Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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15 pages, 5576 KB  
Review
GaN-Based VCSELs with A Monolithic Curved Mirror: Challenges and Prospects
by Tatsushi Hamaguchi
Photonics 2023, 10(4), 470; https://doi.org/10.3390/photonics10040470 - 20 Apr 2023
Cited by 15 | Viewed by 5116
Abstract
In this paper, we introduce how gallium nitride-based (GaN-based) VCSELs with curved mirrors have evolved. The discussion starts with reviewing the fundamentals of VCSELs and GaN-based materials and then introducing the curved-mirror cavity’s principle and history and the latest research where the structure [...] Read more.
In this paper, we introduce how gallium nitride-based (GaN-based) VCSELs with curved mirrors have evolved. The discussion starts with reviewing the fundamentals of VCSELs and GaN-based materials and then introducing the curved-mirror cavity’s principle and history and the latest research where the structure is applied to GaN-based materials to form VCSELs. We prepared these parts so that readers understand how VCSELs with this cavity work and provide excellent characteristics such as efficiency, life, stabilized mode behavior, etc. Finally, we discussed the challenges and prospects of these devices by touching on their potential applications. Full article
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17 pages, 5386 KB  
Review
Progress in Short Wavelength Energy-Efficient High-Speed Vertical-Cavity Surface-Emitting Lasers for Data Communication
by Si-Cong Tian, Mansoor Ahamed and Dieter Bimberg
Photonics 2023, 10(4), 410; https://doi.org/10.3390/photonics10040410 - 6 Apr 2023
Cited by 12 | Viewed by 3989
Abstract
The current progress of energy-efficient high-speed VCSELs based on GaAs substrates is presented. Novel approaches for the design of VCSELs are presented, potentially leading to larger bandwidth bit rates and lower power consumption. The first approach is based on the optimization of the [...] Read more.
The current progress of energy-efficient high-speed VCSELs based on GaAs substrates is presented. Novel approaches for the design of VCSELs are presented, potentially leading to larger bandwidth bit rates and lower power consumption. The first approach is based on the optimization of the VCSEL photon lifetime. The second one introduces a novel design based on oxidizing the apertures from multiple etched holes of varying geometries. These designs are also essential for improving the energy efficiency of future modules by optimizing the match of the electronic driver and the photonic device. Full article
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12 pages, 5621 KB  
Communication
Interpretation of Localized Surface Plasmonic Resonances of Gold Nanoparticles Covered by Polymeric Coatings
by Alkeos Stamatelatos, Maria Tsarmpopoulou, Dimitrios Geralis, Alexandros G. Chronis, Vagelis Karoutsos, Dimitrios Ntemogiannis, Dionysios M. Maratos, Spyridon Grammatikopoulos, Mihail Sigalas and Panagiotis Poulopoulos
Photonics 2023, 10(4), 408; https://doi.org/10.3390/photonics10040408 - 5 Apr 2023
Cited by 5 | Viewed by 6646
Abstract
Plasmonic materials currently have a plethora of applications. How would a dielectric matrix, such as diblock copolymers, tune plasmonic properties? In this work, self-assembled gold nanoparticles were fabricated in medium vacuum conditions on heated Corning glass substrates (kept at 440 °C) under [...] Read more.
Plasmonic materials currently have a plethora of applications. How would a dielectric matrix, such as diblock copolymers, tune plasmonic properties? In this work, self-assembled gold nanoparticles were fabricated in medium vacuum conditions on heated Corning glass substrates (kept at 440 °C) under the coexistence of argon and air by means of DC magnetron sputtering. These samples were compared structurally and optically to samples deposited at room temperature and post annealed. Subsequently, the better of the two preparations, those deposited on heated glass, were covered with three different polymers, namely: Polystyrene-block-polybutadiene-block-polystyrene (PS-b-PBD-b-PS); Polystyrene-co-methyl methacrylate (PS-co-PMMA); and Polystyrene-block-polyisoprene-block-polystyrene (PS-b-PI-b-PS), by means of spin coating. Localized surface plasmon resonances were recorded and analyzed, respectively, for polymer-covered gold nanoparticles, with the width, intensity, and position of the resonances changing according to multiple factors, such as the nanoparticles size and the refractive index of each polymer. Lastly, for purposes of justification and comparison with the experimental results, rigorous theoretical calculations have been carried out. Full article
(This article belongs to the Special Issue Integrated Plasmonic Devices)
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17 pages, 3410 KB  
Article
Requirements and Solutions for Robust Beam Alignment in Fiber-Coupled Free-Space Optical Systems
by Manuel M. Freitas, Marco A. Fernandes, Paulo P. Monteiro, Fernando P. Guiomar and Gil M. Fernandes
Photonics 2023, 10(4), 394; https://doi.org/10.3390/photonics10040394 - 2 Apr 2023
Cited by 11 | Viewed by 5215
Abstract
The continuous growth of Internet data traffic is pushing the current radio-frequency wireless technologies up to their physical limits. To overcome the upcoming bandwidth bottleneck, Free-Space Optics (FSO) is currently deemed as a key breakthrough toward next-generation ultra-high-capacity wireless links. Despite its numerous [...] Read more.
The continuous growth of Internet data traffic is pushing the current radio-frequency wireless technologies up to their physical limits. To overcome the upcoming bandwidth bottleneck, Free-Space Optics (FSO) is currently deemed as a key breakthrough toward next-generation ultra-high-capacity wireless links. Despite its numerous advantages, FSO also entails several particular challenges regarding the mitigation of the stochastic impairments induced by turbulence and the strict alignment requirements. One of the main issues of FSO communication systems is the mitigation of pointing errors and angle-of-arrival (AoA) fluctuations, which arise from misalignments induced by atmospheric turbulence and vibrations at the transmitting and receiving stations. A common approach to mitigate the impact of pointing errors is the use of an acquisition, tracking and pointing (ATP) system on one or both ends of the FSO link. In this paper, we present a characterization of the pointing errors and the AoA impact on the power budget of the FSO link to quantify the misalignment impairments. Afterwards, we experimentally demonstrate an FSO link with an ATP mechanism at both ends, managed by a control plane that enables the continuous and accurate alignment of the FSO link. To increase the misalignment tolerance, the ATP mechanism comprises two stages: the first one is based on a spatial diversity method provided by a quadrant detector, while the second stage maximizes the optical received power. Lastly, the impact of the beam misalignment on the achievable information rate of a coherent optical wireless system is theoretically addressed and characterized. Full article
(This article belongs to the Special Issue Free Space Optics-Based 6G Non-terrestrial Networks)
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20 pages, 16085 KB  
Article
Comparative Performance Analysis of Femtosecond-Laser-Written Diode-Pumped Pr:LiLuF4 Visible Waveguide Lasers
by Davide Baiocco, Ignacio Lopez-Quintas, Javier R. Vázquez de Aldana, Mauro Tonelli and Alessandro Tredicucci
Photonics 2023, 10(4), 377; https://doi.org/10.3390/photonics10040377 - 29 Mar 2023
Cited by 11 | Viewed by 2729
Abstract
In this work, we present the operation of a femtosecond-laser-written diode-pumped visible waveguide laser based on praseodymium-doped lithium lutetium fluoride. The refractive index modification induced by the femtosecond laser in the crystal exhibits an anisotropic behavior, thus enabling the fabrication of different types [...] Read more.
In this work, we present the operation of a femtosecond-laser-written diode-pumped visible waveguide laser based on praseodymium-doped lithium lutetium fluoride. The refractive index modification induced by the femtosecond laser in the crystal exhibits an anisotropic behavior, thus enabling the fabrication of different types of waveguides from single-track structures to stress-induced waveguides and depressed cladding structures. All the waveguides were characterized by realizing transmission measurements and the waveguide design was optimized to obtain extremely low propagation losses, equal to 0.12 dB/cm. Lasing has been achieved at 604 nm and 721 nm from different waveguides. In addition, stable continuous-wave lasing at 698 nm has been obtained in a depressed cladding waveguide. This wavelength corresponds to the one needed for the transition of the atomic clock based on the neutral strontium atom. In the end, we report the observation of laser emission at 645 nm from a depressed cladding waveguide. Full article
(This article belongs to the Special Issue Novel Applications of Solid-State Laser and Future Prospects)
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11 pages, 10853 KB  
Communication
Fiber-Fed 3D Printing of Germanate Glass Optics
by Zhihan Hong, Tao Luo, Shibin Jiang and Rongguang Liang
Photonics 2023, 10(4), 378; https://doi.org/10.3390/photonics10040378 - 29 Mar 2023
Cited by 12 | Viewed by 3346
Abstract
In recent years, 3D printing glass optics has gained massive attention in industry and academia since glass could be an ideal material to make optical elements, including the lens. However, the limitation of materials and printing methods has prevented 3D printing glass optics [...] Read more.
In recent years, 3D printing glass optics has gained massive attention in industry and academia since glass could be an ideal material to make optical elements, including the lens. However, the limitation of materials and printing methods has prevented 3D printing glass optics progress. Therefore, we have developed a novel printing strategy for germanate glass printing instead of pure silica. Moreover, compared with traditional multi-component quartz glass, germanate glass has unmatched advantages for its mid-infrared (MIR) transparency and outstanding visible light imaging performance. Furthermore, compared with non-oxide glass (fluoride glass and chalcogenide glass), germanate glass has much better mechanical, physical, and chemical properties and a high refractive index. Germanate glass has been widely applied in remote sensing, ranging, environmental detection, and biomedical detection. However, it is difficult to shape, cast, polish, and grind for optical and photonics applications such as imaging optics and laser-collimation optics. These drawbacks have made germanate glass inaccessible to complex optical elements and greatly increased their cost. In this report, we use germanate glass fibers with a diameter of 125 µm based on fiber-fed laser heating technology to fabricate an mm-size optical application. In this paper, we combine the fiber-fed laser heating technology with an optimized temperature control process to manufacture high-precision optical elements. Germanate glass optics can be printed with excellent visible light and IR transparency and a smooth surface with roughness under 4 nm. By optimizing the layer-by-layer 3D printing process and the thermal feedback in the printing process, we avoid cracks and minimize surface deformation. This work shows the possibility of the mm-size glass optical elements 3D printing and widens its application for IR optics. Full article
(This article belongs to the Special Issue Direct Laser Writing for Photonic Applications)
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11 pages, 3190 KB  
Article
Bandwidth Expansion of Zero-Power-Consumption Visible Light Communication System
by Yiwu Xu, Xiongbin Chen and Yufeng Wang
Photonics 2023, 10(4), 376; https://doi.org/10.3390/photonics10040376 - 28 Mar 2023
Cited by 2 | Viewed by 2382
Abstract
The data rate of the zero-power-consumption visible light communication system is limited due to the solar cell bandwidth limit. A new method has been proposed to improve the data rate of communication systems. The predistortion circuit based on the nonlinear compensation principle of [...] Read more.
The data rate of the zero-power-consumption visible light communication system is limited due to the solar cell bandwidth limit. A new method has been proposed to improve the data rate of communication systems. The predistortion circuit based on the nonlinear compensation principle of the communication system is added between the transmitter and the receiver to equalize the amplitude–frequency response of the solar cell. Based on the measurement of the original amplitude–frequency response of the system, the zero-pole of the predistortion circuit is calculated, and an accurate equalization circuit is designed by using separate components to expand the 3 dB bandwidth of the system. The test results show that the 3 dB bandwidth of the visible light self-powered communication system is increased from 85 kHz to 750 kHz, and the system bandwidth is expanded by nearly 10 times. Full article
(This article belongs to the Special Issue Visible Light Communications)
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15 pages, 4633 KB  
Article
Analysis of the Emission Features in CdSe/ZnS Quantum Dot-Doped Polymer Fibers
by Xuefeng Peng, Zhijian Wu, Chen Ye, Yang Ding and Wei Liu
Photonics 2023, 10(3), 327; https://doi.org/10.3390/photonics10030327 - 18 Mar 2023
Cited by 4 | Viewed by 3104
Abstract
The emission features of Cdse/ZnS quantum dots doped step-index polymer optical fibers are computationally analyzed in this paper. Spontaneous emission and amplified spontaneous emission were calculated by a theoretical model based on the rate equations in terms of time, fiber length, and wavelength. [...] Read more.
The emission features of Cdse/ZnS quantum dots doped step-index polymer optical fibers are computationally analyzed in this paper. Spontaneous emission and amplified spontaneous emission were calculated by a theoretical model based on the rate equations in terms of time, fiber length, and wavelength. All the calculated parameters are derived from experiments. Through the comparative analysis of the calculated and experimental results of spontaneous emission, we found that the pump power and overlap between the emission and absorption cross-sections may be the two main reasons for the red shift of the output spectra. When the pump power exceeds the threshold of amplified spontaneous emission, the width of the output spectra will rapidly decrease, the output wavelength will fall back toward the maximum emission cross-section, and the final output wavelength will still be affected by the doping concentration and pump power, while amplified spontaneous emission will not be generated when the total number of doped quantum dots is less than 1.27 × 1012. Full article
(This article belongs to the Special Issue Advances in Photonic Materials and Technologies)
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14 pages, 4464 KB  
Article
Adaptive Weighted K-Nearest Neighbor Trilateration Algorithm for Visible Light Positioning
by Kaiyao Wang, Yi He, Xinpeng Huang and Zhiyong Hong
Photonics 2023, 10(3), 319; https://doi.org/10.3390/photonics10030319 - 16 Mar 2023
Cited by 6 | Viewed by 3030
Abstract
An adaptive weighted K-nearest neighbor (AWKNN) trilateration positioning algorithm fused with the channel state information (CSI) is proposed to optimize the accuracy of the visible light positioning. The core concept behind this algorithm is to combine the WKNN algorithm with ranging based on [...] Read more.
An adaptive weighted K-nearest neighbor (AWKNN) trilateration positioning algorithm fused with the channel state information (CSI) is proposed to optimize the accuracy of the visible light positioning. The core concept behind this algorithm is to combine the WKNN algorithm with ranging based on the CSI. The direct path distance estimated by the CSI is utilized to construct a position set consisting of multiple positions and a corresponding distance database containing multiple distance vectors. The error parameters of the weighted combinations of different distance vectors are calculated iteratively to evaluate the impact of different K-values and weights on the positioning accuracy. The proposed algorithm can achieve high-precision trilateration positioning by adaptively selecting the K-value and weight. A typical 4 m × 4 m × 3 m indoor multipath scene with four LEDs is established to simulate the positioning performance. The simulation results reveal that the mean error of the CSI-based AWKNN algorithm achieves 1.84 cm, with a root mean square error (RMSE) of 2.13 cm. Compared with the CSI-based least squares (LS) method, the CSI-based nonlinear LS method, and the CSI-based WKNN method, the average error of this method is decreased by 29%, 16%, and 17%, whereas the RMSE is reduced by 35%, 14%, and 19%. Full article
(This article belongs to the Special Issue Optical Wireless Communications and Applications)
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6 pages, 5566 KB  
Communication
Ultrabroadband OPA in YCOB with a sub-ps Pump Source
by Hugo Pires, Joana Alves, Victor Hariton, Mario Galletti, Celso João and Gonçalo Figueira
Photonics 2023, 10(3), 253; https://doi.org/10.3390/photonics10030253 - 28 Feb 2023
Cited by 3 | Viewed by 3744
Abstract
We demonstrate the broadband optical parametric amplification of near-infrared laser pulses using a single yttrium calcium oxyborate (YCOB) crystal pumped in a noncollinear geometry by a sub-picosecond, milijoule-level source. The crystal uses an optimized orientation for phase matching outside of the principal planes, [...] Read more.
We demonstrate the broadband optical parametric amplification of near-infrared laser pulses using a single yttrium calcium oxyborate (YCOB) crystal pumped in a noncollinear geometry by a sub-picosecond, milijoule-level source. The crystal uses an optimized orientation for phase matching outside of the principal planes, enabling ultrabroadband amplification (gain of ∼800) in the range of 750–950 nm and supporting down to 7 fs pulses. Full article
(This article belongs to the Special Issue Ultrafast Lasers: Science and Applications)
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16 pages, 1726 KB  
Article
Towards Microbial Food Safety of Sprouts: Photodynamic Decontamination of Seeds
by Andreas Fellner, Christoph Hamminger, Michael Fefer, Jun Liu and Kristjan Plaetzer
Photonics 2023, 10(3), 239; https://doi.org/10.3390/photonics10030239 - 22 Feb 2023
Cited by 1 | Viewed by 3536
Abstract
The climate crisis is one of the biggest challenges for humanity in the 21st century. Production and consumption of meat contributes to global warming by causing emissions of climate-relevant gases. Freshly grown sprouts are part of an alternative, as they are less polluting [...] Read more.
The climate crisis is one of the biggest challenges for humanity in the 21st century. Production and consumption of meat contributes to global warming by causing emissions of climate-relevant gases. Freshly grown sprouts are part of an alternative, as they are less polluting but still a nutritious food. However, warm humid sprouting conditions may cause pathogenic microorganisms to thrive. Decontamination methods for raw sprouts are therefore relevant. Photodynamic Inactivation (PDI) is a novel approach that uses photoactivatable molecules (photosensitisers, PS) and visible or near-infrared light to produce reactive oxygen species (ROS). These ROS kill microorganisms by oxidative processes. Here, we test the application of PDI based on sodium-magnesium-chlorophyllin (Chl, approved as food additive E140) for photo-decontamination of mung bean, radish, and buckwheat seeds. Seeds were contaminated with Listeria innocua, serving as a model system for Listeria monocytogenes, subjected to PDI using an LED array with 395 nm and tested for remaining bacterial contamination by CFU counting. PDI based on 100 µM Chl reduces the bacterial load of mung bean and radish seeds by 99.9% (radiant exposure 56.4 J/cm2 and 28.2 J/cm2, respectively), and of buckwheat seeds by <90% reduction after illumination with 28.2 J/cm2. Neither weight nor the germination rates of seeds are affected by PDI. Interestingly, the effect of PDI on seeds is partially maintained on stored sprouts after germination: The bacterial load on mung bean sprouts is reduced by more than 99.9% after phototreatment of seeds with 100 µM Chl and illumination at 56.4 J/cm2. In conclusion, we suggest PDI based on Chl as an effective and biocompatible method for the decontamination of seeds and sprouts for human consumption from Listeria. Full article
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19 pages, 1619 KB  
Article
Revisiting Experimental Signatures of the Ponderomotive Force
by Bjorn Manuel Hegelich, Lance Labun and Ou Z. Labun
Photonics 2023, 10(2), 226; https://doi.org/10.3390/photonics10020226 - 20 Feb 2023
Cited by 5 | Viewed by 4931
Abstract
The classical theory of single-electron dynamics in focused laser pulses is the foundation of both the relativistic ponderomotive force (RPF), which underlies models of laser-collective-plasma dynamics, and the discovery of novel strong-field radiation dynamics. Despite this bedrock importance, consensus eludes the community as [...] Read more.
The classical theory of single-electron dynamics in focused laser pulses is the foundation of both the relativistic ponderomotive force (RPF), which underlies models of laser-collective-plasma dynamics, and the discovery of novel strong-field radiation dynamics. Despite this bedrock importance, consensus eludes the community as to whether acceleration of single electrons in vacuum has been observed in experimental conditions. We analyze an early experiment on the RPF with respect to several features that were neglected in modeling and that can restore consistency between theory predictions and experimental data. The right or wrong pulse profile function, laser parameters, or initial electron distribution can each make or break the agreement between predictions and data. The laser phase at which the electron’s interaction with the pulse begins has a large effect, explaining why much larger energies are achieved by electrons liberated in the focal region by photoionization from high-Z atoms and by electrons ejected from a plasma mirror. Finally, we compute the difference in a typical electron spectrum arising from fluctuating focal spot size in state-of-the-art ultra-relativistic laser facilities. Our results emphasize the importance of thoroughly characterizing laser parameters in order to achieve quantitatively accurate predictions and the precision required for discovery science. Full article
(This article belongs to the Special Issue Progress in Laser Accelerator and Future Prospects)
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16 pages, 2857 KB  
Review
Development and Application of THz Gyrotrons for Advanced Spectroscopic Methods
by Svilen Sabchevski and Mikhail Glyavin
Photonics 2023, 10(2), 189; https://doi.org/10.3390/photonics10020189 - 10 Feb 2023
Cited by 17 | Viewed by 3506
Abstract
Nowadays, gyrotrons are used in numerous and diverse fields of research and technology. Their most prominent application is to electron cyclotron resonance plasma heating and current drive-in reactors for controlled thermonuclear fusion. Another matured field is the thermal microwave treatment of materials in [...] Read more.
Nowadays, gyrotrons are used in numerous and diverse fields of research and technology. Their most prominent application is to electron cyclotron resonance plasma heating and current drive-in reactors for controlled thermonuclear fusion. Another matured field is the thermal microwave treatment of materials in industrial-grade gyrotron-based technological systems. The unique spectral properties of gyrotron radiation, frequency tunability, and the possibility for precise control and modulation of both the output power and frequency have made the gyrotrons attractive and appropriate radiation sources for various novel advanced spectroscopic techniques. Among them are ESR (electron spin resonance), NMR-DNP (nuclear magnetic resonance with a signal enhancement through dynamic nuclear polarization), XDMR (X-ray detected magnetic resonance), acoustic molecular spectroscopy, as well as high-precision spectroscopy for measuring the SFS (super-fine splitting of the energy levels of positronium). In this review paper, we present both the current status and the most remarkable recent achievements of these methods implemented in gyrotron-based spectroscopy systems and discuss the main trends in the development of their dedicated radiation sources operating in the THz frequency range. Full article
(This article belongs to the Special Issue Terahertz Spectroscopy and Imaging)
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19 pages, 13958 KB  
Article
Observation of Giant Angular Goos-Hanchen Shifts Enhanced by Surface Plasmon Resonance in Subwavelength Grating
by Nikolai I. Petrov, Yuri M. Sokolov, Vladimir V. Stoiakin, Viktor A. Danilov, Vladimir V. Popov and Boris A. Usievich
Photonics 2023, 10(2), 180; https://doi.org/10.3390/photonics10020180 - 8 Feb 2023
Cited by 9 | Viewed by 2580
Abstract
The effect of the Goos-Hanchen (GH) angular shift for a visible light beam under the excitation of surface plasmon resonance (SPR) in a metal subwavelength grating has been investigated. Extremely large angular GH shifts have been demonstrated for a subwavelength grating with an [...] Read more.
The effect of the Goos-Hanchen (GH) angular shift for a visible light beam under the excitation of surface plasmon resonance (SPR) in a metal subwavelength grating has been investigated. Extremely large angular GH shifts have been demonstrated for a subwavelength grating with an optimal depth. The high sensitivity of the beam shape transformation and the GH shift to a change in the angle of incidence near the SPR has been shown by rigorous electromagnetic simulation and demonstrated experimentally. The focusing of the reflected beam near the subwavelength grating surface has been demonstrated. Full article
(This article belongs to the Special Issue Integrated Plasmonic Devices)
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14 pages, 6531 KB  
Article
Distortion Detection of Lithographic Projection Lenses Based on Wavefront Measurement
by Tian Li, Jian Wang, Shaolin Zhou, Haiyang Quan, Lei Chen, Junbo Liu, Jing Du, Xianchang Zhu and Song Hu
Photonics 2023, 10(2), 168; https://doi.org/10.3390/photonics10020168 - 4 Feb 2023
Viewed by 5286
Abstract
As with the decreasing feature size prompted by Moore’s law and the continuous technological advancements in the semiconductor industry, the distortion of the projection lens is an important factor that affects the overlay. In this paper, we propose a wavefront-measurement-based method to detect [...] Read more.
As with the decreasing feature size prompted by Moore’s law and the continuous technological advancements in the semiconductor industry, the distortion of the projection lens is an important factor that affects the overlay. In this paper, we propose a wavefront-measurement-based method to detect the projection lens distortion in the lithographic system. By normalizing the coordinates of the Shack–Hartmann system with the image displacements represented in the Z2 and Z3 terms of Zernike coefficients, the offsets between the actual image points and the ideal image points can be determined. By offset collection at an array of 7 × 7 field points to establish an overdetermined system of equations, the proposed method can simultaneously detect the distortions of translation, magnification, rotation, decentering distortion, thin prism distortion, and third-order radial distortion. This distortion measurement method is highly flexible for distortion measurement with portable and compactly integrated sensors, enabling the real-time and cost-efficient measurement of wave aberration and distortion. For proof-of-concept experiments, a projection lens with a numerical aperture (NA) of 0.58 for i-line (365 nm) is used for experimental testing. The results reveal that the repeatability accuracy of distortion detection is 51 nm and the 72 h long-term reproducibility is 143 nm. Full article
(This article belongs to the Special Issue Optical Measurement Systems)
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17 pages, 4797 KB  
Review
The Progress and Trend of Heterogeneous Integration Silicon/III-V Semiconductor Optical Amplifiers
by Wenqi Shi, Canwen Zou, Yulian Cao and Jianguo Liu
Photonics 2023, 10(2), 161; https://doi.org/10.3390/photonics10020161 - 3 Feb 2023
Cited by 17 | Viewed by 10662
Abstract
Silicon photonics is a revolutionary technology in the integrated photonics field which has experienced rapid development over the past several decades. High-quality III-V semiconductor components on Si platforms have shown their great potential to realize on-chip light-emitting sources for Si photonics with low-cost [...] Read more.
Silicon photonics is a revolutionary technology in the integrated photonics field which has experienced rapid development over the past several decades. High-quality III-V semiconductor components on Si platforms have shown their great potential to realize on-chip light-emitting sources for Si photonics with low-cost and high-density integration. In this review, we will focus on semiconductor optical amplifiers (SOAs), which have received considerable interest in diverse photonic applications. SOAs have demonstrated high performance in various on-chip optical applications through different integration technologies on Si substrates. Moreover, SOAs are also considered as promising candidates for future light sources in the wavelength tunable laser, which is one of the key suitable components in coherent optical devices. Understanding the development and trends of heterogeneous integration Silicon/III-V SOA will help researchers to come up with effective strategies to combat the emerging challenges in this family of devices, progressing towards next-generation applications. Full article
(This article belongs to the Special Issue Integrated Microwave Photonics)
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12 pages, 2010 KB  
Article
Real-Time Chlorophyll-a Pigment Monitoring of Chlamydomonas reinhardtii in a Controlled Environment Using Pulsed LED Fluorescence LiDAR System
by Jumar G. Cadondon, Edgar A. Vallar, Tatsuo Shiina and Maria Cecilia D. Galvez
Photonics 2023, 10(2), 144; https://doi.org/10.3390/photonics10020144 - 30 Jan 2023
Cited by 5 | Viewed by 2415
Abstract
The real-time chlorophyll-a pigment monitoring of C. reinhardtii is studied using our developed LED fluorescence light detection and ranging (LiDAR) system. It features a portable set-up that uses a pulsed LED module with an excitation wavelength of 385 nm. We were able to [...] Read more.
The real-time chlorophyll-a pigment monitoring of C. reinhardtii is studied using our developed LED fluorescence light detection and ranging (LiDAR) system. It features a portable set-up that uses a pulsed LED module with an excitation wavelength of 385 nm. We were able to monitor the different growth phases of C. reinhardtii with specific cultivation parameters. The developed fluorescence LiDAR system showed the linear correlation of its chlorophyll-a signal with the optical density and EEM fluorescence measurements at 680 nm emission wavelength. Water quality and weather parameters were also measured, which explains the variation in the growth dynamics of C. reinhardtii during the sampling period. The results from the monitoring demonstrated a different technique that can be used in estimating algal biomass in the environment. Full article
(This article belongs to the Special Issue Micro Fluorescence Detectors/Sensors and Their Applications)
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8 pages, 12673 KB  
Communication
Experimental Demonstration of Attoseconds-at-Harmonics at the SASE3 Undulator of the European XFEL
by Andrei Trebushinin, Gianluca Geloni, Svitozar Serkez, Giuseppe Mercurio, Natalia Gerasimova, Theophilos Maltezopoulos, Marc Guetg and Evgeny Schneidmiller
Photonics 2023, 10(2), 131; https://doi.org/10.3390/photonics10020131 - 27 Jan 2023
Cited by 7 | Viewed by 3970
Abstract
We report on observations of single spike spectra (3–13% of events) upon employing a previously proposed method for single spike generation via harmonic conversion. The method was tested at the soft X-ray SASE3 undulator of the European XFEL. The first part of the [...] Read more.
We report on observations of single spike spectra (3–13% of events) upon employing a previously proposed method for single spike generation via harmonic conversion. The method was tested at the soft X-ray SASE3 undulator of the European XFEL. The first part of the undulator allows one to amplify bunching at the fundamental as well as the higher harmonics. The downstream undulator is tuned to a harmonic, the fourth in our case, to amplify pulses with a shorter duration. We estimate the generated pulse duration within such a subset of short pulses at a level of 650 as. Considering the demonstrated probability of single spike events, this method is attractive for high repetition-rate free electron lasers. Full article
(This article belongs to the Special Issue Ultrafast Lasers: Science and Applications)
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8 pages, 1230 KB  
Communication
Fiber Optic All-Polarization Weak Magnetic Field Sensor Based on Sagnac Interferometer
by Cui Liang, Zhihang Zhang, Dengwei Zhang, Tengchao Huang and Shuangliang Che
Photonics 2023, 10(2), 101; https://doi.org/10.3390/photonics10020101 - 17 Jan 2023
Cited by 5 | Viewed by 2835
Abstract
A novel fiber-optic magnetic field sensor, based on a Sagnac structure, is proposed with the approach of polarization interference detection. The sensor takes advantage of common path interference, combining with a high magnetic field sensitivity sensing unit, composed of magneto-optical crystal, and magnetic [...] Read more.
A novel fiber-optic magnetic field sensor, based on a Sagnac structure, is proposed with the approach of polarization interference detection. The sensor takes advantage of common path interference, combining with a high magnetic field sensitivity sensing unit, composed of magneto-optical crystal, and magnetic field concentrators, to achieve high resolution, high stability, and large dynamic measurement of DC magnetic field signals. In this paper, the theoretical model is established and the related theory is derived in detail. The key technologies in the system are thoroughly investigated and verified. Experimental research on the proposed system is demonstrated and the results show that a DC magnetic field resolution of 5.6 nT and a dynamic range of larger than 70 dB is achieved. Furthermore, the linearity of the system is greater than 99.8% and the instability is less than 0.5%. Full article
(This article belongs to the Special Issue Optical Measurement Systems and Instruments)
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17 pages, 6093 KB  
Article
Enhanced Performance of a Cascaded Receiver Consisting of a DNN-Based Waveform-to-Symbol Converter and Modified NN-Based DD-LMS in CAP Underwater VLC System
by Xianhao Lin, Fangchen Hu and Nan Chi
Photonics 2023, 10(1), 79; https://doi.org/10.3390/photonics10010079 - 10 Jan 2023
Cited by 7 | Viewed by 4439
Abstract
Underwater visible light communication (UVLC) based on LEDs has become a competitive candidate, which is able to provide high data rates, low latency and low cost for next-generation wireless communication technologies. However, it is still challenging to achieve high-speed communication because of bottleneck [...] Read more.
Underwater visible light communication (UVLC) based on LEDs has become a competitive candidate, which is able to provide high data rates, low latency and low cost for next-generation wireless communication technologies. However, it is still challenging to achieve high-speed communication because of bottleneck problems such as bandwidth limitation and linear and nonlinear distortions. Traditional Deep-learning Neural Network (DNN)-based waveform-to-symbol converter is verified to be an effective method to alleviate them, but impractical due to high complexity. To achieve a better tradeoff between communication performance and computation complexity, a cascaded receiver consisting of a DNN-based waveform-to-symbol converter and modified Neural Network (NN)-based decision-directed least mean square (DD-LMS) is then innovatively proposed. With fewer taps and nodes than the traditional converter, the front-stage converter could mitigate the majority of Inter-Symbol Interference (ISI) and signal nonlinear distortions. Then modified NN-based DD-LMS is cascaded to improve communication performance by reducing phase offset, making received constellation points more concentrated and closer to standard constellation points. Compared with the traditional converter, the cascaded receiver could achieve 89.6% of signal Vpp dynamic range with 12.4% of complexity in the 64APSK UVLC system. Moreover, the ratio of signal Vpp dynamic range and total trainable parameters is 1.24 × 10−1 mV, while that of the traditional converter is 1.95 × 10−2 mV. The cascaded receiver used in 64APSK UVLC systems is experimentally verified to achieve enhanced performance, thus as a promising scheme for future high-speed underwater VLC. Full article
(This article belongs to the Special Issue Visible Light Communications)
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7 pages, 1924 KB  
Communication
Intra-Cavity Raman Laser Operating at 1193 nm Based on Graded-Index Fiber
by Chunhua Hu and Ping Sun
Photonics 2023, 10(1), 33; https://doi.org/10.3390/photonics10010033 - 28 Dec 2022
Cited by 1 | Viewed by 2139
Abstract
Nonlinear Raman frequency conversion is an important technical scheme to obtain special optical band lasers based on conventional ion-doped lasers. In our work, we designed an intra-cavity Raman fiber laser based on graded index fiber (GRIF) as the Raman gain medium. Based on [...] Read more.
Nonlinear Raman frequency conversion is an important technical scheme to obtain special optical band lasers based on conventional ion-doped lasers. In our work, we designed an intra-cavity Raman fiber laser based on graded index fiber (GRIF) as the Raman gain medium. Based on the fundamental-frequency 1080-nanometer laser, efficient first-order and second-order Stokes Raman lasers were obtained, respectively. When the power of the fundamental-frequency 1080-nanometer laser was 33.4 W, the output power of the second-order 1193-nanometer laser was 11.39 W. The corresponding conversion efficiency was 34.1%. To our knowledge, this is the first report of a second-order Raman output based on a GRIF and intra-cavity structure. In the experiment, the spectrum-purification process with the increase in power was also observed. Our experimental results prove that the intracavity Raman-laser system based on graded index fiber with a high optical conversion efficiency has important application potential for obtaining new special-application bands. Full article
(This article belongs to the Special Issue High Power Fiber Laser and Amplifiers)
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18 pages, 4341 KB  
Article
Identification of Browning in Human Adipocytes by Partial Least Squares Regression (PLSR), Infrared Spectral Biomarkers, and Partial Least Squares Discriminant Analysis (PLS-DA) Using FTIR Spectroscopy
by Dong-Hyun Shon, Se-Jun Park, Suk-Jun Yoon, Yang-Hwan Ryu and Yong Ko
Photonics 2023, 10(1), 2; https://doi.org/10.3390/photonics10010002 - 21 Dec 2022
Cited by 3 | Viewed by 2701
Abstract
We aimed to identify the browning of white adipocytes using partial least squares regression (PLSR), infrared spectral biomarkers, and partial least squares discriminant analysis (PLS-DA) with FTIR spectroscopy instead of molecular biology. PLSR helps distinguish human beige adipocytes treated with norepinephrine and rosiglitazone. [...] Read more.
We aimed to identify the browning of white adipocytes using partial least squares regression (PLSR), infrared spectral biomarkers, and partial least squares discriminant analysis (PLS-DA) with FTIR spectroscopy instead of molecular biology. PLSR helps distinguish human beige adipocytes treated with norepinephrine and rosiglitazone. When PLSR was based on the selected regions of 3997–3656 and 1618–938 cm−1, PLSR achieved an R2 of cross-validation of 88.95, a root mean square error of cross validation (RMSECV) of 2.13, and a ratio performance deviation (RPD) of 3.01. Infrared spectral biomarkers [1635 cm−1 (β-sheet amide I), 879–882, 860–3 cm−1 (A-form helix), and 629–38 cm−1 (OH out-of-plane bending)] were identified in human beige adipocytes based on spectral differences between human beige adipocytes and human white adipocytes, principal component analysis-linear discriminant analysis (PCA-LDA) cluster vector, U-test, and Fisher’s score per wavenumber. PLS-DA yielded a useful classification of adipocytes and expression distribution of adipogenesis genes in adipocytes. PLSR, infrared spectral biomarkers, and PLS-DA using FTIR spectroscopy are proposed as effective tools for identifying specific biological activities in a limited environment through features that do not require labeling and are relatively inexpensive in terms of time and labor. Full article
(This article belongs to the Special Issue Biomedical Spectroscopy: Techniques and Applications)
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26 pages, 4599 KB  
Review
Line Field Optical Coherence Tomography
by Samuel Lawman, Zijian Zhang, Yao-Chun Shen and Yalin Zheng
Photonics 2022, 9(12), 946; https://doi.org/10.3390/photonics9120946 - 7 Dec 2022
Cited by 8 | Viewed by 4929
Abstract
The line field (LF) design choice for the lateral image formation mechanism (lateral format) has historically been a fraction of the whole optical coherence tomography (OCT) field. However, as the OCT technology develops, the parallelised acquisition of LF-OCT formats (LF-time domain (TD)-OCT, LF-spectral [...] Read more.
The line field (LF) design choice for the lateral image formation mechanism (lateral format) has historically been a fraction of the whole optical coherence tomography (OCT) field. However, as the OCT technology develops, the parallelised acquisition of LF-OCT formats (LF-time domain (TD)-OCT, LF-spectral domain (SD)-OCT, LF-swept source (SS)-OCT) offers benefits and capabilities, which may mean it is now becoming more mainstream. Prior reviews on OCT have focused on scanning point (SP) and, to a lesser extent, full field (FF), lateral formats, with, to our knowledge, no prior review specifically on the LF lateral format. Here, we address this gap in the literature by reviewing the history of each LF-OCT format, identifying the applications it has had and providing generic system design overviews. We then provide an analysis and discussion of the benefits and drawbacks of the format. Full article
(This article belongs to the Special Issue Recent Advances in Optical Coherence Tomography)
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16 pages, 2735 KB  
Article
DeepGOMIMO: Deep Learning-Aided Generalized Optical MIMO with CSI-Free Detection
by Xin Zhong, Chen Chen, Shu Fu, Zhihong Zeng and Min Liu
Photonics 2022, 9(12), 940; https://doi.org/10.3390/photonics9120940 - 5 Dec 2022
Cited by 4 | Viewed by 2109
Abstract
Generalized optical multiple-input multiple-output (GOMIMO) techniques have been recently shown to be promising for high-speed optical wireless communication (OWC) systems. In this paper, we propose a novel deep learning-aided GOMIMO (DeepGOMIMO) framework for GOMIMO systems, wherein channel state information (CSI)-free detection can be [...] Read more.
Generalized optical multiple-input multiple-output (GOMIMO) techniques have been recently shown to be promising for high-speed optical wireless communication (OWC) systems. In this paper, we propose a novel deep learning-aided GOMIMO (DeepGOMIMO) framework for GOMIMO systems, wherein channel state information (CSI)-free detection can be enabled by employing a specially designed deep neural network (DNN)-based MIMO detector. The CSI-free DNN detector mainly consists of two modules: one is the preprocessing module, which is designed to address both the path loss and channel crosstalk issues caused by MIMO transmission, and the other is the feedforward DNN module, which is used for joint detection of spatial and constellation information by learning the statistics of both the input signal and the additive noise. Our simulation results clearly verify that, in a typical indoor 4 × 4 MIMO-OWC system using both generalized optical spatial modulation (GOSM) and generalized optical spatial multiplexing (GOSMP) with unipolar nonzero 4-level pulse-amplitude modulation (4-PAM) modulation, the proposed CSI-free DNN detector achieves near the same bit error rate (BER) performance as the optimal joint maximum-likelihood (ML) detector, but with much-reduced computational complexity. Moreover, because the CSI-free DNN detector does not require instantaneous channel estimation to obtain accurate CSI, it enjoys the unique advantages of improved achievable data rate and reduced communication time delay in comparison to the CSI-based zero-forcing DNN (ZF-DNN) detector. Full article
(This article belongs to the Special Issue Advances in Visible Light Communication)
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18 pages, 4110 KB  
Article
Modelling and Design of Holographic Optical Elements for Beam-Coupling Applications for a Range of Incident Beam Angles
by Dipanjan Chakraborty, Rosen Georgiev, Sinead Aspell, Vincent Toal, Izabela Naydenova, Dervil Cody and Suzanne Martin
Photonics 2022, 9(12), 936; https://doi.org/10.3390/photonics9120936 - 3 Dec 2022
Cited by 13 | Viewed by 4127
Abstract
Theoretical modelling has been used to calculate the holographic recording beam angles required in air (at any recording wavelength) to produce a Volume Holographic Optical Element (VHOE) for any defined input and output beam angles. The approach is used to facilitate the design [...] Read more.
Theoretical modelling has been used to calculate the holographic recording beam angles required in air (at any recording wavelength) to produce a Volume Holographic Optical Element (VHOE) for any defined input and output beam angles. The approach is used to facilitate the design and fabrication of diffractive coupling elements through a holographic process that avoids the use of coupling prisms during recording and will help in the design of recording arrangements that better suit the mass production of low-cost elements, especially those designed for non-normal incidence. In this study, the recording angles needed for a range of recording wavelengths were explored for VHOE couplers designed for input angles (in air) ranging from 0° to −55°. Then, in order to validate the model, holographic recording in Bayfol HX 200 photopolymer at 532 nm was used to fabricate photopolymer VHOE couplers for 633 nm light (−45° input angle in air). Bragg curves obtained experimentally for different probe wavelengths (403 nm, 532 nm and 633 nm) confirm the recording of the desired grating structures to a precision of ±1°, and coupling is demonstrated at 633 nm with a diffraction efficiency of up to 72%. Furthermore, the model is used to identify the origins of some weaker spurious gratings observed alongside the expected ones. Full article
(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)
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7 pages, 9380 KB  
Communication
A Deep Reinforcement Learning Algorithm for Smart Control of Hysteresis Phenomena in a Mode-Locked Fiber Laser
by Alexey Kokhanovskiy, Alexey Shevelev, Kirill Serebrennikov, Evgeny Kuprikov and Sergey Turitsyn
Photonics 2022, 9(12), 921; https://doi.org/10.3390/photonics9120921 - 30 Nov 2022
Cited by 7 | Viewed by 2632
Abstract
We experimentally demonstrate the application of a double deep Q-learning network algorithm (DDQN) for design of a self-starting fiber mode-locked laser. In contrast to the static optimization of a system design, the DDQN reinforcement algorithm is capable of learning the strategy of dynamic [...] Read more.
We experimentally demonstrate the application of a double deep Q-learning network algorithm (DDQN) for design of a self-starting fiber mode-locked laser. In contrast to the static optimization of a system design, the DDQN reinforcement algorithm is capable of learning the strategy of dynamic adjustment of the cavity parameters. Here, we apply the DDQN algorithm for stable soliton generation in a fiber laser cavity exploiting a nonlinear polarization evolution mechanism. The algorithm learns the hysteresis phenomena that manifest themselves as different pumping-power thresholds for mode-locked regimes for diverse trajectories of adjusting optical pumping. Full article
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18 pages, 5011 KB  
Article
Nonlinear Impairment Compensation Using Transfer Learning-Assisted Convolutional Bidirectional Long Short-Term Memory Neural Network for Coherent Optical Communication Systems
by Xueyuan Luo, Chenglin Bai, Xinyu Chi, Hengying Xu, Yaxuan Fan, Lishan Yang, Peng Qin, Zhiguo Wang and Xiuhua Lv
Photonics 2022, 9(12), 919; https://doi.org/10.3390/photonics9120919 - 29 Nov 2022
Cited by 8 | Viewed by 2646
Abstract
By combining the nonlinear impairment features derived from the first-order perturbation theory, we propose a nonlinear impairment compensation (NLC) scheme based on the transfer learning-assisted convolutional bidirectional long short-term Memory (CNN-BiLSTM) neural network structure. When considering the correlation of [...] Read more.
By combining the nonlinear impairment features derived from the first-order perturbation theory, we propose a nonlinear impairment compensation (NLC) scheme based on the transfer learning-assisted convolutional bidirectional long short-term Memory (CNN-BiLSTM) neural network structure. When considering the correlation of nonlinear impairment between preceding and succeeding consecutive adjacent symbols on the current moment symbol and integrating the multidimensional feature extraction and time memory characteristics of CNN-BiLSTM, the nonlinear impairment information contained in the input feature can be fully utilized to accurately predict the nonlinear impairment showing significant compensation effect. Meanwhile, transfer learning (TL) is introduced to greatly reduce the complexity of the scheme on the basis of high compensation performance. To verify the effectiveness of the proposed scheme, we construct single-channel (SC) and 5-channel 28 GBaud polarization division multiplexing 16 quadrature amplitude modulation (PDM-16QAM)/85 GBaud PDM-64QAM simulation systems, and SC and 3-channel 28 GBaud PDM-16QAM experimental systems. The experimental results show that when compared with simple recurrent neural network (SRNN) NLC and DBP 20 steps per span (DBP20StPs), the Q-factor gain of our scheme is about 1 dB and 1.7 dB in the SC system, and about 1.1 dB and 1.5 dB in the 3-channel system at the optimal launch power, respectively. It is interesting to highlight that, by applying TL to the simulation and experimental systems, our scheme based on only 5% of the training samples can achieve compensation performance comparable to or higher quality than retraining at various launch powers. Full article
(This article belongs to the Special Issue Optical Fiber Communication Systems)
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17 pages, 5635 KB  
Article
An Experimental and Numerical Study of the Impact of Ambient Light of SiPMs in VLC Receivers
by William Matthews and Steve Collins
Photonics 2022, 9(12), 888; https://doi.org/10.3390/photonics9120888 - 22 Nov 2022
Cited by 5 | Viewed by 2635
Abstract
Silicon photomultiplier’s relatively large area and ability to detect single photons makes them attractive as receivers for visible light communications. However, their non-linear response has a negative impact on the receiver performance, including making them particularly sensitive to ambient light. Experiments and Monte [...] Read more.
Silicon photomultiplier’s relatively large area and ability to detect single photons makes them attractive as receivers for visible light communications. However, their non-linear response has a negative impact on the receiver performance, including making them particularly sensitive to ambient light. Experiments and Monte Carlo simulations have been used to study this non-linearity. The resulting detailed understanding of the origins of the non-linear response leads to concerns over the accuracy of some previous simulations of SiPMs. In addition, it leads to simple methods to determine the maximum rate at which an SiPM can count photons and of determining the impact of a SiPMs non-linearity on its performance of a receiver. Finally, a method of determining which filters should be used to protect an SiPM from ambient light is proposed. Full article
(This article belongs to the Special Issue Advances in Visible Light Communication)
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8 pages, 3788 KB  
Communication
Experimental Detection of Initial System–Environment Entanglement in Open Systems
by Gaoyan Zhu, Dengke Qu, Lei Xiao and Peng Xue
Photonics 2022, 9(11), 883; https://doi.org/10.3390/photonics9110883 - 21 Nov 2022
Cited by 1 | Viewed by 2528
Abstract
We experimentally investigate how initial entanglement between the system and environment can be detected in an open system by using some prior knowledge of the joint evolutions. The protocol we employed requires classical optimization on the results after performing measurements on the system [...] Read more.
We experimentally investigate how initial entanglement between the system and environment can be detected in an open system by using some prior knowledge of the joint evolutions. The protocol we employed requires classical optimization on the results after performing measurements on the system state. Such an approach does not require a full 2-qubit QST, and works in scenarios where one has access to the system only. We demonstrate the protocol on both pure entangled states and mixed entangled states. The obtained results show the experimental accessibility and validity of the protocol. Compared with the previous methods, which also assume access only to the system, this protocol is less demanding in terms of measurement and state preparation. The experimental results also show that, using the knowledge of the interaction, we can fine-tune the protocol, thus showing the potential of the protocol for developing experimentally feasible and practical entanglement detection methods. Full article
(This article belongs to the Section Quantum Photonics and Technologies)
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13 pages, 3112 KB  
Article
First-Passage-Time Analysis of the Pulse-Timing Statistics in a Two-Section Semiconductor Laser under Excitable and Noisy Conditions
by Daan Lenstra, Lukas Puts and Weiming Yao
Photonics 2022, 9(11), 860; https://doi.org/10.3390/photonics9110860 - 14 Nov 2022
Cited by 2 | Viewed by 2025
Abstract
A two-section semiconductor laser can exhibit excitability for certain parameter settings. When used as a photonic spiking neuron, it is relevant to investigate its sensitivity to noise due to, e.g., spontaneous emission. Under excitable conditions, the system emits irregularly timed noise-triggered pulses. Their [...] Read more.
A two-section semiconductor laser can exhibit excitability for certain parameter settings. When used as a photonic spiking neuron, it is relevant to investigate its sensitivity to noise due to, e.g., spontaneous emission. Under excitable conditions, the system emits irregularly timed noise-triggered pulses. Their statistics is analyzed in terms of a first-passage time distribution for the fluctuating intensity to reach the threshold for excitable response. Two analytic approximations valid for short and long times, respectively, are derived which very well explain measured and simulated pulse-repetition time distributions. This provides physical insight into the noise-triggered spiking mechanism. Full article
(This article belongs to the Special Issue Advancements in Semiconductor Lasers)
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9 pages, 4011 KB  
Communication
Ultra-Wideband Polarization Insensitive Angle Filter Based on ENZ Characteristics and Dynamic Antireflection Structures
by Baofei Wan, Haining Ye and Haifeng Zhang
Photonics 2022, 9(11), 854; https://doi.org/10.3390/photonics9110854 - 12 Nov 2022
Cited by 4 | Viewed by 2408
Abstract
Bandwidth expansion has always been an important dimension in investigating angle filters (AFs) and is critical for optical communication and radar detection. In this paper, the AF with strong selectivity is realized by using the epsilon-near-zero (ENZ) jump characteristic of YaBa2Cu [...] Read more.
Bandwidth expansion has always been an important dimension in investigating angle filters (AFs) and is critical for optical communication and radar detection. In this paper, the AF with strong selectivity is realized by using the epsilon-near-zero (ENZ) jump characteristic of YaBa2Cu3O7 material. At the same time, for both the TE and the TM waves in the range of 237~1000 THz, the transmissivity of the AF is stronger than 0.9 by using dynamic antireflection structures (AFSs). The transfer matrix method is suitable for theoretical calculation, and the impedance matching theory is introduced to analyze the features of the AF. The increment of the thickness of superconductor material can effectively enhance the selectivity of the AF structure, and the consequence is the attenuation of transmission performances. If the temperature is covered from 0 K to 85 K, the filtering performance higher than 0.9 can still be maintained for two polarization waves. For these explicit performances, the proposed design may provide a new idea for widening the frequency bandwidth of the AF. Full article
(This article belongs to the Special Issue Photonic Crystals: Physics and Devices)
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6 pages, 1415 KB  
Opinion
Advances in Photovoltaic Technologies from Atomic to Device Scale
by Christin David and Robert Hussein
Photonics 2022, 9(11), 837; https://doi.org/10.3390/photonics9110837 - 8 Nov 2022
Cited by 1 | Viewed by 2229
Abstract
The question of how energy resources can be efficiently used is likewise of fundamental and technological interest. In this opinion, we give a brief overview on developments of harvesting solar energy across different length scales and address some strategies to tackle economic and [...] Read more.
The question of how energy resources can be efficiently used is likewise of fundamental and technological interest. In this opinion, we give a brief overview on developments of harvesting solar energy across different length scales and address some strategies to tackle economic and ecological challenges, in particular with a view to sustainability and toward a circular economy. On the mesoscopic scale, the emergence of thermodynamic laws in open quantum systems is of central importance and how they can be employed for efficient quantum thermal machines and batteries. The broad tunability of band gaps in quantum dot systems makes them attractive for hybrid photovoltaic devices. Complementary, machine learning-aided band gap engineering and the high-throughput screening of novel materials assist with improving absorption characteristics. On the device scale, hybrid concepts of optical control via metasurfaces enable a multitude of functionalities such as a directed re-emission of embedded photoluminescent materials or field enhancement effects from nanostructures. Advanced techniques in computational nanophotonics concern a topology optimization of nanostructured layers together with multiobjective optimization toward specific light management tasks. On the industrial level, modern manufacturers explore 3D printing and flexible solar cell platforms obtained from roll-to-roll technologies. The remote control of solar parks through applications via the Internet of Things opens up new strategies to expand to difficult terrain where human interaction is only required to a limited extent. Full article
(This article belongs to the Special Issue Advances in Photovoltaic Technologies from Atomic to Device Scale)
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11 pages, 3857 KB  
Article
Design and Characteristics of Diamond-Assisted Ring-Core Fiber for Space Division Multiplexing
by Yujing Song, Jingjing Zheng, Li Pei, Jing Huang, Tigang Ning, Jing Li, Jianshuai Wang and Bing Bai
Photonics 2022, 9(10), 766; https://doi.org/10.3390/photonics9100766 - 13 Oct 2022
Cited by 2 | Viewed by 2360
Abstract
In this paper, a novel diamond-assisted ring-core fiber (DRF) is proposed. With the introduction of a low-refractive-index diamond-shaped region located in the center of the core, the proposed fiber effectively eliminates spatial degeneracy of the LPmn mode groups and maintains a low [...] Read more.
In this paper, a novel diamond-assisted ring-core fiber (DRF) is proposed. With the introduction of a low-refractive-index diamond-shaped region located in the center of the core, the proposed fiber effectively eliminates spatial degeneracy of the LPmn mode groups and maintains a low level of birefringence. Under the fiber structure parameters proposed in this paper, the effective refractive index difference (Δneff) between the spatial modes supported by the fiber in the entire C-band is greater than 2.25 × 10−4, and the Δneff between adjacent modes falls within the scope of (2.11~9.41) × 10−4. The degree of degenerate separation between the two polarization modes of all modes is very low, which is 2~3 orders of magnitude lower than that of the spatial mode. By discussing the mode characteristics of DRF and several other center-assisted ring-core fibers, the method that can be used to manipulate the spatial mode degenerate separation with structural symmetry is obtained, which can be applied to provide guidance for similar fiber designs. The proposed fiber structure is a promising candidate in space division multiplexing systems. Full article
(This article belongs to the Special Issue Optical Fiber Communication Systems)
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25 pages, 2087 KB  
Article
Nonlinear Spectrum Modulation in the Anomalous Dispersion Regime Using Second- and Third-Order Solitons
by Thiago D. S. De Menezes, Chaoran Tu, Valentin Besse, Maurice O’Sullivan, Vladimir S. Grigoryan, Curtis R. Menyuk and Ivan T. Lima Jr.
Photonics 2022, 9(10), 748; https://doi.org/10.3390/photonics9100748 - 10 Oct 2022
Cited by 2 | Viewed by 1826
Abstract
We study the robustness of a nonlinear frequency-division multiplexing (NFDM) system, based on the Zakharov-Shabat spectral problem (ZSSP), that is comprised of two independent quadrature phase-shift keyed (QPSK) channels modulated in the discrete spectrum associated with two distinct eigenvalues. Among the many fiber [...] Read more.
We study the robustness of a nonlinear frequency-division multiplexing (NFDM) system, based on the Zakharov-Shabat spectral problem (ZSSP), that is comprised of two independent quadrature phase-shift keyed (QPSK) channels modulated in the discrete spectrum associated with two distinct eigenvalues. Among the many fiber impairments that may limit this system, we focus on determining the limits due to third-order dispersion, the Raman effect, amplified spontaneous emission (ASE) noise from erbium-doped fiber amplifiers (EDFAs), and fiber losses with lumped gain from EDFAs. We examine the impact of these impairments on a 1600-km system by analyzing the Q-factor calculated from the error vector magnitude (EVM) of the received symbols. We found that the maximum launch power due to these impairments is: 13 dBm due to third-order dispersion, 11 dBm due to the Raman effect, 3 dBm due to fiber losses with lumped gain, and 2 dBm due to these three impairments combined with ASE noise. The maximum launch power due to all these impairments combined is comparable to that of a conventional wavelength-division multiplexing (WDM) system, even though WDM systems can operate over a much larger bandwidth and, consequently, have a much higher data throughput when compared with NFDM systems. We find that fiber losses in practical fiber transmission systems with lumped gain from EDFAs is the most stringent limiting factor in the performance of this NFDM system. Full article
(This article belongs to the Section Optical Communication and Network)
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17 pages, 1777 KB  
Article
On the Optimisation of Illumination LEDs for VLP Systems
by José Miguel Menéndez and Heidi Steendam
Photonics 2022, 9(10), 750; https://doi.org/10.3390/photonics9100750 - 10 Oct 2022
Cited by 5 | Viewed by 2212
Abstract
Recent studies have explored the synergy of illumination and positioning using indoor lighting infrastructure. While these studies mainly focused on the analysis of the performance of visible light positioning, these works did not consider the illumination aspects of such combined systems. In this [...] Read more.
Recent studies have explored the synergy of illumination and positioning using indoor lighting infrastructure. While these studies mainly focused on the analysis of the performance of visible light positioning, these works did not consider the illumination aspects of such combined systems. In this paper, we analyse the illumination aspects based on the main illumination characteristics defined in the European Standard EN 12464-1, i.e., the horizontal illuminance and the uniformity of illuminance. As in the standard, we distinguish between a task area, where visual activities are performed that demand higher illuminance and uniformity, and a surrounding area that borders the former. In our analysis, we derive simple rules of thumb to determine the number and placement of LEDs to satisfy the constraints on the horizontal illuminance and uniformity for a given area. Full article
(This article belongs to the Special Issue Advances in Visible Light Communication)
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16 pages, 4884 KB  
Article
A Fast Accurate Attention-Enhanced ResNet Model for Fiber-Optic Distributed Acoustic Sensor (DAS) Signal Recognition in Complicated Urban Environments
by Xinyu Liu, Huijuan Wu, Yufeng Wang, Yunlin Tu, Yuwen Sun, Liang Liu, Yuanfeng Song, Yu Wu and Guofeng Yan
Photonics 2022, 9(10), 677; https://doi.org/10.3390/photonics9100677 - 21 Sep 2022
Cited by 11 | Viewed by 2624
Abstract
The fiber-optic distributed acoustic sensor (DAS), which utilizes existing communication cables as its sensing media, plays an important role in urban infrastructure monitoring and natural disaster prediction. In the face of a wide, dynamic environment in urban areas, a fast, accurate DAS signal [...] Read more.
The fiber-optic distributed acoustic sensor (DAS), which utilizes existing communication cables as its sensing media, plays an important role in urban infrastructure monitoring and natural disaster prediction. In the face of a wide, dynamic environment in urban areas, a fast, accurate DAS signal recognition method is proposed with an end-to-end attention-enhanced ResNet model. In preprocessing, an objective evaluation method is used to compare the distinguishability of different input features with the Euclidean distance between the posterior probabilities classified correctly and incorrectly; then, an end-to-end ResNet is optimized with the chosen time-frequency feature as input, and a convolutional block attention module (CBAM) is added, which can quickly focus on key information from different channels and specific signal structures and improves the system recognition performance further. The results show that the proposed ResNet+CBAM model has the best performance in recognition accuracy, convergence rate, generalization capability, and computational efficiency compared with 1-D CNN, 2-D CNN, ResNet, and 2-D CNN+CBAM. An average accuracy of above 99.014% can be achieved in field testing; while dealing with multi-scenario scenes and inconsistent laying or burying environments, it can still be kept above 91.08%. The time cost is only 3.3 ms for each signal sample, which is quite applicable in online long-distance distributed monitoring applications. Full article
(This article belongs to the Special Issue Optical Fiber Physical and Mechanical Sensors)
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11 pages, 1956 KB  
Communication
An All-Dielectric Color Filter, with a Wider Color Gamut
by Lizhen Zeng, Yuting Yang and Gongli Xiao
Photonics 2022, 9(10), 680; https://doi.org/10.3390/photonics9100680 - 21 Sep 2022
Cited by 5 | Viewed by 2465
Abstract
Due to their extraordinary abilities to manipulate light propagation at the nanoscale, dielectric resonators that generate electric and magnetic Mie resonances for minimal optical loss have recently attracted great interest. Based on an all-dielectric metasurface, made of H-type silicon nanoarrays, this study proposed [...] Read more.
Due to their extraordinary abilities to manipulate light propagation at the nanoscale, dielectric resonators that generate electric and magnetic Mie resonances for minimal optical loss have recently attracted great interest. Based on an all-dielectric metasurface, made of H-type silicon nanoarrays, this study proposed and constructed a visible-wavelength-range color filter, with high-quality Mie resonance and the ability to synthesize new colors. Using the finite-difference time-domain (FDTD) approach, we can create a larger color gamut by modifying the H-type array’s structural properties. The all-dielectric color filter suggested has a high color saturation and narrow bandwidth. The Mie resonance can be adjusted by manipulating the structural characteristics. By translating the reflectance spectrum into color coordinates and using the CIE1931 chromaticity diagram, a wide range of colors can be generated. This color filter offers a larger color range and saturation than other color filters. We produced color passband filters that span the visible spectrum using Mie resonator arrays, based on an H-type nanoresonator. This technology could have many applications, including high-resolution color printing, color-tunable switches, and sensing systems. Full article
(This article belongs to the Topic Optical and Optoelectronic Materials and Applications)
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7 pages, 1607 KB  
Communication
High Power Mid-Infrared Quantum Cascade Lasers Grown on Si
by Steven Slivken, Nirajman Shrestha and Manijeh Razeghi
Photonics 2022, 9(9), 626; https://doi.org/10.3390/photonics9090626 - 1 Sep 2022
Cited by 6 | Viewed by 2493
Abstract
This article details the demonstration of a strain-balanced, InP-based mid-infrared quantum cascade laser structure that is grown directly on a Si substrate. This is facilitated by the creation of a metamorphic buffer layer that is used to convert from the lattice constant of [...] Read more.
This article details the demonstration of a strain-balanced, InP-based mid-infrared quantum cascade laser structure that is grown directly on a Si substrate. This is facilitated by the creation of a metamorphic buffer layer that is used to convert from the lattice constant of Si (0.543 nm) to that of InP (0.587 nm). The laser geometry utilizes two top contacts in order to be compatible with future large-scale integration. Unlike previous reports, this device is capable of room temperature operation with up to 1.6 W of peak power. The emission wavelength at 293 K is 4.82 μm, and the device operates in the fundamental transverse mode. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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14 pages, 3126 KB  
Article
Plasma Dynamics Characterization for Improvement of Resonantly Enhanced Harmonics Generation in Indium and Tin Laser-Produced Plasmas
by Vyacheslav V. Kim, Jelena Butikova, Jurgis Grube, Anatolijs Sarakovskis and Rashid A. Ganeev
Photonics 2022, 9(9), 600; https://doi.org/10.3390/photonics9090600 - 24 Aug 2022
Cited by 3 | Viewed by 2005
Abstract
In this study, we characterize the properties of indium and tin laser-induced plasmas responsible for efficient high-order harmonics generation of the ultrashort pulses propagating through these media. The optimally formed plasma was determined using the analysis of the time-resolved variations in the spectral [...] Read more.
In this study, we characterize the properties of indium and tin laser-induced plasmas responsible for efficient high-order harmonics generation of the ultrashort pulses propagating through these media. The optimally formed plasma was determined using the analysis of the time-resolved variations in the spectral and morphological features of spreading indium and tin plasma components under different regimes of laser ablation. We report the measurements of plasma velocities under different regimes of ablation and correlate them with the optimal delay between the heating and probe laser pulses for the generation of harmonics with the highest yield. Electron temperatures and densities are determined using the integrated and time-resolved spectral measurements of plasmas. The resonance-enhanced harmonics are compared with other harmonics from the point of view of the modulation of plasma characteristics. The harmonics of 800 and 1200–2200 nm lasers and their second-harmonic fields were analyzed at optimal conditions of Sn and In plasma formation. The novelty of this work is the implementation of the diagnostics of the dynamics of plasma characteristics for the determination of the optimal plasma formation for harmonics generation. Such an approach allows for the demonstration of the maximal harmonic yield from the studied plasma and the definition of the various resonance-induced harmonic generation conditions. Full article
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17 pages, 3213 KB  
Article
Resonant Coupling of Hermite-Gaussian Transverse Modes in the Triangular Cavity of a Cavity Ring-down Spectroscope
by Yijie Ren, Changxiang Yan, Xiamiao Zhang and Chunhui Hu
Photonics 2022, 9(9), 595; https://doi.org/10.3390/photonics9090595 - 23 Aug 2022
Cited by 1 | Viewed by 2202
Abstract
During resonance in resonant cavities, such as those used in laser or cavity ring-down spectroscopes (CRDS), resonant coupling between higher-order transverse modes and fundamental modes can seriously affect the quality of the beam and introduce measurement errors. Several coupling models, such as thermal [...] Read more.
During resonance in resonant cavities, such as those used in laser or cavity ring-down spectroscopes (CRDS), resonant coupling between higher-order transverse modes and fundamental modes can seriously affect the quality of the beam and introduce measurement errors. Several coupling models, such as thermal deformation coupling and scattering coupling, have been established according to existing coupling theory and specific application scenarios; however, these coupling models have not been attributed to a unified theory. In this paper, we reveal that the same resonant coupling excitation factors exist under different types of environmental perturbation. The conditions and range of resonant coupling in a CRDS ring-down cavity are systematically analyzed, and a preferential coupling model of the middle-order modes is proposed. The time-domain characteristics of the CRDS are used in experiments to analyze the resonant coupling between the modes in a weak energy system. The order and coupling range of the middle-order modes involved in resonant coupling are verified using the modal filtering characteristics of the triangular cavity; this paper presents a unified explanation for various types of resonant coupling and also provides a new approach to resonant coupling experiments performed in high-finesse resonant cavities. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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13 pages, 4012 KB  
Article
Demonstration of Yb-Doped Fiber Amplifier Operating near 980 nm with the Slope Efficiency Close to the Theoretical Limit
by Zhaode Li, Shangde Zhou, Aimin Liu, Jianqiu Cao, Zhihe Huang and Jinbao Chen
Photonics 2022, 9(8), 571; https://doi.org/10.3390/photonics9080571 - 12 Aug 2022
Cited by 2 | Viewed by 2961
Abstract
In this paper, the scalability of slope efficiency of a Yb-doped fiber amplifier operating near 980 nm is studied with the core-pumping scheme. By means of numerical prediction, it is found that the theoretical limit of slope efficiency should be about 92.2%. Then, [...] Read more.
In this paper, the scalability of slope efficiency of a Yb-doped fiber amplifier operating near 980 nm is studied with the core-pumping scheme. By means of numerical prediction, it is found that the theoretical limit of slope efficiency should be about 92.2%. Then, the experiment study is carried out. An 85.3% slope efficiency of emission around 980 nm is achieved with the seed light around 976.5 nm, and the strong in-band amplified spontaneous emission (ASE) is supposed to be a factor limiting the upscaling of slope efficiency. In order to suppress the in-band ASE, the double-wavelength fiber oscillator near 980 nm is fabricated and used as the seed source, with which the slope efficiency is elevated to 90.7%. Such slope efficiency is very close to the theoretical limit and sets a new record of slope efficiency for the Yb-doped fiber amplifier operating near 980 nm, to the best of our knowledge. It is also revealed that the suppression of in-band ASE should be of great importance to elevate the slope efficiency of a Yb-doped fiber amplifier operating near 980 nm. Full article
(This article belongs to the Special Issue Rare-Earth-Doped Fiber Lasers and Amplifiers)
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29 pages, 3831 KB  
Review
AI-Enabled Intelligent Visible Light Communications: Challenges, Progress, and Future
by Jianyang Shi, Wenqing Niu, Yinaer Ha, Zengyi Xu, Ziwei Li, Shaohua Yu and Nan Chi
Photonics 2022, 9(8), 529; https://doi.org/10.3390/photonics9080529 - 29 Jul 2022
Cited by 37 | Viewed by 6720
Abstract
Visible light communication (VLC) is a highly promising complement to conventional wireless communication for local-area networking in future 6G. However, the extra electro-optical and photoelectric conversions in VLC systems usually introduce exceeding complexity to communication channels, in particular severe nonlinearities. Artificial intelligence (AI) [...] Read more.
Visible light communication (VLC) is a highly promising complement to conventional wireless communication for local-area networking in future 6G. However, the extra electro-optical and photoelectric conversions in VLC systems usually introduce exceeding complexity to communication channels, in particular severe nonlinearities. Artificial intelligence (AI) techniques are investigated to overcome the unique challenges in VLC, whereas considerable obstacles are found in practical VLC systems applied with intelligent learning approaches. In this paper, we present a comprehensive study of the intelligent physical and network layer technologies for AI-empowered intelligent VLC (IVLC). We first depict a full model of the visible light channel and discuss its main challenges. The advantages and disadvantages of machine learning in VLC are discussed and analyzed by simulation. We then present a detailed overview of advances in intelligent physical layers, including optimal coding, channel emulator, MIMO, channel equalization, and optimal decision. Finally, we envision the prospects of IVLC in both the intelligent physical and network layers. This article lays out a roadmap for developing machine learning-based intelligent visible light communication in 6G. Full article
(This article belongs to the Special Issue Advances in Visible Light Communication)
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10 pages, 3205 KB  
Article
A Theoretical Design of Chiral Molecules through Conformational Lock towards Circularly Polarized Luminescence
by Lewen Wang, Tengfei He, Hailiang Liao, Yige Luo, Wen Ou, Yinye Yu, Wan Yue, Guankui Long, Xingzhan Wei and Yecheng Zhou
Photonics 2022, 9(8), 532; https://doi.org/10.3390/photonics9080532 - 29 Jul 2022
Viewed by 3930
Abstract
Circularly polarized (CP) light has shown great potential in quantum computing, optical communications, and three-dimensional displays. It is still a challenge to produce high-efficiency and high-purity CP light. Herein, we proposed a strategy to design chiral organic small molecules for CP light generation. [...] Read more.
Circularly polarized (CP) light has shown great potential in quantum computing, optical communications, and three-dimensional displays. It is still a challenge to produce high-efficiency and high-purity CP light. Herein, we proposed a strategy to design chiral organic small molecules for CP light generation. These kinds of chiral molecules are formed by achiral light-emitting groups and achiral alkyl chains through conformational lock, which indicates that chirality can also be introduced into achiral light-emitting groups through rational molecular design. The chirality of these molecules can be further tuned by changing the length of the alkyl chains connecting the diketopyrrolopyrrole unit. The chiroptical properties of these molecules are confirmed by calculated electronic circular dichroism and chiral emission spectra, and further confirmed in experiments. The strategy developed in this work will greatly enlarge the candidate library of chiral luminescent materials. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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11 pages, 1959 KB  
Article
Photoacoustic Detection of Pollutants Emitted by Transportation System for Use in Automotive Industry
by Reza Hadjiaghaie Vafaie, Roya Shafiei Pour, Ardashir Mohammadzadeh, Jihad H. Asad and Amir Mosavi
Photonics 2022, 9(8), 526; https://doi.org/10.3390/photonics9080526 - 28 Jul 2022
Cited by 7 | Viewed by 2202
Abstract
In photoacoustic spectroscopy, the signal is inversely proportional to the resonant cell volume. Photoacoustic spectroscopy (PAS) is an absorption spectroscopy technique that is suitable for detecting gases at low concentrations. This desirable feature has created a growing interest in miniaturizing PA cells in [...] Read more.
In photoacoustic spectroscopy, the signal is inversely proportional to the resonant cell volume. Photoacoustic spectroscopy (PAS) is an absorption spectroscopy technique that is suitable for detecting gases at low concentrations. This desirable feature has created a growing interest in miniaturizing PA cells in recent years. In this paper, a simulation of a miniaturized H-type photoacoustic cell consisting of two buffer holes and a resonator was performed in order to detect CO, NH3, NO, and CH4 pollutants. These gases are the main components of the air pollutants that are produced by the automotive industry. The linear forms of the continuity, Navier–Stokes equations, and the energy equation were solved using the finite element method in a gaseous medium. The generated pressure could be measured by a MEMS sensor. Photoacoustic spectroscopy has proven to be a sensitive method for detecting pollutant gases. The objectives of the measurements were: determining the proper position of the pressure gauge sensor; measuring the frequency response; measuring the frequency response changes at different temperatures; studying the local velocity at the resonant frequency; and calculating the quality factor. The acoustic quality coefficient, acoustic response (pressure), local velocity, frequency response, and the effect of different temperatures on the frequency response were investigated. A frequency response measurement represents the fact that different gases have different resonance frequencies, for which CO and NO gases had values of 23.131 kHz and 23.329 kHz, respectively. The difference between these gases was 200 Hz. NH3 and CH4 gases with values of 21.206 kHz and 21.106 kHz were separable with a difference of 100 Hz. In addition, CO and NO gases had a difference of 2000 Hz compared to NH3 and CH4, which indicates the characteristic fingerprint of the designed cell in the detection of different gases. Better access to high-frequency acoustic signals was the goal of the presented model in this paper. Full article
(This article belongs to the Special Issue Photonic Application in the Automotive Industry)
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10 pages, 3268 KB  
Communication
Detection of a Spinning Object at Different Beam Sizes Based on the Optical Rotational Doppler Effect
by Song Qiu, Ruoyu Tang, Xiangyang Zhu, Tong Liu and Yuan Ren
Photonics 2022, 9(8), 517; https://doi.org/10.3390/photonics9080517 - 25 Jul 2022
Cited by 6 | Viewed by 2396
Abstract
The rotational Doppler effect (RDE), as a counterpart of the conventional well-known linear Doppler effect in the rotating frame, has attracted increasing attention in recent years for rotating object detection. However, the effect of the beam size on the RDE is still an [...] Read more.
The rotational Doppler effect (RDE), as a counterpart of the conventional well-known linear Doppler effect in the rotating frame, has attracted increasing attention in recent years for rotating object detection. However, the effect of the beam size on the RDE is still an open question. In this article, we investigated the influence of the size of the probe light; i.e., the size of the ring-shaped orbital angular momentum (OAM)-carrying optical vortex (OV), on the RDE. Both the light coaxial and noncoaxial incident conditions were considered in our work. We analyzed the mechanism of the influence on the RDE under the light coaxial, lateral misalignment, and oblique incidence conditions based on the small-scatterer model. A proof-of-concept experiment was performed to verify the theoretical predictions. It was shown that both the signal-to-noise ratio and the frequency spectrum width were related to the OV size. The larger the beam size, the stronger the RDE signal observed in the practical detection. Especially in the lateral misalignment condition, the large OV size effectively reduced the signal spreading and enhanced the signal strength. These findings may be useful for practical application of the optical RDE in remote sensing and metrology. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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12 pages, 1105 KB  
Review
Review of Quality Optimization of Electron Beam Based on Laser Wakefield Acceleration
by Kangnan Jiang, Wentao Wang, Ke Feng and Ruxin Li
Photonics 2022, 9(8), 511; https://doi.org/10.3390/photonics9080511 - 23 Jul 2022
Cited by 4 | Viewed by 3786
Abstract
Compared with state-of-the-art radio frequency accelerators, the gradient of laser wakefield accelerators is 3–4 orders of magnitude higher. This is of great significance in the development of miniaturized particle accelerators and radiation sources. Higher requirements have been proposed for the quality of electron [...] Read more.
Compared with state-of-the-art radio frequency accelerators, the gradient of laser wakefield accelerators is 3–4 orders of magnitude higher. This is of great significance in the development of miniaturized particle accelerators and radiation sources. Higher requirements have been proposed for the quality of electron beams, owing to the increasing application requirements of tabletop radiation sources, specifically with the rapid development of free-electron laser devices. This review briefly examines the electron beam quality optimization scheme based on laser wakefield acceleration and presents some representative studies. In addition, manipulation of the electron beam phase space by means of injection, plasma profile distribution, and laser evolution is described. This review of studies is beneficial for further promoting the application of laser wakefield accelerators. Full article
(This article belongs to the Special Issue Progress in Laser Accelerator and Future Prospects)
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15 pages, 13392 KB  
Article
Flexible Multiplane Structured Illumination Microscope with a Four-Camera Detector
by Karl A. Johnson, Daniel Noble, Rosa Machado, Tristan C. Paul and Guy M. Hagen
Photonics 2022, 9(7), 501; https://doi.org/10.3390/photonics9070501 - 20 Jul 2022
Cited by 6 | Viewed by 3344
Abstract
Fluorescence microscopy provides an unparalleled tool for imaging biological samples. However, producing high-quality volumetric images quickly and without excessive complexity remains a challenge. Here, we demonstrate a four-camera structured illumination microscope (SIM) capable of simultaneously imaging multiple focal planes, allowing for the capture [...] Read more.
Fluorescence microscopy provides an unparalleled tool for imaging biological samples. However, producing high-quality volumetric images quickly and without excessive complexity remains a challenge. Here, we demonstrate a four-camera structured illumination microscope (SIM) capable of simultaneously imaging multiple focal planes, allowing for the capture of 3D fluorescent images without any axial movement of the sample. This setup allows for the acquisition of many different 3D imaging modes, including 3D time lapses, high-axial-resolution 3D images, and large 3D mosaics. We imaged mitochondrial motions in live cells, neuronal structure in Drosophila larvae, and imaged up to 130 µm deep into mouse brain tissue. After SIM processing, the resolution measured using one of the four cameras improved from 357 nm to 253 nm when using a 30×/1.05 NA objective. Full article
(This article belongs to the Special Issue Advances and Application of Super-resolution Optical Microscopy)
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10 pages, 21938 KB  
Article
Exploration of Deformation of F-Actin during Macropinocytosis by Confocal Microscopy and 3D-Structured Illumination Microscopy
by Linyu Xu, Yanwei Zhang, Song Lang and Yan Gong
Photonics 2022, 9(7), 461; https://doi.org/10.3390/photonics9070461 - 30 Jun 2022
Cited by 2 | Viewed by 2545
Abstract
Since their invention, confocal microscopy and super-resolution microscopy have become important choices in cell biology research. Macropinocytosis is a critical form of endocytosis. Deformation of the cell membrane is thought to be closely related to the movement of F-actin during macropinocytosis. However, it [...] Read more.
Since their invention, confocal microscopy and super-resolution microscopy have become important choices in cell biology research. Macropinocytosis is a critical form of endocytosis. Deformation of the cell membrane is thought to be closely related to the movement of F-actin during macropinocytosis. However, it is still unclear how the morphology of F-actin and the membrane change during this process. In this study, confocal microscopy was utilized for macroscopic time-series imaging of the cell membranes and F-actin in cells induced by phorbol 12-myristate 13-acetate (PMA). Super-resolution structured illumination microscopy (SIM), which can overcome the diffraction limit, was used to demonstrate the morphological characteristics of F-actin filaments. Benefiting from the advantages of SIM in terms of resolution and 3D imaging, we speculated on the regular pattern of the deformation of F-actin during macropinocytosis. The detailed visualization of structures also helped to validate the speculation regarding the role of F-actin filaments in macropinocytosis in previous studies. The results obtained in this study will provide a better understanding of the mechanisms underlying macropinocytosis and endocytosis. Full article
(This article belongs to the Special Issue Advances and Application of Super-resolution Optical Microscopy)
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11 pages, 4314 KB  
Communication
High-Efficiency and High-Power Multijunction InGaAs/InP Photovoltaic Laser Power Converters for 1470 nm
by Simon Fafard and Denis P. Masson
Photonics 2022, 9(7), 438; https://doi.org/10.3390/photonics9070438 - 21 Jun 2022
Cited by 39 | Viewed by 8470
Abstract
The high-efficiency capabilities of multijunction laser power converters are demonstrated for high-power applications with an optical input of around 1470 nm. The InP-based photovoltaic power converting III-V semiconductor devices are designed here, with 10 lattice-matched subcells (PT10-InGaAs/InP), using thin InGaAs absorbing layers connected [...] Read more.
The high-efficiency capabilities of multijunction laser power converters are demonstrated for high-power applications with an optical input of around 1470 nm. The InP-based photovoltaic power converting III-V semiconductor devices are designed here, with 10 lattice-matched subcells (PT10-InGaAs/InP), using thin InGaAs absorbing layers connected by transparent tunnel junctions. The results confirm that such long-wavelength power converter devices are capable of producing electrical output voltages greater than 4–5 V. The characteristics are compatible with common electronics requirements, and the optical input is well suited for propagation over long distances through fiber-based optical links. Conversion efficiencies of ~49% are measured at electrical outputs exceeding 7 W for an input wavelength of 1466 nm at 21 °C. The Power Converter Performance Chart has been updated with these PT10-InGaAs/InP results. Full article
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13 pages, 2684 KB  
Article
Electric Field Sensor Based on High Q Fano Resonance of Nano-Patterned Electro-Optic Materials
by Xiaowei Yin, Fengli Liu, Wentao Qiu, Can Liu, Heyuan Guan and Huihui Lu
Photonics 2022, 9(6), 431; https://doi.org/10.3390/photonics9060431 - 17 Jun 2022
Cited by 3 | Viewed by 4084
Abstract
This paper presents theoretical studies of Fano resonance based electric-field (E-field) sensors. E-field sensor based on two electro-optical (EO) materials i.e., barium titanate (BaTiO3, BTO) nanoparticles and relaxor ferroelectric material Pb(Mg1/3Nb2/3)O3-PbTiO [...] Read more.
This paper presents theoretical studies of Fano resonance based electric-field (E-field) sensors. E-field sensor based on two electro-optical (EO) materials i.e., barium titanate (BaTiO3, BTO) nanoparticles and relaxor ferroelectric material Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) combined with nanostructure are studied. As for the BTO based E-field sensor, a configuration of filling the BTO nanoparticles into a nano-patterned thin film silicon is proposed. The achieved resonance quality factor (Q) is 11,855 and a resonance induced electric field enhancement factor is of around 105. As for the design of PMN-PT based E-field sensor, a configuration by combining two square lattice air holes in PMN-PT thin film but with one offsetting hole left is chosen. The achieved resonance Q is of 9,273 and an electric field enhancement factor is of around 96. The resonance wavelength shift sensitivity of PMN-PT nanostructured can reach up to 4.768 pm/(V/m), while the BTO based nanostructure has a sensitivity of 0.1213 pm/(V/m). If a spectrum analyzer with 0.1 pm resolution is considered, then the minimum detection of the electric field Emin is 20 mV/m and 0.82 V/m for PMN-PT and BTO based nanostructures, respectively. The nano-patterned E-field sensor studied here are all dielectric, it has therefore the advantage of large measurement bandwidth, high measurement fidelity, high spatial resolution and high sensitivity. Full article
(This article belongs to the Special Issue Advances in Photonic Integrated Devices and Circuits)
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