Subjects -> PHYSICS (Total: 857 journals)
    - MECHANICS (22 journals)
    - NUCLEAR PHYSICS (53 journals)
    - OPTICS (92 journals)
    - PHYSICS (625 journals)
    - SOUND (25 journals)
    - THERMODYNAMICS (30 journals)

OPTICS (92 journals)

Showing 1 - 91 of 91 Journals sorted alphabetically
ACS Photonics     Hybrid Journal   (Followers: 16)
Advanced Optical Materials     Hybrid Journal   (Followers: 11)
Advanced Photonics     Open Access   (Followers: 3)
Advanced Photonics Research     Open Access   (Followers: 2)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 24)
Advances in Nonlinear Optics     Open Access   (Followers: 9)
Advances in Optical Technologies     Open Access   (Followers: 3)
Advances in Optics     Open Access   (Followers: 11)
Advances in Optics and Photonics     Full-text available via subscription   (Followers: 17)
Annual Review of Vision Science     Full-text available via subscription   (Followers: 4)
APL : Organic Electronics and Photonics     Hybrid Journal   (Followers: 3)
Applied Optics     Hybrid Journal   (Followers: 48)
Applied Physics B: Lasers and Optics     Hybrid Journal   (Followers: 34)
Atmospheric and Oceanic Optics     Hybrid Journal   (Followers: 8)
Biomedical Optics Express     Open Access   (Followers: 6)
Biomedical Photonics     Open Access  
Chinese Optics Letters     Full-text available via subscription   (Followers: 8)
EPJ Photovoltaics     Open Access   (Followers: 2)
European Journal of Hybrid Imaging     Open Access  
Fiber and Integrated Optics     Hybrid Journal   (Followers: 21)
Frontiers of Optoelectronics     Hybrid Journal   (Followers: 3)
High Power Laser Science and Engineering     Open Access   (Followers: 4)
Hindsight : The Journal of Optometry History     Open Access   (Followers: 1)
IEEE Photonics Journal     Open Access   (Followers: 17)
IEEE Photonics Technology Letters     Hybrid Journal   (Followers: 14)
International Journal of Optics     Open Access   (Followers: 14)
International Journal of Optics and Applications     Open Access   (Followers: 7)
International Journal of Optoelectronic Engineering     Open Access   (Followers: 1)
International Journal of Spectroscopy     Open Access   (Followers: 6)
International Journal of Sustainable Lighting     Open Access  
Journal of Astronomical Telescopes, Instruments, and Systems     Hybrid Journal   (Followers: 6)
Journal of Atomic, Molecular, and Optical Physics     Open Access   (Followers: 13)
Journal of Biomedical Photonics & Engineering     Open Access  
Journal of Laser Applications     Full-text available via subscription   (Followers: 14)
Journal of Mass Spectrometry and Advances in the Clinical Lab     Open Access  
Journal of Modern Optics     Hybrid Journal   (Followers: 12)
Journal of Nanoelectronics and Optoelectronics     Full-text available via subscription   (Followers: 1)
Journal of Nonlinear Optical Physics & Materials     Hybrid Journal   (Followers: 2)
Journal of Optical Microsystem     Hybrid Journal   (Followers: 1)
Journal of Optical Technology     Full-text available via subscription   (Followers: 4)
Journal of Optics     Hybrid Journal   (Followers: 14)
Journal of Optics Applications     Open Access   (Followers: 14)
Journal of Optoelectronics Engineering     Open Access   (Followers: 5)
Journal of Photonics     Open Access   (Followers: 5)
Journal of Photonics for Energy     Hybrid Journal   (Followers: 2)
Journal of Physics B: Atomic, Molecular and Optical Physics     Hybrid Journal   (Followers: 32)
Journal of the Optical Society of America A     Hybrid Journal   (Followers: 11)
Journal of the Optical Society of America B     Hybrid Journal   (Followers: 12)
Journal of the Optical Society of Korea     Open Access   (Followers: 2)
Laser & Photonics Reviews     Hybrid Journal   (Followers: 5)
Laser Physics     Hybrid Journal   (Followers: 2)
Lasers in Medical Science     Hybrid Journal   (Followers: 2)
LEUKOS : The Journal of the Illuminating Engineering Society     Hybrid Journal  
Materials Today Electronics     Open Access   (Followers: 2)
Microwave and Optical Technology Letters     Hybrid Journal   (Followers: 11)
Nature Photonics     Full-text available via subscription   (Followers: 37)
Ophthalmic and Physiological Optics     Hybrid Journal   (Followers: 4)
Optica     Open Access   (Followers: 6)
Optical and Quantum Electronics     Hybrid Journal   (Followers: 3)
Optical Engineering     Hybrid Journal   (Followers: 22)
Optical Fiber Technology     Hybrid Journal   (Followers: 8)
Optical Materials     Hybrid Journal   (Followers: 10)
Optical Materials : X     Open Access  
Optical Materials Express     Open Access   (Followers: 7)
Optical Memory and Neural Networks     Hybrid Journal   (Followers: 2)
Optical Nanoscopy     Open Access   (Followers: 1)
Optical Review     Hybrid Journal   (Followers: 2)
Optics & Laser Technology     Hybrid Journal   (Followers: 26)
Optics and Lasers in Engineering     Hybrid Journal   (Followers: 37)
Optics and Photonics Journal     Open Access   (Followers: 18)
Optics and Photonics Letters     Open Access   (Followers: 11)
Optics and Photonics News     Partially Free   (Followers: 7)
Optics and Spectroscopy     Hybrid Journal   (Followers: 8)
Optics Communications     Hybrid Journal   (Followers: 17)
Optics Express     Open Access   (Followers: 23)
Optics Letters     Hybrid Journal   (Followers: 19)
Optik     Hybrid Journal   (Followers: 9)
Optik & Photonik     Open Access  
Optoelectronics Letters     Hybrid Journal   (Followers: 1)
Photochem     Open Access  
Photonic Sensors     Open Access   (Followers: 8)
Photonics     Open Access   (Followers: 4)
Photonics Letters of Poland     Open Access  
Photonics Research     Open Access   (Followers: 2)
PhotonicsViews     Hybrid Journal  
Progress in Optics     Full-text available via subscription   (Followers: 6)
Results in Optics     Open Access   (Followers: 3)
SIAM Journal on Imaging Sciences     Hybrid Journal   (Followers: 7)
Thin Solid Films     Hybrid Journal   (Followers: 11)
Trends in Opto-Electro & Optical Communications     Full-text available via subscription   (Followers: 1)
Virtual Journal for Biomedical Optics     Hybrid Journal   (Followers: 1)
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Journal Cover
Journal Prestige (SJR): 0.709
Citation Impact (citeScore): 2
Number of Followers: 4  

  This is an Open Access Journal Open Access journal
ISSN (Online) 2304-6732
Published by MDPI Homepage  [258 journals]
  • Photonics, Vol. 10, Pages 234: Automatic Choroid Vascularity Index
           Calculation in Optical Coherence Tomography Images with Low-Contrast
           Sclerochoroidal Junction Using Deep Learning

    • Authors: Roya Arian, Tahereh Mahmoudi, Hamid Riazi-Esfahani, Hooshang Faghihi, Ahmad Mirshahi, Fariba Ghassemi, Alireza Khodabande, Raheleh Kafieh, Elias Khalili Khalili Pour
      First page: 234
      Abstract: The choroidal vascularity index (CVI) is a new biomarker defined for retinal optical coherence tomography (OCT) images for measuring and evaluating the choroidal vascular structure. The CVI is the ratio of the choroidal luminal area (LA) to the total choroidal area (TCA). The automatic calculation of this index is important for ophthalmologists but has not yet been explored. In this study, we proposed a fully automated method based on deep learning for calculating the CVI in three main steps: 1—segmentation of the choroidal boundary, 2—detection of the choroidal luminal vessels, and 3—computation of the CVI. The proposed method was evaluated in complex situations such as the presence of diabetic retinopathy and pachychoroid spectrum. In pachychoroid spectrum, the choroid is thickened, and the boundary between the choroid and sclera (sclerochoroidal junction) is blurred, which makes the segmentation more challenging. The proposed method was designed based on the U-Net model, and a new loss function was proposed to overcome the segmentation problems. The vascular LA was then calculated using Niblack’s local thresholding method, and the CVI value was finally computed. The experimental results for the segmentation stage with the best-performing model and the proposed loss function used showed Dice coefficients of 0.941 and 0.936 in diabetic retinopathy and pachychoroid spectrum patients, respectively. The unsigned boundary localization errors in the presence of diabetic retinopathy were 3 and 20.7 μm for the BM boundary and sclerochoroidal junction, respectively. Similarly, the unsigned errors in the presence of pachychoroid spectrum were 21.6 and 76.2 μm for the BM and sclerochoroidal junction, respectively. The performance of the proposed method to calculate the CVI was evaluated; the Bland–Altman plot indicated an acceptable agreement between the values allocated by experts and the proposed method in the presence of diabetic retinopathy and pachychoroid spectrum.
      Citation: Photonics
      PubDate: 2023-02-21
      DOI: 10.3390/photonics10030234
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 235: Two-State Lasing in Microdisk Laser Diodes
           with Quantum Dot Active Region

    • Authors: Ivan Makhov, Konstantin Ivanov, Eduard Moiseev, Anna Dragunova, Nikita Fominykh, Yuri Shernyakov, Mikhail Maximov, Natalia Kryzhanovskaya, Alexey Zhukov
      First page: 235
      Abstract: The two-state lasing phenomenon, which manifests itself in simultaneous laser emission through several optical transitions of quantum dots, is studied in microdisk diode lasers with different cavity diameters. The active region represents a multiply stacked array of self-organized InAs/InGaAs/GaAs quantum dots emitting in the wavelength range of 1.1–1.3 µm. Two-state lasing, which involves the ground-state and the first excited-state optical transitions, is observed in microdisks with cavity diameters of 20 to 28 µm, whereas two-state lasing via the first and the second excited-state optical transitions is observed in 9 µm microdisks. The threshold currents for one-state and two-state lasing are investigated as functions of the microdisk diameter. Optical loss in the microdisk lasers is evaluated by comparing the two-state lasing behavior of the microdisks with that of edge-emitting stripe lasers made of the same epitaxial wafer.
      Citation: Photonics
      PubDate: 2023-02-21
      DOI: 10.3390/photonics10030235
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 236: Handwritten Digits Recognition Based on a
           Parallel Optoelectronic Time-Delay Reservoir Computing System

    • Authors: Dianzuo Yue, Yushuang Hou, Chunxia Hu, Cunru Zang, Yingzhe Kou
      First page: 236
      Abstract: In this work, the performance of an optoelectronic time-delay reservoir computing system for performing a handwritten digit recognition task is numerically investigated, and a scheme to improve the recognition speed using multiple parallel reservoirs is proposed. By comparing four image injection methods based on a single time-delay reservoir, we find that when injecting the histograms of oriented gradient (HOG) features of the digit image, the accuracy rate (AR) is relatively high and is less affected by the offset phase. To improve the recognition speed, we construct a parallel time-delay reservoir system including multi-reservoirs, where each reservoir processes part of the HOG features of one image. Based on 6 parallel reservoirs with each reservoir possessing 100 virtual nodes, the AR can reach about 97.8%, and the reservoir processing speed can reach about 1 × 106 digits per second. Meanwhile, the parallel reservoir system shows strong robustness to the parameter mismatch between multi-reservoirs.
      Citation: Photonics
      PubDate: 2023-02-22
      DOI: 10.3390/photonics10030236
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 237: Vortical Differential Scattering of Twisted
           Light by Dielectric Chiral Particles

    • Authors: Ju Wang, Zhiwei Cui, Yiyu Shi, Shenyan Guo, Fuping Wu
      First page: 237
      Abstract: Twisted light carrying orbital angular momentum inherently possesses a handedness, which would produce chiroptical responses by chiral matter. In this work, a scheme of vortical differential scattering (VDS) was utilized to investigate the chiroptical responses of dielectric chiral particles to the twisted light. The simulation results showed that the dielectric chiral particles have obvious VDS signals under the illumination of twisted light with opposite topological charges. The larger the relative chiral parameter of the particles, the more obvious the VDS signals. The extreme value of the VDS signals can be enhanced by reducing the waist radius of the twisted light or by adopting the circularly polarized twisted light. In addition, non-spherical dielectric chiral particles exhibit more obvious VDS signals compared with spherical ones. These findings are expected to find potential applications in the detection and identification of chiral substances.
      Citation: Photonics
      PubDate: 2023-02-22
      DOI: 10.3390/photonics10030237
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 238: High-Power Supersymmetric Semiconductor
           Laser with a Narrow Linewidth

    • Authors: Yuanbo Xu, Ting Fu, Jian Fan, Wenzhen Liu, Hongwei Qu, Mingjin Wang, Wanhua Zheng
      First page: 238
      Abstract: We have designed and fabricated a kind of supersymmetric slotted Fabry–Perot semiconductor laser near 1550 nm to achieve a single-mode, high-power, and narrow-linewidth operation. The structure of the laser is composed of an electrically pumped broad ridge waveguide in the middle to provide optical gain, a group of periodic slots etched near the front facet to suppress the extra longitudinal modes and achieve a narrow linewidth, and a pair of passive superpartner waveguides located on both sides to filter out the high-order lateral modes in the broad waveguide. The device measured under the temperature of 25 °C shows an output power of 113 mW, a single-lobe lateral far-field distribution with the full width at half maximum of 7.8°, a peak wavelength of 1559.7 nm with the side-mode suppression ratio of 48.5 dB, and an intrinsic linewidth of 230 kHz at the bias current of 800 mA. The device is a promising candidate for cost-effective light sources for coherent communication systems and LiDARs.
      Citation: Photonics
      PubDate: 2023-02-22
      DOI: 10.3390/photonics10030238
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 239: Towards Microbial Food Safety of Sprouts:
           Photodynamic Decontamination of Seeds

    • Authors: Andreas Fellner, Christoph Hamminger, Michael Fefer, Jun Liu, Kristjan Plaetzer
      First page: 239
      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 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.
      Citation: Photonics
      PubDate: 2023-02-22
      DOI: 10.3390/photonics10030239
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 240: Application of the Improved Grinding
           Technology to Freeform Surface Manufacturing

    • Authors: Lirong Peng, Xingchang Li, Lingzhong Li, Qiang Cheng, Xiao Luo, Xiaoqin Zhou, Xuejun Zhang
      First page: 240
      Abstract: In order to meet the manufacturing requirements of modern space remote sensors for high-precision freeform optical parts, the grinding technology and its application were studied. The objective of this paper was to improve the application effect of traditional grinding technology in the processing of hard and brittle materials, and then apply it in specific fields. Therefore, the influence of key process factors such as cutting speed and removal depth on subsurface damage (SSD) was studied based on orthogonal experiments, and an improved grinding technology characterized by low SSD and high surface shape accuracy was formed. Then, the effect of this grinding technology was further verified by the high-precision manufacturing of freeform surfaces. A surface of a 130 mm diameter freeform surface was machined by improved grinding technology and combined polishing technology, the final root mean square of surface shape reached 12.1 nm. The improved grinding technology can reduce SSD from 20 μm to 10 μm, and improve the manufacturing efficiency of freeform surfaces above 30% when the cut speed is 20 m/s and the remove depth is 10 μm. The proposed technology can be applied to the extreme manufacturing of hard and brittle materials.
      Citation: Photonics
      PubDate: 2023-02-22
      DOI: 10.3390/photonics10030240
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 241: Effect of a Novel Handheld
           Photobiomodulation Therapy Device in the Management of Chemoradiation
           Therapy-Induced Oral Mucositis in Head and Neck Cancer Patients: A Case
           Series Study

    • Authors: In-Young Jo, Hyung-Kwon Byeon, Myung-Jin Ban, Jae-Hong Park, Sang-Cheol Lee, Young-Kyun Won, Yun-Su Eun, Jae-Yun Kim, Na-Gyeong Yang, Sul-Hee Lee, Pyeongan Lee, Nam-Hun Heo, Sujin Jo, Hoonhee Seo, Sukyung Kim, Ho-Yeon Song, Jung-Eun Kim
      First page: 241
      Abstract: Oral mucositis (OM) is a debilitating adverse event in patients undergoing treatment for cancer. This study aimed to evaluate the therapeutic effect of a novel handheld photobiomodulation therapy (PBMT) device on chemoradiation therapy (CRT)-induced OM in patients with head and neck cancer. Head and neck cancer patients undergoing CRT who developed moderate-to-severe OM during treatment were enrolled. After PBMT and at 2 and 4 weeks after PBMT, the mean value of OM grade decreased significantly from 2.63 to 2.13, 1.31, and 0.75, respectively (p < 0.05, p < 0.001, and p < 0.001). Moreover, we observed significant improvement in health-related quality of life (HRQoL) after PBMT compared to baseline through a validated questionnaire; EORTC QLQ-C30. In the present study, the use of this PBMT device in the management of CRT-induced OM in patients with head and neck cancer was generally well tolerated and resulted in the improvement of OM. However, evidence supporting its use remains lacking owing to limitations such as the small number of participants and lack of a control group. Therefore, further mechanistic studies and large-scale randomized controlled trials are needed to confirm the effectiveness of PBMT in the treatment of CRT-induced OM, as shown in our results.
      Citation: Photonics
      PubDate: 2023-02-22
      DOI: 10.3390/photonics10030241
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 242: Study on the Technology and Mechanism of
           Cleaning Architectural Aluminum Formwork for Concrete Pouring by High
           Energy and High Repetition Frequency Pulsed Laser

    • Authors: Gao, Xu, Zhu, Zhang, Zeng
      First page: 242
      Abstract: In the field of construction, the surface of architectural aluminum formwork for concrete pouring will remain the concrete adhesion layer of heterogeneous composite structures. In view of the difficulty of removing the concrete adhesion layer, we studied the technology and mechanism of removing the concrete adhesion layer by laser cleaning technology in this paper. We analyzed the composition and distribution characteristics of residual concrete on the surface of architectural aluminum formwork, set up a laser cleaning test system, carried out laser cleaning experiments on the concrete layer on the surface of architectural aluminum formwork under different storage times, and analyzed the mechanism of removing the concrete adhesion layer by laser cleaning. The experimental results showed that the residual time of concrete will affect the quality and efficiency of laser cleaning concrete residue on the surface of architectural aluminum formwork for concrete pouring. For concrete residues with short residual time, lasering can achieve efficient and high-quality cleaning. A nanosecond pulsed laser could strengthen the surface hardness of the aluminum alloy template during cleaning, which is helpful in improving the durability of the aluminum alloy template. The main mechanisms of laser cleaning to remove the concrete adhesion layer on the surface of architectural aluminum formwork is that the bubbles and water bubbles in the loose structure of concrete instantly absorb high-energy laser and make the concrete aggregate continuously air-burst. This paper provides technological and theoretical support for the application of laser cleaning technology to remove residual concrete on the surface of architectural aluminum formwork for concrete pouring in the field of construction.
      Citation: Photonics
      PubDate: 2023-02-22
      DOI: 10.3390/photonics10030242
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 243: Sensing Performance Analysis of Spiral
           Metasurface Utilizing Phase Spectra Measurement Technique

    • Authors: Oleg Kameshkov, Vasily Gerasimov, Sergei Kuznetsov
      First page: 243
      Abstract: We have demonstrated both numerically and experimentally a 2D plasmonic metamaterial the unit cell of which comprised an Archimedean spiral with a C-shaped resonator. Such metasurface enables the excitation of spoof localized plasmon resonances (LPRs) in the terahertz frequency range, similar in properties to the familiar LPRs in the visible range. We have compared the thin-film sensing potentials of the fundamental and dark resonant modes supported by the metasurface in the range of 0.2–0.5 THz. Both the amplitude and phase transmission spectra have been studied. A sensitivity of 21.1%/RIU (78.7 GHz/RIU) and a figure of merit (FOM) of 14.4 RIU−1 have been achieved. The FOM and Q factor obtained from the phase transmission spectra were shown to be about twice higher than those obtained from the amplitude spectra.
      Citation: Photonics
      PubDate: 2023-02-23
      DOI: 10.3390/photonics10030243
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 244: CO2 and Diode Lasers vs. Conventional
           Surgery in the Disinclusion of Palatally Impacted Canines: A Randomized
           Controlled Trial

    • Authors: Alessandra Impellizzeri, Martina Horodynski, Gaspare Palaia, Gerardo La Monaca, Daniele Pergolini, Antonella Polimeni, Umberto Romeo, Gabriella Galluccio
      First page: 244
      Abstract: Background: The aim of this RCT is to show the effectiveness of laser technology for the exposure of palatally impacted canines, using a CO2 or diode laser, and to evaluate the possible bio-stimulation effect of the laser on the spontaneous eruption of the canine. Methods: This study was carried out on a sample of 27 patients, divided randomly into three groups: treated with a CO2 laser (Group A), treated with a diode laser (Group B), and treated with a cold blade (Group C). Monitoring was performed at 1, 8, and 16 weeks after surgery, through photo and digital scans performed with a CS3500 intraoral scanner. Results: It was found that the average total eruptions are 4.55 mm for Group A, 5.36 mm for Group B, and 3.01 mm for Group C. The difference in eruption between groups A and B is not significant. Comparing the laser groups with the control group, it has emerged that the difference in eruption is statistically significant. Conclusion: A significant tooth movement was observed in both Groups A and B. The response of the canine to the bio-stimulation of the laser can be considered effective, resulting in a statistically significant difference between the study groups and the control group. Both lasers have the same bio-stimulatory action on the eruption of canines.
      Citation: Photonics
      PubDate: 2023-02-23
      DOI: 10.3390/photonics10030244
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 245: Natural Flexible and Responsive 2D Photonic
           Materials with Micro-Sandwich Structure

    • Authors: Xijin Pan, Haoyang Chi, Gangsheng Zhang
      First page: 245
      Abstract: Here, we report a two-dimensional (2D) amorphous photonic structure (APS) discovered in the central layer of the periostracum of the mussel Perna canaliculus, based on field emission scanning electron microscopy, X-ray diffractometer, attenuated total reflection Fourier transform infrared spectroscopy, and fiber optic spectrometry combined with the image processing technology and pair correlation function analysis. This APS contains ~29% in volume of protein fibers embedded in a protein matrix. These fibers, with diameters of 103 ± 17 nm, are densely arranged and unevenly crimped. In addition, they are locally parallel with each other and exhibit short-range order with a nearest-neighbor distance of 189 nm. Interestingly, the APS is humidity-responsive with a vivid green structural color (~530 nm) in the wet state, which disappears in the dry state. Moreover, the APS is sandwiched by two dense layers in the periostracum, which is flexible in wet and can spontaneously or artificially deform into various shapes. We hope this APS may provide new inspirations for the design and synthesis of 2D amorphous photonic materials.
      Citation: Photonics
      PubDate: 2023-02-23
      DOI: 10.3390/photonics10030245
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 246: TPDNet: Texture-Guided Phase-to-DEPTH
           Networks to Repair Shadow-Induced Errors for Fringe Projection

    • Authors: Jiaqiong Li, Beiwen Li
      First page: 246
      Abstract: This paper proposes a phase-to-depth deep learning model to repair shadow-induced errors for fringe projection profilometry (FPP). The model comprises two hourglass branches that extract information from texture images and phase maps and fuses the information from the two branches by concatenation and weights. The input of the proposed model contains texture images, masks, and unwrapped phase maps, and the ground truth is the depth map from CAD models. A loss function was chosen to consider image details and structural similarity. The training data contain 1200 samples in the verified virtual FPP system. After training, we conduct experiments on the virtual and real-world scanning data, and the results support the model’s effectiveness. The mean absolute error and the root mean squared error are 1.0279 mm and 1.1898 mm on the validation dataset. In addition, we analyze the influence of ambient light intensity on the model’s performance. Low ambient light limits the model’s performance as the model cannot extract valid information from the completely dark shadow regions in texture images. The contribution of each branch network is also investigated. Features from the texture-dominant branch are leveraged as guidance to remedy shadow-induced errors. Information from the phase-dominant branch network makes accurate predictions for the whole object. Our model provides a good reference for repairing shadow-induced errors in the FPP system.
      Citation: Photonics
      PubDate: 2023-02-24
      DOI: 10.3390/photonics10030246
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 247: Tailoring Large Asymmetric
           Laguerre–Gaussian Beam Array Using Computer-Generated Holography

    • Authors: Sumit Kumar Singh, Yoshikazu Adachi, Kenji Kinashi, Naoto Tsutsumi Tsutsumi, Sakai, Boaz Jessie Jackin
      First page: 247
      Abstract: Laguerre–Gaussian beams are structured light beams with a donut-shaped symmetric intensity profile and a helical phase profile. The beam profile is defined by a quantized parameter known as the mode number which extends to infinity. The availability of unbounded modes makes these beams a promising candidate for next-generation optical computing, and optical communication technologies. The symmetric intensity profile of a Laguerre–Gaussian beam can be made asymmetric through certain techniques and these beams are known by the term `asymmetric Laguerre–Gaussian beams’. Here, the asymmetricity adds another degree of freedom to the beam (apart from its mode number) which helps in encoding more information compared to a symmetric beam. However, in order to harness the benefits of all the available degrees of freedom, it is required to generate a large number of such beams in a multiplexed fashion. Here, we report the generation of such a large array of asymmetric Laguerre–Gaussian beams for the first time. Computer-generated holography and spatial multiplexing techniques were employed to generate a large array comprising of 12 × 16 = 192 asymmetric Laguerre–Gaussian beams with an arbitrary mode index and asymmetricity.
      Citation: Photonics
      PubDate: 2023-02-24
      DOI: 10.3390/photonics10030247
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 248: Perfect Invisibility Modes in Dielectric

    • Authors: Vasily V. Klimov, Dmitry V. Guzatov
      First page: 248
      Abstract: With the help of the original mathematical method for solving Maxwell’s equations, it is shown that in dielectric waveguides along with usual waveguides and quasi-normal modes, there are perfect invisibility modes or perfect non-scattering modes. In contrast to the usual waveguide modes, at eigenfrequencies of the perfect invisibility modes, light can propagate in free space. The properties of the invisibility modes in waveguides of circular and elliptical cross-sections are analyzed in detail. It is shown that at the eigenfrequencies of the perfect invisibility modes, the power of the light scattered from the waveguide tends to zero and the optical fiber becomes invisible. The found modes can be used to create highly sensitive nanosensors and other optical nanodevices, where radiation and scattering losses should be minimal.
      Citation: Photonics
      PubDate: 2023-02-26
      DOI: 10.3390/photonics10030248
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 249: Temperature-Insensitive Ferrofluid-Clad
           Microfiber Bragg Grating for Magnetic Field Sensing

    • Authors: Haimei Luo, Yangyang Liu, Liyuan Nie, Zeng Wang, Xiaoyong Gao, Yifan Wang, Jiajia Zhao, Guiqiang Liu, Shaoyi Xu
      First page: 249
      Abstract: In this paper, a temperature-insensitive ferrofluid (FF)-clad microfiber Bragg Grating (MF-BG) magnetic field sensor is proposed. Through optimizing the diameter of MF-BG, we can effectively suppress its thermal property. The experimental research results show that when the diameter of MF-BG is ~2.94 μm, its reflection spectrum shift owing to ambient temperature change can be substantially small within the range of 20–80 °C. The thermal stable sensor has a magnetic field sensitivity of 0.667 pm/Gs with a linearity of more than 0.985 at 20 °C.
      Citation: Photonics
      PubDate: 2023-02-26
      DOI: 10.3390/photonics10030249
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 250: Polarization-Independent Terahertz Surface
           Plasmon Resonance Biosensor for Species Identification of Panax and

    • Authors: Songyan Hu, Can Sun, Xu Wu, Yan Peng
      First page: 250
      Abstract: In this paper, we proposed a polarization-independent terahertz surface plasmon resonance (SPR) biosensor based on an angular cyclic element structure. The biosensor has the advantages of high sensitivity detection and high stability against the polarization change of incident terahertz light. Based on the principle that the spatial longitudinal electric field of the SPR biosensor is nonlinear and sensitive to the dielectric constant of the sample, we theoretically proved that specific nonlinear response curves with certain saturating speed and amplitude can be formed to identify different samples. The biosensor was applied to identify Panax (notoginseng, ginseng and American ginseng, 48 samples each) and Paeonia (white peony and red peony, 48 samples each) with the accuracy of 95.8% and 94.4%, respectively. The standard deviations (SD) were less than 0.347% and 0.403%, respectively. Therefore, the polarization-independent terahertz biosensor can rapidly and accurately identify Panax species and Paeonia species. These results provide a new reference for rapid and low-cost identification of medicine species.
      Citation: Photonics
      PubDate: 2023-02-27
      DOI: 10.3390/photonics10030250
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 251: Optical Chirality of Gold Chiral Helicoid
           Nanoparticles in the Strong Coupling Region

    • Authors: Haowei Cheng, Kun Liang, Xuyan Deng, Lei Jin, Jingcheng Shangguan, Jiasen Zhang, Jiaqi Guo, Li Yu
      First page: 251
      Abstract: The far- and near-field chirality properties are usually characterized by circular dichroism (CD) and optical chirality (OC), respectively. As a light–matter interaction for the hybrid states consisting of plasmons and excitons, the strong coupling interactions can affect the original chiral electromagnetic modes. However, there are few works on this influence process, which prevents an in-depth understanding of chirality. Here, we theoretically investigate both the far-field and near-field characteristics of the chiral plasmonic gold helicoid nanoparticle (GHNP) to explore the chirality mechanism further. We found that the electromagnetic field distribution of GHNP consists of one dark mode and two bright modes. The dark mode is observed more clearly in CD than in extinction spectra. Two bright modes can strongly couple with excitons respectively, which is confirmed by the anticrossing behavior and mode splitting exhibited in the extinction and CD spectra. We also analyzed the near-field OC distribution of the GHNP hybrid system and obtained the chiral responses as well as the spectral correspondence between OC and CD. Furthermore, although the strong coupling interaction changes the energy levels, resulting in mode splitting, the chiral hotspot distributions of both the upper polariton branch and lower polariton branch are consistent with the original bright mode in OC maps. Our findings provide guidance for the design of structures with strong chiral responses and enhance the comprehension of chiral strong coupling systems.
      Citation: Photonics
      PubDate: 2023-02-27
      DOI: 10.3390/photonics10030251
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 252: Thermal Lensing and Laser-Induced Damage in
           Special Pure Chalcogenide Ge35As10S55 and Ge20As22Se58 Glasses under
           Quasi-CW Fiber Laser Irradiation at 1908 nm

    • Authors: Oleg Antipov, Anton Dobrynin, Yuri Getmanovskiy, Ella Karaksina, Vladimir Shiryaev, Maksim Sukhanov, Tatiana Kotereva
      First page: 252
      Abstract: Special pure chalcogenide glass is the material of choice for many mid-infrared optical fibers and fiber lasers. In this paper, the thermo-optical lensing and laser-induced damage were studied in Ge35As10S55 and Ge20As22Se58 glasses and compared with the well-studied As2S3 glass. The thermal Z-scan technique with the quasi-CW Tm-doped fiber laser at 1908 nm was applied to study thermal lensing in chalcogenide glass. The laser-induced damage of various chalcogenide glasses was determined using the one-on-one procedure. The thermal nonlinear refractive index of the Ge35As10S55 and Ge20As22Se58 glasses was found to be lower than that of the As2S3 glass. The laser-induced damage threshold of the Ge20As22Se58 glass was determined to be higher than that of the Ge35As10S55 glass. The difference in the thermal damage threshold of the Ge35As10S55 and Ge20As22Se58 glasses and their lower value in comparison with the As2S3 glass were explained by a deviation from the stoichiometry of glass compositions and their tendency to crystallize.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030252
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 253: Ultrabroadband OPA in YCOB with a sub-ps
           Pump Source

    • Authors: Hugo Pires, Joana Alves, Victor Hariton, Mario Galletti, Celso João, Gonçalo Figueira
      First page: 253
      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, enabling ultrabroadband amplification (gain of ∼800) in the range of 750–950 nm and supporting down to 7 fs pulses.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030253
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 254: Ensquared Energy and Optical Centroid
           Efficiency in Optical Sensors: Part 1, Theory

    • Authors: Marija Strojnik, Beethoven Bravo-Medina, Robert Martin, Yaujen Wang
      First page: 254
      Abstract: High-performance megapixel focal plane arrays with small pixels have been widely used in modern optical remote sensing, astronomical, and surveillance instruments. In the prediction models applied in the traditional instrument performance analysis, the image of a point source is assumed to fall on the center of a detector pixel. A geometrical image of a point source in the realistic optical system may actually fall on any position on the detector pixel because the sensor’s line of sight includes pointing errors and jitter. This traditional assumption may lead to an optimistic error, estimated at between 10% and 20%. We present the critical factors that impact the performance estimate in a realistic instrument design based on the prediction for the noise-equivalent power (NEP). They are the optical centroid efficiency (OCE) and the ensquared energy, or more precisely, the energy on the rectangular detector pixel (EOD). We performed the simulation studies for imaging with an optical system with and without a generalized rectangular central obscuration.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030254
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 255: Pulse Measurement from a Polluted Frequency
           Resolved Optical Gating Trace Based on Half-Trace Retrieval Algorithm

    • Authors: Liangze Pan, Xiaoping Ouyang, Xuejie Zhang, Cheng Liu, Jianqiang Zhu
      First page: 255
      Abstract: A half-trace retrieval algorithm based on an extended-ptychographical iterative engine algorithm is proposed to reconstruct the temporal structure of pulse from a polluted and recorded frequency-resolved optical gating (FROG) trace that was modulated by poor spatial profile of output pulses, stray light, or misalignment of the measurement setup. In the proposed algorithm, the probe pulse and the gated pulse were retrieved simultaneously from a recorded FROG trace with a half-delay range, and the measured pulse was obtained by combining the different edges of the probe pulse and the gated pulse. Numerical simulations were carried out to verify the feasibility of the proposed algorithm. A single-shot picoseconds (ps)−THG−FROG setup with a 100-μJ ps laser system and an online ps−SHG−FROG setup in PW laser system were built to test the proposed algorithm experimentally. The results show that the temporal structure of pulses retrieved by the half-trace retrieval algorithm is closer to the real temporal structure than that retrieved by the conventional ptychographical algorithm when the recorded FROG trace is badly polluted.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030255
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 256: Method for the Quantum Metric Tensor
           Measurement in a Continuous Variable System

    • Authors: Ling-Shan Lin, Hao-Long Zhang, Zhen-Biao Yang
      First page: 256
      Abstract: As a fundamental concept, geometry is widely used in understanding physical phenomena. In quantum mechanics, geometry is related to the system’s quantum state and can be characterized by the quantum geometric tensor (QGT), whose real part is referred to as the quantum metric tensor (QMT), which defines the distance between two neighboring quantum states in the projected Hilbert space. Several pieces of research based on discrete variables have been proposed to extract the QMT, but research with the use of continuous variables is lacking. Here, we propose a method to extract the QMT of a continuous variable system, specified here as a cat-qubit. The method is developed by constructing the Kerr nonlinear parametric oscillator (KNPO) and by modulating it with external drives to induce adiabatic dynamics process within the state subspace spanned by the even and odd Scho¨dinger cat states. The method paves the way for exploring the geometry for continuous variable systems.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030256
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 257: Nanotubes in Chitin Mode Locker for Passive
           Mode−Locked Fibre Laser in 2.0 µm Region

    • Authors: Nur Nadhirah Mohamad Rashid, Harith Ahmad, Mohammad Faizal Ismail, Muhammad Quisar Lokman, Siti Nur Fatin Zuikafly, Hafizal Yahaya, Nur Azmah Nordin, Wan Mohd Fazli Wan Nawawi, Fauzan Ahmad
      First page: 257
      Abstract: This research demonstrated an ultrafast passively mode-locked thulium-holmium doped fibre laser (THDFL) using a carbon nanotube (CNT)-chitin composite film as a saturable absorber (SA). The CNTs were fabricated using ultrasonic-assisted liquid-phase exfoliation, and the chitin biopolymer was derived from oyster mushrooms (Pleurotus Ostreatus). The free-standing SA successfully performed a mode-locking operation at a threshold input pump power of 203 mW with an operating wavelength of 1908.53 nm. The generated mode-locked pulses had repetition rate, pulse width, and signal-to-noise ratio (SNR) values of 16 MHz, 1.1 ps, and 69 dB, respectively. The work demonstrates the potential of CNTs embedded in chitin biopolymer as a sustainable and environmentally friendly SA for a wide range of applications, particularly for pulsed lasers.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030257
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 258: FPGA-Based Hardware Implementation of
           Homodyne Demodulation for Optical Fiber Sensors

    • Authors: Abimael Jiménez, Ángel Sauceda, Antonio Muñoz, José Duarte, José Mireles
      First page: 258
      Abstract: Homodyne demodulation is a convenient technique for signal detection in interferometric sensors. The demodulation process is typically developed using analog circuits. However, to improve the performance of the demodulator, a digital system must be employed. In this study, we developed an optical fiber sensor by combining: a) a Michelson interferometer, b) a micro-electro-mechanical system (MEMS) device, and c) a field-programmable gate array (FPGA)-based interrogator. Signal processing was integrated into the FPGA-embedded system. The homodyne demodulation algorithm was implemented with hardware modules developed in the hardware description language (HDL) to provide a portable, low-cost, and scalable digital system. The present study successfully demonstrates the development and validation of an FPGA-based interrogator capable of processing interferograms through a homodyne demodulation scheme. The experimental results reveal proper displacement measurements of the proof-mass MEMS and the low amount of hardware resources used. The displacement measurements obtained from the system matched those obtained from a certified characterization system. As the system can be easily reconfigured to the required measured signal, a similar measurement methodology can be developed using other demodulation schemes and optical fiber sensors.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030258
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 259: Optimum Design of Glass–Air
           Disordered Optical Fiber with Two Different Element Sizes

    • Authors: Jiajia Zhao, Changbang He, Haimei Luo, Yali Zhao, Yiyu Mao, Wangyang Cai
      First page: 259
      Abstract: This paper presents a detailed study investigating the effect of the material refractive index distribution at the local position of a glass–air disordered optical fiber (G-DOF) on its localized beam radius. It was found that the larger the proportion of the glass material, the smaller its localized beam radius, which means that the transverse Anderson localization (TAL) effect would be stronger. Accordingly, we propose a novel G-DOF with large-size glass elements doped in the fiber cross-section. The simulation results show that the doped large-size glass elements can reduce the localized beam radius in the doped region and has a very tiny effect on the undoped region, thus contributing to reducing the average localized beam radius of G-DOF.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030259
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 260: The Acceleration Phenomenon of Shock Wave
           Induced by Nanosecond Laser Irradiating Silicon Assisted by Millisecond

    • Authors: Jingyi Li, Wei Zhang, Ye Li, Guangyong Jin
      First page: 260
      Abstract: The propagating evolution of shock waves induced by a nanosecond pulse laser (ns laser) irradiating silicon assisted by a millisecond pulse laser (ms laser) is investigated experimentally. A numerical model of 2D axisymmetric two-phase flow is established to obtain the spatial distribution of shock wave velocity. Two types of shock wave acceleration phenomenon are found. The mechanism of the shock wave acceleration phenomenon is discussed. The experimental and numerical results show that the initial stage of ms laser-induced plasma can provide the initial ions to increase probability of collision ionization between free electrons and vapor atoms. The velocity of the ns laser-induced shock wave is accelerated. Furthermore, the ms laser-induced plasma as the propagation medium can also accelerate the ns laser-induced shock wave. The shock wave acceleration methods obtained in this paper can promote the development of laser propulsion technology.
      Citation: Photonics
      PubDate: 2023-02-28
      DOI: 10.3390/photonics10030260
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 261: Inverse Saturable Absorption Mechanism in
           Mode-Locked Fiber Lasers with a Nonlinear Amplifying Loop Mirror

    • Authors: Xiang Zhang, Yong Shen, Xiaokang Tang, Qu Liu, Hongxin Zou
      First page: 261
      Abstract: From the perspective of the differential phase delay experienced by the two counterpropagating optical fields, the self-starting of the mode-locked fiber laser with a non-linear amplifying loop mirror (NALM) is theoretically studied. Although it is generally believed that NALM shows a saturable absorption effect on both continuous wave (CW) light and pulses, we find a counter-intuitive fact that cross-phase modulation (XPM) leads to opposite signs of differential non-linear phase shifts (NPSs) in these two cases, resulting in inverse saturable absorption (ISA) during the pulse formation process. The ISA is not helpful for the self-starting of laser mode-locking and can be alleviated by introducing a non-reciprocal phase shifter into the fiber loop. These results are helpful for optimizing the design of NALM and lowering the self-starting threshold of the high-repetition-rate mode-locked fiber laser.
      Citation: Photonics
      PubDate: 2023-03-01
      DOI: 10.3390/photonics10030261
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 262: Photophysical Properties of Bright
           Luminescent Polyethyleneimine@Carbon Nanodots and Their Application in
           White Light-Emitting Diodes

    • Authors: Junming Zhang, Ailing Yang, Kang Zhang
      First page: 262
      Abstract: Highly fluorescent carbon nanodots (CNDs) have broad application prospects in optoelectronics, energy, biological imaging, and other fields because of their good solubility in water, adjustable photoluminescence (PL), low toxicity, good biocompatibility, and stable chemical properties. In this paper, polyethyleneimine@CNDs (PEI@CNDs) with unique excitation- and concentration-dependent PL properties were synthesized by one-pot hydrothermal approach. The morphology, structure, surface chemistry, photophysical properties, and stability of the PEI@CNDs were well probed. The PEI@CNDs solution at low concentration displayed blue PL with a quantum yield of 50.6%. As the concentrations of the PEI@CNDs increase, the PL colors changed from blue, cyan, and green, to greenish-yellow. At low concentration, the excitation-independent and excitation-dependent PL property is mainly caused by carbon core and surface state emission. However, at higher concentration, the quenched blue emission and enhanced green emission were found. This is mainly attributed to the aggregate-related inner filter effect, electron transfer, and surface states. Mixing 10.0 mg/mL of PEI@CNDs with polyvinyl alcohol can be used to construct composite films, which were combined with the blue light-emitting diode to construct white light-emitting diodes with white and warm white emissions.
      Citation: Photonics
      PubDate: 2023-03-02
      DOI: 10.3390/photonics10030262
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 263: Local Field Enhancement Due to the Edge
           States of Nanoplasmonic Crystal

    • Authors: Behrokh Beiranvand, Rustam A. Khabibullin, Alexander S. Sobolev
      First page: 263
      Abstract: In this paper, we describe the effect of local electric field enhancement due to the existence of photonic edge states in a nanoplasmonic crystal. These states can be excited by a normal incident wave and are localized along the continuous line defect, where translational symmetry is broken. The nanoplasmonic crystal is formed by a triangular lattice of SiO2 cylinders on top of SiO2 and Ag thin films. Numerical simulations demonstrated that edge modes that are concentrated around a defect in a nanophotonic crystal may result in 12 field enhancements of the electric field for the incident plane wave of wavelength 545 nm. This effect can be employed for improving the sensitivity of surface-enhanced Raman scattering (SERS) spectroscopy, increasing the Purcell factor of quantum systems and improving the efficiency of higher harmonic generation.
      Citation: Photonics
      PubDate: 2023-03-02
      DOI: 10.3390/photonics10030263
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 264: Hybrid Fluorescence and Frequency-Domain
           Photoacoustic Microscopy for Imaging Development of Parhyale hawaiensis

    • Authors: George J. Tserevelakis, Emmanouela Tekonaki, Maria Kalogeridi, Ioannis Liaskas, Anastasios Pavlopoulos, Giannis Zacharakis
      First page: 264
      Abstract: Parhyale hawaiensis is a marine crustacean which has emerged as a powerful model organism to study molecular and cellular mechanisms linked to embryonic development and regenerative processes. Recently, several fluorescence-based optical microscopy techniques have been employed for the study of Parhyale to obtain anatomical descriptions, analyze gene expression patterns and reconstruct cell lineages. Aiming at the expansion of the imaging repertoire for this emerging model organism, we introduce a low-cost hybrid diagnostic system which integrates confocal fluorescence and frequency domain photoacoustic (FDPA) microscopy modalities, concurrently capturing both the radiative and radiationless relaxations of molecules following their excitation by an intensity-modulated laser source. We initially characterize the hybrid microscope in terms of PA signal generation efficiency and lateral spatial resolution, and subsequently evaluate its capabilities for the in vivo imaging of unlabelled and fluorescently labelled Parhyale embryos found at different stages of development. The recorded hybrid images have revealed a remarkable contrast complementarity between the integrated imaging modes, providing valuable information regarding cells’ structure, nuclei location, cellular membranes and yolk distribution. Our findings may pave the way for the broader adoption of inexpensive hybrid optical and PA microscopy methods in developmental biology, significantly upgrading the capabilities of the currently used technologies.
      Citation: Photonics
      PubDate: 2023-03-02
      DOI: 10.3390/photonics10030264
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 265: Turbulence Aberration Restoration Based on
           Light Intensity Image Using GoogLeNet

    • Authors: Huimin Ma, Weiwei Zhang, Xiaomei Ning, Haiqiu Liu, Pengfei Zhang, Jinghui Zhang
      First page: 265
      Abstract: Adaptive optics (AO) is an effective method to compensate the wavefront distortion caused by atmospheric turbulence and system distortion. The accuracy and speed of aberration restoration are important factors affecting the performance of adaptive optics correction. In recent years, an AO correction method based on a convolutional neural network (CNN) has been proposed for the non-iterative extraction of light intensity image features and recovery of phase information. This method can directly predict the Zernike coefficient of the wavefront from the measured light intensity image and effectively improve the real-time correction ability of the AO system. In this paper, a turbulence aberration restoration based on two frames of a light intensity image using GoogLeNet is established. Three depth scales of GoogLeNet and different amounts of data training are tested to verify the accuracy of Zernike phase difference restoration at different turbulence intensities. The results show that the training of small data sets easily overfits the data, while the training performance of large data sets is more stable and requires a deeper network, which is conducive to improving the accuracy of turbulence aberration restoration. The restoration effect of third-order to seventh-order aberrations is significant under different turbulence intensities. With the increase in the Zernike coefficient, the error increases gradually. However, there are valley points lower than the previous growth for the 10th-, 15th-, 16th-, 21st-, 28th- and 29th-order aberrations. For higher-order aberrations, the greater the turbulence intensity, the greater the restoration error. The research content of this paper can provide a network design reference for turbulence aberration restoration based on deep learning.
      Citation: Photonics
      PubDate: 2023-03-02
      DOI: 10.3390/photonics10030265
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 266: Evaluation of Residual Corneal Stromal Bed
           Elasticity by Optical Coherence Elastography Based on Acoustic Radiation

    • Authors: Yidi Wang, Yubao Zhang, Gang Shi, Sizhu Ai, Guo Liu, Xiao Han, Xingdao He
      First page: 266
      Abstract: Despite the rapidly growing popularity of laser vision correction (LVC) in the correction of myopia, its quantitative evaluation has not been thoroughly investigated. In this paper, an acoustic radiation force–optical coherence elastography (ARF-OCE) system was proposed to evaluate LVC by measuring the residual stromal bed (RSB) elasticity, because it is directly relevant to the RSB thickness that is critical to maintaining normal corneal function. As expected, the Young’s modulus of the RSB was calculated, then its relationship with the RSB thickness was determined. More significantly, a specific thickness was revealed in which the Young’s modulus changed dramatically, which may imply that there is a high risk of complication caused by over-cutting of the cornea. To the best of our knowledge, this is the first ARF-OCE imaging of the RSB, which may help to determine the safe RSB thickness and thus may help us to quantitatively assess LVC surgery.
      Citation: Photonics
      PubDate: 2023-03-02
      DOI: 10.3390/photonics10030266
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 267: An Experimental Study Measuring the Image
           Field Angle of an Electron Beam Using a Streak Tube

    • Authors: Houzhi Cai, Xuan Deng, Lihong Niu, Qinlao Yang, Jingjin Zhang
      First page: 267
      Abstract: The final stage of an inertial confinement fusion (ICF) experiment requires the diagnostic instruments to have the ability to obtain multiple images with high spatiotemporal resolution due to its extremely short duration. However, the influence of field curvature in the streak tube may lead to resolution differences between each image from single line-of-sight (SLOS) technology. In order to achieve high-precision adaptive adjustments, the direction and depth of adjustment should be determined rapidly, which means that the diagnostic instrument must work within the image depth of field of its detector imaging system, requiring it to measure the image field angle of the electron beam. Here, a method based on the streak tube using the combination of planar and spherical fluorescent screens to directly calculate the image field angle of the electron beam from the rear image quality has been proposed for the first time, and its effectiveness has been proved by experiments. It is expected to provide a basis for the diagnostic equipment in ICF experiments to achieve adaptive high-precision adjustment of the focusing voltage to obtain a series of high-resolution images.
      Citation: Photonics
      PubDate: 2023-03-03
      DOI: 10.3390/photonics10030267
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 268: Long-Wavelength VCSELs: Status and

    • Authors: Andrey Babichev, Sergey Blokhin, Evgenii Kolodeznyi, Leonid Karachinsky, Innokenty Novikov, Anton Egorov, Si-Cong Tian, Dieter Bimberg
      First page: 268
      Abstract: Single-mode long-wavelength (LW) vertical-cavity surface-emitting lasers (VCSELs) present an inexpensive alternative to DFB-lasers for data communication in next-generation giga data centers, where optical links with large transmission distances are required. Narrow wavelength-division multiplexing systems demand large bit rates and single longitudinal and transverse modes. Spatial division multiplexing transmission through multicore fibers using LW VCSELs is enabling still larger-scale data center networks. This review discusses the requirements for achieving high-speed modulation, as well as the state-of-the-art. The hybrid short-cavity concept allows for the realization of f3dB frequencies of 17 GHz and 22 GHz for 1300 nm and 1550 nm range VCSELs, respectively. Wafer-fusion (WF) concepts allow the realization of long-time reliable LW VCSELs with a record single-mode output power of more than 6 mW, 13 GHz 3 dB cut-off frequency, and data rates of 37 Gbit/s for non-return-to-zero (NRZ) modulation at 1550 nm.
      Citation: Photonics
      PubDate: 2023-03-03
      DOI: 10.3390/photonics10030268
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 269: Effect of Laser Cleaning Parameters on
           Surface Filth Removal of Porcelain Insulator

    • Authors: Chunhua Fang, Tao Hu, Ziheng Pu, Peng Li, Tian Wu, Jinbo Jiang, Aoqi Sun, Yao Zhang
      First page: 269
      Abstract: To study the influence of the laser power, scanning speed, and cleaning water content on the laser cleaning effect and obtain the best cleaning parameters, this paper conducted a simulation analysis of the laser cleaning process and carried out a pulse laser cleaning of porcelain insulators experiment to verify. The results show that the cleaning rate gradually increases as the laser power increases from 20 W to 25 W. As the scanning speed increases from 1000 mm/s to 2500 mm/s, the laser overlapping rate gradually decreases, and the cleaning takes the lead in increasing and then decreasing. The appropriate cleaning water content is conducive to laser cleaning; when the water content is 0.115 g, the cleaning efficiency reaches the highest value of 98.20%. When the laser power is 25 W, and the scanning speed is 2000 mm/s, the cleaning efficiency can reach the highest value of 96.87%. This paper shows that the reasonable choice of cleaning parameters can effectively clean the insulator surface filth and obtain a better surface morphology.
      Citation: Photonics
      PubDate: 2023-03-03
      DOI: 10.3390/photonics10030269
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 270: Influence of Large-Aperture Output
           Wavefront Distribution on Focal Spot in High-Power Laser Facility

    • Authors: Jiamei Li, Hui Yu, Dawei Li, Li Wang, Junyong Zhang, Qiong Zhou, Fengnian Lv, Xingqiang Lu
      First page: 270
      Abstract: To improve the focal spot quality, the output wavefront of the Shenguang-II Upgrade facility is divided into four types based on the spatial frequency and division band of power spectral density. The influence of each on the focal spot was quantitatively studied, and the results indicate that the spatial profile, energy concentration, and peak intensity of the focal spot are mainly affected by low-spatial-frequency, and the relative intensity of the sidelobes is greatly affected by both the low- and mid-spatial counterparts. The peak-to-valley value of the wavefront of the Shenguang-II Upgrade should not exceed 2.27λ under the requirement that 50% of the energy is enclosed within 3 times the diffraction limit (DL), and it should be less than 2.45λ under the requirement that 95% is within 10DL. Meanwhile, the Strehl ratio dropped to within 0.2 under these conditions. These results can be applied to focal quality improvement in designing an adaptive optical system, optical element processing, as well as focal spot prediction in high-power laser facilities.
      Citation: Photonics
      PubDate: 2023-03-03
      DOI: 10.3390/photonics10030270
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 271: SCAPS Empowered Machine Learning Modelling
           of Perovskite Solar Cells: Predictive Design of Active Layer and Hole
           Transport Materials

    • Authors: Mahdi Hasanzadeh Azar, Samaneh Aynehband, Habib Abdollahi, Homayoon Alimohammadi, Nooshin Rajabi, Shayan Angizi, Vahid Kamraninejad, Razieh Teimouri, Raheleh Mohammadpour, Abdolreza Simchi
      First page: 271
      Abstract: Recently, organic–inorganic perovskites have manifested great capacity to enhance the performance of photovoltaic systems, owing to their impressive optical and electronic properties. In this simulation survey, we employed the Solar Cell Capacitance Simulator (SCAPS-1D) to numerically analyze the effect of different hole transport layers (HTLs) (Spiro, CIS, and CsSnI3) and perovskite active layers (ALs) (FAPbI3, MAPbI3, and CsPbI3) on the solar cells’ performance with an assumed configuration of FTO/SnO2/AL/HTL/Au. The influence of layer thickness, doping density, and defect density was studied. Then, we trained a machine learning (ML) model to perform predictions on the performance metrics of the solar cells. According to the SCAPS results, CsSnI3 (as HTL) with a thickness of 220 nm, a defect density of 5 × 1017 cm−3, and a doping density of 5 × 1019 cm−3 yielded the highest power conversion efficiency (PCE) of 23.90%. In addition, a 530 nm-FAPbI3 AL with a bandgap energy of 1.51 eV and a defect density of 1014 cm−3 was more favorable than MAPbI3 (1.55 eV) and CsPbI3 (1.73 eV) to attain a PCE of >24%. ML predicted the performance matrices of the investigated solar cells with ~75% accuracy. Therefore, the FTO/SnO2/FAPbI3/CsSnI3/Au structure would be suitable for experimental studies to fabricate high-performance photovoltaic devices.
      Citation: Photonics
      PubDate: 2023-03-03
      DOI: 10.3390/photonics10030271
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 272: A DIDE-FPP Composite Algorithm for Accurate
           Tunnel Fire Location

    • Authors: Hong Jiang, Yihan Zhao, Chenyang Wang, Lina Cui
      First page: 272
      Abstract: We propose a DIDE-FPP composite algorithm to improve the spatial location accuracy of tunnel fires based on the distributed individuals differential evolution (DIDE) algorithm and the four-point positioning (FPP) method. Using the DIDE algorithm to solve the multimodal optimization problems in tunnel fire location can locate more peaks and improve peak finding, and the FPP method is used to process the peak points located using the DIDE and achieve the spatial location which cannot be achieved otherwise using the DIDE method only. We used 20 multimodal test functions to evaluate the performance of the DIDE-FPP algorithm in peak finding and solving MMOPs. Through experimental comparisons with 13 other existing advanced methods, the comprehensive performance of the proposed DIDE-FPP composite algorithm shows advantages to some extents. Additionally, the combined value of PR (peak ratio) and SR (success rate) on up to 20 experimental functions is relatively high. The spatial positioning accuracy of a tunnel fire warning system using this positioning method can reach the centimeter level.
      Citation: Photonics
      PubDate: 2023-03-03
      DOI: 10.3390/photonics10030272
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 273: LIMPID: A Lightweight Image-to-Curve
           MaPpIng moDel for Extremely Low-Light Image Enhancement

    • Authors: Wanyu Wu, Wei Wang, Xin Yuan, Xin Xu
      First page: 273
      Abstract: Low-light conditions severely degrade the captured image quality with few details, while deep learning approaches are trending towards low-light image enhancement (LLIE) due to their superior performance. However, few methods face the challenges of lower dynamic range and greater noise from extremely low-light directly. Existing methods for extremely low-light enhancement are end-to-end, requiring RAW data as input. Meanwhile, they often lack the potential for real-time mobile deployment owing to the high model complexity. In this paper, we introduce the image-to-curve transformation to ELLIE for the first time and present a Lightweight Image-to-curve MaPpIng moDel for ELLIE (LIMPID). Compared with existing image-to-curve mapping methods, the proposed module is constructed for a wider dynamic range according to the light scattering model. Furthermore, we propose a new pyramid fusion strategy based on Laplacian and Gaussian. This strategy attempts to achieve dynamic fusion of multi-scale images via learnable fusion weight parameters. Specifically, LIMPID consists of a low-resolution dense CNN network stream and a full-resolution guidance stream. First, the curve generation and refinement are achieved in the low-resolution stream constructed on a light scattering model. Then, the curves are up-sampled to full resolution via bilateral grid cells. Finally, the enhanced result is obtained through dynamically adapted multi-scale pyramid fusion. Experimental results show that our method is competitive with existing state-of-the-art methods in terms of performance.
      Citation: Photonics
      PubDate: 2023-03-04
      DOI: 10.3390/photonics10030273
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 274: Optimally Controlled Non-Adiabatic Quantum
           State Transmission in the Presence of Quantum Noise

    • Authors: Xiang-Han Liang, Lian-Ao Wu, Zhao-Ming Wang
      First page: 274
      Abstract: Pulse-controlled non-adiabatic quantum state transmission (QST) was proposed many years ago. However, in practice environmental noise inevitably damages communication quality in the proposal. In this paper, we study the optimally controlled non-adiabatic QST in the presence of quantum noise. By using the Adam algorithm, we find that the optimal pulse sequence can dramatically enhance the transmission fidelity of such an open system. In comparison with the idealized pulse sequence in a closed system, it is interesting to note that the improvement of the fidelity obtained by the Adam algorithm can even be better for a bath strongly coupled to the system. Furthermore, we find that the Adam algorithm remains powerful for different numbers of sites and different types of Lindblad operators, showing its universality in performing optimal control of quantum information processing tasks.
      Citation: Photonics
      PubDate: 2023-03-05
      DOI: 10.3390/photonics10030274
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 275: A.I. Pipeline for Accurate Retinal Layer
           Segmentation Using OCT 3D Images

    • Authors: Mayank Goswami
      First page: 275
      Abstract: An image data set from a multi-spectral animal imaging system was used to address two issues: (a) registering the oscillation in optical coherence tomography (OCT) images due to mouse eye movement and (b) suppressing the shadow region under the thick vessels/structures. Several classical and A.I.-based algorithms, separately and in combination, were tested for each task to determine their compatibility with data from the combined animal imaging system. The hybridization of A.I. with optical flow followed by homography transformation was shown to be effective (correlation value > 0.7) for registration. Resnet50 backbone was shown to be more effective than the famous U-net model for shadow region detection with a loss value of 0.9. A simple-to-implement analytical equation was shown to be effective for brightness manipulation with a 1% increment in mean pixel values and a 77% decrease in the number of zeros. The proposed equation allows the formulation of a constraint optimization problem using a controlling factor α for the minimization of the number of zeros, the standard deviation of the pixel values, and maximizing the mean pixel value. For layer segmentation, the standard U-net model was used. The A.I.-Pipeline consists of CNN, optical flow, RCNN, a pixel manipulation model, and U-net models in sequence. The thickness estimation process had a 6% error compared with manually annotated standard data.
      Citation: Photonics
      PubDate: 2023-03-06
      DOI: 10.3390/photonics10030275
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 276: Research on Magnetic-Induced Error of
           Small-Sized Fiber Optic Gyro Fiber Coil in Space Environment

    • Authors: Guochen Wang, Xingliang Wu, Zicheng Wang, Zhizi Zhang, Fan Yang, Bo Zhao, Runfeng Zhang, Wei Gao
      First page: 276
      Abstract: Spacecraft is severely limited in weight and volume, resulting in a small bending radius of the fiber coil used by IFOG (Interference Fiber Optic Gyroscope). The fiber coil has such a size that the influence of bending on fiber birefringence cannot be ignored. In this paper, we research magnetic-induced errors of small-sized IFOG working in low orbit space. Firstly, we use the Jones matrix to analyze the effects of radial magnetic field and axial magnetic field on IFOG. Secondly, we establish a three-dimensional model for the radial magnetic-induced errors and magnetic-induced errors of minor radius fiber coil. Using the finite element method, we analyze the magnetic-induced error between different levels of the fiber coil. Combined with the birefringence distribution of the minor radius fiber coil, an accurate three-dimensional magnetic-induced error model is established. Thirdly, in the experiment, we design the magnetic-induced error test platform that includes the Fluke standard current source, transconductance amplifier, and Helmholtz coil. The experimental results show that, compared with the traditional calculation method, the three-dimensional magnetic-induced error model reduces the RMSE (Root Mean Square Error) of the radial magnetic field by 56.9% and the RMSE of the axial magnetic field by 35.7%, respectively.
      Citation: Photonics
      PubDate: 2023-03-06
      DOI: 10.3390/photonics10030276
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 277: Function-Versatile Thermo-Optic Switch
           Using Silicon Nitride Waveguide in Polymer

    • Authors: Tao Chen, Zhenming Ding, Zhangqi Dang, Xinhong Jiang, Ziyang Zhang
      First page: 277
      Abstract: A function-versatile thermo-optic switch is proposed and experimentally demonstrated using silicon nitride waveguides embedded in polymer cladding. The device consists of a 1 × 2 input splitter, 2 single-mode waveguides for phase shifting, and a thermally controlled 2 × 2 output coupler to give another degree of freedom in achieving phase-matching conditions. Combining the high waveguide birefringence of the thin silicon nitride waveguide and the excellent thermo-optic property of the polymer material, this device can realize multiple functions by applying different micro-heater powers, i.e., polarization-independent path switching, beam splitting, and polarization beam splitting. For the polarization-independent path switching, the fabricated device has shown a crosstalk suppression better than 10 dB for the TE mode and over 20 dB for the TM mode in the wavelength range from 1500 nm to 1620 nm. For the polarization beam splitting function, the device can reach a polarization extinction ratio greater than 10 dB at selected bands. This simple yet scalable device may find applications in polarization-multiplexed optical communication technology and complex photonic computing networks.
      Citation: Photonics
      PubDate: 2023-03-06
      DOI: 10.3390/photonics10030277
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 278: Prediction of Process Parameters for
           Ultra-Precision Optical Processing Based on Dual-Stacked LSTM

    • Authors: Pengzhi Ang, Minghong Yang, Jun Chen, Jun Cao, Qiuyu Zhu
      First page: 278
      Abstract: High-precision and large-aperture optical components have important applications in modern optics and optoelectronics. However, the traditional continuous polishing technology of optical components relies heavily on the processing experience of the processing personnel. The surface shape of the pitch lap is judged by frequent offline measurement of the surface shape of the processing workpiece, and then the processing personnel judges how to adjust the next process parameters through their own experience, which leads to uncertainty of processing time and low processing efficiency. In this paper, based on the historical processing data, including the surface parameters of workpieces and process parameters before and after each processing, a machine learning-based prediction method of process parameters is proposed. At first, taking the surface shape of the pitch lap as the hidden parameter of the model, a time-series mathematical model of the forward and reverse processing processes is constructed. Theoretical and experimental results show that the prediction method in this paper can effectively reduce the processing time and improve the stability of the workpiece quality.
      Citation: Photonics
      PubDate: 2023-03-06
      DOI: 10.3390/photonics10030278
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 279: Tunable Transparency and Group Delay in
           Cavity Optomechanical Systems with Degenerate Fermi Gas

    • Authors: Fatin Nadiah Yusoff, Muhammad Afiq Zulkifli, Norshamsuri Ali, Shailendra Kumar Singh, Nooraihan Abdullah, Nor Azura Malini Ahmad Hambali, Collins Okon Edet
      First page: 279
      Abstract: We theoretically investigate the optical response and the propagation of an external probe field in a Fabry–Perot cavity, which consists of a mechanical mode of trapped, ultracold, fermionic atoms inside and simultaneously driven by an optical laser field. We investigate the electromagnetically-induced transparency due to coupling of the optical cavity field with the collective density excitations of the ultracold fermionic atoms via radiation pressure force. Moreover, we discuss the variations in the phase and group delay of the transmitted probe field with respect to effective cavity detuning as well as pumping power. It is observed that the transmitted field is lagging in this fermionic cavity optomechanical system. Our study shall provide a method to control the propagation as well as the speed of the transmitted probe field in this kind of fermionic, ultracold, atom-based, optomechanical cavity system, which might have potential applications in optical communications, signal processing and quantum information processing.
      Citation: Photonics
      PubDate: 2023-03-07
      DOI: 10.3390/photonics10030279
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 280: Digital Non-Linear Transmitter Equalization
           for PAM-N-Based VCSEL Links Enabling Robust Data Transmission of 100
           Gbit/s and Beyond

    • Authors: Urs Hecht, Nikolay Ledentsov, Helia Ordouei, Patrick Kurth, Philipp Scholz, Nikolay Ledentsov, Friedel Gerfers
      First page: 280
      Abstract: This paper demonstrates why VCSEL-based transmitter systems are not able to capitalize on higher-order PAM modulation formats (such as PAM-4) to push the link data rate towards 100 Gbit/s with BER of better than 10−5. First, the non-linear and biasing-dependent VCSEL behavior is analyzed in great detail to prove why state-of-the-art VCSELs with linear equalization are not able to reach these bandwidth targets. Consequently, based on an enhanced VCSEL model, a digital non-linear transmit equalizer is proposed to overcome voltage-dependent relaxation frequency shifts as well as data-dependent VCSEL bandwidth variations. The proposed digital non-linear equalizer is compared with a standard linear FFE structure using PAM-4 transmission experiments of 100 Gbit/s and beyond. This way, the proposed non-linear equalizer reveals a BER improvement of more than 30-fold compared to a linear FFE at a data rate of 80 Gbit/s. Finally, at 112 Gbit/s PAM-4 the non-linear equalizer was successfully demonstrated at a BER of 1.5·10−7.
      Citation: Photonics
      PubDate: 2023-03-07
      DOI: 10.3390/photonics10030280
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 281: Polarization-Independent Ultra Wideband RCS
           Reduction Conformal Coding Metasurface Based on Integrated Polarization
           Conversion-Diffusion-Absorption Mechanism

    • Authors: Hamza Asif Khan, Umair Rafique, Syed Muzahir Abbas, Fahad Ahmed, Yifei Huang, Junaid Ahmed Uqaili, Abdelhady Mahmoud
      First page: 281
      Abstract: An ultra wideband (UWB) radar cross-section (RCS) reduction metasurface has received attention in recent years. However, the majority of the research has concentrated on the physics and design of planar surfaces, which do not meet the standards of modern aerodynamics and aesthetics. In this paper, we offer a sophisticated strategy for designing a metasurface that can conform to the shape of any object, even those of moderate curvature, and can also achieve UWB RCS reduction by combining absorption, polarization conversion, and diffusion mechanisms. Firstly, an absorbing-polarization converter is designed, composed of a square patch with a truncated diagonal strip and ring. A thin Rogers RT/Duroid 5880 dielectric substrate layer is used in the structure, which is also appropriate for conformal conditions. The substrate layer and the ground plane are separated by an air gap to enhance the polarization conversion bandwidth (PCBW). For normal incident electromagnetic (EM) waves, the PCBW ranges from 10.8 to 31.3 GHz with polarization conversion ratio (PCR) values greater than 0.9 dB. Up to a 45∘ oblique incidence angle over the aforementioned band, the PCR efficiency is well maintained. Then, the optimized coding metasurface is formed by the Pancharatnam–Berry (PB) phase, consisting of meta-atoms “0” and “1” of the same size but different orientations, to realize the concept of cross-polarization diffusion. A theoretical investigation has been performed to analyze the RCS reduction performance of planar as well as conformal cylindrical surfaces. The results show that more than 10 dB of RCS reduction is experienced over UWB (10.8–31.3 GHz) for planar metasurfaces under linearly and circularly polarized incidence waves. Furthermore, the RCS reduction for cylindrical surfaces can be achieved in a similar frequency band above 10 dB up to an angle of 90∘. It can be deduced that our proposed flexible metasurface can be used as an absorber or a polarization converter and provide broadband RCS reduction, which is essential for multi-function and conformal stealth applications.
      Citation: Photonics
      PubDate: 2023-03-07
      DOI: 10.3390/photonics10030281
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 282: Fiber-Based Techniques to Suppress
           Stimulated Brillouin Scattering

    • Authors: Bin Huang, Jiaqi Wang, Xiaopeng Shao
      First page: 282
      Abstract: Stimulated Brillouin scattering (SBS) is the major factor that limits the maximum optical fiber output power in narrow linewidth applications, which include important fields such as passive optical networks (PONs), high-power fiber amplifiers, and lasers. Great efforts have been dedicated to suppressing the SBS effect and increasing the maximum optical fiber output power. This paper focuses on key fiber-based techniques to suppress SBS. These techniques take advantages of the properties of optical fibers. We present how these properties (electric modes, acoustic modes, and material properties) could be utilized to suppress SBS. The fiber-based techniques are divided into transverse optical fiber design, longitudinal variant fiber design, and external perturbations (strain and temperature) on optical fibers. Transverse optical fiber design focuses on the mechanism electro-acoustic interaction. Large effective area fiber design and acoustic tailoring techniques have been discussed. Longitudinal variant fiber design considers the nonlinear SBS interaction along propagation distance, and various techniques related have been presented. External perturbations (strain and temperature) on optical fibers emphasize on how external static perturbations could modify the SBS effect.
      Citation: Photonics
      PubDate: 2023-03-07
      DOI: 10.3390/photonics10030282
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 283: Research on the Linear Demodulation Range
           and Background Noise of Fiber-Optic Interferometer System

    • Authors: Weitao Wang, Chen Wang, Shuai Qu, Haifeng Qi, Zhiqiang Song, Pengbo Jiang, Jian Guo, Ying Shang, Jiasheng Ni, Gangding Peng
      First page: 283
      Abstract: The linear demodulation range and background noise of the Michelson interferometer system are investigated with a laser phase noise measurement system. We have theoretically and experimentally analyzed the performance of the interferometer system by changing the frequency modulation amplitude of the laser and the optical path difference (OPD) of the interferometer, respectively. It is shown that the linear demodulation range of the Michelson interferometer system is finite, which depends on the parameters of the system, such as the sample frequency, the delay time between two interferometer arms, and the system bandwidth. Furthermore, the experimental results indicate that the background noise of the interferometer system can be reduced by using a sufficiently long OPD so that the smaller true phase information can be detected with the demodulation system. The parameters of the measurement system could be optimized to satisfy the demand of the phase demodulation with different levels, which is of great significance for the phase monitoring interrogator, such as fiber-optical interferometer sensors and distributed acoustic sensors.
      Citation: Photonics
      PubDate: 2023-03-07
      DOI: 10.3390/photonics10030283
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 284: A High-Temperature Multipoint Hydrogen
           Sensor Using an Intrinsic Fabry–Perot Interferometer in Optical

    • Authors: Rongtao Cao, Jingyu Wu, Yang Yang, Mohan Wang, Yuqi Li, Kevin P. Chen
      First page: 284
      Abstract: This paper presents a multiplexable fiber optic chemical sensor with the capability of monitoring hydrogen gas concentration at high temperatures up to 750 °C. The Pd-nanoparticle infused TiO2 films coated on intrinsic Fabry–Perot interferometer (IFPI) array were used as sensory films. Strains induced upon exposure to hydrogen with varied concentrations can be monitored by IFPI sensors. The fiber sensor shows a repetitive and reversible response when exposed to a low level (1–6%) of hydrogen gas. Uniform sensory behavior across all the sensing cavities is demonstrated and reported in this paper.
      Citation: Photonics
      PubDate: 2023-03-08
      DOI: 10.3390/photonics10030284
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 285: Performance Study of Generalized Space Time
           Block Coded Enhanced Fully Optical Generalized Spatial Modulation System
           Based on Málaga Distribution Model

    • Authors: Yi Wang, Rui Zhou
      First page: 285
      Abstract: This paper proposes a generalized space time block coded (GSTBC) enhanced fully optical generalized spatial modulation (EFOGSM) system based on Málaga (M) turbulent channel. GSTBC-EFOGSM adopts the hybrid concept of generalized space time block coded and optical spatial modulation to further utilize the high transmission rate of EFOGSM and the diversity advantage of GSTBC in free space optical (FSO) communication systems. Considering the combined effects of path loss, pointing error and atmospheric turbulence, the Meijer G function is used to derive the closed-form expression for the average bit error rate (ABER) of GSTBC-EFOGSM. Then, the ABER performance, data transmission rate, energy efficiency and computational complexity at the receiver of GSTBC-EFOGSM are compared with other optical spatial modulation schemes by simulation. In addition, the effects of key factors, such as data transmission rate, encoding ratio, number of photodetectors and modulation order, on the ABER performance of the system are also analyzed via simulation. Monte Carlo (MC) simulation is used to verify the correctness of the numerical simulation. The simulation results show that the GSTBC-EFOGSM system has better ABER performance and good performance gain.
      Citation: Photonics
      PubDate: 2023-03-08
      DOI: 10.3390/photonics10030285
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 286: Statistical Tool Size Study for
           Computer-Controlled Optical Surfacing

    • Authors: Weslin C. Pullen, Tianyi Wang, Heejoo Choi, Xiaolong Ke, Vipender S. Negi, Lei Huang, Mourad Idir, Daewook Kim
      First page: 286
      Abstract: Over the past few decades, computer-controlled optical surfacing (CCOS) systems have become more deterministic. A target surface profile can be predictably achieved with a combination of tools of different sizes. However, deciding the optimal set of tool sizes that will achieve the target residual error in the shortest run time is difficult, and no general guidance has been proposed in the literature. In this paper, we present a computer-assisted study on choosing the proper tool size for a given surface error map. First, we propose that the characteristic frequency ratio (CFR) can be used as a general measure of the correction capability of a tool over a surface map. Second, the performance of different CFRs is quantitatively studied with a computer simulation by applying them to guide the tool size selection for polishing a large number of randomly generated surface maps with similar initial spatial frequencies and root mean square errors. Finally, we find that CFR = 0.75 achieves the most stable trade-off between the total run time and the number of iterations and thus can be used as a general criterion in tool size selection for CCOS processes. To the best of our knowledge, the CFR is the first criterion that ties tool size selection to overall efficiency.
      Citation: Photonics
      PubDate: 2023-03-09
      DOI: 10.3390/photonics10030286
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 287: Process Parameters Analysis of Laser Phase
           Transformation Hardening on the Raceway Surface of Shield Main Bearing

    • Authors: Peiyu He, Yi Ding, Shiying Jiang, Hengjie Zhang, Tianyu Shen, Yun Wang
      First page: 287
      Abstract: The main bearing of the shield machine has a huge structure and severe service conditions, which are prone to wear and fatigue damage. To improve the anti-wear and anti-fatigue ability of the raceway surface of the shield main bearing, laser transformation hardening under different parameters of the shield main bearing raceway material 42CrMo steel was researched. The effects of laser power and scanning speed on the phase transformation of 42CrMo steel and the depth of the hardened layer were studied. The numerical model was verified using the theoretical and experimental results. Orthogonal tables of laser processing parameters are established. The results show that the depth of the hardened raceway layer increases with increased laser power and decreased laser scanning speed. According to the results of orthogonal primary and secondary analyses and fuzzy comprehensive evaluation, the depth of the hardened layer of the raceway can reach 1.08 mm, and the hardened layer is relatively uniform (laser power, 2250 W; scanning speed, 20 mm/s; spot length, 5 mm). The research in this paper provides a theoretical basis and technological innovation for the processing methods and engineering applications of high-reliability and long-life shield main bearings, which is of great engineering significance.
      Citation: Photonics
      PubDate: 2023-03-09
      DOI: 10.3390/photonics10030287
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 288: A Staring Tracking Measurement Method of
           Resident Space Objects Based on the Star Tacker

    • Authors: Tingting Xu, Xiubin Yang, Zongqiang Fu, Mo Wu, Suining Gao
      First page: 288
      Abstract: Measuring resident space objects (RSOs) by star trackers has become a research hotspot in space situational awareness. However, the arc length measured by star trackers is too short to complete the high-precision orbit determination of the RSO. In this paper, a staring–tracking measurement (STM) method is proposed to obtain a sufficiently long arc. Firstly, the three-axis attitude calculation model of the satellite is established for tracking RSOs during the staring process. Secondly, an observation method of the RSO location is proposed based on the principle of the angular distance invariance and the imaging mapping function of the star tracker. Finally, the numerical simulations and the ground experiment were conducted to verify the proposed algorithm. Simulation results show that the acquisition time of the measurable arcs is longer than 6 min, and the accuracy of the declination and the ascension can meet the standard for RSO orbit determination. The physical experiment shows that the acquisition time is consistent with that in the simulation. Our work provides a new idea for the realization of high-precision space-based optical measurement.
      Citation: Photonics
      PubDate: 2023-03-09
      DOI: 10.3390/photonics10030288
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 289: A Measurement System with High Precision
           and Large Range for Structured Surface Metrology Based on Atomic Force

    • Authors: Junjie Wu, Xiaoyu Cai, Jiasi Wei, Chen Wang, Yong Zhou, Kaixin Sun
      First page: 289
      Abstract: With the rapid and continuous development of nanomanufacturing technology, the demands for both large range and high precision metrology of structured surfaces are becoming increasingly urgent. This paper proposes a metrological measurement system based on a commercial atomic force microscope. By using the nano-positioning platform from SIOS, the measurement range of the system expands from 110 μm × 110 μm × 20 μm to 25 mm × 25 mm × 5 mm. A signal amplifier with low noise and a high common mode rejection ratio that decreases the noise level of the measurement system to 2 nm is designed. Integration of the metrological system, signal processing, and calibration of the whole system is introduced. Three experimental studies are carried out on an ultrahigh step, an atomic deposition grating, and a cutting tool. The experimental results demonstrate high measurement repeatability and reproducibility in both vertical and lateral directions. By repeating 10 times of measurement, the expended uncertainties of the step and the grating measurement are 36.24 nm and 0.60 nm, respectively. Additionally, measurement of a cutting tool tip is conducted to illustrate the performance of the system. The Ra and Rz values of the tool tip arc ripple are 29.8 nm and 189 nm, respectively.
      Citation: Photonics
      PubDate: 2023-03-10
      DOI: 10.3390/photonics10030289
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 290: Half-Ring Microlasers Based on InGaAs
           Quantum Well-Dots with High Material Gain

    • Authors: Fedor Zubov, Eduard Moiseev, Mikhail Maximov, Alexander Vorobyev, Alexey Mozharov, Yuri Shernyakov, Nikolay Kalyuzhnyy, Sergey Mintairov, Marina Kulagina, Vladimir Dubrovskii, Natalia Kryzhanovskaya, Alexey Zhukov
      First page: 290
      Abstract: We report on half-ring lasers that are 100–200 µm in diameter and are fabricated by cleaving the initial full rings into halves. Characteristics of the half-ring and half-disk lasers fabricated from the same wafer are compared. The active area of the microlasers is based on the quantum heterostructures of mixed (0D/2D) dimensionality, referred to as quantum well-dots with very high material gain. Half-ring lasers show directional light emission and single-mode lasing near the threshold. A maximal continuous-wave output power of 76 mW is achieved for a half-ring that is 200 µm in diameter. Half-rings demonstrate better wall-plug efficiency as compared to half-disks. Lasing in pulse mode is observed up to 140 °C, the characteristic temperature is 100–125 K, depending on the half-ring size. P-side down bonding onto Si-board significantly improves power and temperature characteristics. In CW mode, lasing is maintained up to 97 °C, limited by active-area overheating.
      Citation: Photonics
      PubDate: 2023-03-10
      DOI: 10.3390/photonics10030290
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 291: Recent Advances in Optical Injection
           Locking for Visible Light Communication Applications

    • Authors: Xingchen Liu, Junhui Hu, Qijun Bian, Shulan Yi, Yingnan Ma, Jianyang Shi, Ziwei Li, Junwen Zhang, Nan Chi, Chao Shen
      First page: 291
      Abstract: The introduction of visible light communication (VLC) technology could increase the capacity of existing wireless communication systems towards 6G networks. In practice, VLC can make good use of lighting system infrastructures to transmit data using light fidelity (Li-Fi). The use of semiconductor light sources, including light-emitting diodes (LEDs) and laser diodes (LDs) are essential to VLC technology because these devices are energy-efficient and have long lifespans. To achieve high-speed VLC links, various technologies have been utilized, including injection locking. Optical injection locking (OIL) is an optical frequency and phase synchronization technique that has been implemented in semiconductor laser systems for performance enhancement. High-performance optoelectronic devices with narrow linewidth, wide tunable emission, large modulation bandwidth and high data transmission rates are desired for advanced VLC. Thus, the features of OIL could be promising for building high-performance VLC systems. In this paper, we present a comprehensive review of the implementation of the injection-locking technique in optical communication systems. The enhancement of characteristics through OIL is elucidated. The applications of OIL in VLC systems are discussed. The prospects of OIL for future VLC systems are evaluated.
      Citation: Photonics
      PubDate: 2023-03-10
      DOI: 10.3390/photonics10030291
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 292: Preface for Special Issue: Progress in
           Laser Accelerator and Future Prospects

    • Authors: Toshiki Tajima, Pisin Chen
      First page: 292
      Abstract: In early 2022, one of the authors (Professor T [...]
      Citation: Photonics
      PubDate: 2023-03-10
      DOI: 10.3390/photonics10030292
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 293: Generation of a Fundamental/Doubled
           Frequency Phase-Coded Microwave Signal Based on Polarization Multiplexed

    • Authors: Jing Yin, Yan Zhao, Feng Yang, Dengcai Yang, Yunxin Wang
      First page: 293
      Abstract: Microwave photonic phase-shifting technology can be used to generate high-frequency, broadband, and tunable phase-coded microwave signals, which are helpful in solving the contradiction between the detection range and the range resolution in radar systems. A method for generating a reconfigurable carrier phase-coded signal of a fundamental or doubled carrier frequency, based on polarization multiplexed technology, is proposed and verified by the experiments in this paper. A dual-parallel dual-polarization Mach–Zehnder modulator (DP-DPMZM) and a polarization-dependent phase modulator (PD-PM) were used to load the carrier and the phase-shifting signal, respectively. By reasonably configuring the state of the RF switch and the bias voltages of the sub-DPMZM, the fundamental or doubled carrier frequency can be obtained through photoelectric conversion. The reconfigurable carrier frequency gives the system a wider work bandwidth range and can effectively reduce the frequency requirement for local oscillator (LO) signals. By adjusting the driving voltage, the broadband microwave signal can be phase-shifted within the range of 360°, and when the phase-shifted control signal is a multilevel amplitude signal, it can generate binary, quaternary, or other high-order phase-coded signals, which have high reconfigurable performance and potential application value in multifunctional radar systems. In addition, the scheme has wideband tunability, since no optical filter is involved. The proposed scheme was theoretically analyzed and experimentally verified. Binary, quaternary, and octal phase-coded signals, with fundamental and doubled frequencies centered at 8 GHz and 16 GHz, were successfully generated.
      Citation: Photonics
      PubDate: 2023-03-10
      DOI: 10.3390/photonics10030293
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 294: Dispersion-Oriented Inverse Design of
           Photonic-Crystal Fiber for Four-Wave Mixing Application

    • Authors: Linqiao Gan, Fei Yu, Yazhou Wang, Ning Wang, Xinyue Zhu, Lili Hu, Chunlei Yu
      First page: 294
      Abstract: In this paper, we demonstrate the application of a deep learning neural network (DNN) in the dispersion-oriented inverse design of photonic-crystal fiber (PCF) for the fine-tuning of four-wave mixing (FWM). The empirical formula of PCF dispersion is applied instead of numerical simulation to generate a large dataset of phase-matching curves of various PCF designs, which significantly improves the accuracy of the DNN prediction. The accuracies of DNNs’ predicted PCF structure parameters are all above 95%. The simulations of the DNN-predicted PCFs structure demonstrate that the FWM wavelength has an average numerical mean square error (MAE) of 1.92 nm from the design target. With the help of DNN, we designed and fabricated a specific PCF for wavelength conversion via FWM from 1064 nm to 770 nm for biomedical imaging applications. Pumped by a microchip laser at 1064 nm, the signal wavelength is measured at 770.2 nm.
      Citation: Photonics
      PubDate: 2023-03-10
      DOI: 10.3390/photonics10030294
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 295: Simulated Studies of
           Polarization-Selectivity Multi-Band Perfect Absorber Based on Elliptical
           Metamaterial with Filtering and Sensing Effect

    • Authors: Yinghua Wang, Yubo Kong, Shitong Xu, Jie Li, Guangqiang Liu
      First page: 295
      Abstract: In this work, the Ag-SiO2-Ag metamaterial with elliptical nano-slits was proposed to investigate the multi-band polarization-dependent perfect absorber. It was found that multi-band perfect absorptions can be induced under TE and TM-polarized illuminations. Simulation results showed that the absorption peaks for TE-polarized wave appeared at 337.6 THz and 360.0 THz with 98.5% and 97.6% absorbance, respectively. Conversely, the absorption peaks for TM-polarized wave appeared at 325.7 THz and 366.1 THz with 96.3% and 97.9% absorbance, respectively. As a result, the elliptical metamaterial presented polarization-selectivity property for perfect absorption, and so, the metamaterial can filter out different frequencies of TE- and TM-reflected waves, i.e., the elliptical metamaterial can be used as a reflecting filter. In addition, this work studied the sensing performance of the elliptical metamaterial and showed that the dual-band sensing performances were different at low and high frequencies. The sensitivities (S) to the refractive index reached up to 151.1 THz/RIU and 120.8 THz/RIU for the TE and TM-polarized waves around 337.6 THz and 325.7 THz, which provide promising potential in near-infrared photoelectric sensor and detector. However, both the absorption frequency and intensity of TM-polarized wave were insensitive to the refractive index of the medium around 366.1 THz, and so, the study provides a theoretical basis for infrared stealth of different media.
      Citation: Photonics
      PubDate: 2023-03-11
      DOI: 10.3390/photonics10030295
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 296: Frequency Comb Generation Based on
           Brillouin Random Lasing Oscillation and Four-Wave Mixing Assisted with
           Nonlinear Optical Loop Mirror

    • Authors: Yuxi Pang, Shaonian Ma, Qiang Ji, Xian Zhao, Yongfu Li, Zengguang Qin, Zhaojun Liu, Yanping Xu
      First page: 296
      Abstract: A frequency comb generator (FCG) based on dual-cavity Brillouin random fiber lasing oscillation in the 1.5 μm telecon spectral window is established and experimentally demonstrated. In the half-open main cavity of the dual cavity, the stimulated Brillouin scattering in highly nonlinear fiber (HNLF) and Rayleigh scattering in single-mode fiber are employed to provide sufficient Brillouin gain and the randomly distributed feedback, respectively, for random mode resonance. The sub-cavity includes an Er-doped fiber amplifier to couple back and boost lower-order Stokes and anti-Stokes light for the cascade of stimulated Brillouin scattering to generate multiple higher-order Stokes and anti-Stokes light. Meanwhile, efficient four-wave mixing is stimulated in the HNLF-based main cavity, further enhancing the number and intensity of the resonant Stokes and anti-Stokes light. By taking advantages of the unique transmission characteristics of nonlinear optical loop mirrors, the power deviation between Stokes and anti-Stokes lines is further optimized with 17 orders of stable Stokes lines and 15 orders of stable anti-Stokes lines achieved within the 10 dB power deviation, with maximum optical signal-to-noise ratio (OSNR) of ~22 dB and ~17 dB and minimum OSNR of ~10 dB and ~7.5 dB for Stokes and anti-Stokes lines, respectively. In addition, the dynamic characteristics of the proposed FCG have been experimentally investigated. Such an FCG with fixed frequency spacing will find promising applications in fields of optical communication, microwave, optical sensing, etc.
      Citation: Photonics
      PubDate: 2023-03-11
      DOI: 10.3390/photonics10030296
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 297: Experimental Study on Measuring Petzval
           Image Plane of Streak Tube with Single Image

    • Authors: Houzhi Cai, Yong Wang, Fangke Zong, Lihong Niu, Qinlao Yang, Jingjin Zhang
      First page: 297
      Abstract: In the process of image reconstruction of compressed sensing algorithms, building a measurement matrix related to the parameters of the imaging system is necessary to improve its imaging quality. Additionally, building a compressed ultrafast imaging system based on a streak camera, which includes aberrations in the imaging system, is necessary. However, the aberration coefficient of the streak tube can be obtained only by numerical calculation based on the known internal structure of the streak tube, and it does not apply to a tube with an unknown structure. Based on the Lagrange–Helmholtz relation, which is widely established in electronic optical imaging systems, this study proposes a method to obtain the Petzval image plane of a streak tube by measuring only a single image without considering the internal structure of the streak tube. This method provides a reference for the construction of the measurement matrix in the application of the compressed sensing algorithm; additionally, it provides a test scheme for the performance index of the streak tube after assembly in commercial production to further optimize the assembly process and improve the yield of production.
      Citation: Photonics
      PubDate: 2023-03-11
      DOI: 10.3390/photonics10030297
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 298: High-Performance Dual-Channel Photonic
           Crystal Terahertz Wave Modulator Based on the Defect Mode Disappearance of
           a Combined Microcavity

    • Authors: Gaofang Li, Jie Tan, Yanxia Xu, Haoyang Cui, Bo Tang, Zhejing Jiao, Wei Zhou, Jundong Zeng, Nenghong Xia
      First page: 298
      Abstract: With the working frequency of wireless communication systems moving to a higher terahertz (THz) band, the design of high-performance THz wave modulators has become a pivotal issue to be tackled urgently in THz communication. In this paper, we design a high-performance dual-channel photonic crystal modulator to enable ON–OFF regulation of the THz wave based on the defect mode disappearance of combined microcavities. The modulator introduces Y-type line defects into silicon rod photonic crystals as a dual-channel waveguide and the point defects and ring resonator form a combined microcavity. Due to the refractive index of the ring resonator filler, gallium arsenide, it is tunable with pump light excitation, and the defect mode frequency of the combined microcavity can be dynamically changed. Under pump excitation with a wavelength of 810 nm and an intensity of 0.4 μJ/cm2, 1.34 THz and 1.83 THz dual-channel waves can be OFF due to the defect mode disappearance of the combined microcavity. This is simulated by the time-domain steady-state response and steady-state THz wave field intensity distribution of the modulator by the finite-difference time-domain method. The results indicate that the dual-channel modulator has large modulation depths of 100% and 99.7%, high modulation rates of 4.05 GHz and 4.17 GHz, and low insertion losses of 0.31 dB and 0.18 dB, which lays foundation for the development of high-speed and low-loss THz communication technology.
      Citation: Photonics
      PubDate: 2023-03-11
      DOI: 10.3390/photonics10030298
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 299: Cylindrical Waveguides and Multi-Junction
           Solar Cell Investigated for Two-Dimensional Photorecepto-Conversion Scheme

    • Authors: Yubo Wang, Xingbai Hong, Dan Wu, He Wu, Akira Ishibashi
      First page: 299
      Abstract: Presented is a new cylindrical waveguide (WG) system based on a two-dimensional photoreceptor-conversion scheme (2DPRCS) for lamppost-type solar-cell systems. The optical properties of polydimethylsiloxane (PDMS) were evaluated as the WG material, and we found that the intrinsic optical loss of our PDMS-based waveguide (~3 m−1) is low enough to be used in a 50 mm diameter lamppost 2DPRCS. The reflection solar concentrator (RSC) is also proposed, which can be combined with multijunction Si solar cells for lamppost-type systems that utilize sunlight coming not only from the south side but also from the east and west sides. We believe that, in the near future, this new approach based on 2DPRCS can enable high-efficiency concentrated photovoltaic systems.
      Citation: Photonics
      PubDate: 2023-03-12
      DOI: 10.3390/photonics10030299
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 300: Large-Scale Reconfigurable Integrated
           Circuits for Wideband Analog Photonic Computing

    • Authors: Yuhan Yao, Yanxian Wei, Jianji Dong, Ming Li, Xinliang Zhang
      First page: 300
      Abstract: Photonic integrated circuits (PICs) have been a research hotspot in recent years. Programmable PICs that have the advantages of versatility and reconfigurability that can realize multiple functions through a common structure have been especially popular. Leveraging on-chip couplers and phase shifters, general-purpose waveguide meshes connected in different topologies can be manipulated at run-time and support a variety of applications. However, current waveguide meshes suffer from relatively a low cell amount and limited bandwidth. Here, we demonstrate a reconfigurable photonic integrated computing chip based on a quadrilateral topology network, where typical analog computing functions, including temporal differentiation, integration, and Hilbert transformation, are implemented with a processing bandwidth of up to 40 GHz. By configuring an optical path and changing the splitting ratio of the optical switches in the network, the functions can be switched and the operation order can be tuned. This approach enables wideband analog computing of large-scale PICs in a cost-effective, ultra-compact architecture.
      Citation: Photonics
      PubDate: 2023-03-12
      DOI: 10.3390/photonics10030300
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 301: Modeling and Analysis of Device
           Orientation, Analog and Digital Performance of Electrode Design for High
           Speed Electro-Optic Modulator

    • Authors: Tushar Gaur, Pragya Mishra, Gopalkrishna Hegde, Talabattula Srinivas
      First page: 301
      Abstract: Electro-optic modulators (EOMs) are crucial devices for modern communication enabling high bandwidth optical communication links. Traveling wave electrodes are used to obtain high-speed modulation in these EOMs. We present the electrode design and analysis along with the study of effects of changing orientation on device performance for a thin-film lithium niobate tunable Mach–Zehnder interferometer (MZI) that offers sub-THz bandwidth operations. High velocity and impedance matching with low RF attenuation, high third-order SFDR (∼121 dB/Hz2/3) and a low half-wave voltage length product (1.74 have been achieved for a bandwidth of 136 GHz. High-speed digital modulation using multi-level signal formats (PAM-2, QAM-4 and QAM-16) with low BER for 400 Gbps data has been demonstrated to assess the digital performance of the device.
      Citation: Photonics
      PubDate: 2023-03-12
      DOI: 10.3390/photonics10030301
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 302: Mode-Modulation Structure Based on 650 nm
           Ridge Waveguide Edge-Emitting Laser

    • Authors: Xiao Sun, Peng Liu, Xiangen Ma, Xiaodong Zhang, Jian Su, Kang Chen, Qi Liu, Kai Jiang, Wenjing Tang, Wei Xia, Xiangang Xu
      First page: 302
      Abstract: Traditional laser diodes operating at 650 nm are more prone to high-order mode excitation, resulting in poorer beam quality. In this paper, we designed GaInP–AlGaInP laser diodes (LD) with a 650 nm range and a trench mode-modulation structure based on the structure of edge-emitting laser (EEL) diodes. The effect of the three-trench structure was investigated theoretically and experimentally. The right trench structure laser chips demonstrated good beam quality while maintaining a high power output. An electro-optical conversion efficiency of 56% was demonstrated with a slope efficiency of 1.32 W/A at a 40 mA current. The maximum optical output power reached 40.8 mW.
      Citation: Photonics
      PubDate: 2023-03-12
      DOI: 10.3390/photonics10030302
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 303: Statistical Analysis of Single-Order
           Diffraction Grating with Quasi-Random Structures

    • Authors: Huaping Zang, Zhihao Cui, Lai Wei, Hongjie Liu, Quanping Fan, Yangfan He, Bin Sun, Jihui Chen, Leifeng Cao
      First page: 303
      Abstract: Single-order diffraction gratings with quasi-random structures are effective optical elements in suppressing harmonics contamination. However, background intensity fluctuations introduced by quasi-random structures may affect the measurement of the spectra and the fluctuations lack quantitative description. A unified theoretical method is provided to describe quasi-random diffraction structures with arbitrary distribution functions and an arbitrary number of microstructures. The effect of the number of microstructures and distribution functions on the level of background fluctuations is evaluated. This work provides important guidance for the design and optimization of single-order diffraction gratings, which are attractive for spectral analysis and monochromator applications in synchrotron beam lines.
      Citation: Photonics
      PubDate: 2023-03-13
      DOI: 10.3390/photonics10030303
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 304: All-Monolithically Integrated Self-Scanning
           Addressable VCSEL Array for 3D Sensing

    • Authors: Takashi Kondo, Junichiro Hayakawa, Daisuke Iguchi, Tomoaki Sakita, Takafumi Higuchi, Kei Takeyama, Seiji Ohno, Michiaki Murata, Hiroyuki Usami
      First page: 304
      Abstract: We propose an all-monolithically integrated self-scanning addressable vertical-cavity surface-emitting laser array for time-of-flight measurement. Some advantages of addressable VCSELs for ToF measurement applications include large reductions in power consumption, heat generation, multi-pass noise, and flare noise. In this paper, we discuss the characteristics of the proposed self-scanning addressable VCSEL array. All layers in the epilayer structure of the proposed VCSEL array were formed at once by metal-organic chemical vapor deposition. The device consists of an (Al)GaAs-based thyristor and a conventional top-emitting 940-nm oxide-confined VCSEL on an n-type GaAs substrate. The array contained 12 blocks (4 × 3) that have more than 40 emitters each. The device required only four signals from a field-programmable gate array to select the emitting blocks and one emission signal from a conventional VCSEL driver, even for arrays containing hundreds of blocks. The proposed module is capable of one-block sequential emission, parallel emission from several blocks, and emission from all blocks. The rise and fall times of the fabricated VCSEL array were observed to be 200 and 400 ps, respectively, for each emission mode. The influence of flare noise from an obstacle in front of the camera was dramatically reduced by avoiding emission to the obstacle.
      Citation: Photonics
      PubDate: 2023-03-13
      DOI: 10.3390/photonics10030304
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 305: Spin-Orbit Coupling in Quasi-Monochromatic

    • Authors: Yuriy Egorov, Alexander Rubass
      First page: 305
      Abstract: We investigate the concept that the value of the spin-orbit coupling is the energy efficiency of energy transfer between orthogonal components. The energy efficiency changes as the beam propagates through the crystal. For a fundamental Gaussian beam, its value cannot exceed 50%, while the energy efficiency for Hermite–Gaussian and Laguerre–Gaussian beams of higher orders of the complex argument can reach a value close to 100%. For Hermite–Gauss and Laguerre–Gauss beams of higher orders of real argument, the maximum energy efficiency can only slightly exceed 50%. It is shown that zero-order Bessel–Gauss beams are able to achieve an energy efficiency close to 100% when generating an axial vortex in the orthogonal component in both monochromatic and polychromatic light, while for a polychromatic Laguerre–Gauss or Hermite–Gauss beam of a complex argument, the energy efficiency reduced to a value not exceeding 50%. The spin angular momentum is compensated by changing the orbital angular momentum of the entire beam, which occurs as a result of the difference in the topological charge of the orthogonally polarized component by 2 units.
      Citation: Photonics
      PubDate: 2023-03-13
      DOI: 10.3390/photonics10030305
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 306: Multi-User Visible Light Communication and
           Positioning System Based on Dual-Domain Multiplexing Scheme

    • Authors: Zhongxu Liu, Changyuan Yu
      First page: 306
      Abstract: Visible light communication and positioning (VLCP) is a promising candidate for constructing a multi-functional wireless network with large-scale connectivity and centimeter-level positioning. However, there is still a lack of effective methods to offer simultaneous visible light communication (VLC) and visible light positioning (VLP) functions for multiple users. Thus, we propose a multi-user VLCP system based on a dual-domain multiplexing (DDM) scheme, where both the time and code resources are multiplexed to transmit VLCP signals for multiple users simultaneously. In the proposed system, the data of different users are distinguished by using code division multiplexing technology, while the VLCP signals transmitted from different LEDs are separated by adopting time division multiplexing technology. The performances, including bit-error rate and positioning error, are evaluated through both simulation and experimentation to verify the feasibility of the proposed multi-user VLCP system. In the experiment, a VLCP system with four LED transmitters was able to simultaneously support low-speed VLC with free error and accurate VLP with a 2 cm precision for eight users. This offers an effective solution to support a large number of users with simultaneous VLC and VLP functions in the future multi-functional wireless network.
      Citation: Photonics
      PubDate: 2023-03-13
      DOI: 10.3390/photonics10030306
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 307: The Effect of Quantum Noise on Multipartite
           Entanglement from a Cascaded Parametric Amplifier

    • Authors: Hailong Wang, Yajuan Zhang, Xiong Zhang, Jun Chen, Huaping Gong, Chunliu Zhao
      First page: 307
      Abstract: The tripartite entanglement generated from a cascaded parametric amplifier is always present in the whole gain region in the ideal condition. However, in practical applications, the quantum entanglement is very fragile and easily deteriorated by quantum noise from interactions with external environments, e.g., the avoidable attenuation and amplification operations may lead to some degradation effects on the quantum entanglement. Therefore, in this work, bipartite entanglement for the three pairs and tripartite entanglement in this cascaded parametric amplifier under the circumstances of attenuation and amplification operations are analyzed by using positivity under partial transposition criterion. The results show that tripartite entanglement is robust to the deterioration effects from the attenuation and amplification operations rather than bipartite entanglement. Our results may find some practical applications of multipartite quantum entanglement in quantum secure communications.
      Citation: Photonics
      PubDate: 2023-03-13
      DOI: 10.3390/photonics10030307
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 308: Recent Advances in Coherent Optical
           Communications for Short-Reach: Phase Retrieval Methods

    • Authors: Abdullah S. Karar, Abdul Rahman El Falou, Julien Moussa H. Barakat, Zeynep Nilhan Gürkan, Kangping Zhong
      First page: 308
      Abstract: Short-reach transmission systems traditionally utilize intensity modulation (IM) at the transmitter and direct detection (DD) at the receiver due to their cost-effectiveness, small footprint, and low power consumption. However, with the exponential increase in bandwidth demand, coherent optical communication systems have become necessary for long-haul distances, requiring application-specific integrated circuits (ASIC) and advanced digital signal processing (DSP) algorithms coupled with high-speed digital-to-analog and analog-to-digital converters to achieve Tbit/s speeds. As coherent technology matures, it will eventually become feasible for short-reach transmission. In this context, self-coherent systems have emerged as an intermediary solution, offering advantages over traditional IM/DD systems. While comprehensive review studies exist on self-coherent transceivers, they do not cover recent advances in phase retrieval methods for short-reach optical communications. This review article highlights recent developments in cost-effective self-coherent detection for short-reach systems through comparing the benefits of single sideband (SSB) transmission and Kramers-Kronig detection to carrier-assisted phase retrieval, the Gerchberg-Saxton (GS) algorithm, and the transport of intensity equation (TIE) method.
      Citation: Photonics
      PubDate: 2023-03-13
      DOI: 10.3390/photonics10030308
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 309: Understanding Illumination Effect on
           Saturation Behavior of Thin Film Transistor

    • Authors: Shijie Jiang, Lurong Yang, Chenbo Huang, Qianqian Chen, Wei Zeng, Xiaojian She
      First page: 309
      Abstract: Thin film transistor (TFT) has been a key device for planal drive display technology, and operating the TFT device in a saturation regime is particularly important for driving the light emission at a stable current. Considering the light emission reaches the TFT planal, it is thereby meaningful to understand the effect of illumination on TFT saturation behavior in order to improve the stability of light emission. Through experiments and simulations, our study shows that the drift current of photogenerated carriers can follow a saturation behavior when the channel conductance is dominated by charges induced by gate bias rather than the charges generated by photons, and vice versa. The obtained device physics insights are beneficial for developing TFT technologies that can drive light emission at a stable current.
      Citation: Photonics
      PubDate: 2023-03-13
      DOI: 10.3390/photonics10030309
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 310: Enhancement of the Efficacy of Photodynamic
           Therapy against Uropathogenic Gram-Negative Bacteria Species

    • Authors: Vadim Elagin, Ivan Budruev, Artem Antonyan, Pavel Bureev, Nadezhda Ignatova, Olga Streltsova, Vladislav Kamensky
      First page: 310
      Abstract: Antimicrobial photodynamic therapy (aPDT) was demonstrated to be effective against various species of Gram-positive bacteria. However, the complex structure of a Gram-negative bacteria envelope limits the application of aPDT. Thus, the goal of this study was to improve the efficiency of antimicrobial photodynamic therapy with Fotoditazin against uropathogenic Gram-negative bacteria. The non-ionic detergent Triton X-100 and emulsifier Tween 80 were tested. The effect of extracellular photosensitizer on aPDT efficacy was analyzed. Moreover, the irradiation regime was optimized in terms of the output power and emitting mode. It was found that Triton X-100 at 10% vol enhanced the efficacy of aPDT of E. coli up to 52%. The subsequent observation demonstrated that, when the photosensitizer was removed from the extracellular space, the efficacy of aPDT on various Gram-negative species decreased dramatically. As for the irradiation mode, an increase in the laser output power led to an increase in the aPDT efficacy. The pulsed irradiation mode did not affect the aPDT efficacy. Thus, in order to achieve optimal aPDT efficacy, bacteria should be irradiated at 450-mW output power in the presence of Triton X-100 and a photosensitizer in the extracellular environment. However, it should be noted that the efficacy of aPDT of K. pneumoniae was significantly lower than for other species. The developed aPDT technique may be effective in a native environment of uropathogenic microorganisms.
      Citation: Photonics
      PubDate: 2023-03-14
      DOI: 10.3390/photonics10030310
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 311: Improving the Resistance of AO-OFDM Signal
           to Fiber Four-Wave Mixing Effect Based on Insertion Guard Interval

    • Authors: Kai Lv, Hao Liu, Anxu Zhang, Lipeng Feng, Xia Sheng, Yuyang Liu, Junjie Li, Xiaoli Huo
      First page: 311
      Abstract: In this paper, a method to suppress the impact of the nonlinear effects on an all optical orthogonal frequency division multiplexing (AO-OFDM) system is proposed. By inserting a guard interval (GI), the duty cycle of the optical signal in each symbol period of each subcarrier is decreased, thus generating a ‘zeroed’ temporal. By giving different time delays to the sub-carriers, these ‘zeroed’ temporals and optical signals of the adjacent sub-carriers are interleaved, which reduces the coincidence of the optical signals between the sub-carriers and eliminates the products of the four-wave mixing (FWM) effect to suppress the influence of the nonlinear effect on the system. The simulation results show that for an AO-OFDM system with 32 subcarriers, inserting GI and introducing different delays for each subcarrier can improve the transmission distance by 30 km or enhance the spectral efficiency by 16.7%, considering the 7% hard decision forward error correction (HD-FEC) threshold. Moreover, even when the number of subcarriers is up to 256 and the power of each subcarrier is as high as 0 dBm, our proposed signal optimization scheme can still guarantee that the BER can satisfy the 7% HD-FEC threshold.
      Citation: Photonics
      PubDate: 2023-03-14
      DOI: 10.3390/photonics10030311
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 312: Facile Fabrication of Mixed–Cation
           FA1−XCsXPbI3 Perovskites Thin Films for Photodetector Applications

    • Authors: Fenyun Wang, Pachaiyappan Murugan, Shunhong Dong, Xiaolu Zheng, Jiaxiu Man, Zhiyong Liu, Weibin Zhang, Ting Zhu, Hong-En Wang
      First page: 312
      Abstract: Formamidinium lead triiodide (FAPbI3) perovskite has received great attention because of its distinct optoelectronic property, smaller band gap (~1.5 eV), and higher thermal stability than methylammonium lead triiodide (MAPbI3). However, the efficient synthesis of such perovskite materials on a large scale at a low cost remains a challenge. In this work, mixed-cation FA1−xCsxPbI3 thin films were directly prepared in an atmospheric environment with a high film formation rate, low material loss, low cost, and low requirements for experimental instruments and environment. The as-obtained FAPbI3 films exhibited excellent optoelectronic properties, showing promising applications in the photodetection field.
      Citation: Photonics
      PubDate: 2023-03-14
      DOI: 10.3390/photonics10030312
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 313: Super-Resolution Structured Illumination
           Microscopy for the Visualization of Interactions between Mitochondria and
           Lipid Droplets

    • Authors: Ting He, Xuejuan Hu, Kai Hu, Jingxin Liu, Jiaming Zhang, Yadan Tan, Xiaokun Yang, Hengliang Wang, Yifei Liang, Shiqian Liu, Jianze Ye
      First page: 313
      Abstract: Visualizing the dynamics of fine structures in cells requires noninvasive, long-duration imaging of the intracellular environment at high spatiotemporal resolution and low background noise. With modularized hardware and polarized laser modulation, we developed a nanoscale super-resolution structured illumination microscope (SR-SIM) imaging technique. Combined with a reliable image reconstruction algorithm and timing synchronization of all devices, the super-resolution (SR) images in hepatocytes reached 134.95 nm spatial resolution and 50 fps temporal resolution. This imaging system was able to maintain the optimal operation state over hundreds of time points due to less exposure and low phototoxicity. In hepatocytes, interactions between mitochondria and lipid droplets (LDs) underpin many crucial physiological processes, ranging from cellular metabolism to signaling. In this study, we pioneered the use of the SIM system for imaging the interaction characteristics between mitochondria and LDs. More than 200 hepatocytes were counted and recorded effectively. We found that LDs in an unstable state were divided under mitochondrial contact and fused without it. Among 200 LDs, more than 69% were surrounded by mitochondria that tended to wrap LDs. The SR-SIM imaging technique was demonstrated to break the limitations of conventional imaging methods in spatial-temporal resolution and imaging duration in the field of the dynamic study between mitochondria and LDs.
      Citation: Photonics
      PubDate: 2023-03-14
      DOI: 10.3390/photonics10030313
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 314: Experimental Synthesis and Demonstration of
           the Twisted Laguerre–Gaussian Schell-Mode Beam

    • Authors: Yuning Xia, Haiyun Wang, Lin Liu, Yahong Chen, Fei Wang, Yangjian Cai
      First page: 314
      Abstract: The twisted Laguerre–Gaussian Schell-model (TLGSM) beam is a novel type of partially coherent beam embedded with both the second-order twist phase and the classical vortex phase. The intriguing properties induced by the interaction of the two types of phases have been demonstrated theoretically quite recently. In this work, we introduce a flexible way to experimentally synthesize a TLGSM beam with controllable twist strength. The protocol relies on the discrete pseudo-mode representation for the cross-spectral density of a TLGSM beam, in which the beam is viewed as an incoherent superposition of a finite number of spatially coherent modes. We show that all these pseudo modes endowed with random phases are mutually uncorrelated and can be encoded into a single frame of a dynamic computer-generated hologram. By sequentially displaying dynamic holograms on a single spatial-light modulator, the controllable TLGSM beam can be synthesized experimentally. The joint effect of the two phases on the propagation and self-reconstruction characteristics of the synthesized beam has also been studied in the experiment.
      Citation: Photonics
      PubDate: 2023-03-14
      DOI: 10.3390/photonics10030314
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 315: Effects of Pulsed Red and Near-Infrared
           Light on Neuroblastoma Cells—Pilot Study on Frequency and Duty Cycle

    • Authors: Luyao Tang, Haokuan Qin, Shangfei Lin, Muqing Liu
      First page: 315
      Abstract: Transcranial photobiomodulation (tPBM) is an innovative intervention for a wide range of neurological and psychological conditions. tPBM therapy can enhance the metabolic capacity of neurons and bring about a variety of beneficial changes. This study mainly investigated the photobiological effects of pulsed red and near-infrared (NIR) light on neuron-like neuroblastoma SH-SY5Y cells by in vitro experiments. We covered the irradiation parameters, including wavelength (660, 850 nm), power density (5, 10, 20, 50, 100 mW/cm2), frequency (40, 100, 1000 Hz), and duty cycle (10%, 50%, 90%), finding that pulsed light generated a distinct effect compared with continuous-wave light on the cellular responses. Cell viability, mitochondrial membrane potential (MMP), adenosine triphosphate (ATP), and reactive oxygen species (ROS) showed significant increase after irradiation of the adequate fluence amount (4.8–9.6 J/cm2), and the enhancement was more notable under 40 Hz pulsed lighting. Under pulsed lighting with an average power density of 10 mW/cm2, cells that received irradiation of higher peak power density up to 100 mW/cm2 with a 10% duty cycle showed slightly higher metabolic responses. In addition, it was found that under same total fluence, short-term irradiation with high power density was more effective than long-term irradiation with low power density, which indicated the existence of a threshold to achieve effectiveness.
      Citation: Photonics
      PubDate: 2023-03-15
      DOI: 10.3390/photonics10030315
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 316: THz Pulse Generation and Detection in a
           Single Crystal Layout

    • Authors: Moses Eshovo Ojo, Frederic Fauquet, Patrick Mounaix, Damien Bigourd
      First page: 316
      Abstract: The THz pulse of a few picosecond durations have been generated and detected via optical rectification and electro-optic effect within the same ZnTe crystal. An unbalanced single-shot detection scheme was performed to characterize the signal. As a result, a multicycle signal was obtained, in which two-photon absorption and other associated nonlinear effects were reportedly negligible. The experimental set-up is compact, economical, easy to build and has the added simplicity of facilitating an independent analysis of the horizontal or vertical polarization arm of the THz-modulated chirped probe beam. This work finds a useful application in integrated THz devices, narrow-band THz phonon spectroscopy and spectroscopic investigation of fast-occurring processes.
      Citation: Photonics
      PubDate: 2023-03-15
      DOI: 10.3390/photonics10030316
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 317: Plasmonic Metasurfaces for Superposition of
           Profile-Tunable Tightly Focused Vector Beams and Generation of the
           Structured Light

    • Authors: Lianmeng Li, Xiangyu Zeng, Manna Gu, Yuqin Zhang, Rui Sun, Ziheng Zhang, Guosen Cui, Yuxiang Zhou, Chuanfu Cheng, Chunxiang Liu
      First page: 317
      Abstract: Vector beams (VBs) and their superposition have found important applications in versatile fields such as optical communications, super-resolution microscopy and quantum information, and metasurfaces have enabled the miniaturization and integration of the optical systems manipulating the vector beams, providing potential applications to subwavelength regimes. In this work, we propose a metasurface to realize the superposition of profile-tunable tightly focused VBs, with the novel structured light fields generated. The metasurface is composed of two sets of orthogonal-nanoslit pairs arranged on the inner and outer rings. By realizing the chiral conversion of circularly polarized light with the slit-pairs which act as half-wave plates, and by creating helical phase profiles of optical vortices with the geometrical phase of rotational nano-slit pairs, two focused Bessel VBs are formed. By finely varying the diameters of two sets of rings, the doughnuts of the two Bessel VBs of different orders are tuned to be of the same size, and the superposition of the two VBs is realized. The theoretical analyses of the superimposed fields were presented, the FDTD simulations were performed to optimize the designed metasurfaces, and the experimental measurements were carried out to validate feasibility of the metasurface. The novel and interesting characteristics of the superposed fields different from those of the conventional VBs were demonstrated. This work will be of significance for classical and quantum applications of VBs in various fields.
      Citation: Photonics
      PubDate: 2023-03-15
      DOI: 10.3390/photonics10030317
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 318: Three-Dimensional Mapping Technology for
           Structural Deformation during Aircraft Assembly Process

    • Authors: Yue Liu, Dongming Yan, Lijuan Li, Xuezhu Lin, Lili Guo
      First page: 318
      Abstract: Owing to the assembly state changes during aircraft assembly processes, assembly force-deformation problem occurs. To obtain the structure shape in the product assembly process efficiently and accurately, a three-dimensional (3D) mapping technology for the structural deformation during the aircraft assembly process is proposed combined with a fiber Bragg grating (FBG) optical fiber sensor and binocular vision measurement system. First, this study established a curvature transformation model using optical fiber monitoring data, obtained the 3D spatial deformation of the product, and completed the unification of the optical fiber wavelength change and spatial 3D point coordinate heterogeneous data. Second, a mesh deformation optimization algorithm based on point-cloud optimization was established. Subsequently, the deformation effects of four mesh deformation models were compared to verify the feasibility and accuracy of HEC-Laplace, and the 3D mapping of the product structure shape in the assembly process was realized. Finally, a cantilever wing model was used to verify the deformation of different loading modes. The results show that the product structure changes can be accurately obtained through the proposed technology, thereby improving the accuracy control and overall assembly quality in the aircraft assembly process and providing a theoretical basis for intelligent aircraft assembly.
      Citation: Photonics
      PubDate: 2023-03-16
      DOI: 10.3390/photonics10030318
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 319: Adaptive Weighted K-Nearest Neighbor
           Trilateration Algorithm for Visible Light Positioning

    • Authors: Kaiyao Wang, Yi He, Xinpeng Huang, Zhiyong Hong
      First page: 319
      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 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%.
      Citation: Photonics
      PubDate: 2023-03-16
      DOI: 10.3390/photonics10030319
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 320: Wavefront Sensing by a Common-Path
           Interferometer for Wavefront Correction in Phase and Amplitude by a Liquid
           Crystal Spatial Light Modulator Aiming the Exoplanet Direct Imaging

    • Authors: Andrey Yudaev, Alexander Kiselev, Inna Shashkova, Alexander Tavrov, Alexander Lipatov, Oleg Korablev
      First page: 320
      Abstract: We implemented the common-path achromatic interfero-coronagraph both for the wavefront sensing and the on-axis image component suppression, aiming for the stellar coronagraphy. A common-path achromatic interfero-coronagraph has its optical scheme based on a nulling rotational-shear interferometer. The angle of rotational shear can be chosen at a small angular extent of about 10 deg. Such a small angular shear maintains the coronagraphic contrast degradation known as the stellar leakage effect, caused by a finite stellar size. We study the phase and amplitude wavefront control by a liquid crystal spatial light modulator of reflection type which is used as the pixilated active adaptive optics unit. Therefore, adaptive optics perform a wavefront-correcting input toward a stellar interfero-coronagraph aiming at the direct exoplanet imaging. Presented here are both the numeric evaluations and the lab experiment stand to prove the declared functionality output.
      Citation: Photonics
      PubDate: 2023-03-16
      DOI: 10.3390/photonics10030320
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 321: Optimization of Sampling Mode in Macro
           Fourier Ptychography Imaging Based on Energy Distribution

    • Authors: Runbo Jiang, Dongfeng Shi, Yingjian Wang
      First page: 321
      Abstract: Fourier ptychography imaging technology is a method developed in recent years to achieve high-resolution imaging. In the traditional macro Fourier ptychography technology, the scanning method when the camera captures low-resolution images mostly uses the rectangular linear grid format. These acquired images contain a small amount of complementary information, and a large number of low-resolution images are needed to achieve high-resolution imaging. Redundant measurements will extend the sampling and reconstruction time, and require more computing resources. In this paper, we propose to obtain the target image spectral energy distribution by pre-sampling. And according to the energy distribution, we use irregular and non-uniform sampling modes to restore the target image. With the same number of samples and same reconstruction time, higher resolution imaging can be achieved compared with traditional methods. Simulation and experimental studies are carried out in this paper, and the results confirm the effectiveness of the proposed methods. Compared with the traditional sampling mode, the two sampling modes proposed in this paper increase the resolution from 4.49 lp/mm to 5.66 lp/mm and 5.04 lp/mm respectively.
      Citation: Photonics
      PubDate: 2023-03-16
      DOI: 10.3390/photonics10030321
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 322: Sixty-Nine-Element Voice Coil Deformable
           Mirror for Visible Light Communication

    • Authors: Lv Jiang, Lifa Hu, Qili Hu, Xingyu Xu, Jingjing Wu, Lin Yu, Yang Huang
      First page: 322
      Abstract: To overcome the atmospheric turbulence aberration, and improve the quality of light beam in visible light communication (VLC), a compact 69-element deformable mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice coil actuator were optimized by electromagnetic theory and the finite element method. The DM was optimized from the aspects of thermal deformation, response time, coupling coefficient, and other parameters. Finally, wavefront fitting and residual calculation were completed according to the influence function. The optimized voice coil deformable mirror (VCDM) has a large phase stroke, good thermal stability, a short response time of less than 0.7 ms, and a large first resonance of 2045 Hz. The fitting residuals of the VCDM for the first 10 Zernike modes with a PV value of 8 μm are all below 10 nm (RMS). Compared with a similar DM, the obtained results from our compact VCDM indicate that it has a higher wavefront fitting precision. VCDM corrected complex random aberrations in the VLC scenario and improved the coupling efficiency of the signal beam, proving that the compact VCDM with high performance and low cost has a good application prospect in VLC systems.
      Citation: Photonics
      PubDate: 2023-03-17
      DOI: 10.3390/photonics10030322
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 323: Suppression of Nonlinear Optical Effects in
           DWDM-PON by Frequency Modulation Non-Coherent Detection

    • Authors: Lei Xin, Xiao Xu, Liuge Du, Chonglei Sun, Feng Gao, Jia Zhao
      First page: 323
      Abstract: We propose a simple and cost-effective method, using a direct frequency modulation (FM) and noncoherent detection (NCD) scheme, to suppress the nonlinear optical effects in dense wavelength division multiplexed (DWDM) optical communication. The FM transmitter comprises a directly modulated distributed feedback laser and a saturable semiconductor optical amplifier. In the NCD receiver, an optical slope filter as the FM to intensity modulation (IM) signal convertor is placed before a conventional photodetector. Because the FM signal has more evenly distributed optical power, bit-pattern-dependent nonlinear effects are consequently suppressed. After analyzing the nonlinear effects in the FM-NCD system and traditional IM direct detection (IM-DD) system, we found that the minimum achievable BER of the proposed FM-NCD scheme is 40 dB smaller. Moreover, a 2 Tbps (10 Gb/s × 200 channels) capacity was achieved by the FM-NCD system in 100 km DWDM passive optical networks (PONs), which is twice the capacity of the IM-DD system (10 Gb/s × 100 channels) under the same condition. These results indicate that WDM-PONs with the cost-effective FM-NCD scheme are strong candidates for future broad access networks and show great potential for the combination of optical access and metro networks for future generations of PONs.
      Citation: Photonics
      PubDate: 2023-03-17
      DOI: 10.3390/photonics10030323
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 324: Precise RF Phase Measurement by Optical
           Sideband Generation Using Mach–Zehnder Modulators

    • Authors: Qingchuan Huang, Tetsuya Kawanishi
      First page: 324
      Abstract: A novel radio frequency (RF) phase measurement method that uses optical modulation was proposed. The mathematical model of Mach–Zehnder modulator (MZM) characterization was reviewed. By measuring the output sideband power of the optical modulator, the phase difference of the electric signals fed to the modulator was experimentally measured, and picosecond-level accuracies were achieved. This technique is expected to be useful for radio-over-fiber-based antenna array systems.
      Citation: Photonics
      PubDate: 2023-03-17
      DOI: 10.3390/photonics10030324
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 325: Orbital Angular Momentum Resonances Arising
           from Mode Coupling in Hollow-Core Fibers

    • Authors: Grigory Alagashev, Andrey Pryamikov
      First page: 325
      Abstract: It is known that the growth of the orbital part of the angular momentum of the fundamental air core mode of the negative curvature hollow-core fibers (NCHCFs) with circular polarization occurs at the edge of the transmission bands due to the spin–orbit interaction. In this paper, we consider the resonant behavior of orbital angular momentum (OAM) for a linearly polarized fundamental air core mode in straight and bent NCHCF. The resonant growth of OAM is associated with coupling between the linear polarized fundamental air core mode and the cladding capillary wall modes. The coupling between the modes arises due to crossing and anti-crossing. This OAM growth can be explained by a complex interaction of energy fluxes of the coupled modes under crossing. This phenomenon may be useful for a deeper understanding of the processes arising from mode coupling in fiber optics and nanophotonics, as well as for generating and transmitting OAM modes in micro-structured optical fibers.
      Citation: Photonics
      PubDate: 2023-03-17
      DOI: 10.3390/photonics10030325
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 326: Broad Tunable and High-Purity Photonic
           Microwave Generation Based on an Optically Pumped QD Spin-VCSEL with
           Optical Feedback

    • Authors: Zhenye Shen, Yu Huang, Xin Zhu, Pei Zhou, Penghua Mu, Nianqiang Li
      First page: 326
      Abstract: Spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) with birefringence-induced polarization oscillations have been proposed to generate desired photonic microwave signals. Here, we numerically investigate the generation of photonic microwave signals in an optically pumped quantum dot (QD) spin-VCSEL. First, the influence of intrinsic key parameters on period-one (P1) oscillations and microwave properties is discussed. Second, the difference between microwave generation based on the quantum well (QW) and QD spin-VCSELs is analyzed by controlling the carrier capture rate that is described in the spin-flip model. The QD spin-VCSEL shows superior microwave quality in the low-frequency range (e.g., 10 GHz~20 GHz) compared with the QW spin-VCSEL. Finally, to boost the performance of the generated photonic microwave signal, optical feedback is introduced. The results show that dual-loop feedback can simultaneously narrow the microwave linewidth and suppress the side modes that are derived from the external cavity mode.
      Citation: Photonics
      PubDate: 2023-03-18
      DOI: 10.3390/photonics10030326
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 327: Analysis of the Emission Features in
           CdSe/ZnS Quantum Dot-Doped Polymer Fibers

    • Authors: Xuefeng Peng, Zhijian Wu, Chen Ye, Yang Ding, Wei Liu
      First page: 327
      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. 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.
      Citation: Photonics
      PubDate: 2023-03-18
      DOI: 10.3390/photonics10030327
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 328: Exclusive Effect in Rydberg Atom-Based
           Multi-Band Microwave Communication

    • Authors: Shuhang You, Minghao Cai, Haoan Zhang, Zishan Xu, Hongping Liu
      First page: 328
      Abstract: We have demonstrated a Rydberg atom-based two-band communication with the optically excited Rydberg state coupled to another pair of Rydberg states by two microwave fields, respectively. The initial Rydberg state is excited by a three-color electromagnetically-induced absorption in rubidium vapor cell via cascading transitions, with all of them located in infrared bands: a 780 nm laser servers as a probe to monitor the optical transmittancy via transition 5S1/2→5P3/2, 776 nm and 1260 nm lasers are used to couple the states 5P3/2 and 5D5/2 and states 5D5/2 and 44F7/2. Experimentally, we show that two channel communications carried on the two microwave transitions influence each other irreconcilably, so that they cannot work at their most sensitive microwave-optical conversion points simultaneously. For a remarkable communication quality for both channels, the two microwave fields both have to make concessions to reach a common microwave-optical gain. The optimized balance for the two microwave intensities locates at EMW1=6.5 mV/cm and EMW2=5.5 mV/cm in our case. This mutual exclusive influence is theoretically well-explained by an optical Bloch equation considering all optical and microwave field interactions with atoms.
      Citation: Photonics
      PubDate: 2023-03-19
      DOI: 10.3390/photonics10030328
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 329: Wheel-Based MDM-PON System Incorporating
           OCDMA for Secure Network Resiliency

    • Authors: Meet Kumari, Vivek Arya, Hamza Mohammed Ridha Al-Khafaji
      First page: 329
      Abstract: Wheel-based network resilience passive optical network (PON) based on mode division multiplexing (MDM) can be integrated with optical code division multiple access (OCDMA) schemes efficiently for the fixed and backhaul traffic under normal and break/failure fiber operating conditions. In this work, a bidirectional 10/2.5 Gbit/s hybrid MDM-OCDMA-PON system using multi-weight zero cross-correlation (MWZCC) code is proposed. Donut modes 0 and 1 are incorporated by the MDM technique in the proposed system. The benefit of this work is to offer an inexpensive, high-bandwidth and advanced long-haul network with satisfactory resource utilization ability for fiber links with protection against faults and to improve the reliability along with survivability of the network. The simulation results show the successful realization of the multimode fiber (MMF) link at 1.6 km in the uplink and 1.2 km in the downlink directions under an acceptable bit error rate (BER). The minimum accepted received power of −31 dBm in uplink and −27 dBm in downlink over 1 km link at 10/2.5 Gbit/s rate is obtained. Moreover, the minimum received power of −20 dBm in uplink and −30 dBm downlink is achieved by using MWZCC code compared to other codes handling 58 simultaneous end users. Further, the influence of fiber impairments and connected devices on the proposed approach is numerically evaluated. Moreover, it is shown that the wheel based proposed approach performs well than other topologies for the bidirectional network resilience transmission.
      Citation: Photonics
      PubDate: 2023-03-19
      DOI: 10.3390/photonics10030329
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 330: Performance Analysis of LDPC-Coded OFDM in
           Underwater Wireless Optical Communications

    • Authors: Jianzhong Guo, Jinpeng Xiao, Jing Chen, Xin Shan, Dejin Kong, Yan Wu, Yong Ai
      First page: 330
      Abstract: The performance of Low-Density Parity-Check (LDPC)-coded Orthogonal Frequency Division Multiplexing (OFDM) is investigated over turbulence channels in underwater wireless optical communications (UWOC). The relation between the bit error ratio (BER) and parameters such as the scintillation coefficient, signal-to-noise ratio (SNR), length of LDPC code, and order of OFDM is quantified by simulation. Results show that while the OFDM with subcarrier quadrature amplitude modulation (QAM-OFDM) has slightly better anti-turbulence performance than the OFDM with subcarrier phase shift keying modulation (PSK-OFDM), the LDPC-coded QAM-OFDM has a much better performance than the QAM-OFDM and the LDPC-coded PSK-OFDM, and, at SNR = 12, it decreases the BER by four orders of magnitude compared to the 16QAM-OFDM system when the scintillation coefficient σξ2 = 0.05.
      Citation: Photonics
      PubDate: 2023-03-20
      DOI: 10.3390/photonics10030330
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 331: Non-Collinear Attosecond Streaking without
           the Time Delay Scan

    • Authors: Peng Xu, Xianglin Wang, Huabao Cao, Hao Yuan, Liang-Wen Pi, Yishan Wang, Yuxi Fu, Yonglin Bai, Wei Zhao
      First page: 331
      Abstract: Attosecond streaking provides an extremely high temporal resolution for characterizing light pulses and photoionization processes with attosecond (10−18 s) accuracy, which employs a laser as a streaking field to deflect electrons generated by photoionization. The current attosecond streaking requires a time delay scan between the attosecond pulses and streaking field with attosecond accuracy and a femtosecond range, which is difficult to realize real-time measurement. In this study, we theoretically propose a non-collinear attosecond streaking scheme without the time delay scan, enabling real-time and even the potential to perform single-shot attosecond pulse measurement. In the proposal, time-delay information is projected into longitudinal space, both horizontally and vertically, enabling attosecond pulse characterization with temporal-spatial coupling. From our calculation, down to 70 as pulses with pulse front and wavefront tilt are characterized with high accuracy. Our study not only provides a method toward real-time attosecond pulse measurement, but also an approach for attosecond pump-probe experiments without time delay scan.
      Citation: Photonics
      PubDate: 2023-03-20
      DOI: 10.3390/photonics10030331
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 332: A Novel Measurement Method for Spin
           Polarization Three Axis Spatial Distribution in Spin-Exchange Relaxation
           Free Atomic Magnetometer

    • Authors: Xiujie Fang, Jin Li, Yanning Ma, Kai Wei, Wenfeng Fan, Yueyang Zhai, Wei Quan, Zhisong Xiao
      First page: 332
      Abstract: The measurement of atomic spin polarization distribution in spin-exchange relaxation free (SERF) magnetometer is an important topic for improving the sensitivity and consistency of multi-channel magnetic field measurement applications. A novel spin polarization spatial distribution measurement method is presented based on the transient response of the magnetometer after modulating the pumped light with a chopper. Polarization is obtained by a slow-down factor based on the fast spin-exchange interaction effects. Longitudinal and transverse polarization distributions are measured simultaneously without interrupting the operation of the SERF status. Under different oscillating magnetic fields, the spin polarization is measured at the cell centroid. Residual magnetic field inside the magnetometer is obtained from the linear relationship between the precession frequency and the oscillating magnetic field. The one-dimensional polarization distributions in the x, y, and z axes are measured using a digital micromirror device with a resolution of 0.25 cm. The measurement results conform to the Lambert-Bier absorption law and the Gaussian distribution law. Furthermore, 7 × 7 two-dimensional spatial distribution measurements of polarization on the xy and yz planes are performed. Nonuniformity of 1.04 in the xy plane and 1.82 in the yz plane in the built magnetometer. Compared with other measurement methods, the distribution measurement method proposed is independent of optical depth and suitable for low polarization and high polarization applications. Based on the results of the proposed measurement method of spin polarization spatial distribution, further compensation can improve the application consistency of multi-channel magnetic field measurements and improve the sensitivity of single-channel differential measurements.
      Citation: Photonics
      PubDate: 2023-03-20
      DOI: 10.3390/photonics10030332
      Issue No: Vol. 10, No. 3 (2023)
  • Photonics, Vol. 10, Pages 333: Transmission Properties in Plasma Photonic
           Crystal Controlled by Magnetic Fields

    • Authors: Hailu Wang, Jianfei Li, Liang Guo, Dongliang Ma, Jingfeng Yao, He-Ping Li
      First page: 333
      Abstract: The transmission properties in two-dimensional plasma photonic crystal composed of plasma and yttrium–iron–garnet rods with square lattices are demonstrated under different electron densities and external magnetic fields. The TE and TM modes respond to the permittivity tensor and the permeability tensor produced by the magnetic field. For TM polarization, two distinct attenuation peaks appear in the ranges of 3.4–3.62 GHz and 3.78–4 GHz, induced by the external magnetic fields, and the location of these attenuation peaks can be modulated by modifying the electron densities. For TE polarization, a flat transmission spectrum was obtained in the range of 4–4.6 dB by increasing the electron density to 3×1012 cm−3. Then, a Y-shaped plasma photonic crystal waveguide is designed. The transmission path can be modulated by changing the direction of the external magnetic field. By regulating the electron density, switching the Y-shaped waveguide on and off can be achieved.
      Citation: Photonics
      PubDate: 2023-03-20
      DOI: 10.3390/photonics10030333
      Issue No: Vol. 10, No. 3 (2023)
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