Photonics

10 pages, 1117 KiB

Open AccessCommunication

Efficient Direct Detection of Twin Single-Sideband Quadrature-Phase Shift Keying Using a Single Detector with Hierarchical Blind-Phase Search

by Hongbo Zhang, Jiao Liu, Guo-Wei Lu, Min Zhang, Feng Wan, Ju Cai, Weiwei Ling and Liming Hu

Photonics 2024, 11(7), 624; https://doi.org/10.3390/photonics11070624 (registering DOI) - 29 Jun 2024

Abstract

We propose a novel reception scheme for twin single-sideband (twin-SSB) signals using just a single photodetector (PD), significantly reducing the system complexity and cost. To detect a twin-SSB with power-unbalanced quadrature-phase shift keying (QPSK) sidebands upon detection via a single PD at the [...] Read more.

We propose a novel reception scheme for twin single-sideband (twin-SSB) signals using just a single photodetector (PD), significantly reducing the system complexity and cost. To detect a twin-SSB with power-unbalanced quadrature-phase shift keying (QPSK) sidebands upon detection via a single PD at the receiver side, two QPSKs carried in two sidebands are coherently superposed and detected in a 16-ary quadrature amplitude modulation (16-QAM) format. This technique notably diminishes the linearity and effective number of bits required for the transmitter components in high-speed optical transmission systems. Moreover, a hierarchical blind-phase search (HBPS) algorithm is proposed to compensate for the imperfect phase rotation of QPSK signals during transmission. To demonstrate the effectiveness of our proposed method, we successfully conducted simulations of 112 Gb/s 16-QAM signal transmission over a 10 km standard single-mode fiber (SSMF), achieving bit error ratios (BERs) of

7.84 \times 10^{- 4}

, well below the 7% hard-decision forward error correction (HD-FEC) threshold of

3.8 \times 10^{- 3}

. In addition, the synthetic transmission scheme proposed in this paper is compared with the traditional 16-QAM signal transmission scheme, and the results show that the proposed scheme does not introduce a performance cost with the same received optical power (ROP) and transmission distance. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing II)

15 pages, 2724 KiB

Open AccessArticle

Lights off the Image: Highlight Suppression for Single Texture-Rich Images in Optical Inspection Based on Wavelet Transform and Fusion Strategy

by Xiang Sun, Lingbao Kong, Xiaoqing Wang, Xing Peng and Guangxi Dong

Photonics 2024, 11(7), 623; https://doi.org/10.3390/photonics11070623 (registering DOI) - 28 Jun 2024

Viewed by 51

Abstract

A wavelet-transform-based highlight suppression method is presented, aiming at suppressing the highlights of single image with complex texture. The strategy involves the rough extraction of specular information, followed by extracting the high-frequency information in specular information based on multi-level wavelet transform to enhance [...] Read more.

A wavelet-transform-based highlight suppression method is presented, aiming at suppressing the highlights of single image with complex texture. The strategy involves the rough extraction of specular information, followed by extracting the high-frequency information in specular information based on multi-level wavelet transform to enhance the texture information in the original images by fusion strategy, and fusing with the same-level specular information to achieve the highlight suppression image. The experimental results demonstrate that the proposed method effectively removed large-area highlights while preserving texture details, and demonstrated the authenticity of the highlight estimation and the ‘lights off’ effect in the highlight-suppressed images. Overall, the method offers a feasibility for addressing the challenges of highlight suppression for visual detection image with rich texture and large-area highlights. Full article

(This article belongs to the Special Issue New Perspectives in Optical Design)

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20 pages, 1265 KiB

Open AccessReview

Advances in Femtosecond Coherent Anti-Stokes Raman Scattering for Thermometry

by Kaiyuan Song, Mingze Xia, Sheng Yun, Yuan Zhang, Sheng Zhang, Hui Ge, Yanyan Deng, Meng Liu, Wei Wang, Longfei Zhao, Yulei Wang, Zhiwei Lv and Yuanqin Xia

Photonics 2024, 11(7), 622; https://doi.org/10.3390/photonics11070622 (registering DOI) - 28 Jun 2024

Abstract

The combustion process is complex and harsh, and the supersonic combustion flow field is also characterized by short duration and supersonic speed, which makes the real-time diagnostic technology for the transient environment extremely demanding. It is of great significance to realize high time-resolved [...] Read more.

The combustion process is complex and harsh, and the supersonic combustion flow field is also characterized by short duration and supersonic speed, which makes the real-time diagnostic technology for the transient environment extremely demanding. It is of great significance to realize high time-resolved accurate measurement of temperature, component concentration, and other parametric information of the combustion field to study the transient chemical reaction dynamics of the combustion field. Femtosecond CARS spectroscopy can effectively avoid the collision effect between particles in the measurement process and reduce the influence of the non-resonant background to improve the measurement accuracy and realize the time-resolved measurement on a millisecond scale. This paper introduces the development history of femtosecond CARS spectroscopy, points out its advantages and disadvantages, and looks forward to the future development trend to carry out high time-resolved measurements, establish a database of temperature changes in various complex combustion fields, and provide support for the study of engine mechanisms. Full article

(This article belongs to the Special Issue Emerging Topics in High-Power Laser and Light–Matter Interactions)

13 pages, 10590 KiB

Open AccessArticle

Simplified 1.5 μm Distributed Feedback Semiconductor Laser (DFB-LD) Frequency Stabilization System Based on Gas Absorption Chamber

by Ju Wang, Ye Gao, Jinlong Yu, Ziheng Cai, Hao Luo and Chuang Ma

Photonics 2024, 11(7), 621; https://doi.org/10.3390/photonics11070621 (registering DOI) - 28 Jun 2024

Viewed by 25

Abstract

The classical 1.5

μ

m band frequency-stabilized laser using acetylene gas saturated absorption can achieve high frequency stability and reproducibility, but its system design is complex and bulky. For some practical applications, a simple, compact system containing anti-interference abilities is preferred. In this [...] Read more.

The classical 1.5

μ

m band frequency-stabilized laser using acetylene gas saturated absorption can achieve high frequency stability and reproducibility, but its system design is complex and bulky. For some practical applications, a simple, compact system containing anti-interference abilities is preferred. In this study, a low-cost and simple-structured 1.5

μ

m frequency-stabilized laser is constructed using digital control methods, wavelength modulation technology, and acetylene gas absorption. The fiber input and output optical devices of the system significantly simplify the optical path and reduce the volume of the system. The error signal is obtained by the first-order differential method, and a combination of the high-speed comparator circuit and the microcontroller unit (MCU) is used to detect the error signal. Through the feedback control method of coarse temperature adjustment and fine current adjustment, the second-level frequency stability of the laser is stabilized within 100 kHz, that is, the frequency stability reaches 10

​^{- 10}

. The designed system achieved continuous and stable operation for more than 6 h, and the long-term frequency stability reached 10

​^{- 9}

. Full article

(This article belongs to the Special Issue Laser Technology and Applications)

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10 pages, 3161 KiB

Open AccessCommunication

Polarization-Dependent Formation of Extremely Compressed Femtosecond Wave Packets and Supercontinuum Generation in Fused Silica

by Ilia Geints and Olga Kosareva

Photonics 2024, 11(7), 620; https://doi.org/10.3390/photonics11070620 (registering DOI) - 28 Jun 2024

Viewed by 50

Abstract

Previous studies of formation of extremely compressed wave packets during femtosecond filamentation in the region of anomalous group velocity dispersion in solid dielectrics mostly considered the case of linearly polarized laser pulses. However, recent results suggest potential applications of polarization state manipulation for [...] Read more.

Previous studies of formation of extremely compressed wave packets during femtosecond filamentation in the region of anomalous group velocity dispersion in solid dielectrics mostly considered the case of linearly polarized laser pulses. However, recent results suggest potential applications of polarization state manipulation for ultrafast laser writing of optical structures in bulk solid-state media. In the present work, evolution of radiation polarization parameters during formation of such extreme wave packets at the pump wavelength of 1900 nm in fused silica is studied numerically on the basis of the carrier-resolved unidirectional pulse propagation equation (UPPE). It was revealed that initial close-to-circular polarization leads to higher intensity of the anti-Stokes wing in the spectrum of the generated supercontinuum. Numerical simulations indicate a complex, space–time variant polarization state, and the resulting spatiotemporal electric field distribution exhibits a strong dependence on the initial polarization of the femtosecond pulse. At the same time, electric field polarization tends to linear one in the region with the highest field strength regardless of the initial parameters. The origin of this behavior is attributed to the properties of the supercontinuum components generation during filament-induced plasma formation. Full article

(This article belongs to the Special Issue Ultrafast Intense Laser Filamentation and Beyond)

12 pages, 1858 KiB

Open AccessArticle

High–Speed Laser Modulation for Low–Noise Micro–Cantilever Array Deflection Measurement

by Weiwei Xue, Yong Su and Qingchuan Zhang

Photonics 2024, 11(7), 619; https://doi.org/10.3390/photonics11070619 (registering DOI) - 28 Jun 2024

Viewed by 46

Abstract

In this paper, an innovative approach is introduced to address the noise issues associated with micro–cantilever array deflection measurement systems employing multiple lasers. Conventional systems are affected by laser mode hopping during switching, resulting in wavelength instability and beam spot fluctuations that take [...] Read more.

In this paper, an innovative approach is introduced to address the noise issues associated with micro–cantilever array deflection measurement systems employing multiple lasers. Conventional systems are affected by laser mode hopping during switching, resulting in wavelength instability and beam spot fluctuations that take several hundred milliseconds to stabilize. To mitigate these limitations, a high–speed laser modulation technique is utilized, leveraging the averaging effect over multiple modulation cycles within the sampling window. By driving the lasers with a high–frequency carrier signal, a low–noise and stable output suitable for micro–cantilever beam deflection measurement is achieved. The effectiveness of this approach is demonstrated by simultaneously modulating the lasers and rapidly observing the spectral and centroid variations during high–speed switching using a custom–built high–speed spectrometer. The centroid fluctuations are also analyzed under different modulation frequencies. The experimental results confirm that the high–speed modulation method can reduce the standard deviation of beam spot fluctuations by more than 90%, leading to significant improvements in noise reduction compared to traditional laser switching methods. The proposed high–speed laser modulation approach offers a promising solution for enhancing the precision and stability of multi–laser micro–cantilever array deflection measurement systems. Full article

(This article belongs to the Special Issue Recent Advances in 3D Optical Measurement)

17 pages, 4876 KiB

Open AccessArticle

Temperature-Dependent Localized Surface Plasmon Resonances of Noble Nanoparticles Covered with Polymers

by Dimitrios Ntemogiannis, Maria Tsarmpopoulou, Constantinos Moularas, Yiannis Deligiannakis, Alkeos Stamatelatos, Dionysios M. Maratos, Nikolaos G. Ploumis, Vagelis Karoutsos, Spyridon Grammatikopoulos, Mihail Sigalas and Panagiotis Poulopoulos

Photonics 2024, 11(7), 618; https://doi.org/10.3390/photonics11070618 (registering DOI) - 28 Jun 2024

Viewed by 53

Abstract

Self-assembled gold and silver nanoparticles were fabricated in medium vacuum conditions on Corning glass substrates by means of DC magnetron sputtering. The samples were deposited either at 420 °C or 440 °C, or they were initially deposited at room temperature followed by post [...] Read more.

Self-assembled gold and silver nanoparticles were fabricated in medium vacuum conditions on Corning glass substrates by means of DC magnetron sputtering. The samples were deposited either at 420 °C or 440 °C, or they were initially deposited at room temperature followed by post annealing. Subsequently, they were covered with three different polymers, namely Polystyrene-block-polybutadiene-blockpolystyrene (PS-b-PBD-b-PS), Polystyrene-co-methyl methacrylate (PS-co-PMMA) and Polystyreneblock-polyisoprene-block-polystyrene (PS-b-PI-b-PS), using spin coating. Localized surface plasmon resonances were recorded in the temperature range of −25 °C–100 °C. We show that the resonance position changes systematically as a function of temperature. Theoretical calculations carried out via the Rigorous Coupled Wave Analysis support the experimental results. Based on these findings, the investigated materials demonstrate potential as components for the development of temperature sensors. Full article

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

10 pages, 980 KiB

Open AccessArticle

A CMOS Inverter-Based Active Feedback Transimpedance Amplifier

by Somi Park, Sunkyung Lee, Bobin Seo, Yejin Choi, Yunji Song, Yeojin Chon, Shinhae Choi and Sung-Min Park

Photonics 2024, 11(7), 617; https://doi.org/10.3390/photonics11070617 (registering DOI) - 28 Jun 2024

Viewed by 46

Abstract

This paper presents an inverter-based active feedback transimpedance amplifier (IAF-TIA), in which an active feedback is applied to a voltage-mode inverter-based TIA, and therefore, the controlled positive regeneration process enables the proposed IAF-TIA to achieve the limiting operations for input currents greater than [...] Read more.

This paper presents an inverter-based active feedback transimpedance amplifier (IAF-TIA), in which an active feedback is applied to a voltage-mode inverter-based TIA, and therefore, the controlled positive regeneration process enables the proposed IAF-TIA to achieve the limiting operations for input currents greater than 100 μA_pp. However, the active inverter feedback mechanism might be prone to instability, hence mandating a very careful optimization of the loop gain. For this purpose, a diode-connected NMOS transistor is employed as a switch in the feedback path with its gate connected to the input, which helps not only to mitigate the corresponding issue but also to accommodate large input currents up to 1.5 mA_pp. The proposed IAF-TIA implemented in a standard 180 nm CMOS process demonstrates a 70.5 dBΩ transimpedance gain, 1.21 GHz bandwidth, 4.3 noise current spectral density, 63.5 dB input dynamic range, and 23.6 mW power dissipation from a single 1.8 V supply. The chip core occupies an area of 180 × 50 μm², including an on-chip P⁺/N-well/Deep N-well avalanche photodiode as an optical detector. Full article

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

16 pages, 743 KiB

Open AccessArticle

Impact of Optical-to-Electrical Conversion on the Design of an End-to-End Learning RGB-LED-Based Visible Light Communication System

by Jose Martin Luna-Rivera, Jose Rabadan, Julio Rufo, Carlos A. Gutierrez, Victor Guerra and Rafael Perez-Jimenez

Photonics 2024, 11(7), 616; https://doi.org/10.3390/photonics11070616 (registering DOI) - 28 Jun 2024

Viewed by 56

Abstract

Visible Light Communication (VLC) is emerging as a promising technology to meet the demands of fifth-generation (5G) networks and the Internet of Things (IoT). This study introduces a novel RGB-LED-based VLC system design that leverages autoencoders, addressing the often overlooked impact of optical-to-electrical [...] Read more.

Visible Light Communication (VLC) is emerging as a promising technology to meet the demands of fifth-generation (5G) networks and the Internet of Things (IoT). This study introduces a novel RGB-LED-based VLC system design that leverages autoencoders, addressing the often overlooked impact of optical-to-electrical (O/E) conversion efficiency. Unlike traditional methods, our autoencoder-based system not only improves communication performance but also mitigates the negative effects of O/E conversion. Through comprehensive simulations, we show that the proposed autoencoder structure enhances system robustness, achieving superior performance compared to traditional VLC systems. By quantitatively assessing the impact of O/E conversion—a critical aspect previously overlooked in the literature—our work bridges a crucial gap in VLC research. This contribution not only advances the understanding of VLC systems but also provides a strong foundation for future enhancements in 5G and IoT connectivity. Full article

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

10 pages, 1825 KiB

Open AccessArticle

Single Trench Fiber-Enabled High-Power Fiber Laser

by Yi An, Fengchang Li, Huan Yang, Xiao Chen, Liangjin Huang, Zhiping Yan, Min Jiang, Baolai Yang, Peng Wang, Zhiyong Pan, Zongfu Jiang and Pu Zhou

Photonics 2024, 11(7), 615; https://doi.org/10.3390/photonics11070615 (registering DOI) - 28 Jun 2024

Viewed by 60

Abstract

As a novel design of large-mode-area fiber, the single trench fiber (STF) providing high higher-order-mode suppression with a large mode area for the fundamental mode shows potential for high-power and high-brightness applications. However, the output power of STFs has remained relatively low over [...] Read more.

As a novel design of large-mode-area fiber, the single trench fiber (STF) providing high higher-order-mode suppression with a large mode area for the fundamental mode shows potential for high-power and high-brightness applications. However, the output power of STFs has remained relatively low over the past decade. In this paper, we first conducted a design process for STFs and determined the optimal ratio of the fiber structural parameters. Following this ratio, we fabricated an ytterbium-doped STF and demonstrated an all-fiberized fiber amplifier. The system achieved an output power of 2.5 kW with an M² factor of 1.396. To the best of our knowledge, the power of the STF in this study is approximately three times higher than the previous single-mode power record. Full article

(This article belongs to the Special Issue Research on Rare-Earth-Doped Fiber Lasers)

12 pages, 13534 KiB

Open AccessArticle

A Practicable Optoelectronic Oscillator with Ultra-Low Phase Noise

by Ziyue Zheng, Jinlong Yu, Ju Wang, Chuang Ma, Hao Luo, Xuemin Su and Ye Gao

Photonics 2024, 11(7), 614; https://doi.org/10.3390/photonics11070614 (registering DOI) - 28 Jun 2024

Viewed by 62

Abstract

In this paper, an optoelectronic oscillator (OEO) with ultra-low phase noise and high stability based on the injection-locked and phase-locked loop is proposed. In theory, the injection-locked frequency range of the injection signal is studied based on the phase dynamics equation, and the [...] Read more.

In this paper, an optoelectronic oscillator (OEO) with ultra-low phase noise and high stability based on the injection-locked and phase-locked loop is proposed. In theory, the injection-locked frequency range of the injection signal is studied based on the phase dynamics equation, and the phase noise performance of the injection-locked OEO is analyzed. The role of the phase-locked loop on the frequency stability of the OEO is analyzed based on the phase-locked loop transfer function. In addition, this paper builds an injection-locked OEO based on a phase-locked loop. The injection-locked signal is the high-frequency output of the multiplication crystal oscillator (MCO). At the same time, this MCO synchronously outputs a low-frequency signal, which is used as the reference signal of the phase-locked loop. The experimental results show that the proposed OEO output frequency is 10 GHz, and the phase noise is −89.25 dBc/Hz@100 Hz, −121.71 dBc/Hz@1 kHz, and −145.39 dBc/Hz@10 kHz; the side-mode suppression ratio is 80 dB; the frequency stability is 2.06 × 10

^{- 11}

@1 s, 9.03 × 10

^{- 11}

@10 s, 1.03 × 10

^{- 10}

@100 s, and 3.03 × 10

^{- 10}

@1000 s. Consistent with the theoretical analysis results, the solution takes into account the frequency stability, side-mode suppression ratio, and phase noise performance. The simple structure is more advantageous in practical applications. Full article

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

23 pages, 523 KiB

Open AccessReview

Machine Learning in Short-Reach Optical Systems: A Comprehensive Survey

by Chen Shao, Elias Giacoumidis, Syed Moktacim Billah, Shi Li, Jialei Li, Prashasti Sahu, André Richter, Michael Faerber and Tobias Kaefer

Photonics 2024, 11(7), 613; https://doi.org/10.3390/photonics11070613 (registering DOI) - 28 Jun 2024

Viewed by 81

Abstract

Recently, extensive research has been conducted to explore the utilization of machine learning (ML) algorithms in various direct-detected and (self)-coherent short-reach communication applications. These applications encompass a wide range of tasks, including bandwidth request prediction, signal quality monitoring, fault detection, traffic prediction, and [...] Read more.

Recently, extensive research has been conducted to explore the utilization of machine learning (ML) algorithms in various direct-detected and (self)-coherent short-reach communication applications. These applications encompass a wide range of tasks, including bandwidth request prediction, signal quality monitoring, fault detection, traffic prediction, and digital signal processing (DSP)-based equalization. As a versatile approach, ML demonstrates the ability to address stochastic phenomena in optical systems networks where deterministic methods may fall short. However, when it comes to DSP equalization algorithms such as feed-forward/decision-feedback equalizers (FFEs/DFEs) and Volterra-based nonlinear equalizers, their performance improvements are often marginal, and their complexity is prohibitively high, especially in cost-sensitive short-reach communications scenarios such as passive optical networks (PONs). Time-series ML models offer distinct advantages over frequency-domain models in specific contexts. They excel in capturing temporal dependencies, handling irregular or nonlinear patterns effectively, and accommodating variable time intervals. Within this survey, we outline the application of ML techniques in short-reach communications, specifically emphasizing their utilization in high-bandwidth demanding PONs. We introduce a novel taxonomy for time-series methods employed in ML signal processing, providing a structured classification framework. Our taxonomy categorizes current time-series methods into four distinct groups: traditional methods, Fourier convolution-based methods, transformer-based models, and time-series convolutional networks. Finally, we highlight prospective research directions within this rapidly evolving field and outline specific solutions to mitigate the complexity associated with hardware implementations. We aim to pave the way for more practical and efficient deployment of ML approaches in short-reach optical communication systems by addressing complexity concerns. Full article

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

16 pages, 7547 KiB

Open AccessArticle

Research on Lateral Inhibition Network Based on Cell Membrane Electrical Model

by Dao-Han Qi, Ming-Jie Sun and Qing-Zhong Cai

Photonics 2024, 11(7), 612; https://doi.org/10.3390/photonics11070612 - 28 Jun 2024

Viewed by 106

Abstract

Lateral inhibition is a prevalent occurrence within the biological neural system, enhancing the human brain’s ability to perceive edge information within a given scene. With the increasing prominence of neural network-based machine vision, there is a significant importance in incorporating this crucial biological [...] Read more.

Lateral inhibition is a prevalent occurrence within the biological neural system, enhancing the human brain’s ability to perceive edge information within a given scene. With the increasing prominence of neural network-based machine vision, there is a significant importance in incorporating this crucial biological mechanism into the field of machine vision. However, current research on lateral inhibition networks is divorced from biological reality, especially in the study of the inhibition coefficient. To address this issue, we proposed a lateral inhibition network based on the cell membrane electrical model and applied it to image enhancement. Firstly, we analyzed the visual formation mechanism and the lateral inhibition principle, laying the theoretical foundation. Secondly, leveraging the cell membrane electrical model, we construct a lateral inhibition network with a negative exponential distribution. Finally, our experiment demonstrates that a lateral inhibition network with a negative exponential distribution has better image enhancement ability than other distributions. Using images processed with lateral inhibition as an input improved the classification accuracy of the GoogLeNet neural network by 3.39%. Full article

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15 pages, 2109 KiB

Open AccessArticle

Compact On-Chip Metalens-Assisted Optical Switch Enabling Efficient and Scalable Beam Switching

by Chenxi Wang, Hongliang Li, Jinke Li and Sang-Shin Lee

Photonics 2024, 11(7), 611; https://doi.org/10.3390/photonics11070611 - 27 Jun 2024

Viewed by 155

Abstract

We propose and demonstrate an integrated optical switch that leverages an optical phased array (OPA) and an on-chip metalens, highlighting its potential for efficient and scalable beam switching across multiple ports within a compact footprint. The device consists of an input multimode interference [...] Read more.

We propose and demonstrate an integrated optical switch that leverages an optical phased array (OPA) and an on-chip metalens, highlighting its potential for efficient and scalable beam switching across multiple ports within a compact footprint. The device consists of an input multimode interference (MMI) coupler, a phase modulator (PM) array, a beam-transformation region featuring an on-chip metalens layer, and a tapered waveguide array serving as the output ports. The PM array, engineered to effectively manipulate multiple phases for a waveguide array using a single voltage, utilizes metal strips of varying lengths to streamline operation. The on-chip metalens, characterized by varying slot lengths, facilitates the wavefront manipulation of the fast Fourier transform, resulting in beam deflection with a focusing length of 20 µm. The simulated validation of the proposed compact optical switch demonstrated efficient beam deflection, yielding a 1 × 8 beam switching at a wavelength of 1550 nm. Combinations of diverse OPAs and metalens configurations resulted in potential scalability, allowing for the realization of optical switches with pathway numbers ranging from 4 to 16. This development of a metalens-assisted optical switch on a compact chip presents significant practical implications for enhancing data transmission efficiency and scalability in photonic integrated circuits. Full article

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

18 pages, 814 KiB

Open AccessReview

Overview on Space-Based Optical Orbit Determination Method Employed for Space Situational Awareness: From Theory to Application

by Zhe Zhang, Gaopeng Zhang, Jianzhong Cao, Cheng Li, Weining Chen, Xin Ning and Zheng Wang

Photonics 2024, 11(7), 610; https://doi.org/10.3390/photonics11070610 - 27 Jun 2024

Viewed by 177

Abstract

Leveraging space-based optical platforms for space debris and defunct spacecraft detection presents several advantages, including a wide detection range, immunity to cloud cover, and the ability to maintain continuous surveillance on space targets. As a result, it has become an essential approach for [...] Read more.

Leveraging space-based optical platforms for space debris and defunct spacecraft detection presents several advantages, including a wide detection range, immunity to cloud cover, and the ability to maintain continuous surveillance on space targets. As a result, it has become an essential approach for accomplishing tasks related to space situational awareness. However, the prediction of the orbits of space objects is crucial for the success of such missions, and current technologies face challenges related to accuracy, reliability, and practical efficiency. These challenges limit the performance of space-based optical space situational awareness systems. To drive progress in this field and establish a more effective and reliable space situational awareness system based on space optical platforms, this paper conducts a retrospective overview of research advancements in this area. It explores the research landscape of orbit determination methods, encompassing orbit association methods, initial orbit determination methods, and precise orbit determination methods, providing insights from international perspectives. The article concludes by highlighting key research areas, challenges, and future trends in current space situational awareness systems and orbit determination methods. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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29 pages, 5992 KiB

Open AccessArticle

Toward Converged Satellite/Fiber 1550 nm DS-BB84 QKD Networks: Feasibility Analysis and System Requirements

by Aristeidis Stathis, Argiris Ntanos, Nikolaos K. Lyras, Giannis Giannoulis, Athanasios D. Panagopoulos and Hercules Avramopoulos

Photonics 2024, 11(7), 609; https://doi.org/10.3390/photonics11070609 - 27 Jun 2024

Viewed by 229

Abstract

Satellite-based QKD is currently being developed to revolutionize global cryptographic key exchange by facilitating secure communication among remote parties at a global scale. By overcoming the exponential loss of fiber transmission, satellite-to-Earth communication can seamlessly interconnect vast distances as the link budget of [...] Read more.

Satellite-based QKD is currently being developed to revolutionize global cryptographic key exchange by facilitating secure communication among remote parties at a global scale. By overcoming the exponential loss of fiber transmission, satellite-to-Earth communication can seamlessly interconnect vast distances as the link budget of such links is sufficient to support QKD links. In terms of this direction, DV-QKD implementations seems to be technologically ahead since key exchange has been experimentally demonstrated to perform much more efficiently by providing key rates that are orders of magnitude higher compared to entanglement-based key exchange. However, the specific requirements to support effectively functional DV-QKD satellite-to-ground links are yet to be defined. This work attempts to define the satellite and ground segment system requirements needed in order to achieve functional QKD service for various satellites orbits (LEO, MEO, and GEO). Finite key size effects are being considered to determine the minimum block sizes that are required for secure key generation between a satellite node and a ground terminal for a single satellite pass. The atmospheric link channel is modeled with consideration of the most important degradation effects such as turbulence and atmospheric and pointing loss. Critical Tx and Rx system parameters, such as the source’s intrinsic Quantum Bit Error Rate (iQBER), the Rx telescope aperture size, and detection efficiency, were investigated in order to define the minimum requirements to establish an operation satellite-to-ground QKD link under specific assumptions. The performance of each downlink scenario was evaluated for the wavelength of 1550 nm in terms of link availability, link budget, and in the distilling of secure key volumes over time. Finally, the feasibility and requirements for distributing the collected space photons via terrestrial telecom fibers was also studied and discussed, leading to the proposal of a more futuristic WDM-enabled satellite QKD architecture. This comprehensive analysis aims to contribute to the advancement and implementation of effective satellite-based QKD systems, which can further exploit the ground fiber segment to realize converged space/terrestrial QKD networks. Full article

(This article belongs to the Special Issue Optical Satellite Communications for Quantum Networking)

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7 pages, 1117 KiB

Open AccessCommunication

Efficient Optical Coupling between Dielectric Strip Waveguides and a Plasmonic Trench Waveguide

by Jia-Ren Wu, Anjali Chandel, Chiashain Chuang and Sheng Hsiung Chang

Photonics 2024, 11(7), 608; https://doi.org/10.3390/photonics11070608 - 27 Jun 2024

Viewed by 172

Abstract

Buttcoupling is the most efficient way to excite surface plasmon polariton (SPP) waves at dielectric/metal interfaces in order to realize applications in broadband and ultra-compact integrated circuits (IOCs). We propose a reasonable waveguide structure to efficiently excite and collect the SPP waves supported [...] Read more.

Buttcoupling is the most efficient way to excite surface plasmon polariton (SPP) waves at dielectric/metal interfaces in order to realize applications in broadband and ultra-compact integrated circuits (IOCs). We propose a reasonable waveguide structure to efficiently excite and collect the SPP waves supported in a plasmonic trench waveguide in the long-haul telecommunication wavelength range. Our simulation results show that the coupling efficiency between the dielectric strip waveguides and a plasmonic trench waveguide can be optimized, which is dominated by the zigzag propagation path length in the dielectric strip loaded on the metal substrate. It is noted that nearly a 100% coupling efficiency can be achieved when the distance between the excitation source and the plasmonic waveguide is about 6.76 μm. Full article

(This article belongs to the Special Issue Integrated Waveguide-Based Photonic Devices)

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17 pages, 4638 KiB

Open AccessArticle

MT_Net: A Multi-Scale Framework Using the Transformer Block for Retina Layer Segmentation

by Enyu Liu, Xiang He, Junchen Yue, Yanxin Guan, Shuai Yang, Lei Zhang, Aiqun Wang, Jianmei Li and Weiye Song

Photonics 2024, 11(7), 607; https://doi.org/10.3390/photonics11070607 - 27 Jun 2024

Viewed by 223

Abstract

Variations in the thickness of retinal layers serve as early diagnostic indicators for various fundus diseases, and precise segmentation of these layers is essential for accurately measuring their thickness. Optical Coherence Tomography (OCT) is an important non-invasive tool for diagnosing various eye diseases [...] Read more.

Variations in the thickness of retinal layers serve as early diagnostic indicators for various fundus diseases, and precise segmentation of these layers is essential for accurately measuring their thickness. Optical Coherence Tomography (OCT) is an important non-invasive tool for diagnosing various eye diseases through the acquisition and layering of retinal images. However, noise and artifacts in images present significant challenges in accurately segmenting retinal layers. We propose a novel method for retinal layer segmentation that addresses these issues. This method utilizes ConvNeXt as the backbone network to enhance multi-scale feature extraction and incorporates a Transformer–CNN module to improve global processing capabilities. This method has achieved the highest segmentation accuracy on the Retina500 dataset, with a mean Intersection over Union (mIoU) of 81.26% and an accuracy (Acc) of 91.38%, and has shown excellent results on the public NR206 dataset. Full article

(This article belongs to the Special Issue OCT Technology Advances and Their Applications in Disease Studies)

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11 pages, 1930 KiB

Open AccessArticle

Second Harmonic Generation of Twisted Vector Vortex Beams Using aβ-BaB₂O₄ Crystal

by Chang Liu, Ying Guan, Yan Wu, Xiaobo Hu, Khian-Hooi Chew and Rui-Pin Chen

Photonics 2024, 11(7), 606; https://doi.org/10.3390/photonics11070606 - 26 Jun 2024

Viewed by 148

Abstract

In this study, we demonstrate both theoretically and experimentally second harmonic generation (SHG) of a twisted vector vortex optical field (TVVOF) using a nonlinear type-II phase-matched β-BaB₂O₄ (BBO) crystal. Our study introduces a novel method to manipulate SHG by independently modulating the two [...] Read more.

In this study, we demonstrate both theoretically and experimentally second harmonic generation (SHG) of a twisted vector vortex optical field (TVVOF) using a nonlinear type-II phase-matched β-BaB₂O₄ (BBO) crystal. Our study introduces a novel method to manipulate SHG by independently modulating the two orthogonal polarization components of a TVVOF. This flexibility in controlling SHG can be achieved through accurate experimental adjustments of the polarization components. Furthermore, we reveal that the SHG can be dynamically tuned by varying the angle between the polarization direction of the optical field and the principal axis of the BBO crystal via rotation. These findings provide a new approach for the flexible manipulation of SHG in structured vector optical fields, which have potential applications in optical communication, quantum optics, and photonic device engineering. Full article

(This article belongs to the Special Issue Nonlinear Optics and Hyperspectral Polarization Imaging)

11 pages, 19918 KiB

Open AccessArticle

Novel Spectrometer Designs for Laser-Driven Ion Acceleration

by Antonia Morabito, Kwinten Nelissen, Mauro Migliorati and Sargis Ter-Avetisyan

Photonics 2024, 11(7), 605; https://doi.org/10.3390/photonics11070605 - 26 Jun 2024

Viewed by 238

Abstract

We propose novel spectrometer designs that aim to enhance the measured spectral range of ions on a finite-sized detector. In contrast to the traditional devices that use a uniform magnetic field, in which the deflection of particles increases inversely proportional to their momentum, [...] Read more.

We propose novel spectrometer designs that aim to enhance the measured spectral range of ions on a finite-sized detector. In contrast to the traditional devices that use a uniform magnetic field, in which the deflection of particles increases inversely proportional to their momentum, in a gradient magnetic field, the deflection of particles will decrease due to the reduction of the magnetic field along their propagation. In this way, low-energy ions can reach the detector because they are deflected less, compared to the uniform field case. By utilizing a gradient magnetic field, the non-linear dispersion of ions in a homogeneous magnetic field approaches nearly linear dispersion behavior. Nonetheless, the dispersion of low-energy ions, using a dipole field, remains unnecessarily high. In this article, we discuss the employed methodology and present simulation results of the spectrometer with an extended ion spectral range, focusing on the minimum detectable energy (energy dynamic range) and energy resolution. Full article

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

14 pages, 2966 KiB

Open AccessArticle

Simulation and Analysis of a Near-Perfect Solar Absorber Based on SiO₂-Ti Cascade Optical Cavity

by Peng Chen, Yingting Yi, Qianju Song, Zao Yi, Yougen Yi, Shubo Cheng, Jianguo Zhang, Chaojun Tang, Tangyou Sun and Qingdong Zeng

Photonics 2024, 11(7), 604; https://doi.org/10.3390/photonics11070604 - 26 Jun 2024

Viewed by 305

Abstract

The main development direction for current solar technology is to improve absorption efficiency and stability. To bridge this gap, we design in this paper a structure consisting of two multilayer disc stacks of different radii, one topped by a TiO₂ disc and [...] Read more.

The main development direction for current solar technology is to improve absorption efficiency and stability. To bridge this gap, we design in this paper a structure consisting of two multilayer disc stacks of different radii, one topped by a TiO₂ disc and the other by a cascade disc stack composed of SiO₂-Ti, for use in thermal emitters and solar absorbers. The innovation of our work is the exploitation of multiple Fabry–Perot resonances in SiO₂-Ti cascade optical cavities to develop absorber bandwidths while investigating it in the field of thermal emission and many aspects affecting the efficiency of the absorber. The finite difference time domain method (FDTD) results show absorption averages as high as 96.68% with an absorption bandwidth of 2445 nm (A > 90%) at 280 nm–3000 nm solar incidence and even higher weighted averages as high as 98.48% at 1.5 solar air mass (AM) illumination. In order to investigate the physical mechanisms of our designed absorber in a high absorption state, we analyzed the electric field distributions of its four absorption peaks and concluded that its high absorption is mainly caused by the coupling of multiple Fabry–Perot resonance modes in the cascaded optical cavity. While considering this high efficiency, we also investigated the effect of complex environments such as extreme high temperatures and changes in the angle of incidence of the absorber, and the results show that the thermal radiation efficiency of the emitter is 96.79% at an operating temperature of 1700 K, which is higher than its thermal radiation efficiency of 96.38% at an operating temperature of 1500 K, which is a perfect result. On the other hand, we conclude that the designed structure is independent of polarization, while the absorber still has 88.22% absorption at incidence angles of up to 60°, both in transverse electric (TE) and transverse magnetic (TM) modes. The results of this study can help improve the performance of future solar absorbers and expand their application areas. Full article

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

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17 pages, 3540 KiB

Open AccessArticle

A Critical Analysis of the Thermo-Optic Time Constant in Si Photonic Devices

by David Coenen, Minkyu Kim, Herman Oprins, Joris Van Campenhout and Ingrid De Wolf

Photonics 2024, 11(7), 603; https://doi.org/10.3390/photonics11070603 - 26 Jun 2024

Viewed by 332

Abstract

The use of integrated heaters is widespread in silicon photonics for waveguide temperature control. The dynamical behavior of the heaters is important for determining their usefulness for certain applications. There exists ambiguity in the literature when it comes to reporting the thermo-optic time [...] Read more.

The use of integrated heaters is widespread in silicon photonics for waveguide temperature control. The dynamical behavior of the heaters is important for determining their usefulness for certain applications. There exists ambiguity in the literature when it comes to reporting the thermo-optic time constants of Si photonic devices. Many studies report devices with different heating and cooling times without providing an explanation to this phenomenon. In this paper, a comprehensive theoretical framework is developed for interpreting experimental results. This framework is developed for interferometric devices (Mach–Zehnder-based) and resonant devices (rings). With this framework, the impact of measurement conditions on the obtained thermo-optic time constant can be simulated, and we provide an explanation to the observed difference between heating and cooling time constants. We also provide guidelines on how to disentangle optical non-linearities from the pure thermal response, which should be useful in for future reporting of thermo-optic time constants. Full article

(This article belongs to the Special Issue Emerging Trends in Silicon Photonics)

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14 pages, 2794 KiB

Open AccessArticle

Design and Analysis of Orthogonal Polarization Point Diffraction Pinhole Plate

by Ziyu Han, Wenlu Feng, Zhilin Zhang and Qianbo Lu

Photonics 2024, 11(7), 602; https://doi.org/10.3390/photonics11070602 - 26 Jun 2024

Viewed by 248

Abstract

The pinhole plate is a key component of the point diffraction interferometer (PDI). The reasonable improvement and simulation of this device would enhance the application of point diffraction interferometry technology during the measurement of wavefronts. The traditional point diffraction interferometry measurement method is [...] Read more.

The pinhole plate is a key component of the point diffraction interferometer (PDI). The reasonable improvement and simulation of this device would enhance the application of point diffraction interferometry technology during the measurement of wavefronts. The traditional point diffraction interferometry measurement method is easily disturbed by environmental noise, making it difficult to obtain high-precision dynamic measurements. This paper introduces a four-step phase-shift PDI that can be employed in a common optical path. By using the principle of the finite-difference time-domain method (FDTD), a simulation model of the orthogonal polarization point diffraction pinhole plate (OP-PDPP) structure is established. The results show that when Cr is used as the film material in the pinhole plate, the parameters include a film thickness of 150 nm, a pinhole diameter of 2 μm, a wire grid period of 150 nm, and a wire grid width of 100 nm; in addition, the comprehensive extinction ratio of the pinhole plate is the greatest and the diffraction wavefront error is the smallest. Finally, the constructed experimental system is used to test the wavefront of a flat sample with a 25.4 mm aperture, and the test results are compared with those of the ZYGO interferometer. The difference in the peak-to-valley (PV) value between the OP-PDI and the ZYGO interferometer measurement is 0.0028λ, with an RMS value difference of 0.0011λ; this verifies the feasibility of the scheme proposed in this paper. The experimental results show that the proposed OP-PDPP is an effective tool for high-precision dynamic measurement. Full article

20 pages, 6113 KiB

Open AccessReview

Continuous-Wave Self-Raman Vanadate Lasers Generating Versatile Visible Wavelengths

by Di Li, Chien-Yen Huang, Xiu-Wei Chang, Hsing-Chih Liang and Yung-Fu Chen

Photonics 2024, 11(7), 601; https://doi.org/10.3390/photonics11070601 - 26 Jun 2024

Viewed by 222

Abstract

In this review, the developments of efficient high-power CW orange-lime-green lasers by using intracavity stimulated Raman Scattering (SRS) in Nd-doped vanadate lasers are systematically discussed. The overall properties of the spontaneous Raman spectra in Nd:YVO₄ and Nd:GdVO₄ crystals are overviewed. The [...] Read more.

In this review, the developments of efficient high-power CW orange-lime-green lasers by using intracavity stimulated Raman Scattering (SRS) in Nd-doped vanadate lasers are systematically discussed. The overall properties of the spontaneous Raman spectra in Nd:YVO₄ and Nd:GdVO₄ crystals are overviewed. The critical phase matchings of using the lithium triborate (LBO) crystals for sum frequency generation (SFG) and second harmonic generation (SHG) are thoroughly reviewed. We make a detailed review for achieving the individual green-lime-orange emissions from the self-Raman Nd:YVO₄ and Nd:GdVO₄ lasers with LBO crystals. The following is to review the dual-wavelength operations of the lime-green and orange-green lasers. Finally, the procedure for generating the triple-wavelength operation of orange-lime-green simultaneous emissions is completely described. The present review is expected to be useful for developing compact, efficient, high-power CW visible lasers for applications including medical treatment, biology, spectroscopy, and remote sensing. Full article

(This article belongs to the Special Issue Advanced Lasers and Their Applications II)

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14 pages, 3087 KiB

Open AccessArticle

Design of Photonic Molecule-Based Multiway Beam Splitter/Coupler with Variable Division Ratio

by Yury E. Geints

Photonics 2024, 11(7), 600; https://doi.org/10.3390/photonics11070600 - 26 Jun 2024

Viewed by 187

Abstract

An optical beam splitter is used for dividing an input optical beam into several separate beams with a specific power ratio. Usually, conventional optical beam splitters have bulky dimensions (many optical wavelengths) and a fixed dividing ratio, which significantly limit the design of [...] Read more.

An optical beam splitter is used for dividing an input optical beam into several separate beams with a specific power ratio. Usually, conventional optical beam splitters have bulky dimensions (many optical wavelengths) and a fixed dividing ratio, which significantly limit the design of new miniaturized optical devices and integrated optical circuits. We propose and investigate in detail a novel physical concept of a highly miniaturized (up to two working wavelengths) planar optical resonant splitter/coupler with a switching element comprising a photonic molecule (PM) pair dispersing input optical fluxes in multiple directions with a tailored power ratio. The structural design of the proposed splitter is based on a silicon-on-insulator (SOI) platform and composed of high-quality resonators in the form of electromagnetically coupled submicron-sized microcylinders. The control on the power division ratio and the selection of optical beam directions is realized by tuning the photonic splitter structure to the corresponding resonance of the PM supermode. Compared to known analogs, the proposed design is easy and cheap in fabrication. Because of its tiny dimensions, it is suitable for integration into a “System-on-a-chip” platform and can dynamically change the beam power division ratio by input wave-phase manipulation. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

13 pages, 4548 KiB

Open AccessArticle

Deep Learning-Assisted High-Pass-Filter-Based Fixed-Threshold Decision for Free-Space Optical Communications

by Yan Gao, Qian-Wen Jing, Min-Fang Liu, Wen-Hao Zong and Yan-Qing Hong

Photonics 2024, 11(7), 599; https://doi.org/10.3390/photonics11070599 - 26 Jun 2024

Viewed by 201

Abstract

This paper proposes a deep learning (DL)-assisted high-pass-filter (HPF)-based fixed-threshold decision (FTD) for free-space optical (FSO) communication. HPF is applied to reduce the scintillation effect by filtering out the low-frequency components of the received signal. However, the performance is limited owing to the [...] Read more.

This paper proposes a deep learning (DL)-assisted high-pass-filter (HPF)-based fixed-threshold decision (FTD) for free-space optical (FSO) communication. HPF is applied to reduce the scintillation effect by filtering out the low-frequency components of the received signal. However, the performance is limited owing to the signal distortion from HPF and remnant scintillation effect due to insufficient filtering. Therefore, the DL model is adopted to improve the performance of HPF-based scintillation effect compensation. The multilayer perceptron (MLP) model is used to adaptively select the peak frequency component of the received signal as the optimized cutoff frequency of HPF. Furthermore, recurrent neural network (RNN) and long short-term memory (LSTM) models are cascaded after HPF to compensate for the remnant scintillation effect and recover the signal distortion without the optimization of HPF cutoff frequency. The simulation was conducted under different turbulence channels and data rates. Simulation results showed that MLP-assisted adaptive optimized cutoff frequency and cascaded LSTM and HPF methods were close to the adaptive-threshold decision with precise channel state information under various turbulence channel degrees. Full article

(This article belongs to the Special Issue Advanced Technologies in Optical Wireless Communications)

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17 pages, 6133 KiB

Open AccessArticle

Laser Machining at High ∼PW/cm² Intensity and High Throughput

by Nan Zheng, Ričardas Buividas, Hsin-Hui Huang, Dominyka Stonytė, Suresh Palanisamy, Tomas Katkus, Maciej Kretkowski, Paul R. Stoddart and Saulius Juodkazis

Photonics 2024, 11(7), 598; https://doi.org/10.3390/photonics11070598 - 26 Jun 2024

Viewed by 230

Abstract

Laser machining by ultra-short (sub-ps) pulses at high intensity offers high precision, high throughput in terms of area or volume per unit time, and flexibility to adapt processing protocols to different materials on the same workpiece. Here, we consider the challenge of optimization [...] Read more.

Laser machining by ultra-short (sub-ps) pulses at high intensity offers high precision, high throughput in terms of area or volume per unit time, and flexibility to adapt processing protocols to different materials on the same workpiece. Here, we consider the challenge of optimization for high throughput: how to use the maximum available laser power and larger focal spots for larger ablation volumes by implementing a fast scan. This implies the use of high-intensity pulses approaching ∼PW/cm

^{2}

at the threshold where tunneling ionization starts to contribute to overall ionization. A custom laser micromachining setup was developed and built to enable high speed, large-area processing, and easy system reconfiguration for different tasks. The main components include the laser, stages, scanners, control system, and software. Machining of metals such as Cu, Al, or stainless steel and fused silica surfaces at high fluence and high exposure doses at high scan speeds up to 3 m/s were tested for the fluence scaling of ablation volume, which was found to be linear. The largest material removal rate was 10 mm

^{3}

/min for Cu and 20 mm

^{3}

/min for Al at the maximum power 80 W (25 J/cm

^{2}

per pulse). Modified surfaces are color-classified for their appearance, which is dependent on surface roughness and chemical modification. Such color-coding can be used as a feedback parameter for industrial process control. Full article

(This article belongs to the Special Issue Advanced Photonic Sensing and Measurement II)

30 pages, 1515 KiB

Open AccessArticle

Generation of Narrow Beams of Super High-Energy Gamma Quanta in the Resonant Compton Effect in the Field of a Strong X-ray Wave

by Sergei P. Roshchupkin and Sergey B. Makarov

Photonics 2024, 11(7), 597; https://doi.org/10.3390/photonics11070597 - 26 Jun 2024

Viewed by 188

Abstract

The article presents a theoretical study of Oleinik resonances in the process of scattering a gamma quantum by an ultrarelativistic electron in the field of a strong electromagnetic wave with intensities up to

10^{27} {Wcm}^{- 2}

. The resonant kinematics for [...] Read more.

The article presents a theoretical study of Oleinik resonances in the process of scattering a gamma quantum by an ultrarelativistic electron in the field of a strong electromagnetic wave with intensities up to

10^{27} {Wcm}^{- 2}

. The resonant kinematics for three possible resonant reaction channels in a strong external field have been studied in detail. It is shown that under resonant conditions, the scattering channels of the reaction effectively split into two first-order processes according to the fine structure constant, such as the external field-stimulated Compton effect. The annihilation channel of the reaction effectively decays into direct and reverse the external field-stimulated Breit–Wheeler processes. In the absence of interference from the reaction channels, a resonant differential cross-section was obtained in a strong external electromagnetic field. The cases when the energy of the initial electrons significantly exceeds the energy of the initial gamma quanta have been studied. At the same time, all particles (initial and final) fly in a narrow cone away from the direction of wave propagation. The conditions under which the energy of ultrarelativistic initial electrons is converted into the energy of a finite gamma quantum are studied. It is shown that the resonant differential cross-section of such a process significantly (by several orders of magnitude) exceeds the corresponding nonresonant cross-section. This theoretical study predicts a number of new physical effects that may explain the high-energy fluxes of gamma quanta produced near neutron stars and magnetars. Full article

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

12 pages, 7225 KiB

Open AccessCommunication

Demonstration of Power-over-Fiber with Watts of Output Power Capabilities over Kilometers or at Cryogenic Temperatures

by Simon Fafard and Denis Masson

Photonics 2024, 11(7), 596; https://doi.org/10.3390/photonics11070596 - 26 Jun 2024

Viewed by 220

Abstract

We demonstrate the use of laser diodes and multijunction photovoltaic power converters to efficiently deliver watts of electrical power for long-distance or cryogenic applications. Transmission through single-mode and multi-mode fibers at the wavelengths of 808 nm and 1470/1550 nm are studied. An electrical [...] Read more.

We demonstrate the use of laser diodes and multijunction photovoltaic power converters to efficiently deliver watts of electrical power for long-distance or cryogenic applications. Transmission through single-mode and multi-mode fibers at the wavelengths of 808 nm and 1470/1550 nm are studied. An electrical output power of ~0.1 W is obtained after a 5 km transmission through a standard single-mode SMF28 fiber fed with 0.25 W of optical power. An electrical output power of ~1 W is demonstrated after a 5 km transmission with a standard OM1 multi-mode fiber fed with ~2.5 W. Photovoltaic conversion efficiencies reaching Eff ~49% are obtained with an output voltage of ~5 V using commercial multijunction laser power converters. For low-temperature applications, an ultra-sensitive silicon photomultiplier (SiPM) is used to detect the residual light leaked from fibers as the temperature is decreased. Our study demonstrates that specific fiber types enable low-loss transmission compatible with cryogenic requirements and without light leakage triggering of the SiPM. A cryogenic power-over-fiber system at ~1470 nm is demonstrated with ~2 W of electrical power converted over a 10 m distance having a conversion efficiency of Eff > 65% at 77 K. Full article

(This article belongs to the Special Issue High-Power Infrared Laser Systems: Design, Characterization, and Applications)

20 pages, 1045 KiB

Open AccessArticle

Adaptive Flow Timeout Management in Software-Defined Optical Networks

by Krystian Radamski, Wojciech Ząbek, Jerzy Domżał and Robert Wójcik

Photonics 2024, 11(7), 595; https://doi.org/10.3390/photonics11070595 - 26 Jun 2024

Viewed by 261

Abstract

Current trends in network traffic management rely on the efficient control of individual flows. Software-defined networking popularized this notion. Per-flow management is perfectly viable in standard IP networks, in which packet processing is in the electric domain. However, optical networks provide more restrictions [...] Read more.

Current trends in network traffic management rely on the efficient control of individual flows. Software-defined networking popularized this notion. Per-flow management is perfectly viable in standard IP networks, in which packet processing is in the electric domain. However, optical networks provide more restrictions and constraints making per-flow traffic management difficult. One of the most important challenges is to reduce the concurrent number of flows present in the flow tables to make the switching process quicker. In this paper, we propose a mechanism to manage flow timeout values that uses idle timeout and hard timeout parameters. To calculate the appropriate values of the parameters, the mechanism analyzes the packet inter-arrival times. The algorithm also takes into account the current occupancy of the flow table. Full article

(This article belongs to the Special Issue Optical Communication and Networks Facilitating Emerging Applications and Services)

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