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Photonics, Volume 11, Issue 5 (May 2024) – 94 articles

Cover Story (view full-size image): Chirped pulse amplification (CPA) is the golden standard for obtaining powerful ultrashort laser pulses. However, wavelength-tunable CPA systems are rarely reported. The output parameters' flexibility is desirable in various fields such as biomedical imaging, sensing, nonlinear spectroscopy and optical parametric amplification. This work presents a 1720 nm–1800 nm tunable CPA system based on a Tm-doped fiber. The experimental results are empowered by numerical simulation, which suggests further steps for the improvement of system performance. This is the first demonstration of a wavelength-tunable CPA system beyond 1.1 µm, which may inspire the development of similar systems at other wavelengths. View this paper
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15 pages, 2530 KiB  
Article
Next-Generation Dual Transceiver FSO Communication System for High-Speed Trains in Neom Smart City
by Yehia Elsawy, Ayshah S. Alatawi, Mohamed Abaza, Azza Moawad and El-Hadi M. Aggoune
Photonics 2024, 11(5), 483; https://doi.org/10.3390/photonics11050483 - 20 May 2024
Viewed by 501
Abstract
Smart cities like Neom require efficient and reliable transportation systems to support their vision of sustainable and interconnected urban environments. High-speed trains (HSTs) play a crucial role in connecting different areas of the city and facilitating seamless mobility. However, to ensure uninterrupted communication [...] Read more.
Smart cities like Neom require efficient and reliable transportation systems to support their vision of sustainable and interconnected urban environments. High-speed trains (HSTs) play a crucial role in connecting different areas of the city and facilitating seamless mobility. However, to ensure uninterrupted communication along the rail lines, advanced communication systems are essential to expand the coverage range of each base station (BS) while reducing the handover frequency. This paper presents the dual transceiver free space optical (FSO) communication system as a solution to achieve these objectives in the operational environment of HSTs in Neom city. Our channel model incorporates log-normal (LN) and gamma–gamma (GG) distributions to represent channel impairments and atmospheric turbulence in the city. Furthermore, we integrated the siding loop model, providing valuable insights into the system in real-world scenarios. To assess the system’s performance, we formulated the received signal-to-noise ratio (SNR) of the network under assumed fading conditions. Additionally, we analyzed the system’s bit error rate (BER) analytically and through Monte Carlo simulation. A comparative analysis with reconfigurable intelligent surfaces (RIS) and relay-assisted FSO communications shows the superior coverage area and efficiency of the dual transceiver model. A significant reduction of up to 76% and 99% in the number of required BSs compared to RIS and relay, respectively, is observed. This reduction leads to fewer handovers and lower capital expenditure (CAPEX) costs. Full article
(This article belongs to the Special Issue Next-Generation Free-Space Optical Communication Technology)
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11 pages, 2797 KiB  
Communication
Sensing Characteristic Analysis of All-Dielectric Metasurfaces Based on Fano Resonance in Near-Infrared Regime
by Yongpeng Zhao, Qingfubo Geng, Jian Liu and Zhaoxin Geng
Photonics 2024, 11(5), 482; https://doi.org/10.3390/photonics11050482 - 20 May 2024
Viewed by 416
Abstract
A novel, all-dielectric metasurface, featuring a missing wedge-shaped nanodisk, is proposed to investigate optical characteristics. By introducing symmetry-breaking to induce Fano resonance, the metasurface achieves an impressive Q-factor of 1202 in the near-infrared spectrum, with a remarkably narrow full width at half maximum [...] Read more.
A novel, all-dielectric metasurface, featuring a missing wedge-shaped nanodisk, is proposed to investigate optical characteristics. By introducing symmetry-breaking to induce Fano resonance, the metasurface achieves an impressive Q-factor of 1202 in the near-infrared spectrum, with a remarkably narrow full width at half maximum (FWHM) of less than 1 nm. The ability to adjust the wavelength resonance by manipulating the structure of the wedge-shaped nanodisk offers a simple and efficient approach for metasurface design. This breakthrough holds great potential for various applications in sensing and optical filtering, marking a significant advancement in the field of nanophotonics. Full article
(This article belongs to the Special Issue Advanced Photonic Sensing and Measurement II)
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15 pages, 3310 KiB  
Article
Training a Dataset Simulated Using RGB Images for an End-to-End Event-Based DoLP Recovery Network
by Changda Yan, Xia Wang, Xin Zhang, Conghe Wang, Qiyang Sun and Yifan Zuo
Photonics 2024, 11(5), 481; https://doi.org/10.3390/photonics11050481 - 20 May 2024
Viewed by 352
Abstract
Event cameras are bio-inspired neuromorphic sensors that have emerged in recent years, with advantages such as high temporal resolutions, high dynamic ranges, low latency, and low power consumption. Event cameras can be used to build event-based imaging polarimeters, overcoming the limited frame rates [...] Read more.
Event cameras are bio-inspired neuromorphic sensors that have emerged in recent years, with advantages such as high temporal resolutions, high dynamic ranges, low latency, and low power consumption. Event cameras can be used to build event-based imaging polarimeters, overcoming the limited frame rates and low dynamic ranges of existing systems. Since events cannot provide absolute brightness intensity in different angles of polarization (AoPs), degree of linear polarization (DoLP) recovery in non-division-of-time (non-DoT) event-based imaging polarimeters is an ill-posed problem. Thus, we need a data-driven deep learning approach. Deep learning requires large amounts of data for training, and constructing a dataset for event-based non-DoT imaging polarimeters requires significant resources, scenarios, and time. We propose a method for generating datasets using simulated polarization distributions from existing red–green–blue images. Combined with event simulator V2E, the proposed method can easily construct large datasets for network training. We also propose an end-to-end event-based DoLP recovery network to solve the problem of DoLP recovery using event-based non-DoT imaging polarimeters. Finally, we construct a division-of-time event-based imaging polarimeter simulating an event-based four-channel non-DoT imaging polarimeter. Using real-world polarization events and DoLP ground truths, we demonstrate the effectiveness of the proposed simulation method and network. Full article
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9 pages, 4244 KiB  
Article
Carbon Dot-Decorated Polystyrene Microspheres for Whispering-Gallery Mode Biosensing
by Anton A. Starovoytov, Evgeniia O. Soloveva, Kamilla Kurassova, Kirill V. Bogdanov, Irina A. Arefina, Natalia N. Shevchenko, Tigran A. Vartanyan, Daler R. Dadadzhanov and Nikita A. Toropov
Photonics 2024, 11(5), 480; https://doi.org/10.3390/photonics11050480 - 20 May 2024
Viewed by 450
Abstract
Whispering gallery mode (WGM) resonators doped with fluorescent materials find impressive applications in biological sensing. They do not require special conditions for the excitation of WGM inside that provide the basis for in vivo sensing. Currently, the problem of materials for in vivo [...] Read more.
Whispering gallery mode (WGM) resonators doped with fluorescent materials find impressive applications in biological sensing. They do not require special conditions for the excitation of WGM inside that provide the basis for in vivo sensing. Currently, the problem of materials for in vivo WGM sensors are substantial since their fluorescence should have stable optical properties as well as they should be biocompatible. To address this we present WGM microresonators of 5–7 μm, where the dopant is made of carbon quantum dots (CDs). CDs are biocompatible since they are produced from carbon and demonstrate bright optical emission, which shows different bands depending on the excitation wavelength. The WGM sensors developed here were tested as label-free biosensors by detecting bovine serum albumin molecules. The results showed WGM frequency shifting, with the limit of detection down to 1016 M level. Full article
(This article belongs to the Special Issue Advancements in Optical Metamaterials)
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13 pages, 6278 KiB  
Article
Experimental Study on Evolution of Chemical Structure Defects and Secondary Contaminative Deposition during HF-Based Etching
by Xiao Shen, Feng Shi, Shuo Qiao, Xing Peng and Ying Xiong
Photonics 2024, 11(5), 479; https://doi.org/10.3390/photonics11050479 - 20 May 2024
Viewed by 365
Abstract
Post-processing based on HF etching has become a highly preferred technique in the fabrication of fused silica optical elements in various high-power laser systems. Previous studies have thoroughly examined and confirmed the elimination of fragments and contamination. However, limited attention has been paid [...] Read more.
Post-processing based on HF etching has become a highly preferred technique in the fabrication of fused silica optical elements in various high-power laser systems. Previous studies have thoroughly examined and confirmed the elimination of fragments and contamination. However, limited attention has been paid to nano-sized chemical structural defects and secondary precursors that arise during the etching process. Therefore, in this paper, a set of fused silica samples are prepared and undergo the etching process under different parameters. Subsequently, an atomic force microscope, scanning electron microscope and fluorescence spectrometer are applied to analyze sample surfaces, and then an LIDT test based on the R-on-1 method is applied. The findings revealed that appropriate etching configurations will lead to certain LIDT improvement (from initial 7.22 J/cm2 to 10.76 J/cm2), and HF-based etching effectively suppresses chemical structural defects, while additional processes are recommended for the elimination of micron- to nano-sized secondary deposition contamination. Full article
(This article belongs to the Special Issue New Perspectives in Optical Design)
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24 pages, 19086 KiB  
Article
Analysis of the Polarization Distribution and Spin Angular Momentum of the Interference Field Obtained by Co-Planar Beams with Linear and Circular Polarization
by Svetlana N. Khonina, Andrey V. Ustinov, Alexey P. Porfirev and Sergey V. Karpeev
Photonics 2024, 11(5), 478; https://doi.org/10.3390/photonics11050478 - 19 May 2024
Viewed by 312
Abstract
Interference of two and four light beams with linear or circular polarization is studied analytically and numerically based on the Richards–Wolf formalism. We consider such characteristics of the interference fields as the distribution of intensity, polarization, and spin angular momentum density. The generation [...] Read more.
Interference of two and four light beams with linear or circular polarization is studied analytically and numerically based on the Richards–Wolf formalism. We consider such characteristics of the interference fields as the distribution of intensity, polarization, and spin angular momentum density. The generation of light fields with 1D and 2D periodic structure of both intensity and polarization is demonstrated. We can control the periodic structure both by changing the polarization state of the interfering beams and by changing the numerical aperture of focusing. We consider examples with a basic configuration, as well as those with a certain symmetry in the polarization state of the interfering beams. In some cases, increasing the numerical aperture of the focusing system significantly affects the generated distributions of both intensity and polarization. Experimental results, obtained using a polarization video camera, are in good agreement with the simulation results. The considered light fields can be used in laser processing of thin films of photosensitive (as well as polarization-sensitive) materials in order to create arrays of various ordered nano- and microstructures. Full article
(This article belongs to the Special Issue Structured Light Beams: Science and Applications)
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13 pages, 4516 KiB  
Article
Broadband High-Linear FMCW Light Source Based on Spectral Stitching
by Liang Sun, Xinguang Zhou, Haohao Zhao, Shichang Xu, Zihan Wu, Guohui Yuan and Zhuoran Wang
Photonics 2024, 11(5), 477; https://doi.org/10.3390/photonics11050477 - 19 May 2024
Viewed by 335
Abstract
The key to realizing a high-performance frequency-modulated continuous wave (FMCW) laser frequency-sweeping light source is how to extend the frequency-swept bandwidth and eliminate the effect of nonlinearity. To solve these issues, this paper designs a broadband high-linear FMCW frequency-sweeping light source system based [...] Read more.
The key to realizing a high-performance frequency-modulated continuous wave (FMCW) laser frequency-sweeping light source is how to extend the frequency-swept bandwidth and eliminate the effect of nonlinearity. To solve these issues, this paper designs a broadband high-linear FMCW frequency-sweeping light source system based on the combination of fixed temperature control and digital optoelectronic phase-locked loop (PLL), which controls the temperatures of the two lasers separately and attempts to achieve the coarse spectral stitching based on a time-division multiplexing scheme. Furthermore, we uses the PLL to correct the frequency error more specifically after the coarse stitching, which achieves the spectrum fine stitching and, meanwhile, realizes the nonlinearity correction. The experimental results show that our scheme can successfully achieve bandwidth expansion and nonlinearity correction, and the sweeping bandwidth is twice as much as that of the original single laser. The full-width half-maximum (FWHM) of the FMCW output is reduced from 150 kHz to 6.1 kHz, which exhibits excellent nonlinear correction performance. The relative error of the FMCW ranging system based on this frequency-swept light source is also reduced from 1.628% to 0.673%. Therefore, our frequency-swept light source with excellent performance has a promising application in the FMCW laser ranging system. Full article
(This article belongs to the Special Issue Advanced Lasers and Their Applications II)
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12 pages, 3334 KiB  
Article
Chirped Integrated Bragg Grating Design
by José Ángel Praena and Alejandro Carballar
Photonics 2024, 11(5), 476; https://doi.org/10.3390/photonics11050476 - 19 May 2024
Viewed by 333
Abstract
We analyze the two classic methods for chirped Integrated Bragg Gratings (IBGs) in Silicon-on-Insulator technology using the transfer matrix method based on the effective refractive index (neff) technique, which translates the geometry of an IBG into a matrix of n [...] Read more.
We analyze the two classic methods for chirped Integrated Bragg Gratings (IBGs) in Silicon-on-Insulator technology using the transfer matrix method based on the effective refractive index (neff) technique, which translates the geometry of an IBG into a matrix of neff depending on the wavelength. We also implement a procedure that allows engineering of the chirped IBG parameters, given a required bandwidth (BW) and group delay (GD). Finally, a complementary method for designing chirped IBG is proposed, showing a significant improvement in the bandwidth of the device or a moderation in the variation of the geometrical parameters of the grating. Full article
(This article belongs to the Special Issue Silicon Photonics Devices and Integrated Circuits)
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15 pages, 5146 KiB  
Article
A Fast Time Synchronization Method for Large Scale LEO Satellite Networks Based on A Bionic Algorithm
by Yue Xu, Tao Dong, Jie Yin, Ziyong Zhang, Zhihui Liu, Hao Jiang and Jing Wu
Photonics 2024, 11(5), 475; https://doi.org/10.3390/photonics11050475 - 19 May 2024
Viewed by 391
Abstract
A fast time synchronization method for large-scale LEO satellite networks based on a bionic algorithm is proposed. Because the inter-satellite links are continuously established and interrupted due to the relative motion of the satellites, the topology of the LEO satellite networks is time [...] Read more.
A fast time synchronization method for large-scale LEO satellite networks based on a bionic algorithm is proposed. Because the inter-satellite links are continuously established and interrupted due to the relative motion of the satellites, the topology of the LEO satellite networks is time varying. Firstly, according to the ephemeris information in navigation messages, a connection table which records the connections between satellites is generated. Then, based on the connection table, the current satellite network topology is calculated and generated. Furthermore, a bionic algorithm is used to select some satellites as time source nodes and calculate the hierarchy of the clock transmission tree. By taking the minimum level of the time transmission tree as the optimization objective, the time source nodes and the clock stratums of the whole satellite networks are obtained. Finally, the onboard computational center broadcasts the time layer table to all the satellites in the LEO satellite networks and the time synchronization links can be established or recovered fast. Full article
(This article belongs to the Special Issue Novel Advances in Optical Communications)
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12 pages, 4476 KiB  
Article
Polarization-Dependent Fiber Metasurface with Beam Collimating and Deflecting
by Yuemin Ma, Di Sang, Yi Lin, Qiang An, Zhanshan Sun and Yunqi Fu
Photonics 2024, 11(5), 474; https://doi.org/10.3390/photonics11050474 - 18 May 2024
Viewed by 302
Abstract
Metasurfaces can arbitrarily manipulate the amplitude, phase, and polarization of optical fields on subwavelength scales. Due to their arbitrary manipulation and compact size, the metasurface can be well integrated with optical fibers. Herein, we demonstrate a polarization-dependent metasurface using birefringent meta-atoms, which can [...] Read more.
Metasurfaces can arbitrarily manipulate the amplitude, phase, and polarization of optical fields on subwavelength scales. Due to their arbitrary manipulation and compact size, the metasurface can be well integrated with optical fibers. Herein, we demonstrate a polarization-dependent metasurface using birefringent meta-atoms, which can independently control X- and Y-polarization incident light. Each meta-atom allows for the division of phase into 16 steps ranging from 0 to 2π for both X- and Y-polarization, resulting in 256 nanopillars selected from the meta-atom library to satisfy the required phase. With the different effective refractive indices of the cuboid meta-atoms along the X- and Y-axis, we can achieve collimation of the X-polarization emitted beam from an optical fiber while deflecting orthogonally polarized light. As a result, the proposed metasurface collimates an X-polarized beam with a beam radius of 20 μm at z = 1 mm and 43.9 μm at z = 2 mm. Additionally, the metasurface can effectively deflect the Y-polarized beam to 36.01°, consistent with the results of the theoretical computation. The proposed metasurface exhibits a deflection efficiency of 55.6% for Y-polarized beams with a relative polarization efficiency of 82.2%, while the efficiency for the X-polarization is 71.4%. Our work is considered a promising application for optical communication, sensing, and quantum measurement. Full article
(This article belongs to the Special Issue Fiber Optic Sensors: Science and Applications)
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12 pages, 3930 KiB  
Article
Nanosecond Laser Fabrication of Dammann Grating-like Structure on Glass for Bessel-Beam Array Generation
by Prasenjit Praharaj and Manoj Kumar Bhuyan
Photonics 2024, 11(5), 473; https://doi.org/10.3390/photonics11050473 - 18 May 2024
Viewed by 353
Abstract
The generation of optical beam arrays with prospective uses within the realms of microscopy, photonics, non-linear optics, and material processing often requires Dammann gratings. Here, we report the direct fabrication of one- and two-dimensional Dammann grating-like structures on soda lime glass using a [...] Read more.
The generation of optical beam arrays with prospective uses within the realms of microscopy, photonics, non-linear optics, and material processing often requires Dammann gratings. Here, we report the direct fabrication of one- and two-dimensional Dammann grating-like structures on soda lime glass using a nanosecond pulsed laser beam with a 1064 nm wavelength. Using the fabricated grating, an axicon lens, and an optical magnification system, we propose a scheme of generation of a diverging array of zero-order Bessel beams with a sub-micron-size central core, extending longitudinally over several hundred microns. Two different grating fabrication strategies are also proposed to control the number of Bessel beams in an array. It was demonstrated that Bessel beams of 12 degrees conical half-angle in an array of up to [5 × 5] dimensions can be generated using a suitable combination of Dammann grating, axicon lens and focusing optics. Full article
(This article belongs to the Special Issue Laser Processing and Modification of Materials)
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12 pages, 15402 KiB  
Article
Compact Low Loss Ribbed Asymmetric Multimode Interference Power Splitter
by Yanfeng Liang, Huanlin Lv, Baichao Liu, Haoyu Wang, Fangxu Liu, Shuo Liu, Yang Cong, Xuanchen Li and Qingxiao Guo
Photonics 2024, 11(5), 472; https://doi.org/10.3390/photonics11050472 - 17 May 2024
Viewed by 433
Abstract
Optical power splitters (OPSs) are utilized extensively in integrated photonic circuits, drawing significant interest in research on power splitters with adjustable splitting ratios. This paper introduces a compact, low-loss 1 × 2 asymmetric multimode interferometric (MMI) optical power splitter on a silicon-on-insulator (SOI) [...] Read more.
Optical power splitters (OPSs) are utilized extensively in integrated photonic circuits, drawing significant interest in research on power splitters with adjustable splitting ratios. This paper introduces a compact, low-loss 1 × 2 asymmetric multimode interferometric (MMI) optical power splitter on a silicon-on-insulator (SOI) platform. The device is simulated using the finite difference method (FDM) and eigenmode expansion solver (EME). It is possible to attain various output power splitting ratios by making the geometry of the MMI central section asymmetric relative to the propagation axis. Six distinct optical power splitters are designed with unconventional splitting ratios in this paper, which substantiates that the device can achieve any power splitter ratios (PSRs) in the range of 95:5 to 50:50. The dimensions of the multimode section were established at 2.9 × (9.5–10.9) μm. Simulation results show a range of unique advantages of the device, including a low extra loss of less than 0.4 dB, good fabrication tolerance, and power splitting ratio fluctuation below 3% across the 1500 nm to 1600 nm wavelength span. Full article
(This article belongs to the Special Issue Optical Fiber Communication Systems and Networks)
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11 pages, 5670 KiB  
Article
Mechanical Assessment in Atherosclerosis Based on Photoacoustic Viscoelasticity Imaging
by Xingchao Zhang, Xiaohan Shi, Hui Wu, Caixun Bai, Junshan Xiu and Yue Zhao
Photonics 2024, 11(5), 471; https://doi.org/10.3390/photonics11050471 - 17 May 2024
Viewed by 398
Abstract
Early identification of vulnerable plaques is a major challenge in diagnosis and assessment of atherosclerosis. In atherosclerotic plaque development, the proportion change in components caused plaque mechanical property change and induced plaque rupture. In this paper, a photoacoustic viscoelasticity imaging (PAVEI) technique was [...] Read more.
Early identification of vulnerable plaques is a major challenge in diagnosis and assessment of atherosclerosis. In atherosclerotic plaque development, the proportion change in components caused plaque mechanical property change and induced plaque rupture. In this paper, a photoacoustic viscoelasticity imaging (PAVEI) technique was proposed to measure the viscosity–elasticity ratio of atherosclerotic plaque and evaluated for the potential in characterizing vulnerable plaques. Apolipoprotein E-knockout mice fed with a high-fat/high-cholesterol diet were chosen as the atherosclerotic model. Plaque component phantoms were examined to demonstrate the high efficiency of PAVEI in detecting the proportion change in components compared to single elasticity or viscosity detection. Finally, atherosclerotic plaques from mice aortas at different stages were imaged by PAVEI, which provided an insight into the compositional and functional characterization of vulnerability plaques and suggested its potential applications in the identification of high-risk plaques. Full article
(This article belongs to the Special Issue Advanced Techniques in Biomedical Optical Imaging)
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10 pages, 2354 KiB  
Article
Enhanced Photon-Pair Generation Based on Thin-Film Lithium Niobate Doubly Resonant Photonic Crystal Cavity
by Jinmian Zhu, Fengli Liu, Fangheng Fu, Yuming Wei, Tiefeng Yang, Heyuan Guan and Huihui Lu
Photonics 2024, 11(5), 470; https://doi.org/10.3390/photonics11050470 - 17 May 2024
Viewed by 446
Abstract
In this work, a doubly resonant photonic crystal (PhC) cavity is proposed to enhance second harmonic generation (SHG) efficiency and photon pair generation rate (PGR). Through the exploration of geometry parameters, a band-edge mode within the light cone is identified as the first [...] Read more.
In this work, a doubly resonant photonic crystal (PhC) cavity is proposed to enhance second harmonic generation (SHG) efficiency and photon pair generation rate (PGR). Through the exploration of geometry parameters, a band-edge mode within the light cone is identified as the first harmonic (FH) mode, and a band-edge mode outside the light cone is designated as the second harmonic (SH). Subsequently, by increasing the layers of the core region, a heterostructure PhC cavity is designed. The results showcase a doubly resonant PhC cavity achieving a 133/W SHG efficiency and a photon pair generation rate of 3.7 × 108/s. The exceptional conversion efficiency is attributed to the high quality factors Q observed in the FH and SH modes with values of approximately 280,000 and 2100, respectively. The remarkably high Q factors compensate for nonlinear efficiency degradation caused by detuning, simultaneously making the manufacturing process easier and more feasible. This work is anticipated to provide valuable insights into efficient nonlinear conversion and photon pair generation rates. Full article
(This article belongs to the Special Issue Advances in Integrated Photonics)
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15 pages, 4537 KiB  
Article
High-Q Multiband Narrowband Absorbers Based on Two-Dimensional Graphene Metamaterials
by Aijun Zhu, Pengcheng Bu, Lei Cheng, Cong Hu and Rabi Mahapatra
Photonics 2024, 11(5), 469; https://doi.org/10.3390/photonics11050469 - 16 May 2024
Viewed by 413
Abstract
In this paper, an absorber with multi-band, tunable, high Q, and high sensitivity, based on terahertz periodic two-dimensional patterned graphene surface plasmon resonance (SPR), is proposed. The absorber consists of a bottom metal film separated by a periodically patterned graphene metamaterial structure and [...] Read more.
In this paper, an absorber with multi-band, tunable, high Q, and high sensitivity, based on terahertz periodic two-dimensional patterned graphene surface plasmon resonance (SPR), is proposed. The absorber consists of a bottom metal film separated by a periodically patterned graphene metamaterial structure and a SiO2 dielectric layer, where the patterned graphene layer is etched by “+” and “L” shapes and circles. It has simple structural features that can greatly simplify the fabrication process. We have analyzed the optical properties of a graphene surface plasmon perfect metamaterial absorber based on graphene in the terahertz region using the finite-difference method in time domain (FDTD). The results show that the absorber device exhibits three perfect absorption peaks in the terahertz bands of f1 = 1.55 THz, f2 = 4.19 THz, and f3 = 6.92 THz, with absorption rates as high as 98.70%, 99.63%, and 99.42%, respectively. By discussing the effects of parameters such as the geometrical dimensions of patterned graphene metamaterial structure “+” width W1, “L” width W2, circular width R, and the thickness of the dielectric layer on the absorption performance of absorber, as well as investigating the chemical potential and relaxation time of patterned-layer graphene material, it was found that the amplitude of the absorption peaks and the frequency of resonance of absorber devices can be dynamically adjusted. Finally, we simulated the spectra as the surrounding refractive index n varied to better evaluate the sensing performance of the structure, yielding structural sensitivities up to 382 GHz/RIU. Based on this study, we find that the results of our research will open new doors for the use of multi-band, tunable, polarization-independent metamaterial absorbers that are insensitive to large-angle oblique incidence. Full article
(This article belongs to the Special Issue Photonic Devices Based on Plasmonic or Dielectric Nanostructures)
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16 pages, 9701 KiB  
Article
Compact Quantum Random Number Generator Based on a Laser Diode and a Hybrid Chip with Integrated Silicon Photonics
by Xuyang Wang, Tao Zheng, Yanxiang Jia, Jin Huang, Xinyi Zhu, Yuqi Shi, Ning Wang, Zhenguo Lu, Jun Zou and Yongmin Li
Photonics 2024, 11(5), 468; https://doi.org/10.3390/photonics11050468 - 16 May 2024
Viewed by 420
Abstract
In this study, a compact and low-power-consumption quantum random number generator (QRNG) based on a laser diode and a hybrid chip with integrated silicon photonics is proposed and verified experimentally. The hybrid chip’s size is 8.8 × 2.6 × 1 mm3, [...] Read more.
In this study, a compact and low-power-consumption quantum random number generator (QRNG) based on a laser diode and a hybrid chip with integrated silicon photonics is proposed and verified experimentally. The hybrid chip’s size is 8.8 × 2.6 × 1 mm3, and the power of the entropy source is 80 mW. A common-mode rejection ratio greater than 40 dB was achieved using an optimized 1 × 2 multimode interferometer structure. A method for optimizing the quantum-to-classical noise ratio is presented. A quantum-to-classical noise ratio of approximately 9 dB was achieved when the photoelectron current is 1 μA using a balance homodyne detector with a high dark current GeSi photodiode. The proposed QRNG has the potential for use in scenarios of moderate MHz random number generation speed, with low power, small volume, and low cost prioritized. Full article
(This article belongs to the Topic Hybrid and Heterogeneous Integration on Photonic Circuits)
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12 pages, 5941 KiB  
Article
Boundary Feedback Fiber Random Microcavity Laser Based on Disordered Cladding Structures
by Hongyang Zhu, Bingquan Zhao, Zhi Liu, Zhen He, Lihong Dong, Hongyu Gao and Xiaoming Zhao
Photonics 2024, 11(5), 467; https://doi.org/10.3390/photonics11050467 - 16 May 2024
Viewed by 439
Abstract
The cavity form of complex microcavity lasers predominantly relies on disordered structures, whether found in nature or artificially prepared. These structures, characterized by disorder, facilitate random lasing through the feedback effect of the cavity boundary and the internal scattering medium via various mechanisms. [...] Read more.
The cavity form of complex microcavity lasers predominantly relies on disordered structures, whether found in nature or artificially prepared. These structures, characterized by disorder, facilitate random lasing through the feedback effect of the cavity boundary and the internal scattering medium via various mechanisms. In this paper, we report on a random fiber laser employing a disordered scattering cladding medium affixed to the inner cladding of a hollow-core fiber. The internal flowing liquid gain establishes a stable liquid-core waveguide environment, enabling long-term directional coupling output for random laser emission. Through theoretical analysis and experimental validation, we demonstrate that controlling the disorder at the cavity boundary allows liquid-core fiber random microcavities to exhibit random lasing output with different mechanisms. This provides a broad platform for in-depth research into the generation and control of complex microcavity lasers, as well as the detection of scattered matter within micro- and nanostructures. Full article
(This article belongs to the Special Issue Advancements in Fiber Lasers and Their Applications)
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11 pages, 2614 KiB  
Article
The Generation of Equal-Intensity and Multi-Focus Optical Vortices by a Composite Spiral Zone Plate
by Huaping Zang, Jingzhe Li, Chenglong Zheng, Yongzhi Tian, Lai Wei, Quanping Fan, Shaoyi Wang, Chuanke Wang, Juan Xie and Leifeng Cao
Photonics 2024, 11(5), 466; https://doi.org/10.3390/photonics11050466 - 15 May 2024
Viewed by 441
Abstract
We propose a new vortex lens for producing multiple focused coaxial vortices with approximately equal intensities along the optical axis, termed equal-intensity multi-focus composite spiral zone plates (EMCSZPs). In this typical methodology, two concentric conventional spiral zone plates (SZPs) of different focal lengths [...] Read more.
We propose a new vortex lens for producing multiple focused coaxial vortices with approximately equal intensities along the optical axis, termed equal-intensity multi-focus composite spiral zone plates (EMCSZPs). In this typical methodology, two concentric conventional spiral zone plates (SZPs) of different focal lengths were composited together and the alternate transparent and opaque zones were arranged with specific m-bonacci sequence. Based on the Fresnel–Kirchhoff diffraction theory, the focusing properties of the EMCSZPs were calculated in detail and the corresponding demonstration experiment was been carried out to verify our proposal. The investigations indicate that the EMCSZPs indeed exhibit superior performance, which accords well with our physical design. In addition, the topological charges (TCs) of the multi-focus vortices can be flexibly selected and controlled by optimizing the parameters of the zone plates. These findings which were demonstrated by the performed experiment may open new avenues towards improving the performance of biomedical imaging, quantum computation and optical manipulation. Full article
(This article belongs to the Special Issue Space Division Multiplexing Techniques)
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14 pages, 2136 KiB  
Article
Simulation of a Pulsed Metastable Helium Lidar
by Jiaxin Lan, Yuli Han, Ruocan Zhao, Tingdi Chen, Xianghui Xue, Dongsong Sun, Hang Zhou, Zhenwei Liu and Yingyu Liu
Photonics 2024, 11(5), 465; https://doi.org/10.3390/photonics11050465 - 15 May 2024
Viewed by 480
Abstract
Measurements of atmosphere density in the upper thermosphere and exosphere are of great significance for studying space–atmosphere interactions. However, the region from 200 km to 1000 km has been a blind area for traditional ground-based active remote sensing techniques due to the limitation [...] Read more.
Measurements of atmosphere density in the upper thermosphere and exosphere are of great significance for studying space–atmosphere interactions. However, the region from 200 km to 1000 km has been a blind area for traditional ground-based active remote sensing techniques due to the limitation of facilities and the paucity of neutral atmosphere. To fulfill this gap, the University of Science and Technology of China is developing a powerful metastable helium resonance fluorescent lidar incorporating a 2 m aperture telescope, a high-energy 1083 nm pulsed laser, as well as a superconducting nanowire single-photon detector (SNSPD) with high quantum efficiency and low dark noise. The system is described in detail in this work. To evaluate the performance of the lidar system, numerical simulation is implemented. The results show that metastable helium density measurements can be achieved with a relative error of less than 20% above 370 km in winter and less than 200% in 270–460 km in summer, demonstrating the feasibility of metastable helium lidar. Full article
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11 pages, 4949 KiB  
Article
The Generation of Circularly Polarized Isolated Attosecond Pulses with Tunable Helicity from CO Molecules in Polarization Gating Laser Fields
by Shiju Chen, Hua Yuan, Feng Wang, Jiahang Song, Yue Zhao, Chunhui Yang, Tianxin Ou, Ru Zhang, Qiang Chang and Yuping Sun
Photonics 2024, 11(5), 464; https://doi.org/10.3390/photonics11050464 - 15 May 2024
Viewed by 458
Abstract
We theoretically demonstrate a scheme to generate circularly polarized (CP) isolated attosecond pulses (IAPs) with tunable helicity using a polarization gating laser field interacting with the CO molecule. The results show that a broadband CP supercontinuum is produced from the oriented CO molecule, [...] Read more.
We theoretically demonstrate a scheme to generate circularly polarized (CP) isolated attosecond pulses (IAPs) with tunable helicity using a polarization gating laser field interacting with the CO molecule. The results show that a broadband CP supercontinuum is produced from the oriented CO molecule, which supports the generation of an IAP with an ellipticity of 0.98 and a duration of 90 as. Furthermore, the helicity of the generated harmonics and IAP can be effectively controlled by modulating the laser field and the orientation angle of the CO molecule. Our method will advance research on chiral-specific dynamics and magnetic circular dichroism on the attosecond timescale. Full article
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15 pages, 6857 KiB  
Article
Generation of Propagation-Dependent OAM Self-Torque with Chirped Spiral Gratings
by Ruediger Grunwald, Mathias Jurke, Max Liebmann, Alexander Treffer and Martin Bock
Photonics 2024, 11(5), 463; https://doi.org/10.3390/photonics11050463 - 15 May 2024
Viewed by 448
Abstract
The application of non-uniform spiral gratings to control the structure, topological parameters and propagation of orbital angular momentum (OAM) beams was studied experimentally with coherent near-infrared light. Adapted digital spiral grating structures were programmed into the phase map of a high-resolution liquid-crystal-on-silicon spatial [...] Read more.
The application of non-uniform spiral gratings to control the structure, topological parameters and propagation of orbital angular momentum (OAM) beams was studied experimentally with coherent near-infrared light. Adapted digital spiral grating structures were programmed into the phase map of a high-resolution liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). It is shown that characteristic spatio-spectral anomalies related to Gouy phase shift can be used as pointers to quantify rotational beam properties. Depending on the sign and gradient of spatially variable periods of chirped spiral gratings (CSGs), variations in rotation angle and angular velocity were measured as a function of the propagation distance. Propagation-dependent self-torque is introduced in analogy to known local self-torque phenomena of OAM beams as obtained by the superposition of temporally chirped or phase-modulated wavepackets. Applications in metrology, nonlinear optics or particle trapping are conceivable. Full article
(This article belongs to the Special Issue Structured Light Beams: Science and Applications)
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11 pages, 4572 KiB  
Article
Characterizing Extreme Events in a Fabry–Perot Laser with Optical Feedback
by Shanshan Ge, Yu Huang, Kun Li, Pei Zhou, Penghua Mu, Xin Zhu and Nianqiang Li
Photonics 2024, 11(5), 462; https://doi.org/10.3390/photonics11050462 - 15 May 2024
Viewed by 382
Abstract
The study of extreme events (EEs) in photonics has expanded significantly due to straightforward implementation conditions. EEs have not been discussed systematically, to the best of our knowledge, in the chaotic dynamics of a Fabry–Perot laser with optical feedback, so we address this [...] Read more.
The study of extreme events (EEs) in photonics has expanded significantly due to straightforward implementation conditions. EEs have not been discussed systematically, to the best of our knowledge, in the chaotic dynamics of a Fabry–Perot laser with optical feedback, so we address this in the current contribution. Herein, we not only find EEs in all modes but also divide the EEs in total output into two categories for further discussion. The two types of EEs have similar statistical features to conventional rogue waves. The occurrence probability of EEs undergoes a saturation effect as the feedback strength increases. Additionally, we analyze the influence of feedback strength, feedback delay, and pump current on the probability of EEs defined by two criteria of EEs and find similar trends. We hope that this work contributes to a deep understanding and serves as inspiration for further research into various multimode semiconductor laser systems. Full article
(This article belongs to the Special Issue Advanced Lasers and Their Applications II)
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11 pages, 2457 KiB  
Article
Integrated Analysis of Line-Of-Sight Stability of Off-Axis Three-Mirror Optical System
by Yatao Lu, Bin Sun, Gui Mei, Qinglei Zhao, Zhongshan Wang, Yang Gao and Shuxin Wang
Photonics 2024, 11(5), 461; https://doi.org/10.3390/photonics11050461 - 15 May 2024
Viewed by 371
Abstract
As a space camera works in orbit, the stress rebound caused by gravity inevitably results in the deformation of its optomechanical structure, and the relative position change between different optical components will affect the Line-Of-Sight pointing of the camera. In this paper, the [...] Read more.
As a space camera works in orbit, the stress rebound caused by gravity inevitably results in the deformation of its optomechanical structure, and the relative position change between different optical components will affect the Line-Of-Sight pointing of the camera. In this paper, the optical sensitivity calculation of a space camera’s Line-Of-Sight pointing is realized based on the optomechanical constraint equations, and the Line-Of-Sight equations are constructed using the second type of response (DRESP2) method to realize an optomechanical integrated analysis of the camera’s Line-Of-Sight stability at the structural finite element solver level. The verification results show that the Line-Of-Sight stability error is 6.38%, meaning that this method can identify the sensitive optical elements of the optical system efficiently and quickly. Thus, the method in this paper has important significance as a reference for the analysis of the Line-Of-Sight stability of complex optical systems. Full article
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16 pages, 3641 KiB  
Review
Features of Adaptive Phase Correction of Optical Wave Distortions under Conditions of Intensity Fluctuations
by Vladimir Lukin
Photonics 2024, 11(5), 460; https://doi.org/10.3390/photonics11050460 - 14 May 2024
Viewed by 502
Abstract
An analysis of the features of measurements and correction of phase distortions in optical waves propagating in the atmosphere at various levels of turbulence was performed. It is shown that with increasing intensity fluctuations, the limiting capabilities of phase correction decrease, and the [...] Read more.
An analysis of the features of measurements and correction of phase distortions in optical waves propagating in the atmosphere at various levels of turbulence was performed. It is shown that with increasing intensity fluctuations, the limiting capabilities of phase correction decrease, and the phase of an optical wave that has passed through a turbulence layer consists of two components: potential and vortex. It was found that even in the region of weak fluctuations there is an overlap of spectral filtering functions for intensity and phase fluctuations. Areas of turbulence inhomogeneities have been identified that will have mutual influence and negatively affect the operation of the phase meter. It is noted that correlation functions, both phase and intensity, are less susceptible to this compared to structural functions. The results of experimental studies on the reconstruction of the wavefront of laser radiation distorted by atmospheric turbulence using a Shack–Hartmann wavefront sensor during vignetting and central screening of the entrance pupil in the optical system are presented. Studies have been carried out on the propagation of laser radiation along a horizontal atmospheric path for various levels of turbulence. The results are analyzed in terms of Zernike polynomials. Full article
(This article belongs to the Special Issue Advances in Structured Light Generation and Manipulation)
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9 pages, 6506 KiB  
Article
Influence of the Experimental Setup on Electromagnetic Pulses in the VHF Band at Relativistic High-Power Laser Facilities
by Michael Ehret, Luca Volpe, Jon Imanol Apiñaniz, Maria Dolores Rodríguez-Frías and Giancarlo Gatti
Photonics 2024, 11(5), 459; https://doi.org/10.3390/photonics11050459 - 14 May 2024
Viewed by 516
Abstract
We present experimental results for the controlled mitigation of the electromagnetic pulses (EMPs) produced in the interactions of a 1 PW high-power 30 fs Ti:Sa laser VEGA-3 with solid-density targets transparent to laser-forward-accelerated relativistic electrons. This study aims at the band of very [...] Read more.
We present experimental results for the controlled mitigation of the electromagnetic pulses (EMPs) produced in the interactions of a 1 PW high-power 30 fs Ti:Sa laser VEGA-3 with solid-density targets transparent to laser-forward-accelerated relativistic electrons. This study aims at the band of very high frequencies (VHFs), i.e., those in the hundreds of MHz, which comprise the fundamental cavity modes of the rectangular VEGA-3 vacuum chamber. We demonstrate mode suppression by a tailoring of the laser-produced space charge distribution. Full article
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15 pages, 13683 KiB  
Article
A 3D Reconstruction Method Based on Homogeneous De Bruijn-Encoded Structured Light
by Weimin Li and Songlin Li
Photonics 2024, 11(5), 458; https://doi.org/10.3390/photonics11050458 - 14 May 2024
Viewed by 366
Abstract
Structured light three-dimensional reconstruction is one of the important methods for non-contact acquisition of sparse texture object surfaces. Variations in ambient illumination and disparities in object surface reflectance can significantly impact the fidelity of three-dimensional reconstruction, introducing considerable inaccuracies. We introduce a robust [...] Read more.
Structured light three-dimensional reconstruction is one of the important methods for non-contact acquisition of sparse texture object surfaces. Variations in ambient illumination and disparities in object surface reflectance can significantly impact the fidelity of three-dimensional reconstruction, introducing considerable inaccuracies. We introduce a robust method for color speckle structured light encoding, which is based on a variant of the De Bruijn sequence, termed the Homogeneous De Bruijn Sequence. This innovative approach enhances the reliability and accuracy of structured light techniques for three-dimensional reconstruction by utilizing the distinctive characteristics of Homogeneous De Bruijn Sequences. Through a pruning process applied to the De Bruijn sequence, a structured light pattern with seven distinct color patches is generated. This approach ensures a more equitable distribution of speckle information. Full article
(This article belongs to the Section Optical Interaction Science)
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10 pages, 5013 KiB  
Article
Mode Heterogeneous Multimode Power Splitter Based on Cascaded Mode-Dependent Splitters and Converters
by Xin Xu, Hongliang Chen, Xin Fu and Lin Yang
Photonics 2024, 11(5), 457; https://doi.org/10.3390/photonics11050457 - 14 May 2024
Viewed by 443
Abstract
To the best of our knowledge, a novel concept of mode heterogeneity for the design of multimode devices is presented in this paper and applied to the design of scalable multimode power splitters. Based on a cascade of mode-dependent splitters and converters, we [...] Read more.
To the best of our knowledge, a novel concept of mode heterogeneity for the design of multimode devices is presented in this paper and applied to the design of scalable multimode power splitters. Based on a cascade of mode-dependent splitters and converters, we achieve beam splitting and mode conversion for four modes from TE0 to TE3 in the bandwidth from 1525 nm to 1560 nm. The measurements of the device at 1550 nm show excellent performance, with the insertion loss ranging from 0.16 dB to 0.63 dB, crosstalk all below −16.71 dB, and power uniformity between 0.026 dB and 0.168 dB. Full article
(This article belongs to the Special Issue Optical Communication, Sensing and Network)
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13 pages, 8880 KiB  
Article
Exploring the Origin of Lissajous Geometric Modes from the Ray Tracing Model
by Xin-Liang Zheng, Yu-Han Fang, Wei-Che Chung, Cheng-Li Hsieh and Yung-Fu Chen
Photonics 2024, 11(5), 456; https://doi.org/10.3390/photonics11050456 - 13 May 2024
Viewed by 402
Abstract
In this paper, we use the geometric optics and discuss the path of laser beam in a simple laser (concave-plano) cavity with the birefringence crystal. In specific lengths of the laser cavity, we can observe various types of Lissajous-like structural laser modes that [...] Read more.
In this paper, we use the geometric optics and discuss the path of laser beam in a simple laser (concave-plano) cavity with the birefringence crystal. In specific lengths of the laser cavity, we can observe various types of Lissajous-like structural laser modes that can be simulated using our ray tracing model. At the end of this paper, we provide an adjusted ABCD matrix. With the adjusted ABCD matrix and iterative calculation, we can obtain the 3D trajectories which are similar to the experimental results. These structural laser modes can be realized by a Nd:YVO4 solid-state laser with off-axis pumping. From the comparison between the experimental data and the numerical data, we clarify the relationship between the 3D Lissajous-like structural laser modes and ray trajectory in the laser cavity. Full article
(This article belongs to the Special Issue Emerging Topics in Structured Light)
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14 pages, 5228 KiB  
Article
Analytical Model of Point Spread Function under Defocused Degradation in Diffraction-Limited Systems: Confluent Hypergeometric Function
by Feijun Song, Qiao Chen, Xiongxin Tang and Fanjiang Xu
Photonics 2024, 11(5), 455; https://doi.org/10.3390/photonics11050455 - 13 May 2024
Viewed by 384
Abstract
In recent years, optical systems near the diffraction limit have been widely used in high-end applications. Evidently, an analytical solution of the point spread function (PSF) will help to enhance both understanding and dealing with the imaging process. This paper analyzes the Fresnel [...] Read more.
In recent years, optical systems near the diffraction limit have been widely used in high-end applications. Evidently, an analytical solution of the point spread function (PSF) will help to enhance both understanding and dealing with the imaging process. This paper analyzes the Fresnel diffraction of diffraction-limited optical systems in defocused conditions. For this work, an analytical solution of the defocused PSF was obtained using the series expansion of the confluent hypergeometric functions. The analytical expression of the defocused optical transfer function is also presented herein for comparison with the PSF. Additionally, some characteristic parameters for the PSF are provided, such as the equivalent bandwidth and the Strehl ratio. Comparing the PSF obtained using the fast Fourier transform algorithm of an optical system with known, detailed parameters to the analytical solution derived in this paper using only the typical parameters, the root mean square errors of the two methods were found to be less than 3% in the weak and medium defocus range. The attractive advantages of the universal model, which is independent of design details, objective types, and applications, are discussed. Full article
(This article belongs to the Special Issue Emerging Topics in High-Power Laser and Light–Matter Interactions)
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15 pages, 10765 KiB  
Article
Dual-Polarization Conversion and Coding Metasurface for Wideband Radar Cross-Section Reduction
by Saima Hafeez, Jianguo Yu, Fahim Aziz Umrani, Yibo Huang, Wang Yun and Muhammad Ishfaq
Photonics 2024, 11(5), 454; https://doi.org/10.3390/photonics11050454 - 11 May 2024
Viewed by 531
Abstract
Modern stealth application systems require integrated meta-devices to operate effectively and have gained significant attention recently. This research paper proposes a 1-bit coding metasurface (CM) design. The fundamental component of the proposed CM is integrated to convert linearly polarized incoming electromagnetic waves into [...] Read more.
Modern stealth application systems require integrated meta-devices to operate effectively and have gained significant attention recently. This research paper proposes a 1-bit coding metasurface (CM) design. The fundamental component of the proposed CM is integrated to convert linearly polarized incoming electromagnetic waves into their orthogonal counterpart within frequency bands of 12.37–13.03 GHz and 18.96–32.37 GHz, achieving a polarization conversion ratio exceeding 99%. Furthermore, it enables linear-to-circular polarization conversion from 11.80 to 12.29, 13.17 to 18.44, and 33.33 to 40.35 GHz. A second element is produced by rotating a fundamental component by 90°, introducing a phase difference of π (pi) between them. Both elements are arranged in an array using a random aperiodic coding sequence to create a 1-bit CM for reducing the radar cross-section (RCS). The planar structure achieved over 10 dB RCS reduction for polarized waves in the frequency bands of 13.1–13.8 GHz and 20.4–30.9 GHz. A prototype was fabricated and tested, with the experimental results showing a good agreement with the simulated outcomes. The proposed design holds potential applications in radar systems, reflector antennas, stealth technologies, and satellite communication. Full article
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