Photonics

12 pages, 2377 KiB

Open AccessArticle

Low-Cost Optical Filters Based on SiO_xC_y:H and Ag Thin Films Fabricated by Plasma Enhanced Chemical Vapor Deposition and Sputtering

by Ahmed Kotbi, Michael Lejeune, Pierre Barroy, Ilham Hamdi Alaoui, Wiaam El Hakim, Frederic Lamarque and Andreas Zeinert

Photonics 2024, 11(11), 1096; https://doi.org/10.3390/photonics11111096 (registering DOI) - 20 Nov 2024

Abstract

Hexamethyldisiloxane (HMDSO) is an organosilicon compound with a modifiable bandgap, depending on the deposition conditions. This material has many unique properties due to its stability, low toxicity, and strong adhesion, making it useful as a protective barrier against corrosion, moisture, and oxidation. In [...] Read more.

Hexamethyldisiloxane (HMDSO) is an organosilicon compound with a modifiable bandgap, depending on the deposition conditions. This material has many unique properties due to its stability, low toxicity, and strong adhesion, making it useful as a protective barrier against corrosion, moisture, and oxidation. In this work, HMDSO films were deposited on glass substrates by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique at different deposition times. The optical properties of HMDSO films, such as dielectric permittivity, refractive index, extinction and absorption coefficients, and band gap energy, are inferred from transmission and reflection spectra. As the deposition time increased, the real part of the dielectric constant, the refractive index, and the bandgap energy showed a decrease, dropping from 4.24 to 3.40, from 2.06 to 1.84, and from 2.85 eV to 2.03 eV, respectively. The latter result is determined using classical models such as the O’Leary-Johnson-Lim (‘OJL’) interband transition and the harmonic oscillator model. HMDSO and Silver are used in this study for the fabrication of optical filters using two types of structures, a multiple cavity metal–dielectric (MCMD) and the Fabry–Perot structure. The silver layers are deposited by a sputtering process. The MCMD optical filter shows a higher transmittance of about 30%, but a wide range of wavelengths is transmitted. In contrast, the Fabry–Perot filter showed high contrast but a lower transmittance of about 20%. Full article

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

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15 pages, 15053 KiB

Open AccessArticle

Simple Direct Measurement of the Orbital Stokes Parameters in Structured Vortex Beams

by Alexander Volyar, Mikhail Bretsko, Server Khalilov and Yana Akimova

Photonics 2024, 11(11), 1095; https://doi.org/10.3390/photonics11111095 (registering DOI) - 20 Nov 2024

Abstract

An analogy with the polarization Stokes parameters and symplectic methods of the second-order intensity moment matrix allowed us to develop a simple technique for measuring the orbital Stokes parameters followed by mapping the structured beam states onto the orbital Poincaré sphere. The measurement [...] Read more.

An analogy with the polarization Stokes parameters and symplectic methods of the second-order intensity moment matrix allowed us to develop a simple technique for measuring the orbital Stokes parameters followed by mapping the structured beam states onto the orbital Poincaré sphere. The measurement process involves only two shots of the beam intensity patterns in front of a cylindrical lens and in its double focus. Such a simple measurement approach is based on the reciprocity effect between the experimentally measured cross-intensity element

W_{x y}

and the orbital angular momentum of the intensity moment matrix. For experiments, we chose two types of two-parameter structured beams, namely, structured Laguerre–Gaussian beams and binomial beams. We obtained a good agreement between our theoretical background and the experiments, as well as the results of other authors. Full article

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

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19 pages, 11818 KiB

Open AccessArticle

Enhancing Alignment Accuracy in Laser Wireless Power Transmission Systems Using Integrated Target Detection and Perturbation-Observation Method

by Jinsong Kang, Liangrong Sun, Yanping Zhou and Yunfeng Bai

Photonics 2024, 11(11), 1094; https://doi.org/10.3390/photonics11111094 (registering DOI) - 20 Nov 2024

Abstract

This paper introduces a high-precision alignment method for laser wireless power transmission (LWPT) systems, integrating neural network-based target detection with a perturbation-observation technique. The objective is to enhance the alignment accuracy between the laser spot and the photovoltaic array, thereby improving energy transfer [...] Read more.

This paper introduces a high-precision alignment method for laser wireless power transmission (LWPT) systems, integrating neural network-based target detection with a perturbation-observation technique. The objective is to enhance the alignment accuracy between the laser spot and the photovoltaic array, thereby improving energy transfer efficiency. The method’s key feature is its ability to achieve these results without requiring additional optical components, simplifying system design. Continual assessment and adjustment based on real-time output power data ensure optimal alignment, maximizing the photovoltaic array power output. Experimental results demonstrated that the proposed method achieved an initial alignment precision with pixel errors below 3%, translating to a physical error of approximately 7 mm. Fine-tuning through the perturbation-observation method further optimized the alignment, resulting in a photovoltaic array power output of 98.70% of its maximum potential. This hybrid approach provides a reliable solution for boosting the performance of LWPT systems, offering significant potential for practical applications. Full article

(This article belongs to the Special Issue Latest Papers Related to OWPT 2024 on the Topics of Devices, Components and Systems)

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11 pages, 2679 KiB

Open AccessArticle

Analysis of Randomization Capacity in Quantum Noise Randomized Cipher System

by Mingrui Zhang, Shuang Wei, Yuang Li, Yajie Li, Yongli Zhao and Jie Zhang

Photonics 2024, 11(11), 1093; https://doi.org/10.3390/photonics11111093 (registering DOI) - 20 Nov 2024

Abstract

We propose and verify a method for analyzing the randomization capacity in a 160 km quantum noise randomized cipher system with different data modulation formats. The randomization capacity is defined as the difference in mutual information between Alice and Bob while the randomization [...] Read more.

We propose and verify a method for analyzing the randomization capacity in a 160 km quantum noise randomized cipher system with different data modulation formats. The randomization capacity is defined as the difference in mutual information between Alice and Bob while the randomization level is at 0 and at its maximum, under the condition of error-free transmission. Our experimental analysis examines the capacity of quantum noise randomized cipher systems under different optical signal-to-noise ratios for each modulation format. Additionally, we analyze the noise masking values while the randomization reaches its capacity. The experimental results indicate that the binary phase shift-keying-based quantum noise randomized cipher system achieves the highest randomization capacity and highest noise masking value. Full article

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

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16 pages, 7263 KiB

Open AccessArticle

Inscription and Thermal Stability of Fiber Bragg Gratings in Hydrogen-Loaded Optical Fibers Using a 266 nm Pulsed Laser

by Xiangxi Zhu, Zixuan Xin, Haoming Zhu, Hongye Wang, Xin Cheng, Hwa-Yaw Tam, Hang Qu and Xuehao Hu

Photonics 2024, 11(11), 1092; https://doi.org/10.3390/photonics11111092 - 20 Nov 2024

Abstract

Fiber Bragg gratings (FBGs) have gained substantial research interest due to their exceptional sensing capabilities. Traditionally, FBG fabrication has required the use of pre-hydrogenated fibers and high-cost laser systems such as excimer lasers at 193 nm or femtosecond lasers. In this study, we [...] Read more.

Fiber Bragg gratings (FBGs) have gained substantial research interest due to their exceptional sensing capabilities. Traditionally, FBG fabrication has required the use of pre-hydrogenated fibers and high-cost laser systems such as excimer lasers at 193 nm or femtosecond lasers. In this study, we present the first instance of FBG inscription in hydrogen-loaded, standard single-mode silica optical fibers using a more affordable 266 nm solid-state pulsed laser combined with a scanning phase mask lithography technique. We systematically explored the effects of pulse energy and scanning speed on the quality and spectral characteristics of the gratings, achieving reflectivities as high as 99.81%. Additionally, we tracked the spectral evolution during the FBG inscription process, demonstrating uniform growth of the core mode. We also investigated the stability of the core mode during a 24-h thermal annealing process up to 150 °C. The sensitivity was 10.7 pm/°C in the range of 0 to 130 °C. Furthermore, strain measurement was conducted based on the FBG annealed at 100 °C, showing a sensitivity of 0.943 pm/µε in the range of 0 to 1667 µε. Full article

(This article belongs to the Special Issue Advances in Polymer Optical Fiber Sensors: Materials, Designs and Applications)

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17 pages, 5969 KiB

Open AccessArticle

Rapid Autofocus Method Based on LED Oblique Illumination for Metaphase Chromosome Microscopy Imaging System

by Changliang Yu, Fangqiu Ding, Zhenyu Ma and Yuguo Tang

Photonics 2024, 11(11), 1091; https://doi.org/10.3390/photonics11111091 - 20 Nov 2024

Abstract

In clinical practice, microscopes are commonly used for imaging chromosomes to diagnose genetic diseases. Achieving precise and rapid autofocusing is a significant challenge in the advancement of high-throughput chromosome imaging systems. Here, we introduce a rapid autofocus method based on LED oblique illumination [...] Read more.

In clinical practice, microscopes are commonly used for imaging chromosomes to diagnose genetic diseases. Achieving precise and rapid autofocusing is a significant challenge in the advancement of high-throughput chromosome imaging systems. Here, we introduce a rapid autofocus method based on LED oblique illumination for dual-objective configuration in metaphase chromosome imaging system. Our method utilizes a programmable LED array for sample illumination, employing a sequential activation of two LEDs from opposing angles to create oblique illumination. The defocus distance is ascertained through image cross-correlation calculation. Illumination with multiple LEDs in the array is used to acquire bright-field images after completing the focusing. Our method can perform continuous autofocus under a 10× objective and a 100× oil immersion objective, with average focusing errors of 1.29 μm and 0.12 μm, respectively. The total imaging time for a single sample has been significantly reduced from approximately 10 min with conventional methods to just 2 min. This study provides preliminary evidence supporting the viability of developing a next-generation high-throughput chromosome scanner employing a LED array. Full article

(This article belongs to the Section Optical Interaction Science)

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15 pages, 3783 KiB

Open AccessArticle

Exploring Changes in Ocular Aberrations for Different Fixation and Accommodation Stimuli

by María Mechó-García, Rute J. Macedo-de-Araújo, Paulo Fernandes and José Manuel González-Méijome

Photonics 2024, 11(11), 1090; https://doi.org/10.3390/photonics11111090 - 20 Nov 2024

Abstract

Background: Given the lack of standardization in stimulus types for assessing accommodation, we aimed to evaluate accommodative response (AR) and Zernike coefficients using four different stimuli. Methods: Sixteen healthy subjects aged 22–32 years participated. Four black transilluminated stimuli (Snellen 6/12 “E”, 6/6 “e”, [...] Read more.

Background: Given the lack of standardization in stimulus types for assessing accommodation, we aimed to evaluate accommodative response (AR) and Zernike coefficients using four different stimuli. Methods: Sixteen healthy subjects aged 22–32 years participated. Four black transilluminated stimuli (Snellen 6/12 “E”, 6/6 “e”, Maltese Cross 6/12 “X”, 6/6 “x”) were used to stimulate accommodation from 0 D to 5 D, in 1 D increments, using the irx3 aberrometer. From the results, AR was calculated with Seidel defocus and the change in Zernike coefficient value between the non-accommodative state and the fully accommodative state (5 D) was determined. Results: Larger pupils were observed with stimulus “E” (p-value < 0.05). The mean AR at the maximum accommodative level (5 D) for the different stimuli was −1.88 ± 1.00 for “E”, −2.60 ± 1.44 for “X”, −2.00 ± 1.32 for “e”, and −2.40 ± 1.27 for “x”. No statistically significant differences were found between AR and Zernike coefficients with the four different accommodative stimuli (p-value > 0.05, one-way ANOVA). Conclusions: The study evaluated accommodative stimulus design and size on AR and Zernike coefficients and found no significant differences. However, stimuli with higher spatial frequencies (“e” and “E”) provided larger ARs compared to the other stimuli. Full article

(This article belongs to the Special Issue Novel Techniques and Applications of Ophthalmic Optics)

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24 pages, 7512 KiB

Open AccessArticle

Color Reproduction of Chinese Painting Under Multi-Angle Light Source Based on BRDF

by Xinting Li, Jie Feng and Jie Liu

Photonics 2024, 11(11), 1089; https://doi.org/10.3390/photonics11111089 - 20 Nov 2024

Abstract

It is difficult to achieve high-precision color reproduction using traditional color reproduction methods when the angle is changed, and, for large-sized artefacts, it is also significantly difficult to collect a large amount of data and reproduce the colors. In this paper, we use [...] Read more.

It is difficult to achieve high-precision color reproduction using traditional color reproduction methods when the angle is changed, and, for large-sized artefacts, it is also significantly difficult to collect a large amount of data and reproduce the colors. In this paper, we use three Bidirectional Reflectance Distribution Function (BRDF) modeling methods based on spectral imaging techniques, namely, the five-parameter model, the Cook–Torrance model and the segmented linear interpolation model. We investigated the color reproduction of color chips with matte surfaces and Chinese paintings with rough surfaces under unknown illumination angles. Experiments have shown that all three models can effectively perform image reconstruction under small illumination angle intervals. The segmented linear interpolation model exhibits a higher stability and accuracy in color reconstruction under small and large illumination angle intervals; it can not only reconstruct color chips and Chinese painting images under any illumination angle, but also achieve high-quality image color reconstruction standards in terms of objective data and intuitive perception. The best test model (segmented linear interpolation) performs well in reconstruction, reconstructing Chinese paintings at 65° and 125° with an illumination angle interval of 10°. The average RMSE of the selected reference color blocks is 0.0450 and 0.0589, the average CIEDE2000 color difference is 1.07 and 1.50, and the SSIM values are 0.9227 and 0.9736, respectively. This research can provide a theoretical basis and methodological support for accurate color reproduction as well as the large-sized scientific prediction of artifacts at any angle, and has potential applications in cultural relic protection, art reproduction, and other fields. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements: 2nd Edition)

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10 pages, 2907 KiB

Open AccessArticle

Induced Emission on Transitions from Vibrational Excited Levels of the KrF Molecule

by Sofia Yampolskaya, Arcady Yastremskii, Yuri Panchenko, Alexey Puchikin and Sergey Bobrovnikov

Photonics 2024, 11(11), 1088; https://doi.org/10.3390/photonics11111088 - 20 Nov 2024

Abstract

The paper considers the possibility of extending the spectral region of the wavelength tuning of a discharge KrF amplifier due to induced transitions from the vibrational excited states of the electronic level B. The model of the KrF amplifier on a He/Kr/F₂ [...] Read more.

The paper considers the possibility of extending the spectral region of the wavelength tuning of a discharge KrF amplifier due to induced transitions from the vibrational excited states of the electronic level B. The model of the KrF amplifier on a He/Kr/F₂ mixture is presented, in which the behavior of the vibrational level populations is consistent with the excitation conditions of the active medium. The simulation results show that the shift in the operating wavelength to the short-wavelength region is possible in excitation modes, when the birth rate of excimer molecules is greater than the rate of their relaxation from upper to lower vibrational levels. The theoretical dependences of gain on the wavelength for different pressures were obtained. They confirm the possibility of tuning the KrF amplifier wavelength in the range of up to 10 nm while maintaining a gain of at least 0.5 of its maximum value. Full article

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

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14 pages, 2522 KiB

Open AccessArticle

Quantitative Investigation of Layer-by-Layer Deposition and Dissolution Kinetics by New Label-Free Analytics Based on Low-Q-Whispering Gallery Modes

by Mateusz Olszyna, Algi Domac, Jasmine Zimmer and Lars Dähne

Photonics 2024, 11(11), 1087; https://doi.org/10.3390/photonics11111087 - 19 Nov 2024

Abstract

A new instrument for label-free measurements based on optical Low-Q Whispering Gallery Modes (WGMs) for various applications is used for a detailed study of the deposition and release of Layer-by-Layer polymer coatings. The two selected coating pairs interact either via hydrogen bonding or [...] Read more.

A new instrument for label-free measurements based on optical Low-Q Whispering Gallery Modes (WGMs) for various applications is used for a detailed study of the deposition and release of Layer-by-Layer polymer coatings. The two selected coating pairs interact either via hydrogen bonding or electrostatic interactions. Their assembly was followed by common Quartz Crystal Microbalance (QCM) technology and the Low-Q WGMs. In contrast to planar QCM sensor chips of 1 cm, the WGM sensors are fluorescent spherical beads with diameters of 10.2 µm, enabling the detection of analyte quantities in the femtogram range in tiny volumes. The beads, with a very smooth surface and high refractive index, act as resonators for circular light waves that can revolve up to 10,000 times within the bead. The WGM frequencies are highly sensitive to changes in particle diameter and the refractive index of the surrounding medium. Hence, the adsorption of molecules shifts the resonance frequency, which is detected by a robust instrument with a high-resolution spectrometer. The results demonstrate the high potential of the new photonic measurement and its advantages over QCM technology, such as cheap sensors (billions in one Eppendorf tube), simple pre-functionalization, much higher statistic safety by hundreds of sensors for one measurement, 5–10 times faster analysis, and that approx. 25, 000 fewer analyte molecules are needed for one sensor. In addition, the deposited molecule amount is not superposed by hydrated water as for QCM. A connection between sensors and instruments does not exist, enabling application in any transparent environment, like microfluidics, drop-on slides, Petri dishes, well plates, cell culture vasculature, etc. Full article

(This article belongs to the Special Issue Fundamentals, Advances, and Applications in Optical Sensing)

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14 pages, 9197 KiB

Open AccessArticle

Real-Time Observations of Leaf Vitality Extinction by Dynamic Speckle Imaging

by Elise Colin, Enrique Garcia-Caurel, Karine Adeline, Aurélien Plyer and Xavier Orlik

Photonics 2024, 11(11), 1086; https://doi.org/10.3390/photonics11111086 - 19 Nov 2024

Abstract

Sap flow within a leaf is a critical indicator of plant vitality and health. This paper introduces an easy-to-use, non-invasive and real-time imaging method for sap microcirculation imaging. From the coherent backscattering of light on a leaf, we show that the acquisition frequency [...] Read more.

Sap flow within a leaf is a critical indicator of plant vitality and health. This paper introduces an easy-to-use, non-invasive and real-time imaging method for sap microcirculation imaging. From the coherent backscattering of light on a leaf, we show that the acquisition frequency of dynamic speckle can be linked to the microcirculation speed inside the leaf. Unlike conventional methods based on speckle contrast, which use integration times long enough to observe temporal decorrelation within a single image, our approach operates in a regime where speckle patterns appear ‘frozen’ in each frame of a given sequence. This ‘frozen’ state implies that any decorrelation of the speckle pattern within a frame is negligible. However, between successive frames, decorrelation becomes substantial, and it is this inter-frame decorrelation that enables the extraction of dynamic information. In this context, the integration time primarily influences the radiometric levels, while the frame acquisition rate emerges as the key parameter for generating activity index maps. Thus, by accessing different ranges of sap flow activity levels by varying the frame acquisition rate, we reveal, in a non-invasive way, the anatomy of the leaf’s circulatory network with unprecedented richness. We experimentally validate the ability of the method to characterize the vitality of a fig leaf in real time by observing the continuous decrease in sap circulation, first in the smaller vessels and then in the larger ones, following the cutting of the leaf over a 48 h period. Full article

(This article belongs to the Special Issue Optical Imaging Innovations and Applications)

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13 pages, 4582 KiB

Open AccessArticle

Dual-Wavelength Confocal Laser Speckle Contrast Imaging Using a Deep Learning Approach

by E Du, Haohan Zheng, Honghui He, Shiguo Li, Cong Qiu, Weifeng Zhang, Guoqing Wang, Xingquan Li, Lan Ma, Shuhao Shen and Yuan Zhou

Photonics 2024, 11(11), 1085; https://doi.org/10.3390/photonics11111085 - 18 Nov 2024

Abstract

This study developed a novel dual-wavelength confocal laser speckle imaging platform. The system includes both visible and near-infrared lasers and two imaging modes: confocal and wide-field laser speckle contrast imaging. The experimental results confirm that the proposed system can be used to measure [...] Read more.

This study developed a novel dual-wavelength confocal laser speckle imaging platform. The system includes both visible and near-infrared lasers and two imaging modes: confocal and wide-field laser speckle contrast imaging. The experimental results confirm that the proposed system can be used to measure not only blood flow but also blood oxygen saturation. Additionally, we proposed a blood flow perfusion imaging method called BlingNet (a blood flow imaging CNN) based on the laser speckle contrast imaging technique and deep learning approach. Compared to the traditional nonlinear fitting method, this method has superior accuracy and robustness with higher imaging speed, making real-time blood flow imaging possible. Full article

(This article belongs to the Special Issue New Perspectives in Biomedical Optics and Optical Imaging)

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14 pages, 6865 KiB

Open AccessArticle

Research on Support Structure of Rectangular Cryogenic Infrared Lens with Large Aperture

by Mingdong Shao, Jiang Guo, Hongyu Qi, Xinyuan Pang and Yibo Li

Photonics 2024, 11(11), 1084; https://doi.org/10.3390/photonics11111084 - 18 Nov 2024

Abstract

This paper presents the design and optimization of a composite flexible support structure aimed at addressing the challenges associated with maintaining the positional accuracy and surface integrity of large-aperture cryogenic infrared lenses with long focal lengths. The primary objective of the structure is [...] Read more.

This paper presents the design and optimization of a composite flexible support structure aimed at addressing the challenges associated with maintaining the positional accuracy and surface integrity of large-aperture cryogenic infrared lenses with long focal lengths. The primary objective of the structure is to maintain precise lens alignment while preserving the surface shape under operational conditions. The design complexities and underlying principles of the flexible support structure are systematically explored. A mechanical model of the flexible support structure was derived based on its structural characteristics, and the equilibrium equation was established to ensure the lens meets thermal deformation requirements in various directions. Optimization of key design parameters was conducted for a lens operating at 200 K, measuring 304 mm × 230 mm. The gravitational deformation of the optimized lens exhibited a root mean square (RMS) surface accuracy of 7.72 nm in the X direction, 7.08 nm in the Y direction, and 9.60 nm in the Z direction for lens surface 1. For lens surface 2, RMS values were 8.62 nm in the X direction, 8.41 nm in the Y direction, and 9.64 nm in the Z direction. At 200 K and lower temperatures, the RMS values of lens surfaces 1 and 2 were 2.41 nm and 2.74 nm, respectively, with a first-order mode frequency of 143.37 Hz. Full article

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

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12 pages, 9300 KiB

Open AccessArticle

Field Experiments of Distributed Acoustic Sensing Measurements

by Haiyan Shang, Lin Zhang and Shaoyi Chen

Photonics 2024, 11(11), 1083; https://doi.org/10.3390/photonics11111083 - 18 Nov 2024

Abstract

Modern, large bridges and tunnels represent important nodes in transportation arteries and have a significant impact on the development of transportation. The health and safety monitoring of these structures has always been a significant concern and is reliant on various types of sensors. [...] Read more.

Modern, large bridges and tunnels represent important nodes in transportation arteries and have a significant impact on the development of transportation. The health and safety monitoring of these structures has always been a significant concern and is reliant on various types of sensors. Distributed acoustic sensing (DAS) with telecommunication fibers is an emerging technology in the research areas of sensing and communication. DAS provides an effective and low-cost approach for the detection of various resources and seismic activities. In this study, field experiments are elucidated, using DAS for the Hong Kong–Zhuhai–Macao Bridge, and for studying vehicle trajectories, earthquakes, and other activities. The basic signal-processing methods of filtering and normalization are adopted for analyzing the data obtained with DAS. With the proposed DAS technology, the activities on shore, vehicle trajectories on bridges and in tunnels during both day and night, and microseisms within 200 km were successfully detected. Enabled by DAS technology and mass fiber networks, more studies on sensing and communication systems for the monitoring of bridge and tunnel engineering are expected to provide future insights. Full article

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

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20 pages, 5621 KiB

Open AccessReview

Computer Science Integrations with Laser Processing for Advanced Solutions

by Serguei P. Murzin

Photonics 2024, 11(11), 1082; https://doi.org/10.3390/photonics11111082 - 18 Nov 2024

Abstract

This article examines the role of computer science in enhancing laser processing techniques, emphasizing the transformative potential of their integration into manufacturing. It discusses key areas where computational methods enhance the precision, adaptability, and performance of laser operations. Through advanced modeling and simulation [...] Read more.

This article examines the role of computer science in enhancing laser processing techniques, emphasizing the transformative potential of their integration into manufacturing. It discusses key areas where computational methods enhance the precision, adaptability, and performance of laser operations. Through advanced modeling and simulation techniques, a deeper understanding of material behavior under laser irradiation was achieved, enabling the optimization of processing parameters and a reduction in defects. The role of intelligent control systems, driven by machine learning and artificial intelligence, was examined, showcasing how a real-time data analysis and adjustments lead to improved process reliability and quality. The utilization of computer-generated diffractive optical elements (DOEs) was emphasized as a means to precisely control laser beam characteristics, thus broadening the application opportunities across various industries. Additionally, the significance of predictive modeling and data analyses in enhancing manufacturing effectiveness and sustainability is discussed. While challenges such as the need for specialized expertise and investment in new technologies persist, this article underscores the considerable advantages of integrating computer science with laser processing. Future research should aim to address these challenges, further improving the quality, adaptability, and sustainability of manufacturing processes. Full article

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13 pages, 3428 KiB

Open AccessArticle

Modeling of Graded-Index Raman Fiber Amplifiers with Pump Depletion

by Sonali Maity, Anuj P. Lara, Samudra Roy and Govind P. Agrawal

Photonics 2024, 11(11), 1081; https://doi.org/10.3390/photonics11111081 - 18 Nov 2024

Abstract

Graded-index (GRIN) fibers are often used for making high-power Raman amplifiers. We employ numerical and semi-analytical techniques to model such amplifiers and include not only the signal’s amplification and pump’s depletion but also various nonlinear interactions between the signal and pump beams and [...] Read more.

Graded-index (GRIN) fibers are often used for making high-power Raman amplifiers. We employ numerical and semi-analytical techniques to model such amplifiers and include not only the signal’s amplification and pump’s depletion but also various nonlinear interactions between the signal and pump beams and the self-imaging effects within the GRIN fiber. We solve the coupled nonlinear equations of the pump and signal beams numerically. We also employ the variational technique to obtain simpler equations that can be solved much faster than the full model and still agree with it in most cases of practical interest. We discuss the evolution dynamics of the pump and signal beams, along with a novel process of energy exchange between the two beams because of self-imaging inside the GRIN fiber. The dependence of the signal’s amplification on various input parameters is analyzed in detail to optimize the device’s design and enhance the signal’s amplification for a given pump power and fiber length. Based on our analysis, we establish a resonant condition for the maximum energy transfer from the pump to the signal being amplified. We further show that the periodic self-imaging of the pump and signal beams inside a GRIN fiber leads to higher output powers compared to step-index fibers. Full article

(This article belongs to the Special Issue Fabrication of Optical Fiber and Fiber Amplifiers: From Design to Applications)

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12 pages, 4728 KiB

Open AccessArticle

A Widely and Continuously Tunable Single-Mode Transmitter Based on a Hybrid Microcavity Laser

by Miao-Qing Wang, Bin Zhang, Zhen-Ning Zhang, You-Zeng Hao, Zun-Hao Hu, Yue-De Yang, Jin-Long Xiao, António L. Teixeira and Yong-Zhen Huang

Photonics 2024, 11(11), 1080; https://doi.org/10.3390/photonics11111080 - 17 Nov 2024

Abstract

A method for achieving the single-mode and efficient unidirectional emission of a whispering gallery mode (WGM) semiconductor laser is presented herein. Hybrid square-rectangular lasers (HSRLs) and hybrid square/rhombus-rectangular lasers (HSRRLs) consisting of a Fabry–Pérot (FP) cavity and a square or rhombus cavity microcavity [...] Read more.

A method for achieving the single-mode and efficient unidirectional emission of a whispering gallery mode (WGM) semiconductor laser is presented herein. Hybrid square-rectangular lasers (HSRLs) and hybrid square/rhombus-rectangular lasers (HSRRLs) consisting of a Fabry–Pérot (FP) cavity and a square or rhombus cavity microcavity are described. In addition, a transmitter optical subassembly (TOSA) based on an HSRRL chip was fabricated, which has a wide and continuous wavelength tuning range. Wavelength channels from 1555.75 nm to 1568.15 nm with a spacing of 50 GHz were demonstrated with a good side mode suppression ratio (SMSR) and good output power. These devices have the potential to meet the typical requirements of optical communication networks. Full article

(This article belongs to the Special Issue Advanced Lasers and Their Applications, 2nd Edition )

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13 pages, 4599 KiB

Open AccessArticle

Accurate, Fast, and Non-Destructive Net Charge Measurement of Levitated Nanoresonators Based on Maxwell Speed Distribution Law

by Peng Chen, Nan Li, Tao Liang, Peitong He, Xingfan Chen, Dawei Wang and Huizhu Hu

Photonics 2024, 11(11), 1079; https://doi.org/10.3390/photonics11111079 - 17 Nov 2024

Abstract

Nanoscale resonant devices based on optical tweezers are widely used in the field of precision sensing. In the process of driving the nanoresonator based on the Coulomb force, the real-time, precise regulation of the charge carried by the charged resonator is essential for [...] Read more.

Nanoscale resonant devices based on optical tweezers are widely used in the field of precision sensing. In the process of driving the nanoresonator based on the Coulomb force, the real-time, precise regulation of the charge carried by the charged resonator is essential for continuous manipulation. However, the accuracy of the existing charge measurement methods for levitated particles is low, and these methods cannot meet the needs of precision sensing. In this study, a novel net charge measurement protocol for levitated particles based on spatial speed statistics is proposed. High-precision mass measurement based on Maxwell’s rate distribution law is the basis for improving the accuracy of charge measurement, and accurate measurement of net charge can be achieved by periodic electric field driving. The error of net charge measurement is less than 7.3% when the pressure is above 0.1 mbar, while it can be less than 0.76% at 10 mbar. This proposed method features real-time, high-precision, non-destructive, and in situ measurement of the net charge of particles in the medium vacuum, which provides new solutions for practical problems in the fields of high-precision sensing and nano-metrology based on levitated photodynamics. Full article

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15 pages, 4253 KiB

Open AccessArticle

Effects of Thickness and Grain Size on Harmonic Generation in Thin AlN Films

by J. Seres, E. Seres, E. Céspedes, L. Martinez-de-Olcoz, M. Zabala and T. Schumm

Photonics 2024, 11(11), 1078; https://doi.org/10.3390/photonics11111078 - 16 Nov 2024

Abstract

High-harmonic generation from solid films is an attractive method for converting infrared laser pulses to ultraviolet and vacuum ultraviolet wavelengths and for examining the films using the generation process. In this work, AlN thin films grown on a sapphire substrate are studied. Below-band-gap [...] Read more.

High-harmonic generation from solid films is an attractive method for converting infrared laser pulses to ultraviolet and vacuum ultraviolet wavelengths and for examining the films using the generation process. In this work, AlN thin films grown on a sapphire substrate are studied. Below-band-gap third harmonics and above-band-gap fifth harmonics were generated using a Ti:sapphire oscillator running at 800 nm. A strong enhancement of the fifth-harmonic signal in the forward direction was observed from thicker 39 nm and 100 nm films compared to thinner 8 nm and 17 nm films. For the fifth harmonic generated in the backward direction, and also for the third harmonic in both the forward and backward directions, only a weak dependence of the harmonic signal on the film thickness was measured. Using both X-ray diffraction and dependence of the fifth harmonic on the laser polarization measurements, these behaviors are attributed to the crystallization and the grain size of the films, promising fifth-harmonic generation as a suitable tool to study AlN film properties. Full article

(This article belongs to the Special Issue Advances in Laser Field Manipulation)

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