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Photonics
Volume 8
Issue 11
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Photonics, Volume 8, Issue 11 (November 2021) – 65 articles

Cover Story (view full-size image): It is called the “white pollutant” and it represents one of the environmental plagues of our days. Plastics is everywhere. Most importantly, it is where it should not be: oceans, mountains, air. Replacing plastics in modern technologies requires a shift in the way we think of scenarios with which physics has long been familiar. Resonant cavities and emitters belong to one of the most science-fiction-named branches of physics: Cavity Quantum Electrodynamics (C-QED), being the stage where technological breakthroughs become reality. The question is: can a C-QED framework be rethought in an eco-friendly way? In this study, we address such a challenge, envisioning solutions in which the compulsive demand for technological advancement meets the compelling yet silent demand of our planet for more respect. View this paper
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17 pages, 7309 KiB  
Article
A Full-Aperture Image Synthesis Method for the Rotating Rectangular Aperture System Using Fourier Spectrum Restoration
by Guomian Lv, Hao Xu, Huajun Feng, Zhihai Xu, Hao Zhou, Qi Li and Yueting Chen
Photonics 2021, 8(11), 522; https://doi.org/10.3390/photonics8110522 - 22 Nov 2021
Cited by 6 | Viewed by 2527
Abstract
The novel rotating rectangular aperture (RRA) system provides a good solution for space-based, large-aperture, high-resolution imaging tasks. Its imaging quality depends largely on the image synthesis algorithm, and the mainstream multi-frame deblurring approach is sophisticated and time-consuming. In this paper, we propose a [...] Read more.
The novel rotating rectangular aperture (RRA) system provides a good solution for space-based, large-aperture, high-resolution imaging tasks. Its imaging quality depends largely on the image synthesis algorithm, and the mainstream multi-frame deblurring approach is sophisticated and time-consuming. In this paper, we propose a novel full-aperture image synthesis algorithm for the RRA system, based on Fourier spectrum restoration. First, a numerical simulation model is established to analyze the RRA system’s characteristics and obtain the point spread functions (PSFs) rapidly. Then, each image is used iteratively to calculate the increment size and update the final restored Fourier spectrum. Both the simulation’s results and the practical experiment’s results show that our algorithm performs well in terms of objective evaluation and time consumption. Full article
(This article belongs to the Special Issue Smart Pixels and Imaging)
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10 pages, 2044 KiB  
Communication
Anisotropic Non-Kolmogorov Turbulence Spectrum with Anisotropic Tilt Angle
by Chao Zhai
Photonics 2021, 8(11), 521; https://doi.org/10.3390/photonics8110521 - 20 Nov 2021
Cited by 2 | Viewed by 1567
Abstract
With the in-depth study of atmospheric turbulence, scholars have identified that the anisotropy of turbulence cells should not be forgotten. The anisotropic non-Kolmogorov turbulence model can better characterize the actual situation of atmospheric turbulence. However, the results of recent experiments by Wang et [...] Read more.
With the in-depth study of atmospheric turbulence, scholars have identified that the anisotropy of turbulence cells should not be forgotten. The anisotropic non-Kolmogorov turbulence model can better characterize the actual situation of atmospheric turbulence. However, the results of recent experiments by Wang et al. and Beason et al. demonstrate that the turbulence cell has an anisotropic tilt angle, i.e., the long axis of turbulence cell may not be horizontal to the ground but has a certain angle with the ground. In this paper, we derive the anisotropic non-Kolmogorov turbulence spectra for the horizontal and satellite links with anisotropic tilt angle. Then by use of these spectra, the analytical expressions of scintillation index in the horizontal and satellite links are derived for the weak fluctuation condition. The calculation results display that the scintillation index for the horizontal and satellite links vary with the changes of anisotropic tilt angle and azimuth angle. Therefore, the anisotropic tilt angle is indispensable in the horizontal and satellite links. Full article
(This article belongs to the Section Optical Communication and Network)
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8 pages, 1939 KiB  
Article
Simultaneous Enhancement of Contrast and Power of Femtosecond Laser Pulses by Nonlinear Interferometer
by Yasser Nada and Efim Khazanov
Photonics 2021, 8(11), 520; https://doi.org/10.3390/photonics8110520 - 19 Nov 2021
Viewed by 1811
Abstract
We showed that the nonlinear Mach–Zehnder interferometer may be used not only for enhancing temporal contrast, as proposed earlier, but also for increasing pulse power due to efficient pulse compression. The interferometer introduces into the output pulse a nonlinear phase equal to π/2. [...] Read more.
We showed that the nonlinear Mach–Zehnder interferometer may be used not only for enhancing temporal contrast, as proposed earlier, but also for increasing pulse power due to efficient pulse compression. The interferometer introduces into the output pulse a nonlinear phase equal to π/2. This allows increasing laser power by a factor of 1.5 only by means of a chirped mirror. Use of an additional nonlinear plate leads to a multi-fold power increase retaining the contrast enhancement. Full article
(This article belongs to the Special Issue Advances in Modern Photonics)
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7 pages, 467 KiB  
Communication
An Electro-Optic, Actively Q-Switched Tm:YAP/KGW External-Cavity Raman Laser at 2273 nm and 2344 nm
by Rotem Nahear, Neria Suliman, Yechiel Bach and Salman Noach
Photonics 2021, 8(11), 519; https://doi.org/10.3390/photonics8110519 - 19 Nov 2021
Cited by 4 | Viewed by 1870
Abstract
This paper presents a KGW Raman laser with an external-cavity configuration in the 2 μm region. The Raman laser is pumped by unique, electro-optic, actively Q-switched Tm:Yap laser, emitting at 1935 nm. The electro-optic modulation is based on a KLTN crystal, enabling the [...] Read more.
This paper presents a KGW Raman laser with an external-cavity configuration in the 2 μm region. The Raman laser is pumped by unique, electro-optic, actively Q-switched Tm:Yap laser, emitting at 1935 nm. The electro-optic modulation is based on a KLTN crystal, enabling the use of a short crystal length, with a relatively low driving voltage. Due to the KGW bi-axial properties, the Raman laser is able to lase separately at two different output wavelengths, 2273 and 2344 nm. The output energies and pulse durations for these two lines are 0.42 mJ/pulse at 18.2 ns, and 0.416 mJ/pulse at 14.7 ns, respectively. This is the first implementation of a KGW crystal pumped by an electro-optic active Q-switched Tm:Yap laser in the SWIR spectral range. Full article
(This article belongs to the Special Issue High-Power Lasers and Amplifiers)
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17 pages, 2687 KiB  
Article
Applications of THz Spectral Imaging in the Detection of Agricultural Products
by Hongyi Ge, Ming Lv, Xuejing Lu, Yuying Jiang, Guofang Wu, Guangming Li, Li Li, Zhi Li and Yuan Zhang
Photonics 2021, 8(11), 518; https://doi.org/10.3390/photonics8110518 - 17 Nov 2021
Cited by 43 | Viewed by 5246
Abstract
Agricultural products need to be inspected for quality and safety, and the issue of safety of agricultural products caused by quality is frequently investigated. Safety testing should be carried out before agricultural products are consumed. The existing technologies for inspecting agricultural products are [...] Read more.
Agricultural products need to be inspected for quality and safety, and the issue of safety of agricultural products caused by quality is frequently investigated. Safety testing should be carried out before agricultural products are consumed. The existing technologies for inspecting agricultural products are time-consuming and require complex operation, and there is motivation to develop a rapid, safe, and non-destructive inspection technology. In recent years, with the continuous progress of THz technology, THz spectral imaging, with the advantages of its unique characteristics, such as low energies, superior spatial resolution, and high sensitivity to water, has been recognized as an efficient and feasible identification tool, which has been widely used for the qualitative and quantitative analyses of agricultural production. In this paper, the current main performance achievements of the use of THz images are presented. In addition, recent advances in the application of THz spectral imaging technology for inspection of agricultural products are reviewed, including internal component detection, seed classification, pesticide residues detection, and foreign body and packaging inspection. Furthermore, machine learning methods applied in THz spectral imaging are discussed. Finally, the existing problems of THz spectral imaging technology are analyzed, and future research directions for THz spectral imaging technology are proposed. Recent rapid development of THz spectral imaging has demonstrated the advantages of THz radiation and its potential application in agricultural products. The rapid development of THz spectroscopic imaging combined with deep learning can be expected to have great potential for widespread application in the fields of agriculture and food engineering. Full article
(This article belongs to the Special Issue Driving Spectroscopy and Laser Physics toward Biological, Agricultural, and Medical Applications)
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8 pages, 3820 KiB  
Communication
Image Contrast Improvement in Interference-Dark-Field Digital Holographic Microscopy
by Chi-Ching Chang, Yang-Kun Chew, Huang-Tian Chan, Mei-Fang Chou and Je-Chung Wang
Photonics 2021, 8(11), 517; https://doi.org/10.3390/photonics8110517 - 17 Nov 2021
Cited by 1 | Viewed by 2320
Abstract
Conventional dark-field digital holographic microscopy (DHM) techniques require the use of specialized optics, and, thus, obtaining dark-field images with high contrast has a high cost. Herein, we propose a DHM system that uses an interference-dark-field technique for improving image contrast. Unlike conventional dark-field [...] Read more.
Conventional dark-field digital holographic microscopy (DHM) techniques require the use of specialized optics, and, thus, obtaining dark-field images with high contrast has a high cost. Herein, we propose a DHM system that uses an interference-dark-field technique for improving image contrast. Unlike conventional dark-field DHM, the proposed technique does not require expensive and specialized optical elements, or a complicated optical setup, to obtain dark-field images. The proposed technique employs a pure optical basis method to suppress scattering noise—namely, interference-dark-field—and mainly adopts an arbitrary micro-phase shifting method to achieve destructive interference for obtaining holograms. Under the framework of the proposed technique and through the observation of the USAF 1951 resolution target, the reconstructed image can retain the high contrast of the interference-dark-field DHM. The image contrast is enhanced by at least 43% compared to that which is obtained by conventional dark-field DHM. The resolution of the system can be as high as 0.87 μm. The proposed technique can switch between bright-field and dark-field DHM and prevents damage to the sample, which results from high-intensity illumination in conventional techniques. Full article
(This article belongs to the Special Issue Advances in Optical Metrology)
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10 pages, 2880 KiB  
Communication
Ultra-Compact Power Splitters with Low Loss in Arbitrary Direction Based on Inverse Design Method
by Yanhong Xu, Hansi Ma, Tong Xie, Junbo Yang and Zhenrong Zhang
Photonics 2021, 8(11), 516; https://doi.org/10.3390/photonics8110516 - 16 Nov 2021
Cited by 13 | Viewed by 2675
Abstract
The power splitter is a device that splits the energy from an input signal into multiple outputs with equal or uneven energy. Recently, the use of algorithms to intelligently design silicon-based photonic devices has attracted widespread attention. Thus, many optimization algorithms, which are [...] Read more.
The power splitter is a device that splits the energy from an input signal into multiple outputs with equal or uneven energy. Recently, the use of algorithms to intelligently design silicon-based photonic devices has attracted widespread attention. Thus, many optimization algorithms, which are called inverse design algorithms, have been proposed. In this paper, we use the Direct Binary Search (DBS) algorithm designed with three 1 × 3 power splitters with arbitrary directions theoretically. They have any direction and can be connected to other devices in any direction, which greatly reduces the space occupied by the optical integrated circuit. Through the simulation that comes about, we are able to get the insertion loss (IL) of the device we designed to be less than 5.55 dB, 5.49 dB, and 5.32 dB, separately. Then, the wavelength is 1530–1560 nm, so it can be used in the optical communication system. To discuss the impact of the footprint on device performance, we also designed another device with the same function as the second one from the above three devices. Its IL is less than 5.40 dB. Although it occupies a larger area, it has an advantage in IL. Through the design results, three 1 × 3 power splitters can be freely combined to realize any direction, multi-channel, ultra-compact power splitters, and can be better connected with different devices to achieve different functions. At the same time, we also show an example of a combination. The IL of each port of the combined 1 × 6 power splitter is less than 8.82 dB. Full article
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13 pages, 8672 KiB  
Article
Hybrid Ring- and Tree-Topology RoF Transmission System with Disconnection Protection
by Chung-Yi Li, Ching-Hung Chang and Zih-Guei Lin
Photonics 2021, 8(11), 515; https://doi.org/10.3390/photonics8110515 - 16 Nov 2021
Cited by 7 | Viewed by 1973
Abstract
This paper proposes a hybrid ring- and tree-topology radio over fiber (RoF) transmission system with self-disconnection protection that can support the high distribution density of base stations (BSs) in a metropolitan area and strengthen the network quality of service through self-disconnection protection. The [...] Read more.
This paper proposes a hybrid ring- and tree-topology radio over fiber (RoF) transmission system with self-disconnection protection that can support the high distribution density of base stations (BSs) in a metropolitan area and strengthen the network quality of service through self-disconnection protection. The number of supportable BS in the system can be increased significantly by integrating the time- and wavelength-division multiplexing techniques and properly utilizing a new-generation single-line bidirectional add/drop multiplexer (SBOADM) into the proposed system. Moreover, when the ring–fiber link of the system is interrupted for any reason, the system operator can recover the broken connections quickly only by transforming an optical switch state at the CO end to allow the downlink optical signals to transmit along the clockwise and counterclockwise directions of the ring–fiber link simultaneously. In this case, the downstream optical signals can be delivered to each set of BS-groups through the two-way transmission characteristics of the SBOADM automatically, and the uplink optical signals, originally, from each set of BS-groups can be transmitted back to the CO end along the opposite direction of the downlink signal-routing path. In this way, the interference caused by fiber breakage can be avoided immediately, and the entire transport system can be reconnected to ensure the quality of network services. Our experimental results prove that the overall transmission performances are similar to those under normal circumstances. Full article
(This article belongs to the Special Issue Optical Wireless Communication (OWC) Systems)
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11 pages, 441 KiB  
Article
Experimental Demonstration of Fine-Grained Steering Inequality of Two-Qubit Mixed States
by Zhi-Hao Bian and Cong-Yue Yin
Photonics 2021, 8(11), 514; https://doi.org/10.3390/photonics8110514 - 15 Nov 2021
Cited by 2 | Viewed by 1892
Abstract
Quantum steering, as a cornerstone of quantum information, is usually used to witness the quantum correlation of bipartite and multi-partite states. Here, we experimentally demonstrate the quantum steering inequality of two-qubit mixed states based on the fine-grained uncertainty relation. Our experimental results show [...] Read more.
Quantum steering, as a cornerstone of quantum information, is usually used to witness the quantum correlation of bipartite and multi-partite states. Here, we experimentally demonstrate the quantum steering inequality of two-qubit mixed states based on the fine-grained uncertainty relation. Our experimental results show that the steering inequality has potent sensitivity to Werner states and Bell diagonal states. The steering strategy exhibits a strong ability to identify that Werner states are steerable when the decoherence coefficient a>12. Compared to the steering inequality obtained by another stratagem, the steering witness criteria of mixed states based on the fine-grained uncertainty relation demonstrated in our experiment has better precision and accuracy. Moreover, the detection efficiency in our measurement setup is only required to be 50% to close the detection loophole, which means our approach needs less detector efficiency to certificate the steerability of mixed states. Full article
(This article belongs to the Section Quantum Photonics and Technologies)
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9 pages, 17242 KiB  
Communication
Super-Resolution Imaging with Patchy Microspheres
by Qingqing Shang, Fen Tang, Lingya Yu, Hamid Oubaha, Darwin Caina, Songlin Yang, Sorin Melinte, Chao Zuo, Zengbo Wang and Ran Ye
Photonics 2021, 8(11), 513; https://doi.org/10.3390/photonics8110513 - 15 Nov 2021
Cited by 13 | Viewed by 3487
Abstract
The diffraction limit is a fundamental barrier in optical microscopy, which restricts the smallest resolvable feature size of a microscopic system. Microsphere-based microscopy has proven to be a promising tool for challenging the diffraction limit. Nevertheless, the microspheres have a low imaging contrast [...] Read more.
The diffraction limit is a fundamental barrier in optical microscopy, which restricts the smallest resolvable feature size of a microscopic system. Microsphere-based microscopy has proven to be a promising tool for challenging the diffraction limit. Nevertheless, the microspheres have a low imaging contrast in air, which hinders the application of this technique. In this work, we demonstrate that this challenge can be effectively overcome by using partially Ag-plated microspheres. The deposited Ag film acts as an aperture stop that blocks a portion of the incident beam, forming a photonic hook and an oblique near-field illumination. Such a photonic hook significantly enhanced the imaging contrast of the system, as experimentally verified by imaging the Blu-ray disc surface and colloidal particle arrays. Full article
(This article belongs to the Special Issue Photonic Jet: Science and Application)
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13 pages, 29160 KiB  
Communication
Influence of Source Parameters and Non-Kolmogorov Turbulence on Evolution Properties of Radial Phased-Locked Partially Coherent Vortex Beam Array
by Jiao Wang, Mingjun Wang, Sichen Lei, Zhenkun Tan, Chenbai Wang and Yuanfei Wang
Photonics 2021, 8(11), 512; https://doi.org/10.3390/photonics8110512 - 15 Nov 2021
Cited by 3 | Viewed by 1827
Abstract
Partially coherent optical vortices have been applicated widely to reduce the influence of atmospheric turbulence, especially for free-space optical (FSO) communication. Furthermore, the beam array is an effective way to increase the power of the light source, and can increase the propagation distance [...] Read more.
Partially coherent optical vortices have been applicated widely to reduce the influence of atmospheric turbulence, especially for free-space optical (FSO) communication. Furthermore, the beam array is an effective way to increase the power of the light source, and can increase the propagation distance of the FSO communication system. Herein, we innovatively report evolution properties of the radial phased-locked partially coherent vortex (RPLPCV) beam array in non-Kolmogorov turbulence. The analytical expressions for the cross-spectral density and the average intensity of an RPLPCV beam array propagated through non-Kolmogorov turbulence are obtained. The numerical results reveal that the intensity distribution of the RPLPCV array propagated in the non-Kolmogorov turbulence is gradually converted to a standard Gaussian distribution. In addition, the larger the radial radius, radial number and waist radius are, the smaller the coherence length is. Moreover, the longer the wavelength is, the shorter the propagation distance required for the intensity distribution of the RPLPCV beam array to be converted into a Gaussian distribution in the non-Kolmogorov turbulence. The research in this paper provides a theoretical reference for the selection of light sources and the suppression of turbulence effects in wireless optical communication. Full article
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12 pages, 1931 KiB  
Review
Secure Continuous-Variable Quantum Key Distribution with Machine Learning
by Duan Huang, Susu Liu and Ling Zhang
Photonics 2021, 8(11), 511; https://doi.org/10.3390/photonics8110511 - 13 Nov 2021
Cited by 11 | Viewed by 2960
Abstract
Quantum key distribution (QKD) offers information-theoretical security, while real systems are thought not to promise practical security effectively. In the practical continuous-variable (CV) QKD system, the deviations between realistic devices and idealized models might introduce vulnerabilities for eavesdroppers and stressors for two parties. [...] Read more.
Quantum key distribution (QKD) offers information-theoretical security, while real systems are thought not to promise practical security effectively. In the practical continuous-variable (CV) QKD system, the deviations between realistic devices and idealized models might introduce vulnerabilities for eavesdroppers and stressors for two parties. However, the common quantum hacking strategies and countermeasures inevitably increase the complexity of practical CV systems. Machine-learning techniques are utilized to explore how to perceive practical imperfections. Here, we review recent works on secure CVQKD systems with machine learning, where the methods for detections and attacks were studied. Full article
(This article belongs to the Special Issue The Interplay between Photonics and Machine Learning)
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15 pages, 2217 KiB  
Article
Architecture and Performance Evaluation of a Novel Optical Packet Switch with Input Concentrators
by Hongzhen Yang, Xiuwei Mao, Zilu Fang, Wanke Chen, Ting Wang, Shuna Yang, Yuhu Zhao and Hao Chi
Photonics 2021, 8(11), 510; https://doi.org/10.3390/photonics8110510 - 12 Nov 2021
Cited by 2 | Viewed by 1672
Abstract
In this paper, we propose a novel optical packet switch (OPS) architecture with input concentrators, which employ multi-input single-output optical buffers to aggregate all the incoming traffic into a small size switching fabric. Accordingly, the physical size, the number of the needed wavelength [...] Read more.
In this paper, we propose a novel optical packet switch (OPS) architecture with input concentrators, which employ multi-input single-output optical buffers to aggregate all the incoming traffic into a small size switching fabric. Accordingly, the physical size, the number of the needed wavelength converters, and the economic cost of the total OPS node are decreased dramatically. However, the deployment of input concentrators introduces additional packet loss and delay, except from the contention at the switch output. A Markov model is presented to study the packet loss ratio (PLR) and average packet delay given by the input concentrators. The corresponding closed form expressions are given. The model also demonstrates that the system performance can be greatly improved by increasing the buffer size when the traffic load is not larger than 0.69315. The analytical values are compared with the simulation results. All the obtained results show that the proposed model provides satisfactory approximations under different network scenarios. Moreover, the economic cost savings of the proposed OPS node at the present time and its evolution as a function of time are also discussed in detail. The proposed architecture can also be applied in a packet enhanced optical transport network (OTN). Full article
(This article belongs to the Section Optical Communication and Network)
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20 pages, 11350 KiB  
Article
Simulation Study on the Effect of Doping Concentrations on the Photodetection Properties of Mg2Si/Si Heterojunction Photodetector
by Hong Yu, Chenggui Gao, Jiang Zou, Wensheng Yang and Quan Xie
Photonics 2021, 8(11), 509; https://doi.org/10.3390/photonics8110509 - 11 Nov 2021
Cited by 10 | Viewed by 2850
Abstract
To develop and design an environmentally friendly, low-cost shortwave infrared (SWIR) photodetector (PD) material and extend the optical response cutoff wavelengths of existing silicon photodetectors beyond 1100 nm, high-performance silicon-compatible Mg2Si/Si PDs are required. First, the structural model of the Mg [...] Read more.
To develop and design an environmentally friendly, low-cost shortwave infrared (SWIR) photodetector (PD) material and extend the optical response cutoff wavelengths of existing silicon photodetectors beyond 1100 nm, high-performance silicon-compatible Mg2Si/Si PDs are required. First, the structural model of the Mg2Si/Si heterojunction was established using the Silvaco Atlas module. Second, the effects of the doping concentrations of Mg2Si and Si on the photoelectric properties of the Mg2Si/Si heterojunction PD, including the energy band, breakdown voltage, dark current, forward conduction voltage, external quantum efficiency (EQE), responsivity, noise equivalent power (NEP), detectivity, on/off ratio, response time, and recovery time, were simulated. At different doping concentrations, the heterojunction energy band shifted, and a peak barrier appeared at the conduction band of the Mg2Si/Si heterojunction interface. When the doping concentrations of Si and Mg2Si layer were 1017, and 1016 cm−3, respectively, the Mg2Si/Si heterojunction PD could obtain optimal photoelectric properties. Under these conditions, the maximum EQE was 70.68% at 800 nm, the maximum responsivity was 0.51 A/W at 1000 nm, the minimum NEP was 7.07 × 10−11 WHz–1/2 at 1000 nm, the maximum detectivity was 1.4 × 1010 Jones at 1000 nm, and the maximum on/off ratio was 141.45 at 1000 nm. The simulation and optimization result also showed that the Mg2Si/Si heterojunction PD could be used for visible and SWIR photodetection in the wavelength range from 400 to 1500 nm. The results also provide technical support for the future preparation of eco-friendly heterojunction photodetectors. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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8 pages, 25123 KiB  
Article
Quantitative Phase Imaging to Study the Effect of Sodium Dodecyl Surfactant on Adherent L929 Fibroblasts on Tissue Culture Plates
by Sonthikan Sitthisang, Jeeranan Boonruangkan, Meng Fatt Leong, Kerm Sin Chian and Young-Jin Kim
Photonics 2021, 8(11), 508; https://doi.org/10.3390/photonics8110508 - 11 Nov 2021
Cited by 4 | Viewed by 1902
Abstract
Decellularization is the process of removing cellular components from native tissues or organs to obtain an acellular, collagenous scaffold for use in tissue engineering and organ regeneration. Surfactants are widely used to produce acellular scaffolds for clinical applications. However, cell–surfactants interactions have not [...] Read more.
Decellularization is the process of removing cellular components from native tissues or organs to obtain an acellular, collagenous scaffold for use in tissue engineering and organ regeneration. Surfactants are widely used to produce acellular scaffolds for clinical applications. However, cell–surfactants interactions have not been studied in depth. Cell-surfactant interaction was studied in a time-lapsed manner using sodium dodecyl sulfate (SDS) solution (surfactant) on adherent L929 fibroblasts as a test solution, phosphate-buffered saline (PBS) solution as control solution (isotonic), and deionized water as positive test solution (hypotonic), respectively. The QPI results show changes in the relative height and cross-sectional area of the cells, with various test solutions and exposure times. In particular, it was observed that the removal of the cell with SDS involved the disruption of the cellular membrane and detachment of the cell contents from the adhering surface. This study demonstrated the feasibility of using the QPI technique to understand the decellularization process. Full article
(This article belongs to the Section Biophotonics and Biomedical Optics)
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11 pages, 5816 KiB  
Article
Ultrafast High-Voltage Kicker System for Ion-Clearing Gaps
by Alexander Yu. Smirnov, Ronald Agustsson, Stephen V. Benson, Dmitry Gavryushkin, Jiquan Guo, Sergey V. Kutsaev, Adam Moro, Gunn Tae Park, Alexei V. Smirnov, Haipeng Wang and Shukui Zhang
Photonics 2021, 8(11), 507; https://doi.org/10.3390/photonics8110507 - 11 Nov 2021
Viewed by 2749
Abstract
Ionization scattering of electron beams with residual gas molecules causes ion trapping in electron rings, both in a collider and electron cooling system. These trapped ions may cause emittance growth, tune shift, halo formation, and coherent coupled bunch instabilities. In order to clear [...] Read more.
Ionization scattering of electron beams with residual gas molecules causes ion trapping in electron rings, both in a collider and electron cooling system. These trapped ions may cause emittance growth, tune shift, halo formation, and coherent coupled bunch instabilities. In order to clear the ions and prevent them from accumulating turn after turn, the gaps in a temporal structure of the beam are typically used. Typically, the gap in the bunch train has a length of a few percent of the ring circumference. In those regions, the extraction electrodes with high pulsed voltages are introduced. In this paper, we present the design consideration and initial test results of the high-voltage pulsed kicker hardware that includes vacuum device and pulsed voltage driver, capable of achieving over 3 kV of deflecting voltage amplitude, rise and fall times of less than 10 ns, 100 ns flat-top duration at 1.4 MHz repetition rate. Full article
(This article belongs to the Special Issue Advances and Application of Electron Beam Dynamics)
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8 pages, 3014 KiB  
Article
Simulated Study of High-Sensitivity Gas Sensor with a Metal-PhC Nanocavity via Tamm Plasmon Polaritons
by Liang Li and Haoyue Hao
Photonics 2021, 8(11), 506; https://doi.org/10.3390/photonics8110506 - 10 Nov 2021
Cited by 4 | Viewed by 1920
Abstract
An optical configuration was designed and simulated with a metal-photonic crystal (PhC) nanocavity, which had high sensitivity on gas detection. The simulated results shows that this configuration can generate a strong photonic localization through exciting Tamm plasmon polaritons. The strong photonic localization highly [...] Read more.
An optical configuration was designed and simulated with a metal-photonic crystal (PhC) nanocavity, which had high sensitivity on gas detection. The simulated results shows that this configuration can generate a strong photonic localization through exciting Tamm plasmon polaritons. The strong photonic localization highly increases the sensitivity of gas detection. Furthermore, this configuration can be tuned to sense gases at different conditions through an adjustment of the detection light wavelength, the period number of photonic crystal and the thickness of the gas cavity. The sensing routes to pressure variations of air were revealed. The simulation results showed that the detection precision of the proposed device for gas pressure could reach 0.0004 atm. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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13 pages, 2450 KiB  
Communication
Photocurrent Enhancement of PtSe2 Photodetectors by Using Au Nanorods
by Tatsuya Nakazawa, Donghyun Kim, Shinichi Kato, Jusang Park, Jwamin Nam and Hyungjun Kim
Photonics 2021, 8(11), 505; https://doi.org/10.3390/photonics8110505 - 10 Nov 2021
Cited by 7 | Viewed by 3054
Abstract
Compact and highly sensitive near-infrared photodetectors that are operable at room temperature are required for light detection and ranging and medical devices. Two-dimensional (2D) PtSe2, a transition metal dichalcogenide, is a candidate material for near-infrared light detection. However, the photoresponse properties [...] Read more.
Compact and highly sensitive near-infrared photodetectors that are operable at room temperature are required for light detection and ranging and medical devices. Two-dimensional (2D) PtSe2, a transition metal dichalcogenide, is a candidate material for near-infrared light detection. However, the photoresponse properties of 2D PtSe2 are currently inferior to those of commercial materials. The localized surface plasmon resonance of Au has been widely used for photoelectric field enhancement and in photochemical reactions associated with phase relaxation from plasmon states that occur at specific wavelengths. Spherical Au nanocolloids exhibit an extinction peak in the visible light region, whereas nanorods can be tuned to exhibit the extinction peak in the near-infrared region by controlling their aspect ratio. In this study, hybrid Au nanorod/2D PtSe2 structure was fabricated via spin coating nanorods, with plasmon peaks in the near-infrared region, on 2D PtSe2. Furthermore, the effect of the concentration of the nanorod solution on the photoresponse of nanorod/2D PtSe2 was investigated. The photocurrent of 5 nM Au nanorod-coated 2D PtSe2 was fivefold higher than that of bare 2D PtSe2. The responsivity was maximum 908 μW/A at 0.5 V bias voltage. In addition, the photocurrent enhancement mechanism by Au nanorods is discussed. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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11 pages, 4334 KiB  
Article
Usability of Tilted Plasmon Antenna with Structured Light
by Rafael Quintero-Torres, Jorge Luis Domínguez-Juárez, Mariia Shutova and Alexei V. Sokolov
Photonics 2021, 8(11), 504; https://doi.org/10.3390/photonics8110504 - 9 Nov 2021
Cited by 1 | Viewed by 1798
Abstract
We study the effect of oblique illumination on the functioning of a plasmonic nanoantenna for chiral light. The antenna is designed to receive a structured beam of light and produce a nanosized near-field distribution that possesses nonzero orbital angular momentum. The design consists [...] Read more.
We study the effect of oblique illumination on the functioning of a plasmonic nanoantenna for chiral light. The antenna is designed to receive a structured beam of light and produce a nanosized near-field distribution that possesses nonzero orbital angular momentum. The design consists of metal (gold) microrods laid on a dielectric surface and is compatible with well-developed nanofabrication techniques. Experimental arrangements often require such an antenna to operate in a tilted geometry, where input light is incident on the antenna at an oblique angle. We analyze the limitations that the angled illumination imposes and discuss approaches to mitigate these limitations. Through our numerical simulations, we find that tilt angles require modifications to the antenna design. Our analysis can guide current and future experimental configurations to push the limits of resolution and sensitivity. Full article
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13 pages, 2337 KiB  
Article
Multi-mJ Scaling of 5-Optical Cycle, 3 µm OPCPA
by Joana Alves, Hugo Pires, Celso P. João and Gonçalo Figueira
Photonics 2021, 8(11), 503; https://doi.org/10.3390/photonics8110503 - 9 Nov 2021
Cited by 2 | Viewed by 2470
Abstract
We present the design of an ultrafast optical parametric chirped pulse amplifier (OPCPA) operating at 3 µm yielding few-cycle pulses and multi-mJ output energy. This design demonstrates that with a configuration of a single crystal or combination of crystals (KTA and MgO:LN) it [...] Read more.
We present the design of an ultrafast optical parametric chirped pulse amplifier (OPCPA) operating at 3 µm yielding few-cycle pulses and multi-mJ output energy. This design demonstrates that with a configuration of a single crystal or combination of crystals (KTA and MgO:LN) it is possible to achieve output energies above the mJ with sufficient bandwidth to allow compression to just 5-optical cycles. Here, we consider a 1 µm mJ-level picosecond chirped pulse amplifier (CPA), a typical pumping source for this type of non-linear amplifiers. Compression with a simple bulk material enables reaching close to the pulse Fourier-transform limited duration, paving the way to high energy, ultrafast mid-infrared pulses. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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16 pages, 814 KiB  
Article
Optimization of Network Coding Resources Based on Improved Quantum Genetic Algorithm
by Tianyang Liu, Qiang Sun, Huachun Zhou and Qi Wei
Photonics 2021, 8(11), 502; https://doi.org/10.3390/photonics8110502 - 8 Nov 2021
Cited by 2 | Viewed by 1643
Abstract
The problem of network coding resource optimization with a known topological structure is NP-hard. Traditional quantum genetic algorithms have the disadvantages of slow convergence and difficulty in finding the optimal solution when dealing with this problem. To overcome these disadvantages, this paper proposes [...] Read more.
The problem of network coding resource optimization with a known topological structure is NP-hard. Traditional quantum genetic algorithms have the disadvantages of slow convergence and difficulty in finding the optimal solution when dealing with this problem. To overcome these disadvantages, this paper proposes an adaptive quantum genetic algorithm based on the cooperative mutation of gene number and fitness (GNF-QGA). This GNF-QGA adopts the rotation angle adaptive adjustment mechanism. To avoid excessive illegal individuals, an illegal solution adjustment mechanism is added to the GNF-QGA. A solid demonstration was provided that the proposed algorithm has a fast convergence speed and good optimization capability when solving network coding resource optimization problems. Full article
(This article belongs to the Section Optical Communication and Network)
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8 pages, 2656 KiB  
Communication
Generation of Switchable Chirp Waveforms in the Photonic Domain with Immunity to Dispersion-Induced Power Fading
by Chaoqun Huang, Jun Ou and Hao Chi
Photonics 2021, 8(11), 501; https://doi.org/10.3390/photonics8110501 - 8 Nov 2021
Cited by 1 | Viewed by 1923
Abstract
A novel photonic approach to generating switchable multi-format chirp waveforms using a dual-drive dual-parallel Mach–Zehnder modulator (DD-DPMZM) is proposed and experimentally demonstrated. By properly controlling the bias voltage on the DD-DPMZM, different chirp RF waveforms, including the dual-, down-, and up-chirp waveforms, can [...] Read more.
A novel photonic approach to generating switchable multi-format chirp waveforms using a dual-drive dual-parallel Mach–Zehnder modulator (DD-DPMZM) is proposed and experimentally demonstrated. By properly controlling the bias voltage on the DD-DPMZM, different chirp RF waveforms, including the dual-, down-, and up-chirp waveforms, can be obtained when an RF signal and a chirp RF signal are injected into the modulator. A main feature of this approach is that it can eliminate chromatic dispersion-induced RF power fading, which is highly desired in distributed multi-functional radars based on radio over fiber. There is no polarization control and optical filtering in the given scheme, which also improves the stability and feasibility of the approach. An experiment successfully demonstrated the generation and switching of the multi-format chirp waveforms and the capability of immunity to dispersion-induced power fading. Full article
(This article belongs to the Section New Applications Enabled by Photonics Technologies and Systems)
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10 pages, 2440 KiB  
Communication
High Speed Visible Light Communication Using Digital Power Domain Multiplexing of Orthogonal Frequency Division Multiplexed (OFDM) Signals
by Wahyu-Hendra Gunawan, Yang Liu, Chi-Wai Chow, Yun-Han Chang and Chien-Hung Yeh
Photonics 2021, 8(11), 500; https://doi.org/10.3390/photonics8110500 - 8 Nov 2021
Cited by 10 | Viewed by 2644
Abstract
In order to increase transmission capacity, multiplexing schemes in different physical dimensions, including time, frequency, modulation quadrature, polarization, and space, can be employed. In this work, we propose and demonstrate a red color laser-diode (LD) based visible-light-communication (VLC) system using two kinds of [...] Read more.
In order to increase transmission capacity, multiplexing schemes in different physical dimensions, including time, frequency, modulation quadrature, polarization, and space, can be employed. In this work, we propose and demonstrate a red color laser-diode (LD) based visible-light-communication (VLC) system using two kinds of digital domain multiplexing schemes, orthogonal-frequency-division-multiplexing (OFDM) and power-domain division-multiplexing (PowDM). The two digital domain multiplexed data can achieve data rates of 1.66 Gbit/s and 6.41 Gbit/s, respectively, providing a total data rate of 8.07 Gbit/s, fulfilling the pre-forward error correction (pre-FEC) bit-error-rate (BER) limit. The measured signal-to-noise ratios (SNRs) are 10.96 dB and 14.45 dB, respectively. Here, similar to OFDM, the PowDM can enhance the total system capacity by allowing acceptable signal spectra overlapping among different power division signals to maximize the bandwidth utilization. An experiment to verify and evaluate the proposed work is performed. The modulation and demodulation of OFDM and PowDM are discussed. The optimum power levels of the individual signals in the PowDM signal are also analyzed. Full article
(This article belongs to the Special Issue Optical Wireless Communication (OWC) Systems)
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12 pages, 2044 KiB  
Communication
Wide Area Uniform Illumination Scheme Using LED Matrix for Optogenetic Cardiac Pacing
by Ida Izadi, Vanessa Dusend, Abdulaziz Takrouni, Noreen Nudds, Kamil Gradkowski, Peter O’Brien, Philipp Sasse and Brian Corbett
Photonics 2021, 8(11), 499; https://doi.org/10.3390/photonics8110499 - 8 Nov 2021
Cited by 2 | Viewed by 2443
Abstract
Control of heart rhythm is vital in the case of arrhythmia. Cardiac optogenetics is a promising technique to replace electrical stimulation in a next generation of pacemakers and defibrillators. Therefore, further research towards optimizing light delivery methods is essential. A major requirement is [...] Read more.
Control of heart rhythm is vital in the case of arrhythmia. Cardiac optogenetics is a promising technique to replace electrical stimulation in a next generation of pacemakers and defibrillators. Therefore, further research towards optimizing light delivery methods is essential. A major requirement is the uniform stimulation of all cells in the area of interest while reducing side effects such as photodamage. Here, a 2 × 2 blue (470 nm, InGaN-based) light-emitting diode (LED) optoelectronic module for uniform ex vivo cardiac muscle illumination is demonstrated. It satisfies two important requirements in optogenetics, which are high illumination homogeneity and high irradiance. CCD camera images show an average 90% homogeneity over the central illumination area of close to 38 mm2 at 1 cm distance from the light source. The module is used to perform physiological experiments on channelrhodopsin 2-expressing Langendorff-perfused mouse hearts. Successful ventricular pacing is obtained for an optical power density threshold below 2 mW/mm2 with light pulses as short as 1 ms. For 10 ms long pulses, the threshold was below 0.2 mW/mm2. The large homogeneous illumination area enabled optogenetic pacing with less than half the optical power of previous attempts with smaller areas of 2 mm2 and thus, presumably, will result in less phototoxicity. Full article
(This article belongs to the Section Biophotonics and Biomedical Optics)
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17 pages, 331 KiB  
Review
Role of Pascalization in Milk Processing and Preservation: A Potential Alternative towards Sustainable Food Processing
by Muhmmad Farhan Jahangir Chughtai, Muhammad Adil Farooq, Syeda Aiman Ashfaq, Sonia Khan, Adnan Khaliq, Sergey Antipov, Maksim Rebezov, Mars Khayrullin, Alla Vorobeva, Elena Nelyubina, Muthu Thiruvengadam and Mohammad Ali Shariati
Photonics 2021, 8(11), 498; https://doi.org/10.3390/photonics8110498 - 8 Nov 2021
Cited by 9 | Viewed by 4257
Abstract
Renewed technology has created a demand for foods which are natural in taste, minimally processed, and safe for consumption. Although thermal processing, such as pasteurization and sterilization, effectively limits pathogenic bacteria, it alters the aroma, flavor, and structural properties of milk and milk [...] Read more.
Renewed technology has created a demand for foods which are natural in taste, minimally processed, and safe for consumption. Although thermal processing, such as pasteurization and sterilization, effectively limits pathogenic bacteria, it alters the aroma, flavor, and structural properties of milk and milk products. Nonthermal technologies have been used as an alternative to traditional thermal processing technology and have the ability to provide safe and healthy dairy products without affecting their nutritional composition and organoleptic properties. Other than nonthermal technologies, infrared spectroscopy is a nondestructive technique and may also be used for predicting the shelf life and microbial loads in milk. This review explains the role of pascalization or nonthermal techniques such as high-pressure processing (HPP), pulsed electric field (PEF), ultrasound (US), ultraviolet (UV), cold plasma treatment, membrane filtration, micro fluidization, and infrared spectroscopy in milk processing and preservation. Full article
(This article belongs to the Special Issue Driving Spectroscopy and Laser Physics toward Biological, Agricultural, and Medical Applications)
18 pages, 5259 KiB  
Review
Chalcogenide Glass Microfibers for Mid-Infrared Optics
by Dawei Cai, Yu Xie, Xin Guo, Pan Wang and Limin Tong
Photonics 2021, 8(11), 497; https://doi.org/10.3390/photonics8110497 - 5 Nov 2021
Cited by 11 | Viewed by 3374
Abstract
With diameters close to the wavelength of the guided light, optical microfibers (MFs) can guide light with tight optical confinement, strong evanescent fields and manageable waveguide dispersion and have been widely investigated in the past decades for a variety of applications. Compared to [...] Read more.
With diameters close to the wavelength of the guided light, optical microfibers (MFs) can guide light with tight optical confinement, strong evanescent fields and manageable waveguide dispersion and have been widely investigated in the past decades for a variety of applications. Compared to silica MFs, which are ideal for working in visible and near-infrared regions, chalcogenide glass (ChG) MFs are promising for mid-infrared (mid-IR) optics, owing to their easy fabrication, broad-band transparency and high nonlinearity, and have been attracting increasing attention in applications ranging from near-field coupling and molecular sensing to nonlinear optics. Here, we review this emerging field, mainly based on its progress in the last decade. Starting from the high-temperature taper drawing technique for MF fabrication, we introduce basic mid-IR waveguiding properties of typical ChG MFs made of As2S3 and As2Se3. Then, we focus on ChG-MF-based passive optical devices, including optical couplers, resonators and gratings and active and nonlinear applications of ChG MFs for mid-IR Raman lasers, frequency combs and supercontinuum (SC) generation. MF-based spectroscopy and chemical/biological sensors are also introduced. Finally, we conclude the review with a brief summary and an outlook on future challenges and opportunities of ChG MFs. Full article
(This article belongs to the Special Issue Novel Specialty Optical Fibers and Applications)
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14 pages, 727 KiB  
Article
Thermo-Optic Phase Tuners Analysis and Design for Process Modules on a Silicon Nitride Platform
by Rubén Alemany, Pascual Muñoz, Daniel Pastor and Carlos Domínguez
Photonics 2021, 8(11), 496; https://doi.org/10.3390/photonics8110496 - 5 Nov 2021
Cited by 10 | Viewed by 3161
Abstract
In this paper, we present a systematic design for manufacturing analysis for thermo-optic phase tuners, framed within the process modules available on a silicon nitride platform. Departing from an established technology platform, the heat distribution in various micro-structures was analyzed, both in steady [...] Read more.
In this paper, we present a systematic design for manufacturing analysis for thermo-optic phase tuners, framed within the process modules available on a silicon nitride platform. Departing from an established technology platform, the heat distribution in various micro-structures was analyzed, both in steady and transient states, employing a 2D heat transfer model solved numerically. Multi-parametric simulations were performed on designs combining trenches and substrate undercut, by varying their position and dimensions. The simulation results were compared to a reference conventional fully-clad cross-section. Deep air-filled trenches are shown to reduce the power consumption up to 70%, alongside a thermal crosstalk phase shift reduction of more than one order of magnitude (0.045 π rad/mm), at the expense of a slightly lower bandwidth (11.8 kHz). The design with trenches and substrate undercut lowers the power consumption up to 97%, decreases two orders of magnitude the crosstalk (0.006 π rad/mm), at the cost of less than one order of magnitude in bandwidth (0.9 kHz). In the works, we selected three different heater materials (Cr/Au, Al, poly-silicon) offered by the fab and four different heater widths (2.5 to 7 μm). Their combinations are related to performance, reliability and durability of the devices, strongly linked to temperature, current density, and Omegaic resistance. The different figures of merit defined, and the methodology followed, can be mimicked by future designers to take design decisions at bird’s eye. Full article
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11 pages, 1451 KiB  
Communication
Efficacy of Photodynamic Inactivation against the Major Human Antibiotic-Resistant Uropathogens
by Nadezhda Ignatova, Tatiana Ivanova, Artem Antonyan, Ivan Budruev, Olga Streltsova, Vadim Elagin and Vladislav Kamensky
Photonics 2021, 8(11), 495; https://doi.org/10.3390/photonics8110495 - 5 Nov 2021
Cited by 6 | Viewed by 2035
Abstract
Photodynamic inactivation (PDI) is considered to be an effective method of prevention of postoperative complications of urolithiasis. The present study shows a complex approach to assess the efficacy of PDI of drug resistant bacteria associated with renal calculi. Bacterial strains associated with renal [...] Read more.
Photodynamic inactivation (PDI) is considered to be an effective method of prevention of postoperative complications of urolithiasis. The present study shows a complex approach to assess the efficacy of PDI of drug resistant bacteria associated with renal calculi. Bacterial strains associated with renal calculi were isolated and identified using standard methods of bacteriological analysis and tested for drug resistance to 10 antibiotics by the disco-diffusion method. Uropathogenic bacterial strains present in 78.7 ± 5.2% of the infected samples from the total number of analyzed calculi. The most frequent representatives belonged to the genera Staphylococcus, Escherichia, and Enterococcus. All tested strains showed high antibiotic resistance. Representatives of the most common bacterial genera in the calculi were used as models for the selection of PD exposure modes. It was found that the maximum time of photosensitizer accumulation depends on the structure of the bacterial cell wall: 30 min for Gram-negative strains and 60 min for Gram-positive ones. Optimal modes of PD exposure to antibiotic-resistant uropathogenic microorganisms were selected: 50 µg/mL Fotoditazin and 150 mW laser power. The maximal bactericidal activity of PDI against uropathogenic microorganisms was shown for Enterococcus faecalis, and Staphylococcus aureus. The bacteriostatic effect was found against Escherichia coli and Proteus mirabilis. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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14 pages, 3679 KiB  
Article
Determination of Main Spectral and Luminescent Characteristics of Winter Wheat Seeds Infected with Pathogenic Microflora
by Alexey M. Bashilov, Igor Yu. Efremenkov, Mikhail V. Belyakov, Alexander V. Lavrov, Anatoly A. Gulyaev, Stanislav A. Gerasimenko, Sergei I. Borzenko and Andrey A. Boyko
Photonics 2021, 8(11), 494; https://doi.org/10.3390/photonics8110494 - 4 Nov 2021
Cited by 9 | Viewed by 2054
Abstract
In connection with the constant growth of demand for high-quality food products, there is a need to develop effective methods for storing agricultural products, and the registration and predicting infection in the early stages. The studying of the physical properties of infected plants [...] Read more.
In connection with the constant growth of demand for high-quality food products, there is a need to develop effective methods for storing agricultural products, and the registration and predicting infection in the early stages. The studying of the physical properties of infected plants and seeds has fundamental importance for determining crop losses, conducting a survey of diseases, and assessing the effectiveness of their control (assessment of the resistance of crops and varieties, the effect of fungicides, etc.). Presently, photoluminescent methods for diagnosing seeds in the ultraviolet and visible ranges have not been studied. For research, seeds of winter wheat were selected, and were infected with one of the most common and dangerous diseases for plants—fusarium. The research of luminescence was carried out based on a hardware–software complex consisting of a multifunctional spectrofluorometer “Fluorat-02-Panorama”, a computer with software “Panorama Pro” installed, and an external camera for the samples under study. Spectra were obtained with a diagnostic range of winter wheat seeds of 220–400 nm. Based on the results obtained for winter wheat seeds, it is possible to further develop a method for determining the degree of fusarium infection. Full article
(This article belongs to the Special Issue Driving Spectroscopy and Laser Physics toward Biological, Agricultural, and Medical Applications)
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8 pages, 2730 KiB  
Communication
In-Situ Depth Measurement of Laser Micromachining
by Xiaoming Chen, Ying Xu, Nan-Kuang Chen, Shannon Shy and Hsiang-Chen Chui
Photonics 2021, 8(11), 493; https://doi.org/10.3390/photonics8110493 - 4 Nov 2021
Cited by 7 | Viewed by 2509
Abstract
Precision laser micromachining plays an important role in the biomedical, electronics, and material processing industries. During laser drilling, precision depth detection with micrometer-level resolution is required, particularly with blind-hole or heterogeneous structures. We present an optical detection system utilizing an optical confocal structure, [...] Read more.
Precision laser micromachining plays an important role in the biomedical, electronics, and material processing industries. During laser drilling, precision depth detection with micrometer-level resolution is required, particularly with blind-hole or heterogeneous structures. We present an optical detection system utilizing an optical confocal structure, experimentally confirmed to achieve a >95% accuracy for micron-diameter holes that are tens-of-microns deep. This system can be easily integrated into commercial laser micromachining processes, and can be employed in laser drilling and three-dimensional active-feedback laser printing. Full article
(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)
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