Photonics

17 pages, 3039 KiB

Open AccessArticle

Dedicated Path Protection with Flexible Switching Selection in Passive Optical 5G Xhaul Access Networks

by Mirosław Klinkowski

Photonics 2024, 11(10), 908; https://doi.org/10.3390/photonics11100908 - 26 Sep 2024

This work addresses the optimized planning of survivable optical 5G Xhaul access networks employing passive Wavelength Division Multiplexing (WDM) technologies. Specifically, it focuses on the reliability of optical transmission paths connecting remote radio sites to a central hub ensured by using a novel, [...] Read more.

This work addresses the optimized planning of survivable optical 5G Xhaul access networks employing passive Wavelength Division Multiplexing (WDM) technologies. Specifically, it focuses on the reliability of optical transmission paths connecting remote radio sites to a central hub ensured by using a novel, cost-effective, flexible, and dedicated path protection (DPP-F) scheme, protecting against single-link failures. The proposed DPP-F network protection approach allows for switching of individual wavelengths or the complete multiplexed WDM signal, flexibly applying the best switching option according to given traffic demands. Concurrently, it enables traffic aggregation on the transmission paths from the end and intermediate nodes to minimize the overall network deployment cost. The problem of selecting primary (working) and backup (protection) paths, together with the selection of the best switching and traffic aggregation options, is modeled and solved as a mixed-integer linear programming (MILP) optimization problem. To evaluate the cost savings achieved with DPP-F, we compare it with two reference DPP schemes based on switching the entire multiplexed WDM signal (DPP-M) and individual wavelengths (DPP-W). Numerical experiments conducted across a wide range of network scenarios reveal, among other things, that DPP-F’s performance is at least as good as that of the reference methods, bringing significant cost savings (from several to tens of percent) in most of the analyzed network scenarios. Full article

(This article belongs to the Special Issue Optical Communication Networks: Advancements and Future Directions)

7 pages, 2079 KiB

Open AccessArticle

Optical Angular Momentum Beam Generation Using Coherent Beam Combination

by Przemyslaw Gontar, Lukasz Gorajek, Waldemar Zendzian and Jan Jabczyński

Photonics 2024, 11(10), 907; https://doi.org/10.3390/photonics11100907 - 26 Sep 2024

Abstract

(1) Background: The significant progress observed over the last two decades in coherent beam combining (CBC) technology has mainly focused on its applications in high-energy physics and laser weapons. This work provides insight into the basic principles of CBC and the search for [...] Read more.

(1) Background: The significant progress observed over the last two decades in coherent beam combining (CBC) technology has mainly focused on its applications in high-energy physics and laser weapons. This work provides insight into the basic principles of CBC and the search for an alternative, namely optical angular momentum (OAM) generation using CBC. (2) Methods: A semi-analytical model based on the paraxial wave equation was explored, generating OAM-CBC beams by manipulating the tilts and phases of the CBC (T&P-CBC) of hexagonal architecture. (3) Results: The specially arranged T&P-CBC shows typical properties of OAM, such as annular profiles for the zero diffraction order and 1st-order replicas in the far field and correlation coefficients of 1% between different OAM-CBC fields. (4) Conclusions: The differences between classical OAM beams and OAM-CBC are substantial due to hexagonal lattice properties. Moreover, applications in free space optical communications are feasible as T&P CBC fulfills the main conditions and requirements for OAM generation. Full article

(This article belongs to the Special Issue Progress in OAM Beams: Recent Innovations and Future Perspectives)

► Show Figures

Figure 1

17 pages, 11324 KiB

Open AccessArticle

Design and Simulation of a High-Responsivity Dielectric Metasurface Si-Based InGaAs Photodetector

by Hengyang Dong, Yujie Wu, Hongbo Zheng, Pandi Chen, Wenhao Deng, Liuhong Ma, Xinyuan Dong, Zhiyong Duan and Mengke Li

Photonics 2024, 11(10), 906; https://doi.org/10.3390/photonics11100906 - 26 Sep 2024

Abstract

A Si-based photodetector is the core device of Si-based optical interconnection; its material and performance are the key factors restricting its development. This paper conducts theoretical research on the issues of lattice mismatch between heterogeneous materials and low device responsivity in Si-based InGaAs [...] Read more.

A Si-based photodetector is the core device of Si-based optical interconnection; its material and performance are the key factors restricting its development. This paper conducts theoretical research on the issues of lattice mismatch between heterogeneous materials and low device responsivity in Si-based InGaAs photodetectors for the 1550 nm optical communication band. The material mismatch issue is addressed through the use of the high-aspect ratio trapping (ART) epitaxial technique, enabling the realization of high-performance Si-based III-V materials. By introducing a dielectric metasurface into the top layer of the structure, the light absorption efficiency is enhanced, realizing broadband optical absorption enhancement for Si-based photodetectors. This paper mainly focuses on designing the optimal parameters of the dielectric metasurface structure based on the finite-difference time-domain (FDTD) Solutions to achieve the performance analysis of a high-responsivity 1550 nm Si-based InGaAs photodetector. The results show that the quantum efficiency of the dielectric metasurface structure is theoretically estimated to be 88.8% and the response rate is 1.11 A/W, which is 2%~16% higher than that of the unetched structure in the whole band. The research results of this paper will provide new ideas for the development of novel, high-performance, and miniaturized Si-based photodetectors and lay a theoretical foundation for Si-based optical interconnection. Full article

(This article belongs to the Special Issue Group IV Photonics: Advances and Applications)

17 pages, 2624 KiB

Open AccessReview

Light Disturbance Analysis and Applications

by Rafaela S. Alves-de-Carvalho, Rute J. Macedo-de-Araújo and José M. González-Méijome

Photonics 2024, 11(10), 905; https://doi.org/10.3390/photonics11100905 - 26 Sep 2024

Abstract

This narrative review synthesizes recent basic and clinical research on visual disturbances in low-light environments, highlighting the evaluation techniques for these conditions. It focuses on the degradation of visual acuity under dim lighting, exacerbated by pupil dilation, known as night vision disturbance (NVD). [...] Read more.

This narrative review synthesizes recent basic and clinical research on visual disturbances in low-light environments, highlighting the evaluation techniques for these conditions. It focuses on the degradation of visual acuity under dim lighting, exacerbated by pupil dilation, known as night vision disturbance (NVD). Key contributors to NVD include optical scattering, intraocular diffraction, ocular aberrations, and uncorrected refractive errors, all significantly impacting quality of life and functional abilities. This review also examines the effects of aging, eye disorders, surgical interventions, and corneal irregularities on NVD. It details the definitions, distinctions, and measurement methodologies for various optical phenomena, using both objective and subjective approaches, such as visual function questionnaires, simulators, and the light disturbance analyzer (LDA). The LDA is validated for clinical characterization and quantification of light distortion, proving useful in both clinical and research settings. This review advocates for continued innovation in therapeutic interventions to improve patient outcomes and alleviate the impact of visual disturbances. Full article

(This article belongs to the Special Issue Optical Technology for Challenging Conditions：Methods and Applications)

► Show Figures

Figure 1

16 pages, 2934 KiB

Open AccessArticle

Real-Time Simulation of Clear Sky Background Radiation in Gas Infrared Remote Sensing Monitoring

by Shengquan Shu, Jianguo Liu, Liang Xu, Yuhao Wang, Yasong Deng and Yongfeng Sun

Photonics 2024, 11(10), 904; https://doi.org/10.3390/photonics11100904 - 26 Sep 2024

Abstract

During the process of infrared remote sensing monitoring, obtaining real-time measurements of sky background radiation is extremely inconvenient. The current methods incur a certain amount of lag. In this study, within the existing theoretical framework, a fast transmittance calculation method using interpolation was [...] Read more.

During the process of infrared remote sensing monitoring, obtaining real-time measurements of sky background radiation is extremely inconvenient. The current methods incur a certain amount of lag. In this study, within the existing theoretical framework, a fast transmittance calculation method using interpolation was adopted, and a simplified transmission model was established. This led to the development of a new and simplified method for rapid temperature and humidity retrieval. Compared to the line-by-line integration method, the interpolation method significantly improves the speed of transmittance calculation by several tens of times, while maintaining a high level of accuracy. The relative deviation between the results obtained using the interpolation method and those obtained through line-by-line integration is less than 1 ‱. With the proposed method, temperature and humidity profile information can be retrieved from measured spectra within 5 min and corresponding background spectra can be obtained. The differences between the calculated background radiation and the measured spectra using the new method are smaller, making it more suitable for calculating sky background radiation. Additionally, the rapid retrieval results of the temperature profiles in the lower atmosphere have a certain level of accuracy (the mean deviation is less than 2 K). Full article

(This article belongs to the Special Issue Laser as a Detection: From Spectral Imaging to LiDAR for Remote Sensing Applications)

► Show Figures

Figure 1

20 pages, 3793 KiB

Open AccessArticle

Enhancing Tactile Internet Reliability: AI-Driven Resilience in NG-EPON Networks

by Andrew Tanny Liem, I-Shyan Hwang, Razat Kharga and Chin-Hung Teng

Photonics 2024, 11(10), 903; https://doi.org/10.3390/photonics11100903 - 26 Sep 2024

Abstract

To guarantee the reliability of Tactile Internet (TI) applications such as telesurgery, which demand extremely high reliability and are experiencing rapid expansion, we propose a novel smart resilience mechanism for Next-Generation Ethernet Passive Optical Networks (NG-EPONs). Our architecture integrates Artificial Intelligence (AI) and [...] Read more.

To guarantee the reliability of Tactile Internet (TI) applications such as telesurgery, which demand extremely high reliability and are experiencing rapid expansion, we propose a novel smart resilience mechanism for Next-Generation Ethernet Passive Optical Networks (NG-EPONs). Our architecture integrates Artificial Intelligence (AI) and Software-Defined Networking (SDN)-Enabled Broadband Access (SEBA) platform to proactively enhance network reliability and performance. By harnessing the AI’s capabilities, our system automatically detects and localizes fiber faults, establishing backup communication links using Radio Frequency over Glass (RFoG) to prevent service disruptions. This empowers NG-EPONs to maintain uninterrupted, high-quality network service even in the face of unexpected failures, meeting the stringent Quality-of-Service (QoS) requirements of critical TI applications. Our AI model, rigorously validated through 5-fold cross-validation, boasts an average accuracy of 81.49%, with a precision of 84.33%, recall of 78.18%, and F1-score of 81.00%, demonstrating its robust performance in fault detection and prediction. The AI model triggers immediate corrective actions through the SDN controller. Simulation results confirm the efficacy of our proposed mechanism in terms of delay, system throughputs and packet drop rate, and bandwidth waste, ultimately ensuring the delivery of high-quality network services. Full article

(This article belongs to the Special Issue Machine Learning Applied to Optical Communication Systems)

► Show Figures

Figure 1

18 pages, 7146 KiB

Open AccessArticle

Non-Invasive Optoacoustic Imaging for In-Depth Cultural Heritage Diagnostics

by George J. Tserevelakis, Eleanna Pirgianaki, Kristalia Melessanaki, Giannis Zacharakis and Costas Fotakis

Photonics 2024, 11(10), 902; https://doi.org/10.3390/photonics11100902 - 25 Sep 2024

Viewed by 205

Abstract

The complex composition of cultural heritage (CH) items presents significant challenges in assessing their condition and predicting potential risks of material degradation. Typically employed diagnostic optical methods are inevitably limited by light scattering, thus restricting in-depth investigations of objects with complex structural and [...] Read more.

The complex composition of cultural heritage (CH) items presents significant challenges in assessing their condition and predicting potential risks of material degradation. Typically employed diagnostic optical methods are inevitably limited by light scattering, thus restricting in-depth investigations of objects with complex structural and optical properties. To address this issue, we introduce a novel reflection-mode optoacoustic (OA) diagnostic system for non-contact and non-invasive measurements of CH, placing emphasis on the detection of ageing-related modifications in artistic media such as paints. In this direction, the sensitivity of OA measurements was proven to be up to two orders of magnitude higher than conventional absorption spectroscopy assessments. Furthermore, we have evaluated the in-depth imaging capabilities of the developed OA system, demonstrating that it can offer superior contrast levels of sketches beneath opaque paint layers compared to standard near-infrared diagnostic techniques. The current OA imaging technology may advance state-of-the-art diagnostic capabilities in CH preservation by delivering unprecedented depth-to-resolution ratios combined with exceptional optical absorption sensitivity in a non-invasive manner. These features are crucial for the early detection of material degradation and the comprehensive analysis of CH objects, facilitating the development of optimal conservation strategies to prolong their lifespan and preserve their aesthetic value. Full article

► Show Figures

Figure 1

15 pages, 3150 KiB

Open AccessArticle

Research on the Conversion Coefficient in Coherent Φ-OTDR and Its Intrinsic Impact on Localization Accuracy

by Zhen Zhong, Ningmu Zou and Xuping Zhang

Photonics 2024, 11(10), 901; https://doi.org/10.3390/photonics11100901 - 25 Sep 2024

Viewed by 203

Abstract

Phase-sensitive optical time domain reflectometry (Φ-OTDR) plays a crucial role in localizing and monitoring seismic waves, underwater structures, etc. Accurate localization of external perturbations along the fiber is essential for addressing these challenges effectively. The conversion coefficient, which links the detected phase signal [...] Read more.

Phase-sensitive optical time domain reflectometry (Φ-OTDR) plays a crucial role in localizing and monitoring seismic waves, underwater structures, etc. Accurate localization of external perturbations along the fiber is essential for addressing these challenges effectively. The conversion coefficient, which links the detected phase signal to the perturbation signal on the fiber, has a significant impact on localization accuracy. This makes the characteristic of parameters relative to the conversion coefficient in Φ-OTDR a subject of deep research. Based on the coherent Φ-OTDR mathematical model, parameters like the modulus, the statistical phase, the phase change, and the peak difference are analyzed with and without the static region, respectively. When perturbations are homogeneously distributed along the fiber, the absence of static region on the phase change-fiber length plane leads to a nonlinear phase change relationship. This deviation from the expected linear relationship in the presence of static region means that the static region is essential for higher localization accuracy. The absence of static region results in a standard deviation of 0.042263 m for the localization deviation value, which could be theoretically reduced by a new sensor design with a static region. These findings underscore the importance of the conversion coefficient and the relevance of the static region in Φ-OTDR to achieving accurate and effective localization. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement: 2nd Edition)

► Show Figures

Figure 1

11 pages, 8232 KiB

Open AccessArticle

High-Precision Tracking of Free-Space Optical Communication System on Mobile Platforms

by Ning Sun, Yuehui Wang, Yuanda Wu and Jianguo Liu

Photonics 2024, 11(10), 900; https://doi.org/10.3390/photonics11100900 - 25 Sep 2024

Viewed by 128

Abstract

We propose a new free-space optical (FSO) communication system for moving platform tracking, which can achieve high precision aiming and tracking. Our prototype system consists of three parts. As a coarse sighting structure, the electro-optical pod module is used for target searching and [...] Read more.

We propose a new free-space optical (FSO) communication system for moving platform tracking, which can achieve high precision aiming and tracking. Our prototype system consists of three parts. As a coarse sighting structure, the electro-optical pod module is used for target searching and coarse sighting in the initial stage. As a precise aiming structure, the precise targeting loads module located inside the electro-optical pod module uses miniaturized tubular folding optical path technology for high-precision alignment and tracking. The bottom module of the system is used for communication. In the tracking process, the control unit uses spot offset collected by CCD to perform decoupling calculation and then compensates the offset by swinging tracking and aiming structure. We did track experiments on a mobile platform. The experiment successfully tracked a moving target at 100 m distance, and the tracking error was less than 1 mrad. The proposed system can provide stable communication links between the mobile platforms. Full article

(This article belongs to the Special Issue Challenges and Opportunities in Wireless Optical Communication)

► Show Figures

Figure 1

13 pages, 4666 KiB

Open AccessArticle

Tilted Wire Metamaterials Enabling Ultra-Broadband Absorption from Middle to Very Long Infrared Regimes

by Pan Wang, Chengyu Xiao, Shaowen Chen, Mengqi Zhang, Ya Sun, Haoyu Wang, Jin Zhang and Han Zhou

Photonics 2024, 11(10), 899; https://doi.org/10.3390/photonics11100899 - 25 Sep 2024

Viewed by 221

Abstract

Infrared metamaterial absorbers underpin many entrenched scientific and technical applications, including radiative cooling, energy harvesting, infrared detectors, and microbolometers. However, achieving both perfect and ultra-broadband absorption remains an unmet scientific challenge because the traditional metamaterial absorber strategy suffers from complex multi-sized resonators and [...] Read more.

Infrared metamaterial absorbers underpin many entrenched scientific and technical applications, including radiative cooling, energy harvesting, infrared detectors, and microbolometers. However, achieving both perfect and ultra-broadband absorption remains an unmet scientific challenge because the traditional metamaterial absorber strategy suffers from complex multi-sized resonators and multiple meta-element patterns. We demonstrate a simple ultra-broadband infrared metamaterial absorber consisting of tilted graphite wires and an Al reflector. The proposed tilted wires-based metamaterial (TWM) absorber exhibits absorption of above 0.95 across the middle to very long-wavelength infrared spectrum (3–30 µm). By increasing the aspect ratio, the bandwidth can be expanded and achieve near-perfect absorption in the 3–50 μm spectral range. The excellent infrared absorptance performance primarily originates from the ohmic loss induced by the electromagnetic coupling between neighboring tilted wires. Furthermore, we propose a typical three-layer equivalent model featuring a resonator/insulator/reflector configuration that requires more than 84 resonant cavities to obtain comparable infrared absorptance. Our high-performance TWM absorber could accelerate the development of next-generation infrared thermal emitters and devices and other technologies that require infrared absorption. Full article

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

► Show Figures

Figure 1

9 pages, 1617 KiB

Open AccessArticle

Nd:YVO₄ Random Laser with Preferential Emission at 1340 nm over 1064 nm

by Jessica Dipold, Luciana R. P. Kassab and Niklaus U. Wetter

Photonics 2024, 11(10), 898; https://doi.org/10.3390/photonics11100898 - 25 Sep 2024

Viewed by 184

Abstract

Neodymium-doped yttrium vanadate random lasers have presented exceptional efficiency and output power at the 1064 nm emission wavelength. However, emission at 1340 nm has not yet been observed for these random lasers, even though regular bulk lasers have presented many impressive properties in [...] Read more.

Neodymium-doped yttrium vanadate random lasers have presented exceptional efficiency and output power at the 1064 nm emission wavelength. However, emission at 1340 nm has not yet been observed for these random lasers, even though regular bulk lasers have presented many impressive properties in this infrared region. Here, we present a dual-emission Nd³⁺:YVO₄ pellet random laser, which emits at both 1064 nm and 1340 nm using a 585 nm pump wavelength, showing a new property corresponding to a much lower laser threshold at 1340 nm than with 1064 nm. Full article

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

► Show Figures

Figure 1

13 pages, 2094 KiB

Open AccessArticle

Secrecy Performance Analysis of Hybrid RF/FSO System under Different Eavesdropping Strategies

by Xinkang Song, Xiang Wang, Xin Li, Shanghong Zhao and Qin Tian

Photonics 2024, 11(10), 897; https://doi.org/10.3390/photonics11100897 - 24 Sep 2024

Viewed by 185

Abstract

In this paper, we analyze the confidentiality of a hybrid radio frequency (RF)/free-space optical (FSO) system with regard to physical layer security (PLS). In this system, signals are transmitted between the source and destination using RF and FSO links, with the destination employing [...] Read more.

In this paper, we analyze the confidentiality of a hybrid radio frequency (RF)/free-space optical (FSO) system with regard to physical layer security (PLS). In this system, signals are transmitted between the source and destination using RF and FSO links, with the destination employing the maximal-ratio combining (MRC) scheme. A non-cooperative target (NCT) is assumed to have eavesdropping capabilities for RF and FSO signals in both collusion and non-collusion strategies. The Nakagami-m distribution models fading RF links, while FSO links are characterized by the Málaga (

M

) distribution. Exact closed-form expressions for the system’s secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived based on the generalized Meijer G-function with two variables. Asymptotic expressions for the SOP are also obtained under high-signal-to-noise-ratio (SNR) regimes. These conclusions are validated through Monte Carlo simulations. The superiority of the hybrid RF/FSO system in improving the communication security of a single link is confirmed in its comparison with conventional means of RF communication. Full article

(This article belongs to the Section Optical Communication and Network)

► Show Figures

Figure 1

16 pages, 7626 KiB

Open AccessArticle

Distributed Acoustic Sensing: A Promising Tool for Finger-Band Anomaly Detection

by Kunpeng Zhang, Haochu Ku, Su Wang, Min Zhang, Xiangge He and Hailong Lu

Photonics 2024, 11(10), 896; https://doi.org/10.3390/photonics11100896 - 24 Sep 2024

Viewed by 172

Abstract

The straddle-type monorail is an electric-powered public vehicle widely known for its versatility and ease of maintenance. The finger-band is a critical connecting structure for the straddle-type monorail, but issues such as loose bolts are inevitable over time. Manual inspection is the primary [...] Read more.

The straddle-type monorail is an electric-powered public vehicle widely known for its versatility and ease of maintenance. The finger-band is a critical connecting structure for the straddle-type monorail, but issues such as loose bolts are inevitable over time. Manual inspection is the primary method for detecting bolt looseness in the finger-band, but this approach could be more efficient and resistant to missed detections. In this study, we conducted a straddle-type monorail finger-band-anomaly-monitoring experiment using Distributed Acoustic Sensing (DAS), a distributed multi-point-monitoring system widely used in railway monitoring. We analyzed track vibration signals’ time-domain and frequency-domain characteristics under different monorail operating conditions. Our findings revealed the following: 1. DAS can effectively identify the monorail’s operating status, including travel direction, starting and braking, and real-time train speed measurement. 2. Time-domain signals can accurately pinpoint special track structures such as turnouts and finger-bands. Passing trains over finger-bands also results in notable energy reflections in the frequency domain. 3. After the finger-band bolts loosen, there is a significant increase in vibration energy at the finger-band position, with the degree of energy increase corresponding to the extent of loosening. Full article

(This article belongs to the Special Issue Distributed Optical Fiber Sensing Technology)

► Show Figures

Figure 1

11 pages, 4925 KiB

Open AccessArticle

Growth of Low-Temperature Epitaxial Lithium Niobate Thin Films and Guided-Wave Optical Properties

by Thanh Ngoc Kim Bui, Estelle Wagner, Rahma Moalla, William Maudez, Karim Dogheche, Romain Bachelet, Bruno Masenelli, Giacomo Benvenuti, Denis Rémiens and El Hadj Dogheche

Photonics 2024, 11(10), 895; https://doi.org/10.3390/photonics11100895 - 24 Sep 2024

Viewed by 295

Abstract

LiNbO₃ thin films are grown on a c-plane (0001) sapphire wafer at a relatively low substrate temperature by chemical beam vapor deposition (CBVD) in Sybilla equipment. Raman measurements only evidence the LiNbO₃ phase, while HR-XRD diffractograms demonstrate a c-axis-oriented growth with [...] Read more.

LiNbO₃ thin films are grown on a c-plane (0001) sapphire wafer at a relatively low substrate temperature by chemical beam vapor deposition (CBVD) in Sybilla equipment. Raman measurements only evidence the LiNbO₃ phase, while HR-XRD diffractograms demonstrate a c-axis-oriented growth with only (006) and (0012) planes measured. The rocking curve is symmetric, with a full width at half maximum (FWHM) of 0.04°. The morphology and topography observed by SEM and AFM show very low roughness, with rms equaling 2.0 nm. The optical properties are investigated by a guided-wave technique using prism coupling. The ordinary refractive index (n_o) and extraordinary refractive index (n_e) at different wavelengths totally match with the LiNbO₃ bulk, showing the high microstructural quality of the film. The film composition is estimated by Raman and bi-refringence and shows a congruent or near-stoichiometric LiNbO₃. Full article

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

► Show Figures

Figure 1

Journal Menu

Journal Browser

Photonics, Volume 11, Issue 10 (October 2024) – 14 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI