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Photonics, Volume 11, Issue 7 (July 2024) – 100 articles

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5 pages, 771 KiB  
Communication
Birefringence and Anisotropy of the Losses Due to Two-Photon Absorption of Femtosecond Pulses in Crystals
by Valeri Kovalev and George Krasin
Photonics 2024, 11(7), 683; https://doi.org/10.3390/photonics11070683 - 22 Jul 2024
Viewed by 168
Abstract
It is shown that the two-photon absorption (TPA)-induced losses in a non-centrosymmetric crystal reduce considerably when the angle θ between the polarization vector of incident radiation and the optical c-axis is 45°. In such a geometry of interaction in a Ca3 [...] Read more.
It is shown that the two-photon absorption (TPA)-induced losses in a non-centrosymmetric crystal reduce considerably when the angle θ between the polarization vector of incident radiation and the optical c-axis is 45°. In such a geometry of interaction in a Ca3(VO4)2 crystal, the effective TPA coefficient for 300 fs laser pulses at θ = 45° is 3.5 ± 0.5 times lower than its maximum at θ = 0°, which is more than two times higher than reported earlier in the literature. Full article
(This article belongs to the Section Optical Interaction Science)
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17 pages, 6477 KiB  
Article
Polarized-Speckle Deviation Imaging through Scattering Media under Strong Background Light Interference
by Si He, Xia Wang and Linhao Li
Photonics 2024, 11(7), 682; https://doi.org/10.3390/photonics11070682 - 22 Jul 2024
Viewed by 166
Abstract
A crucial challenge faced by noninvasive imaging through strongly scattering media is overcoming background light interference. Polarization-based anti-scattering methods can eliminate background light interference, but fail to utilize speckle images that do not contain unscattered object light for object reconstruction. Although speckle correlation [...] Read more.
A crucial challenge faced by noninvasive imaging through strongly scattering media is overcoming background light interference. Polarization-based anti-scattering methods can eliminate background light interference, but fail to utilize speckle images that do not contain unscattered object light for object reconstruction. Although speckle correlation imaging (SCI) methods can utilize speckle images for object reconstruction, it is difficult to achieve stable high-quality reconstruction and overcome background light interference using these methods. In this study, we propose a polarized-speckle deviation imaging (PSDI) method to overcome background light interference and achieve high-quality imaging through strongly scattering media. PSDI utilizes the bispectrum and autocorrelation of polarized speckle image deviations to reconstruct the Fourier phase and amplitude spectra of the object image, respectively. Experimental results show that when the background light is polarized and unpolarized, PSDI can achieve stable high-fidelity reconstruction of a polarized object when the signal-to-background ratio (SBR) is lower than −7 dB and −9 dB, respectively. PSDI bridges the gap between imaging with strongly scattered light and overcoming strong background light interference, and is expected to find widespread applications in fields such as biomedical imaging, astronomical observation, underwater imaging, and remote sensing. Full article
(This article belongs to the Special Issue Polarization Optics)
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13 pages, 6112 KiB  
Article
Automatic Defect Detection Instrument for Spherical Surfaces of Optical Elements
by Yali Shi, Mei Zhang and Mingwei Li
Photonics 2024, 11(7), 681; https://doi.org/10.3390/photonics11070681 - 22 Jul 2024
Viewed by 199
Abstract
In order to realize automatic surface defect detection for large aperture precision spherical optical elements, an automatic surface defect detection instrument has been designed. The instrument consists of a microscopic imaging system, illumination system, motion scanning system, and a software algorithm system. Firstly, [...] Read more.
In order to realize automatic surface defect detection for large aperture precision spherical optical elements, an automatic surface defect detection instrument has been designed. The instrument consists of a microscopic imaging system, illumination system, motion scanning system, and a software algorithm system. Firstly, a multi-angle channel illumination source and a coaxial illumination source were designed. Bright and dark field images of surface defects were captured by cooperating with an automatic zoom microscope. Then, algorithms for scanning trajectory planning, image stitching, and intelligent defect recognition were designed to achieve full-aperture surface image acquisition and defect quantification detection. The automated defect detection process of the instrument is summarized and introduced. Finally, the experimental platform was constructed, which can work well for the optical elements with a maximum diameter of 400 mm and a relative aperture R/D value of 1. It takes about 15 min to detect an optical element with a diameter of 200 mm in dark-field imaging mode. As a result, the minimum line width of scratch detectable is 2 μm and the minimum diameter of pitting detectable is 4 μm. Clearly, the instrument can realize the automatic detection of surface defects of spherical optical elements, and has the advantages of a high efficiency, stability, reliability, quantification, and data traceability. Full article
(This article belongs to the Special Issue Optical Imaging and Measurements)
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11 pages, 3504 KiB  
Article
Low-Bit-Depth Detection for Phase Retrieval with Higher Efficiency in Holographic Data Storage
by Hongjie Liu, Shujun Zheng, Yongkun Lin, Haiyang Song, Xianmiao Xu, Xiong Li, Jihong Zheng, Qiang Cao, Xiao Lin and Xiaodi Tan
Photonics 2024, 11(7), 680; https://doi.org/10.3390/photonics11070680 - 21 Jul 2024
Viewed by 225
Abstract
In the past, comprehensive information was imperative for image processing, prompting a preference for high-depth cameras. However, in our research, we discovered that the abundance of image details may impede phase retrieval. Consequently, this paper presents an iterative phase retrieval method based on [...] Read more.
In the past, comprehensive information was imperative for image processing, prompting a preference for high-depth cameras. However, in our research, we discovered that the abundance of image details may impede phase retrieval. Consequently, this paper presents an iterative phase retrieval method based on a low bit depth. Through simulations and experiments, this approach has proven effective in evidently enhancing phase retrieval outcomes. Furthermore, the concept of low bit depth holds promise for broader application across diverse domains within the field of image retrieval. Full article
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9 pages, 5034 KiB  
Communication
A Reduction in the Rotational Velocity Measurement Deviation of the Vortex Beam Superposition State for Tilted Object
by Hongyang Wang, Yinyin Yan, Zijing Zhang, Hao Liu, Xinran Lv, Chengshuai Cui, Hao Yun, Rui Feng and Yuan Zhao
Photonics 2024, 11(7), 679; https://doi.org/10.3390/photonics11070679 - 21 Jul 2024
Viewed by 259
Abstract
In measuring object rotational velocity using vortex beam, the incident light on a tilted object causes spectral broadening, which significantly interferes with the identification of the true rotational Doppler shift (RDS) peak. We employed a velocity decomposition method to analyze the relationship between [...] Read more.
In measuring object rotational velocity using vortex beam, the incident light on a tilted object causes spectral broadening, which significantly interferes with the identification of the true rotational Doppler shift (RDS) peak. We employed a velocity decomposition method to analyze the relationship between the spectral extremum and the central frequency shift caused by the object tilt. Compared with the linear growth trend observed when calculating the object rotational velocity using the frequency peak with the maximum amplitude, the central frequency calculation method effectively reduced the deviation rate of the RDS and velocity measurement value from the true value, even at large tilt angles. This approach increased the maximum tilt angle for a 1% relative error from 0.221 to 0.287 rad, representing a 29.9% improvement. When the tilt angle was 0.7 rad, the velocity measurement deviation reduction rate can reach 5.85%. Our work provides crucial support for achieving high-precision rotational velocity measurement of tilted object. Full article
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13 pages, 5921 KiB  
Article
Photoacoustic Image Analysis of Dental Tissue Using Two Wavelengths: A Comparative Study
by Marco P. Colín-García, Misael Ruiz-Veloz, Luis Polo-Parada, Rosalba Castañeda-Guzmán, Gerardo Gutiérrez-Juárez, Argelia Pérez-Pacheco and Roberto G. Ramírez-Chavarría
Photonics 2024, 11(7), 678; https://doi.org/10.3390/photonics11070678 - 21 Jul 2024
Viewed by 303
Abstract
This work compares photoacoustic images of a tooth by analyzing the signals generated with wavelengths 532 and 355 nm. This comparison addresses the differences in the optical properties of dental tissue for these wavelengths that affect the resulting photoacoustic images. A pulsed Nd:YAG [...] Read more.
This work compares photoacoustic images of a tooth by analyzing the signals generated with wavelengths 532 and 355 nm. This comparison addresses the differences in the optical properties of dental tissue for these wavelengths that affect the resulting photoacoustic images. A pulsed Nd:YAG laser was used to illuminate a complete extracted tooth sample, and 2D photoacoustic images (PAIs) were reconstructed using the single-sensor scanning synthetic aperture focusing technique (SSC-SAFT), which is a suitable method for our experimental system with forward detection mode. Signal comparison was conducted using sinogram, signal-to-noise ratio (SNR), root mean square (RMS), arrival time, maximum amplitude, and fast Fourier transform (FFT). PAI comparison utilized intensity profile, edge correlation, and image composition tools. The signal analysis revealed that at 532 nm, the signals exhibited longer decay time and a wider distribution of vibration frequencies due to higher laser pulse energy and greater optical penetration depth. Conversely, at 355 nm, the signals had shorter decay times and a lower frequency distribution, which was attributed to lower energy but improved optical absorption, resulting in reconstructed images with better sharpness and contour definition. This study contributes to the advancement of photoacoustic imaging technology in dentistry by providing insights that could optimize signal generation and image reconstruction for dental tissue. Full article
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8 pages, 12033 KiB  
Communication
Output Characteristics of External-Cavity Mode-Hop-Free Tunable Laser Source in C+L Band
by Jisheng Sun, Liqiang Qiu, Lei Liu, Liwen Sheng, Yudong Cui, Lin Huang, Mengchun Pan, Fushun Nian and Jiafei Hu
Photonics 2024, 11(7), 677; https://doi.org/10.3390/photonics11070677 - 21 Jul 2024
Viewed by 281
Abstract
Tunable laser sources with a wide wavelength tuning range, mode-hop-free (MHF) operation, and high spectral purity are essential for applications such as high-resolution spectroscopy, coherent detection, and intelligent fiber sensing. In this paper, we present a wide-range tunable laser source that operates without [...] Read more.
Tunable laser sources with a wide wavelength tuning range, mode-hop-free (MHF) operation, and high spectral purity are essential for applications such as high-resolution spectroscopy, coherent detection, and intelligent fiber sensing. In this paper, we present a wide-range tunable laser source that operates without mode hopping, based on external cavity feedback using a semiconductor gain chip as the laser gain medium. The wavelength, power, and spectral characteristics of the laser are experimentally measured. A wide MHF continuous wavelength tuning range from 1480 nm to 1620 nm with a side-mode suppression ratio of more than 61.65 dB is achieved. An output optical power of more than 11.14 dBm with good power stability can also be realized in the full C+L band. This proposed external-cavity tunable laser source features a narrow intrinsic linewidth and MHF tunable radiation with a maximum sweep speed of 200 nm/s, enabling practical applications such as high-resolution vector spectrum analysis. Full article
(This article belongs to the Special Issue Emerging Topics in High-Power Laser and Light–Matter Interactions)
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21 pages, 11278 KiB  
Article
Numerical Simulation of the Laser Welding Process for Diamond Saw Blades
by Qiang Xu, Xiaodie Cao, Yibo Liu, Yanjun Xu and Jiajun Wu
Photonics 2024, 11(7), 676; https://doi.org/10.3390/photonics11070676 - 19 Jul 2024
Viewed by 284
Abstract
The development and application of laser welding transition layer technology is pivotal for manufacturing high-performance diamond saw blades. Despite its importance, there is a need for more precise modeling to optimize welding parameters and enhance blade performance. This study employs SYSWELD software to [...] Read more.
The development and application of laser welding transition layer technology is pivotal for manufacturing high-performance diamond saw blades. Despite its importance, there is a need for more precise modeling to optimize welding parameters and enhance blade performance. This study employs SYSWELD software to simulate the laser welding process, demonstrating high accuracy in predicting the molten pool shape. A cross-scale multi-field coupling model was established using the finite element method, incorporating temperature field, phase transformation, grain morphology, stress field, and fatigue performance. A comprehensive life cycle assessment identified optimal welding parameters. The results indicate that a laser welding speed of 26 mm/s and a power of 1700 W minimize weld stress, reduce the digital volume correlation (DVC) value, and enhance fatigue resistance. Additionally, welding tests confirmed that using 1700 W produced the highest tooth strength of 1200 MPa, validating the simulation results. This study addresses existing gaps in modeling accuracy and parameter optimization, offering a robust framework for improving the performance and reliability of laser-welded diamond saw blades. Full article
(This article belongs to the Special Issue Laser Processing and Modification of Materials)
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14 pages, 3552 KiB  
Article
Design and Study of Low Loss, High Birefringence Quasi-Symmetric Hollow-Core Anti-Resonant Fiber
by Binhao Gao, Fang Tan, Dexiao Chen, Shunfa Cui, Zhiyong Hou, Yuze Zhang, Weichun Wang, Yumeng Ban and Dechun Zhou
Photonics 2024, 11(7), 675; https://doi.org/10.3390/photonics11070675 - 19 Jul 2024
Viewed by 249
Abstract
Low-loss, high-birefringence, bend-resistant hollow-core anti-resonant fibers for infrared wavelengths have important applications in the fields of precision interferometric sensing, laser systems, and optical communications. In this paper, an eight-tube cladding quasi-symmetric hollow-core anti-resonant fiber is proposed, and two other anti-resonant fibers are designed [...] Read more.
Low-loss, high-birefringence, bend-resistant hollow-core anti-resonant fibers for infrared wavelengths have important applications in the fields of precision interferometric sensing, laser systems, and optical communications. In this paper, an eight-tube cladding quasi-symmetric hollow-core anti-resonant fiber is proposed, and two other anti-resonant fibers are designed based on this fiber structure. The finite element analysis method is used to numerically analyze the limiting loss, birefringence coefficient, bending resistance, and other properties of the three optical fibers after the optimized design. The results show that the limiting loss of the three optical fibers at λ = 1.55 μm is lower than 10−4 magnitude, and all of them obtain a birefringence coefficient of 10−4 magnitude; at the same time, the three optical fibers have their own characteristics and advantages, and the first optical fiber can reach a birefringence coefficient of 9.25 × 10−4 at λ = 1.52 μm.The limiting loss at λ = 1.55 μm is 3.42 × 10−5 dB/km. The minimum bending radius of the three types of anti-resonant fibers is less than 40 mm, which represents good bending characteristics, and the eight-tube cladding quasi-symmetric optical fiber has a bending loss of less than 2.10 × 10−3 dB/km when the bending radius is 28 mm. The three types of optical fibers have obtained good results in improving the mutual constraints between low limiting loss and high birefringence, with better results than the other two types. The obtained results have high development potential. Full article
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14 pages, 1121 KiB  
Article
Low-Cost High-Speed Fiber-Coupled Interferometer for Precise Surface Profilometry
by Sebastian Hagemeier, Yijian Zou, Tobias Pahl, Felix Rosenthal and Peter Lehmann
Photonics 2024, 11(7), 674; https://doi.org/10.3390/photonics11070674 - 19 Jul 2024
Viewed by 357
Abstract
Due to their contactless and fast measuring capabilities, laser interferometers represent an interesting alternative to tactile stylus instruments for surface profilometry. In addition to these outstanding attributes, acquisition costs play a major role in industry, limiting the frequent use of optical profilometers, which [...] Read more.
Due to their contactless and fast measuring capabilities, laser interferometers represent an interesting alternative to tactile stylus instruments for surface profilometry. In addition to these outstanding attributes, acquisition costs play a major role in industry, limiting the frequent use of optical profilometers, which are significantly more expensive than tactile profilometers. We present a low-cost laser distance-measuring interferometer featuring axial repeatability below 1 nm at acquisition rates of 38,000 height values per second. The sensor’s performance is validated on several surface standards, achieving lateral scan velocities up to 160 mm/s. Further to high scan velocities, the high acquisition rate enables improved measurement accuracy by averaging measured height values. For example, the standard deviation of 625 pm for repeated measurements can be reduced to 265 pm at the expense of the data rate. However, the sensor concept provides the potential for further improvements in data rate and measurement repeatability. Full article
(This article belongs to the Special Issue Advances in Optical Fiber Sensing Technology)
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11 pages, 3871 KiB  
Article
Optical and Scintillation Properties of Tb-Doped Gadolinium Pyrosilicate Single Crystals
by Prom Kantuptim, Takumi Kato, Daisuke Nakauchi, Nakarin Pattanaboonmee, Noriaki Kawaguchi, Kenichi Watanabe, Weerapong Chewpraditkul and Takayuki Yanagida
Photonics 2024, 11(7), 673; https://doi.org/10.3390/photonics11070673 - 19 Jul 2024
Viewed by 369
Abstract
Gadolinium pyrosilicate (GPS, Gd2Si2O7) single crystals with different doping concentrations of Tb (0.1–2.0 mol%) are successfully fabricated using the floating-zone technique. In this work, the dependence of Tb-doping concentration on the photoluminescence (PL) and scintillation properties of [...] Read more.
Gadolinium pyrosilicate (GPS, Gd2Si2O7) single crystals with different doping concentrations of Tb (0.1–2.0 mol%) are successfully fabricated using the floating-zone technique. In this work, the dependence of Tb-doping concentration on the photoluminescence (PL) and scintillation properties of Tb-doped GPS (Tb:GPS) has been investigated. The PL emission contour graph shows multiple emissions, with the strongest emissions at 378 nm for 0.1% and 0.5% Tb-doping and 544 nm for 1.0% and 2.0% Tb-doping, corresponding to Tb3+ 4f-4f transitions. The PL lifetimes of the specimens range from 4.89 to 5.22 ms. The scintillation spectra exhibit comparable wavelength and intensity trends to the PL emission. The scintillation lifetimes of the specimens range from 2.41 to 3.88 ms. The Tb:GPS specimens demonstrate a relatively excessive afterglow level, with Af20 values ranging from 1640 to 7250 ppm and Af40 values ranging from 136 to 362 ppm. Using recently developed pulse height measurement for millisecond decay scintillators, under excitation at 662 keV γ-rays, the 1.0% Tb:GPS specimen exhibits the highest scintillation light yield among all other specimens at 95,600 ph/MeV, making Tb:GPS one of the highest light yield oxide scintillators. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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12 pages, 803 KiB  
Article
VCSELs with Stable Linear Polarization Emission Induced by Dielectric Columnar Thin Film Mirrors
by Krassimir Panajotov
Photonics 2024, 11(7), 672; https://doi.org/10.3390/photonics11070672 - 18 Jul 2024
Viewed by 264
Abstract
We propose and analyze numerically new approaches to force the laser emission from VCSELs in a well-defined linear polarization independent of the existing phase and amplitude anisotropies by using dielectric columnar thin-film (CTF) layers in the distributed Bragg reflector (DBR). In one approach, [...] Read more.
We propose and analyze numerically new approaches to force the laser emission from VCSELs in a well-defined linear polarization independent of the existing phase and amplitude anisotropies by using dielectric columnar thin-film (CTF) layers in the distributed Bragg reflector (DBR). In one approach, we have demonstrated CTF-VCSELs with top DBR consisting of two alternating CTF layers grown in orthogonally oriented planes and with high and low refractive index for one linear polarization while having the same value of the refractive index value for the orthogonal linear polarization. Such CTF-VCSELs have large dichroism of the mirror losses for two orthogonal linear polarizations. We have also shown DBR designs with parallel columnar orientations of the two CTF dielectric materials. In a second approach, we implement only one CTF layer in the dielectric DBR chosen in such a way that only one linearly polarized longitudinal mode is resonant in the CTF-VCSEL while light with the orthogonally oriented linear polarization is out of resonance and thus cannot lase. Simple estimation of the polarization mode suppression ratio for the different exemplary designs of CTF-VCSELs based on TiO2 and TaO2 dielectric CTFs results in values as high as 80 dB, which compares favorably to the existing alternative approaches. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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17 pages, 8301 KiB  
Article
Improved Res-UNet Network for Phase Unwrapping of Interferometric Gear Tooth Flank Measurements
by Xian Wang, Chaoyang Ju, Yufan Xuan, Ting Shi, Feiqi Yang, Yun Liu, Ke Kou and Yichao Zhao
Photonics 2024, 11(7), 671; https://doi.org/10.3390/photonics11070671 - 18 Jul 2024
Viewed by 272
Abstract
This article introduces an improved deep learning network, GRU-Net, designed to facilitate direct and precise phase unwrapping of wrapped phase measurements in gear tooth surface interferometry. GRU-Net incorporates a Gram matrix within each down-sampling process to compute style loss, thereby capturing essential stripe [...] Read more.
This article introduces an improved deep learning network, GRU-Net, designed to facilitate direct and precise phase unwrapping of wrapped phase measurements in gear tooth surface interferometry. GRU-Net incorporates a Gram matrix within each down-sampling process to compute style loss, thereby capturing essential stripe structure information features. This network exhibits enhanced capability in handling larger and more intricate gear tooth interferograms, particularly in scenarios involving pronounced noise and aliasing, while still yielding favorable outcomes. A comparative evaluation was conducted, contrasting GRU-Net with the Res-UNet network and other conventional methods. The results demonstrate that GRU-Net surpasses the alternative approaches in terms of unwrapping accuracy, noise resilience, and anti-aliasing capabilities, with accuracy improved by at least 24%, exhibiting significantly superior performance. Additionally, in contrast to the Res-UNet network, GRU-Net demonstrates accelerated learning speed and generates more compact models. Full article
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22 pages, 868 KiB  
Protocol
TransPhoM-DS Study Grant Report: Rationale and Protocol for Investigating the Efficacy of Low-Power Transcranial Photobiomodulation on Language, Executive Function, Attention, and Memory in Down Syndrome
by Willians Fernando Vieira, David Richer Araujo Coelho, Maia Gersten, Aura Maria Hurtado Puerto, Stefani Kalli, Guillermo Gonzalez-Garibay, Kayla McEachern, Julie A. Clancy, Brian G. Skotko, Leonard Abbeduto, Angela John Thurman, Margaret B. Pulsifer, Elizabeth Corcoran, Anita E. Saltmarche, Margaret A. Naeser and Paolo Cassano
Photonics 2024, 11(7), 670; https://doi.org/10.3390/photonics11070670 - 18 Jul 2024
Viewed by 429
Abstract
Down syndrome (DS) is the leading genetic cause of intellectual disability globally, affecting about 1 in every 800 births. Individuals with DS often face various neuropsychiatric conditions alongside intellectual disabilities due to altered brain development. Despite the diverse phenotypic expressions of DS, typical [...] Read more.
Down syndrome (DS) is the leading genetic cause of intellectual disability globally, affecting about 1 in every 800 births. Individuals with DS often face various neuropsychiatric conditions alongside intellectual disabilities due to altered brain development. Despite the diverse phenotypic expressions of DS, typical physical characteristics frequently influence language development and acquisition. EEG studies have identified abnormal oscillatory patterns in individuals with DS. Emerging interventions targeting the enhancement of gamma (40 Hz) neuronal oscillations show potential for improving brain electrical activity and cognitive functions in this population. However, effective cognitive interventions for DS remain scarce. Extensive research indicates that transcranial photobiomodulation (t-PBM) with near-infrared (NIR) light can penetrate deeply into the cerebral cortex, modulate cortical excitability, and enhance cerebral perfusion and oxygenation. Furthermore, t-PBM has been shown to improve cognitive functions such as language, attention, inhibition, learning, and memory, including working memory. This study presents the rationale and design of an ongoing randomized, sham-controlled clinical trial aimed at assessing the effectiveness of t-PBM using NIR light in enhancing the language abilities of individuals with DS. Full article
(This article belongs to the Section Biophotonics and Biomedical Optics)
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7 pages, 1840 KiB  
Brief Report
Compact and High-Efficiency Liquid-Crystal-on-Silicon for Augmented Reality Displays
by Zhenyi Luo, Yuqiang Ding, Fenglin Peng, Ziqian He, Yun Wang and Shin-Tson Wu
Photonics 2024, 11(7), 669; https://doi.org/10.3390/photonics11070669 - 17 Jul 2024
Viewed by 368
Abstract
Compact and high efficiency microdisplays are essential for lightweight augmented reality (AR) glasses to ensure longtime wearing comfort. Liquid-crystal-on-silicon (LCoS) is a promising candidate because of its high-resolution density, high brightness, and low cost. However, its bulky illumination system with a polarizing beam [...] Read more.
Compact and high efficiency microdisplays are essential for lightweight augmented reality (AR) glasses to ensure longtime wearing comfort. Liquid-crystal-on-silicon (LCoS) is a promising candidate because of its high-resolution density, high brightness, and low cost. However, its bulky illumination system with a polarizing beam splitter (PBS) cube remains an urgent issue to be overcome. To reduce the volume of the LCoS illumination system, here, we propose a compact structure with four thin PBS cuboids. Through simulations, the optical efficiency of 36.7% for an unpolarized input light can be achieved while maintaining reasonably good spatial uniformity. Such a novel design is expected to have a significant impact on future compact and lightweight AR glasses. Full article
(This article belongs to the Special Issue Liquid Crystals in Photonics II)
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17 pages, 4053 KiB  
Article
Computation Theory of Large-Scale Partially Coherent Imaging by the Modified Modal Expansion Method
by Jiaqi Li and Huaijiang Yang
Photonics 2024, 11(7), 668; https://doi.org/10.3390/photonics11070668 - 17 Jul 2024
Viewed by 350
Abstract
The numerical calculation of partially coherent imaging involves a fourfold integral, which is numerically complex and impracticable to be calculated directly. The use of coherent-mode decomposition (CMD) can make this problem more manageable but finding the coherent-modes for complicated partial coherent fields (without [...] Read more.
The numerical calculation of partially coherent imaging involves a fourfold integral, which is numerically complex and impracticable to be calculated directly. The use of coherent-mode decomposition (CMD) can make this problem more manageable but finding the coherent-modes for complicated partial coherent fields (without already-known coherent-mode expansion) are rather computationally intensive. In this letter, a modified modal expansion method is proposed, which significantly reduces the requirement of computational resources. The propagation of partial coherence in imaging systems with extremely large sampling number could be handled by an ordinary computer. A comparison between the new method and the traditional method in terms of memory resource requirements and computational time consumption is also detailed in this article. We will also show that this method could deal with the anisoplanatic imaging cases while maintaining the same computational efficiency. Full article
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17 pages, 4183 KiB  
Article
Wavelength Dependence of Modal Bandwidth of Multimode Fibers for High Data Rate Transmission and Its Implications
by Xin Chen, Hao Dong, Hao Chen, Jason E. Hurley, Zoren D. Bullock and Ming-Jun Li
Photonics 2024, 11(7), 667; https://doi.org/10.3390/photonics11070667 - 17 Jul 2024
Viewed by 404
Abstract
Vertical-cavity surface-emitting laser (VCSEL)-based transmission over multimode fiber (MMF) has achieved data rates of 100G per lane and is progressing towards 200G per lane. Recently, high-data-rate MMFs derived from OM3 and OM4 have been proposed. These fibers exhibit higher effective modal bandwidths at [...] Read more.
Vertical-cavity surface-emitting laser (VCSEL)-based transmission over multimode fiber (MMF) has achieved data rates of 100G per lane and is progressing towards 200G per lane. Recently, high-data-rate MMFs derived from OM3 and OM4 have been proposed. These fibers exhibit higher effective modal bandwidths at 910 nm, leading to a different wavelength dependence compared to conventional OM3 and OM4 MMFs. Understanding the wavelength dependence of these fibers is crucial to address their utilization in a broader range of applications. Through Monte Carlo simulations, we have obtained the low-end boundary of the effective modal bandwidths (EMBs) for these fibers, revealing capability improvements over the existing OM3 and OM4. The high-data-rate OM4 performs the same as or better than OM5 from 840 nm to 920 nm, while also showing a high bandwidth for the 850–870 nm wavelength window, favoring VCSELs with center wavelengths shifted toward 860 nm. We also obtained the link bandwidth, which includes both modal bandwidth and chromatic dispersion contributions, and the transmission reaches for various types of transceivers. We find that for both high-data-rate OM3 and high-data-rate OM4, the link bandwidth stays above the value at 850 nm until around 910 nm, delivering a similar transmission performance from 850 to 910 nm without declining towards longer wavelengths, unlike the standard OM3 and OM4. This characteristic favors a wider range of wavelength choices for VCSELs and enables optimal deployments for various applications. Full article
(This article belongs to the Special Issue New Perspectives in Optical Design)
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14 pages, 2905 KiB  
Article
An Adjustment Strategy for Tilted Moiré Fringes via Deep Q-Network
by Chuan Jin, Dajie Yu, Haifeng Sun, Junbo Liu, Ji Zhou and Jian Wang
Photonics 2024, 11(7), 666; https://doi.org/10.3390/photonics11070666 - 17 Jul 2024
Viewed by 306
Abstract
Overlay accuracy, one of the three fundamental indicators of lithography, is directly influenced by alignment precision. During the alignment process based on the Moiré fringe method, a slight angular misalignment between the mask and wafer will cause the Moiré fringes to tilt, thereby [...] Read more.
Overlay accuracy, one of the three fundamental indicators of lithography, is directly influenced by alignment precision. During the alignment process based on the Moiré fringe method, a slight angular misalignment between the mask and wafer will cause the Moiré fringes to tilt, thereby affecting the alignment accuracy. This paper proposes a leveling strategy based on the DQN (Deep Q-Network) algorithm. This strategy involves using four consecutive frames of wafer tilt images as the input values for a convolutional neural network (CNN), which serves as the environment model. The environment model is divided into two groups: the horizontal plane tilt environment model and the vertical plane tilt environment model. After convolution through the CNN and training with the pooling operation, the Q-value consisting of n discrete actions is output. In the DQN algorithm, the main contributions of this paper lie in three points: the adaptive application of environmental model input, parameter optimization of the loss function, and the possibility of application in the actual environment to provide some ideas. The environment model input interface can be applied to different tilt models and more complex scenes. The optimization of the loss function can match the leveling of different tilt models. Considering the application of this strategy in actual scenarios, motion calibration and detection between the mask and the wafer provide some ideas. To verify the reliability of the algorithm, simulations were conducted to generate tilted Moiré fringes resulting from tilt angles of the wafer plate, and the phase of the tilted Moiré fringes was subsequently calculated. The angle of the wafer was automatically adjusted using the DQN algorithm, and then various angles were measured. Repeated measurements were also conducted at the same angle. The angle deviation accuracy of the horizontal plane tilt environment model reached 0.0011 degrees, and the accuracy of repeated measurements reached 0.00025 degrees. The angle deviation accuracy of the vertical plane tilt environment model reached 0.0043 degrees, and repeated measurements achieved a precision of 0.00027 degrees. Moreover, in practical applications, it also provides corresponding ideas to ensure the determination of the relative position between the mask and wafer and the detection of movement, offering the potential for its application in the industry. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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10 pages, 3914 KiB  
Communication
Performance Investigation of Joint LUT and GS Algorithm at the Transceiver for Nonlinear and CD Compensation
by Xiaoying Zhang, Jiahao Huo, Haolin Bai, Peng Qin, Wei Huangfu and Keping Long
Photonics 2024, 11(7), 665; https://doi.org/10.3390/photonics11070665 - 17 Jul 2024
Viewed by 331
Abstract
In order to meet the increasing requirements of speed and distance, an advanced digital signal processing (DSP) algorithm is preferred without changing the system structure in intensity modulation and the direct detection (IM/DD) system. As the transmission distance increases, the power fading induced [...] Read more.
In order to meet the increasing requirements of speed and distance, an advanced digital signal processing (DSP) algorithm is preferred without changing the system structure in intensity modulation and the direct detection (IM/DD) system. As the transmission distance increases, the power fading induced by dispersion must be mitigated. In addition, linear and nonlinear inter symbol interference (ISI) introduced by bandwidth limitation and device imperfections becomes an obstacle to achieving higher capacity. The Gerchberg–Saxton (GS) algorithm was recently used to compensate for dispersion. In this paper, GS-based pre- and post-compensation schemes in the IM/DD system with nonlinearity were investigated. We investigated and compared the performance of the GS-based pre- and post-compensation algorithm in a 28 GB aud four-level pulse amplitude modulation (PAM-4) transmission over 40 km standard single-mode fiber (SSMF). The bit error rate (BER) achieved a threshold of 3.8 × 10−3 using look-up-table (LUT), FFE, and the GS-based pre-compensation algorithm without iterations. Turning to the GS-based post-compensation scheme, 80 iterations are needed. However, the demand for FFE is reduced. The algorithm selection depends on the tolerance of the transmitter or receiver complexity in specific scenarios. The joint LUT and GS-based pre-compensation algorithm may be a preferable approach in scenarios where a low-complexity receiver is desired. Full article
(This article belongs to the Section Optical Communication and Network)
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8 pages, 219 KiB  
Article
A Mathematical Model for Axial Length Estimation in a Myopic Pediatric Population Based on Easily Obtainable Variables
by Veronica Noya-Padin, Noelia Nores-Palmas, Alba Castro-Giraldez, Maria J. Giraldez, Hugo Pena-Verdeal and Eva Yebra-Pimentel
Photonics 2024, 11(7), 664; https://doi.org/10.3390/photonics11070664 - 17 Jul 2024
Viewed by 382
Abstract
Determining the axial length (AL) of the eye is of significant interest in the management of myopia. However, the devices that allow this value to be obtained are either expensive, for example, optical biometers, or inconvenient for use in pediatric population, such is [...] Read more.
Determining the axial length (AL) of the eye is of significant interest in the management of myopia. However, the devices that allow this value to be obtained are either expensive, for example, optical biometers, or inconvenient for use in pediatric population, such is the case with ultrasound biometers. Therefore, this study aimed to develop a mathematical model for estimating the AL value based on easily obtainable variables, with the novel addition of body height to the analysis. A total of 170 eyes of 85 myopic volunteers (mean age of 10.8 ± 1.45 years, ranging from 7 to 14 years) were included in the analysis. Participants underwent anamnesis, keratometry by NVISION-K 5001, subjective refraction by an optometrist, AL measurement by the Topcon MYAH biometer, and body height measurement. Spearman’s correlation test was employed to analyze the relationships between AL and keratometry, spherical equivalent, body height (Sperman’s correlation, all r ≥ 0.267, all p < 0.001), and age (Spearman’s correlation, p = 0.081). Subsequently, multiple regression analysis was conducted on the variables that demonstrated a previous correlation. The mathematical model obtained permits the estimation of AL based on average keratometry, spherical equivalent, and body height. This model is significant (p < 0.001) and explains 82.4% of AL variability. Full article
(This article belongs to the Special Issue Latest Developments in Ocular Biometry)
16 pages, 9500 KiB  
Review
Bismuth-Doped Fiber Lasers and Amplifiers Operating from O- to U-Band: Current State of the Art and Outlook
by Sergey Alyshev, Aleksandr Khegai, Andrey Umnikov and Sergei Firstov
Photonics 2024, 11(7), 663; https://doi.org/10.3390/photonics11070663 - 17 Jul 2024
Viewed by 425
Abstract
The development of unique optical materials that provide amplification and lasing in new wavelength ranges is a major scientific problem, the solution of which is becoming the basis for the emergence of new optical technologies, which are primarily targeting the expanding of operating [...] Read more.
The development of unique optical materials that provide amplification and lasing in new wavelength ranges is a major scientific problem, the solution of which is becoming the basis for the emergence of new optical technologies, which are primarily targeting the expanding of operating wavelengths in silica glass. In fact, one of the notable advances in the field of fiber optics over the past two decades has been the production of a new type of laser-active fibers (namely bismuth-doped fibers), which has made it possible to cover previously inaccessible (for rare-earth-doped fibers) spectral ranges, in particular O-, E-, S-, and U-telecom bands. The advance in this direction has led to further growth of the technological capabilities in the telecom industry for amplification and generation of optical radiation in various wavelength bands, which will result in the near future to overcoming the problem known as “capacity crunch” by means of expanding the data transmission range. Recently, bismuth-doped fibers have been actively studying in order to improve their characteristics, which would allow for efficient implementation of optical devices based on bismuth-doped fibers (BDFs) with deployed telecommunications systems. This is one of the dynamically developing areas, where progress has already manifested in form of emergence of new achievements, in particular commercially available various types of BDFs, as well as a series of novel fiber-optic amplifiers for the O- and E-bands. In this review, a number of scientific studies that have already led to a noticeable progress in the field of optical properties of BDFs and the practical implementation of optical devices (lasers and amplifiers) based on them are presented and discussed, with much attention to the achievements of recent years. Full article
(This article belongs to the Special Issue Fiber Lasers: Recent Advances and Applications)
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17 pages, 5880 KiB  
Article
Design and Optimization of an Ultraviolet Scattering Communication System Based on Duty Cycle Regulation
by Yu Jiao, Yingkai Zhao, Li Kuang, Ranxi Lin, Jin Ning and Jianguo Liu
Photonics 2024, 11(7), 662; https://doi.org/10.3390/photonics11070662 - 16 Jul 2024
Viewed by 294
Abstract
In this paper, a novel ultraviolet (UV) scatter communication scheme is presented, designed to dynamically adjust the signal duty cycle to optimize on–off keying (OOK) modulation and reduce the bit error rate (BER), particularly under varying rate settings. This approach addresses the significant [...] Read more.
In this paper, a novel ultraviolet (UV) scatter communication scheme is presented, designed to dynamically adjust the signal duty cycle to optimize on–off keying (OOK) modulation and reduce the bit error rate (BER), particularly under varying rate settings. This approach addresses the significant challenge posed by LED tailing effects, which cause signal fluctuations and increase BER in high-speed communications. This BER suppression scheme is proposed for the first time in UV communication research, enhancing communication performance without the need for additional hardware or complex algorithms. A UV communication model that incorporates both path loss and LED tailing effects is introduced, with the probability density function of the signal from transmitter to receiver derived. By varying the signal duty cycle, tailing-induced BER is effectively minimized. Additionally, a closed-form expression for signal transmission BER using a single-scattering model is provided, and the proposed UV communication system is validated through comprehensive simulations and experimental tests. The results indicate that LED tailing has a pronounced impact on BER at higher communication speeds, while its effects are less significant at lower speeds. By optimizing the duty cycle parameters for various communication rates, findings demonstrate that lower duty cycle settings significantly reduce the BER at higher speeds. This further demonstrates the excellent performance of the proposed UV communication solution for OOK-modulated optical communication. Full article
(This article belongs to the Section Optical Communication and Network)
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18 pages, 10563 KiB  
Article
Illumination Field Uniformity Correction by Novel Finger Arrays for Lithography Illumination System
by Shaoqin Luo, Junbo Liu, Chuan Jin and Ji Zhou
Photonics 2024, 11(7), 661; https://doi.org/10.3390/photonics11070661 - 15 Jul 2024
Viewed by 358
Abstract
In order to correct the integrated nonuniformity of a lithographic illumination field, a high-precision uniformity correction method for an advanced lithographic illumination system is proposed. The method adopts the opaque finger array structure and improves correction ability and accuracy by optimizing the arrangement [...] Read more.
In order to correct the integrated nonuniformity of a lithographic illumination field, a high-precision uniformity correction method for an advanced lithographic illumination system is proposed. The method adopts the opaque finger array structure and improves correction ability and accuracy by optimizing the arrangement and structure of the unit without changing the width of each unit. The correction accuracy is expressed as the percentage of the corrected integrated nonuniformity. Through theoretical analysis and simulation, it can be seen that the correction accuracy of a staggered finger array is better than 0.22%. When staggered and layered, the correction accuracy of a finger array is better than 0.14%, which is better than that of a non-layered finger array. When staggered, layered, and chamfered of each unit, the correction accuracy of the finger array structure is better than 0.12%. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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11 pages, 2611 KiB  
Article
Symmetry-Engineered Dual Plasmon-Induced Transparency via Triple Bright Modes in Graphene Metasurfaces
by Yanrui Cao and Tian Sang
Photonics 2024, 11(7), 660; https://doi.org/10.3390/photonics11070660 - 15 Jul 2024
Viewed by 356
Abstract
Dynamical manipulation of plasmon-induced transparency (PIT) in graphene metasurfaces is promising for optoelectronic devices such as optical switching and modulating; however, previous design approaches are limited within one or two bright/dark modes, and the realization of dual PIT windows through triple bright modes [...] Read more.
Dynamical manipulation of plasmon-induced transparency (PIT) in graphene metasurfaces is promising for optoelectronic devices such as optical switching and modulating; however, previous design approaches are limited within one or two bright/dark modes, and the realization of dual PIT windows through triple bright modes in graphene metasurfaces is seldom mentioned. Here, we demonstrate that dual PIT can be realized through a symmetry-engineered graphene metasurface, which consists of the graphene central cross (GCC) and graphene rectangular ring (GRR) arrays. The GCC supports a bright mode from electric dipole (ED), the GRR supports two nondegenerate bright modes from ED and electric quadrupole (EQ) due to the C2v symmetry breaking, and the resonant coupling of these three bright modes induces the dual PIT windows. A triple coupled-oscillator model (TCM) is proposed to evaluate the transmission performances of the dual PIT phenomenon, and the results are in good agreement with the finite-difference time-domain (FDTD) method. In addition, the dual PIT windows are robust to the variation of the structural parameters of the graphene metasurface except for the y-directioned length of the GRR. By changing the carrier mobility of graphene, the amplitudes of the two PIT windows can be effectively tuned. The alteration of the Fermi level of graphene enables the dynamic modulation of the dual PIT with good performances for both modulation degree (MD) and insertion loss (IL). Full article
(This article belongs to the Special Issue Photonic Crystals: Physics and Devices, 2nd Edition)
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12 pages, 2898 KiB  
Communication
Polarization Influence on Er3+-Doped Multi-Wavelength Brillouin Fiber Laser Based on Fiber Loop Mirror
by Yunqi Hao, Miao Miao, Weitong Liao and Kun Yang
Photonics 2024, 11(7), 659; https://doi.org/10.3390/photonics11070659 - 13 Jul 2024
Viewed by 294
Abstract
Polarization influences on the performance of multi-wavelength Brillouin Er3+-doped fiber laser are investigated by adjusting the polarization controller (PC) in the fiber loop mirror (FLM), where the linear laser cavity is composed of a fiber-tailed mirror and an FLM, and the [...] Read more.
Polarization influences on the performance of multi-wavelength Brillouin Er3+-doped fiber laser are investigated by adjusting the polarization controller (PC) in the fiber loop mirror (FLM), where the linear laser cavity is composed of a fiber-tailed mirror and an FLM, and the stimulated Brillouin scattering (SBS) and the Er3+-doped fiber amplification (EDFA) simultaneously serve as the cavity gain. We realized 1–7 Brillouin laser lines by increasing the 980 nm pump power. For the first-order Brillouin laser, the signal–noise ratio (SNR) and optical intensity present a sinusoidal envelope; the conversion efficiency changes significantly from 0.56465 dBm/mw to 0.44975 dBm/mw by adjusting the ring’s angle in the PC; the first-order SBS thresholds are 20.4 mw, 36.1 mw and 28.5 mw at different angles θ2 = 36°, 276° and 300°, respectively; flatness between the two Brillouin lasers change obviously from 2.863 dB to 41.801 dB with different ring angles; the second-order Brillouin laser is suppressed and disappears finally at Δθ2 = −64° to −84° and 106°~136° angle variation. For the fifth-order Brillouin laser, the highest-order Brillouin laser line is seriously suppressed until it disappears at some angle variations similarly. The powers and wavelength stabilities for one-, three- and seven-wavelength Brillouin fiber lasers were measured in 1 h, and the obtained Er3+-doped multi-wavelength Brillouin fiber laser (MWBFL) worked stably during that time, but the stabilities become worse with higher SBS orders. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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1 pages, 130 KiB  
Correction
Correction: Jiang et al. Role of Pyramidal Low-Dimensional Semiconductors in Advancing the Field of Optoelectronics. Photonics 2024, 11, 370
by Ao Jiang, Shibo Xing, Haowei Lin, Qing Chen and Mingxuan Li
Photonics 2024, 11(7), 658; https://doi.org/10.3390/photonics11070658 - 12 Jul 2024
Viewed by 224
Abstract
In the original publication [...] Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
8 pages, 1448 KiB  
Article
Optical Rogue Waves in Fiber Lasers
by Hani J. Kbashi and Sergey V. Sergyev
Photonics 2024, 11(7), 657; https://doi.org/10.3390/photonics11070657 - 12 Jul 2024
Viewed by 401
Abstract
Optical rogue waves are a nonlinear phenomenon that offers a unique opportunity to gain fundamental insights into wave interaction and behavior, and the evolution of complex systems. Optical systems serve as a suitable testbed for the well-controlled investigation of this natural phenomenon, which [...] Read more.
Optical rogue waves are a nonlinear phenomenon that offers a unique opportunity to gain fundamental insights into wave interaction and behavior, and the evolution of complex systems. Optical systems serve as a suitable testbed for the well-controlled investigation of this natural phenomenon, which cannot be easily studied in an ocean environment. Additionally, such systems offer practical applications in telecommunications and optical signal processing, making this topic a vital area of research. Fiber lasers are considered the best candidates for demonstrating and investigating the emergence of optical rogue waves. In particular, they offer significant advantages in nonlinear dynamics due to faster field evolution and a higher number of events that can be recorded within a relatively short time. In this paper, we present the development mechanisms of optical rogue wave events. It was found that multimode vector instability, pulse–pulse interaction, and soliton rain are the main nonlinear dynamics leading to the formation of optical rogue wave events. Full article
(This article belongs to the Special Issue Advanced Lasers and Their Applications II)
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16 pages, 971 KiB  
Article
Revolutionizing Firefighting: UAV-Based Optical Communication Systems for Wildfires
by Mohammad Furqan Ali, Dushantha Nalin K. Jayakody and P. Muthuchidambaranathan
Photonics 2024, 11(7), 656; https://doi.org/10.3390/photonics11070656 - 11 Jul 2024
Viewed by 442
Abstract
Wildfires are one of the most devastating natural disasters in the world. This study proposes an innovative optical wildfire communication system (OWC) that leverages advanced optical technologies for wildfire monitoring and seamless communication towards the 5G and beyond (5GB) wireless networks. The multi-input–multi-output [...] Read more.
Wildfires are one of the most devastating natural disasters in the world. This study proposes an innovative optical wildfire communication system (OWC) that leverages advanced optical technologies for wildfire monitoring and seamless communication towards the 5G and beyond (5GB) wireless networks. The multi-input–multi-output (MIMO) optical link among communication nodes is designed by gamma–gamma (GG) distribution under consideration of intensity modulation and direct-detection (IM/DD) following an on–off-keying (OOK) scheme. In this study, the performance metrics of the proposed MIMO link that enables unmanned aerial vehicles (UAVs) are analytically derived. The end-to-end (E2E) performance metrics and the novel closed-form expressions for the average BER (ABER) and outage probability (Pout) are investigated for the proposed system models. Furthermore, the simulation results are obtained based on the real experimental data. The obtained results in this study are improved spatial resolution and accuracy, enabling the detection by communication of even small-scale wildfires at their inception stages. In the further perspective of this research, the development of the proposed system holds the potential to revolutionize wildfire prevention and control efforts, making a substantial impact on safeguarding ecosystems, communities, and economies from the devastating effects of fires. Full article
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10 pages, 2180 KiB  
Article
Design and Fabrication of Metasurfaces-Based Polarizing Beam Splitter with Tailored Deflection Angles for 940-nm Wavelength
by Kuan-Cheng Peng, Ju-Lin Pan, Jin-Li Weng, Yun-Han Lee, Jui-An Chiang and Guo-Dung Su
Photonics 2024, 11(7), 655; https://doi.org/10.3390/photonics11070655 - 11 Jul 2024
Viewed by 377
Abstract
Polarizing beam splitters (PBSs) are fundamental components of optical systems and are crucial for sensing, communication, and imaging tasks. Traditional PBS devices, assembled using right-angle prisms with dielectric coatings, face challenges such as bulkiness and limited versatility in deflection directions. To address these [...] Read more.
Polarizing beam splitters (PBSs) are fundamental components of optical systems and are crucial for sensing, communication, and imaging tasks. Traditional PBS devices, assembled using right-angle prisms with dielectric coatings, face challenges such as bulkiness and limited versatility in deflection directions. To address these limitations, we meticulously make metasurfaces for enhanced PBS performance. Metasurfaces, composed of subwavelength structures, manipulate wavefronts, polarization, and light intensity. Using metasurfaces in the design of PBS devices, we can precisely tailor the structure to manipulate the deflection angles of light beams, ensuring that they align with the desired specifications. Our experimental results closely align with simulation outcomes, showcasing deflection angles of a 1.5 mm diameter metasurface near ±15 degrees for s- and p-polarizations in a wavelength of 940-nm. Full article
(This article belongs to the Special Issue Polarization Optics)
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11 pages, 3607 KiB  
Article
Characterization of Single Frequency Fiber-Laser-Based Ultrasound Sensor
by Wei Zhu, Qiang Lu, Bo Yang, Rui Tian, Hao Luo, Chao Cai, Zhijun Yan and Luming Zhao
Photonics 2024, 11(7), 654; https://doi.org/10.3390/photonics11070654 - 11 Jul 2024
Viewed by 431
Abstract
In this paper, we demonstrated a distributed feedback fiber-laser- (DFB-FL) based ultrasound detection system with a high signal-to-noise ratio (SNR), high sensitivity and wide frequency response range. The DFB-FL was fabricated by UV-inscribing a π phase-shifted grating in the Erbium–Ytterbium co-doped fiber using [...] Read more.
In this paper, we demonstrated a distributed feedback fiber-laser- (DFB-FL) based ultrasound detection system with a high signal-to-noise ratio (SNR), high sensitivity and wide frequency response range. The DFB-FL was fabricated by UV-inscribing a π phase-shifted grating in the Erbium–Ytterbium co-doped fiber using the phase mask method. The theory of DFB-FL and the sensing principle has been discussed and analyzed. The sensing signal was demodulated via an unbalanced Mach–Zehnder interferometer (MZI) system. The experimental results showed that the sensitivity of the sensor reached 75.18 mV/kPa and the flat frequency response range covered over 30 MHz, which covered the ultrasonic detection frequency range of abnormal discharge in the electric power system. The SNR of this DFB-FL was 42.9 dB, and the corresponding noise-equivalent pressure was calculated as 0.12 kPa. Full article
(This article belongs to the Special Issue Cutting-Edge Developments in Fiber Laser)
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