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Photonics, Volume 11, Issue 10 (October 2024) – 98 articles

Cover Story (view full-size image): Optical frequency combs (OFCs), as a type of multi-wavelength light source, can be widely applied in various fields such as spectroscopy, atomic clocks, optical communication, and arbitrary waveform generation. We propose and experimentally demonstrate an approach for generating a wideband OFC featuring multiple comb lines and wavelength tunability based on a gain-switched weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD) under multi-wavelength optical injection. The experiment achieves an OFC with a bandwidth of 292 GHz containing 147 lines, which has some virtues including a small free spectral range, a large bandwidth, and tenability. This OFC possesses application prospects in a variety of fields such as high-density optical communication and spectroscopy. View this paper
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1 pages, 157 KiB  
Correction
Correction: Hofstetter et al. Monolithically Integrated Michelson Interferometer Using an InGaAs/InAlAs Quantum Cascade Laser at λ = 4 µm. Photonics 2024, 11, 593
by Daniel Hofstetter, Hans Beck and David P. Bour
Photonics 2024, 11(10), 992; https://doi.org/10.3390/photonics11100992 - 21 Oct 2024
Viewed by 308
Abstract
There was an error in the original publication [...] Full article
13 pages, 2844 KiB  
Review
Leveraging Optical Coherence Tomography and Angiography Artifacts to Identify Clinicopathological Correlates in Macular Disorders
by Luca Scuderi, Serena Fragiotta, Chiara Ciancimino, Marco Mafrici, Marco Mazzola, Monica Varano, Tommaso Rossi and Mariacristina Parravano
Photonics 2024, 11(10), 991; https://doi.org/10.3390/photonics11100991 - 21 Oct 2024
Viewed by 496
Abstract
Optical Coherence Tomography (OCT) and Optical Coherence Tomography Angiography (OCTA) are pivotal imaging techniques in diagnosing and managing macular disorders, providing high-resolution cross-sectional images of the retina. Although OCT artifacts are often deemed undesirable, they can paradoxically offer valuable insights into retinal pathology. [...] Read more.
Optical Coherence Tomography (OCT) and Optical Coherence Tomography Angiography (OCTA) are pivotal imaging techniques in diagnosing and managing macular disorders, providing high-resolution cross-sectional images of the retina. Although OCT artifacts are often deemed undesirable, they can paradoxically offer valuable insights into retinal pathology. This review explores the potential of OCT and OCTA artifacts to serve as indicators of pathological correlates in various macular conditions. The study emphasizes the importance of recognizing and leveraging these artifacts to refine clinicopathologic correlates characterizing several macular disorders, including age-related macular degeneration, diabetic retinopathy, and retinal vascular occlusive disease. OCT artifacts can reflect the ultrastructure and composition of pathological features, and their recognition can thus expand the understanding of the pathogenesis and improve the diagnostic interpretation of macular disorders. With the widespread use of OCT and OCTA technologies, identifying artifacts with clinicopathologic significance is of paramount importance and may have significant implications for management and prognosis. Full article
(This article belongs to the Special Issue Technologies and Applications of Biophotonics)
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13 pages, 4948 KiB  
Article
Feature Vector Effectiveness Evaluation for Pattern Selection in Computational Lithography
by Yaobin Feng, Jiamin Liu, Hao Jiang and Shiyuan Liu
Photonics 2024, 11(10), 990; https://doi.org/10.3390/photonics11100990 - 21 Oct 2024
Viewed by 522
Abstract
Pattern selection is crucial for optimizing the calibration process of optical proximity correction (OPC) models in computational lithography. However, it remains a challenge to achieve a balance between representative coverage and computational efficiency. This work presents a comprehensive evaluation of the feature vectors’ [...] Read more.
Pattern selection is crucial for optimizing the calibration process of optical proximity correction (OPC) models in computational lithography. However, it remains a challenge to achieve a balance between representative coverage and computational efficiency. This work presents a comprehensive evaluation of the feature vectors’ (FVs’) effectiveness in pattern selection for OPC model calibration, leveraging key performance indicators (KPIs) based on Kullback–Leibler divergence and distance ranking. Through the construction of autoencoder-based FVs and fast Fourier transform (FFT)-based FVs, we compare their efficacy in capturing critical pattern features. Validation experimental results indicate that autoencoder-based FVs, particularly augmented with the lithography domain knowledge, outperform FFT-based counterparts in identifying anomalies and enhancing lithography model performance. These results also underscore the importance of adaptive pattern representation methods in calibrating the OPC model with evolving complexities. Full article
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11 pages, 2128 KiB  
Article
New Yellow Azo Pyridone Derivatives with Enhanced Thermal Stability for Color Filters in Image Sensors
by Sunwoo Park, Sangwook Park, Saeyoung Oh, Hyukmin Kwon, Hayoon Lee, Kiho Lee, Chun Yoon and Jongwook Park
Photonics 2024, 11(10), 989; https://doi.org/10.3390/photonics11100989 - 21 Oct 2024
Viewed by 494
Abstract
Two new yellow azo pyridone derivatives, (E)-6-hydroxy-1-(3-methoxypropyl)-4-methyl-2-oxo-5-(p-tolyldiazenyl)-1,2-dihydropyridine-3-carbonitrile (APY-M) and 5,5′-((1E,1′E)-(methylenebis(4,1-phenylene))bis(diazene-2,1-diyl))bis(6-hydroxy-4-methyl-2-oxo-1,2-dihydropyridine-3-carbonitrile) (APY-D), were designed and synthesized as yellow colorants for image sensors. The properties of these new compounds were evaluated in both solution and color filter film forms, focusing on their optical and thermal [...] Read more.
Two new yellow azo pyridone derivatives, (E)-6-hydroxy-1-(3-methoxypropyl)-4-methyl-2-oxo-5-(p-tolyldiazenyl)-1,2-dihydropyridine-3-carbonitrile (APY-M) and 5,5′-((1E,1′E)-(methylenebis(4,1-phenylene))bis(diazene-2,1-diyl))bis(6-hydroxy-4-methyl-2-oxo-1,2-dihydropyridine-3-carbonitrile) (APY-D), were designed and synthesized as yellow colorants for image sensors. The properties of these new compounds were evaluated in both solution and color filter film forms, focusing on their optical and thermal characteristics. The molar extinction coefficient values of APY-M and APY-D in solution were found to be 2.7 × 105 and 3.0 × 105 L/mol·cm, respectively. The transmittance of the newly synthesized compounds met commercial requirements, showing values below 0.21% at 435 nm and above 97.1% at 530 nm. APY-D exhibited a molar extinction coefficient value in solution that was 1.15 times higher than that of the commercially used yellow colorant Disperse Yellow 241. Both newly synthesized compounds satisfied the decomposition temperature requirement of over 230 °C, which is essential for the color filter manufacturing process in image sensors. In particular, APY-D, with its dimeric structure and increased molecular weight, demonstrated enhanced thermal stability, with a 50 °C increase in decomposition temperature compared to Disperse Yellow 241. Color filter films for image sensors were fabricated using the new compounds, and their thermal resistance was evaluated. APY-D maintained its transmittance due to the enhanced thermal stability provided by its dimer structure and increased molecular weight. Consequently, APY-D is anticipated to be a promising candidate for use as a yellow colorant in image sensors, owing to its excellent optical and thermal properties. Full article
(This article belongs to the Special Issue Organic Optoelectronic Materials and Their Applications)
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18 pages, 706 KiB  
Article
A Python-Based Indoor Channel Model with Multi-Wavelength Propagation for Color Shift Keying
by Juan F. Gutiérrez, Diego Sandoval and Jesus M. Quintero
Photonics 2024, 11(10), 988; https://doi.org/10.3390/photonics11100988 - 20 Oct 2024
Viewed by 686
Abstract
Color shift keying is a modulation scheme for visible light communication that uses fixtures with three or more narrow-spectral light-emitting diodes to transmit data while fulfilling the primary function of illumination. When this modulation is used indoors, the reflectivity of the walls strongly [...] Read more.
Color shift keying is a modulation scheme for visible light communication that uses fixtures with three or more narrow-spectral light-emitting diodes to transmit data while fulfilling the primary function of illumination. When this modulation is used indoors, the reflectivity of the walls strongly affects the inter-channel interference and illumination quality. In this paper we present an indoor channel model that takes into account multi-wavelength propagation. This model is available as an open-source Python package. The model calculates the inter-channel interference, illuminance, correlated color temperature, and color rendering index at the receiver position. The Python package includes a module for estimating the symbol error rate. To validate the model, we computed the received power at each color photodetector for four different indoor scenarios. The model demonstrated a color rendering index of less than 15 when using IEEE-based color shift keying and non-uniform illumination on a horizontal plane. The simulation determined the required luminous flux to achieve a symbol error rate of less than 105 when the photodetector is at the center of the indoor space and vertically below the light source. To maintain a symbol error rate less than 105, the luminous flux increases when the photodetector is displaced in a diagonal direction from the center of the plane. Full article
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9 pages, 3571 KiB  
Communication
High-Linearity Dual-Parallel Mach–Zehnder Modulators in Thin-Film Lithium Niobate
by Tao Yang, Lutong Cai, Zhanhua Huang and Lin Zhang
Photonics 2024, 11(10), 987; https://doi.org/10.3390/photonics11100987 - 20 Oct 2024
Viewed by 641
Abstract
Microwave photonic (MWP) systems are inseparable from conversions of microwave electrical signals into optical signals, and their performances highly depend on the linearity of electro-optic modulators. Thin-film lithium niobate (TFLN) is expected to be an ideal platform for future microwave photonic systems due [...] Read more.
Microwave photonic (MWP) systems are inseparable from conversions of microwave electrical signals into optical signals, and their performances highly depend on the linearity of electro-optic modulators. Thin-film lithium niobate (TFLN) is expected to be an ideal platform for future microwave photonic systems due to its compact size, low optical loss, linear electro-optic effect, and high bandwidth. In this paper, we propose a TFLN modulator with a low voltage–length product (VπL) of 1.97 V·cm and an ultra-high-linearity carrier-to-distortion ratio (CDR) of 112.33 dB, using a dual-parallel Mach–Zehnder interferometer configuration. It provides an effective approach to fully suppress the third-order intermodulation distortions (IMD3), leading to 76 dB improvement over a single Mach–Zehnder modulator (MZM) in TFLN. The proposed TFLN modulator would enable a wide variety of applications in integrated MWP systems with large-scale integration, low power consumption, low optical loss, and high bandwidth. Full article
(This article belongs to the Special Issue New Perspectives in Microwave Photonics)
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6 pages, 1201 KiB  
Communication
The Time Response of a Uniformly Doped Transmission-Mode NEA AlGaN Photocathode Applied to a Solar-Blind Ultraviolet Detecting System
by Jinjuan Du, Xiyao Li, Tiantian Jia, Hongjin Qiu, Yang Li, Rui Pu, Quanchao Zhang, Hongchang Cheng, Xin Guo, Jiabin Qiao and Huiyang He
Photonics 2024, 11(10), 986; https://doi.org/10.3390/photonics11100986 - 19 Oct 2024
Viewed by 433
Abstract
Due to the excellent quantum conversion and spectral response characteristics of the AlGaN photocathode, it has become the most promising III-V group semiconductor photocathode in solar-blind signal photoconversion devices in the ultraviolet band. Herein, the influence factors of the time-resolved characteristics of the [...] Read more.
Due to the excellent quantum conversion and spectral response characteristics of the AlGaN photocathode, it has become the most promising III-V group semiconductor photocathode in solar-blind signal photoconversion devices in the ultraviolet band. Herein, the influence factors of the time-resolved characteristics of the AlGaN photocathode are researched by solving the photoelectron continuity equation and photoelectron flow density equation, such as the AlN/AlGaN interface recombination rate, AlGaN electron diffusion coefficient, and AlGaN activation layer thickness. The results show that the response time of the AlGaN photocathode decreases gradually with the increase in AlGaN photoelectron diffusion coefficient and AlN/AlGaN interface recombination rate, but the response time of the AlGaN photocathode gradually becomes saturated with the further increase in AlN/AlGaN interface recombination rate. When the thickness of the AlGaN photocathode is reduced from 250 nm to 50 nm, the response time of the AlGaN photocathode decreases from 63.28 ps to 9.91 ps, and the response time of AlGaN photocathode greatly improves. This study provides theoretical guidance for the development of a fast response UV detector. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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24 pages, 12773 KiB  
Article
Anticrossing and Mode Coupling in Bent All-Glass Leakage Channel Microstructured Optical Fibers with Large Mode Area
by Alexander N. Denisov, Vladislav V. Dvoyrin and Sergey L. Semjonov
Photonics 2024, 11(10), 985; https://doi.org/10.3390/photonics11100985 - 19 Oct 2024
Viewed by 416
Abstract
This paper presents the results of a detailed theoretical study of the bending properties of original all-glass leakage channel microstructured optical fibers (LC MOFs) over a bending radius range from 3 cm to 11 cm. These LC MOFs contain two layers of fluorine-doped [...] Read more.
This paper presents the results of a detailed theoretical study of the bending properties of original all-glass leakage channel microstructured optical fibers (LC MOFs) over a bending radius range from 3 cm to 11 cm. These LC MOFs contain two layers of fluorine-doped silica glass elements with reduced refractive index, different diameters, and different distances between them. We determined the spatial distributions of the electric field components of different modes in addition to the usual parameters such as effective refractive indices, bending losses, and spatial intensity distributions. A detailed analysis showed that three modes for each polarization have to be considered to correctly calculate the bending losses. Two pairs of these three modes couple in two distinct bending radius ranges, specifically near 3.68 cm and near 5.95 cm, and the mode coupling in these pairs is resonant. The resulting bending losses of the LC MOF for two polarizations are very close to each other and have two maxima at bending radii of 3.68 cm and 5.95 cm. However, the nature of these maxima is not resonant; they are caused by the combined influence of all three modes, each of which has specific dependencies of losses and other parameters on the bending radius that exhibit quasi-resonant behavior near the corresponding bending radii. Full article
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11 pages, 2935 KiB  
Article
Precise Reflectance/Transmittance Measurements of Highly Reflective Optics with Saturated Cavity Ring-Down Signals
by Yanling Han, Bincheng Li, Jing Wang, Hao Cui and Tianming Wang
Photonics 2024, 11(10), 984; https://doi.org/10.3390/photonics11100984 - 19 Oct 2024
Viewed by 427
Abstract
In this paper, a data processing approach was developed to accurately extract the ring-down time and amplitude of the saturated cavity ring-down (CRD) signal; both were utilized to determine simultaneously the high reflectance and residual transmittance of highly reflective (HR) mirrors with a [...] Read more.
In this paper, a data processing approach was developed to accurately extract the ring-down time and amplitude of the saturated cavity ring-down (CRD) signal; both were utilized to determine simultaneously the high reflectance and residual transmittance of highly reflective (HR) mirrors with a dual-channel CRD configuration. The influence of saturation was eliminated by deleting the beginning saturated data points of the saturated CRD signal and fitting the remaining non-saturated CRD signal to a single-exponential function. By comparing the reflectance/transmittance measurement results of HR samples obtained via data processing of saturated CRD signals and via single-exponentially fitting non-saturated CRD signals with utilization of neutral density filter(s) to eliminate saturation, it was found that the reflectances obtained with both methods were in excellent agreement, while the residual transmittance obtained with the saturated CRD signal was more accurate than that obtained with the neutral-density-filter-attenuated non-saturated CRD signal. The proposed data processing method eliminated the need to use the neutral density filters, therefore avoiding the adding of the optical density error to the uncertainty of residual transmittance measurement and improving the measurement accuracy. The proposed data processing method also extended the dynamic range of the dual-channel CRD scheme for simultaneous measurement of reflectance, transmittance and optical loss. Full article
(This article belongs to the Special Issue Optoelectronic Detection Technologies and Applications)
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11 pages, 5796 KiB  
Article
Real-Time Resolution Enhancement of Confocal Laser Scanning Microscopy via Deep Learning
by Zhiying Cui, Yi Xing, Yunbo Chen, Xiu Zheng, Wenjie Liu, Cuifang Kuang and Youhua Chen
Photonics 2024, 11(10), 983; https://doi.org/10.3390/photonics11100983 - 19 Oct 2024
Viewed by 626
Abstract
Confocal laser scanning microscopy is one of the most widely used tools for high-resolution imaging of biological cells. However, the imaging resolution of conventional confocal technology is limited by diffraction, and more complex optical principles and expensive optical-mechanical structures are usually required to [...] Read more.
Confocal laser scanning microscopy is one of the most widely used tools for high-resolution imaging of biological cells. However, the imaging resolution of conventional confocal technology is limited by diffraction, and more complex optical principles and expensive optical-mechanical structures are usually required to improve the resolution. This study proposed a deep residual neural network algorithm that can effectively improve the imaging resolution of the confocal microscopy in real time. The reliability and real-time performance of the algorithm were verified through imaging experiments on different biological structures, and an imaging resolution of less than 120 nm was achieved in a more cost-effective manner. This study contributes to the real-time improvement of the imaging resolution of confocal microscopy and expands the application scenarios of confocal microscopy in biological imaging. Full article
(This article belongs to the Special Issue Advanced Optical Microscopy and Imaging Technology)
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16 pages, 3824 KiB  
Article
A Hybrid Network Integrating MHSA and 1D CNN–Bi-LSTM for Interference Mitigation in Faster-than-Nyquist MIMO Optical Wireless Communications
by Minghua Cao, Qing Yang, Genxue Zhou, Yue Zhang, Xia Zhang and Huiqin Wang
Photonics 2024, 11(10), 982; https://doi.org/10.3390/photonics11100982 - 19 Oct 2024
Viewed by 520
Abstract
To mitigate inter-symbol interference (ISI) caused by Faster-than-Nyquist (FTN) technology in a multiple input multiple output (MIMO) optical wireless communication (OWC) system, we propose an ISI cancellation algorithm that combines multi-head self-attention (MHSA), a one-dimensional convolutional neural network (1D CNN), and bi-directional long [...] Read more.
To mitigate inter-symbol interference (ISI) caused by Faster-than-Nyquist (FTN) technology in a multiple input multiple output (MIMO) optical wireless communication (OWC) system, we propose an ISI cancellation algorithm that combines multi-head self-attention (MHSA), a one-dimensional convolutional neural network (1D CNN), and bi-directional long short-term memory (Bi-LSTM). This hybrid network extracts data features using 1D CNN and captures sequential information with Bi-LSTM, while incorporating MHSA to comprehensively reduce ISI. We analyze the impact of antenna numbers, acceleration factors, wavelength, and turbulence intensity on the system’s bit error rate (BER) performance. Additionally, we compare the waveform graphs and amplitude–frequency characteristics of FTN signals before and after processing, specifically comparing sampled values of four-pulse-amplitude modulation (4PAM) signals with those obtained after ISI cancellation. The simulation results demonstrate that within the Mazo limit for selecting acceleration factors, our proposal achieves a 7 dB improvement in BER compared to the conventional systems without deep learning (DL)-based ISI cancellation algorithms. Furthermore, compared to systems employing a point-by-point elimination adaptive pre-equalization algorithm, our proposal exhibits comparable BER performance to orthogonal transmission systems while reducing computational complexity by 31.15%. Full article
(This article belongs to the Special Issue Advanced Technologies in Optical Wireless Communications)
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11 pages, 4528 KiB  
Article
Random Raman Lasing in Diode-Pumped Multi-Mode Graded-Index Fiber with Femtosecond Laser-Inscribed Random Refractive Index Structures of Various Shapes
by Alexey G. Kuznetsov, Zhibzema E. Munkueva, Alexandr V. Dostovalov, Alexey Y. Kokhanovskiy, Polina A. Elizarova, Ilya N. Nemov, Alexandr A. Revyakin, Denis S. Kharenko and Sergey A. Babin
Photonics 2024, 11(10), 981; https://doi.org/10.3390/photonics11100981 - 18 Oct 2024
Viewed by 420
Abstract
Diode-pumped multi-mode graded-index (GRIN) fiber Raman lasers provide prominent brightness enhancement both in linear and half-open cavities with random distributed feedback via natural Rayleigh backscattering. Femtosecond laser-inscribed random refractive index structures allow for the sufficient reduction in the Raman threshold by means of [...] Read more.
Diode-pumped multi-mode graded-index (GRIN) fiber Raman lasers provide prominent brightness enhancement both in linear and half-open cavities with random distributed feedback via natural Rayleigh backscattering. Femtosecond laser-inscribed random refractive index structures allow for the sufficient reduction in the Raman threshold by means of Rayleigh backscattering signal enhancement by +50 + 66 dB relative to the intrinsic fiber level. At the same time, they offer an opportunity to generate Stokes beams with a shape close to fundamental transverse mode (LP01), as well as to select higher-order modes such as LP11 with a near-1D longitudinal random structure shifted off the fiber axis. Further development of the inscription technology includes the fabrication of 3D ring-shaped random structures using a spatial light modulator (SLM) in a 100/140 μm GRIN multi-mode fiber. This allows for the generation of a multi-mode diode-pumped GRIN fiber random Raman laser at 976 nm with a ring-shaped output beam at a relatively low pumping threshold (~160 W), demonstrated for the first time to our knowledge. Full article
(This article belongs to the Special Issue Advancements in Fiber Lasers and Their Applications)
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17 pages, 5605 KiB  
Review
Imaging of Live Cells by Digital Holographic Microscopy
by Emilia Mitkova Mihaylova
Photonics 2024, 11(10), 980; https://doi.org/10.3390/photonics11100980 - 18 Oct 2024
Viewed by 582
Abstract
Imaging of microscopic objects is of fundamental importance, especially in life sciences. Recent fast progress in electronic detection and control, numerical computation, and digital image processing, has been crucial in advancing modern microscopy. Digital holography is a new field in three-dimensional imaging. Digital [...] Read more.
Imaging of microscopic objects is of fundamental importance, especially in life sciences. Recent fast progress in electronic detection and control, numerical computation, and digital image processing, has been crucial in advancing modern microscopy. Digital holography is a new field in three-dimensional imaging. Digital reconstruction of a hologram offers the remarkable capability to refocus at different depths inside a transparent or semi-transparent object. Thus, this technique is very suitable for biological cell studies in vivo and could have many biomedical and biological applications. A comprehensive review of the research carried out in the area of digital holographic microscopy (DHM) for live-cell imaging is presented. The novel microscopic technique is non-destructive and label-free and offers unmatched imaging capabilities for biological and bio-medical applications. It is also suitable for imaging and modelling of key metabolic processes in living cells, microbial communities or multicellular plant tissues. Live-cell imaging by DHM allows investigation of the dynamic processes underlying the function and morphology of cells. Future applications of DHM can include real-time cell monitoring in response to clinically relevant compounds. The effect of drugs on migration, proliferation, and apoptosis of abnormal cells is an emerging field of this novel microscopic technique. Full article
(This article belongs to the Special Issue Technologies and Applications of Digital Holography)
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12 pages, 3471 KiB  
Article
Erbium-Doped Tunable Fiber Laser Based on a Vernier Effect Filter
by Yuanzhen Liu, Hailong Xu, Kexin Zhu, Yicun Yao, Yuman Suo and Liqiang Zhang
Photonics 2024, 11(10), 979; https://doi.org/10.3390/photonics11100979 - 18 Oct 2024
Viewed by 396
Abstract
A novel vernier effect filter is designed utilizing two cascaded Mach–Zehnder interferometers (MZIs). Integrating the filter into an erbium-doped fiber laser (EDFL), the tunability of laser wavelength is achieved. Each MZI comprises two sequentially interconnected 3 dB optical couplers (OCs), where the incoming [...] Read more.
A novel vernier effect filter is designed utilizing two cascaded Mach–Zehnder interferometers (MZIs). Integrating the filter into an erbium-doped fiber laser (EDFL), the tunability of laser wavelength is achieved. Each MZI comprises two sequentially interconnected 3 dB optical couplers (OCs), where the incoming light is initially split into two arms at the first OC and subsequently recombined at the second OC. Interference occurs due to the optical path difference between these two beams. Notably, the two MZIs exhibit closely matched free spectral ranges (FSRs), leading to the formation of a broadened envelope in the superimposed spectrum. By delicately adjusting the optical path difference between the two arms of one MZI, a little drift of the interference spectrum is induced. This small amount of drift, in turn, triggers a significant movement of the envelope, giving rise to the so-called vernier effect. Integrating the vernier effect filter into an EDFL, the wavelength of the fiber laser can be tuned from 1542.56 nm to 1556.62 nm, with a tuning range of 14.06 nm. Furthermore, by employing a high-precision stepper motor, a remarkable tuning accuracy of 0.01 nm is attainable. The side mode suppression ratio of all wavelengths is above 55 dB. In comparison to reported tunable fiber lasers utilizing MZI filters, the proposed fiber laser in this study offers enhanced precision and a more user-friendly tuning process. Full article
(This article belongs to the Special Issue Cutting-Edge Developments in Fiber Laser)
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11 pages, 2396 KiB  
Article
Effect of Er:YAG Laser-Activated Irrigation with Side-Firing Spiral Endo Tip on Dentin Mineral Composition of Tooth Root Canals
by Sharonit Sahar-Helft, Adi Farber, Nathanyel Sebbane, Coral Helft, Roni Dakar, Vitaly Gutkin, Ronit Vogt Sionov and Doron Steinberg
Photonics 2024, 11(10), 978; https://doi.org/10.3390/photonics11100978 - 18 Oct 2024
Viewed by 476
Abstract
Background: Treating tooth root canal systems with Er:YAG laser together with irrigants has been shown to be effective in reducing biofilms formed by Enterococcus faecalis. This study investigated whether laser-activated irrigation (LAI) with side-firing Endo tip (LiteTouch™; Light Instruments, Yokneam, Israel) affects [...] Read more.
Background: Treating tooth root canal systems with Er:YAG laser together with irrigants has been shown to be effective in reducing biofilms formed by Enterococcus faecalis. This study investigated whether laser-activated irrigation (LAI) with side-firing Endo tip (LiteTouch™; Light Instruments, Yokneam, Israel) affects dentin mineral composition when used with common endodontic irrigants. Methods: Root canals of extracted human teeth were treated with Er:YAG laser using a side-firing Endo tip combined with 17% ethylenediaminetetraacetic acid (EDTA) and/or 2.5% NaOCl in continuous or intermittent mode for 60 s. Dentin mineral composition (Ca, P, O) in coronal, middle, and apical regions of root canals was examined by energy dispersive X-ray spectroscopy. Results: The use of LAI with continuous EDTA resulted in the largest reduction in Ca and P levels. A final NaOCl rinse mitigated the EDTA-mediated mineral loss in all root canal regions and increased the O content. Likewise, the reduced Ca/O and Ca/P ratios caused by continuous EDTA irrigation were reversed when combined with a final NaOCl rinse. Conclusions: LAI with Er:YAG Endo tip using continuous EDTA irrigation followed by NaOCl caused minimal dentin mineral loss and can therefore be considered to be a safe treatment module for cleaning root canals. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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15 pages, 3317 KiB  
Article
Holographic Multi-Notch Filters Recorded with Simultaneous Double-Exposure Contact Mirror-Based Method
by Bing-Han Zhuang, Sheng-Chun Hung, Kun-Huang Chen, Chien-Hung Yeh and Jing-Heng Chen
Photonics 2024, 11(10), 977; https://doi.org/10.3390/photonics11100977 - 18 Oct 2024
Viewed by 475
Abstract
This study presents a novel simultaneous double-exposure contact mirror-based method for fabricating holographic multi-notch filters with dual operational central wavelengths. The proposed method leverages coupled wave theory, the geometric relationships of K-vectors, and a reflection-type recording setup, incorporating additional reflecting mirrors to guide [...] Read more.
This study presents a novel simultaneous double-exposure contact mirror-based method for fabricating holographic multi-notch filters with dual operational central wavelengths. The proposed method leverages coupled wave theory, the geometric relationships of K-vectors, and a reflection-type recording setup, incorporating additional reflecting mirrors to guide the recording beams. To validate the approach, a holographic notch filter was fabricated using photopolymer recording materials, resulting in operational wavelengths of 531.13 nm and 633.01 nm. The measured diffraction efficiencies at these wavelengths were ηs = 52.35% and ηp = 52.45% for 531.13 nm, and ηs = 67.30% and ηp = 67.40% for 633.01 nm. The component’s performance was analyzed using s- and p-polarized spectral transmission intensities at various reconstruction angles, revealing polarization-independent characteristics under normal incidence and polarization-dependent behavior under oblique incidence. The study also explored the relationships between recording parameters, such as incident angle, wavelength, emulsion expansion, and dispersion. The findings demonstrate that the first operational central wavelength is primarily influenced by the recording wavelength, while the second is primarily determined by the incident angle, covering a range from visible light to near-infrared. This method offers significant potential for cost-effective, mass-produced filters in optoelectronic applications. Full article
(This article belongs to the Special Issue Advances in Holography and Its Applications)
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11 pages, 2362 KiB  
Article
Time-Dependent Resistance of Sol–Gel HfO2 Films to In Situ High-Temperature Laser Damage
by Haojie Liu, Ziwei Hao, Zirun Peng, Miao Zhang, Peizhong Feng and Cheng Xu
Photonics 2024, 11(10), 976; https://doi.org/10.3390/photonics11100976 - 18 Oct 2024
Viewed by 389
Abstract
Laser damage in films under long-term high-temperature conditions is a significant concern for advancing laser applications. This study focused on HfO2 films prepared using the sol–gel method with HfCl4 as a precursor. It examined the effects of temperature on various properties [...] Read more.
Laser damage in films under long-term high-temperature conditions is a significant concern for advancing laser applications. This study focused on HfO2 films prepared using the sol–gel method with HfCl4 as a precursor. It examined the effects of temperature on various properties of the films, including their optical properties, microstructure, surface morphology, absorption, and laser-induced damage threshold (LIDT). The prepared film demonstrated desirable characteristics at the high temperature of 423 K, such as high transmittance, low absorption, and high LIDT. As the duration of its high-temperature exposure increased, the LIDT of the films gradually decreased. An intriguing finding was that the film’s LIDT exhibited an exponential decay pattern with prolonged heating time. This observation could be attributed to the power-law increase in defects on both the internal and surface areas of the film as the duration of high-temperature exposure lengthened. Moreover, even after a 15-day heating period at 423 K, the film maintained an LIDT of 12.9 J/cm2, indicating its potential applicability in practical high-temperature environments. This study provided a general pattern and a universal formula for understanding the laser damage of sol–gel films at high temperatures over time. Furthermore, it opened possibilities for future developments of laser films suitable for extreme environments. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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8 pages, 3225 KiB  
Communication
Generation of High-Quality Cylindrical Vector Beams from All-Few-Mode Fiber Laser
by Pingping Xiao, Zhen Tang, Fei Wang, Yaqiong Lu and Zuxing Zhang
Photonics 2024, 11(10), 975; https://doi.org/10.3390/photonics11100975 - 17 Oct 2024
Viewed by 380
Abstract
Transverse mode control of laser intracavity oscillation is crucial for generating high-purity cylindrical vector beams (CVBs). We utilized the mode conversion and mode selection properties of two-mode long-period fiber gratings (TM-LPFGs) and two-mode fiber Bragg gratings (TM-FBGs) to achieve intracavity hybrid-mode oscillations of [...] Read more.
Transverse mode control of laser intracavity oscillation is crucial for generating high-purity cylindrical vector beams (CVBs). We utilized the mode conversion and mode selection properties of two-mode long-period fiber gratings (TM-LPFGs) and two-mode fiber Bragg gratings (TM-FBGs) to achieve intracavity hybrid-mode oscillations of LP01 and LP11 from an all-few-mode fiber laser. A mode-locked pulse output with a repetition rate of 12.46 MHz and a signal-to-noise ratio of 53 dB was achieved with a semiconductor saturable absorber mirror (SESAM) for mode-locking, at a wavelength of 1550.32 nm. The 30 dB spectrum bandwidth of the mode-locked pulse was 0.13 nm. Furthermore, a high-purity CVB containing radially polarized and azimuthally polarized LP11 modes was generated. The purity of the obtained CVB was greater than 99%. The high-purity CVB pulses have great potential for applications in optical tweezers, high-speed mode-division multiplexing communication, and more. Full article
(This article belongs to the Special Issue Single Frequency Fiber Lasers and Their Applications)
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12 pages, 6298 KiB  
Article
A CMOS Optoelectronic Transimpedance Amplifier Using Concurrent Automatic Gain Control for LiDAR Sensors
by Yeojin Chon, Shinhae Choi and Sung-Min Park
Photonics 2024, 11(10), 974; https://doi.org/10.3390/photonics11100974 - 17 Oct 2024
Viewed by 390
Abstract
This paper presents a novel optoelectronic transimpedance amplifier (OTA) for short-range LiDAR sensors used in 180 nm CMOS technology, which consists of a main transimpedance amplifier (m-TIA) with an on-chip P+/N-well/Deep N-well avalanche photodiode (P+/NW/DNW APD) and a replica [...] Read more.
This paper presents a novel optoelectronic transimpedance amplifier (OTA) for short-range LiDAR sensors used in 180 nm CMOS technology, which consists of a main transimpedance amplifier (m-TIA) with an on-chip P+/N-well/Deep N-well avalanche photodiode (P+/NW/DNW APD) and a replica TIA with another on-chip APD, not only to acquire circuit symmetry but to also obtain concurrent automatic gain control (AGC) function within a narrow single pulse-width duration. In particular, for concurrent AGC operations, 3-bit PMOS switches with series resistors are added in parallel with the passive feedback resistor in the m-TIA. Then, the PMOS switches can be turned on or off in accordance with the DC output voltage amplitudes of the replica TIA. The post-layout simulations reveal that the OTA extends the dynamic range up to 74.8 dB (i.e., 1 µApp~5.5 mApp) and achieves a 67 dBΩ transimpedance gain, an 830 MHz bandwidth, a 16 pA/Hz noise current spectral density, a −31 dBm optical sensitivity for a 10−12 bit error rate, and a 6 mW power dissipation from a single 1.8 V supply. The chip occupies a core area of 200 × 120 µm2. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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18 pages, 1067 KiB  
Article
Quantitative Analysis of Acquisition Speed of High-Precision FLIM Technologies via Simulation and Modeling
by Jinzheng Lu, Ling Miao, Jiaxing Wen, Qiang Li, Jingwei Chen, Qiang Yang, Xing Zhang, Jin Li, Yuchi Wu, Yue Yang, Sixin Wu, Wenbo Mo and Qiang Xiang
Photonics 2024, 11(10), 973; https://doi.org/10.3390/photonics11100973 - 17 Oct 2024
Viewed by 587
Abstract
In practical applications such as cancer diagnosis and industrial detection, there is a critical demand for fast fluorescence lifetime imaging (Fast-FLIM). The Fast-FLIM systems suitable for complex environments are typically achieved by enhancing the hardware performance of time-correlated single-photon counting (TCSPC), with an [...] Read more.
In practical applications such as cancer diagnosis and industrial detection, there is a critical demand for fast fluorescence lifetime imaging (Fast-FLIM). The Fast-FLIM systems suitable for complex environments are typically achieved by enhancing the hardware performance of time-correlated single-photon counting (TCSPC), with an acquisition speed of about a few frames per second (fps). However, due to the limitation of single-photon acquisition, the imaging speed is still far from the demand of practical application. The synchroscan streak camera (SC) maps signals from the temporal dimension to the spatial dimension, effectively overcoming the long acquisition time caused by single-photon acquisition. This paper constructs a method to calculate the acquisition time for the TCSPC-FLIM and SC-FLIM systems, and it quantitatively compares the speed. The research demonstrates that the main factors limiting the acquisition speed of the FLIM systems are the photon emission rate, the photon counting rate, the required SNR, the dwell time, and the number of parallel channels. In high-quality and large-scale lifetime imaging, the acquisition speed of the SC-FLIM is at least 104 times faster than that of the TCSPC-FLIM. Therefore, the synchroscan streak camera has more significant potential to promote Fast-FLIM. Full article
(This article belongs to the Section Biophotonics and Biomedical Optics)
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45 pages, 8541 KiB  
Review
Polymer-Based Optical Guided-Wave Biomedical Sensing: From Principles to Applications
by Malhar A. Nagar and Davide Janner
Photonics 2024, 11(10), 972; https://doi.org/10.3390/photonics11100972 - 17 Oct 2024
Viewed by 621
Abstract
Polymer-based optical sensors represent a transformative advancement in biomedical diagnostics and monitoring due to their unique properties of flexibility, biocompatibility, and selective responsiveness. This review provides a comprehensive overview of polymer-based optical sensors, covering the fundamental operational principles, key insights of various polymer-based [...] Read more.
Polymer-based optical sensors represent a transformative advancement in biomedical diagnostics and monitoring due to their unique properties of flexibility, biocompatibility, and selective responsiveness. This review provides a comprehensive overview of polymer-based optical sensors, covering the fundamental operational principles, key insights of various polymer-based optical sensors, and the considerable impact of polymer integration on their functional capabilities. Primary attention is given to all-polymer optical fibers and polymer-coated optical fibers, emphasizing their significant role in “enabling” biomedical sensing applications. Unlike existing reviews focused on specific polymer types and optical sensor methods for biomedical use, this review highlights the substantial impact of polymers as functional materials and transducers in enhancing the performance and applicability of various biomedical optical sensing technologies. Various sensor configurations based on waveguides, luminescence, surface plasmon resonance, and diverse types of polymer optical fibers have been discussed, along with pertinent examples, in biomedical applications. This review highlights the use of biocompatible, hydrophilic, stimuli-responsive polymers and other such functional polymers that impart selectivity, sensitivity, and stability, improving interactions with biological parameters. Various fabrication techniques for polymer coatings are also explored, highlighting their advantages and disadvantages. Special emphasis is given to polymer-coated optical fiber sensors for biomedical catheters and guidewires. By synthesizing the latest research, this review aims to provide insights into polymer-based optical sensors’ current capabilities and future potential in improving diagnostic and therapeutic outcomes in the biomedical field. Full article
(This article belongs to the Special Issue Emerging Trends in Optical Fiber Sensors and Sensing Techniques)
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28 pages, 10257 KiB  
Article
Thomson Scattering and Radiation Reaction from a Laser-Driven Electron
by Ignacio Pastor, Luis Roso, Ramón F. Álvarez-Estrada and Francisco Castejón
Photonics 2024, 11(10), 971; https://doi.org/10.3390/photonics11100971 - 17 Oct 2024
Viewed by 618
Abstract
We investigate the dynamics of electrons initially counter-propagating to an ultra-fast ultra-intense near-infrared laser pulse using a model for radiation reaction based on the classical Landau–Lifshitz–Hartemann equation. The electrons, with initial energies of 1 GeV, interact with laser fields of up to [...] Read more.
We investigate the dynamics of electrons initially counter-propagating to an ultra-fast ultra-intense near-infrared laser pulse using a model for radiation reaction based on the classical Landau–Lifshitz–Hartemann equation. The electrons, with initial energies of 1 GeV, interact with laser fields of up to 1023 W/cm2. The radiation reaction effects slow down the electrons and significantly alter their trajectories, leading to distinctive Thomson scattering spectra and radiation patterns. It is proposed to use such spectra, which include contributions from harmonic and Doppler-shifted radiation, as a tool to measure laser intensity at focus. We discuss the feasibility of this approach for state-of-the-art and near-future laser technologies. We propose using Thomson scattering to measure the impact of radiation reaction on electron dynamics, thereby providing experimental scenarios for validating our model. This work aims to contribute to the understanding of electron behavior in ultra-intense laser fields and the role of radiation reaction in such extreme conditions. The specific properties of Thomson scattering associated with radiation reaction, shown to be dominant at the intensities of interest here, are highlighted and proposed as a diagnostic tool, both for this phenomenon itself and for laser characterization in a non-intrusive way. Full article
(This article belongs to the Special Issue Photon-Photon Collision Using Extreme Lasers)
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8 pages, 3598 KiB  
Article
Camouflage Breaking with Stereo-Vision-Assisted Imaging
by Han Yao, Libang Chen, Jinyan Lin, Yikun Liu and Jianying Zhou
Photonics 2024, 11(10), 970; https://doi.org/10.3390/photonics11100970 - 16 Oct 2024
Viewed by 486
Abstract
Camouflage is a natural or artificial process that prevents an object from being detected, while camouflage breaking is a countering process for the identification of the concealed object. We report that a perfectly camouflaged object can be retrieved from the background and detected [...] Read more.
Camouflage is a natural or artificial process that prevents an object from being detected, while camouflage breaking is a countering process for the identification of the concealed object. We report that a perfectly camouflaged object can be retrieved from the background and detected with stereo-vision-assisted three-dimensional (3D) imaging. The analysis is based on a binocular neuron energy model applied to general 3D settings. We show that a perfectly concealed object with background interference can be retrieved with vision stereoacuity to resolve the hidden structures. The theoretical analysis is further tested and demonstrated with distant natural images taken by a drone camera, processed with a computer and displayed using autostereoscopy. The recovered imaging is presented with the removal of background interference to demonstrate the general applicability for camouflage breaking with stereo imaging and sensing. Full article
(This article belongs to the Special Issue Optical Imaging Innovations and Applications)
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12 pages, 3068 KiB  
Article
Performance Exploration of Optical Wireless Video Communication Based on Adaptive Block Sampling Compressive Sensing
by Jinwang Li, Haifeng Yao, Keyan Dong, Yansong Song, Tianci Liu, Zhongyu Cao, Weihao Wang, Yixiang Zhang, Kunpeng Jiang and Zhi Liu
Photonics 2024, 11(10), 969; https://doi.org/10.3390/photonics11100969 - 16 Oct 2024
Viewed by 409
Abstract
Optical wireless video transmission technology combines the advantages of high data rates, enhanced security, large bandwidth capacity, and strong anti-interference capabilities inherent in optical communication, establishing it as a pivotal technology in contemporary data transmission networks. However, video data comprises a large volume [...] Read more.
Optical wireless video transmission technology combines the advantages of high data rates, enhanced security, large bandwidth capacity, and strong anti-interference capabilities inherent in optical communication, establishing it as a pivotal technology in contemporary data transmission networks. However, video data comprises a large volume of image information, resulting in substantial data flow with significant redundant bits. To address this, we propose an adaptive block sampling compressive sensing algorithm that overcomes the limitations of sampling inflexibility in traditional compressive sensing, which often leads to either redundant or insufficient local sampling. This method significantly reduces the presence of redundant bits in video images. First, the sampling mechanism of the block-based compressive sensing algorithm was optimized. Subsequently, a wireless optical video transmission experimental system was developed using a Field-Programmable Gate Array chip. Finally, experiments were conducted to evaluate the transmission of video optical signals. The results demonstrate that the proposed algorithm improves the peak signal-to-noise ratio by over 3 dB compared to other algorithms, with an enhancement exceeding 1.5 dB even in field tests, thereby significantly optimizing video transmission quality. This research contributes essential technical insights for the enhancement of wireless optical video transmission performance. Full article
(This article belongs to the Special Issue Next-Generation Free-Space Optical Communication Technologies)
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11 pages, 4067 KiB  
Article
Picometer-Sensitivity Surface Profile Measurement Using Swept-Source Phase Microscopy
by Jinyun Yue, Jinze Cui, Zhaobo Zheng, Jianjun Liu, Yu Zhao, Shiwei Cui, Yao Yu, Yi Wang, Yuqian Zhao, Jingmin Luan, Jian Liu and Zhenhe Ma
Photonics 2024, 11(10), 968; https://doi.org/10.3390/photonics11100968 - 15 Oct 2024
Viewed by 408
Abstract
In recent years, the Swept-Source Phase Microscope (SS-PM) has gained more attention due to its greater robustness to sample motion and lower signal decay with depth. However, the mechanical wavelength tuning of the swept source creates small variations in the wavenumber sampling of [...] Read more.
In recent years, the Swept-Source Phase Microscope (SS-PM) has gained more attention due to its greater robustness to sample motion and lower signal decay with depth. However, the mechanical wavelength tuning of the swept source creates small variations in the wavenumber sampling of spectra that introduce serious phase noise. We present a software post-processing method to eliminate phase noise in SS-PM. This method does not require high-quality swept light sources or high-precision synchronization devices and achieves ~72 pm displacement sensitivity using a conventional SS-PM system. We compare the performance of this method with traditional software-based methods by measuring phase fluctuations. The phase fluctuations in the traditional software-based method are five times those of the proposed method, which means the proposed method has better sensitivity. Using this method, we reconstructed phase images of air wedges and resolution plates to demonstrate the SS-PM’s potential for high-sensitivity surface profiling measurement. Finally, we discuss the advantages of SS-PM over traditional Spectral-Domain PM techniques. Full article
(This article belongs to the Section Data-Science Based Techniques in Photonics)
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14 pages, 1712 KiB  
Article
DeepChaos+: Signal Detection Quality Enhancement of High-Speed DP-16QAM Optical Fiber Communication Based on Chaos Masking Technique with Deep Generative Models
by Dao Anh Vu, Nguyen Khoi Hoang Do, Huyen Ngoc Thi Nguyen, Hieu Minh Dam, Thuy Thanh Thi Tran, Quyen Xuan Nguyen and Dung Cao Truong
Photonics 2024, 11(10), 967; https://doi.org/10.3390/photonics11100967 - 15 Oct 2024
Viewed by 517
Abstract
In long-haul WDM (wavelength division multiplexing) optical communication systems utilizing the DP-16QAM modulation scheme, traditional methods for removing chaos have exhibited poor performance, resulting in a high bit error rate of 102 between the original signal and the removed chaos signal. [...] Read more.
In long-haul WDM (wavelength division multiplexing) optical communication systems utilizing the DP-16QAM modulation scheme, traditional methods for removing chaos have exhibited poor performance, resulting in a high bit error rate of 102 between the original signal and the removed chaos signal. To address this issue, we propose DeepChaos+, a machine learning-based approach for chaos removal in WDM transmission systems. Our framework comprises two key points: (1) DeepChaos+ automatically generates a dataset that accurately reflects the features of the original signals in the communication system, which eliminates the need for time-consuming data simulation, streamlining the process significantly; (2) it allows for the training of a lightweight model that provides fast prediction times while maintaining high accuracy. This allows for both efficient and reliable signal reconstruction. Through extensive experiments, we demonstrate that DeepChaos+ achieves accurate reconstruction of the original signal with a significantly reduced bit error rate of approximately 105. Additionally, DeepChaos+ exhibits high efficiency in terms of processing time, facilitating fast and reliable signal reconstruction. Our results underscore the effectiveness of DeepChaos+ in removing chaos from WDM transmission systems. By enhancing the reliability and efficiency of chaotic secure channels in optical fiber communication systems, DeepChaos+ holds the potential to improve data transmission in high-speed networks. Full article
(This article belongs to the Special Issue Machine Learning Applied to Optical Communication Systems)
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9 pages, 4275 KiB  
Communication
Solution Doping of PMMA-Based Step-Index Polymer Optical Fibers by Rhodamine B Near Glass Transition Temperature of PMMA
by Yinhua Ma, Dewen Fu and Zhi-Feng Zhang
Photonics 2024, 11(10), 966; https://doi.org/10.3390/photonics11100966 - 15 Oct 2024
Viewed by 555
Abstract
Solution doping is a facile approach to fabricating photoactive polymer optical fibers (POFs). However, previous studies reveal that only the cladding of step-index POFs can be doped by the solution doping method in methanol or aqueous solutions, whereas the fiber core is hardly [...] Read more.
Solution doping is a facile approach to fabricating photoactive polymer optical fibers (POFs). However, previous studies reveal that only the cladding of step-index POFs can be doped by the solution doping method in methanol or aqueous solutions, whereas the fiber core is hardly doped. To dope the fiber core as well as the cladding, this study attempts to dope PMMA-based step-index POFs by raising the doping temperatures to near the Tg of PMMA. The results show that a considerable amount of rhodamine B (RhB) is doped in the fiber core, though the amount is still much less than that in the cladding. The highest content in the fiber core is 0.479 mg/g, which is achieved by doping the POFs in water at 110 °C for 8 h. At the same condition, the RhB content of the cladding is 11.5 mg/g. It is found that the high-temperature doping process leads to dramatic axial shrinkage and radial expansion of the POFs, due to the relaxation of the fiber core. The wrinkled cladding after doping suggests that the macromolecule orientation of the core is much higher than that of the cladding, and high orientation should be the main reason why the core is much more difficult to dope than the cladding. Additionally, the doping process at 90 °C in water does not increase the fiber loss regardless of the tremendous POF structure change. In short, the core of PMMA-based step-index POFs can be doped at a temperature near the Tg of the PMMA, making the solution doping technique more practicable for POF doping. Full article
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25 pages, 5097 KiB  
Review
Non-Pharmacological Therapies for Management of Temporomandibular Myofascial Pain Syndrome: Laser Photobiomodulation or Dry Needling? Meta-Analyses of Human Clinical Trials
by Jumana Alsarhan, Rita El Feghali, Thaer Alkhudari and Stefano Benedicenti
Photonics 2024, 11(10), 965; https://doi.org/10.3390/photonics11100965 - 14 Oct 2024
Viewed by 739
Abstract
This review aims to compare the effect of photobiomodulation therapy (PBMT) using visible and near-infrared diode laser wavelengths to that of the dry needling technique (DNT) on the management of orofacial pain in patients with Temporomandibular Disorder Myofascial Pain Syndrome (TMD/MPS) in term [...] Read more.
This review aims to compare the effect of photobiomodulation therapy (PBMT) using visible and near-infrared diode laser wavelengths to that of the dry needling technique (DNT) on the management of orofacial pain in patients with Temporomandibular Disorder Myofascial Pain Syndrome (TMD/MPS) in term of effectiveness, speed of recovery, and lasting of treatment. A systematic search of multiple electronic databases was carried out to identify the relevant clinical trials published between 1 January 2010 and 1 January 2024. The included studies were limited to human subjects who had orofacial pain associated with Axis 1 of TMD/MPS, involving two genders with age >18 years and were treated either with photobiomodulation using diode laser with wavelengths ranging from 600 up to 1200 nanometer (nm), or with the dry needling (DN) technique (superficial SDN or deep DDN), as a non-pharmacological therapies to decrease the intensity of orofacial pain associated with TMD/MPS. The risk of bias for included studies was assessed using the Cochrane RoB tool (for randomized studies). Three distinct meta-analyses were performed to quantify the pooled effects of PBM and DN in the management of TMD/MPS myofascial pain and deactivation of myofascial trigger points (MTPs). The meta-analyses were performed using Review Manager (RevMan) 5.3 from Cochrane. The confidence interval (CI) was established at 95% and p-values of less than 0.05 (p < 0.05) were considered statistically significant. Statistical heterogeneity was assessed using I2. Qualitative data were extracted and summarized in tables for each group study, while quantitative data were reported as Mean and Standard Deviation (SD) values for assessment variables in each sub-group study. The results among groups were systematically evaluated to draw the final conclusion. A rigorous electronic and manual search revealed 4150 possible articles. Following the application of the inclusion and exclusion criteria, twelve eligible studies were included in the analysis. Both PBMT and DNT were found to be effective in controlling the myalgia pain and primary symptoms associated with TMD/MPS, as well as deactivating the MTPs. DNT was statistically superior in terms of recovery time while PBMT was the more effective long-term therapy. Full article
(This article belongs to the Section Biophotonics and Biomedical Optics)
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11 pages, 2069 KiB  
Article
Inverse Design of Reflectionless Thin-Film Multilayers with Optical Absorption Utilizing Tandem Neural Network
by Su Kalayar Swe and Heeso Noh
Photonics 2024, 11(10), 964; https://doi.org/10.3390/photonics11100964 - 14 Oct 2024
Viewed by 735
Abstract
The traditional approach to optical design faces limitations as photonic devices grow increasingly complex, requiring advanced functionalities. Recently, machine learning algorithms have gained significant interest for extracting structural designs from customized wavelength spectra, surpassing traditional simulation methods known for their time-consuming nature and [...] Read more.
The traditional approach to optical design faces limitations as photonic devices grow increasingly complex, requiring advanced functionalities. Recently, machine learning algorithms have gained significant interest for extracting structural designs from customized wavelength spectra, surpassing traditional simulation methods known for their time-consuming nature and resource-demanding computational requirements. This study focuses on the inverse design of a reflectionless multilayer thin-film structure across a specific wavelength region, utilizing a tandem neural network (TNN) approach. The method effectively addresses the non-uniqueness problem in training inverse neural networks. Data generation via the transfer matrix method (TMM) involves simulating the optical behavior of a multilayer structure comprising alternating thin films of silicon dioxide (SiO2) and silicon (Si). This innovative design considers both reflection and absorption properties to achieve near-zero reflection. We aimed to manipulate the structure’s reflectivity by implementing low-index and high-index layers along with Si absorption layers to attain specific optical properties. Our TNN demonstrated an MSE accuracy of less than 0.0005 and a maximum loss of 0.00781 for predicting the desired spectrum range, offering advanced capabilities for forecasting arbitrary spectra. This approach provides insights into designing multilayer thin-film structures with near-zero reflection and highlights the potential for controlling absorption materials to enhance optical performance. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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12 pages, 3497 KiB  
Article
Dynamic Attention Mixer-Based Residual Network Assisted Design of Holographic Metasurface
by Lei Zhu, Hongda Zhang, Liang Dong, Zhengliang Lv and Xumin Ding
Photonics 2024, 11(10), 963; https://doi.org/10.3390/photonics11100963 - 14 Oct 2024
Viewed by 492
Abstract
Multi-channel holographic metasurfaces have great potential for applications in wireless communications and radar. However, geometric phase-based multichannel metasurface units often have complex phase spectra, making the design of holographic metasurfaces complex and time-consuming. To address this challenge, we propose a dynamic attention mixer-based [...] Read more.
Multi-channel holographic metasurfaces have great potential for applications in wireless communications and radar. However, geometric phase-based multichannel metasurface units often have complex phase spectra, making the design of holographic metasurfaces complex and time-consuming. To address this challenge, we propose a dynamic attention mixer-based residual network to streamline the optimization and design of a multi-channel holographic metasurface unit. We conduct validation using multi-channel metasurface units, with a training set mean squared error (MSE) of 0.003 and a validation set MSE of 0.4. Additionally, we calculate the mean absolute error (MAE) for the geometric parameters θ1 and θ2 of the backward-predicted metasurface units in the validation set, which are 0.2° and 0.6°, respectively. Compared to traditional networks, our method achieves robust learning outcomes without the need for extensive datasets and provides accurate results even in complex electromagnetic responses. It is believed that the method presented in this paper is also applicable to the design of other artificial materials or multifunctional metasurfaces. Full article
(This article belongs to the Special Issue Emerging Trends in Metamaterials and Metasurfaces Research)
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