Photonics

16 pages, 2686 KiB

Open AccessEditor’s ChoiceArticle

Kramers–Kronig Transmission with a Crosstalk-Dependent Step Multiple-Input Multiple-Output Volterra Equalizer in a Seven-Core Fiber

by Feng Tian, Tianze Wu, Chao Yu, Chuxuan Wang, Mohai Yue, Ran Gao, Qi Zhang, Zhipei Li, Qinghua Tian, Fu Wang and Xiangjun Xin

Photonics 2023, 10(9), 1017; https://doi.org/10.3390/photonics10091017 - 5 Sep 2023

Cited by 2 | Viewed by 1202

Abstract

In this paper, we experimentally demonstrate a net bit rate of 261.7 Gbit/s in a seven-core transmission system with a Kramers–Kronig (KK) receiver. The 10 GBaud 16-level quadrature amplitude modulation (QAM) signal is transmitted over a 2.5 km seven-core fiber, and the relationship [...] Read more.

In this paper, we experimentally demonstrate a net bit rate of 261.7 Gbit/s in a seven-core transmission system with a Kramers–Kronig (KK) receiver. The 10 GBaud 16-level quadrature amplitude modulation (QAM) signal is transmitted over a 2.5 km seven-core fiber, and the relationship between carrier-to-signal power ratio, signal power, frequency spacing, and optical power is analyzed. Moreover, a multiple-input multiple-output (MIMO) Volterra equalization algorithm with crosstalk-dependent steps is proposed to compensate for inter-core crosstalk and impairments induced by other devices. Compared to the single-input single-output (SISO) Volterra equalizer, the CSPR can be reduced by 1.3 dB, and the received power gain can reach up to 0.7 dB. Full article

(This article belongs to the Special Issue Optical Fiber Transmission Systems)

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22 pages, 1161 KiB

Open AccessEditor’s ChoiceArticle

Comparison between the Propagation Properties of Bessel–Gauss and Generalized Laguerre–Gauss Beams

by Colin J. R. Sheppard and Miguel A. Porras

Photonics 2023, 10(9), 1011; https://doi.org/10.3390/photonics10091011 - 4 Sep 2023

Cited by 3 | Viewed by 2265

Abstract

The connections between Laguerre–Gauss and Bessel–Gauss beams, and between Hermite–Gauss and cosine-Gauss beams are investigated. We review different asymptotic expressions for generalized Laguerre and Hermite polynomials of large radial/transverse order. The amplitude variations of generalized Laguerre–Gauss beams, including standard and elegant Laguerre–Gauss beams [...] Read more.

The connections between Laguerre–Gauss and Bessel–Gauss beams, and between Hermite–Gauss and cosine-Gauss beams are investigated. We review different asymptotic expressions for generalized Laguerre and Hermite polynomials of large radial/transverse order. The amplitude variations of generalized Laguerre–Gauss beams, including standard and elegant Laguerre–Gauss beams as special cases, are compared with Bessel–Gauss beams. Bessel–Gauss beams can be well-approximated by elegant Laguerre–Gauss beams. For non-integral values of the Laguerre function radial order, a generalized Laguerre–Gauss beam with integer order matches the width of the central lobe well, even for low radial orders. Previous approximations are found to be inaccurate for large azimuthal mode number (topolgical charge), and an improved approximation for this case is also introduced. Full article

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17 pages, 4198 KiB

Open AccessEditor’s ChoiceReview

Machine Learning for Self-Coherent Detection Short-Reach Optical Communications

by Qi Wu, Zhaopeng Xu, Yixiao Zhu, Yikun Zhang, Honglin Ji, Yu Yang, Gang Qiao, Lulu Liu, Shangcheng Wang, Junpeng Liang, Jinlong Wei, Jiali Li, Zhixue He, Qunbi Zhuge and Weisheng Hu

Photonics 2023, 10(9), 1001; https://doi.org/10.3390/photonics10091001 - 31 Aug 2023

Cited by 9 | Viewed by 2621

Abstract

Driven by emerging technologies such as the Internet of Things, 4K/8K video applications, virtual reality, and the metaverse, global internet protocol traffic has experienced an explosive growth in recent years. The surge in traffic imposes higher requirements for the data rate, spectral efficiency, [...] Read more.

Driven by emerging technologies such as the Internet of Things, 4K/8K video applications, virtual reality, and the metaverse, global internet protocol traffic has experienced an explosive growth in recent years. The surge in traffic imposes higher requirements for the data rate, spectral efficiency, cost, and power consumption of optical transceivers in short-reach optical networks, including data-center interconnects, passive optical networks, and 5G front-haul networks. Recently, a number of self-coherent detection (SCD) systems have been proposed and gained considerable attention due to their spectral efficiency and low cost. Compared with coherent detection, the narrow-linewidth and high-stable local oscillator can be saved at the receiver, significantly reducing the hardware complexity and cost of optical modules. At the same time, machine learning (ML) algorithms have demonstrated a remarkable performance in various types of optical communication applications, including channel equalization, constellation optimization, and optical performance monitoring. ML can also find its place in SCD systems in these scenarios. In this paper, we provide a comprehensive review of the recent progress in SCD systems designed for high-speed optical short- to medium-reach transmission links. We discuss the diverse applications and the future perspectives of ML for these SCD systems. Full article

(This article belongs to the Special Issue Machine Learning Applied to Optical Communication Systems)

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13 pages, 850 KiB

Open AccessEditor’s ChoiceArticle

Higher-Order Optomechanical Nonlinearity Based on the Mechanical Effect of Light

by Qin Wu and Hao-Jin Sun

Photonics 2023, 10(9), 991; https://doi.org/10.3390/photonics10090991 - 30 Aug 2023

Viewed by 1083

Abstract

Nonlinear cavity optomechanics based on the mechanical effect of light has recently received considerable attention due to its potential applications in high-precision metrology. In this work, we theoretically studied the third-order optomechanical nonlinearity by using a perturbative approach, and an analytical solution is [...] Read more.

Nonlinear cavity optomechanics based on the mechanical effect of light has recently received considerable attention due to its potential applications in high-precision metrology. In this work, we theoretically studied the third-order optomechanical nonlinearity by using a perturbative approach, and an analytical solution is given, which can be extended to cases of higher-order optomechanical nonlinearity. Furthermore, the generation of a third-order sideband is analyzed in detail, and the results show that the amplitude of the third-order sideband shows a high dependence on the control field detuning, suggesting that the high-order nonlinear intensity can be enhanced by properly adjusting the detuning of the laser field rather than by a strong laser drive. In addition to providing insight into optomechanical nonlinearity, the analytical description of third-order optomechanical nonlinearity based on the mechanical effects of light may find applications in ultra-high precision measurement under low power conditions. Full article

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11 pages, 8213 KiB

Open AccessEditor’s ChoiceArticle

Microcomb-Driven Optical Convolution for Car Plate Recognition

by Zhenming He, Junwei Cheng, Xinyu Liu, Bo Wu, Heng Zhou, Jianji Dong and Xinliang Zhang

Photonics 2023, 10(9), 972; https://doi.org/10.3390/photonics10090972 - 25 Aug 2023

Cited by 4 | Viewed by 1776

Abstract

The great success of artificial intelligence (AI) calls for higher-performance computing accelerators, and optical neural networks (ONNs) with the advantages of high speed and low power consumption have become competitive candidates. However, most of the reported ONN architectures have demonstrated simple MNIST handwritten [...] Read more.

The great success of artificial intelligence (AI) calls for higher-performance computing accelerators, and optical neural networks (ONNs) with the advantages of high speed and low power consumption have become competitive candidates. However, most of the reported ONN architectures have demonstrated simple MNIST handwritten digit classification tasks due to relatively low precision. A microring resonator (MRR) weight bank can achieve a high-precision weight matrix and can increase computing density with the assistance of wavelength division multiplexing (WDM) technology offered by dissipative Kerr soliton (DKS) microcomb sources. Here, we implement a car plate recognition task based on an optical convolutional neural network (CNN). An integrated DKS microcomb was used to drive an MRR weight-bank-based photonic processor, and the computing precision of one optical convolution operation could reach 7 bits. The first convolutional layer was realized in the optical domain, and the remaining layers were performed in the electrical domain. Totally, the optoelectronic computing system (OCS) could achieve a comparable performance with a 64-bit digital computer for character classification. The error distribution obtained from the experiment was used to emulate the optical convolution operation of other layers. The probabilities of the softmax layer were slightly degraded, and the robustness of the CNN was reduced, but the recognition results were still acceptable. This work explores an MRR weight-bank-based OCS driven by a soliton microcomb to realize a real-life neural network task for the first time and provides a promising computational acceleration scheme for complex AI tasks. Full article

(This article belongs to the Special Issue Optical Computing and Optical Neural Networks)

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13 pages, 5176 KiB

Open AccessEditor’s ChoiceEssay

Integrated Encapsulation and Implementation of a Linear-Mode APD Detector for Single-Pixel Imaging Lidar

by Akang Lv, Kee Yuan, Jian Huang, Dongfeng Shi, Shiguo Zhang, Yafeng Chen and Zixin He

Photonics 2023, 10(9), 970; https://doi.org/10.3390/photonics10090970 - 24 Aug 2023

Viewed by 1651

Abstract

Single-pixel imaging lidar is a novel technology that leverages single-pixel detectors without spatial resolution and spatial light modulators to capture images by reconstruction. This technique has potential imaging capability in non-visible wavelengths compared with surface array detectors. An avalanche photodiode (APD) is a [...] Read more.

Single-pixel imaging lidar is a novel technology that leverages single-pixel detectors without spatial resolution and spatial light modulators to capture images by reconstruction. This technique has potential imaging capability in non-visible wavelengths compared with surface array detectors. An avalanche photodiode (APD) is a device in which the internal photoelectric effect and the avalanche multiplication effect are exploited to detect and amplify optical signals. An encapsulated APD detector, with an APD device as the core, is the preferred photodetector for lidar due to its high quantum efficiency in the near-infrared waveband. However, research into APD detectors in China is still in the exploratory period, when most of the work focuses on theoretical analysis and experimental verification. This is a far cry from foreign research levels in key technologies, and the required near-infrared APD detectors with high sensitivity and low noise have to be imported at a high price. In this present study, an encapsulated APD detector was designed in a linear mode by integrating a bare APD tube, a bias power circuit, a temperature control circuit and a signal processing circuit, and the corresponding theoretical analysis, circuit design, circuit simulation and experimental tests were carried out. Then, the APD detector was applied in the single-pixel imaging lidar system. The study showed that the bias power circuit could provide the APD with an operating voltage of DC 1.6 V to 300 V and a ripple voltage of less than 4.2 mV. Not only that, the temperature control circuit quickly changed the operating state of the Thermo Electric Cooler (TEC) to stabilize the ambient temperature of the APD and maintain it at 25 ± 0.3 °C within 5 h. The signal processing circuit was designed with a multi-stage amplification cascade structure, effectively raising the gain of signal amplification. By comparison, the trial also suggested that the encapsulated APD detector and the commercial Licel detector had a good agreement on the scattered signal, such as a repetition rate and pulse width response under the same lidar environment. Therefore, target objects in real atmospheric environments could be imaged by applying the encapsulated APD detector to the near-infrared single-pixel imaging lidar system. Full article

(This article belongs to the Topic Advances in Optical Sensors)

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9 pages, 5327 KiB

Open AccessEditor’s ChoiceCommunication

Single-Shot Phase-Contrast Imaging with a Single Grating

by Xin Liu, Lang Liu, Jianheng Huang, Yaohu Lei and Ji Li

Photonics 2023, 10(9), 968; https://doi.org/10.3390/photonics10090968 - 24 Aug 2023

Cited by 2 | Viewed by 1613

Abstract

In the field of X-ray phase-contrast imaging, a time-saving approach and preservation of details are crucial factors for obtaining phase-contrast images. In this manuscript, a single grating imaging system is proposed to perform the X-ray phase-contrast imaging. Instead of the time-consuming phase-stepping method, [...] Read more.

In the field of X-ray phase-contrast imaging, a time-saving approach and preservation of details are crucial factors for obtaining phase-contrast images. In this manuscript, a single grating imaging system is proposed to perform the X-ray phase-contrast imaging. Instead of the time-consuming phase-stepping method, this system uses a single-shot algorithm to retrieve the distribution of samples’ attenuation and phase gradient. Unlike the single-shot Fourier transform algorithm, which truncates the high-frequency component of the image and reduces the spatial resolution, our method can retrieve the attenuation and phase information images with the same spatial resolution as the images acquired directly by the X-ray detector used. Furthermore, by using a large-size X-ray detector (29 cm × 23 cm), the imaging system can be configured as either a microscopic instrument or a normal large field-of-view imaging system. Finally, a series of experiments were performed to validate the feasibility of the proposed method. Full article

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

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11 pages, 3096 KiB

Open AccessEditor’s ChoiceCommunication

Frequency Comb Fiber Generator Based on Photonic Bandgap Amplifier

by Aleksei Abramov, Dmitry Korobko and Igor Zolotovskii

Photonics 2023, 10(9), 965; https://doi.org/10.3390/photonics10090965 - 23 Aug 2023

Cited by 2 | Viewed by 1219

Abstract

We report on a model of a fiber frequency comb generator that develops an approach to harmonically mode-locked fiber laser design based on dissipative four-wave mixing. In our version of this approach, we assume an amplifying one-dimensional photonic crystal as a key cavity [...] Read more.

We report on a model of a fiber frequency comb generator that develops an approach to harmonically mode-locked fiber laser design based on dissipative four-wave mixing. In our version of this approach, we assume an amplifying one-dimensional photonic crystal as a key cavity element combining the properties of an intra-cavity filter and a power amplifier. Using standard equations describing the signal transformation in the ring cavity and the output fiber cascade, we have demonstrated the possibility of the application of the proposed model as a generator of broadband frequency comb with controllable line spacing. Full article

(This article belongs to the Special Issue Optical Fiber Lasers and Amplifiers. Practical Applications of Fiber-Based Laser Sources)

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15 pages, 3271 KiB

Open AccessEditor’s ChoiceArticle

Fourier Single-Pixel Imaging Based on Online Modulation Pattern Binarization

by Xinding Jiang, Ziyi Tong, Zhongyang Yu, Pengfei Jiang, Lu Xu, Long Wu, Mingsheng Chen, Yong Zhang, Jianlong Zhang and Xu Yang

Photonics 2023, 10(9), 963; https://doi.org/10.3390/photonics10090963 - 23 Aug 2023

Cited by 2 | Viewed by 1372

Abstract

Down-sampling Fourier single-pixel imaging is typically achieved by truncating the Fourier spectrum, where exclusively the low-frequency Fourier coefficients are extracted while discarding the high-frequency components. However, the truncation of the Fourier spectrum can lead to an undesired ringing effect in the reconstructed result. [...] Read more.

Down-sampling Fourier single-pixel imaging is typically achieved by truncating the Fourier spectrum, where exclusively the low-frequency Fourier coefficients are extracted while discarding the high-frequency components. However, the truncation of the Fourier spectrum can lead to an undesired ringing effect in the reconstructed result. Moreover, the original Fourier single-pixel imaging necessitated grayscale Fourier basis patterns for illumination. This requirement limits imaging speed because digital micromirror devices (DMDs) generate grayscale patterns at a lower refresh rate. In order to solve the above problem, a fast and high-quality Fourier single-pixel imaging reconstruction method is proposed in the paper. In the method, the threshold binarization of the Fourier base pattern is performed online to improve the DMD refresh rate, and the reconstruction quality of Fourier single-pixel imaging at a low-sampling rate is improved by generating an adversarial network. This method enables fast reconstruction of target images with higher quality despite low-sampling rates. Compared with conventional Fourier single-pixel imaging, numerical simulation and experimentation demonstrate the effectiveness of the proposed method. Notably, this method is particularly significant for fast Fourier single-pixel imaging applications. Full article

(This article belongs to the Special Issue Nonlinear Optics and Hyperspectral Polarization Imaging)

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11 pages, 2285 KiB

Open AccessEditor’s ChoiceArticle

An Efficient Silicon Grating Coupler for a 2 μm Waveband Based on a Polysilicon Overlay

by Yifan Wu, Yuzhou Wu, Jiefeng Xu, Xi Wang, You Wu, Yanglin Chen, Jiahang Li and Ke Xu

Photonics 2023, 10(8), 952; https://doi.org/10.3390/photonics10080952 - 20 Aug 2023

Cited by 2 | Viewed by 2056

Abstract

The short-wavelength mid-infrared spectral range of the 2 μm waveband has the advantages of low transmission loss and broad gain bandwidth, making it a promising candidate for the next optical fiber communication window. It is thus highly desired to develop high-performance silicon photonic [...] Read more.

The short-wavelength mid-infrared spectral range of the 2 μm waveband has the advantages of low transmission loss and broad gain bandwidth, making it a promising candidate for the next optical fiber communication window. It is thus highly desired to develop high-performance silicon photonic components in this waveband. Here, an efficient dual-layer grating coupler was designed on a 220 nm thick silicon-on-insulator based on raised polysilicon to address the low directionality issue. For the fiber tilted at an angle of 10°, the grating coupler’s simulated coupling efficiency reaches 80.3% (−0.95 dB) at a wavelength of 2002 nm. The 1 dB bandwidth is 66 nm. The structure is completely compatible with the standard silicon photonic fabrication process, making it suitable for large volume fabrication. Full article

(This article belongs to the Special Issue Silicon and Silicon Nitride Integrated Photonics: Challenges and Opportunities)

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18 pages, 8696 KiB

Open AccessEditor’s ChoiceArticle

Analysis and Prediction of Image Quality Degradation Caused by Diffraction of Infrared Optical System Turning Marks

by Haokun Ye, Jianping Zhang, Shangnan Zhao, Mingxin Liu and Xin Zhang

Photonics 2023, 10(8), 937; https://doi.org/10.3390/photonics10080937 - 17 Aug 2023

Viewed by 1545

Abstract

This paper addresses the issue of reduced image quality due to annular turning marks formed by single-point diamond turning (SPDT) during the processing of metal-based mirrors and infrared lenses. An ideal single-point diamond turning marks diffraction action model to quantitatively analyze the impact [...] Read more.

This paper addresses the issue of reduced image quality due to annular turning marks formed by single-point diamond turning (SPDT) during the processing of metal-based mirrors and infrared lenses. An ideal single-point diamond turning marks diffraction action model to quantitatively analyze the impact of turning marks diffraction on imaging quality degradation is proposed. Based on this model, a fast estimation algorithm for the optical modulation transfer function of the system under turning marks diffraction (TMTF) is proposed. The results show that the TMTF algorithm achieves high computational accuracy, with a relative error of only 3% in diffraction efficiency, while being hundreds of times faster than rigorous coupled wave analysis (RCWA). This method is significant for reducing manufacturing costs and improving production efficiency, as it avoids the problem of being unable to compute large-size optical systems due to computational resource and time constraints. Full article

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13 pages, 3680 KiB

Open AccessEditor’s ChoiceCommunication

Vertical Multi-Junction Laser Power Converters with 61% Efficiency at 30 W Output Power and with Tolerance to Beam Non-Uniformity, Partial Illumination, and Beam Displacement

by Simon Fafard and Denis Masson

Photonics 2023, 10(8), 940; https://doi.org/10.3390/photonics10080940 - 17 Aug 2023

Cited by 16 | Viewed by 3274

Abstract

Stable and reliable optical power converting devices are obtained using vertical multi-junction laser power converters. They are based on the GaAs and the InP material systems and are used for power-over-fiber or power-beaming applications. This study demonstrates that, in addition to providing the [...] Read more.

Stable and reliable optical power converting devices are obtained using vertical multi-junction laser power converters. They are based on the GaAs and the InP material systems and are used for power-over-fiber or power-beaming applications. This study demonstrates that, in addition to providing the overall best conversion efficiencies with output voltages ideal for various applications, these semiconductor photovoltaic devices are very tolerant to beam non-uniformity, partial illumination, or beam displacement variations. Examples are given with two tight beams, each covering as little as ~7% of the cell area. An optical input power of 10 W was converted with still an efficiency of Eff ~59.4%. For an input power of 20 W, the illuminated area was set to ~22% without significantly affecting the conversion efficiency of Eff ~60%. Remarkably, for a beam diameter at ~65% of the chip length (i.e., covering ~35% of the chip area), a converted power of 29.5 W was obtained using a 12-junction GaAs device with a conversion efficiency of 61%. For a 10 junction InP-based device, an efficiency of Eff = 51.1% was obtained at an output voltage reaching as high as V_oc = 5.954 V for an average optical intensity of 69 W/cm² and an illumination area of ~57%. Full article

(This article belongs to the Topic Photovoltaic Materials and Devices)

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14 pages, 5257 KiB

Open AccessEditor’s ChoiceArticle

Simple Method of Light Field Calculation for Shaping of 3D Light Curves

by Svetlana N. Khonina, Alexey P. Porfirev, Sergey G. Volotovskiy, Andrey V. Ustinov and Sergey V. Karpeev

Photonics 2023, 10(8), 941; https://doi.org/10.3390/photonics10080941 - 17 Aug 2023

Cited by 3 | Viewed by 1486

Abstract

We propose a method for generating three-dimensional light fields with given intensity and phase distributions using purely phase transmission functions. The method is based on a generalization of the well-known approach to the design of diffractive optical elements that focus an incident laser [...] Read more.

We propose a method for generating three-dimensional light fields with given intensity and phase distributions using purely phase transmission functions. The method is based on a generalization of the well-known approach to the design of diffractive optical elements that focus an incident laser beam into an array of light spots in space. To calculate purely phase transmission functions, we use amplitude encoding, which made it possible to implement the designed elements using a single spatial light modulator. The generation of light beams in the form of rings, spirals, Lissajous figures, and multi-petal “rose” distributions uniformly elongated along the optical axis in the required segment is demonstrated. It is also possible to control the three-dimensional structure of the intensity and phase of the shaped light fields along the propagation axis. The experimentally generated intensity distributions are in good agreement with the numerically obtained results and show high potential for the application of the proposed method in laser manipulation with nano- and microparticles, as well as in laser material processing. Full article

(This article belongs to the Special Issue Light Focusing and Optical Vortices)

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14 pages, 4065 KiB

Open AccessEditor’s ChoiceArticle

A 1083 nm Narrow-Linewidth DFB Semiconductor Laser for Quantum Magnetometry

by Mengying Wu, Haiyang Yu, Wenyu Wang, Shaojie Li, Yulian Cao and Jianguo Liu

Photonics 2023, 10(8), 934; https://doi.org/10.3390/photonics10080934 - 15 Aug 2023

Cited by 1 | Viewed by 1746

Abstract

A 1083 nm laser, corresponding to a characteristic spectral line of ³He 2³S₁-2³P, is the core light source for spin-exchange optical pumping-free technology, and thus has important developmental significance. In this paper, precise wavelength 1083.34 nm [...] Read more.

A 1083 nm laser, corresponding to a characteristic spectral line of ³He 2³S₁-2³P, is the core light source for spin-exchange optical pumping-free technology, and thus has important developmental significance. In this paper, precise wavelength 1083.34 nm semiconductor lasers with 285 mW output power, −144.73 dBc/Hz RIN noise and 30.9952 kHz linewidth have been successfully achieved via reasonable chips design, high-quality epitaxial growth process and ultra-low reflectivity coating fabrication. All the results show the highest output power and ultra-narrow linewidth of the single-frequency 1083 nm DFB semiconductor laser achieved in this paper, which can fully satisfy the requirement of quantum magnetometers. Full article

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11 pages, 4176 KiB

Open AccessEditor’s ChoiceArticle

Dual-Band Laser Stealth Based on Quasi Photonic Crystals

by Man Yuan, Jianjing Zhao, Xinye Liao and Xin He

Photonics 2023, 10(8), 931; https://doi.org/10.3390/photonics10080931 - 14 Aug 2023

Cited by 1 | Viewed by 1345

Abstract

A quasi photonic crystal (QPC) dual-band absorber for laser stealth is designed and numerically studied. It consists of a defective two-dimensional photonic crystal on a thick Ni film. The defective photonic crystal is a continuous Ge layer with air holes, but some of [...] Read more.

A quasi photonic crystal (QPC) dual-band absorber for laser stealth is designed and numerically studied. It consists of a defective two-dimensional photonic crystal on a thick Ni film. The defective photonic crystal is a continuous Ge layer with air holes, but some of the holes are periodically removed. Under a normal incidence that is perpendicular to the plane of the defects, the absorptivity can achieve 92.8% at the 1.064 μm wavelength and 93.2% at the 1.55 μm wavelength. Within large incident angles (<45 degrees), the dual-band absorptivity is still >80%. Additionally, the emissivity is as low as 5.8%~20.0% and 2.8%~5.8% in the 3–5 μm and 8–14 μm atmospheric windows. It is found that the introduced defects can couple the incidence into the structure and lead to spectral peaks (electromagnetic resonances) even without the bottom Ni film. With the help of the high-loss Ni film, the resonances are transformed into magnetic or/and electric modes of different orders. As a result, the QPC generates four absorption peaks. They are superimposed in pairs, resulting in enhanced absorption of the two laser wavelengths. Full article

(This article belongs to the Special Issue Advances in Photonic Materials and Technologies)

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14 pages, 9207 KiB

Open AccessEditor’s ChoiceArticle

Experimental Comparison of Carrier Phase Recovery Algorithms for Uniform and Probabilistically Shaped QAM in a 324.1 Gb/S Fiber-mm-Wave Integration System at W-Band

by Junhao Zhang, Jiao Zhang, Qingsong Wang, Jian Chen, Wei Luo, Shitong Xiang, Yuancheng Cai, Bingchang Hua, Mingzheng Lei, Yucong Zou, Liang Tian, Xingyu Chen and Min Zhu

Photonics 2023, 10(8), 927; https://doi.org/10.3390/photonics10080927 - 12 Aug 2023

Viewed by 1658

Abstract

We have experimentally implemented a photonics-aided large-capacity fiber-mm-wave wireless communication system employing a simple dual-polarized single-input single-output (SISO) wireless based on polarization multiplexing at the W-band. To compare the performance of different algorithms, 18G-baud, and 35G-baud 16-level quadrature-amplitude-modulation (16QAM), probabilistically shaped 16QAM (PS-16QAM), [...] Read more.

We have experimentally implemented a photonics-aided large-capacity fiber-mm-wave wireless communication system employing a simple dual-polarized single-input single-output (SISO) wireless based on polarization multiplexing at the W-band. To compare the performance of different algorithms, 18G-baud, and 35G-baud 16-level quadrature-amplitude-modulation (16QAM), probabilistically shaped 16QAM (PS-16QAM), 64QAM and PS-64QAM signal using different carrier phase recovery (CPR) algorithms are transmitted in the system. Moreover, we compare the Viterbi–Viterbi (VV), improved new algorithm based on VV (NVV), blind phase search (BPS), and two-stage BPS algorithms’ computational complexity to better compare different algorithms. Using the experiment result, we can demonstrate that the BPS algorithm is about half a magnitude better than the NVV algorithm for PS-QAM signals, while the NVV algorithm has the lowest computational complexity. Additionally, we also achieve error-free wireless transmission at a net data rate of 324.1 Gb/s with the bit error ratio (BER) below the forward-error correction (FEC) threshold of 1 × 10⁻² assuming soft-decision forward-error correction (SD-FEC) when using the BPS algorithm. Full article

(This article belongs to the Section Optical Communication and Network)

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9 pages, 2089 KiB

Open AccessEditor’s ChoiceCommunication

Inverse Design of Broadband Absorption in the Visible with Plasmonic Multilayered Planar Structures

by Davi F. Rêgo, Igor L. Gomes de Souza, Vitaly F. Rodriguez-Esquerre and Gilliard N. Malheiros-Silveira

Photonics 2023, 10(8), 922; https://doi.org/10.3390/photonics10080922 - 11 Aug 2023

Cited by 1 | Viewed by 1331

Abstract

Plasmonic structures based on stacked layers of metal and dielectric materials excel as broadband absorbers because of the nonlinear relationship between the compound materials’ dispersion characteristics and the multilayered structure’s actual performance. In this work, radiation absorption along the plasmonic absorber is studied. [...] Read more.

Plasmonic structures based on stacked layers of metal and dielectric materials excel as broadband absorbers because of the nonlinear relationship between the compound materials’ dispersion characteristics and the multilayered structure’s actual performance. In this work, radiation absorption along the plasmonic absorber is studied. Broadband absorptance spectra play an important role in applications such as photovoltaics, detectors, modulators, and emitters. We propose and analyze plasmonic stacked structures that exhibit high broadband absorption. For this purpose, an inverse design approach has been implemented using a conventional genetic algorithm as a global optimizer in conjunction with a pattern search as a local optimizer. The proposed strategy found structures with absorption covering the visible spectrum, maintaining its performance for high incident angles. Full article

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

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13 pages, 4973 KiB

Open AccessEditor’s ChoiceArticle

LiNEV: Visible Light Networking for Connected Vehicles

by Osama Saied, Omprakash Kaiwartya, Mohammad Aljaidi, Sushil Kumar, Mufti Mahmud, Rupak Kharel, Farah Al-Sallami and Charalampos C. Tsimenidis

Photonics 2023, 10(8), 925; https://doi.org/10.3390/photonics10080925 - 11 Aug 2023

Cited by 5 | Viewed by 2070

Abstract

DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) has been introduced to visible light networking framework for connected vehicles (LiNEV) systems as a modulation and multiplexing scheme. This is to overcome the light-emitting diode (LED) bandwidth limitation, as well as to reduce the inter-symbol [...] Read more.

DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) has been introduced to visible light networking framework for connected vehicles (LiNEV) systems as a modulation and multiplexing scheme. This is to overcome the light-emitting diode (LED) bandwidth limitation, as well as to reduce the inter-symbol interference caused by the multipath road fading. Due to the implementation of the inverse fast Fourier transform, DC-OFDM suffers from its large peak-to-average power ratio (PAPR), which degrades the performance in LiNEV systems, as the LEDs used in the vehicles’ headlights have a limited optical power-current linear range. To tackle this issue, discrete Fourier transform spread-optical pulse amplitude modulation (DFTS-OPAM) has been proposed as an alternative modulation scheme for LiNEV systems instead of DCO-OFDM. In this paper, we investigate the system performance of both schemes considering the light-emitting diode linear dynamic range and LED 3 dB modulation bandwidth limitations. The simulation results indicate that DCO-OFDM has a 9 dB higher PAPR value compared with DFTS-OPAM. Additionally, it is demonstrated that DCO-OFDM requires an LED with a linear range that is twice the one required by DFTS-OPAM for the same high quadrature amplitude modulation (QAM) order. Furthermore, the findings illustrate that when the signal bandwidth of both schemes significantly exceeds the LED modulation bandwidth, DCO-OFDM outperforms DFTS-OPAM, as it requires a lower signal-to-noise ratio at a high QAM order. Full article

(This article belongs to the Special Issue Advances in Visible Light Communication)

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23 pages, 16196 KiB

Open AccessEditor’s ChoiceArticle

Nonlocal Hydrodynamic Model with Viscosive Damping and Generalized Drude–Lorentz Term

by Milan Burda and Ivan Richter

Photonics 2023, 10(8), 913; https://doi.org/10.3390/photonics10080913 - 9 Aug 2023

Viewed by 1262

Abstract

The response of plasmonic metal particles to an electromagnetic wave produces significant features at the nanoscale level. Different properties of the internal composition of a metal, such as its ionic background and the free electron gas, begin to manifest more prominently. As the [...] Read more.

The response of plasmonic metal particles to an electromagnetic wave produces significant features at the nanoscale level. Different properties of the internal composition of a metal, such as its ionic background and the free electron gas, begin to manifest more prominently. As the dimensions of the nanostructures decrease, the classical local theory gradually becomes inadequate. Therefore, Maxwell’s equations need to be supplemented with a relationship determining the dynamics of current density which is the essence of nonlocal plasmonic models. In this field of physics, the standard (linearized) hydrodynamic model (HDM) has been widely adopted with great success, serving as the basis for a variety of simulation methods. However, ongoing efforts are also being made to expand and refine it. Recently, the GNOR (general nonlocal optical response) modification of the HDM has been used, with the intention of incorporating the influence of electron gas diffusion. Clearly, from the classical description of fluid dynamics, a close relationship between viscosive damping and diffusion arises. This offers a relevant motivation for introducing the GNOR modification in an alternative manner. The standard HDM and its existing GNOR modification also do not include the influence of interband electron transitions in the conduction band and other phenomena that are part of many refining modifications of the Drude–Lorentz and other models of metal permittivity. In this article, we present a modified version of GNOR-HDM that incorporates the viscosive damping of the electron gas and a generalized Drude–Lorentz term. In the selected simulations, we also introduce Landau damping, which corrects the magnitude of the standard damping constant of the electron gas based on the size of the nanoparticle. We have chosen a spherical particle as a suitable object for testing and comparing HD models and their modifications because it allows the calculation of precise analytical solutions for the interactions and, simultaneously, it is a relatively easily fabricated nanostructure in practice. Our contribution also includes our own analytical method for solving the HDM interaction of a plane wave with a spherical particle. This method forms the core of calculations of the characteristic quantities, such as the extinction cross-sections and the corresponding components of electric fields and current densities. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Photonics Sensors)

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19 pages, 5900 KiB

Open AccessEditor’s ChoiceArticle

Optical Trapping of Chiral Particles by Dual Laser Beams

by Jing Bai, Cheng-Xian Ge and Zhen-Sen Wu

Photonics 2023, 10(8), 905; https://doi.org/10.3390/photonics10080905 - 4 Aug 2023

Cited by 4 | Viewed by 1784

Abstract

In this paper, an analytical method for studying the radiation force (RF) of chiral spheres generated by dual laser beams is presented under the framework of generalized Lorenz–Mie theory (GLMT). According to the coordinate transformation relations, the arbitrarily incident laser beam is represented [...] Read more.

In this paper, an analytical method for studying the radiation force (RF) of chiral spheres generated by dual laser beams is presented under the framework of generalized Lorenz–Mie theory (GLMT). According to the coordinate transformation relations, the arbitrarily incident laser beam is represented by vector spherical harmonic functions (VSHFs) in the sphere system. The entire induced field expression coefficients of dual laser beams can be obtained by superposition of each illuminated field. Based on the momentum conservation theory, the concrete expression of lateral and axial RF on chiral sphere is derived. The current theories are shown to be valid by comparison with the existing reference. To investigate the stable capture state of chiral sphere, the influences of the corresponding parameters of chiral particles and dual laser beams on the trapping and manipulation are investigated in detail. The analytical study on the RF of dual laser beams on chiral particles is an efficient method for improving optical tweezers technology and can become an encouraging approach to realize the high accuracy operation of chiral particles. Full article

(This article belongs to the Topic Applications of Photonics, Laser, Plasma and Radiation Physics)

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10 pages, 6637 KiB

Open AccessEditor’s ChoiceCommunication

The Effect of Electron Escape Rate on the Nonlinear Dynamics of Quantum Dot Lasers under Optical Feedback

by Qingqing Wang, Zhengmao Wu, Yanfei Zheng and Guangqiong Xia

Photonics 2023, 10(8), 878; https://doi.org/10.3390/photonics10080878 - 28 Jul 2023

Cited by 1 | Viewed by 1189

Abstract

When theoretically investigating the nonlinear dynamics of quantum dot lasers (QDLs), the parameter value of the electron escape rate (C^e) is sometimes approximated to zero to simplify the calculation. However, the value of C^e is dependent on the energy [...] Read more.

When theoretically investigating the nonlinear dynamics of quantum dot lasers (QDLs), the parameter value of the electron escape rate (C^e) is sometimes approximated to zero to simplify the calculation. However, the value of C^e is dependent on the energy interval between the ground state (GS) and the excited state (ES) in the conduction band and is affected by the operation temperature. As a result, such simplified approximation treatments may lead to inaccurate results. In this study, after considering the effect of C^e, we investigate the nonlinear dynamics of QDLs with and without optical feedback based on the asymmetric electron-hole carrier rate equation model. The simulation results show that without optical feedback, the lasing conditions for ES and GS in free-running QDLs are dependent on the value of C^e. A larger C^e is more helpful for the ES emission, and the GS emission will stop lasing if C^e is large enough. Through analyzing the dynamical characteristics of GS and ES in QDLs with optical feedback under different C^e values, it can be found that the dynamical characteristics are strongly correlative with C^e. Full article

(This article belongs to the Special Issue Lasers and Dynamic of Systems)

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15 pages, 2130 KiB

Open AccessEditor’s ChoiceArticle

High-Order Harmonics Generation in Selenium-Containing Plasmas

by Rashid A. Ganeev

Photonics 2023, 10(7), 854; https://doi.org/10.3390/photonics10070854 - 24 Jul 2023

Cited by 4 | Viewed by 1166

Abstract

The studies of the high-order harmonics generated in Se-containing plasmas are reported. The ablation of selenium in a vacuum allowed for the formation of a plasma demonstrating high-order harmonics generation and resonance enhancement of the harmonic at the shortest wavelength reported so far [...] Read more.

The studies of the high-order harmonics generated in Se-containing plasmas are reported. The ablation of selenium in a vacuum allowed for the formation of a plasma demonstrating high-order harmonics generation and resonance enhancement of the harmonic at the shortest wavelength reported so far (λ ≈ 22.9 nm, E_ph ≈ 54.14 eV). This harmonic corresponds to the 35th order of the 800-nm-class lasers. The influence of the presence of selenium in the molecular state (ZnSe and HgSe) on the suppression of the resonance effect during harmonics generation in plasma is studied. The enhanced 35th harmonic was analyzed by different methods of plasma formation using nanosecond, picosecond, and femtosecond pulses. The enhancement factor of the resonance-enhanced harmonic was measured to be 32× compared with the neighboring lower-order harmonics in the case of the picosecond-pulses-induced Se plasma. The role of the strong ionic transition of Se in the region of 22.7 nm in the observation of the resonance-induced enhancement of a single harmonic is discussed. Full article

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14 pages, 797 KiB

Open AccessEditor’s ChoiceReview

Atmospheric Pre-Compensation of Ground-to-Space Communications with Adaptive Optics: Past, Present and Future—A Field Review

by Noelia Martinez

Photonics 2023, 10(7), 858; https://doi.org/10.3390/photonics10070858 - 24 Jul 2023

Cited by 3 | Viewed by 2576

Abstract

Conventionally used in astronomy, adaptive optics (AO) systems measure and correct for turbulence and, therefore, have the capability to mitigate the impact of the atmosphere on the ground-to-space communication links. Historically, there have been two main streams, respectively, advocating to use or not [...] Read more.

Conventionally used in astronomy, adaptive optics (AO) systems measure and correct for turbulence and, therefore, have the capability to mitigate the impact of the atmosphere on the ground-to-space communication links. Historically, there have been two main streams, respectively, advocating to use or not use adaptive optics on optical communications. This paper aims to present a comprehensive review of the field of AO-based uplink pre-compensation. It will cover the technical challenges associated with uplink correction, provide an overview of the state-of-the-art research and demonstrations from the early days to the present, and discuss the future prospects of AO-based uplink pre-compensation and potential trade-offs between performance, cost, and operational considerations. Full article

(This article belongs to the Special Issue New Perspectives in Free-Space Optical Communications and Networks)

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15 pages, 6480 KiB

Open AccessEditor’s ChoiceArticle

Research on Indoor Visible Light Location Based on Fusion Clustering Algorithm

by Chenghu Ke, Yuting Shu and Xizheng Ke

Photonics 2023, 10(7), 853; https://doi.org/10.3390/photonics10070853 - 23 Jul 2023

Cited by 2 | Viewed by 1495

Abstract

Aiming at the problem of large positioning errors in the boundary area, a new location fingerprint location method based on a fusion clustering algorithm is proposed. This clustering-based method embodies the idea of rough location first and then fine location. Firstly, the edge [...] Read more.

Aiming at the problem of large positioning errors in the boundary area, a new location fingerprint location method based on a fusion clustering algorithm is proposed. This clustering-based method embodies the idea of rough location first and then fine location. Firstly, the edge regions of the received signal strength (RSS) samples which are greatly affected by reflection are divided using the k-medoids algorithm, and then the center part is clustered via density-based spatial clustering of applications with noise (DBSCAN). In the actual location estimation stage, the points to be measured can only be located in one of the classified areas, and combined with the optimal k-nearest neighbor algorithm (WOKNN) to match the location. The results show that the average positioning error of the algorithm is 13 cm in an indoor environment of 5 m × 5 m × 3 m. Compared with the traditional method without clustering, the positioning accuracy of the edge area is increased by 21%, and the overall improvement is 33.8%, which proves that the proposed algorithm effectively improves the efficiency of real-time positioning and indoor positioning accuracy. Full article

(This article belongs to the Special Issue Application of Adaptive Optics Theory and Technology in Optical Wireless Communication)

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10 pages, 3291 KiB

Open AccessEditor’s ChoiceCommunication

Efficient 1054 nm Raman Random Fiber Laser

by Pan Wang, Shengtao Lin, Jiaojiao Zhang, Xingyu Bao, Longqun Ni, Yifei Qi and Zinan Wang

Photonics 2023, 10(7), 851; https://doi.org/10.3390/photonics10070851 - 22 Jul 2023

Cited by 4 | Viewed by 1828

Abstract

Low–coherence laser is regarded as the key to mitigating laser–plasma instability (LPI) in laser–driven inertial confinement fusion (ICF), where LPI can decrease the laser energy coupled to the target. With the merits of low coherence, high spectral stability, and flexible output characteristics, the [...] Read more.

Low–coherence laser is regarded as the key to mitigating laser–plasma instability (LPI) in laser–driven inertial confinement fusion (ICF), where LPI can decrease the laser energy coupled to the target. With the merits of low coherence, high spectral stability, and flexible output characteristics, the Raman random fiber laser (RRFL) is considered to be a candidate light source in ICF. In this paper, the 1054 nm RRFL with high slope efficiency is achieved for the first time. In the RRFL pump source design section, we have optimized the ytterbium–doped fiber (YDF) length by simulation and amplified the power by Master Oscillator Power Amplifier (MOPA) to realize a 1011 nm YDF laser with 47.3 dB optical signal–to–noise ratio (OSNR). In terms of RRFL cavity design, a fiber loop mirror and Rayleigh scattering in the HI 1060 Flex fiber provide wideband point feedback and random distributed feedback, respectively. Based on this system, we achieve an RRFL output with 0.4 nm half–maximum full width, 182% slope efficiency, and 41.3 dB OSNR. This work will provide guidance for the application of RRFL in high–energy–density physics research. Full article

(This article belongs to the Special Issue High Power Fiber Laser and Amplifiers)

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10 pages, 1770 KiB

Open AccessEditor’s ChoiceArticle

All-Fiber Narrow-Bandwidth Mode-Locked Laser Based on Polarization-Dependent Helical Long-Period Grating

by Ying Wan, Chen Jiang, Zuxing Zhang, Yaya Mao, Jianxin Ren, Jianxiang Wen and Yunqi Liu

Photonics 2023, 10(7), 842; https://doi.org/10.3390/photonics10070842 - 21 Jul 2023

Cited by 2 | Viewed by 1963

Abstract

As a crucial component of nonlinear polarization rotation (NPR) mode locking, optical fiber gratings offer advantages such as polarization modulation capability, stability, fiber compatibility, and preparation maturity, making them a vital technological foundation for achieving NPR mode locking. Here, a polarization-maintaining fiber helical [...] Read more.

As a crucial component of nonlinear polarization rotation (NPR) mode locking, optical fiber gratings offer advantages such as polarization modulation capability, stability, fiber compatibility, and preparation maturity, making them a vital technological foundation for achieving NPR mode locking. Here, a polarization-maintaining fiber helical long-period grating (PMF-HLPG) was designed and fabricated as a polarizer using the

{CO}_{2}

-laser direct-write technique to realize the NPR effect. A homemade fiber Bragg grating (FBG) was also introduced into the laser system to enable a narrow-bandwidth lasing output and wavelength tunability. Based on the PMF-HLPG and FBG mentioned above, an all-fiber mode-locked laser with a spectra bandwidth of 0.15 nm was constructed to generate stable short pulses with a fundamental repetition rate of 12.7122 MHz and a pulse duration of 30.08 ps. In particular, its signal-to-noise ratio is up to 84.5 dB, showing the high stability of the laser. Further, the operating wavelength of the laser can be tuned from 1559.65 nm to 1560.29 nm via heating the FBG while maintaining its mode-locked state with stability. The results indicate that the PMF-HLPG could be used as a polarizer to meet the NPR mechanism for ultrashort pulse laser applications in optical communication, optical sensing, and biomedical imaging. Full article

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8 pages, 4421 KiB

Open AccessEditor’s ChoiceCommunication

Photonic-Assisted Microwave Frequency Measurement Using High Q-Factor Microdisk with High Accuracy

by Mengyao Zhao, Wenyu Wang, Lei Shi, Chicheng Che and Jianji Dong

Photonics 2023, 10(7), 847; https://doi.org/10.3390/photonics10070847 - 21 Jul 2023

Cited by 4 | Viewed by 1928

Abstract

Frequency measurement plays a crucial role in radar, communication, and various applications. The photonic-assisted frequency measurement method offers several advantages, including resistance to electromagnetic interference, broad bandwidth, and low power consumption. Notably, frequency-to-time mapping enables the measurement of various microwave signal types, such [...] Read more.

Frequency measurement plays a crucial role in radar, communication, and various applications. The photonic-assisted frequency measurement method offers several advantages, including resistance to electromagnetic interference, broad bandwidth, and low power consumption. Notably, frequency-to-time mapping enables the measurement of various microwave signal types, such as single-frequency, multiple-frequency, frequency hopping, and chirped signals. However, the accuracy of this method is currently limited due to the absence of resonant devices with high-quality factors, which are essential for achieving higher-precision measurements. In this work, a frequency measurement method based on an ultrahigh-quality-factor microdisk is proposed. By establishing a correlation between the time difference and the frequency to be measured, a reduction in measurement error to below 10 MHz within a frequency measurement range of 3 GHz is realized. Our work introduces a new approach to frequency measurement using optical devices, opening new possibilities in this field. Full article

(This article belongs to the Special Issue Microwave Photonic Techniques)

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10 pages, 4213 KiB

Open AccessEditor’s ChoiceCommunication

Study on Cortisol Sensing Principle Based on Fluorophore and Aptamer Competitive Assay on Polymer Optical Fiber

by Vivek Semwal, Jonas Højgaard, Emil Møller, Ole Bang and Jakob Janting

Photonics 2023, 10(7), 840; https://doi.org/10.3390/photonics10070840 - 20 Jul 2023

Cited by 1 | Viewed by 2292

Abstract

In this study, we present a polymer optical fiber fluorophore/aptamer competitive assay-based cortisol sensing principle. We developed a low-cost, two-fiber perpendicular design for fluorophore-based sensing with less input light interference and high output signal intensity. The design is suitable for narrow stokes shift [...] Read more.

In this study, we present a polymer optical fiber fluorophore/aptamer competitive assay-based cortisol sensing principle. We developed a low-cost, two-fiber perpendicular design for fluorophore-based sensing with less input light interference and high output signal intensity. The design is suitable for narrow stokes shift fluorophores. We have demonstrated the cortisol sensing principle based on the competition between tagged and normal cortisol. To date, the sensing design has exhibited a slow response, and we identified possible modifications for improvement. Our estimation shows that with miniaturization and a modified sensor assay compartment design, a less than one-hour response time can be achieved. The reported sensing principle and low-cost new design will be helpful for the future development of fluorophore-based fiber optic aptasensors that can potentially be used in a wet environment for online sensing. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Photonics Sensors)

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9 pages, 2483 KiB

Open AccessEditor’s ChoiceCommunication

Non-Contact Real-Time Measurement of Refractive Index of Flowing Liquid Based on Optical Coherence Tomography

by Hongbo Fu, Weijian Gao, Zixin Lin, Zhemin Zeng, Wen Shi and Jian Zhang

Photonics 2023, 10(7), 841; https://doi.org/10.3390/photonics10070841 - 20 Jul 2023

Cited by 1 | Viewed by 1961

Abstract

The refractive index (RI) is one of the liquid’s most important physical parameters of liquid. The change of RI usually indicates the change of liquid properties, and this relation leads to broad application. This paper proposes a method based on optical coherence tomography [...] Read more.

The refractive index (RI) is one of the liquid’s most important physical parameters of liquid. The change of RI usually indicates the change of liquid properties, and this relation leads to broad application. This paper proposes a method based on optical coherence tomography (OCT) to measure the RI of liquid in real time. A series of targeted image-processing techniques play a vital role in this method. Benefiting from the advantages of OCT, this method does not require the operators to come into direct contact with liquids. Moreover, the principles and techniques adopted in this method imply that the measuring range of RI of unknown liquids is unlimited. The effectiveness of this method is validated by the experiment measuring the RI of sucrose liquids with gradient concentration. Another experiment thoroughly verifies this method’s feasibility in predicting sucrose concentration based on real-time measured RI. This simple and easy proposed method indicates an immense potential application prospect in the industry and scientific research. Full article

(This article belongs to the Special Issue Advanced Techniques in Biomedical Optical Imaging)

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10 pages, 4068 KiB

Open AccessEditor’s ChoiceCommunication

Effect of Contact Angle on Friction Properties of Superhydrophobic Nickel Surface

by Junyuan Huang, Zhiwei Zhu, Ling Zhang, Dongdong Guo, Zhen Niu and Wei Zhang

Photonics 2023, 10(7), 829; https://doi.org/10.3390/photonics10070829 - 17 Jul 2023

Cited by 3 | Viewed by 1952

Abstract

Due to their excellent performance, superhydrophobic materials have received a lot of attention and research in friction reduction and wear resistance. However, the effect of different contact angles of superhydrophobicity on friction and wear properties has not been thoroughly studied. In this paper, [...] Read more.

Due to their excellent performance, superhydrophobic materials have received a lot of attention and research in friction reduction and wear resistance. However, the effect of different contact angles of superhydrophobicity on friction and wear properties has not been thoroughly studied. In this paper, a nanosecond pulsed laser was used to realize the preparation of a superhydrophobic nickel surface, which indeed reduced the coefficient of friction but also increased the wear volume when compared to the unprocessed surface. As the contact angle of the superhydrophobic nickel surface increased, the coefficient of friction gradually increased, and the wear volume decreased gradually in superhydrophobic nickel surfaces. When the laser energy density was 1 J/cm², the contact angle was 150.3° and the minimum friction coefficient was 0.4. However, when the laser energy density was 50 J/cm², the maximum contact angle was 156.4° and the minimum wear volume was 4.23 × 10⁷ μm³. The friction direction also influenced the tribological properties of the superhydrophobic-textured surface. This method makes it possible to process superhydrophobic surfaces with more suitable friction and wear properties. Full article

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

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9 pages, 1961 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Large Area Wide Bandwidth THz Phase Shifter Plate for High Intensity Field Applications

by Can Koral, Zahra Mazaheri and Antonello Andreone

Photonics 2023, 10(7), 825; https://doi.org/10.3390/photonics10070825 - 15 Jul 2023

Cited by 2 | Viewed by 1472

Abstract

We present the design, fabrication, and experimental test of a THz all-dielectric phase shifter plate. The design consists of two wave plate zones coupled in a perpendicular orientation with respect to each other. A large surface area device is realized by an additive [...] Read more.

We present the design, fabrication, and experimental test of a THz all-dielectric phase shifter plate. The design consists of two wave plate zones coupled in a perpendicular orientation with respect to each other. A large surface area device is realized by an additive manufacturing technique using Acrylonitrile Butadiene Styrene (ABS). Its characteristics are analytically evaluated and experimentally measured in the THz band using time domain spectroscopy and imaging routines. The proposed design enables the creation of quasi-ideal phase retardation in between the two planes with good uniformity on a large surface area. We also achieve the flexibility to select the plane of symmetry around the chosen central axes of choice with a sensitive control over the electromagnetic field polarization direction without inducing any temporal shifts in between the wave front components of the traversed beam. Due to its inherent simplicity and robustness, the phase shifter can be easily scaled at higher frequencies and potentially used in several advanced applications, including free-electron laser (FEL) systems where an accurate polarization control of high intensity beams is required. Full article

(This article belongs to the Special Issue Terahertz Spectroscopy and Imaging)

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10 pages, 5044 KiB

Open AccessEditor’s ChoiceCommunication

Engineering Substrate-Mediated Localized Surface Plasmons in Gold Nanodiscs

by Anisha Chirumamilla, Maria H. Salazar, Deyong Wang, Peter K. Kristensen, Duncan S. Sutherland, Manohar Chirumamilla, Vladimir N. Popok and Kjeld Pedersen

Photonics 2023, 10(7), 821; https://doi.org/10.3390/photonics10070821 - 14 Jul 2023

Viewed by 1655

Abstract

A variety of nanostructures capable of generating strong local electromagnetic fields (hot spots) in interaction with radiation have been under intensive investigation towards plasmonic applications in surface-enhanced Raman scattering (SERS), biosensing, broadband absorbers, thermophotovoltaics, photocatalysis, etc. In many cases, these nanostructures are formed [...] Read more.

A variety of nanostructures capable of generating strong local electromagnetic fields (hot spots) in interaction with radiation have been under intensive investigation towards plasmonic applications in surface-enhanced Raman scattering (SERS), biosensing, broadband absorbers, thermophotovoltaics, photocatalysis, etc. In many cases, these nanostructures are formed on a surface or embedded into a near-surface layer of the dielectric substrate, making some part of the field dissipate into the bulk and not contribute to the desired plasmonic functionality. To reduce such losses, the interface between the metallic nanostructures and the dielectric environment should be engineered. In the current work, Au nanodiscs are fabricated on Si posts of very small diameter (pin-shaped structures), enabling them to decouple the strong optical near fields localized at the nanodiscs from the bulk Si substrate. The Si post diameter is optimized by adjusting the gas flow rates in reactive-ion etching, resulting in a minimum post diameter of 20 nm at the nanodisc interface. The effect of this diameter on the localized surface plasmon resonance of the nanodisc is investigated with linear optical spectroscopic measurements, where a significant spectral blue shift of the resonance band is noticed compared to similar discs formed on bulk Si surface. The experimental results are compared with modelling where a 3-fold increase in the electric field enhancement is demonstrated. The fabricated pin-shaped nanostructures are tested in SERS measurements showing a significant increase in the enhancement factor in the order of 10⁶. Thus, this work suggests a way of engineering 3D morphology to tune the substrate influence on the plasmonic properties of nanostructures and to develop efficient nanofabrication technologies. Full article

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11 pages, 2282 KiB

Open AccessEditor’s ChoiceArticle

Two-Stage Link Loss Optimization of Divergent Gaussian Beams for Narrow Field-of-View Receivers in Line-of-Sight Indoor Downlink Optical Wireless Communication (Invited)

by Xinda Yan, Yuzhe Wang, Chao Li, Fan Li, Zizheng Cao and Eduward Tangdiongga

Photonics 2023, 10(7), 815; https://doi.org/10.3390/photonics10070815 - 13 Jul 2023

Cited by 4 | Viewed by 1877

Abstract

The predominant focus of research in high-speed optical wireless communication (OWC) lies in line-of-sight (LOS) links with narrow infrared beams. However, the implementation of precise tracking and steering necessitates delicate active devices, thereby presenting a formidable challenge in establishing a cost-effective wireless transmission. [...] Read more.

The predominant focus of research in high-speed optical wireless communication (OWC) lies in line-of-sight (LOS) links with narrow infrared beams. However, the implementation of precise tracking and steering necessitates delicate active devices, thereby presenting a formidable challenge in establishing a cost-effective wireless transmission. Other than using none-line-of-sight (NLOS) links with excessive link losses and multi-path distortions, the simplification of the tracking and steering process can be alternatively achieved through the utilization of divergent optical beams in LOS. This paper addresses the issue by relaxing the stringent link budget associated with divergent Gaussian-shaped optical beams and narrow field-of-view (FOV) receivers in LOS OWC through the independent optimization of geometrical path loss and fiber coupling loss. More importantly, the geometrical path loss is effectively mitigated by modifying the transverse intensity distribution of the optical beam using manipulations of multi-mode fibers (MMFs) in an all-fiber configuration. In addition, the sufficiently excited higher order modes (HOMs) of MMFs enable a homogenized distribution of received optical powers (ROPs) within the coverage area, which facilitates the mobility of end-users. Comparative analysis against back-to-back links without free-space transmission demonstrates the proposed scheme’s ability to achieve low power penalties. With the minimized link losses, experimental results demonstrate a 10 Gbps error-free (BER < 10⁻¹³) LOS OWC downlink transmission at 2.5 m over an angular range of 10° × 10° without using any optical pre-amplifications at a typical PIN receiver. The proposed scheme provides a simple and low-cost solution for high-speed and short-range indoor wireless applications. Full article

(This article belongs to the Special Issue Advances in Visible Light Communication)

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19 pages, 5968 KiB

Open AccessEditor’s ChoiceReview

Principle and Recent Development in Photonic Time-Stretch Imaging

by Guoqing Wang, Yuan Zhou, Rui Min, E Du and Chao Wang

Photonics 2023, 10(7), 817; https://doi.org/10.3390/photonics10070817 - 13 Jul 2023

Cited by 3 | Viewed by 2192

Abstract

Inspiring development in optical imaging enables great applications in the science and engineering industry, especially in the medical imaging area. Photonic time-stretch imaging is one emerging innovation that attracted a wide range of attention due to its principle of one-to-one-to-one mapping among space-wavelength-time [...] Read more.

Inspiring development in optical imaging enables great applications in the science and engineering industry, especially in the medical imaging area. Photonic time-stretch imaging is one emerging innovation that attracted a wide range of attention due to its principle of one-to-one-to-one mapping among space-wavelength-time using dispersive medium both in spatial and time domains. The ultrafast imaging speed of the photonics time-stretch imaging technique achieves an ultrahigh frame rate of tens of millions of frames per second, which exceeds the traditional imaging methods in several orders of magnitudes. Additionally, regarding ultrafast optical signal processing, it can combine several other optical technologies, such as compressive sensing, nonlinear processing, and deep learning. In this paper, we review the principle and recent development of photonic time-stretch imaging and discuss the future trends. Full article

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17 pages, 45939 KiB

Open AccessEditor’s ChoiceArticle

Route to Chaos in a Unidirectional Ring of Three Diffusively Coupled Erbium-Doped Fiber Lasers

by José Octavio Esqueda de la Torre, Juan Hugo García-López, Rider Jaimes-Reátegui, Guillermo Huerta-Cuellar, Vicente Aboites and Alexander N. Pisarchik

Photonics 2023, 10(7), 813; https://doi.org/10.3390/photonics10070813 - 12 Jul 2023

Cited by 7 | Viewed by 1282

Abstract

We numerically investigate the dynamics of a ring consisting of three unidirectionally coupled Erbium-Doped Fiber Lasers (EDLFs) without external pump modulation. The study focuses on the system behavior as the coupling strength is varied, employing a six-dimensional mathematical model that includes three variables [...] Read more.

We numerically investigate the dynamics of a ring consisting of three unidirectionally coupled Erbium-Doped Fiber Lasers (EDLFs) without external pump modulation. The study focuses on the system behavior as the coupling strength is varied, employing a six-dimensional mathematical model that includes three variables for laser intensities and three variables for population inversions of all lasers. Our primary objective is to understand the system evolution towards chaos from a stable equilibrium in the ring, considering the impact of increasing coupling strength. To analyze the system’s behavior, we employ various techniques such as time series analysis, power spectra, Poincaré sections, bifurcation diagrams, and Lyapunov exponents. During the transition to chaos, the system undergoes a Hopf bifurcation and a series of torus bifurcations. An essential aspect of this study is the exploration of a rotating wave propagating along the ring, where the wave nature (periodic, quasiperiodic, or chaotic) depends on the coupling strength. Additionally, we observe the coexistence of periodic and chaotic orbits within a specific range of the coupling strength. However, for very strong coupling, this bistability disappears, resulting in a monostable system with a single limit cycle. This regime exhibits potential for applications that demand short laser pulses with a substantial increase in peak power, reaching nearly 20 times higher levels compared to the continuous mode when the lasers are uncoupled. This discovery holds particular importance for optical communication systems, especially considering the attenuation optical signals experience when transmitted over long distances. Full article

(This article belongs to the Special Issue Lasers and Dynamic of Systems)

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20 pages, 4453 KiB

Open AccessEditor’s ChoiceArticle

Hierarchical Feature Enhancement Algorithm for Multispectral Infrared Images of Dark and Weak Targets

by Shuai Yang, Zhihui Zou, Yingchao Li, Haodong Shi and Qiang Fu

Photonics 2023, 10(7), 805; https://doi.org/10.3390/photonics10070805 - 11 Jul 2023

Cited by 1 | Viewed by 1090

Abstract

A multispectral infrared zoom optical system design and a single-frame hierarchical guided filtering image enhancement algorithm are proposed to address the technical problems of low contrast, blurred edges, and weak signal strength of single-spectrum infrared imaging of faint targets, which are easily drowned [...] Read more.

A multispectral infrared zoom optical system design and a single-frame hierarchical guided filtering image enhancement algorithm are proposed to address the technical problems of low contrast, blurred edges, and weak signal strength of single-spectrum infrared imaging of faint targets, which are easily drowned out by noise. The multispectral infrared zoom optical system, based on the theory of complex achromatic and mechanical positive group compensation, can simultaneously acquire multispectral image information for faint targets. The single-frame hierarchical guided filtering image enhancement algorithm, which extracts the background features and detailed features of faint targets in a hierarchical manner and then weights fusion, effectively enhances the target and suppresses the interference of complex background and noise. Solving multi-frame processing increases data storage and real-time challenges. The experimental verification of the optical system design and image enhancement algorithm proposed in this paper separately verified that the experimental enhancement was significant, with the combined use improving Mean Square Error (MSE) by 14.32, Signal-Noise Ratio (SNR) by 11.64, Peak Signal-to-Noise Ratio (PSNR) by 12.78, and Structural Similarity (SSIM) by 14.0% compared to guided filtering. This research lays the theoretical foundation for the research of infrared detection and tracking technology for clusters of faint targets. Full article

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12 pages, 379 KiB

Open AccessEditor’s ChoiceArticle

Energy Efficiency Optimization for SLIPT-Enabled NOMA System

by Danyang Chen, Qingxuan Wang, Jianping Wang, Zhao Li, Shuai Wu, Rui Hao, Kai Fan, Huimin Lu and Jianli Jin

Photonics 2023, 10(7), 791; https://doi.org/10.3390/photonics10070791 - 9 Jul 2023

Cited by 3 | Viewed by 1306

Abstract

For the upcoming sixth generation (6G) networks, the application of simultaneous lightwave information and power transfer (SLIPT) in a non-orthogonal multiple access (NOMA) system is a potential solution to improve energy efficiency (EE). In this paper, we propose a novel SLIPT-enabled NOMA multi-user [...] Read more.

For the upcoming sixth generation (6G) networks, the application of simultaneous lightwave information and power transfer (SLIPT) in a non-orthogonal multiple access (NOMA) system is a potential solution to improve energy efficiency (EE). In this paper, we propose a novel SLIPT-enabled NOMA multi-user system with power splitting (PS) protocol and investigate the effect of system parameters on EE. In addition, to enhance the energy harvesting and information receiving performance of the proposed system, we build up an optimization framework that aims to maximize the EE of the system by jointly optimizing the power allocation of the users and the PS coefficient. We introduce a two-step particle swarm optimization (PSO) algorithm to solve this problem while satisfying the constraints of maximum transmit power, the minimum achievable data rate, and the minimum harvested energy. The numerical results demonstrate the SLIPT-enabled NOMA system using PSO algorithm has significantly improved up to 3.83

\times 10^{6}

bit/s/J in terms of EE over the traditional orthogonal multiple access (OMA) systems. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Communication in China)

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15 pages, 4542 KiB

Open AccessEditor’s ChoiceArticle

Angle-Dependent Transport Theory-Based Ray Transfer Function for Non-Contact Diffuse Optical Tomographic Imaging

by Stephen Hyunkeol Kim, Jingfei Jia and Andreas H. Hielscher

Photonics 2023, 10(7), 767; https://doi.org/10.3390/photonics10070767 - 3 Jul 2023

Viewed by 1307

Abstract

This work presents a generalized angle-dependent ray transfer function that can accurately map the angular and spatial distribution of light intensities on the tissue surface onto a camera image plane in a non-contact camera-based imaging system. The method developed here goes beyond existing [...] Read more.

This work presents a generalized angle-dependent ray transfer function that can accurately map the angular and spatial distribution of light intensities on the tissue surface onto a camera image plane in a non-contact camera-based imaging system. The method developed here goes beyond existing ray transfer models that apply to angle-averaged tomographic data alone. The angle-dependent ray transfer operator was constructed using backward ray tracing based on radiation surface theory. The proposed method was validated using numerical phantoms and experimental data from an actual non-contact imaging system. Full article

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10 pages, 2940 KiB

Open AccessEditor’s ChoiceCommunication

Intrusion Monitoring Based on High Dimensional Random Matrix by Using Ultra-Weak Fiber Bragg Grating Array

by Hongcan Gu, Junbing Huang, Su Wu, Ciming Zhou, Zhiqiang Zhang, Cong Liu and Yandong Pang

Photonics 2023, 10(7), 733; https://doi.org/10.3390/photonics10070733 - 27 Jun 2023

Viewed by 1183

Abstract

In order to ensure that a perimeter security system can work effectively, a convenient and effective event detection algorithm has an important engineering significance. Given the above background, in this paper, we propose a high reliability intrusion event recognition method and vibration sensing [...] Read more.

In order to ensure that a perimeter security system can work effectively, a convenient and effective event detection algorithm has an important engineering significance. Given the above background, in this paper, we propose a high reliability intrusion event recognition method and vibration sensing system, based on ultra-weak fiber Bragg grating array, by using high dimensional random matrix. We obtain a high sensitivity optical interference signal by constructing a patch-matched optical interference system, then compose the demodulated interference signal into a high-dimensional random matrix. The statistical characteristics of the matrix for the Marcenko-Pastur (M-P) law and ring law are used to confirm the presence of intrusion events efficiently, which can reflect the limit spectrum distribution of the high-dimensional random matrix; meanwhile, the abnormal state quantity and moment are obtained. Further, the average spectral radius value is used to judge the fault cause. Field experimental results show that the proposed method can effectively obtain the correct monitoring data for the sensor array. By comparing the monitoring results of normal operation and crusher operation, we can detect the intrusion event in 4.5 s, and the accuracy rate can reach more than 90%, which verifies that the proposed high-dimensional random matrix analysis method can work properly, proving a practical engineering application prospect. Full article

(This article belongs to the Special Issue Optically Active Nanomaterials for Sensing Applications)

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9 pages, 3127 KiB

Open AccessEditor’s ChoiceCommunication

Experimental Generation of Structured Light Beams through Highly Anisotropic Scattering Media with an Intensity Transmission Matrix Measurement

by Qiannan Lei, Haokai Gong, Shijie Tu, Yangjian Cai and Qian Zhao

Photonics 2023, 10(7), 737; https://doi.org/10.3390/photonics10070737 - 27 Jun 2023

Cited by 1 | Viewed by 1692

Abstract

Structured light beams have played important roles in the fields of optical imaging and optical manipulation. However, light fields scatter when they encounter highly anisotropic scattering media, such as biological tissue, which destroys their original structured fields and turns them into speckle fields. [...] Read more.

Structured light beams have played important roles in the fields of optical imaging and optical manipulation. However, light fields scatter when they encounter highly anisotropic scattering media, such as biological tissue, which destroys their original structured fields and turns them into speckle fields. To reconstruct structured light beams through highly anisotropic scattering media, we present a method based on intensity transmission matrix which only relates the input and output light intensity distributions. Compared with the conventional method which relies on the measurement of complex-valued transmission matrix, our scheme is easy to implement, fast and stable. With the assistance of spatial filters, three kinds of structured light beams, Bessel-like beams, vortex beams and cylindrical vector beams, were constructed experimentally through a ZnO scattering layer. The present method is expected to promote optical applications through highly anisotropic scattering media. Full article

(This article belongs to the Special Issue Technologies and Applications of Biophotonics)

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13 pages, 7244 KiB

Open AccessEditor’s ChoiceArticle

First Experimental Demonstration of the Wide-Field Amplitude Surface Plasmon Resonance Microscopy in the Terahertz Range

by Vasiliy Valerievich Gerasimov, Oleg Eduardovich Kameshkov, Alexey Konstantinovich Nikitin, Ildus Shevketovich Khasanov, Alexey Georgievich Lemzyakov, Irina Veniaminovna Antonova, Artem Ilyich Ivanov, Nghiem Thi Ha Lien, Nguyen Trong Nghia, Le Tu Anh, Nguyen Quoc Hung and Ta Thu Trang

Photonics 2023, 10(7), 723; https://doi.org/10.3390/photonics10070723 - 24 Jun 2023

Cited by 1 | Viewed by 1649

Abstract

We have demonstrated the wide-field amplitude surface plasmon resonance (SPR) microscopy technique in the terahertz (THz) range. A Zeonex polymer prism was utilized to excite surface plasmon polaritons (SPPs) through attenuated total reflection (ATR) in an Otto configuration. Coherent quasimonochromatic radiation with a [...] Read more.

We have demonstrated the wide-field amplitude surface plasmon resonance (SPR) microscopy technique in the terahertz (THz) range. A Zeonex polymer prism was utilized to excite surface plasmon polaritons (SPPs) through attenuated total reflection (ATR) in an Otto configuration. Coherent quasimonochromatic radiation with a wavelength of approximately 197 μm, generated by the Novosibirsk free electron laser, was employed. Our results indicate that the SPR microscopy method is applicable for investigating the planar surfaces of semiconductors at THz frequencies, provided that the SPPs’ cutoff frequency is close to the probing radiation frequency. This condition ensures that the propagation length of the SPPs is comparable to the radiation wavelength. By varying the air gap between the prism and the surface under examination, we acquired images of a polypropylene coating 20 µm thick and a graphene coating 35 nm thick on a flat indium antimonide substrate. The boundary between the coated and uncoated regions can be precisely localized through determination of the kink in the reflection coefficient of the THz radiation beam that illuminates the boundary between the regions if the optimal conditions for the generation of the SPPs in the uncoated region are met. Full article

(This article belongs to the Special Issue Terahertz Spectroscopy and Imaging)

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16 pages, 4443 KiB

Open AccessEditor’s ChoiceReview

Sb-Based Low-Noise Avalanche Photodiodes

by Joe C. Campbell, John P. R. David and Seth R. Bank

Photonics 2023, 10(7), 715; https://doi.org/10.3390/photonics10070715 - 22 Jun 2023

Cited by 4 | Viewed by 3150

Abstract

Accurate detection of weak optical signals is a key function for a wide range of applications. A key performance parameter is the receiver signal-to-noise ratio, which depends on the noise of the photodetector and the following electrical circuitry. The circuit noise is typically [...] Read more.

Accurate detection of weak optical signals is a key function for a wide range of applications. A key performance parameter is the receiver signal-to-noise ratio, which depends on the noise of the photodetector and the following electrical circuitry. The circuit noise is typically larger than the noise of photodetectors that do not have internal gain. As a result, a detector that provides signal gain can achieve higher sensitivity. This is accomplished by increasing the photodetector gain until the noise associated with the gain mechanism is comparable to that of the output electrical circuit. For avalanche photodiodes (APDs), the noise that arises from the gain mechanism, impact ionization, increases with gain and depends on the material from which the APD is fabricated. Si APDs have established the state-of-the-art for low-noise gain for the past five decades. Recently, APDs fabricated from two Sb-based III-V compound quaternary materials, Al_xIn_1-xAs_ySb_1-y and Al_xGa_1-xAs_ySb_1-y, have achieved noise characteristics comparable to those of Si APDs with the added benefit that they can operate in the short-wave infrared (SWIR) and extended SWIR spectral regions. This paper describes the materials and device characteristics of these APDs and their performance in different spectral regions. Full article

(This article belongs to the Special Issue Advances in Avalanche Photodiodes)

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9 pages, 3397 KiB

Open AccessEditor’s ChoiceCommunication

All-Polarization-Maintaining, Mode-Locking Fiber Front-End Laser Delivering Both the Picosecond Seed Laser and the Femtosecond Seed Laser

by Yinuo Zhang, Hao Zhang, Kong Gao, Wenchao Qiao, Tianli Feng, Xian Zhao and Yizhou Liu

Photonics 2023, 10(6), 665; https://doi.org/10.3390/photonics10060665 - 8 Jun 2023

Viewed by 1658

Abstract

An ytterbium-doped, mode-locking fiber front-end laser, delivering both a femtosecond seed laser and picosecond seed laser, was demonstrated. The fundamental repetition rate of the 1031 nm mode-locked laser was 32.77 MHz, realized with the all-polarization-maintaining (all-PM) nonlinear amplifying loop mirror (NALM). The femtosecond [...] Read more.

An ytterbium-doped, mode-locking fiber front-end laser, delivering both a femtosecond seed laser and picosecond seed laser, was demonstrated. The fundamental repetition rate of the 1031 nm mode-locked laser was 32.77 MHz, realized with the all-polarization-maintaining (all-PM) nonlinear amplifying loop mirror (NALM). The femtosecond seed laser and the picosecond seed laser were delivered after carefully optimizing the nonlinear amplification process. The corresponding pulse durations were 85 fs and 2.88 ps, with average power of 171 mW and 562.5 mW, respectively. Full article

(This article belongs to the Special Issue Ultrafast Laser Systems)

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21 pages, 9221 KiB

Open AccessEditor’s ChoiceReview

A Review of Advanced Transceiver Technologies in Visible Light Communications

by Cuiwei He and Chen Chen

Photonics 2023, 10(6), 648; https://doi.org/10.3390/photonics10060648 - 3 Jun 2023

Cited by 10 | Viewed by 3492

Abstract

Visible Light Communication (VLC) is an emerging technology that utilizes light-emitting diodes (LEDs) for both indoor illumination and wireless communications. It has the potential to enhance the existing WiFi network and connect a large number of high-speed internet users in future smart home [...] Read more.

Visible Light Communication (VLC) is an emerging technology that utilizes light-emitting diodes (LEDs) for both indoor illumination and wireless communications. It has the potential to enhance the existing WiFi network and connect a large number of high-speed internet users in future smart home environments. Over the past two decades, VLC techniques have made significant strides, resulting in transmission data rates increasing from just a few Mbps to several tens of Gbps. These achievements can be attributed to the development of various transceiver technologies. At the transmitter, LEDs should provide high-quality light for illumination and support wide modulation bandwidths. Meanwhile, at the receiver, optics systems should have functions such as optical filtering, light concentration, and, ideally, a wide field of view (FOV). The photodetector must efficiently convert the optical signal into an electrical signal. Different VLC systems typically consider various transceiver designs. In this paper, we provide a survey of some important emerging technologies used to create advanced optical transceivers in VLC. Full article

(This article belongs to the Special Issue Advances in Visible Light Communication)

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25 pages, 7076 KiB

Open AccessEditor’s ChoiceReview

A Review on Image Sensor Communication and Its Applications to Vehicles

by Ruiyi Huang and Takaya Yamazato

Photonics 2023, 10(6), 617; https://doi.org/10.3390/photonics10060617 - 26 May 2023

Cited by 5 | Viewed by 3051

Abstract

Image sensor communication (ISC), also known as optical camera communication, is a form of visible light communication that utilizes image sensors rather than a single photodiode, for data reception. ISC offers spatial separation properties and robustness to ambient noise, making it suitable for [...] Read more.

Image sensor communication (ISC), also known as optical camera communication, is a form of visible light communication that utilizes image sensors rather than a single photodiode, for data reception. ISC offers spatial separation properties and robustness to ambient noise, making it suitable for outdoor applications such as intelligent transportation systems (ITSs). This review analyzes the research trends in ISC, specifically concerning its application in ITSs. Our focus is on various ISC receivers, including rolling shutter cameras, global shutter high-speed cameras, optical communication image sensors, and event cameras. We analyze how each of these receivers is being utilized in ISC vehicular applications. In addition, we highlight the use of ISC in range estimation techniques and the ability to achieve simultaneous communication and range estimation. By examining these topics, we aim to provide a comprehensive overview of the role of ISC technology in ITSs and its potential for future development. Full article

(This article belongs to the Special Issue Advances in Visible Light Communication)

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10 pages, 1487 KiB

Open AccessEditor’s ChoiceCommunication

Optical Chaos in Saturated Nonlinear Media

by Fuqiang Li, Ziyang Chen, Jie Song, Meng Li and Cibo Lou

Photonics 2023, 10(5), 600; https://doi.org/10.3390/photonics10050600 - 22 May 2023

Cited by 1 | Viewed by 1340

Abstract

In the study of the evolution of Gaussian beam in saturated nonlinear media, it is found that the probability of optical rogue waves changes with the change of nonlinearity. The light intensity distribution on the exit surface of nonlinear medium can be characterized [...] Read more.

In the study of the evolution of Gaussian beam in saturated nonlinear media, it is found that the probability of optical rogue waves changes with the change of nonlinearity. The light intensity distribution on the exit surface of nonlinear medium can be characterized by scintillation index, and the change of rogue wave corresponds to the evolution of scintillation index. The rogue wave probability shows a complex trend with the evolution of nonlinearity. The Lyapunov exponent and power spectrum method are used to determine that the probability of rogue wave is chaotic with nonlinear evolution. Full article

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11 pages, 16655 KiB

Open AccessEditor’s ChoiceArticle

Study on the Influence of Underwater LED Illumination on Bidirectional Underwater Wireless Optical Communication

by Kelin Sun, Biao Han, Jingchuan Yang, Bo Li, Bin Zhang, Kaibin Liu and Chen Li

Photonics 2023, 10(5), 596; https://doi.org/10.3390/photonics10050596 - 21 May 2023

Cited by 4 | Viewed by 1384

Abstract

Underwater wireless optical communication (UWOC) is acknowledged as a useful way to transmit data in the ocean for short-distance applications. Carrying a UWOC device on mobile platforms is quite practical in ocean engineering, which is helpful to exploit its advantages. In application, such [...] Read more.

Underwater wireless optical communication (UWOC) is acknowledged as a useful way to transmit data in the ocean for short-distance applications. Carrying a UWOC device on mobile platforms is quite practical in ocean engineering, which is helpful to exploit its advantages. In application, such a platform needs a camera to observe the surroundings and guide its action. Since the majority of ocean is always dark, active illumination is necessary to imaging. When UWOC works in such an environment, its performance is affected by the illumination light noise. In this paper, we study the influence of underwater LED illumination on bidirectional UWOC with the Monte Carlo method. We simulate forward noise from LED illumination to the opposite receiver in the cooperative terminal, and the backscattering noise on the adjacent receiver in the same terminal. The results show that the forward noise is reduced with the increase of theabsorption coefficient, scattering coefficient, transmitting distance, and separated distance between receiver and the optical axis of LED. However, it becomes greater with the field of view (FOV) of the receiver. The backscattering noise is reduced with the increase of the absorption coefficient and separated distance between receiver and LED. However, it becomes greater with the FOV and scattering coefficient, while it has little relation with transmitting distance. In order to reduce these two kinds of noises, besides inserting an optical filter in the receivers and narrowing their FOV, the optical axis of LED light should keep away from the receivers. The results in this paper are helpful for UWOC application. Full article

(This article belongs to the Special Issue Focus on Nonlinear Processing and Detection Technologies of Weak Optical Signal)

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9 pages, 1501 KiB

Open AccessEditor’s ChoiceCommunication

Photoresponse of Graphene Channel in Graphene-Oxide–Silicon Photodetectors

by Kuo-Chih Lee, Yu-Hsien Chuang, Chen-Kai Huang, Hui Li, Guo-En Chang, Kuan-Ming Hung and Hung Hsiang Cheng

Photonics 2023, 10(5), 568; https://doi.org/10.3390/photonics10050568 - 12 May 2023

Viewed by 1894

Abstract

Graphene-on-silicon photodetectors exhibit broadband detection capabilities with high responsivities, surpassing those of their counterpart semiconductors fabricated purely using graphene or Si. In these studies, graphene channels were considered electrically neutral, and signal amplification was typically attributed to the photogating effect. By contrast, herein, [...] Read more.

Graphene-on-silicon photodetectors exhibit broadband detection capabilities with high responsivities, surpassing those of their counterpart semiconductors fabricated purely using graphene or Si. In these studies, graphene channels were considered electrically neutral, and signal amplification was typically attributed to the photogating effect. By contrast, herein, we show graphene channels to exhibit p-type characteristics using a structure wherein a thin oxide layer insulated the graphene from Si. The p-type carrier concentration is higher (six-times) than the photoaging-induced carrier concentration and dominates the photocurrent. Additionally, we demonstrate photocurrent tunability in the channel. By operating this device under a back-gated bias, photocurrent tuning is realized with not only amplification but also attenuation. Gate amplification produces a current equal to the photogating current at a low bias (0.2 V), and it is approximately two orders of magnitude larger at a bias of 2 V, indicating the operation effectiveness. Meanwhile, photocurrent attenuation enables adjustments in the detector output for compatibility with read-out circuits. A quantification model of gate-dependent currents is further established based on the simulation model used for metal–oxide–semiconductor devices. Thus, this study addresses fundamental issues concerning graphene channels and highlights the potential of such devices as gate-tunable photodetectors in high-performance optoelectronics. Full article

(This article belongs to the Special Issue Advanced Photonic Sensing and Measurement)

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15 pages, 3379 KiB

Open AccessEditor’s ChoiceReview

Review of 2 × 2 Silicon Photonic Switches

by Wencheng Yue, Yan Cai and Mingbin Yu

Photonics 2023, 10(5), 564; https://doi.org/10.3390/photonics10050564 - 11 May 2023

Cited by 7 | Viewed by 4152

Abstract

With the advent of 5G, artificial intelligence (AI), Internet of Things (IoT), cloud computing, Internet plus, and so on, data traffic is exploding and higher requirements are put forward for information transmission and switching. Traditional switching requires optical/electrical/optical conversions, which brings additional power [...] Read more.

With the advent of 5G, artificial intelligence (AI), Internet of Things (IoT), cloud computing, Internet plus, and so on, data traffic is exploding and higher requirements are put forward for information transmission and switching. Traditional switching requires optical/electrical/optical conversions, which brings additional power consumption and requires the deployment of large amounts of cooling equipment. This increases the cost and complexity of the system. Moreover, limited by the electronic bottleneck, electrical switching will suffer from many problems such as bandwidth, delay, crosstalk, and so on, with the continuous reduction in device footprint. Optical switching does not require optical/electrical/optical conversions and has lower power consumption, larger capacity, and lower cost. Silicon photonic switches received much attention because of their compatibility with the complementary metal-oxide-semiconductor (CMOS) process and are anticipated to be potential candidates to replace electrical switches in many applications such as data center and telecommunication networks. 2 × 2 silicon photonic switches are the basic components to build the large-scale optical switching matrices. Thus, this review article mainly focuses on the principle and state of the art of 2 × 2 silicon photonic switches, including electro-optic switches, thermo-optic switches, and nonvolatile silicon photonic switches assisted by phase-change materials. Full article

(This article belongs to the Section Optical Communication and Network)

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11 pages, 3700 KiB

Open AccessEditor’s ChoiceArticle

Quantum Dot Lasers Directly Grown on 300 mm Si Wafers: Planar and In-Pocket

by Kaiyin Feng, Chen Shang, Eamonn Hughes, Andrew Clark, Rosalyn Koscica, Peter Ludewig, David Harame and John Bowers

Photonics 2023, 10(5), 534; https://doi.org/10.3390/photonics10050534 - 6 May 2023

Cited by 10 | Viewed by 5335

Abstract

We report for the first time the direct growth of quantum dot (QD) lasers with electrical pumping on 300 mm Si wafers on both a planar template and in-pocket template for in-plane photonic integration. O-band lasers with five QD layers were grown with [...] Read more.

We report for the first time the direct growth of quantum dot (QD) lasers with electrical pumping on 300 mm Si wafers on both a planar template and in-pocket template for in-plane photonic integration. O-band lasers with five QD layers were grown with molecular beam epitaxy (MBE) in a 300 mm reactor and then fabricated into standard Fabry–Perot ridge waveguide cavities. Edge-emitting lasers are demonstrated with high yield and reliable results ready for commercialization and scaled production, and efforts to make monolithically integrated lasing cavities grown on silicon-on-insulator (SOI) wafers vertically aligned and coupled to SiN waveguides on the same chip show the potential for 300 mm-scale Si photonic integration with in-pocket direct MBE growth. Full article

(This article belongs to the Special Issue Nanophotonics Pioneer: Prof. Dr. Dieter Bimberg ‘Green Photonics Networks: From VCSELs to Nanophotonics’)

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