Photonics

8 pages, 758 KiB

Open AccessArticle

Role of Diffuser Autocorrelation and Spatial Translation in Computational Ghost Imaging

by Yishai Albeck, Shimon Sukholuski, Orit Herman, Talya Arusi-Parpar, Sharon Shwartz and Eliahu Cohen

Photonics 2025, 12(7), 650; https://doi.org/10.3390/photonics12070650 - 26 Jun 2025

Abstract

Ghost imaging (GI) is an imaging modality typically based on correlations between a single-pixel (bucket) detector collecting the electromagnetic field which was transmitted through or reflected from an object and a high-resolution detector which measures the field that did not interact with the [...] Read more.

Ghost imaging (GI) is an imaging modality typically based on correlations between a single-pixel (bucket) detector collecting the electromagnetic field which was transmitted through or reflected from an object and a high-resolution detector which measures the field that did not interact with the object. When using partially coherent sources, fluctuations can be introduced into a beam by rotating or translating a diffuser, and then the beam is split into two beams with identical intensity fluctuations. In computational GI, the diffuser with an unknown scatter distribution is replaced by a diffuser with a known scatter distribution so that the reference beam and high-resolution detector can be discarded. In this work, we wish to examine how the relation between the diffuser’s autocorrelation length and its spatial displacement affects the quality of image reconstruction obtained with these methods. We first analyze this general question theoretically and simulatively, and we then present some specific, proof-of-principle results we obtained in an optical setup. Finally, we discuss the relation between theory and experiment, suggesting some general conclusions regarding the preferred working points. Full article

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24 pages, 5413 KiB

Open AccessArticle

Evaluating MIMO-VLC System Performance: Modulation Techniques and Ambient Light Interference Effects

by Emad S. Hassan, Abdoh Jabbari and Ayman A. Alharbi

Photonics 2025, 12(7), 649; https://doi.org/10.3390/photonics12070649 (registering DOI) - 26 Jun 2025

Abstract

Visible light communication (VLC) is an emerging optical wireless technology capable of delivering high data rates for both indoor and outdoor environments. When combined with multiple-input, multiple-output (MIMO) systems, VLC demonstrates enhanced capacity, extended transmission range, and improved reliability. However, VLC systems are [...] Read more.

Visible light communication (VLC) is an emerging optical wireless technology capable of delivering high data rates for both indoor and outdoor environments. When combined with multiple-input, multiple-output (MIMO) systems, VLC demonstrates enhanced capacity, extended transmission range, and improved reliability. However, VLC systems are susceptible to ambient light interference, which can degrade performance. This paper investigates the performance of MIMO-VLC systems using three modulation techniques: non-return to zero (NRZ), return to zero (RZ), and quadrature phase shift keying (QPSK). The study evaluates the VLC systems in terms of bit error rate (BER), quality factor (Q-factor), and received power over varying link distances. The obtained results show that MIMO-based systems outperform single-input, single-output (SISO) systems in terms of transmission range, with MIMO achieving up to 1450 m using QPSK, compared to 1125 m for SISO. Under ambient light noise, MIMO-based systems experience a greater reduction in transmission distance (13.6%) compared to SISO (6.2%), but the overall performance gain of MIMO compensates for this degradation. Among the modulation schemes, NRZ and QPSK provide the best performance, showing greater resilience to ambient light interference. The findings confirm that MIMO–VLC systems, particularly with NRZ and QPSK, offer a robust solution for overcoming interference and maximizing transmission distance in real-world applications. Full article

(This article belongs to the Special Issue Optical Wireless Communication in 5G and Beyond)

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16 pages, 5292 KiB

Open AccessArticle

A Large-Bandwidth Electro-Optic Modulator with U-T Double-Layer Traveling-Wave Electrode Structure Based on Thin-Film Lithium Niobate

by Yuxiang Hao, Haiou Li, Yue Li, Haisheng Li, Yingbo Liu, Jiayu Yang and Liangpeng Qin

Photonics 2025, 12(7), 648; https://doi.org/10.3390/photonics12070648 - 26 Jun 2025

Abstract

Thin-film lithium niobate (TFLN) electro-optic modulators serve as critical components in microwave photonic systems. To improve device performance, we developed a U-T double-layer traveling-wave electrode configuration. Using finite element analysis, we systematically simulated and optimized both modulation efficiency and radiofrequency characteristics, ultimately realizing [...] Read more.

Thin-film lithium niobate (TFLN) electro-optic modulators serve as critical components in microwave photonic systems. To improve device performance, we developed a U-T double-layer traveling-wave electrode configuration. Using finite element analysis, we systematically simulated and optimized both modulation efficiency and radiofrequency characteristics, ultimately realizing a low half-wave voltage-length product of 1.77 V·cm, a minimal optical loss of 0.022 dB/cm, and an ultra-wide modulation bandwidth surpassing 100 GHz. Full article

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11 pages, 2910 KiB

Open AccessCommunication

Theoretical Study on Low-Chirp Directly Modulated DFB Lasers with (110)-Oriented Quantum Well

by Jianwei Li, Mengzhu Hu, Xinyang Su, Yanting Liu and Ke Zhan

Photonics 2025, 12(7), 647; https://doi.org/10.3390/photonics12070647 - 25 Jun 2025

Abstract

The low-chirp operation of distributed feedback lasers is highly desirable in high-speed and high-bit rate optical transmission. In this article, we address this issue by theoretically investigating the possibility of further a reduction in the linewidth enhancement factor (LEF) of a quantum well [...] Read more.

The low-chirp operation of distributed feedback lasers is highly desirable in high-speed and high-bit rate optical transmission. In this article, we address this issue by theoretically investigating the possibility of further a reduction in the linewidth enhancement factor (LEF) of a quantum well (QW). The energy band structure of AlGaInAs quantum-well DFB lasers grown with a (110) crystal orientation in the active region of the L-band has been theoretically analyzed using multi-band k.p perturbation theory, by reducing the asymmetry of conduction bands and valence bands and thus the linewidth enhancement factor parameter, which is related to the frequency chirp. Simulation results show that the LEF of the directly modulated DFB laser is reduced from 2.434 to 1.408 by designing the (110)-oriented compression-strained Al_0.06Ga_0.24InAs multiple-quantum-well structure, and the eye diagram of the (110)-oriented quantum-well DFB laser with a digital signal transmission of 20 km is significantly better than the (001) crystal-oriented quantum-well DFB laser for the 10Gbps optical fiber communication system, thus achieving a longer distance and higher-quality optical signal transmission. Full article

(This article belongs to the Section Optoelectronics and Optical Materials)

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12 pages, 2278 KiB

Open AccessCommunication

An All-Optical Plasmon Modulator with a High Extinction Ratio Based on the Resonance of a Silver Block

by Jimi Fang, Sisi Yang, Xuefang Hu, Changgui Lu and Mengjia Lu

Photonics 2025, 12(7), 646; https://doi.org/10.3390/photonics12070646 - 25 Jun 2025

Abstract

Conventional all-optical modulators based on surface plasmon polaritons (SPPs) primarily utilize the nonlinear effect of a given material for modulation. Their performance is heavily dependent on the optical properties of the dielectric materials used and requires high pumping power. However, manipulating SPPs by [...] Read more.

Conventional all-optical modulators based on surface plasmon polaritons (SPPs) primarily utilize the nonlinear effect of a given material for modulation. Their performance is heavily dependent on the optical properties of the dielectric materials used and requires high pumping power. However, manipulating SPPs by controlling electron concentrations offers a material-independent approach suitable for all-optical modulators. In this paper, we propose a hybrid gold–ITO–silver block structure integrated within a Mach–Zehnder interferometer configuration to address this problem. The gold–ITO interface effectively localizes propagating SPPs. The pump light excites localized surface plasmons (LSPs) in the silver block, generating surface electric fields that modulate the electron concentration in the adjacent ITO layer. The extinction ratio is 50.8 dB when the electron concentration changes by 3.3 × 10²⁰ cm⁻³, indicating that this structure is an all-optical modulator with a high extinction ratio. This approach shows significant promise for reducing pump power and enhancing the performance of all-optical modulators. Full article

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20 pages, 1686 KiB

Open AccessArticle

Dynamic Security-Aware Resource Allocation in Quantum Key Distribution-Enabled Optical Networks

by Vimal Bhatia, Adolph Kasegenya and Bowen Chen

Photonics 2025, 12(7), 645; https://doi.org/10.3390/photonics12070645 - 25 Jun 2025

Abstract

The demand for secure communication in the age of quantum technologies has driven progress in quantum key distribution (QKD) techniques for optical networks. This research addresses the issues of high blocking probabilities (BPs) and the proper utilization of quantum resources in varying network [...] Read more.

The demand for secure communication in the age of quantum technologies has driven progress in quantum key distribution (QKD) techniques for optical networks. This research addresses the issues of high blocking probabilities (BPs) and the proper utilization of quantum resources in varying network loads by introducing a novel heuristic approach, termed dynamic security-aware quantum resource allocation (D-SQRA), designed for dynamic resource allocation in QKD-enabled optical networks. We propose two D-SQRA algorithms to employ an adaptive resource assignment (RA) strategy that concurrently addresses routing, wavelength, and time-slot selection while dynamically modifying security levels according to the real-time network load and resource availability. We evaluate the proposed D-SQRA performance against two conventional methods, namely, fixed security quantum resource allocation (F-SQRA) and baseline quantum resource allocation (B-QRA). We discuss the results for NSFNET and UBN24 topologies for network security performance metrics such as network security performance (NSP), BP, quantum key utilization (QKU), and time-slot utilization. The results show that the proposed D-SQRA algorithms provide significant improvement with respect to conventional techniques in addressing proper resource utilization and management by reducing BPs of the new incoming connection requests. Full article

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

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17 pages, 4222 KiB

Open AccessArticle

Grooved High-Reflective Films for Ultraviolet Emission Enhancement

by Hengrui Zhang, Zhanhua Huang and Lin Zhang

Photonics 2025, 12(7), 644; https://doi.org/10.3390/photonics12070644 - 25 Jun 2025

Abstract

Conventional ultraviolet microplasma sources typically lack a back-reflection structure, resulting in radiative power loss from the backside. To enhance the emission efficiency of ultraviolet microplasma devices around 220 nm, we propose a multilayer reflective coating composed of alternating high- and low-refractive-index layers of [...] Read more.

Conventional ultraviolet microplasma sources typically lack a back-reflection structure, resulting in radiative power loss from the backside. To enhance the emission efficiency of ultraviolet microplasma devices around 220 nm, we propose a multilayer reflective coating composed of alternating high- and low-refractive-index layers of Al₂O₃ and SiO₂, within a V-shaped groove. Key structural parameters, including the number of alternating film layer pairs, groove width, and light source position, are investigated to show their effects on ultraviolet reflection characteristics. The results show that reducing the groove width greatly enhances light reflection. When the groove width is 6.5 μm, the device exhibits a reflection efficiency of 47.82% and power enhancement of 91.66%, representing improvements of 2.5-fold and 4.2-fold, respectively, compared to non-optimized cases. Device performance is also influenced by the offset of the light source, which is more sensitive along the horizontal direction. This study provides a practical solution for developing high-efficiency ultraviolet emission devices. Full article

(This article belongs to the Special Issue Recent Progress in Integrated Photonics)

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12 pages, 1285 KiB

Open AccessArticle

Performance Analysis of Space-to-Ground Downlink for Polarization Shift Keying Optical Communications with a Gaussian-Schell Model Beam

by Jiajie Wu, Yuwei Zhang, Qingyan Li, Siyuan Yu and Jianjie Yu

Photonics 2025, 12(7), 643; https://doi.org/10.3390/photonics12070643 - 24 Jun 2025

Abstract

Free-space optical communication has emerged as a pivotal technology for space-to-ground downlinks; however, signal degradation caused by atmospheric turbulence continues to pose a significant challenge. In this study, a model for the polarization transmission characteristics of a Gaussian-Schell model (GSM) beam in downlink [...] Read more.

Free-space optical communication has emerged as a pivotal technology for space-to-ground downlinks; however, signal degradation caused by atmospheric turbulence continues to pose a significant challenge. In this study, a model for the polarization transmission characteristics of a Gaussian-Schell model (GSM) beam in downlink was established, and conditions sufficient for maintaining the polarization transmission characteristics were derived. The impact of the source spatial coherence on the performance of optical communication systems using circular polarization shift keying (CPolSK) modulation was investigated. Additionally, models for the probability density distribution and scintillation index of the optical intensity under atmospheric turbulence were developed along with a bit error rate model for the optical communication system. The effects of the laser spatial coherence on these models were also analyzed. The results indicate that the optimal performance in the turbulent downlink is achieved with fully coherent light, where the GSM-beam-based CPolSK-modulated system demonstrates a reduction of 1.51 dB in the required power compared to that of an on–off keying system. The implications of this study suggest that optimizing spatial coherence could significantly enhance the reliability of space-to-ground communication systems under atmospheric disturbances. Full article

(This article belongs to the Special Issue Advanced Methods in Exploring Light–Matter Interactions and Nonlinear Effects Optics Applications)

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13 pages, 6651 KiB

Open AccessArticle

Research on Metal Mesh Coupling Mirrors Utilizing Metasurfaces for Optically Pumped Gas THz Lasers

by Lijie Geng, Zhenxiang Fu, Shuaifei Song, Chenglong Bi, Wenyan Zhang, Ruiliang Zhang, Kun Yang and Yanchen Qu

Photonics 2025, 12(7), 642; https://doi.org/10.3390/photonics12070642 - 24 Jun 2025

Abstract

Optically pumped gas terahertz (THz) lasers (OPGTLs) as reliable sources of THz radiation have been extensively utilized within THz application areas. In this paper, a substrate-free metal mesh coupler based on the metasurfaces principle was designed for continuous wave OPGTL, which is suitable [...] Read more.

Optically pumped gas terahertz (THz) lasers (OPGTLs) as reliable sources of THz radiation have been extensively utilized within THz application areas. In this paper, a substrate-free metal mesh coupler based on the metasurfaces principle was designed for continuous wave OPGTL, which is suitable for the Fabry–Perot (FP) THz resonator. The parameters of substrate-free metal mesh are calculated by the Ulrich equivalent circuit model, and the influence of metal mesh period and linewidth on its transmittance is analyzed quantitatively. Taking the THz laser with the 118.8 µm of CH₃OH optically pumped by the 9.6 µm CO₂ laser line for instance, two kinds of metal mesh were devised as input and output couplers of the resonator, and the transmittance and reflectance of the metal meshes are verified by the finite-difference time-domain (FDTD) method. Furthermore, the transmitted and reflected light fields of the FP resonant cavity metal mesh mirrors were simulated by using the FDTD method under the vertical incidence of both pump light and THz waves. Validation of the optical field characteristics of the substrate-free metal meshes confirmed their suitability as ideal input and output coupling cavity mirrors for FP resonant cavities in optically pumped gas THz lasers. Full article

(This article belongs to the Special Issue Recent Advances in Infrared Lasers and Applications)

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10 pages, 1717 KiB

Open AccessCommunication

Sensitivity Enhancement of Fault Detection Utilizing Feedback Compensation for Time-Delay Signature of Chaotic Laser

by Haoran Guo, Hui Liu, Min Zhang, Xiaomin Guo, Yuanyuan Guo, Hong Han and Tong Zhao

Photonics 2025, 12(7), 641; https://doi.org/10.3390/photonics12070641 - 24 Jun 2025

Abstract

Fiber fault detection based on the time-delay signature of an optical feedback semiconductor laser has the advantages of high sensitivity, precise location, and a simple structure, which make it widely applicable. The sensitivity of this method is determined by the feedback strength inducing [...] Read more.

Fiber fault detection based on the time-delay signature of an optical feedback semiconductor laser has the advantages of high sensitivity, precise location, and a simple structure, which make it widely applicable. The sensitivity of this method is determined by the feedback strength inducing the nonlinear state of the laser. This paper proposes a feedback compensation method to reduce the requirement of the fault echo intensity for the laser to enter the nonlinear state, significantly enhancing detection sensitivity. Numerical simulations analyze the impact of feedback compensation parameters on fault detection sensitivity and evaluate the performance of the laser operating at different pump currents. The results show that this method achieves a 9.33 dB improvement in sensitivity compared to the original approach, effectively addressing the challenges of detecting faults with high insertion losses in optical networks. Full article

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12 pages, 3981 KiB

Open AccessArticle

On-Chip Silicon Photonic Neural Networks Based on Thermally Tunable Microring Resonators for Recognition Tasks

by Huan Zhang, Beiju Huang, Chuantong Cheng, Biao Jiang, Lei Bao and Yiyang Xie

Photonics 2025, 12(7), 640; https://doi.org/10.3390/photonics12070640 - 24 Jun 2025

Abstract

Leveraging the human brain as a paradigm of energy-efficient computation, considerable attention has been paid to photonic neurons and neural networks to achieve higher computing efficiency and lower energy consumption. This study experimentally demonstrates on-chip silicon photonic neurons and neural networks based on [...] Read more.

Leveraging the human brain as a paradigm of energy-efficient computation, considerable attention has been paid to photonic neurons and neural networks to achieve higher computing efficiency and lower energy consumption. This study experimentally demonstrates on-chip silicon photonic neurons and neural networks based on thermally tunable microring resonators (MRRs) implement weighting and nonlinear operations. The weight component consists of eight cascaded MRRs thermally tuned within wavelength division multiplexing (WDM) architecture. The nonlinear response depends on the MRR’s nonlinear transmission spectrum, which is analogous to the rectified linear unit (ReLU) function. The matrix multiplication and recognition task of digits 2, 3, and 5 represented by seven-segment digital tube are successfully completed by using the photonic neural networks constructed by the photonic neurons based on the on-chip thermally tunable MRR as the nonlinear units. The power consumption of the nonlinear unit was about 5.65 mW, with an extinction ratio of about 25 dB between different digits. The proposed photonic neural network is CMOS-compatible, which makes it easy to construct scalable and large-scale multilayer neural networks. These findings reveal that there is great potential for highly integrated and scalable neuromorphic photonic chips. Full article

(This article belongs to the Special Issue Silicon Photonics: From Fundamentals to Future Directions)

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11 pages, 6080 KiB

Open AccessArticle

Single-Shot Femtosecond Raster-Framing Imaging with High Spatio-Temporal Resolution Using Wavelength/Polarization Time Coding

by Yang Yang, Yongle Zhu, Xuanke Zeng, Dong He, Li Gu, Zhijian Wang and Jingzhen Li

Photonics 2025, 12(7), 639; https://doi.org/10.3390/photonics12070639 - 24 Jun 2025

Abstract

This paper introduces a single-shot ultrafast imaging technique termed wavelength and polarization time-encoded ultrafast raster imaging (WP-URI). By integrating raster imaging principles with wavelength- and polarization-based temporal encoding, the system uses a spatial raster mask and time–space mapping to aggregate multiple two-dimensional temporal [...] Read more.

This paper introduces a single-shot ultrafast imaging technique termed wavelength and polarization time-encoded ultrafast raster imaging (WP-URI). By integrating raster imaging principles with wavelength- and polarization-based temporal encoding, the system uses a spatial raster mask and time–space mapping to aggregate multiple two-dimensional temporal raster images onto a single detector plane, thereby enabling the effective spatial separation and extraction of target information. Finally, the target dynamics are recovered using a reconstruction algorithm based on the Nyquist–Shannon sampling theorem. Numerical simulations demonstrate the single-shot acquisition of four dynamic frames at 25 trillion frames per second (Tfps) with an intrinsic spatial resolution of 50 line pairs per millimeter (lp/mm) and a wide field of view. The WP-URI technique achieves unparalleled spatio-temporal resolution and frame rates, offering significant potential for investigating ultrafast phenomena such as matter interactions, carrier dynamics in semiconductor devices, and femtosecond laser–matter processes. Full article

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13 pages, 2607 KiB

Open AccessArticle

Defect-Induced Modulation of Electronic and Optical Properties in Monolayer CsPb₂Br₅: Implications for Fiber-Optic Sensing Applications

by Meiqi An, Wenxuan Fan, Shengsheng Wei and Junqiang Wang

Photonics 2025, 12(7), 638; https://doi.org/10.3390/photonics12070638 - 24 Jun 2025

Abstract

Two−dimensional halide perovskites have emerged as promising optoelectronic materials, yet the uncontrolled defect formation during synthesis remains a critical challenge for their practical applications. In this work, we systematically investigate the structural, electronic, and optical properties of monolayer CsPb₂Br₅ in [...] Read more.

Two−dimensional halide perovskites have emerged as promising optoelectronic materials, yet the uncontrolled defect formation during synthesis remains a critical challenge for their practical applications. In this work, we systematically investigate the structural, electronic, and optical properties of monolayer CsPb₂Br₅ in two representative configurations: ds−CsPb₂Br₅ and ss−CsPb₂Br₅. By introducing four types of vacancy defects—V_Br−c, V_Br−b, V_Cs, and V_Pb, we analyze their structural distortions, formation energies, and their impact on band structure and optical response using first−principles calculations. Our results reveal that Br−related vacancies are energetically most favorable and induce shallow defect levels and absorption edge redshifts in the ds−CsPb₂Br₅ structure, while in the ss−CsPb₂Br₅ configuration, only V_Br−b forms a defect state. V_Pb and V_Cs lead to significant sub−bandgap absorption enhancement and dielectric response due to band−edge reorganization, despite not introducing in−gap states. Notably, V_Br−c exhibits distinct infrared absorption in the ss−CsPb₂Br₅ model without electronic trap formation. These findings underscore the critical influence of defect type and slab asymmetry on the optoelectronic behavior of CsPb₂Br₅, providing guidance for defect engineering in perovskite−based optoelectronic applications. Full article

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

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13 pages, 3019 KiB

Open AccessArticle

Efficient Design of a Terahertz Metamaterial Dual-Band Absorber Using Multi-Objective Firefly Algorithm Based on a Multi-Cooperative Strategy

by Guilin Li, Yan Huang, Yurong Wang, Weiwei Qu, Hu Deng and Liping Shang

Photonics 2025, 12(7), 637; https://doi.org/10.3390/photonics12070637 - 24 Jun 2025

Abstract

Terahertz metamaterial dual-band absorbers are used for multi-target detection and high-sensitivity sensing in complex environments by enhancing information that reflects differences in the measured substances. Traditional design processes are complex and time-consuming. Machine learning-based methods, such as neural networks and deep learning, require [...] Read more.

Terahertz metamaterial dual-band absorbers are used for multi-target detection and high-sensitivity sensing in complex environments by enhancing information that reflects differences in the measured substances. Traditional design processes are complex and time-consuming. Machine learning-based methods, such as neural networks and deep learning, require a large number of simulations to gather training samples. Existing design methods based on single-objective optimization often result in uneven multi-objective optimization, which restricts practical applications. In this study, we developed a metamaterial absorber featuring a circular split-ring resonator with four gaps nested in a “卍” structure and used the Multi-Objective Firefly Algorithm based on Multiple Cooperative Strategies to achieve fast optimization of the absorber’s structural parameters. A comparison revealed that our approach requires fewer iterations than the Multi-Objective Particle Swarm Optimization and reduces design time by nearly half. The absorber designed using this method exhibited two resonant peaks at 0.607 THz and 0.936 THz, with absorptivity exceeding 99%, indicating near-perfect absorption and quality factors of 31.42 and 30.08, respectively. Additionally, we validated the absorber’s wave-absorbing mechanism by applying impedance-matching theory. Finally, we elucidated the resonance-peak formation mechanism of the absorber based on the surface current and electric-field distribution at the resonance frequencies. These results confirmed that the proposed dual-band metamaterial absorber design is efficient, representing a significant step toward the development of metamaterial devices. Full article

(This article belongs to the Special Issue Thermal Radiation and Micro-/Nanophotonics)

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23 pages, 7515 KiB

Open AccessArticle

Strategies for Suppression and Compensation of Signal Loss in Ptychography

by Ruoru Li, Zijian Xu, Sheng Chen, Shuhan Wu, Yingling Zhang, Xiangzhi Zhang and Renzhong Tai

Photonics 2025, 12(7), 636; https://doi.org/10.3390/photonics12070636 - 23 Jun 2025

Abstract

X-ray ptychography is an ultrahigh resolution imaging technique widely used in synchrotron radiation facilities. Its imaging performance relies on the quality of the acquired signals. However, the X-ray detectors used often suffer from signal loss due to sensor gaps, beamstops, defective pixels, overexposure, [...] Read more.

X-ray ptychography is an ultrahigh resolution imaging technique widely used in synchrotron radiation facilities. Its imaging performance relies on the quality of the acquired signals. However, the X-ray detectors used often suffer from signal loss due to sensor gaps, beamstops, defective pixels, overexposure, or other factors, resulting in degraded image quality. To suppress and compensate for the effects of signal loss, we proposed the known probe approach to partially recover the lost signals and introduced the high probe divergence strategy by investigating the effects of probe divergence on reconstruction quality under signal loss conditions. Both simulation and experiment results show that high probe divergence can effectively suppress the impact of signal loss on reconstruction quality while using a known probe as the initial probe for reconstruction can largely recover missing signals in Fourier space, resulting in a much better image than using a guessed initial probe. These strategies allow for high-quality imaging in the presence of signal loss without secondary data acquisition, significantly improving experimental efficiency and reducing radiation damage compared to previous strategies. Full article

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

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24 pages, 20729 KiB

Open AccessArticle

Chaotic Image Encryption System as a Proactive Scheme for Image Transmission in FSO High-Altitude Platform

by Ping Zhang, Jingfeng Jie, Zhi Liu and Keyan Dong

Photonics 2025, 12(7), 635; https://doi.org/10.3390/photonics12070635 - 23 Jun 2025

Abstract

To further enhance the stability and security of image transmission in FSO (Free Space Optics) aviation platforms, this paper proposes a communication transmission scheme that integrates a chaotic image encryption system with the HAP (high-altitude platform) environment. This scheme effectively combines the chaotic [...] Read more.

To further enhance the stability and security of image transmission in FSO (Free Space Optics) aviation platforms, this paper proposes a communication transmission scheme that integrates a chaotic image encryption system with the HAP (high-altitude platform) environment. This scheme effectively combines the chaotic image encryption algorithm with the atmospheric turbulence channel transmission process, improving the anti-interference capabilities and security of HAP optical communication for image transmission. First, a five-dimensional hyperchaotic system with complex dynamic characteristics is introduced, and the system’s chaotic behaviors and dynamic properties are explored. The improved system model incorporates chaotic mapping and DNA coding techniques, forming a robust chaotic image encryption system, whose performance is experimentally validated. Next, the feasibility of integrating the chaotic image encryption system with HAP optical communication is discussed. A detailed description of the corresponding turbulence model and test conditions is provided. To verify the scheme’s feasibility, plaintext images of varying sizes are selected for experiments, comparing the transmission performance of both unencrypted and encrypted images under three turbulence levels: weak, medium, and strong. The impact on image communication quality is quantitatively analyzed using PSNR (Peak Signal-to-Noise Ratio) and SSIM (Structural Similarity Index measure). Finally, the effect of malicious interception attacks, caused by noise interference from different levels of atmospheric turbulence, is examined. The robustness and feasibility of the proposed scheme are validated, providing a promising approach for integrating HAP optical communication’s anti-turbulence capabilities with chaotic image encryption. Full article

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16 pages, 3161 KiB

Open AccessArticle

Multi-Link Fragmentation-Aware Deep Reinforcement Learning RSA Algorithm in Elastic Optical Network

by Jing Jiang, Yushu Su, Jingchi Cheng and Tao Shang

Photonics 2025, 12(7), 634; https://doi.org/10.3390/photonics12070634 - 22 Jun 2025

Abstract

Deep reinforcement learning has been extensively applied for resource allocation in elastic optical networks. However, many studies focus on link-level state analysis and rarely discuss the influence between links, which may affect the performance of allocation algorithms. In this paper, we propose a [...] Read more.

Deep reinforcement learning has been extensively applied for resource allocation in elastic optical networks. However, many studies focus on link-level state analysis and rarely discuss the influence between links, which may affect the performance of allocation algorithms. In this paper, we propose a multi-link fragmentation deep reinforcement learning-based routing and spectrum allocation algorithm (MFDRL-RSA). We number the links using a breadth-first numbering algorithm. Based on the numbering results, high-frequency links are selected to construct the network state matrix that reflects the resource distribution. According to the state matrix, we calculate a multi-link fragmentation degree, quantifying resource fragmentation within a representative subset of network. The MFDRL-RSA algorithm enhances the accuracy of the agent’s decision-making by incorporating it into the reward function, thereby improving its performance in routing decisions, which contributes to the overall allocation performance. Simulation results show that MFDRL-RSA achieves lower blocking rates compared to the reference algorithms, with reductions of 16.34%, 13.01%, and 7.42% in the NSFNET network and 19.33%, 15.17%, and 9.95% in the Cost-239 network. It also improves spectrum utilization by 12.28%, 9.83%, and 6.32% in NSFNET and by 13.92%, 11.55%, and 8.26% in Cost-239. Full article

(This article belongs to the Special Issue Advancements and Future Perspectives in All-Optical Detection and Reliability Improvement Technologies)

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10 pages, 1928 KiB

Open AccessCommunication

Magnetic Field and Temperature Dual-Parameter Optical Fiber Sensor Based on Fe₃O₄ Magnetic Film

by Shichun Xiong, Haojie Zhang, Zhongwei Cao, Yipeng Lu, Rui Zhou and Zhiguo Zhang

Photonics 2025, 12(7), 633; https://doi.org/10.3390/photonics12070633 - 22 Jun 2025

Abstract

A dual-parameter optical fiber sensor for measuring the magnetic field and temperature based on the Fabry–Perot interferometer (FPI) and magnetic polymer film was proposed and designed, realizing dual-parameter measurement of temperature and the magnetic field. The sensor uses the excellent elasticity and thermal [...] Read more.

A dual-parameter optical fiber sensor for measuring the magnetic field and temperature based on the Fabry–Perot interferometer (FPI) and magnetic polymer film was proposed and designed, realizing dual-parameter measurement of temperature and the magnetic field. The sensor uses the excellent elasticity and thermal expansion coefficient of PDMS and the magnetostrictive effect of Fe₃O₄ magnetic polymer film to provide magnetic field and temperature detection while maintaining good reusability, achieving a magnetic field sensitivity and temperature sensitivity of 69 pm/mT and 390 pm/K, respectively. The sensor has the advantages of a low cost, a simple manufacturing process, good linearity, and a sensitive temperature response. It has broad application prospects in medicine, geography, aerospace, and other fields. Full article

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19 pages, 563 KiB

Open AccessArticle

The Analysis of Resource Efficiencies for the Allocation Methods Applied in the Proposed OAM&WDM-PON Architecture

by Rastislav Róka

Photonics 2025, 12(7), 632; https://doi.org/10.3390/photonics12070632 - 21 Jun 2025

Abstract

Infrastructures of access networks that mostly exploit the optical fiber medium effectively utilizing wavelength division multiplexing techniques play a key role in advanced F5G fixed networks. The orbital angular momentum technique is highly promising for use within passive optical networks to further increase [...] Read more.

Infrastructures of access networks that mostly exploit the optical fiber medium effectively utilizing wavelength division multiplexing techniques play a key role in advanced F5G fixed networks. The orbital angular momentum technique is highly promising for use within passive optical networks to further increase transmission capacities. So, the utilization of common network resources in wavelength and optical domains will be more important. The main purpose of this paper is to present an analysis of resource efficiencies for various allocation methods applied in the proposed OAM&WDM-PON architecture with a conventional point-to-multipoint topology. This contribution introduces novel static, dynamic and dynamic customized allocation methods for a proposed network design with the utilization of only passive optical splitters in remote nodes. These WDM and OAM channel allocation methods are oriented towards minimizing the number of working wavelengths and OAM channels that will be used for compliance with customers’ requests for data transmitting in the proposed point-to-multipoint OAM&WDM-PON architecture. For analyzing and evaluating the considered allocation methods, a simulation model related to the proposed P2MP OAM&WDM-PON design realized in the MATLAB (R2022A) programming environment is presented with acquired simulation results. Finally, resource efficiencies of the presented novel allocation methods are evaluated from the viewpoint of application in future OAM&WDM-PONs. Full article

(This article belongs to the Special Issue Exploring Optical Fiber Communications: Technology and Applications)

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