Journal Description
Photonics
Photonics
is an international, scientific, peer-reviewed, open access journal on the science and technology of optics and photonics, published monthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 15.5 days after submission; acceptance to publication is undertaken in 2.7 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Companion journal: Optics.
Impact Factor:
2.4 (2022);
5-Year Impact Factor:
2.4 (2022)
Latest Articles
Applications and Development of Multi-Core Optical Fibers
Photonics 2024, 11(3), 270; https://doi.org/10.3390/photonics11030270 - 19 Mar 2024
Abstract
The rapid development of information and communication technology has driven the demand for higher data transmission rates. Multi-core optical fiber, with its ability to transmit multiple signals simultaneously, has emerged as a promising solution to meet this demand. Additionally, due to its characteristics
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The rapid development of information and communication technology has driven the demand for higher data transmission rates. Multi-core optical fiber, with its ability to transmit multiple signals simultaneously, has emerged as a promising solution to meet this demand. Additionally, due to its characteristics such as multi-channel transmission, high integration, spatial flexibility, and versatility, multi-core optical fibers hold vast potential in sensing applications. However, the manufacturing technology of multi-core fiber is still in its early stages, facing challenges such as the design and fabrication of high-quality cores, efficient coupling between cores, and the reduction of crosstalk. In this paper, an overview of the current status and future prospects of multi-core fiber manufacturing technology has been presented, and their limitations will be discussed. Some potential solutions to overcome these challenges will be proposed. Their potential applications in optical fiber sensing will also be summarized.
Full article
(This article belongs to the Special Issue Specialty Optical Fibers: Advance and Sensing Application)
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Open AccessCommunication
Narrow Linewidth 510 nm Laser via Single-Pass Frequency-Tripling by Waveguide PPLNs
by
Yanlin Chen, Jing Zhang, Xiaolang Qiu, Suo Wang, Chuanchuan Li, Haiyang Yu and Xin Wei
Photonics 2024, 11(3), 269; https://doi.org/10.3390/photonics11030269 - 18 Mar 2024
Abstract
A single-frequency narrow linewidth green laser at 510 nm is a vital component for the study of Cesium Rydberg atoms. Here, we demonstrate a 510 nm laser based on single-pass second-harmonic generation (SHG) and sum-frequency generation (SFG) via waveguide Periodically Poled Lithium Niobate
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A single-frequency narrow linewidth green laser at 510 nm is a vital component for the study of Cesium Rydberg atoms. Here, we demonstrate a 510 nm laser based on single-pass second-harmonic generation (SHG) and sum-frequency generation (SFG) via waveguide Periodically Poled Lithium Niobate (PPLN) seeded with a common C-band laser (1530 nm). The final linewidth measured using the delayed self-heterodyne method reaches a narrow linewidth of 4.8 kHz. And, the optical-to-optical conversion efficiency is up to 13.1% and reaches an output power up to 200 mW.
Full article
(This article belongs to the Special Issue Narrow Linewidth Laser Sources and Their Applications)
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Open AccessArticle
A Best-Path Approach to the Design of a Hybrid Space–Ground Quantum Network with Dynamic Constraints
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David L. Bakker, Yannick Jong, Bob P. F. Dirks and Gustavo C. Amaral
Photonics 2024, 11(3), 268; https://doi.org/10.3390/photonics11030268 - 18 Mar 2024
Abstract
The design and operation of quantum networks are both decisive in the current push towards a global quantum internet. Although space-enabled quantum connectivity has already been identified as a beneficial candidate for long-range quantum channels for over two decades, the architecture of a
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The design and operation of quantum networks are both decisive in the current push towards a global quantum internet. Although space-enabled quantum connectivity has already been identified as a beneficial candidate for long-range quantum channels for over two decades, the architecture of a hybrid space–ground network is still a work in progress. Here, we propose an analysis of such a network based on a best-path approach, where either fiber- or satellite-based elementary links can be concatenated to form a repeater chain. The network consisting of quantum information processing nodes, equipped with both ground and space connections, is mapped into a graph structure, where edge weights represent the achievable secret key rates, chosen as the figure of merit for the network analysis. A weight minimization algorithm allows for identifying the best path dynamically, i.e., as the weather conditions, stray light radiance, and satellite orbital position change. From the results, we conclude that satellite links will play a significant role in the future large-scale quantum internet, in particular when node distances exceed 500 km, and both a constellation of satellites—spanning 20 or more satellites—and significant advances in filtering technology are required to achieve continuous coverage.
Full article
(This article belongs to the Special Issue Optical Satellite Communications for Quantum Networking)
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Open AccessArticle
Optimization of Grating Coupler over Single-Mode Silicon-on-Insulator Waveguide to Reach < 1 dB Loss through Deep-Learning-Based Inverse Design
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Chung-Chih Lin, Audrey Na, Yi-Kuei Wu, Likarn Wang and Neil Na
Photonics 2024, 11(3), 267; https://doi.org/10.3390/photonics11030267 - 15 Mar 2024
Abstract
Grating couplers are essential components in silicon photonics that facilitate the coupling of light between waveguides and fibers. Optimization of the grating couplers to reach <1 dB loss when coupling to single-mode fibers (SMFs) has been reported in the literature, but this was
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Grating couplers are essential components in silicon photonics that facilitate the coupling of light between waveguides and fibers. Optimization of the grating couplers to reach <1 dB loss when coupling to single-mode fibers (SMFs) has been reported in the literature, but this was based on silicon-on-insulator (SOI) waveguides supporting multi-modes. In this paper, using a deep-learning model combined with an inverse-design process, we achieve <1 dB losses for grating couplers implemented over single-mode SOI waveguides, i.e., a maximum efficiency of 80.5% (−0.94 dB) for gratings constrained with e-beam (EB) lithography critical dimension (CD), and a maximum efficiency of 77.9% (−1.09 dB) for gratings constrained with deep ultraviolet (DUV) lithography CD. To verify these results, we apply covariance matrix adaptation evolution strategy (CMA-ES) and find that while CMA-ES yields slightly better results, i.e., 82.7% (−0.83 dB) and 78.9% (−1.03 dB) considering e-beam and DUV, respectively, the spatial structures generated by CMA-ES are nearly identical to the spatial structures generated by the deep-learning model combined with the inverse-design process. This suggests that our approach can achieve a representative low-loss structure, and may be used to improve the performance of other types of nanophotonic devices in the future.
Full article
(This article belongs to the Section Optical Communication and Network)
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Open AccessArticle
Modal Phase Modulators Based on Liquid Crystals with 3D-Printed Polymer Microstructures: Increasing Size and Complexity
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Alec Xu, Camron Nourshargh, Patrick S. Salter, Steve J. Elston, Stephen M. Morris and Martin J. Booth
Photonics 2024, 11(3), 266; https://doi.org/10.3390/photonics11030266 - 15 Mar 2024
Abstract
We present extended capabilities in simple liquid crystal-based devices that are applicable to adaptive optics and other related fields requiring wavefront manipulation. The laser-written devices can provide complex phase profiles, but are extremely simple to operate, requiring only a single electrode pair tuned
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We present extended capabilities in simple liquid crystal-based devices that are applicable to adaptive optics and other related fields requiring wavefront manipulation. The laser-written devices can provide complex phase profiles, but are extremely simple to operate, requiring only a single electrode pair tuned between 0 and 10 V RMS. Furthermore, the devices operate in the transmissive mode for easy integration into the optical path. We present here as examples three such devices: the first device reproduces the defocus Zernike polynomial; the second device reproduces a seventh-order Zernike polynomial, tertiary coma; and the last example is of a primary spherical aberration. All devices offer wavelength-scale wavefront manipulation up to more than radians peak-to-peak phase at a wavelength of 660 nm. The coma correction device is significantly more complex, reproducing a mode two orders higher than previous demonstrations, while the spherical device is nearly a full order of magnitude larger, measuring 2 mm in diameter.
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(This article belongs to the Special Issue Liquid Crystals in Photonics)
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Open AccessArticle
Efficient Structure Transformation Based on Sensitivity-Oriented Structure Adjustment for Inverse-Designed Devices
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Yuchen Chen, Jifang Qiu, Zhenli Dong, Lihang Wang, Lan Wu, Suping Jiao, Hongxiang Guo and Jian Wu
Photonics 2024, 11(3), 265; https://doi.org/10.3390/photonics11030265 - 14 Mar 2024
Abstract
Inverse-designed devices with thousands of degrees of freedom could achieve high performance in compact footprints, but typically have complex structure topologies that contain many irregular and tiny features and sharp corners, which tend to lead to a poor robustness to fabrication errors. In
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Inverse-designed devices with thousands of degrees of freedom could achieve high performance in compact footprints, but typically have complex structure topologies that contain many irregular and tiny features and sharp corners, which tend to lead to a poor robustness to fabrication errors. In order to effectively transform the structure of inverse-designed nanophotonic devices into simple structure topologies that have high robustness to fabrication errors without sacrificing device performance, in this paper, we propose a structure adjustment method that innovatively adjusts the structures of inverse-designed devices by introducing their structural sensitivity to the optical performance, extracting the device substructures with high sensitivity and eliminating those with low sensitivity, and, finally, transforming the device structures into simple structure topologies with high robustness and better performance. Two devices (90° crossing and T-junction) were designed and fabrication tolerance simulation was conducted to verify the method. The results show that the devices designed using the proposed method achieved better performance and were more robust to under/over-etched errors.
Full article
(This article belongs to the Special Issue Design and Applications of Novel Nanophotonics Devices)
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Open AccessReview
Femtosecond Laser Microfabrication of Artificial Compound Eyes
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Fan Zhang, Huacheng Xu, Qing Yang, Yu Lu, Guangqing Du and Feng Chen
Photonics 2024, 11(3), 264; https://doi.org/10.3390/photonics11030264 - 14 Mar 2024
Abstract
Over millions of years of evolution, arthropods have intricately developed and fine-tuned their highly sophisticated compound eye visual systems, serving as a valuable source of inspiration for human emulation and tracking. Femtosecond laser processing technology has attracted attention for its excellent precision, programmable
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Over millions of years of evolution, arthropods have intricately developed and fine-tuned their highly sophisticated compound eye visual systems, serving as a valuable source of inspiration for human emulation and tracking. Femtosecond laser processing technology has attracted attention for its excellent precision, programmable design capabilities, and advanced three-dimensional processing characteristics, especially in the production of artificial bionic compound eye structures, showing unparalleled advantages. This comprehensive review initiates with a succinct introduction to the operational principles of biological compound eyes, providing essential context for the design of biomimetic counterparts. It subsequently offers a concise overview of crucial manufacturing methods for biomimetic compound eye structures. In addition, the application of femtosecond laser technology in the production of biomimetic compound eyes is also briefly introduced. The review concludes by highlighting the current challenges and presenting a forward-looking perspective on the future of this evolving field.
Full article
(This article belongs to the Special Issue New Advances in Ultrashort Pulse Fiber Lasers and Their Applications)
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Open AccessArticle
Determining Topological Charge of Bessel-Gaussian Beams Using Modified Mach-Zehnder Interferometer
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Mansi Baliyan and Naveen K. Nishchal
Photonics 2024, 11(3), 263; https://doi.org/10.3390/photonics11030263 - 14 Mar 2024
Abstract
The orbital angular momentum (OAM) associated with structured singular beams carries vital information crucial for studying various properties and applications of light. Determining OAM through the interference of light is an efficient method. The interferogram serves as a valuable tool for analyzing the
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The orbital angular momentum (OAM) associated with structured singular beams carries vital information crucial for studying various properties and applications of light. Determining OAM through the interference of light is an efficient method. The interferogram serves as a valuable tool for analyzing the wavefront of structured beams, especially identifying the order of singularity. In this study, we propose a modified Mach–Zehnder interferometer architecture to effectively determine the topological charge of Bessel–Gaussian (BG) beams. Several numerically generated self-referenced interferograms have been used for analysis. Moreover, this study examines the propagation property and phase distribution within BG beams after they are obstructed by an aperture in the interferometer setup.
Full article
(This article belongs to the Special Issue Structured Light Beams: Science and Applications)
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Open AccessArticle
Experimental Demonstration to Enhance the Curvature Sensitivity of a Fiber Mach–Zehnder Interferometer Based on a Waist-Enlarged Technique Using Polymer
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Laura G. Martinez-Ramirez, Iván Hernández-Romano, Cipriano Guzmán-Cano, Sigifredo Marrujo-García, Arturo A. Fernandez-Jaramillo, Julian M. Estudillo-Ayala, Roberto Rojas-Laguna and Juan M. Sierra-Hernandez
Photonics 2024, 11(3), 262; https://doi.org/10.3390/photonics11030262 - 14 Mar 2024
Abstract
A fiber curvature sensor based on a Mach–Zehnder Interferometer (MZI) constructed using the waist-enlarged technique to splice a segment of non-zero dispersion-shifted fiber (NZ-DSF) between two segments of single mode fiber (SMF) is proposed and experimentally demonstrated. All fabricated sensors presented an improvement
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A fiber curvature sensor based on a Mach–Zehnder Interferometer (MZI) constructed using the waist-enlarged technique to splice a segment of non-zero dispersion-shifted fiber (NZ-DSF) between two segments of single mode fiber (SMF) is proposed and experimentally demonstrated. All fabricated sensors presented an improvement in their curvature sensitivity when they were coated with polydimethylsiloxane (PDMS) polymer. The sensor that exhibited the best performance was 6.5 cm long, with a curvature sensitivity of 8.27 nm/m−1 in a range of 0.69 m−1 (from 1.08 to 1.77 m−1). This sensitivity is 3.22 times higher than that of the sensor without polymer. Additionally, the sensor coated with polymer exhibited cross-sensitivity that is 2.23 times smaller than the sensor without polymer. The easy fabrication and notable performance of this device makes it alluring for structural health monitoring.
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(This article belongs to the Section Lasers, Light Sources and Sensors)
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Open AccessCommunication
Saturated Gain-Induced Non-Reciprocal Transmission and Broadband On-Chip Optical Isolator
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Mingyuan Xue, Haojiang Tong, Hao Dong and Meijia Wang
Photonics 2024, 11(3), 261; https://doi.org/10.3390/photonics11030261 - 14 Mar 2024
Abstract
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To overcome the limitation of dynamic reciprocity, a new method for designing broadband on-chip optical isolators is proposed and demonstrated based on saturated gain, which is able to support simplex and duplex operation modes. By connecting a saturated gain waveguide to an appropriate
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To overcome the limitation of dynamic reciprocity, a new method for designing broadband on-chip optical isolators is proposed and demonstrated based on saturated gain, which is able to support simplex and duplex operation modes. By connecting a saturated gain waveguide to an appropriate linear loss waveguide, broadband isolation is predicted and proved theoretically through saturated gain-induced non-reciprocal transmission. The proposed isolator is numerically demonstrated with an operating band of 59 nm and an isolation ratio of −20 dB at the central wavelength of 1550 nm. It is noteworthy that when the current pump changes, the isolator still works well and keeps the high isolation ratio at a different input power. The footprint of the whole device is 465 μm × 0.35 μm which satisfies the requirement of photonic integrated circuits. The proposed isolator, with the combined advantages of compact footprint, broadband, duplex operation and high isolation, can enable on-chip unidirectional transmission and complex topological routing designation.
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Open AccessReview
Transcranial Photobiomodulation and Chronic Traumatic Brain Injury
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Naomi L. Gaggi, Nathaniel Lewis Roy, Xiaotong Song, Anna Leigh Peterson, Dan V. Iosifescu, Ramon Diaz-Arrastia, Paolo Cassano and Junghoon J. Kim
Photonics 2024, 11(3), 260; https://doi.org/10.3390/photonics11030260 - 13 Mar 2024
Abstract
Traumatic brain injury (TBI) is a common cause of neurologic morbidity for which few effective therapies exist, especially during the chronic stage. A potential therapy for chronic TBI is transcranial photobiomodulation (tPBM). tPBM is a noninvasive neuromodulation technique that uses light to stimulate
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Traumatic brain injury (TBI) is a common cause of neurologic morbidity for which few effective therapies exist, especially during the chronic stage. A potential therapy for chronic TBI is transcranial photobiomodulation (tPBM). tPBM is a noninvasive neuromodulation technique that uses light to stimulate the cortex and increase blood flow and metabolism while also enhancing cognition and improving affect. There has been much work focusing on the efficacy of tPBM in acute TBI in small animals, but much less work has focused on chronic TBI. Patients with chronic TBI manifest microvascular injury, which may serve as a modifiable treatment target for tPBM. There is a need to study and improve tPBM, as the currently implemented protocols targeting microvascular injury have been relatively unsuccessful. This review includes 16 studies, which concluded that after tPBM application, there were improvements in neuropsychological outcomes in addition to increases in cerebral blood flow. However, these conclusions are confounded by differing tPBM parameters, small sample sizes, and heterogenous TBI populations. While these results are encouraging, there is a need to further understand the therapeutic potential of tPBM in chronic TBI.
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(This article belongs to the Section Biophotonics and Biomedical Optics)
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Open AccessCorrection
Correction: Wu et al. A 1083 nm Narrow-Linewidth DFB Semiconductor Laser for Quantum Magnetometry. Photonics 2023, 10, 934
by
Mengying Wu, Haiyang Yu, Wenyu Wang, Shaojie Li, Yulian Cao and Jianguo Liu
Photonics 2024, 11(3), 259; https://doi.org/10.3390/photonics11030259 - 13 Mar 2024
Abstract
Additional Affiliations [...]
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Open AccessCommunication
Double-Junction Cascaded GaAs-Based Broad-Area Diode Lasers with 132W Continuous Wave Output Power
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Jun Wang, Shaoyang Tan, Ye Shao, Wuling Liu, Kun Tian, Yao Xiao, Zhicheng Zhang, Yudan Gou, Lihong Zhu, Bangguo Wang and Shouhuan Zhou
Photonics 2024, 11(3), 258; https://doi.org/10.3390/photonics11030258 - 13 Mar 2024
Abstract
Improving the output power and efficiency of broad-area diode lasers is a prerequisite for the further development of fiber lasers, solid-state laser industries, and direct semiconductor laser applications. At present, the large amount of Joule heat generated by large drive currents and limited
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Improving the output power and efficiency of broad-area diode lasers is a prerequisite for the further development of fiber lasers, solid-state laser industries, and direct semiconductor laser applications. At present, the large amount of Joule heat generated by large drive currents and limited wall-plug efficiency presents the largest challenge for improving these lasers. In this paper, a multi-junction cascade laser with low Joule heat generation is demonstrated, showing large power and conversion efficiency. We fabricated devices with different junction numbers and compared their output power. We present double-junction lasers emitting at ~915 nm with an emitter width of 500 μm, delivering 132.5 W continuous wave output power at 70 A, which is the highest power reported so far for any single-emitter laser. The power conversion efficiencies are 66.7% and 60%, at 100 W and 132 W, respectively.
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(This article belongs to the Section Lasers, Light Sources and Sensors)
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Open AccessArticle
Development of Cryogenic Systems for Astronomical Research
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Yuri Balega, Oleg Bolshakov, Aleksandr Chernikov, Aleksandra Gunbina, Valerian Edelman, Mariya Efimova, Aleksandr Eliseev, Artem Krasilnikov, Igor Lapkin, Ilya Lesnov, Mariya Mansfeld, Mariya Markina, Evgenii Pevzner, Sergey Shitov, Andrey Smirnov, Mickhail Tarasov, Nickolay Tyatushkin, Anton Vdovin and Vyacheslav Vdovin
Photonics 2024, 11(3), 257; https://doi.org/10.3390/photonics11030257 - 13 Mar 2024
Abstract
The article presents a brief review of cooling systems that ensure various temperature levels (from 0.1 K to 230 K) for radio astronomical receivers of photonic and electronic (or optical and radio) devices. The features of various cooling levels and the requirements for
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The article presents a brief review of cooling systems that ensure various temperature levels (from 0.1 K to 230 K) for radio astronomical receivers of photonic and electronic (or optical and radio) devices. The features of various cooling levels and the requirements for the design of the cooling systems are considered in detail, as well as the approaches to designing interfaces for cooled receivers: vacuum, cryogenic, electrical, mechanical, optical, and other interfaces required for effective operation. The presented approaches to design are illustrated by a series of joint developments of the authors carried out over the past 45 years, including those produced over the past year.
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(This article belongs to the Special Issue Optical Systems for Astronomy)
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Open AccessArticle
Second-Order Sidebands and Group Delays in Coupled Optomechanical Cavity System with a Cubic Nonlinear Harmonic Oscillator
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Qiwen Zhao, Ying He, Yanfang Yang, Huifang Zhang and Yi Xu
Photonics 2024, 11(3), 256; https://doi.org/10.3390/photonics11030256 - 12 Mar 2024
Abstract
The generation of second-order sidebands and its associated group delay is an important subject in optical storage and switch. In this work, the efficiency of second-order sideband generation in a coupled optomechanical cavity system with a cubic nonlinear harmonic oscillator is theoretically investigated.
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The generation of second-order sidebands and its associated group delay is an important subject in optical storage and switch. In this work, the efficiency of second-order sideband generation in a coupled optomechanical cavity system with a cubic nonlinear harmonic oscillator is theoretically investigated. It is found that the efficiency of second-order sideband generation can be effectively enhanced with the decrease in decay rate of optomechanical cavity, the increase in coupling strength between two cavities and the power of probe field. The slow light effect (i.e., positive group delay) is also observed in the proposed optomechanical cavity system, and can be controlled with the power of control field.
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(This article belongs to the Special Issue Levitated Optomechanics)
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Open AccessArticle
Fano Resonance Thermo-Optic Modulator Based on Double T-Bus Waveguides-Coupled Micro-Ring Resonator
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Hongpeng Li, Lidan Lu, Guang Chen, Shuai Wang, Jianzhen Ou and Lianqing Zhu
Photonics 2024, 11(3), 255; https://doi.org/10.3390/photonics11030255 - 12 Mar 2024
Abstract
For the silicon optical computing chip, the optical convolution unit based on the micro-ring modulator has been demonstrated to have high integration and large computing density. To further reduce power consumption, a novel, simple Fano resonant thermo-optic modulator is presented with numerical simulation
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For the silicon optical computing chip, the optical convolution unit based on the micro-ring modulator has been demonstrated to have high integration and large computing density. To further reduce power consumption, a novel, simple Fano resonant thermo-optic modulator is presented with numerical simulation and experimental demonstration. This designed Fano resonator comprises double T-shaped waveguides and a micro-ring with a radius of 10 μm. Compared with the free use of bus waveguides, our double T-shaped waveguides generate a phase shift, along with a Fano-like line shape. The experimental results show that the resonant wavelength shift of the designed modulator is 2.4 nm with a driven power of 20 mW. In addition, the maximum spectral resolution and the extinction ratio are 70.30 dB/nm and 12.69 dB, respectively. For our thermo-optic modulator, the optical intensity power consumption sensitivity of 7.60 dB/mW is three times as large as that of the micro-ring modulator. This work has broad potential to provide a low-power-consumption essential component for large-scale on-chip modulation for optical computing with compatible metal oxygen semiconductor processes.
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(This article belongs to the Special Issue Integrated Waveguide-Based Photonic Devices)
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Open AccessArticle
Effects of Excitation Angle on Air-Puff-Stimulated Surface Acoustic Wave-Based Optical Coherence Elastography (SAW-OCE)
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Zhengshuyi Feng, Yilong Zhang, Weiyi Jiang, Weichen Wang, Chunhui Li and Zhihong Huang
Photonics 2024, 11(3), 254; https://doi.org/10.3390/photonics11030254 - 12 Mar 2024
Abstract
Increased stiffness of tissues has been recognised as a diagnostic feature of pathologies. Tissue stiffness characterisation usually involves the detection of tissue response from mechanical stimulation. Air-puff optical coherence elastography (OCE) can generate impulse surface acoustic waves (SAWs) on tissue surface without contact
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Increased stiffness of tissues has been recognised as a diagnostic feature of pathologies. Tissue stiffness characterisation usually involves the detection of tissue response from mechanical stimulation. Air-puff optical coherence elastography (OCE) can generate impulse surface acoustic waves (SAWs) on tissue surface without contact and evaluate the mechanical properties of tissue. This study endeavours to explore the optimal excitation angle for air-puff OCE, a parameter that lacks standardisation at present, by investigating the relationship between the frequency bandwidth and peak-to-peak signal-to-noise ratio (SNR) of SAWs for different excitation angles (relative to the normal surface) of air-puff on the sample, from 5° to 85°, with an interval of 5° applied on the phantom. Due to the unevenness of human hands, 20°, 45° and 70° angles were employed for human skin (10 healthy adults). The results show that a smaller excitation angle could produce higher wave frequency bandwidth; a 5° angle generated an SAW with 1747 Hz frequency bandwidth, while an 85° angle produced an SAW with 1205 Hz. Significant differences were not shown in peak-to-peak SNR comparison between 5° and 65° on the phantom, but between 65° and 85° at the excitation position, a reduction of 48.6% was observed. Furthermore, the group velocity of the SAWs was used to evaluate the bulk Young’s modulus of the human tissue. The outcomes could provide essential guidance for air-puff-based elastography studies in clinical applications and future tissue research.
Full article
(This article belongs to the Special Issue OCT Technology Advances and Their Applications in Disease Studies)
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Open AccessReview
State-of-the-Art Materials Used in MEMS Micromirror Arrays for Photonic Applications
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Shujie Liu, Philipp Kästner, Roland Donatiello, Anup Shrivastava, Marek Smolarczyk, Mustaqim Siddi Que Iskhandar, Md Kamrul Hasan, Giuseppe Caruso, Jiahao Chen, Basma Elsaka, Shilby Baby, Dennis Löber, Thomas Kusserow, Jost Adam and Hartmut Hillmer
Photonics 2024, 11(3), 253; https://doi.org/10.3390/photonics11030253 - 11 Mar 2024
Abstract
This work provides an overview on micromirror arrays based on different material systems such as dielectrics, element silicon, compound semiconductors, metals, and novel 2D materials. The goal is to work out the particular strength of each material system to enable optimum performance for
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This work provides an overview on micromirror arrays based on different material systems such as dielectrics, element silicon, compound semiconductors, metals, and novel 2D materials. The goal is to work out the particular strength of each material system to enable optimum performance for various applications. In particular, this review is intended to draw attention to the fact that MEMS micro-mirrors can be successful in many other material systems besides silicon. In particular, the review is intended to draw attention to two material systems that have so far been used less for MEMS micromirror arrays, that have been less researched, and of which fewer applications have been reported to date: metallic heterostructures and 2D materials. However, the main focus is on metallic MEMS micromirror arrays on glass substrates for applications like personalized light steering in buildings via active windows, energy management, active laser safety goggles, interference microscopy, and endoscopy. Finally, the different micromirror arrays are compared with respect to fabrication challenges, switching speed, number of mirrors, mirror dimensions, array sizes, miniaturization potential for individual mirrors, reliability, lifetime, and hinge methodology.
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(This article belongs to the Special Issue Micro-Mirror Arrays as Versatile Photonic Tools)
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Open AccessArticle
Towards Construction of a Novel Nanometer-Resolution MeV-STEM for Imaging Thick Frozen Biological Samples
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Xi Yang, Liguo Wang, Jared Maxson, Adam Christopher Bartnik, Michael Kaemingk, Weishi Wan, Luca Cultrera, Lijun Wu, Victor Smaluk, Timur Shaftan, Sean McSweeney, Chunguang Jing, Roman Kostin and Yimei Zhu
Photonics 2024, 11(3), 252; https://doi.org/10.3390/photonics11030252 - 11 Mar 2024
Abstract
Driven by life-science applications, a mega-electron-volt Scanning Transmission Electron Microscope (MeV-STEM) has been proposed here to image thick frozen biological samples as a conventional Transmission Electron Microscope (TEM) may not be suitable to image samples thicker than 300–500 nm and various volume electron
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Driven by life-science applications, a mega-electron-volt Scanning Transmission Electron Microscope (MeV-STEM) has been proposed here to image thick frozen biological samples as a conventional Transmission Electron Microscope (TEM) may not be suitable to image samples thicker than 300–500 nm and various volume electron microscopy (EM) techniques either suffering from low resolution, or low speed. The high penetration of inelastic scattering signals of MeV electrons could make the MeV-STEM an appropriate microscope for biological samples as thick as 10 m or more with a nanoscale resolution, considering the effect of electron energy, beam broadening, and low-dose limit on resolution. The best resolution is inversely related to the sample thickness and changes from 6 nm to 24 nm when the sample thickness increases from 1 μm to 10 μm. To achieve such a resolution in STEM, the imaging electrons must be focused on the specimen with a nm size and an mrad semi-convergence angle. This requires an electron beam emittance of a few picometers, which is ~1000 times smaller than the presently achieved nm emittance, in conjunction with less than 10−4 energy spread and 1 nA current. We numerically simulated two different approaches that are potentially applicable to build a compact MeV-STEM instrument: (1) DC (Direct Current) gun, aperture, superconducting radio-frequency (SRF) cavities, and STEM column; (2) SRF gun, aperture, SRF cavities, and STEM column. Beam dynamic simulations show promising results, which meet the needs of an MeV-STEM, a few-picometer emittance, less than 10−4 energy spread, and 0.1–1 nA current from both options. Also, we designed a compact STEM column based on permanent quadrupole quintuplet, not only to demagnify the beam size from 1 m at the source point to 2 nm at the specimen but also to provide the freedom of changing the magnifications at the specimen and a scanning system to raster the electron beam across the sample with a step size of 2 nm and the repetition rate of 1 MHz. This makes it possible to build a compact MeV-STEM and use it to study thick, large-volume samples in cell biology.
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(This article belongs to the Special Issue Advances in X-ray Optics for High-Resolution Imaging)
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Open AccessArticle
Simulation Study on 3D Heterogeneous Photonic Integration with Vertical Microring Coupler
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Jiachen Liu, Yingying Zeng, Haifeng Hu, Ni Zhang, Qiwen Zhan and Xiaogang Chen
Photonics 2024, 11(3), 251; https://doi.org/10.3390/photonics11030251 - 11 Mar 2024
Abstract
We present a simulation-based study on a 3D heterogeneous photonic integration scheme based on a vertical microring coupler (VμRC). Our research introduces a more compact and efficient layout of photonic devices in the vertical direction, surpassing the limitations of traditional planar
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We present a simulation-based study on a 3D heterogeneous photonic integration scheme based on a vertical microring coupler (VμRC). Our research introduces a more compact and efficient layout of photonic devices in the vertical direction, surpassing the limitations of traditional planar integration methods. This investigation focuses on optimizing the performance of the VμRC by analyzing critical parameters such as the dimensions of the microring and the waveguide and the refractive indices of surrounding materials, which serve as the guideline for future manufacturing of the device. The simulation results demonstrate that the careful selection and optimization of these parameters significantly impact the transmittance and coupling characteristics of the VμRC. To demonstrate the validity of this simulation model, we applied it to a few practical cases and achieved comparable results with our previous experiments.
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(This article belongs to the Section Optoelectronics and Optical Materials)
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