Photonics

10 pages, 3846 KiB

Open AccessArticle

Optical Differentiation and Edge Detection Based on Birefringence of Uniaxial Crystals

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

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

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

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

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17 pages, 13853 KiB

Open AccessArticle

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

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

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

Abstract

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

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

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14 pages, 3191 KiB

Open AccessArticle

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

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

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

Abstract

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

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

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

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13 pages, 1772 KiB

Open AccessArticle

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

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

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

Abstract

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

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

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

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12 pages, 8821 KiB

Open AccessArticle

Tunable Slow Light in Valley-Locked Topological Photonic Crystal Waveguide

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

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

Abstract

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

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

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

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9 pages, 784 KiB

Open AccessCommunication

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

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

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

Abstract

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

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

9 pages, 1226 KiB

Open AccessCommunication

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

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

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

Abstract

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

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

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

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13 pages, 10030 KiB

Open AccessArticle

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

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

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

Abstract

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

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

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17 pages, 841 KiB

Open AccessArticle

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

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

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

Abstract

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

μ

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

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

μ

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

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

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15 pages, 2888 KiB

Open AccessArticle

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

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

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

Abstract

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

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

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13 pages, 3845 KiB

Open AccessArticle

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

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

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

Abstract

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

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

{TE}_{0}

,

{TE}_{1}

, and

{TE}_{2}

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

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

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14 pages, 1885 KiB

Open AccessArticle

Featureless Broadband Chaos Through Cascaded Optically Injected Semiconductor Lasers

by Mohammad AlMulla

Photonics 2025, 12(4), 325; https://doi.org/10.3390/photonics12040325 - 31 Mar 2025

Abstract

Optical chaos generated by a semiconductor laser under cascaded optical injection is experimentally and numerically investigated. A semiconductor slave laser under continuous-wave optical injection from a master laser is employed as the chaotic laser. The chaotic output optically injects a third laser to [...] Read more.

Optical chaos generated by a semiconductor laser under cascaded optical injection is experimentally and numerically investigated. A semiconductor slave laser under continuous-wave optical injection from a master laser is employed as the chaotic laser. The chaotic output optically injects a third laser to enhance the chaotic properties. Using three semiconductor lasers coupled in a master-slave configuration without any delay-based components, optical chaos is generated without any time-delay signatures present. Flat broadband chaos is observed with standard and effective bandwidths reaching six and three times the relaxation resonance frequency of the semiconductor laser, respectively. For simultaneous flat and broadband chaos, the chaotic optical injection of the second stage is adjusted for weak injection strength and a high positively detuned frequency. Full article

(This article belongs to the Special Issue Semiconductor Lasers: Innovations, Challenges, and Future Perspectives)

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18 pages, 3947 KiB

Open AccessArticle

Joint Three-Task Optical Performance Monitoring with High Performance and Superior Generalizability Using a Meta-Learning-Based Convolutional Neural Network-Attention Algorithm and Amplitude-Differential Phase Histograms Across WDM Transmission Scenarios

by Di Zhang, Junyao Shi, Yameng Cao and Yan Ling Xue

Photonics 2025, 12(4), 324; https://doi.org/10.3390/photonics12040324 - 31 Mar 2025

Abstract

Nonlinear noise power (NLNP) estimation, optical signal-to-noise ratio (OSNR) monitoring, and modulation format identification (MFI) are crucial for optical performance monitoring (OPM) in future dynamic WDM optical networks. This paper proposes an OPM scheme to simultaneously implement these three tasks in both single-channel [...] Read more.

Nonlinear noise power (NLNP) estimation, optical signal-to-noise ratio (OSNR) monitoring, and modulation format identification (MFI) are crucial for optical performance monitoring (OPM) in future dynamic WDM optical networks. This paper proposes an OPM scheme to simultaneously implement these three tasks in both single-channel and WDM systems by combining amplitude-differential phase histograms (ADPH) with the MAML-CNN-ATT algorithm that integrates model-agnostic meta-learning (MAML), the convolutional neural network (CNN), and the attention mechanism (ATT). The meta-learning algorithms can learn optimal initial model parameters across multiple related tasks, enabling them to quickly adapt to new tasks through fine-tuning with a small amount of data. This results in superior self-adaptability and generalizability, making them more suitable for WDM scenarios than the transfer learning (TL) algorithms. The CNN-ATT algorithm can effectively extract comprehensive features, capturing both local and global dependencies, thus improving the quality of the feature representation. The ADPH sequence data combine the amplitude information and the differential phase information that indicate the signal’s overall characteristics. The results demonstrate that the MAML-CNN-ATT algorithm achieves errors of less than 1 dB in both NLNP estimation and OSNR monitoring tasks while achieving 100% accuracy in the MFI task. It exhibits excellent OPM performance not only in the single channel but also in the WDM transmission, with only a few steps of fine-tuning. The MAML-CNN-ATT algorithm provides a solution with high performance and rapid self-adaptation for the multi-task OPM in dynamic optical networks. Full article

(This article belongs to the Special Issue Enabling Technologies for Optical Communications and Networking)

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12 pages, 2134 KiB

Open AccessArticle

A Self-Healing WDM Access Network with Protected Fiber and FSO Link Paths Effective Against Fiber Breaks

by Tsu-Hsin Wu, Chien-Yu Liao, Chien-Hung Yeh, Yuan-Wen Chen, Yu-Hsin Kao, Sung-Yi Lin, Yu-Heng Lin and Shien-Kuei Liaw

Photonics 2025, 12(4), 323; https://doi.org/10.3390/photonics12040323 - 30 Mar 2025

Abstract

In this article, an additional protected fiber and free-space optical (FSO) link path is proposed, to provide self-healing capabilities for protection against fiber faults in wavelength division multiplexed passive optical network (WDM-PON) systems. The new optical line terminal (OLT), remote node (RN), and [...] Read more.

In this article, an additional protected fiber and free-space optical (FSO) link path is proposed, to provide self-healing capabilities for protection against fiber faults in wavelength division multiplexed passive optical network (WDM-PON) systems. The new optical line terminal (OLT), remote node (RN), and optical network unit (ONU) in the presented PON architecture result in self-protective function against fiber breakpoints. In the measurement, 25 Gbit/s on-off keying (OOK) modulation was applied on each WDM channel to assess the downstream and upstream signals after 25 km single-mode fiber (SMF) and 25 km SMF + 2 m FSO connections, respectively. In addition to using protected fiber paths for self-healing operations. This PON system can also apply the FSO link method. The measured bit error rate (BER) for all downstream and upstream traffic was maintained below 3.8 × 10⁻³ with forward error correction (FEC). The detected optical power sensitivity of the proposed self-restorative fiber- and FSO-based WDM-PON for downstream and upstream WDM signals ranged from −33.5 to −28.5 dBm and from −33 to −28.5 dBm, respectively, and the corresponding power budgets of the downstream and upstream WDM signals were between 29.5 and 30.5 dB and 33 and 38 dB, respectively. Full article

(This article belongs to the Special Issue Free-Space Optical Communication and Networking Technology)

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14 pages, 2486 KiB

Open AccessArticle

High-Performance O-Band Angled Multimode Interference Splitter with Buried Silicon Nitride Waveguide for Advanced Data Center Optical Networks

by Eduard Ioudashkin and Dror Malka

Photonics 2025, 12(4), 322; https://doi.org/10.3390/photonics12040322 - 30 Mar 2025

Abstract

Many current 1 × 2 splitter couplers based on multimode interference (MMI) face difficulties such as significant back reflection and limited flexibility in waveguide segmentation at the output, which necessitate the addition of transitional structures like tapered waveguides or S-Bends. These limitations reduce [...] Read more.

Many current 1 × 2 splitter couplers based on multimode interference (MMI) face difficulties such as significant back reflection and limited flexibility in waveguide segmentation at the output, which necessitate the addition of transitional structures like tapered waveguides or S-Bends. These limitations reduce their effectiveness as photonic data-center applications, where precise waveguide configurations are crucial. To address these challenges, we propose a novel nanoscale 1 × 2 angled multimode interference (AMMI) power splitter with silicon nitride (SiN) buried core and silica cladding. The innovative angled light path design improved performance by minimizing back reflections back to the source and by providing greater flexibility of waveguide interconnections, making the splitter more adaptable for data-center applications. The SiN core was selected due to its lower refractive index contrast with silica compared to silicon, which helps further reduce back reflection. The dimensions of the splitter were optimized using full vectorial beam propagation method (FV-BPM), finite-difference time domain (FDTD), and multivariable optimization scanning tool (MOST) simulations to support transmission across the O-band. Our proposed device demonstrated excellent performance, achieving an excess loss of 0.22 dB and an imbalance of <0.01 dB at the output ports at an operational wavelength of 1.31 µm. The total device length is 101 µm with a thickness of 0.4 µm. Across the entire O-band range (1260–1360 nm), the performance of the splitter presented excess loss of up to 1.57 dB and an imbalance of up to 0.05 dB. Additionally, back reflections at the operational wavelength were measured at −40.96 dB and up to −39.67 dB over the O-band. This silicon-on-insulator (SOI) complementary metal-oxide semiconductor (CMOS) compatible AMMI splitter demonstrates high tolerance for manufacturing deviations due to its geometric layout, dimensions, and material selection. Furthermore, the proposed splitter is well-suited for use in O-band transceiver systems and can enhance data-center optical networks by supporting high-speed, low-loss data transmission. The compact design and CMOS compatibility make this device ideal for integrating into dense, high-performance computing environments, ensuring reliable signal distribution and minimal power loss. The splitter can support multiple communication channels, thus enhancing bandwidth and scalability for next-generation data-center infrastructures. Full article

(This article belongs to the Special Issue Emerging Trends in On-Chip Photonic Integration)

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33 pages, 12750 KiB

Open AccessArticle

Experimental Study on Fiber Optic Strain Characterization of Overlying Rock Layer Movement Forms and States Using DFOS

by Tao Hu, Fengjun Wei, Jintao Wang, Yan Wang, Chunhua Song, Kuiliang Han and Kaiqiang Han

Photonics 2025, 12(4), 321; https://doi.org/10.3390/photonics12040321 (registering DOI) - 30 Mar 2025

Abstract

Mastering the movement laws of hard overlying rock layers is the foundation of the development of coal mining technology and plays an important role in improving coal mine safety production. Therefore, an indoor similar simulation experiment was conducted based on an actual coal [...] Read more.

Mastering the movement laws of hard overlying rock layers is the foundation of the development of coal mining technology and plays an important role in improving coal mine safety production. Therefore, an indoor similar simulation experiment was conducted based on an actual coal mining face to test the strain variations of the pre-embedded optical fibers in the model using distributed fiber optic sensing. Finally, the fiber optic strain distribution curve was used to characterize the movement form and state of the overlying rock layer and fractured rock blocks. The experimental results showed the following. (1) The strain distribution of horizontally laid optical fibers is characterized by an upward trapezoidal convex platform, reflecting the evolution law of various horizontal movement forms of overlying rock layers: voussoir beam → cantilever beam → reverse cantilever beam → voussoir beam. The strain curve of vertically laid optical fibers is characterized by two levels of right-handed trapezoidal protrusions above and below, representing the motion state of the upper voussoir beam–lower cantilever beam structure of the overburden. (2) In addition, as excavation progresses, the range and height of the failure deformation of the overlying rock layers develop in a stepped shape. (3) In the end, the final vertical development heights of the cantilever beam structure and the voussoir beam structure in the overburden were 90.27 m and 24.99 m, respectively. The experimental results are highly consistent with the UDEC numerical simulation and mandatory calculation formulas, thus verifying the feasibility of the experiment. These research results provide theoretical and experimental support for safe coal mining in practical working faces. 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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16 pages, 1659 KiB

Open AccessArticle

Electron-Ion Radiative Recombination Assisted by Bicircular Laser Pulses

by Deeksha Kanti, Jerzy Z. Kamiński, Liang-You Peng and Katarzyna Krajewska

Photonics 2025, 12(4), 320; https://doi.org/10.3390/photonics12040320 - 29 Mar 2025

Abstract

Electron–ion radiative recombination in the presence of a bicircular laser pulse is analyzed beyond the dipole approximation. A bicircular pulse consists of two counter-rotating circularly polarized laser pulses with commensurate carrier frequencies. It is demonstrated that the broad bandwidth radiation can be generated [...] Read more.

Electron–ion radiative recombination in the presence of a bicircular laser pulse is analyzed beyond the dipole approximation. A bicircular pulse consists of two counter-rotating circularly polarized laser pulses with commensurate carrier frequencies. It is demonstrated that the broad bandwidth radiation can be generated in the process and that its spectrum can be significantly enhanced by tailoring the laser field. A special emphasis is put on analyzing temporal properties of generated radiation. Full article

(This article belongs to the Special Issue Ultrashort Laser Pulses)

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13 pages, 3649 KiB

Open AccessArticle

Real-Time Unrepeated Long-Span Field Trial over Deployed 4-Core Fiber Cable Using Commercial 130-Gbaud PCS-16QAM 800 Gb/s OTN Transceivers

by Jian Cui, Chao Wu, Zhuo Liu, Yu Deng, Bin Hao, Leimin Zhang, Ting Zhang, Yuxiao Wang, Bin Wu, Chengxing Zhang, Jiabin Wang, Baoluo Yan, Li Zhang, Yong Chen, Xuechuan Chen, Hu Shi, Lei Shen, Lei Zhang, Jie Luo, Yan Sun, Qi Wan, Cheng Chang, Bing Yan and Ninglun Gu Show full author list Hide full author list

Photonics 2025, 12(4), 319; https://doi.org/10.3390/photonics12040319 - 29 Mar 2025

Abstract

The space-division multiplexed (SDM) transmission technique based on uncoupled multi-core fibers (MCF) shows great implementation potential due to its huge transmission capacity and compatibility with existing transceivers. In this paper, we demonstrate a real-time single-span 106 km field trial over deployed 4-core MCF [...] Read more.

The space-division multiplexed (SDM) transmission technique based on uncoupled multi-core fibers (MCF) shows great implementation potential due to its huge transmission capacity and compatibility with existing transceivers. In this paper, we demonstrate a real-time single-span 106 km field trial over deployed 4-core MCF cable using commercial 800 Gb/s optical transport network (OTN) transceivers. The transceivers achieved a modulation rate of 130 Gbaud with the optoelectronic multiple-chip module (OE-MCM) packaging technique, which enabled the adoption of a highly noise-tolerant probability constellation shaping a 16-array quadrature amplitude modulation (PCS-16QAM) modulation format for 800 Gb/s OTN transceivers, and could realize unrepeated long-span transmission. The 4-core 800 Gb/s transmission systems achieved a real-time transmission capacity of 256 Tb/s with fully loaded 80-wavelength channels over the C+L band. The performance of different kinds of 800 G OTN transceivers with different modulation formats under this long-span unrepeated optical transmission system is also estimated and discussed. This field trial demonstrates the feasibility of applying uncoupled MCF with 800 Gb/s OTN transceivers in unrepeated long-span transmission scenarios and promotes its field implementation in next-generation high-speed optical interconnection systems. Full article

(This article belongs to the Special Issue Optical Networking Technologies for High-Speed Data Transmission)

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19 pages, 3977 KiB

Open AccessArticle

To Stitch or Not to Stitch, That Is the Question: Multi-Gaze Eye Topography Stitching Versus Single-Shot Profilometry

by Wen-Pin Lin, Lo-Yu Wu, Wei-Ren Lin, Lynn White, Richard Wu, Arwa Fathy, Rami Alanazi, Jay Davies and Ahmed Abass

Photonics 2025, 12(4), 318; https://doi.org/10.3390/photonics12040318 - 28 Mar 2025

Abstract

Purpose: To evaluate whether corneal topography map stitching can fully substitute the traditional single-shot capture methods in clinical settings. Methods: This record review study involved the measurement of corneal surfaces from 38 healthy subjects using two instruments: the Medmont Meridia, which employs a [...] Read more.

Purpose: To evaluate whether corneal topography map stitching can fully substitute the traditional single-shot capture methods in clinical settings. Methods: This record review study involved the measurement of corneal surfaces from 38 healthy subjects using two instruments: the Medmont Meridia, which employs a stitching composite topography method, and the Eye Surface Profiler (ESP), a single-shot measurement device. Data were processed separately for right and left eyes, with multiple gaze directions captured by the Medmont device. Surface registration and geometric transformation estimation, including neighbouring cubic interpolation, were applied to assess the accuracy of stitched maps compared to single-shot measurements. Results: The study evaluated eye rotation angles and surface alignment between Medmont topography across various gaze directions and ESP scans. Close eye rotations were found in the right-gaze, left-gaze and up-gaze directions, with rotation angles of around 8°; however, the down-gaze angle was around 15°, almost twice other gaze rotation angles. Root mean squared error (RMSE) analysis revealed notable discrepancies, particularly in the right-, left-, and up-gaze directions, with errors reaching up to 98 µm compared to ESP scans. Additionally, significance analyses showed that surface area ratios highlighted considerable differences, especially in the up-gaze direction, where discrepancies reached 70% for both right and left eyes. Conclusions: Despite potential benefits, the findings highlight a significant mismatch between stitched and single-shot measured surfaces due to digital processing artefacts. Findings suggest that stitching techniques, in their current form, are not yet ready to substitute single-shot topography measurements fully. Although stitching helps fit large-diameter contact lenses, care should be taken regarding the central area, especially if utilising the stitched data for optimising optics or wavefront analysis. Full article

(This article belongs to the Special Issue Recent Advances in Biomedical Optics and Biophotonics)

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