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Direct Acceleration of an Electron Beam with a Radially Polarized Long-Wave Infrared Laser
Computation of the Multi-Spheres Scattering Coefficient Using the Prime Index Method

Journal Description

Photonics

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

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, Ei Compendex, CAPlus / SciFinder, and other databases.
Journal Rank: JCR - Q2 (Optics)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 14.9 days after submission; acceptance to publication is undertaken in 1.9 days (median values for papers published in this journal in the second half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Companion journal: Lights.

Impact Factor: 2.1 (2023); 5-Year Impact Factor: 2.1 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2304-6732

Latest Articles

15 pages, 6801 KiB

Open AccessArticle

TiN-Only Metasurface Absorber for Solar Energy Harvesting

by Hongfu Liu, Jijun Li, Hua Yang, Junqiao Wang, Boxun Li, Han Zhang and Yougen Yi

Photonics 2025, 12(5), 443; https://doi.org/10.3390/photonics12050443 (registering DOI) - 3 May 2025

With global energy demand surging and traditional energy resources diminishing, the solar absorber featuring optimized design shows substantial potential in areas like power generation. This study proposes a solar absorber that is insensitive to wide-angle incidence and polarization. It has a cylindrical structure [...] Read more.

With global energy demand surging and traditional energy resources diminishing, the solar absorber featuring optimized design shows substantial potential in areas like power generation. This study proposes a solar absorber that is insensitive to wide-angle incidence and polarization. It has a cylindrical structure with square holes, which is constructed from titanium nitride (TiN). The calculation results indicate that, for plane waves, the average absorption of this solar absorber across the wavelength range of 300–2500 nm reaches 92.4%. Moreover, its absorption rate of the solar spectrum corresponding to AM1.5 reaches 94.8%. The analysis of the characteristics within the electric and magnetic field profiles indicates that the superior absorption properties arise from a cooperative resonance effect. This effect originates from the interaction among surface plasmon resonance, guided-mode resonance, and cavity resonance. In this study, the geometric parameters of the solar absorber’s structure significantly influence its absorption performance. Therefore, we optimized these parameters to obtain the optimal values. Even at a large incident angle, this absorber maintains high absorption performance and shows insensitivity to the polarization angle. The findings expected from this study are likely to be of considerable practical importance within the realm of solar photothermal conversion. Full article

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

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15 pages, 13117 KiB

Open AccessArticle

Determination of Angle of Refraction in X-Ray Phase-Contrast Imaging Using Geometric Optics Method

by Jun Yang, Fangke Zong, Haoqi Tang, Yang Du and Rongchang Chen

Photonics 2025, 12(5), 442; https://doi.org/10.3390/photonics12050442 - 2 May 2025

The accurate calculation of the angle of refraction of X-rays passing through an object is essential in X-ray phase-contrast imaging. While the wave optics-based method is commonly employed to calculate the angle of refraction, it presents several limitations. First, in cases where the [...] Read more.

The accurate calculation of the angle of refraction of X-rays passing through an object is essential in X-ray phase-contrast imaging. While the wave optics-based method is commonly employed to calculate the angle of refraction, it presents several limitations. First, in cases where the object induces significant phase variations, the angle of refraction becomes divergent. Second, the method fails to adequately account for point-source illumination conditions, particularly the influence of the finite X-ray source size on the angle of refraction. In this study, we demonstrate that a geometric optics-based method can effectively simulate propagation-based X-ray phase-contrast imaging with a low-brilliance X-ray source and compute the angle of refraction more accurately than the wave optics-based method. Our studies reveal that the geometric optics-based method can robustly determine the angle of refraction, even under conditions of substantial phase variations within the object. Furthermore, we show that reducing both the X-ray source size and the detector pixel size increases the angle of refraction in both simulations and experiments. Additionally, our results highlight that the angle of refraction is not invariant. Instead, it increases with the system’s total length and as the object moves closer to the light source. For systems with a Fresnel number of N ≥ 1, our method exhibits full compatibility with wave optics methods and can be extended to grating-based X-ray interferometry. The approach offers a robust alternative for calculating the angle of refraction under diverse imaging conditions. Full article

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12 pages, 5916 KiB

Open AccessArticle

Classical Ghost Imaging with Unknowing Pseudo-Thermal Light

by Junyan Hu, Yan Guo, Binglin Chen, Yikang He, Peiming Li and Baoqing Sun

Photonics 2025, 12(5), 441; https://doi.org/10.3390/photonics12050441 - 2 May 2025

Classical ghost imaging (CGI), an extension of quantum ghost imaging (QGI), enables object reconstruction by leveraging the spatial correlation between a pair of beams. Traditionally, CGI requires a camera or point scan to capture the spatial information of the illumination source with intensity [...] Read more.

Classical ghost imaging (CGI), an extension of quantum ghost imaging (QGI), enables object reconstruction by leveraging the spatial correlation between a pair of beams. Traditionally, CGI requires a camera or point scan to capture the spatial information of the illumination source with intensity fluctuations. In this work, we propose a novel CGI scheme that utilizes an incoherent source to illuminate both the object and the modulations, without introducing any mutual interference between them. Through theoretical analysis and experimental validation, we demonstrate that the reconstruction process relies solely on the modulations and correlation signals of two single-pixel detectors. Concurrently, this scheme is also extended to ghost diffraction, verifying the correlation between two planes that are Fourier transform pairs of the speckle field. Moreover, our study reveals the intricate relationships between the speckle field, modulations, and object, and experimentally verifies the impact of speckle fields on image quality. Notably, this work provides a more comparable framework between CGI and QGI, offering a promising avenue to explore the classical–quantum relationship. Full article

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

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14 pages, 7896 KiB

Open AccessArticle

Ultra-Low-Loss Hollow-Core Anti-Resonant Fiber Combining Double-Tube Nesting and a Single-Layer Anti-Resonant Wall

by Xingtao Zhao, Mu Wang, Wenke Zhang, Jinlong Luo, Chang Liu, Sai Liu and Juncheng Li

Photonics 2025, 12(5), 440; https://doi.org/10.3390/photonics12050440 - 2 May 2025

This study innovatively presents a hollow-core anti-resonant fiber integrating double-tube nesting and a single-layer anti-resonant wall. Featuring an exclusive two-layer cladding configuration along with an outer cladding circular ring, it differs significantly from traditional fibers. After careful parameter optimization, at 1.55 μm wavelength, [...] Read more.

This study innovatively presents a hollow-core anti-resonant fiber integrating double-tube nesting and a single-layer anti-resonant wall. Featuring an exclusive two-layer cladding configuration along with an outer cladding circular ring, it differs significantly from traditional fibers. After careful parameter optimization, at 1.55 μm wavelength, the fiber shows excellent performance. Its confinement loss drops to 0.00088 dB/km, 1–2 orders lower than traditional ones. The proportion between the loss of the lowest higher-order mode and that of the fundamental mode reaches 19,900, indicating excellent single-mode performance. In the case of a bending radius of 11–14.2 cm, the x-polarization loss is below 0.001 dB/km, showing good bending resistance. Through structural comparisons, this paper quantitatively reveals the effects of the anti-resonant wall, cladding tube, and outer cladding ring on fiber performance. From the practical fiber-drawing process, it thoroughly analyzes the impact of the outer connecting tube’s offset angle on fiber performance. This research provides crucial theoretical support for new hollow-core fiber design, manufacture, and application, and is expected to drive technological innovation in this field. Full article

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11 pages, 2208 KiB

Open AccessArticle

Enhanced Localized Electric Field from Surface Plasmon Coupling in a Silver Nanostructure Array with a Silver Thin Film for Bioimaging and Biosensing

by Kota Yamasaki, Ryohei Hatsuoka, Kenji Wada, Tetsuya Matsuyama and Koichi Okamoto

Photonics 2025, 12(5), 439; https://doi.org/10.3390/photonics12050439 - 1 May 2025

The electric field enhancement effect induced by localized surface plasmon resonance (LSPR) plays a critical role in imaging and sensing applications. In particular, nanocube structures with narrow gaps provide large hotspot areas, making them highly promising for high-sensitivity applications. This study predicts the [...] Read more.

The electric field enhancement effect induced by localized surface plasmon resonance (LSPR) plays a critical role in imaging and sensing applications. In particular, nanocube structures with narrow gaps provide large hotspot areas, making them highly promising for high-sensitivity applications. This study predicts the electric field enhancement effect of structures combining silver nanocubes and a 10 nm thick silver thin film using the finite-difference time-domain (FDTD) method. We demonstrate that the interaction between the silver nanocubes and silver thin film allows control over sharp LSPR peaks in the visible wavelength range. Specifically, the structure with a spacer layer between the silver nanocubes and the silver thin film is suitable for multimodal imaging, while the direct contact structure of the silver nanocubes and the silver thin film shows potential as a highly sensitive refractive index sensor. The 10 nm thick silver thin film enables backside illumination due to its transparency in the visible wavelength region, making it compatible with inverted microscopes and allowing for versatile applications, such as living cell imaging and observations in liquid media. These structures are particularly expected to contribute to advancements in bioimaging and biosensing. Full article

(This article belongs to the Special Issue Plasmon-Enhanced Photon Emission in Nanostructures)

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16 pages, 7724 KiB

Open AccessArticle

Synthesis, Optical, and Photocatalytic Properties of the BiVO₄ Semiconductor Nanoparticles with Tetragonal Zircon-Type Structure

by Dragana Marinković, Giancarlo C. Righini and Maurizio Ferrari

Photonics 2025, 12(5), 438; https://doi.org/10.3390/photonics12050438 - 30 Apr 2025

The optical characteristics of semiconductor’s particles are strongly dependent on physicochemical properties and the reduced size of the system. Decreasing the size of the material causes an increase in the ratio between the number of atoms on the surface and the number of [...] Read more.

The optical characteristics of semiconductor’s particles are strongly dependent on physicochemical properties and the reduced size of the system. Decreasing the size of the material causes an increase in the ratio between the number of atoms on the surface and the number of atoms inside the particle, that is, the increase in specific surface area and surface defects. Due to their high surface-area-to-volume ratio and increased number of active sites on the surface, the nanostructured materials with altered optical properties compared to the bulk material are preferable for catalytic reactions. In this study, an ultra-small and very crystalline zircon-nanostructured bismuth vanadate (BiVO₄) semiconductor was prepared by ethylene glycol-assisted synthesis. The nanoparticles have a radius between 2 and 8 nm, as shown by TEM images, and a high Brunauer–Emmett–Teller (BET) specific surface area. The optical, structural, microstructural, and photocatalytic properties were examined in detail. X-ray photoelectron spectroscopy (XPS) technique confirmed the occurrence of Bi, V, and O elements and also found that Bi and V exist in +3 and +5 oxidation states, respectively. The photocatalytic activity of the samples was checked using methyl orange (MO) under UV-Vis lighting. The photocatalytic performance was compared to commercial TiO₂ powder. The results showed tetragonal zircon-type nanostructured BiVO₄ as a promising catalyst for rapid removal of pollutants from wastewater. Full article

(This article belongs to the Special Issue Photonics: 10th Anniversary)

12 pages, 3889 KiB

Open AccessArticle

Design and Research of Photonic Reservoir Computing for Optical Channel Equalization

by Xiaoyan Zuo, Li Pei, Bing Bai, Bowen Bai, Jianshuai Wang, Quan Li and Run Yang

Photonics 2025, 12(5), 437; https://doi.org/10.3390/photonics12050437 - 30 Apr 2025

In this paper, photonic reservoir computing chip architectures for noise equalization in optical fiber communication channels are proposed. These architectures leverage optical computing instead of electrical computing to reduce computational pressure at the receiver and decrease processing latency. We examine the impact of [...] Read more.

In this paper, photonic reservoir computing chip architectures for noise equalization in optical fiber communication channels are proposed. These architectures leverage optical computing instead of electrical computing to reduce computational pressure at the receiver and decrease processing latency. We examine the impact of factors such as the number of reservoir nodes, waveguide delay line length, and the number of input/output ports on equalization performance. We discuss the equalization ability of these architectures under various types of noise. After parameter optimization, the 36-node reservoir layout achieves a three-orders-of-magnitude reduction in bit error rate for 20 km OOK signals after equalization. Additionally, the chip architecture facilitates easy expansion of the all-optical readout layer, offering the possibility for further increasing the equalization speed. Full article

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

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23 pages, 4826 KiB

Open AccessArticle

Visualization of High-Intensity Laser–Matter Interactions in Virtual Reality and Web Browser

by Martin Matys, James P. Thistlewood, Mariana Kecová, Petr Valenta, Martina Greplová Žáková, Martin Jirka, Prokopis Hadjisolomou, Alžběta Špádová, Marcel Lamač and Sergei V. Bulanov

Photonics 2025, 12(5), 436; https://doi.org/10.3390/photonics12050436 - 30 Apr 2025

We present the Virtual Beamline (VBL) application, an interactive web-based platform for visualizing high-intensity laser–matter interactions using particle-in-cell (PIC) simulations, with future potential for experimental data visualization. These interactions include ion acceleration, electron acceleration,

γ

-flash generation, electron–positron pair production, and attosecond and [...] Read more.

We present the Virtual Beamline (VBL) application, an interactive web-based platform for visualizing high-intensity laser–matter interactions using particle-in-cell (PIC) simulations, with future potential for experimental data visualization. These interactions include ion acceleration, electron acceleration,

γ

-flash generation, electron–positron pair production, and attosecond and spiral pulse generation. Developed at the ELI Beamlines facility, VBL integrates a custom-built WebGL engine with WebXR-based Virtual Reality (VR) support, allowing users to explore complex plasma dynamics in non-VR mode on a computer screen or in fully immersive VR mode using a head-mounted display. The application runs directly in a standard web browser, ensuring broad accessibility. VBL enhances the visualization of PIC simulations by efficiently processing and rendering four main data types: point particles, 1D lines, 2D textures, and 3D volumes. By utilizing interactive 3D visualization, it overcomes the limitations of traditional 2D representations, offering enhanced spatial understanding and real-time manipulation of visualization parameters such as time steps, data layers, and colormaps. Users can interactively explore the visualized data by moving their body or using a controller for navigation, zooming, and rotation. These interactive capabilities improve data exploration and interpretation, making VBL a valuable tool for both scientific analysis and educational outreach. The visualizations are hosted online and freely accessible on our server, providing researchers, the general public, and broader audiences with an interactive tool to explore complex plasma physics simulations. By offering an intuitive and dynamic approach to large-scale datasets, VBL enhances both scientific research and knowledge dissemination in high-intensity laser–matter physics. Full article

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26 pages, 4592 KiB

Open AccessReview

Recent Progress in Organic Optoelectronic Synaptic Devices

by Min He and Xin Tang

Photonics 2025, 12(5), 435; https://doi.org/10.3390/photonics12050435 - 30 Apr 2025

Organic semiconductors hold immense promise in the field of optoelectronic synapses due to their tunable optoelectronic properties, mechanical flexibility, and biocompatibility. This review article provides a comprehensive overview of recent advancements in organic optoelectronic synaptic devices. We delve into the fundamental concepts and [...] Read more.

Organic semiconductors hold immense promise in the field of optoelectronic synapses due to their tunable optoelectronic properties, mechanical flexibility, and biocompatibility. This review article provides a comprehensive overview of recent advancements in organic optoelectronic synaptic devices. We delve into the fundamental concepts and classifications of these devices, examine their roles and operational mechanisms, and explore their diverse application scenarios. Additionally, we highlight the current challenges and emerging opportunities in this field, outlining a forward-looking path for the future development and application of these materials and devices in next-generation artificial intelligence (AI). We emphasize the potential of further optimizing organic materials and devices, which could significantly enhance the integration of organic synapses into biointegrated electronics and human–computer interfaces. By addressing key challenges such as material stability, device performance, and scalability, we aim to accelerate the transition from laboratory research to practical applications, paving the way for innovative AI systems that mimic biological neural networks. Full article

(This article belongs to the Special Issue Organic Photodetectors, Displays, and Upconverters)

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12 pages, 2523 KiB

Open AccessArticle

Image Reconstruction Through Multimode Polymer Optical Fiber for Potential Optical Recording of Neural Activity

by Fengling Chen, Siyu Chen, Changjian Zhao, Yanan Zou, Kun Xiao, Zhuo Wang, Arnaldo Leal-Junior and Rui Min

Photonics 2025, 12(5), 434; https://doi.org/10.3390/photonics12050434 - 30 Apr 2025

Despite the growing demand for high-resolution imaging techniques in neuroscience, traditional methods are limited in terms of flexibility and spatial resolution. We explored an approach using multimode polymer optical fiber (POF) and employing a neural network for image reconstruction and studied the ability [...] Read more.

Despite the growing demand for high-resolution imaging techniques in neuroscience, traditional methods are limited in terms of flexibility and spatial resolution. We explored an approach using multimode polymer optical fiber (POF) and employing a neural network for image reconstruction and studied the ability of multimode POF to effectively capture and reconstruct high-quality images. Here, a conventional U-Net model within the framework of convolutional neural networks (CNNs) is applied to the reconstruction of speckle images obtained via POF. The model was trained on an experimental dataset consisting of MNIST graphs and successfully reconstructed high-quality images that closely resemble the original undistorted scene. This study not only highlights the potential of POF in biomedical imaging but also paves the way for more sophisticated optical recording techniques. Full article

(This article belongs to the Special Issue Advances in Polymer Optical Fiber Sensors: Materials, Designs and Applications)

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10 pages, 6739 KiB

Open AccessArticle

High-Performance Microwave-Frequency Comb Generation Based on Directly Modulated Laser with Filtering Operations

by Qianyou Long, Yang Jiang, Jing Xu, Xiaohong Lan, Jinjian Feng, Jiancheng Yu, Yunkun Luo, Tingyi Jiang, Hui Zhang and Yu Wu

Photonics 2025, 12(5), 433; https://doi.org/10.3390/photonics12050433 - 30 Apr 2025

In this paper, a scheme for generating high-quality tunable microwave-frequency combs (MFCs) is proposed. The proposed scheme is based on an initially non-flat MFC generated by a directly modulated laser operating in gain-switching status. Filtering operations are used to increase the flatness of [...] Read more.

In this paper, a scheme for generating high-quality tunable microwave-frequency combs (MFCs) is proposed. The proposed scheme is based on an initially non-flat MFC generated by a directly modulated laser operating in gain-switching status. Filtering operations are used to increase the flatness of the MFC. Concretely, by employing an optical bandpass filter and a two-tap negative-coefficient microwave photonic filter, the flatness of the MFC is significantly optimized. In the experiment, MFCs with adjustable comb spacing from 0.5 GHz to 1.6 GHz and bandwidths ranging from 0 to 26.5 GHz are generated. The flatness is better than ±2.5 dB for the MFC. The proposed scheme provides a simple, efficient, and high-performance solution for generating MFCs, making it a promising candidate for various applications requiring high-quality MFC sources. Full article

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12 pages, 4584 KiB

Open AccessArticle

Characteristics of Fused Silica Exit Surface Damage by Low-Temporal Coherence Light Irradiation

by Chong Shan, Ping Han, Erxi Wang, Fujian Li, Xiaohui Zhao, Huamin Kou, Dapeng Jiang, Qinghui Wu, Xing Peng, Penghao Xu, Yafei Lian, Yuanan Zhao, Liangbi Su, Zhan Sui and Yanqi Gao

Photonics 2025, 12(5), 432; https://doi.org/10.3390/photonics12050432 - 30 Apr 2025

Laser-induced exit surface damage of fused silica is a key bottleneck for its application in high-power laser devices. As low-temporal coherence light (LTCL) has garnered increasing attention for high-power laser-driven inertial confinement fusion, understanding LTCL-induced exit surface damage of fused silica becomes crucial [...] Read more.

Laser-induced exit surface damage of fused silica is a key bottleneck for its application in high-power laser devices. As low-temporal coherence light (LTCL) has garnered increasing attention for high-power laser-driven inertial confinement fusion, understanding LTCL-induced exit surface damage of fused silica becomes crucial for improving the output power capability of LTCL devices. In this study, we characterized damage on the exit surface of fused silica under LTCL irradiation and investigated the physical mechanism of temporal coherence affecting the laser-induced damage threshold (LIDT). The relationship between defect information and temporal coherence was explored using a defect analysis model, and the defect damage process and response to each incident lasers were captured using time-resolved methods and artificially fabricated defects. We elucidate the physical mechanism behind the lower LIDT under LTCL irradiation compared to single longitudinal mode (SLM) pulse lasers. This study not only provides the boundary condition for safe fused silica operation in high-power LTCL devices but also offers deeper insight into the physical properties of LTCL. Full article

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

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11 pages, 3180 KiB

Open AccessCommunication

Cooling Fiber Laser Power Converter Systems by Immersion in Oil

by Denis Masson and Simon Fafard

Photonics 2025, 12(5), 431; https://doi.org/10.3390/photonics12050431 - 30 Apr 2025

We demonstrate the use of Laser Power Converters (LPCs) driven by fiber laser light while immersed in transformer oil for heat management purposes. Reliability tests performed via extended continuous operation using 6–7 W of input power from 808 nm and 976 nm light [...] Read more.

We demonstrate the use of Laser Power Converters (LPCs) driven by fiber laser light while immersed in transformer oil for heat management purposes. Reliability tests performed via extended continuous operation using 6–7 W of input power from 808 nm and 976 nm light propagating through oil show no degradation of components nor transmission losses from the oil for up to 1000 h. The operation of a bare die designed for use with 1040–1080 nm light and in direct contact with oil is also shown to be feasible. We discuss how the use of transformer oil can be beneficial to transfer excess heat away from LPCs in special applications. Full article

(This article belongs to the Special Issue Technologies of Laser Wireless Power Transmission)

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14 pages, 3350 KiB

Open AccessArticle

Feasibility of Photoplethysmography in Detecting Arterial Stiffness in Hypertension

by Parmis Karimpour, James M. May and Panicos A. Kyriacou

Photonics 2025, 12(5), 430; https://doi.org/10.3390/photonics12050430 - 29 Apr 2025

Asymptomatic peripheral artery disease (PAD) poses a silent risk, potentially leading to severe conditions if undetected. Integrating new screening tools into routine general practitioner (GP) visits could enable early detection. This study investigates the feasibility of photoplethysmography (PPG) monitoring for assessing vascular health [...] Read more.

Asymptomatic peripheral artery disease (PAD) poses a silent risk, potentially leading to severe conditions if undetected. Integrating new screening tools into routine general practitioner (GP) visits could enable early detection. This study investigates the feasibility of photoplethysmography (PPG) monitoring for assessing vascular health across different blood pressure (BP) conditions. Custom femoral artery phantoms representing healthy (0.82 MPa), intermediate (1.48 MPa), and atherosclerotic (2.06 MPa) vessels were tested under hypertensive, normotensive, and hypotensive conditions to evaluate PPG’s ability to distinguish between vascular states. Extracted features from the PPG signal, including amplitude, area under the curve (AUC), median upslope–downslope ratio, and median end datum difference, were analysed. Kruskal–Wallis tests revealed significant differences between healthy and unhealthy vessels across BP states, supporting PPG as a screening tool. The fiducial points from the second derivative of the photoplethysmography signal (SDPPG) were analysed. The

\frac{b}{a}

ratio was most pronounced between healthy and unhealthy phantoms under hypertensive conditions (ranging from –2.13 to –2.06), suggesting a change in vascular wall distensibility. Under normotensive conditions, the difference in

\frac{b}{a}

ratios between healthy and unhealthy phantoms was smaller (0.01), and no meaningful difference was observed under hypotensive conditions, suggesting the reduced sensitivity of this metric at lower perfusion pressures. Intermediate states were challenging to detect, particularly under hypotension, suggesting a need for further research. Nonetheless, this study highlights the promise of PPG monitoring in identifying vascular stiffness. Full article

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38 pages, 10775 KiB

Open AccessReview

Comparison of Thin-Film Lithium Niobate, SOH, and POH for Silicon Photonic Modulators

by Tai-Cheng Yu, An-Chen Liu, Wei-Ta Huang, Chang-Chin Wu, Chung-Hsun Li, Tsung-Sheng Kao, Shu-Wei Chang, Chin-Wei Sher, Huang-Yu Lin, Chi-Wai Chow and Hao-Chung Kuo

Photonics 2025, 12(5), 429; https://doi.org/10.3390/photonics12050429 - 29 Apr 2025

Optical modulators are indispensable components in optical communication systems and must be designed to minimize insertion loss, reduce driving voltage, and enhance linearity. State-of-the-art silicon modulator technology has limitations in terms of power, performance, and spatial size. The addition of materials such as [...] Read more.

Optical modulators are indispensable components in optical communication systems and must be designed to minimize insertion loss, reduce driving voltage, and enhance linearity. State-of-the-art silicon modulator technology has limitations in terms of power, performance, and spatial size. The addition of materials such as thin-film lithium niobate (TFLN), silicon–organic hybrids (SOH), and plasma–organic hybrids (POH) has improved the modulation performance in silicon photonics. An evaluation of the differences among these modulators and their respective performance characteristics is conducted. Full article

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19 pages, 5431 KiB

Open AccessArticle

Polarization-Insensitive Silicon Grating Couplers via Subwavelength Metamaterials and Metaheuristic Optimization

by Jorge Parra

Photonics 2025, 12(5), 428; https://doi.org/10.3390/photonics12050428 - 29 Apr 2025

Silicon photonics is the leading platform in photonic integrated circuits (PICs), enabling dense integration and low-cost manufacturing for applications such as data communications, artificial intelligence, and quantum processing, to name a few. However, efficient and polarization-insensitive fiber-to-PIC coupling for multipoint wafer characterization remains [...] Read more.

Silicon photonics is the leading platform in photonic integrated circuits (PICs), enabling dense integration and low-cost manufacturing for applications such as data communications, artificial intelligence, and quantum processing, to name a few. However, efficient and polarization-insensitive fiber-to-PIC coupling for multipoint wafer characterization remains a challenge due to the birefringence of silicon waveguides. Here, we address this issue by proposing polarization-insensitive grating couplers based on subwavelength dielectric metamaterials and metaheuristic optimization. Subwavelength periodic structures were engineered to act as uniaxial homogeneous linear (UHL) materials, enabling tailored anisotropy. On the other hand, particle swarm optimization (PSO) was employed to optimize the coupling efficiency, bandwidth, and polarization-dependent loss (PDL). Numerical simulations demonstrated that a pitch of 100 nm ensures UHL behavior while minimizing leaky waves. Optimized grating couplers achieved coupling efficiencies higher than −3 dB and a PDL of below 1 dB across the telecom C-band (1530–1565 nm). Three optimization strategies were explored, balancing efficiency, the bandwidth, and the PDL while considering the Pareto front. This work establishes a robust framework combining metamaterial engineering with computational optimization, paving the way for high-performance polarization-insensitive grating couplers with potential uses in advanced photonic applications. Full article

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

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16 pages, 3126 KiB

Open AccessArticle

Waveguide Coupled Full-Color Quantum Dot Light-Emitting Diodes Modulated by Microcavities

by Yilan Zhang, Wenhao Wang, Fankai Zheng, Jiajun Zhu, Guanding Mei, Yuxuan Ye, Jieyu Tan, Hechun Zhang, Qiang Jing, Bin He, Kai Wang and Dan Wu

Photonics 2025, 12(5), 427; https://doi.org/10.3390/photonics12050427 - 29 Apr 2025

Integrated light-emitting diodes (LEDs) with waveguides play an important role in applications such as augmented reality (AR) displays, particularly regarding coupling efficiency optimization. Quantum dot light-emitting diodes (QLEDs), an emerging high-performance optoelectronic device, demonstrate substantial potential for next-generation display technologies. This study investigates [...] Read more.

Integrated light-emitting diodes (LEDs) with waveguides play an important role in applications such as augmented reality (AR) displays, particularly regarding coupling efficiency optimization. Quantum dot light-emitting diodes (QLEDs), an emerging high-performance optoelectronic device, demonstrate substantial potential for next-generation display technologies. This study investigates the influence of microcavity modulation on the output of QLEDs coupled with a silicon nitride (SiNx) waveguide by simulating a white light QLED (W-QLED) with a broad spectrum and mixed RGB QDs (RGB-QLED) with a comparatively narrower spectrum. The microcavity converts both W-QLED and RGB-QLED emissions from broadband white-light emissions into narrowband single-wavelength outputs. Specifically, both of them have demonstrated wavelength tuning and full-width at half-maximum (FWHM) narrowing across the visible spectrum from 400 nm to 750 nm due to the microcavity modulation. The resulting RGB-QLED achieves a FWHM of 11.24 nm and reaches 110.76% of the National Television System Committee 1953 (NTSC 1953) standard color gamut, which is a 20.95% improvement over W-QLED. Meanwhile, due to the Purcell effect of the microcavity, the output efficiency of the QLED coupled with a SiNx waveguide is also significantly improved by optimizing the thickness of the Ag anode and introducing a tilted reflective mirror into the SiNx waveguide. Moreover, the optimal output efficiency of RGB-QLED with the tilted Ag mirror is 10.13%, representing a tenfold increase compared to the sample without the tilted Ag mirror. This design demonstrates an efficient and compact approach for the near-eye full-color display technology. Full article

(This article belongs to the Special Issue Quantum Dot Light-Emitting Diodes: Innovations and Applications)

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16 pages, 3746 KiB

Open AccessArticle

Theoretical Research on Large Field-of-View Polarization Imaging Based on Dynamic Vision Sensors

by Xiaotian Lu, Kunpeng Xing, Siran Li, Ziyu Gu and Lei Xin

Photonics 2025, 12(5), 426; https://doi.org/10.3390/photonics12050426 - 29 Apr 2025

The combination of dynamic vision sensors (DVSs) and polarization can overcome the limitation of DVSs whereby they can only detect dynamic scenes, and it also has the ability to detect artificial targets and camouflaged targets, and is thus expected to become a new [...] Read more.

The combination of dynamic vision sensors (DVSs) and polarization can overcome the limitation of DVSs whereby they can only detect dynamic scenes, and it also has the ability to detect artificial targets and camouflaged targets, and is thus expected to become a new means of remote sensing detection. Remote sensing detection often requires the field-of-view (FOV) and width to be large enough to improve detection efficiency, but when large FOV polarization imaging is performed, the polarization state in the edge FOV and the center FOV will not be consistent, which does not meet the paraxial approximation condition, and the inconsistency increases as the angle between the incident light and the optical axis increases. This affects the accuracy of target detection, so in this paper, based on the characteristics of polarization imaging using a DVS, factors such as the polarizer rotation step, incident light polarization state, and incident angle are considered to establish a theoretical model of large FOV polarization imaging using DVSs. And the influence of the detection ability is analyzed for three types of incident conditions, namely linearly polarized light, natural light, and partially polarized light. The results show that when the rotation step is 5°, the highest false alarm rate for natural light incident in the edge FOV will be nearly 53%, and the highest false alarm rate for linearly polarized light incident will be nearly 32%. Full article

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15 pages, 8047 KiB

Open AccessArticle

Compact Four-Channel Optical Emission Module with High Gain

by Xiying Dang, Linyi Li, Man Chen, Zijian Hu, Tianyu Yang, Zeping Zhao and Zhike Zhang

Photonics 2025, 12(5), 425; https://doi.org/10.3390/photonics12050425 - 28 Apr 2025

In this paper, a four-channel optical emission module is developed using hybrid integration technology that integrates directly modulated laser (DML) chips, low-noise amplifier (LNA) chips, and control circuits, with dimensions of 24.4 mm × 21 mm × 5.9 mm. This module enables high-gain [...] Read more.

In this paper, a four-channel optical emission module is developed using hybrid integration technology that integrates directly modulated laser (DML) chips, low-noise amplifier (LNA) chips, and control circuits, with dimensions of 24.4 mm × 21 mm × 5.9 mm. This module enables high-gain signal output and minimizes crosstalk between neighboring channels while improving integration. An equivalent circuit model of radio frequency (RF) signal transmission is established, and the accuracy of the model and the effectiveness of the approach to improve signal gain are verified using simulations and experiments. With optimized thermal management, the module has the ability to operate at stable temperatures across an ambient range of −55 °C to 75 °C. The module has a channel wavelength spacing of approximately 1 nm, and the −3 dB bandwidth of each channel exceeds 20 GHz. The crosstalk between neighboring channels is less than −65 dB. In the range of 0.8~25 GHz, the four-channel gain is approximately 15 dB through the integration of the LNA chip. The module achieves a noise figure (NF) of less than 30 dB. Full article

(This article belongs to the Special Issue Microwave Photonics: Science and Applications)

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20 pages, 2763 KiB

Open AccessReview

Recent Advances of Guided Mode Resonant Sensors Applied to Cancer Biomarker Detection

by Pankaj K. Sahoo, Arshad Ahmad Bhat, Mandeep Singh and Kezheng Li

Photonics 2025, 12(5), 424; https://doi.org/10.3390/photonics12050424 - 28 Apr 2025

Guided mode resonance (GMR)-based sensors have emerged as a promising technology for the early screening of cancer, offering advantages such as sensitivity, specificity, low cost, non-invasiveness, and portability. This review article provides a comprehensive overview of the latest advancements in GMR technology and [...] Read more.

Guided mode resonance (GMR)-based sensors have emerged as a promising technology for the early screening of cancer, offering advantages such as sensitivity, specificity, low cost, non-invasiveness, and portability. This review article provides a comprehensive overview of the latest advancements in GMR technology and its applications in biosensing, with a specific focus on cancer. The current state of cancer diagnosis and the critical need for point-of-care (POC) devices to address these challenges are discussed in detail. Furthermore, the review systematically explores various strategies employed in GMR-based cancer detection including design principles and the integration of advanced technologies. Additionally, it aims to provide researchers valuable insights for developing GMR sensors capable of detecting cancer biomarkers outside the laboratory environment. Full article

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

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