: Design and Application)
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13 pages, 3775 KB  
Article
Broadband Absorption in Mid-Infrared via Trapezoidal Gratings Made of Anisotropic Metamaterial
by Yongze Ren, Jiale Gao, Zhuofan Jiang, Zhaoyan Yang, Jiao Liu, Yue Gou and Yeming Qing
Photonics 2025, 12(9), 932; https://doi.org/10.3390/photonics12090932 - 18 Sep 2025
Viewed by 473
Abstract
Broadband absorption of electromagnetic energy plays an important role in energy harvesting and stealth. Here, we present and demonstrate an absorber with a wide bandwidth of 2.1 μm in mid-infrared. The trapezoidal metamaterial consists of alternating silicon carbide and dielectric films. We have [...] Read more.
Broadband absorption of electromagnetic energy plays an important role in energy harvesting and stealth. Here, we present and demonstrate an absorber with a wide bandwidth of 2.1 μm in mid-infrared. The trapezoidal metamaterial consists of alternating silicon carbide and dielectric films. We have numerically demonstrated that an ultrahigh absorption energy efficiency higher than 97.7% can be calculated from 10.6 μm to 12.7 μm. The proposed absorber has high absorption efficiency at a wide-angle range. The simulation results are consistent with the theoretical calculation based on effective medium theory. The theoretical model simplifies the multilayer structure into an effectively homogeneous metamaterial with hyperbolic dispersion. In addition, the distributions of magnetic field depict that different wavelengths can be trapped at structures with various widths. The mechanism of this phenomenon is attributed to the slowlight modes. Furthermore, a dual-sized absorber is designed to achieve high efficiency and broadband absorption, which is easy to manufacture. Our study has potential applications in the areas of energy harvesting materials, thermal emitters and photovoltaic devices in the mid-infrared. Full article
(This article belongs to the Special Issue Recent Progress in Optical Metamaterials and Metasurfaces)
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13 pages, 2630 KB  
Article
Research on Polar-Axis Direct Solar Radiation Spectrum Measurement Method
by Jingrui Sun, Yangyang Zou, Lu Wang, Jian Zhang, Yu Zhang, Ke Zhang, Yang Su, Junjie Yang, Ran Zhang and Guoyu Zhang
Photonics 2025, 12(9), 931; https://doi.org/10.3390/photonics12090931 - 18 Sep 2025
Viewed by 407
Abstract
High-precision measurements of direct solar radiation spectra are crucial for the development of solar resources, climate change research, and agricultural applications. However, the current measurement systems all rely on a moving two-axis tracking system with a complex structure and many error transmission links. [...] Read more.
High-precision measurements of direct solar radiation spectra are crucial for the development of solar resources, climate change research, and agricultural applications. However, the current measurement systems all rely on a moving two-axis tracking system with a complex structure and many error transmission links. In response to the above problems, a polar-axis rotating solar direct radiation spectroscopic measurement method is proposed, and an overall architecture consisting of a rotating reflector and a spectroradiometric measurement system is constructed, which simplifies the system’s structural form and enables year-round, full-latitude solar direct radiation spectroscopic measurements without requiring moving tracking. The paper focuses on the study of its optical system, optimizes the design of a polar-axis rotating solar direct radiation spectroscopy measurement optical system with a spectral range of 380–780 nm and a spectral resolution better than 2 nm, and carries out spectral reconstruction of the solar direct radiation spectra as well as the assessment of measurement accuracy. The results show that the point error distribution of the AM0 spectral curve ranges from −9.05% to 13.35%, and the area error distribution ranges from −0.04% to 0.09%; the point error distribution of the AM1.5G spectral curve ranges from −9.19% to 13.66%, and the area error distribution ranges from −0.03% to 0.11%. Both exhibit spatial and temporal uniformity exceeding 99.92%, ensuring excellent measurement performance throughout the year. The measurement method proposed in this study enhances the solar direct radiation spectral measurement system. Compared to the existing dual-axis moving tracking measurement method, the system composition is simplified, enabling direct solar radiation spectrum measurement at all latitudes throughout the year without the need for tracking, providing technical support for the development and application of new technologies for solar direct radiation measurement. It is expected to promote future theoretical research and technological breakthroughs in this field. Full article
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31 pages, 6899 KB  
Article
Optimization of Unrepeatered Optical Communication Systems and the Applications in Cabled Ocean Observatories
by Chang Shu, Feng Lyu, Rendong Xu, Jianping Li, Xichen Wang and Liang Xu
Photonics 2025, 12(9), 930; https://doi.org/10.3390/photonics12090930 - 18 Sep 2025
Viewed by 520
Abstract
Conventional repeatered optical communication systems face inherent limitations in terms of reliability, flexibility in optical fiber configuration, and power supply modes, particularly when applied to large-scale cabled ocean observatories, which have highly variable load demands. To address these challenges, a novel hybrid optimization [...] Read more.
Conventional repeatered optical communication systems face inherent limitations in terms of reliability, flexibility in optical fiber configuration, and power supply modes, particularly when applied to large-scale cabled ocean observatories, which have highly variable load demands. To address these challenges, a novel hybrid optimization algorithm (GA + PSO + SA) has been developed to enable simultaneous optimization of multiple critical parameters, including the pump light wavelength, the length of the erbium-doped fiber, and the placement of the remote optical amplifier. This approach represents a significant advancement over conventional single-algorithm methods because it effectively overcomes local optima and achieves global performance optimization. Comprehensive simulations and experimental validation demonstrate that the optimized unrepeatered system achieves transmission distances of 691.8 km using G.654E fibers and over 400 km with standard G.652D fibers, while maintaining excellent signal quality and exceptional stability. This work provides a systematic framework for the design and optimization of ultra-long-haul unrepeatered systems, highlighting their practical applicability in cabled ocean observatories. Full article
(This article belongs to the Special Issue Exploring Optical Fiber Communications: Technology and Applications)
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14 pages, 3320 KB  
Article
SFD-YOLO: A Multi-Angle Scattered Field-Based Optical Surface Defect Recognition Method
by Xuan Liu, Hao Sun, Jian Zhang and Chunyan Wang
Photonics 2025, 12(9), 929; https://doi.org/10.3390/photonics12090929 - 18 Sep 2025
Viewed by 591
Abstract
The surface quality of optical components plays a decisive role in advanced imaging, precision manufacturing, and high-power laser systems, where even defects can induce abnormal scattering and degrade system performance. Addressing the limitations of conventional single-view inspection methods, this study presents a panoramic [...] Read more.
The surface quality of optical components plays a decisive role in advanced imaging, precision manufacturing, and high-power laser systems, where even defects can induce abnormal scattering and degrade system performance. Addressing the limitations of conventional single-view inspection methods, this study presents a panoramic multi-angle scattered light field acquisition approach integrated with deep learning-based recognition. A hemispherical synchronous imaging system is designed to capture complete scattered distributions from surface defects in a single exposure, ensuring both structural consistency and angular completeness of the measured data. To enhance the interpretation of complex scattering patterns, we develop a tailored lightweight network, SFD-YOLO, which incorporates the PSimam attention module for improved salient feature extraction and the Efficient_Mamba_CSP module for robust global semantic modeling. Using a simulated dataset of multi-width scratch defects, the proposed method achieves high classification accuracy with strong generalization and computational efficiency. Compared to the baseline YOLOv11-cls, SFD-YOLO improves Top-1 accuracy from 92.5% to 95.6%, while reducing the parameter count from 1.54 M to 1.25 M and maintaining low computational cost (Flops 4.0G). These results confirm that panoramic multi-angle scattered imaging, coupled with advanced neural architectures, provides a powerful and practical framework for optical surface defect detection, offering valuable prospects for high-precision quality evaluation and intelligent defect inversion in optical inspection. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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27 pages, 2641 KB  
Review
Progress in Passive Silicon Photonic Devices: A Review
by Qidi Liu, Yusheng Bian and Jiawei Xiong
Photonics 2025, 12(9), 928; https://doi.org/10.3390/photonics12090928 - 18 Sep 2025
Viewed by 1922
Abstract
Silicon photonics has emerged as a critical enabling technology for a diverse range of applications, from high-speed data communication and computing to advanced sensing and quantum information processing. This paper provides a comprehensive review of recent progress in the foundational passive devices that [...] Read more.
Silicon photonics has emerged as a critical enabling technology for a diverse range of applications, from high-speed data communication and computing to advanced sensing and quantum information processing. This paper provides a comprehensive review of recent progress in the foundational passive devices that underpin this technological revolution. We survey the state of the art in fundamental building blocks, including strip, rib, and silicon nitride waveguides, with a focus on achieving ultra-low propagation loss. The review details essential components for light coupling and splitting, such as grating couplers, edge couplers, multimode interference couplers, and directional couplers, citing their typical performance metrics. Key wavelength filtering and routing components, including high-Q ring resonators, Mach–Zehnder interferometers, and arrayed waveguide gratings, are analyzed. Furthermore, we provide a comparative overview of the capabilities of major photonic foundries operating on a multi-project wafer model. The paper concludes by discussing persistent challenges in packaging and polarization management, and explores future trends driven by co-packaged optics, inverse design methodologies, and the expansion of silicon photonics into new application domains. Full article
(This article belongs to the Special Issue Recent Progress in Integrated Photonics)
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14 pages, 1533 KB  
Article
Cascaded Cavitation Bubble Excited by a Train of Microsecond Laser Pulses
by Nadezhda A. Kudasheva, Nikita P. Kryuchkov, Arsen K. Zotov, Polina V. Aleksandrova, Oleg I. Pokhodyaev, Kseniya A. Feklisova, Yurii A. Suchkov, Anatoly L. Bondarenko, Ivan V. Simkin, Vladislav A. Samsonov, Sergey G. Ivakhnenko, Irina N. Dolganova, Stanislav O. Yurchenko, Sergey V. Garnov, Kirill I. Zaytsev, David G. Kochiev and Egor V. Yakovlev
Photonics 2025, 12(9), 927; https://doi.org/10.3390/photonics12090927 - 18 Sep 2025
Viewed by 556
Abstract
Although laser cavitation was discovered half a century ago, novel geometries and regimes to excite this effect have been vigorously explored during the past few decades. This research is driven by a variety of applications of laser cavitation in demanding branches of science [...] Read more.
Although laser cavitation was discovered half a century ago, novel geometries and regimes to excite this effect have been vigorously explored during the past few decades. This research is driven by a variety of applications of laser cavitation in demanding branches of science and technology, such as microfabrication, synthesis of nanoparticles, manipulation of cells, surgery, and lithotripsy. In this work, we combine experimental studies using high-repetition-rate imaging and numerical simulations to uncover a novel regime of the laser cavitation observed upon excitation of a liquid by a train of laser pulses with the pulse energy of 140 mJ and duration of 1.2 μs delivered through a quartz optical fiber. Once the lifetime of the initial cavitation bubble (excited by the first laser pulse) is larger than the period between pulses, which is 34.3 μs, the secondary pulses in the train pass the gas in a bubble and evaporate additional liquid. This results in the formation of a cascaded cavitation bubble of larger volume and elongated shape of 4.6 mm length compared to 3.8 mm in case of excitation by a single laser pulse. In addition, the results of acoustic measurements confirm the presence of shock waves in the applied liquid. Finally, potential applications of the uncovered laser cavitation regime are discussed. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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27 pages, 2883 KB  
Article
Design and Optimization of an FSO Network Under Practical Considerations
by Marios Melanitis, Petros S. Bithas, Athanassios Katsis and Hector E. Nistazakis
Photonics 2025, 12(9), 926; https://doi.org/10.3390/photonics12090926 - 17 Sep 2025
Viewed by 566
Abstract
This study investigates the design and optimization of a free-space optical (FSO) wireless communication network employing high-altitude platforms (HAPs). The objective is to explore the parameters that affect the quality and viability of such a network and to develop a method for minimizing [...] Read more.
This study investigates the design and optimization of a free-space optical (FSO) wireless communication network employing high-altitude platforms (HAPs). The objective is to explore the parameters that affect the quality and viability of such a network and to develop a method for minimizing installation costs while maximizing performance. The methodology includes clustering ground nodes using the k-means algorithm and adjusting the emission solid angles for each HAP. Furthermore, to more closely reflect real-world conditions, our analytical investigations also consider the effects of atmospheric turbulence. The network’s performance is evaluated under both daytime and nighttime operational scenarios, taking into account background noise and the layered effects of atmospheric turbulence. These considerations ensure that the results presented in this paper more accurately reflect real-world conditions. The results demonstrate significant performance gains through appropriate parameter selection. Additionally, deploying multiple HAPs enhances network flexibility and resilience. It was shown that in certain scenarios specific combinations of per-HAP configurations offer more than a 70% increase in throughput with a small increase in the cost. The paper’s insights fill an important gap between theoretical FSO network models and the practical design considerations needed for real deployments. Full article
(This article belongs to the Special Issue Innovations in Optical Wireless Communications: Challenges and Opportunities)
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16 pages, 4243 KB  
Article
Mode-Enhanced Surface Plasmon Resonance in Few-Mode Fibers via Dual-Groove Architecture
by Qin Wu, Xiao Liang, Zhaoxin Geng, Shuo Liu and Jia Liu
Photonics 2025, 12(9), 925; https://doi.org/10.3390/photonics12090925 - 17 Sep 2025
Viewed by 474
Abstract
We propose a dual-groove few-mode fiber surface plasmon resonance sensor that exploits the LP11 mode for enhanced plasmonic sensing. The device incorporates two physically separated grooves with distinct metallic coatings, enabling dual-channel operation via wavelength-division multiplexing. Finite element method simulations show that [...] Read more.
We propose a dual-groove few-mode fiber surface plasmon resonance sensor that exploits the LP11 mode for enhanced plasmonic sensing. The device incorporates two physically separated grooves with distinct metallic coatings, enabling dual-channel operation via wavelength-division multiplexing. Finite element method simulations show that the optimized design achieves a maximum sensitivity of 14,800 nm/RIU within the RI range of 1.33–1.40. The introduction of a TiO2–Au bilayer enhances mode coupling and ensures complete spectral separation, thereby improving stability and reducing environmental interference. Biosensing simulations at 37 °C further confirm the practicality of the proposed architecture. Channel 1, filled with ethanol as a temperature-sensitive medium, provides temperature monitoring, while Channel 2 successfully distinguishes between normal and tumor cells, reaching a sensitivity of up to 9428.57 nm/RIU for Jurkat cells. Overall, the TiO2-enhanced dual-channel FMF-SPR sensor combines ultra-high sensitivity, spectral independence, and biosensing capability, demonstrating strong potential for next-generation fiber-optic sensing and biomedical applications. Full article
(This article belongs to the Special Issue Novel Biomedical Optical Spectroscopy, Microscopy and Imaging)
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9 pages, 1995 KB  
Article
Silicon-Based Multimode Complex Bragg Gratings for Spectra-Tailored Filter
by Xiuqiu Shen, Huifang Kang, Wangping Wang, Xiong Liang and Huiye Qiu
Photonics 2025, 12(9), 924; https://doi.org/10.3390/photonics12090924 - 17 Sep 2025
Viewed by 525
Abstract
Multimode waveguide Bragg gratings (MWBGs) provide significant advantages over traditional single-mode counterparts through their mode-coupling operations. Nevertheless, flexible spectral response design methodologies for MWBG-based filter remain less studied. This work introduces a spectral tailoring methodology enabling physically realizable complex responses in MWBGs. We [...] Read more.
Multimode waveguide Bragg gratings (MWBGs) provide significant advantages over traditional single-mode counterparts through their mode-coupling operations. Nevertheless, flexible spectral response design methodologies for MWBG-based filter remain less studied. This work introduces a spectral tailoring methodology enabling physically realizable complex responses in MWBGs. We demonstrate silicon-based multi-channel Gaussian-shaped MWBGs using lateral phase delay modulation (LPDM) apodization. Experimental results confirm close conformance between measured spectral responses and target design specifications. Full article
(This article belongs to the Special Issue Recent Advancement in Microwave Photonics)
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19 pages, 4015 KB  
Article
DynaFlowNet: Flow Matching-Enabled Real-Time Imaging Through Dynamic Scattering Media
by Xuelin Lei, Jiachun Wang, Maolin Wang and Junjie Zhu
Photonics 2025, 12(9), 923; https://doi.org/10.3390/photonics12090923 - 16 Sep 2025
Viewed by 641
Abstract
Imaging through dynamic scattering media remains a fundamental challenge because of severe information loss and the ill-posed nature of the inversion problem. Conventional methods often struggle to strike a balance between reconstruction fidelity and efficiency in evolving environments. In this study, we present [...] Read more.
Imaging through dynamic scattering media remains a fundamental challenge because of severe information loss and the ill-posed nature of the inversion problem. Conventional methods often struggle to strike a balance between reconstruction fidelity and efficiency in evolving environments. In this study, we present DynaFlowNet, a framework that leverages conditional flow matching theory to establish a continuous, invertible mapping from speckle patterns to target images via deterministic ordinary differential equation (ODE) integration. Central to this is the novel temporal–conditional residual attention block (TCResAttnBlock), which is designed to model spatiotemporal scattering dynamics. DynaFlowNet achieves real-time performance at 134.77 frames per second (FPS), which is 117 times faster than diffusion-based models, while maintaining state-of-the-art reconstruction quality (28.46 dB peak signal-to-noise ratio (PSNR), 0.9112 structural similarity index (SSIM), and 0.8832 Pearson correlation coefficient (PCC)). In addition, the proposed framework demonstrates exceptional geometric generalization, with only a 1.05 dB PSNR degradation across unseen geometries, significantly outperforming existing methods. This study establishes a new paradigm for real-time high-fidelity imaging using dynamic scattering media, with direct implications for biomedical imaging, remote sensing, and underwater exploration. Full article
(This article belongs to the Special Issue Optical Imaging Innovations and Applications)
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9 pages, 1725 KB  
Communication
An Ultra-Compact InP 1310/1550 nm Wavelength Division (De)multiplexer Based on Channel-Shaped MMI Coupler
by Wenle Yao, Fei Guo, Mengyang Zhong and Dan Lu
Photonics 2025, 12(9), 922; https://doi.org/10.3390/photonics12090922 - 16 Sep 2025
Viewed by 510
Abstract
An ultra-compact 1310/1550 nm wavelength division (de)multiplexer based on a channel-shaped multimode interference structure was proposed and fabricated on an InP platform. The device has been simulated and optimized with a low insertion loss of 0.1 dB at 1310 nm wavelength and 0.33 [...] Read more.
An ultra-compact 1310/1550 nm wavelength division (de)multiplexer based on a channel-shaped multimode interference structure was proposed and fabricated on an InP platform. The device has been simulated and optimized with a low insertion loss of 0.1 dB at 1310 nm wavelength and 0.33 dB at 1550 nm wavelength. The device features a notably compact footprint with an MMI region just 48 μm in length. Measurements revealed extinction ratios of 7.1 dB at 1310 nm and 5.9 dB at 1550 nm, accompanied by insertion losses of 7.07 dB and 3.03 dB for these wavelengths. Full article
(This article belongs to the Section Optical Communication and Network)
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10 pages, 2892 KB  
Article
Freeform Optics-Based Microlens Array Lighting System Design and Optimization for Machine Vision
by Xing Peng, Zhenfeng Ye and Tengduo Qiao
Photonics 2025, 12(9), 921; https://doi.org/10.3390/photonics12090921 - 15 Sep 2025
Viewed by 618
Abstract
The performance of the lighting system significantly impacts the efficiency and accuracy of the overall defect detection process in additive manufacturing. However, achieving both high optical efficiency and exceptional illuminance uniformity within compact detection areas at typical working distances remains challenging with conventional [...] Read more.
The performance of the lighting system significantly impacts the efficiency and accuracy of the overall defect detection process in additive manufacturing. However, achieving both high optical efficiency and exceptional illuminance uniformity within compact detection areas at typical working distances remains challenging with conventional designs. This paper proposes a novel uniform lighting system design utilizing a freeform optics-based microlens array. Optical performance, focusing on efficiency and uniformity, was optimized across key distances using the Taguchi method. Simulation results demonstrate that the optimized uniform illumination system, featuring a 13 × 13 array with microlens of 2 mm radius positioned 300 mm from the target plane, achieves a high optical efficiency of 93.7% and an outstanding illuminance uniformity of 98.9%. Furthermore, the system maintains good uniformity across different wavelengths, enhancing its versatility. These findings strongly support the feasibility of the proposed freeform optics-based microlens array lighting system for machine vision in laser additive manufacturing defect detection, significantly contributing to improved image contrast. Full article
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12 pages, 1545 KB  
Article
Temperature-Dependent Fluorescent Properties of Single-Photon Emitters in 3C-SiC
by Mengting He, Yurong Wang, Junjie Lin, Yujing Cao, Botao Wu and E Wu
Photonics 2025, 12(9), 920; https://doi.org/10.3390/photonics12090920 - 15 Sep 2025
Viewed by 583
Abstract
Silicon carbide (SiC) is a representative wideband-gap semiconductor with remarkable properties, such as high breakdown field strength, high thermal conductivity, and high carrier saturation mobility. Meanwhile, single-photon emitters (SPEs) in SiC have attracted considerable attention owing to their excellent fluorescence performances and promising [...] Read more.
Silicon carbide (SiC) is a representative wideband-gap semiconductor with remarkable properties, such as high breakdown field strength, high thermal conductivity, and high carrier saturation mobility. Meanwhile, single-photon emitters (SPEs) in SiC have attracted considerable attention owing to their excellent fluorescence performances and promising applications in the quantum realm. Here, we conducted a systematic experimental investigation into the temperature-dependent characteristics of the SPEs in cubic silicon carbide (3C-SiC) crystal. Over a temperature span from 293 K to 373 K, the variations in fluorescence intensity, fluorescence lifetime, fluorescence spectra, polarization characteristics, and second-order autocorrelation function g2(τ) were examined. The fluorescence properties of defects showed extraordinary stabilization even when the temperature was raised to 373 K. Based on the above characteristics and combined with the excellent properties of SiC materials, this study provides strong evidence that SPEs in 3C-SiC can serve as information carriers capable of operating stably under high-temperature conditions. Full article
(This article belongs to the Special Issue Recent Progress in Single-Photon Generation and Detection)
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14 pages, 2308 KB  
Article
Label-Free Detection of Cellular Senescence in Fibroblasts via Third Harmonic Generation
by Meropi Mari, Eleni Kanakousaki, Kyriaki Stampouli, Antonis Kordas, Phanee Manganas, Costas Fotakis, George Filippidis and Anthi Ranella
Photonics 2025, 12(9), 919; https://doi.org/10.3390/photonics12090919 - 15 Sep 2025
Viewed by 603
Abstract
Cellular senescence, a state of irreversible growth arrest in response to stress, plays a dual role in physiology and pathology. While essential for processes such as embryogenesis, wound healing, and tumor suppression, senescence also contributes to aging and age-related diseases, including cancer and [...] Read more.
Cellular senescence, a state of irreversible growth arrest in response to stress, plays a dual role in physiology and pathology. While essential for processes such as embryogenesis, wound healing, and tumor suppression, senescence also contributes to aging and age-related diseases, including cancer and neurodegeneration. The accumulation of senescent cells is linked to aging and numerous age-associated pathologies, making the detection of these cells crucial for understanding and potentially mitigating age-related diseases. Lipid metabolism is a key feature of senescent cells, which undergo significant alterations in lipid composition that influence membrane remodeling and cellular function. Here, we propose the use of third harmonic generation (THG) microscopy, a label-free imaging modality, to assess lipid profiles in senescent and nonsenescent cells. Our study demonstrated that THG can discriminate between senescent and nonsenescent fibroblasts based on their lipid content, suggesting a noninvasive approach for the detection and characterization of cellular senescence. In addition, these findings reveal that lipid content is increased in senescent cells. This methodology has potential applications in the diagnosis and study of age-related pathologies where lipid dysregulation is a hallmark feature. Full article
(This article belongs to the Special Issue New Perspectives in Biomedical Optics and Optical Imaging)
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19 pages, 4303 KB  
Article
Design and Series Product Development of a Space-Based Dyson Spectrometer for Ocean Applications
by Xinyin Jia, Siyuan Li, Xianqiang He, Zhaohui Zhang, Pan Hou, Xin Jiang and Jia Liu
Photonics 2025, 12(9), 918; https://doi.org/10.3390/photonics12090918 - 14 Sep 2025
Viewed by 495
Abstract
An advanced Dyson spectrometer is proposed that redesigns the Dyson prism to make the entire system coaxial and easy to implement for each subassembly, thus greatly enhancing optical design, optical processing, and system alignment. The design concept and fabrication methods, as well as [...] Read more.
An advanced Dyson spectrometer is proposed that redesigns the Dyson prism to make the entire system coaxial and easy to implement for each subassembly, thus greatly enhancing optical design, optical processing, and system alignment. The design concept and fabrication methods, as well as the results of imaging evaluations of the proposed spectrometer, are described in detail. At present, the advanced Dyson spectrometer has been in orbit for more than a year, serving smart agriculture and marine applications. The advanced imaging spectrometer achieves high resolution in both the spectral and spatial directions and low spectral distortion at a high numerical aperture in the working waveband. On the basis of the above research, we have developed three other imaging spectrometers with different performance indicators, including a space-based instrument, an airborne instrument and a ground-based instrument, thus verifying the progress and versatility of advanced Dyson spectrometer technology. Full article
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16 pages, 2431 KB  
Article
Visual Performance and Photobiological Effects of White LED Systems Based on Spectral Compensation
by Xuehua Shen, Huanting Chen, Bin Chen, Xiaoxi Ji and Fangming Qin
Photonics 2025, 12(9), 917; https://doi.org/10.3390/photonics12090917 - 14 Sep 2025
Viewed by 497
Abstract
The visual performance and photobiological effects of white LED systems based on spectral compensation are discussed, specifically focusing on the total optical power, the ratio of scotopic vision luminous flux to photopic vision luminous flux (S/P), the blue light hazard (BLH), and the [...] Read more.
The visual performance and photobiological effects of white LED systems based on spectral compensation are discussed, specifically focusing on the total optical power, the ratio of scotopic vision luminous flux to photopic vision luminous flux (S/P), the blue light hazard (BLH), and the circadian action factor (CAF). Theoretical models are established by integrating the spectral power distribution (SPD) with spectral sensitivity functions associated with the human visual system, and meanwhile, the impacts of LEDs’ electro-thermal characteristics on the mixed spectral structure and optical properties are analyzed. As experimental results demonstrate, an excellent agreement is shown between the calculated and measured values of the total optical power, S/P, BLH, and CAF, in terms of both values and variation trends. These proposed models are expected to serve as effective tools for understanding the visual perception and non-visual biological effects in specific illumination environments. Moreover, they can offer valuable reference frameworks for the development of lighting solutions that are more human-centered and health-oriented. Full article
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10 pages, 1893 KB  
Article
Design of a High-Efficiency Hydrogenated Amorphous Silicon Electro-Absorption Modulator with Embedded Graphene Capacitor
by Babak Hashemi, Sandro Rao, Maurizio Casalino and Francesco Giuseppe Della Corte
Photonics 2025, 12(9), 916; https://doi.org/10.3390/photonics12090916 - 13 Sep 2025
Viewed by 586
Abstract
Waveguide-integrated electro-optical modulators play a crucial role in the design of new-generation photonic integrated circuits. The target of this paper is to demonstrate the potential offered by the association of graphene (Gr) and hydrogenated amorphous silicon (a-Si:H) in enhancing silicon photonics technology, enabling, [...] Read more.
Waveguide-integrated electro-optical modulators play a crucial role in the design of new-generation photonic integrated circuits. The target of this paper is to demonstrate the potential offered by the association of graphene (Gr) and hydrogenated amorphous silicon (a-Si:H) in enhancing silicon photonics technology, enabling, in particular, the fabrication of efficient, wide-bandwidth, highly compact active devices. The design of the proposed electro-optic modulator is based on accurate numerical simulations where Gr is explored as the active material, absorbing (or not) the light propagating along the waveguide core, with its absorption coefficient being tunable through the application of an external electric bias. By strategically embedding two Gr monolayers where the propagating optical field is at its maximum, the performance of the modulator is maximized, resulting in a 39.5 GHz 3 dB bandwidth, corresponding to a 0.34 dB/µm modulation depth. The straightforward feasibility of the proposed structure is bolstered by the use of the Plasma-Enhanced Chemical Vapor Deposition technique, which allows for the deposition of a-Si:H on a silicon-on-insulator platform as a post-processing phase, ensuring potential scalability and practical implementation for advanced photonics. Full article
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12 pages, 4378 KB  
Article
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
Viewed by 507
Abstract
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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