Journal Description
Photonics
Photonics
is an international, scientific, peer-reviewed, open access journal on the science and technology of optics and photonics, published monthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 15.5 days after submission; acceptance to publication is undertaken in 2.7 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Companion journal: Optics.
Impact Factor:
2.4 (2022);
5-Year Impact Factor:
2.4 (2022)
Latest Articles
High-Precision Semiconductor Substrate Thickness Gauge Based on Spectral-Domain Interferometry
Photonics 2024, 11(5), 422; https://doi.org/10.3390/photonics11050422 - 01 May 2024
Abstract
The flatness of semiconductor substrates is an important parameter for evaluating the surface quality of semiconductor substrates. However, existing technology cannot simultaneously achieve high measurement efficiency, large-range thickness measurement, and nanometer-level measurement accuracy in the thickness measurement of semiconductor substrates. To solve the
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The flatness of semiconductor substrates is an important parameter for evaluating the surface quality of semiconductor substrates. However, existing technology cannot simultaneously achieve high measurement efficiency, large-range thickness measurement, and nanometer-level measurement accuracy in the thickness measurement of semiconductor substrates. To solve the problems, we propose to apply the method that combines spectral-domain optical coherence tomography (SD-OCT) with the Hanning-windowed energy centrobaric method (HnWECM) to measure the thickness of semiconductor substrates. The method can be employed in the full-chip thickness measurement of a sapphire substrate, which has a millimeter measuring range, nanometer-level precision, and a sampling rate that can reach up to 80 kHz. In this contribution, we measured the full-chip thickness map of a sapphire substrate by using this method and analyzed the machining characteristics. The measurement results of a high-precision mechanical thickness gauge, which is widely used for thickness measurement in the wafer fabrication process, were compared with the proposed method. The difference between these two methods is 0.373%, which explains the accuracy of the applied method to some extent. The results of 10 sets of repeatability experiments on 250 measurement points show that the maximum relative standard deviation (RSD) at this point is 0.0061%, and the maximum fluctuation is 71.0 nm. The above experimental results prove that this method can achieve the high-precision thickness measurement of the sapphire substrate and is of great significance for improving the surface quality detection level of semiconductor substrates.
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(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement: 2nd Edition)
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Open AccessArticle
Group Control of Photo-Responsive Colloidal Motors with a Structured Light Field
by
Dianyang Li, Huan Wei, Hui Fang and Yongxiang Gao
Photonics 2024, 11(5), 421; https://doi.org/10.3390/photonics11050421 - 01 May 2024
Abstract
Using structured light to drive colloidal motors, due to its advantages of remote manipulation, energy tunability, programmability, and the controllability of spatiotemporal distribution, has been attracting much attention in the fields of targeted drug delivery, environmental control, chemical agent detection, and smart device
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Using structured light to drive colloidal motors, due to its advantages of remote manipulation, energy tunability, programmability, and the controllability of spatiotemporal distribution, has been attracting much attention in the fields of targeted drug delivery, environmental control, chemical agent detection, and smart device design. Here, we focus on studying the group control of colloidal motors made from a photo-responsive organic polymer molecule NO-COP (N,O-Covalent organic polymer). These colloidal motors mainly respond to light intensity patterns. Considering its merits of fast refreshing speed, good programmability, and high-power threshold, we chose a digital micromirror device (DMD) to modulate the structured light field shining on the sample. It was found that under ultraviolet or green light modulation, such colloidal motors exhibit various group behaviors including group spreading, group patterning, and group migration. A qualitative interpretation is also provided for these observations.
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(This article belongs to the Special Issue Emerging Topics in Structured Light)
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Open AccessArticle
Functional Optical Coherence Tomography of Rat Cortical Neurovascular Activation during Monopulse Electrical Stimulation with the Microelectrode Array
by
Lin Yao, Jin Huang, Taixiang Liu, Han Gu, Changpeng Li, Ke Yang, Hongwei Yan, Lin Huang, Xiaodong Jiang, Chengcheng Wang and Qihua Zhu
Photonics 2024, 11(5), 420; https://doi.org/10.3390/photonics11050420 - 30 Apr 2024
Abstract
This paper presents a study to evoke rat cortical functional activities, including hemodynamic and neural tissue signal changes, by monopulse electrical stimulation with a microelectrode array using functional optical coherence tomography (fOCT). Based on the principal component analysis and fuzzy clustering method (PCA-FCM),
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This paper presents a study to evoke rat cortical functional activities, including hemodynamic and neural tissue signal changes, by monopulse electrical stimulation with a microelectrode array using functional optical coherence tomography (fOCT). Based on the principal component analysis and fuzzy clustering method (PCA-FCM), the hemodynamic response of different size blood vessels in rat cortex are analyzed, showing that the hemodynamic response of the superficial large blood vessels is more concentrated. In the regions of neural tissue where blood vessels are removed, positive significant pixels (the intensity of the pixel for five consecutive frames is greater than the average value plus triple standard deviation) and negative significant pixels (the intensity of the pixel for five consecutive frames is less than the average value minus triple standard deviation) exist, and the averaged intensity signal responds rapidly with an onset time of ~20.8 ms. Furthermore, the hemodynamic response was delayed by ~3.5 s from the neural tissue response. fOCT can provide a label-free, large-scale and depth-resolved map of cortical neurovascular activation, which is a promising technology to monitor cortical small-scale neurovascular activities.
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(This article belongs to the Section Biophotonics and Biomedical Optics)
Open AccessArticle
Direct Numerical Modeling as a Tool for Optical Coherence Tomography Development: SNR (Sensitivity) and Lateral Resolution Test Target Interpretation
by
Samuel Lawman and Yao-Chun Shen
Photonics 2024, 11(5), 419; https://doi.org/10.3390/photonics11050419 - 30 Apr 2024
Abstract
Optical Coherence Tomography (OCT) is a growing family of biophotonic imaging techniques, but in the literature there is a lack of easy-to-use tools to universally directly evaluate a device’s theoretical performance for a given metric. Modern computing tools mean that direct numerical modeling
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Optical Coherence Tomography (OCT) is a growing family of biophotonic imaging techniques, but in the literature there is a lack of easy-to-use tools to universally directly evaluate a device’s theoretical performance for a given metric. Modern computing tools mean that direct numerical modeling can, from first principles, simulate the performance metrics of a specific device directly without relying on analytical approximations and/or complexities. Here, we present two different direct numerical models, along with the example MATLAB code for the reader to adapt to their own systems. The first model is of photo-electron shot noise at the detector, the primary noise source for OCT. We use this firstly to evaluate the amount of additional noise present (1.5 dB) for an experimental setup. Secondly, we demonstrate how to use it to precisely quantify the expected shot noise SNR limit difference between time-domain and Fourier-domain OCT systems in a given hypothetical experiment. The second model is used to demonstrate how USAF 1951 test chart images should be interpreted for a given lateral PSF shape. Direct numerical modeling is an easy and powerful basic tool for researchers and developers, the wider use of which may improve the rigor of the OCT literature.
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(This article belongs to the Special Issue Recent Progress in Biophotonics)
Open AccessReview
Hybrid Integrated Silicon Photonics Based on Nanomaterials
by
Domenic Prete, Francesco Amanti, Greta Andrini, Fabrizio Armani, Vittorio Bellani, Vincenzo Bonaiuto, Simone Cammarata, Matteo Campostrini, Samuele Cornia, Thu Ha Dao, Fabio De Matteis, Valeria Demontis, Giovanni Di Giuseppe, Sviatoslav Ditalia Tchernij, Simone Donati, Andrea Fontana, Jacopo Forneris, Roberto Francini, Luca Frontini, Gian Carlo Gazzadi, Roberto Gunnella, Simone Iadanza, Ali Emre Kaplan, Cosimo Lacava, Valentino Liberali, Leonardo Martini, Francesco Marzioni, Claudia Menozzi, Elena Nieto Hernández, Elena Pedreschi, Paolo Piergentili, Paolo Prosposito, Valentino Rigato, Carlo Roncolato, Francesco Rossella, Andrea Salamon, Matteo Salvato, Fausto Sargeni, Jafar Shojaii, Franco Spinella, Alberto Stabile, Alessandra Toncelli, Gabriella Trucco and Valerio Vitaliadd
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Photonics 2024, 11(5), 418; https://doi.org/10.3390/photonics11050418 (registering DOI) - 30 Apr 2024
Abstract
Integrated photonic platforms have rapidly emerged as highly promising and extensively investigated systems for advancing classical and quantum information technologies, since their ability to seamlessly integrate photonic components within the telecommunication band with existing silicon-based industrial processes offers significant advantages. However, despite this
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Integrated photonic platforms have rapidly emerged as highly promising and extensively investigated systems for advancing classical and quantum information technologies, since their ability to seamlessly integrate photonic components within the telecommunication band with existing silicon-based industrial processes offers significant advantages. However, despite this integration facilitating the development of novel devices, fostering fast and reliable communication protocols and the manipulation of quantum information, traditional integrated silicon photonics faces inherent physical limitations that necessitate a challenging trade-off between device efficiency and spatial footprint. To address this issue, researchers are focusing on the integration of nanoscale materials into photonic platforms, offering a novel approach to enhance device performance while reducing spatial requirements. These developments are of paramount importance in both classical and quantum information technologies, potentially revolutionizing the industry. In this review, we explore the latest endeavors in hybrid photonic platforms leveraging the combination of integrated silicon photonic platforms and nanoscale materials, allowing for the unlocking of increased device efficiency and compact form factors. Finally, we provide insights into future developments and the evolving landscape of hybrid integrated photonic nanomaterial platforms.
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(This article belongs to the Special Issue Photonic Integrated Circuits for Information, Computing and Sensing)
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Open AccessArticle
Simulation Method for the Impact of Atmospheric Wind Speed on Optical Signals in Satellite–Ground Laser Communication Links
by
Wujisiguleng Zhao and Chunyi Chen
Photonics 2024, 11(5), 417; https://doi.org/10.3390/photonics11050417 - 30 Apr 2024
Abstract
To analyze the intensity of atmospheric turbulence in a satellite–ground laser communication link, it is important to consider the effect of increased atmospheric turbulence caused by wind speed. Atmospheric turbulence causes a change in the refractive index, which negatively impacts the quality and
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To analyze the intensity of atmospheric turbulence in a satellite–ground laser communication link, it is important to consider the effect of increased atmospheric turbulence caused by wind speed. Atmospheric turbulence causes a change in the refractive index, which negatively impacts the quality and focusing ability of the laser beam by altering its phase front. To simulate the changes in amplitude and phase characteristics of laser beam propagation in atmospheric turbulence caused by wind speed, a transverse translation phase screen is used. To better understand and address the influence of atmospheric wind speed on the phase of optical signals in satellite–ground laser communication links, this paper proposes a Monte Carlo simulation method. This method utilizes the spatial and temporal variations in the refractive index in the atmosphere and integrates the principles of optical signal propagation in the atmosphere to simulate changes in the phase of optical signals under different wind speed conditions. By analyzing the variations in the received optical signal’s power, the Monte Carlo method is employed to simulate phase screens and logarithmic amplitude screens. Additionally, it models the probability density of the statistical behavior of received optical signal’s fluctuations, as well as the time autocorrelation coefficient of optical signals. This paper, under the coupling condition in satellite–ground laser communication links, conducted a Monte Carlo simulation experiment to analyze the characteristics of the optical signal’s fluctuations in the link and discovered that atmospheric wind speed affects the shape of the power spectral density model of the received optical signal. Increasing wind speed leads to a decrease in the time autocorrelation coefficient of the received optical signal and affects the coupling efficiency. The paper then used a cubic spline interpolation fitting method to verify the models of the power spectral density and the autocorrelation time coefficient of the optical signal. This provides a theoretical foundation and practical guidance for the optimization of satellite–ground laser communication systems.
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(This article belongs to the Section Optical Communication and Network)
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Open AccessArticle
Modulation of Second-Order Sideband Efficiency in an Atom-Assisted Optomechanical System
by
Liang-Xuan Fan, Tao Shui, Ling Li and Wen-Xing Yang
Photonics 2024, 11(5), 416; https://doi.org/10.3390/photonics11050416 - 30 Apr 2024
Abstract
We propose an efficient scheme to enhance the generation of optical second-order sidebands (OSSs) in an atom-assisted optomechanical system. The cavity field is coupled with a strong driving field and a weak probe field, and a control field is applied to the atom.
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We propose an efficient scheme to enhance the generation of optical second-order sidebands (OSSs) in an atom-assisted optomechanical system. The cavity field is coupled with a strong driving field and a weak probe field, and a control field is applied to the atom. We use the steady-state method to analyze the nonlinear interaction in the system, which is different from the traditional linear analysis method. The existence of an auxiliary three-level atom driven by the control field significantly enhances the generation of an OSS. It is found that the efficiency of the OSS can be effectively modulated by adjusting the Rabi frequency of the control field, optomechanical cooperativity and atomic coupling strength. Our scheme provides a promising solution for controlling light propagation and has potential application in quantum optical devices and quantum information networks.
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(This article belongs to the Special Issue Optics and Laser: Light Field Manipulation)
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A Novel 4 × 1 MISO-VLC System with FBMC-OQAM Downlink Signals
by
Yufeng Shao, Yanlin Li, Anrong Wang, Yaodong Zhu, Chong Li, Peng Chen, Renjie Zuo, Jie Yuan and Shuanfan Liu
Photonics 2024, 11(5), 415; https://doi.org/10.3390/photonics11050415 - 30 Apr 2024
Abstract
A novel visible-light communication (VLC) system with 4 × 1 multi-input–single-output (MISO) channels is designed. In the system, the filter bank multicarrier (FBMC) and offset quadrature amplitude modulation (OQAM) techniques are used to generate downlink signals. The principles and implementation methods are proposed
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A novel visible-light communication (VLC) system with 4 × 1 multi-input–single-output (MISO) channels is designed. In the system, the filter bank multicarrier (FBMC) and offset quadrature amplitude modulation (OQAM) techniques are used to generate downlink signals. The principles and implementation methods are proposed and analyzed, and the light intensity and received light power distribution of four LED emitters are discussed. The results demonstrate that it not only satisfies the requirements of indoor information access but also provides daily lighting. The used FBMC-OQAM signals exhibit better reception performance than orthogonal frequency division multiplexing (OFDM) signals. The system used has a lower bit error rate (BER) and larger access bandwidth compared to a 1 × 1 single-input–single-output (SISO) system. It has the potential for application advantages in future indoor VLC system applications.
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(This article belongs to the Special Issue Visible Light Communications)
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Open AccessReview
The Structure and Applications of Fused Tapered Fiber Optic Sensing: A Review
by
Siqi Ban and Yudong Lian
Photonics 2024, 11(5), 414; https://doi.org/10.3390/photonics11050414 - 30 Apr 2024
Abstract
Tapered optical fibers have continuously evolved in areas such as distributed sensing and laser generation in recent years. Their high sensitivity, ease of integration, and real-time monitoring capabilities have positioned them as a focal point in optical fiber sensing. This paper systematically introduces
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Tapered optical fibers have continuously evolved in areas such as distributed sensing and laser generation in recent years. Their high sensitivity, ease of integration, and real-time monitoring capabilities have positioned them as a focal point in optical fiber sensing. This paper systematically introduces the structures and characteristics of various tapered optical fiber sensors, providing a comprehensive overview of their applications in biosensing, environmental monitoring, and industrial surveillance. Furthermore, it offers insights into the developmental trends of tapered optical fiber sensing, providing valuable references for future related research and suggesting potential directions for the further advancement of optical fiber sensing.
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(This article belongs to the Special Issue Fabrication of Optical Fiber and Fiber Amplifiers: From Design to Applications)
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Open AccessTechnical Note
Design and Test of a Klystron Intra-Pulse Phase Feedback System for Electron Linear Accelerators
by
Luca Piersanti, Marco Bellaveglia, Fabio Cardelli, Alessandro Gallo, Riccardo Magnanimi, Sergio Quaglia, Michele Scampati, Giorgio Scarselletta, Beatrice Serenellini and Simone Tocci
Photonics 2024, 11(5), 413; https://doi.org/10.3390/photonics11050413 - 29 Apr 2024
Abstract
Beam stability and timing jitter in modern linear accelerators are becoming increasingly important. In particular, if a magnetic or radio-frequency (RF) compression regime is employed, the beam time of arrival jitter at the end of the linac can be strictly correlated with the
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Beam stability and timing jitter in modern linear accelerators are becoming increasingly important. In particular, if a magnetic or radio-frequency (RF) compression regime is employed, the beam time of arrival jitter at the end of the linac can be strictly correlated with the phase noise of the accelerating fields of the RF structure working off-crest. For this reason, since 2008, an RF fast-feedback technique, which acts within each RF pulse, has been successfully employed at LNF-INFN (Laboratori Nazionali di Frascati dell’Istituto Nazionale di Fisica Nucleare) in the SPARC_LAB (Sources for Plasma Accelerators and Radiation Compton with Laser And Beam) facility on S-band ( 2856 MHz) klystrons powered by pulse-forming network (PFN) modulators, as reported in this paper. However, in order to meet the more stringent requirements of plasma wakefield acceleration schemes, some upgrades to this feedback system have been recently carried out. The first prototype has been experimentally tested on a C-band ( 5712 MHz) klystron, driven by a solid-state modulator, in order to investigate the possibility for additional improvement resulting from the inherently more stable power source. In this paper, the design, realization and the preliminary measurement results obtained at SPARC_LAB after such upgrades will be reviewed.
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(This article belongs to the Special Issue Recent Advances in Free Electron Laser Accelerators)
Open AccessArticle
Design and Analysis of a Narrow Linewidth Laser Based on a Triple Euler Gradient Resonant Ring
by
Yikai Wang, Boxia Yan, Mi Zhou, Chenxi Sun, Yan Qi, Yanwei Wang, Yuanyuan Fan and Qian Wang
Photonics 2024, 11(5), 412; https://doi.org/10.3390/photonics11050412 - 29 Apr 2024
Abstract
We designed a narrow-linewidth external-cavity hybrid laser leveraging a silicon-on-insulator triple Euler gradient resonant ring. The laser’s outer cavity incorporates a compact, high-Q resonant ring with low loss. The straight waveguide part of the resonant ring adopts a width of 1.6 μm to
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We designed a narrow-linewidth external-cavity hybrid laser leveraging a silicon-on-insulator triple Euler gradient resonant ring. The laser’s outer cavity incorporates a compact, high-Q resonant ring with low loss. The straight waveguide part of the resonant ring adopts a width of 1.6 μm to ensure low loss transmission. The curved section is designed as an Euler gradient curved waveguide, which is beneficial for low loss and stable single-mode transmission. The design features an effective bending radius of only 26.35 μm, which significantly improves the compactness of the resonant ring and, in turn, reduces the overall footprint of the outer cavity chip. To bolster the laser power and cater to the varying shapes of semiconductor optical amplifier (SOA) spots, we designed a multi-tip edge coupler. Theoretical analysis indicates that this edge coupler can achieve an optical coupling efficiency of 85%. It also reveals that the edge coupler provides 3 dB vertical and horizontal alignment tolerances of 0.76 μm and 2.4 μm, respectively, for a spot with a beam waist radius of 1.98 μm × 0.99 μm. The outer cavity, designed with an Euler gradient micro-ring, can achieve a side-mode suppression ratio (SMSR) of 30 dB within a tuning range of 100 nm, with a round-trip loss of the entire cavity at 1.12 dB, and an expected theoretical laser linewidth of 300 Hz.
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(This article belongs to the Special Issue Narrow Linewidth Laser Sources and Their Applications)
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Open AccessCommunication
Mueller Matrix Polarizing Power
by
José J. Gil
Photonics 2024, 11(5), 411; https://doi.org/10.3390/photonics11050411 - 29 Apr 2024
Abstract
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The transformation of the states of polarization of electromagnetic waves through their interaction with polarimetrically linear media can be represented by the associated Mueller matrices. A global measure of the ability of a linear medium to modify the states of polarization of incident
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The transformation of the states of polarization of electromagnetic waves through their interaction with polarimetrically linear media can be represented by the associated Mueller matrices. A global measure of the ability of a linear medium to modify the states of polarization of incident waves, due to any combination of enpolarizing, depolarizing and retarding properties, is introduced as the distance from the Mueller matrix to the identity matrix. This new descriptor, called the polarizing power, is applicable to any Mueller matrix and can be expressed as a function of the degree of polarimetric purity and the trace of the Mueller matrix. The graphical representation of the feasible values of the polarizing power provides a general view of its main peculiarities and features. The values of the polarizing power for several typical devices are analyzed.
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Open AccessArticle
A Novel Inserting Pilot Radio over Fiber System without the Bit Walk-Off Effect for the Generation and Distribution of Frequency 16-Tupling Millimeter Waves by Mach–Zehnder Modulators
by
Xu Chen, Xinqiao Chen, Siyuan Dai, Bin Li and Ling Wang
Photonics 2024, 11(5), 410; https://doi.org/10.3390/photonics11050410 - 28 Apr 2024
Abstract
A novel inserting pilot scheme to generate and distribute a frequency 16-tupling millimeter wave (MMW) radio over fiber (ROF) system without the bit walk-off effect via Mach–Zehnder modulators (MZMs) is proposed. The operation principle is analyzed and the feasibility of our proposed scheme
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A novel inserting pilot scheme to generate and distribute a frequency 16-tupling millimeter wave (MMW) radio over fiber (ROF) system without the bit walk-off effect via Mach–Zehnder modulators (MZMs) is proposed. The operation principle is analyzed and the feasibility of our proposed scheme is verified by simulation test. The main part of our scheme is a ±8th-order sidebands generator (SG), which is constructed by four MZMs connected in parallel. In the back-to-back (BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±8th-order sidebands are generated by the SG. In the data transmission case, the data signal is first split into two beams, one of which modulates the RF drive signal with an electrical phase modulator (PM) while the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the composite RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can only be modulated to the +8th-order sideband of the output of the SG. The optical carrier from the continuous wave (CW) laser is split into two paths: one is sent into the SG, and the other is used as a pilot signal. The output signal of SG is combined with the pilot signal and is transmitted to the base station (BS) via optical fiber. At the BS, the pilot signal is filtered out by a fiber Bragg grating (FBG) and used as the carrier for the uplink for carrier reuse. After filtering out the pilot, the signal from the FBG, which is composed of ±8th-order sidebands, is injected into a photodetector, and a frequency 16-tupling MMW with downlink data is generated. The key parameters’ influence on the bit error rate (BER) and Q factor in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion and greatly increase the fiber transmission distance but can also effectively improve the performance and the tunability of system. Therefore, it has important application prospects in ROF systems.
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(This article belongs to the Section Optical Communication and Network)
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Open AccessArticle
Far-Field Super-Resolution Optical Microscopy for Nanostructures in a Reflective Substrate
by
Aiqin Zhang, Kunyang Li, Guorong Guan, Haowen Liang, Xiangsheng Xie and Jianying Zhou
Photonics 2024, 11(5), 409; https://doi.org/10.3390/photonics11050409 - 27 Apr 2024
Abstract
The resolution of an optical microscope is determined by the overall point spread function of the system. When examining structures significantly smaller than the wavelength of light, the contribution of the background or surrounding environment can profoundly affect the point spread function. This
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The resolution of an optical microscope is determined by the overall point spread function of the system. When examining structures significantly smaller than the wavelength of light, the contribution of the background or surrounding environment can profoundly affect the point spread function. This research delves into the impact of reflective planar substrate structures on the system’s resolution. We establish a comprehensive forward imaging model for a reflection-type confocal laser scanning optical microscope, incorporating vector field manipulation to image densely packed nanoparticle clusters. Both theoretical and experimental findings indicate that the substrate causes an interference effect between the background field and the scattered field from the nanoparticles, markedly enhancing the overall spatial resolution. The integration of vector field manipulation with an interferometric scattering approach results in superior spatial resolution for imaging isolated particles and densely distributed nanoscale particle clusters even with deep subwavelength gaps as small as 20 nm between them. However, the method still struggles to resolve nanoparticles positioned directly next to each other without any gap, necessitating further work to enhance the resolving ability. This may involve techniques like deconvolution or machine learning-based post-processing methods.
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(This article belongs to the Special Issue Design and Applications of Optical Microscopes)
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Open AccessArticle
Rapid Fabrication of Yttrium Aluminum Garnet Microhole Array Based on Femtosecond Bessel Beam
by
Heng Yang, Yuan Yu, Tong Zhang, Shufang Ma, Lin Chen, Bingshe Xu and Zhiyong Wang
Photonics 2024, 11(5), 408; https://doi.org/10.3390/photonics11050408 - 27 Apr 2024
Abstract
High-aspect-ratio microholes, the fundamental building blocks for microfluidics, optical waveguides, and other devices, find wide applications in aerospace, biomedical, and photonics fields. Yttrium aluminum garnet (YAG) crystals are commonly used in optical devices due to their low stress, hardness, and excellent chemical stability.
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High-aspect-ratio microholes, the fundamental building blocks for microfluidics, optical waveguides, and other devices, find wide applications in aerospace, biomedical, and photonics fields. Yttrium aluminum garnet (YAG) crystals are commonly used in optical devices due to their low stress, hardness, and excellent chemical stability. Therefore, finding efficient fabrication methods to produce high-quality microholes within YAG crystals is crucial. The Bessel beam, characterized by a uniform energy distribution along its axis and an ultra-long depth of focus, is highly suitable for creating high-aspect-ratio structures. In this study, an axicon lens was used to shape the spatial profile of a femtosecond laser into a Bessel beam. Experimental verification showed a significant improvement in the high aspect ratio of the microholes produced in YAG crystals using the femtosecond Bessel beam. This study investigated the effects of the power and defocus parameters of single-pulse Bessel beams on microhole morphology and size, and microhole units with a maximum aspect ratio of more than 384:1 were obtained. Based on these findings, single-pulse femtosecond Bessel processing parameters were optimized, and an array of 181 × 181 microholes in a 400 μm thick YAG crystal was created in approximately 13.5 min. The microhole array had a periodicity of 5 μm and a unit aspect ratio of 315:1, with near-circular top and subface apertures and high repeatability.
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(This article belongs to the Special Issue Laser Processing and Modification of Materials)
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Open AccessArticle
Evaluation of an Erbium-Doped Fiber Ring Laser as an Edge Filtering Device for Fiber Bragg Grating Sensor Interrogation
by
Nikolaos A. Stathopoulos, Christos Lazakis, Iraklis Simos and Christos Simos
Photonics 2024, 11(5), 407; https://doi.org/10.3390/photonics11050407 - 27 Apr 2024
Abstract
An easy-to-implement and cost-effective Fiber Bragg Grating (FBG) sensor interrogation technique based on a ring Erbium-Doped Fiber Laser (EDFL) topology is proposed and experimentally assessed. The FBG sensor is part of the EDFL cavity and must have a central wavelength located within the
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An easy-to-implement and cost-effective Fiber Bragg Grating (FBG) sensor interrogation technique based on a ring Erbium-Doped Fiber Laser (EDFL) topology is proposed and experimentally assessed. The FBG sensor is part of the EDFL cavity and must have a central wavelength located within the linear region of the EDF’s amplified spontaneous emission (ASE) spectrum, which occurs at between 1530 and 1540 nm. In this manner, the wavelength-encoded response of the FBG under strain is converted to a linear variation in the laser output power, removing the need for spectrum analysis as well as any limitations from the use of external edge-filtering components. In addition, the laser linewidth is significantly reduced with respect to the FBG bandwidth, thus improving the resolution of the system, whereas its sensitivity can be controlled through pumping power. The performance of the system has been characterized by modeling and experiments for EDFs with different lengths, doping concentrations, and pumping power levels. The influence of mode-hopping in the laser cavity on the resolution and accuracy of the system has also been investigated.
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(This article belongs to the Special Issue Fiber Optic Sensors: Science and Applications)
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Open AccessArticle
Experimental Study of Fast Orthogonal Frequency Division Multiplexing Transmission over a Random Media Channel for Optical Wireless Communications
by
Lu Zhang and Yanan Chen
Photonics 2024, 11(5), 406; https://doi.org/10.3390/photonics11050406 - 26 Apr 2024
Abstract
In this paper, a 4 amplitude shift keying (4-ASK) fast orthogonal frequency division multiplexing (FOFDM) scheme was experimentally investigated over a turbulent air–water channel for optical wireless communications. The experiment results showed that the 4-ASK-FOFDM modulated signals were not sensitive to weak atmospheric
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In this paper, a 4 amplitude shift keying (4-ASK) fast orthogonal frequency division multiplexing (FOFDM) scheme was experimentally investigated over a turbulent air–water channel for optical wireless communications. The experiment results showed that the 4-ASK-FOFDM modulated signals were not sensitive to weak atmospheric turbulence, and the bit-error rate (BER) was lower than the 7% forward error correction (FEC) limit of 3.8 × 10−3. Under the condition of the same spectra efficiency, the 4-ASK-FOFDM scheme just had a tiny performance penalty compared to the 16-QAM-OFDM scheme. Consequently, the 4-ASK-FOFDM scheme is a promising alternative to the conventional 16-QAM-OFDM scheme in optical wireless communications.
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(This article belongs to the Special Issue Underwater Optical Communications Channel Models: Trends and Challenges)
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Open AccessArticle
High Fidelity Full-Color Optical Sectioning Structured Illumination Microscopy by Fourier Domain Based Reconstruction
by
Shipei Dang, Jia Qian, Wang Ma, Rui Ma, Xing Li, Siying Wang, Chen Bai, Dan Dan and Baoli Yao
Photonics 2024, 11(5), 405; https://doi.org/10.3390/photonics11050405 - 26 Apr 2024
Abstract
The natural color of biological specimens plays a crucial role in body protection, signaling, physiological adaptations, etc. Full-color optical sectioning structured illumination microscopy (OS-SIM) color is a promising approach that can reconstruct biological specimens in three-dimension meanwhile maintaining their natural color. Full-color OS-SIM
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The natural color of biological specimens plays a crucial role in body protection, signaling, physiological adaptations, etc. Full-color optical sectioning structured illumination microscopy (OS-SIM) color is a promising approach that can reconstruct biological specimens in three-dimension meanwhile maintaining their natural color. Full-color OS-SIM takes the advantages of rapid imaging speed, compatibility with fluorescence and non-fluorescence samples, compact configuration, and low cost. However, the commonly used HSV-RMS reconstruction algorithm for full-color OS-SIM faces two issues to be improved. One is the RMS (root-mean-square) OS reconstruction algorithm is prone to background noise, and the other is the reconstruction is bound in RGB and HSV color spaces, consuming more reconstructing time. In this paper, we propose a full-color Fourier-OS-SIM method that allows for the OS reconstruction using the high-frequency spectrum of the sample and thus is immune to the low-frequency background noise. The full-color Fourier-OS-SIM directly runs in the RGB color space, providing an easy way to restore the color information. Simulation and experiments with various samples (pollen grains and tiny animals) demonstrate that the full-color Fourier-OS-SIM method is superior to the HSV-RMS method regarding background noise suppression. Moreover, benefiting from the background noise suppression merit, the quantitative morphological height map analysis with the full-color Fourier-OS-SIM method is more accurate. The proposed full-color Fourier-OS-SIM method is expected to find broad applications in biological and industrial fields where the 3D morphology and the color information of objects both need to be recovered.
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(This article belongs to the Special Issue Emerging Topics in Structured Light)
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Open AccessArticle
Adaptive Modulation Scheme for Soft-Switching Hybrid FSO/RF Links Based on Machine Learning
by
Junhu Shao, Yishuo Liu, Xuxiao Du and Tianjiao Xie
Photonics 2024, 11(5), 404; https://doi.org/10.3390/photonics11050404 - 26 Apr 2024
Abstract
A hybrid free-space optical (FSO) and radio frequency (RF) communication system has been considered an effective way to obtain a good trade-off between spectrum utilization efficiency and high-rate transmission. Utilizing artificial intelligence (AI) to deal with the switching and rate adaption problems between
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A hybrid free-space optical (FSO) and radio frequency (RF) communication system has been considered an effective way to obtain a good trade-off between spectrum utilization efficiency and high-rate transmission. Utilizing artificial intelligence (AI) to deal with the switching and rate adaption problems between FSO/RF links, this paper investigated their modulation adapting mechanism based on a machine learning (ML) algorithm. Hybrid link budgets were estimated for different modulation types in various environments, particularly severe weather conditions. For the adaptive modulation (AM) scheme with different order PPM/PSK/QAM, a rate-compatible soft-switching model for hybrid FSO/RF links was established with a random forest algorithm based on ML. With a given target bit error rate, the model categorized a link budget threshold of the hybrid FSO/RF system over a training data set from local weather records. The switching and modulation adaption accuracy were tested over the testing weather data set especially focusing on rain and fog. Simulation results show that the proposed adaptive modulation scheme based on the random forest algorithm can have a good performance for soft-switching hybrid FSO/RF communication links.
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(This article belongs to the Special Issue Next-Generation Free-Space Optical Communication Technologies)
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VLCMnet-Based Modulation Format Recognition for Indoor Visible Light Communication Systems
by
Xin Zheng, Ying He, Chong Zhang and Pu Miao
Photonics 2024, 11(5), 403; https://doi.org/10.3390/photonics11050403 - 26 Apr 2024
Abstract
In indoor visible light communication (VLC), the received signals are subject to severe interference due to factors such as high-brightness backgrounds, long-distance transmissions, and indoor obstructions. This results in an increase in misclassification for modulation format recognition. We propose a novel model called
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In indoor visible light communication (VLC), the received signals are subject to severe interference due to factors such as high-brightness backgrounds, long-distance transmissions, and indoor obstructions. This results in an increase in misclassification for modulation format recognition. We propose a novel model called VLCMnet. Within this model, a temporal convolutional network and a long short-term memory (TCN-LSTM) module are utilized for direct channel equalization, effectively enhancing the quality of the constellation diagrams for modulated signals. A multi-mixed attention network (MMAnet) module integrates single- and mixed-attention mechanisms within a convolutional neural network (CNN) framework specifically for constellation image classification. This allows the model to capture fine-grained spatial structure features and channel features within constellation diagrams, particularly those associated with high-order modulation signals. Experimental results obtained demonstrate that, compared to a CNN model without attention mechanisms, the proposed model increases the recognition accuracy by 19.2%. Under severe channel distortion conditions, our proposed model exhibits robustness and maintains a high level of accuracy.
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(This article belongs to the Topic Machine Learning in Communication Systems and Networks, 2nd Edition)
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