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10 pages, 4951 KiB

Open AccessArticle

All Fiber Mach–Zehnder Interferometer Based on Intracavity Micro-Waveguide for a Magnetic Field Sensor

by Maoqing Chen, Qifeng Liu and Yong Zhao

Appl. Sci. 2021, 11(23), 11569; https://doi.org/10.3390/app112311569 - 6 Dec 2021

Cited by 3 | Viewed by 2508

Abstract

A magnetic fluid (MF)-based magnetic field sensor with a filling-splicing fiber structure is proposed. The sensor realizes Mach–Zehnder interference by an optical fiber cascade structure consisting of single mode fiber (SMF), multimode fiber (MMF), and single-hole-dual-core fiber (SHDCF). The core in the cladding [...] Read more.

A magnetic fluid (MF)-based magnetic field sensor with a filling-splicing fiber structure is proposed. The sensor realizes Mach–Zehnder interference by an optical fiber cascade structure consisting of single mode fiber (SMF), multimode fiber (MMF), and single-hole-dual-core fiber (SHDCF). The core in the cladding and the core in the air hole of SHDCF are used as the reference and sensing light path, respectively, and the air hole of SHDCF is filled with magnetic fluid to realize magnetic field measurement based on magnetic controlled refractive index (RI) characteristics. The theoretical feasibility of the proposed sensing structure is verified by Rsoft simulation, the optimized length of SHDCF is determined by optical fiber light transmission experiment, and the SHDCFs are well fused without collapse through the special parameter setting. The results show that the sensitivity of the sensor is −116.1 pm/Gs under a magnetic field of 0~200 Gs with a good long-term operation stability. The proposed sensor has the advantages of high stability, fast response, simple structure, and low cost, which has development potential in the field of miniaturized magnetic field sensing. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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19 pages, 4594 KiB

Open AccessArticle

High-Precision Surface Scattering Measurement System and Uncertainty Analysis Applied in Laser Protective Materials Diagnostics

by Zhen Yang, Yanbo Yang, Yong Zhang, Xinmin Guo, Kaichang Lu and Jianlong Zhang

Appl. Sci. 2021, 11(20), 9457; https://doi.org/10.3390/app11209457 - 12 Oct 2021

Cited by 1 | Viewed by 1967

Abstract

The current measurement system of surface scattering rate applied in laser protective materials has the defects of low accuracy, discontinuous diagnosis region and narrow infrared measuring waveband. In order to make up for these shortcomings, a high-precision material-surface-scattering-rate measurement system based on a [...] Read more.

The current measurement system of surface scattering rate applied in laser protective materials has the defects of low accuracy, discontinuous diagnosis region and narrow infrared measuring waveband. In order to make up for these shortcomings, a high-precision material-surface-scattering-rate measurement system based on a three-hole integrating sphere is proposed, which can realize the high-precision quantitative measurement on any region of coating surface from near-infrared to far-infrared band. Firstly, a new quantitative relationship between the luminous flux received by detector and the surface scattering rate of coating is obtained by modifying the existing integrating sphere scattering model. Secondly, a high-precision scattering characteristic measurement system based on a three-hole integrating sphere is designed and achieved. The influence of the main design parameters of the integrating sphere on the expected measuring accuracy of the system is investigated by using a TracePro simulation. Accordingly, the optimal design parameters of the system are given. Then, the main sources of the relative measurement uncertainty for the scattering rate are investigated experimentally, and four main relative uncertainty factors are evaluated quantitatively. Finally, according to the error propagation theory, the total experimental relative measurement uncertainty of the system is obtained, which is ±2.22% and 26–56% higher than the current measuring accuracy. The new coating-scattering-rate measurement system proposed in this paper can provide an effective experimental detection means for high-precision quantitative measurement and a performance evaluation for laser-protective-coating surface-scattering rate. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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13 pages, 4345 KiB

Open AccessArticle

Terahertz Raman Measurements Using a Spatial Heterodyne Raman Spectrometer

by Yuqi Sun, Xiaotian Li, Jiri Galantu, Qihang Chu, Jun Chen, Zhongkai Liu, Xiaotao Mi, Xuefeng Yao and Pan Li

Appl. Sci. 2021, 11(17), 8094; https://doi.org/10.3390/app11178094 - 31 Aug 2021

Cited by 3 | Viewed by 2614

Abstract

We propose a method of measuring the terahertz (THz) Raman spectra of a material. As Raman spectroscopy is a measurement of the relative frequency spectrum relative to the frequency of the excitation source, sometimes it is not necessary to use an expensive THz [...] Read more.

We propose a method of measuring the terahertz (THz) Raman spectra of a material. As Raman spectroscopy is a measurement of the relative frequency spectrum relative to the frequency of the excitation source, sometimes it is not necessary to use an expensive THz source and THz detector. Instead, an ultraviolet, visible, or infrared excitation source and corresponding detector can be used. A combination of prisms and gratings is used to widen the field of view at high resolution. The resolution of the system is 4.945 cm⁻¹ (0.149 THz), and the spectral range is 2531.84 cm⁻¹ (75.963 THz). We measured the THz Raman spectra of solid powder, aqueous solutions, and mixtures, and studied the effects of environment, container material, and time of measurement on the spectra. The results show that the system is not significantly affected by interference from the water environment and has good stability and repeatability. This method can be applied in many fields such as material detection and environmental protection. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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10 pages, 2449 KiB

Open AccessCommunication

Liquid Crystal-Embedded Hollow Core Fiber Temperature Sensor in Fiber Ring Laser

by Weihao Lin, Shengjie Zhou, Yibin Liu, Mang I. Vai and Liyang Shao

Appl. Sci. 2021, 11(15), 7103; https://doi.org/10.3390/app11157103 - 31 Jul 2021

Cited by 6 | Viewed by 2419

Abstract

An optical fiber temperature sensor based on Mach–Zehnder interferometer and thermo-optic effect of the liquid crystal (LC) in fiber ring laser (FRL) system is proposed and experimentally demonstrated. The LC is infiltrated into the core of hollow core fiber, and the resonant wavelength [...] Read more.

An optical fiber temperature sensor based on Mach–Zehnder interferometer and thermo-optic effect of the liquid crystal (LC) in fiber ring laser (FRL) system is proposed and experimentally demonstrated. The LC is infiltrated into the core of hollow core fiber, and the resonant wavelength is more sensitive to temperature variation due to the interaction between the incident light and the cavity infiltrating liquid crystal with high thermal light coefficient. Meanwhile, the FRL system was further used to make the sensor have good performance in the case of high signal-to-noise ratio (∼35 dB), narrow half-height width (FWHM = 0.15 nm), and high sensitivity in the temperature range from 20 °C to 50 °C, with the maximum sensitivity of 1.318 nm/°C. As far as we know, in the FRL system, the liquid crystal material has a better temperature sensing performance than the previous fiber. Nevertheless, the system has the advantages of good repeatability, low cost, simple production, small volume, high sensitivity. In marine microbial culture and detection, it is necessary to carry out high sensitivity measurement within a small temperature variation range. This reliable and excellent temperature performance has a potential application prospect. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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11 pages, 3478 KiB

Open AccessArticle

Trace CH₄ Gas Detection Based on an Integrated Spherical Photoacoustic Cell

by Yexiang Jiao, Hongji Fan, Zhenfeng Gong, Kai Yang, Feiyang Shen, Ke Chen, Liang Mei, Wei Peng and Qingxu Yu

Appl. Sci. 2021, 11(11), 4997; https://doi.org/10.3390/app11114997 - 28 May 2021

Cited by 25 | Viewed by 3391

Abstract

This paper presents an integrated spherical photoacoustic cell (SPAC) for trace methane (CH₄) gas detection. Theoretical analysis and analogue simulations are carried out to analyze the acoustic field distribution of the SPAC at resonant and non-resonant modes. The finite element simulation [...] Read more.

This paper presents an integrated spherical photoacoustic cell (SPAC) for trace methane (CH₄) gas detection. Theoretical analysis and analogue simulations are carried out to analyze the acoustic field distribution of the SPAC at resonant and non-resonant modes. The finite element simulation results based on COMSOL show that the first-order radial resonant frequency and second-order angular resonant frequency are 24,540 Hz and 18,250 Hz, respectively, which show good agreements with the formula analysis results. The integrated SPAC, together with a high-speed spectrometer and a distributed feedback (DFB) laser source, makes up a photoacoustic (PA) spectroscopy (PAS) system, which is employed for CH₄ detection. The minimum detection limit (MDL) is measured to be 126.9 parts per billion (ppb) at an average time of 1000 s. The proposed SPAC has an integrated, miniaturized and all-optical structure, which can be used for remote and long-distance trace gas detection. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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15 pages, 6541 KiB

Open AccessArticle

Investigation of Stray Radiation Suppression in Infrared Imaging System Using a Novel Broadband and High-Absorption Ceramic Coating

by Zhen Yang, Xinmin Guo, Songtao Lu, Yong Zhang, Haili Hu, Kaichang Lu and Jianlong Zhang

Appl. Sci. 2021, 11(11), 4952; https://doi.org/10.3390/app11114952 - 27 May 2021

Cited by 5 | Viewed by 2311

Abstract

Aiming at addressing the vulnerability of the infrared imaging opto-mechanical system to stray radiation interference caused by an external laser, a new method with a broadband and high-absorptivity ceramic coating on the inner wall of the system is proposed to reduce the stray [...] Read more.

Aiming at addressing the vulnerability of the infrared imaging opto-mechanical system to stray radiation interference caused by an external laser, a new method with a broadband and high-absorptivity ceramic coating on the inner wall of the system is proposed to reduce the stray radiation intensity, which is helpful to improve the imaging quality of the detection image. Based on plasma electrolytic oxidation (PEO) technology, the preparation method and properties of a novel ceramic coating are studied, and a long-wave infrared imaging optical system with high-absorption ceramic coating is designed and developed. It is verified for the first time that the high-absorption ceramic coating can suppress the stray radiation in the infrared opto-mechanical system, and the effect of laser incident power and angle on the stray radiation is investigated. The experimental results show that the ceramic coating can achieve 95.4% high absorption in the wavelength range of 0.2–16 μm, which can obviously suppress the stray radiation in the opto-mechanical system of infrared imaging caused by laser. The calculation of the stray radiation suppression ratio shows that, compared with the case without coating, the stray radiation intensity in the system can be reduced by 70% using the ceramic coating. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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18 pages, 10832 KiB

Open AccessArticle

fNIRS Signal Classification Based on Deep Learning in Rock-Paper-Scissors Imagery Task

by Tengfei Ma, Wentian Chen, Xin Li, Yuting Xia, Xinhua Zhu and Sailing He

Appl. Sci. 2021, 11(11), 4922; https://doi.org/10.3390/app11114922 - 27 May 2021

Cited by 13 | Viewed by 3705

Abstract

To explore whether the brain contains pattern differences in the rock–paper–scissors (RPS) imagery task, this paper attempts to classify this task using fNIRS and deep learning. In this study, we designed an RPS task with a total duration of 25 min and 40 [...] Read more.

To explore whether the brain contains pattern differences in the rock–paper–scissors (RPS) imagery task, this paper attempts to classify this task using fNIRS and deep learning. In this study, we designed an RPS task with a total duration of 25 min and 40 s, and recruited 22 volunteers for the experiment. We used the fNIRS acquisition device (FOIRE-3000) to record the cerebral neural activities of these participants in the RPS task. The time series classification (TSC) algorithm was introduced into the time-domain fNIRS signal classification. Experiments show that CNN-based TSC methods can achieve 97% accuracy in RPS classification. CNN-based TSC method is suitable for the classification of fNIRS signals in RPS motor imagery tasks, and may find new application directions for the development of brain–computer interfaces (BCI). Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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15 pages, 3547 KiB

Open AccessArticle

Simultaneous Measurement Method and Error Analysis of Six Degrees of Freedom Motion Errors of a Rotary Axis Based on Polyhedral Prism

by Dong Ma, Jiakun Li, Qibo Feng, Qixin He, Yaowen Ding and Jianying Cui

Appl. Sci. 2021, 11(9), 3960; https://doi.org/10.3390/app11093960 - 27 Apr 2021

Cited by 6 | Viewed by 2162

Abstract

A novel method is proposed for measuring the six degrees-of-freedom (DOF) geometric motion errors of a rotary axis based on a polyhedral prism. An error-sensitive unit which consists of a polyhedral prism and a planar reflector, is designed to carry out measurement of [...] Read more.

A novel method is proposed for measuring the six degrees-of-freedom (DOF) geometric motion errors of a rotary axis based on a polyhedral prism. An error-sensitive unit which consists of a polyhedral prism and a planar reflector, is designed to carry out measurement of all six DOF errors, including the angular positioning error, the tilt motion error around the Y axis, the tilt motion error around the X axis, the radial motion error along the X and Y axes, and the axial motion error along the Z axis. The mathematical error model, including the six DOF geometric motion errors of the rotary axis, the installation errors between the polyhedral prism and the rotary axis, the manufacturing errors of the polyhedral prism, and the position errors of the sensors, are established. The effectiveness of the proposed method and the compensation model was simulated and experimentally verified. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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14 pages, 5018 KiB

Open AccessArticle

A Fast Point Clouds Registration Algorithm for Laser Scanners

by Guangxuan Xu, Yajun Pang, Zhenxu Bai, Yulei Wang and Zhiwei Lu

Appl. Sci. 2021, 11(8), 3426; https://doi.org/10.3390/app11083426 - 12 Apr 2021

Cited by 43 | Viewed by 4495

Abstract

Point clouds registration is an important step for laser scanner data processing, and there have been numerous methods. However, the existing methods often suffer from low accuracy and low speed when registering large point clouds. To meet this challenge, an improved iterative closest [...] Read more.

Point clouds registration is an important step for laser scanner data processing, and there have been numerous methods. However, the existing methods often suffer from low accuracy and low speed when registering large point clouds. To meet this challenge, an improved iterative closest point (ICP) algorithm combining random sample consensus (RANSAC) algorithm, intrinsic shape signatures (ISS), and 3D shape context (3DSC) is proposed. The proposed method firstly uses voxel grid filter for down-sampling. Next, the feature points are extracted by the ISS algorithm and described by the 3DSC. Afterwards, the ISS-3DSC features are used for rough registration with the RANSAC algorithm. Finally, the ICP algorithm is used for accurate registration. The experimental results show that the proposed algorithm has faster registration speed than the compared algorithms, while maintaining high registration accuracy. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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9 pages, 3404 KiB

Open AccessArticle

Advanced Visualization Polarimetric Imaging: Removal of Water Spray Effect Utilizing Circular Polarization

by Fei Liu, Xuan Li, Pingli Han and Xiaopeng Shao

Appl. Sci. 2021, 11(7), 2996; https://doi.org/10.3390/app11072996 - 26 Mar 2021

Cited by 6 | Viewed by 2384

Abstract

Circular polarization (CP) memory is a well-known phenomenon whereby natural light becomes partially circularly polarized after scattering by water spray several times, and the circularly polarized state can be well preserved within a certain propagation distance. In this study, a CP imaging method [...] Read more.

Circular polarization (CP) memory is a well-known phenomenon whereby natural light becomes partially circularly polarized after scattering by water spray several times, and the circularly polarized state can be well preserved within a certain propagation distance. In this study, a CP imaging method combined with the multi-scale analysis in the frequency domain is proposed to enhance the vision in rainy conditions. The images were first decomposed into multi-scales. CP characteristics of light were employed in the low-frequency parts to improve the quality of images in rainy conditions, and the high-frequency parts compensated specific structure information. Experimental results demonstrate that the proposed method can remove the water spray effect thereby improving the vision of degraded rainy-day images. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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11 pages, 4315 KiB

Open AccessArticle

Shape Optimization of an Open Photoacoustic Resonator

by Said El-Busaidy, Bernd Baumann, Marcus Wolff and Lars Duggen

Appl. Sci. 2021, 11(6), 2571; https://doi.org/10.3390/app11062571 - 13 Mar 2021

Cited by 6 | Viewed by 2232

Abstract

Photoacoustic (PA) measurements with open resonators usually provide poor detection sensitivity due to signal leakage at the resonator opening. We have recently demonstrated three different approaches for modelling the photoacoustic signal of open resonators. In this work, one of the approaches is applied [...] Read more.

Photoacoustic (PA) measurements with open resonators usually provide poor detection sensitivity due to signal leakage at the resonator opening. We have recently demonstrated three different approaches for modelling the photoacoustic signal of open resonators. In this work, one of the approaches is applied for the optimization of the geometry of the T-shaped resonator for improved signal strength and thus sensitivity. The results from the numerical optimization show an increase in the photoacoustic signal by a factor of approximately 7.23. They are confirmed using numerical methods other than the one applied for the optimization and by experimental measurement. The measurement shows an increase in the photoacoustic signal by a factor of approximately 2.34. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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Review

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21 pages, 23163 KiB

Open AccessReview

Noise Measurement and Reduction in Mode-Locked Lasers: Fundamentals for Low-Noise Optical Frequency Combs

by Haochen Tian, Youjian Song and Minglie Hu

Appl. Sci. 2021, 11(16), 7650; https://doi.org/10.3390/app11167650 - 20 Aug 2021

Cited by 18 | Viewed by 5133

Abstract

After five decades of development, mode-locked lasers have become significant building blocks for many optical systems in scientific research, industry, and biomedicine. Advances in noise measurement and reduction are motivated for both shedding new light on the fundamentals of realizing ultra-low-noise optical frequency [...] Read more.

After five decades of development, mode-locked lasers have become significant building blocks for many optical systems in scientific research, industry, and biomedicine. Advances in noise measurement and reduction are motivated for both shedding new light on the fundamentals of realizing ultra-low-noise optical frequency combs and their extension to potential applications for standards, metrology, clock comparison, and so on. In this review, the theoretical models of noise in mode-locked lasers are first described. Then, the recent techniques for timing jitter, carrier-envelope phase noise, and comb-line noise measurement and their stabilization are summarized. Finally, the potential of the discussed technology to be fulfilled in novel optical frequency combs, such as electro-optic (EO) modulated combs, microcombs, and quantum cascade laser (QCL) combs, is envisioned. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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20 pages, 59625 KiB

Open AccessReview

Retina-like Imaging and Its Applications: A Brief Review

by Qun Hao, Yu Tao, Jie Cao, Mingyuan Tang, Yang Cheng, Dong Zhou, Yaqian Ning, Chun Bao and Huan Cui

Appl. Sci. 2021, 11(15), 7058; https://doi.org/10.3390/app11157058 - 30 Jul 2021

Cited by 13 | Viewed by 3613

Abstract

The properties of the human eye retina, including space-variant resolution and gaze characters, provide many advantages for numerous applications that simultaneously require a large field of view, high resolution, and real-time performance. Therefore, retina-like mechanisms and sensors have received considerable attention in recent [...] Read more.

The properties of the human eye retina, including space-variant resolution and gaze characters, provide many advantages for numerous applications that simultaneously require a large field of view, high resolution, and real-time performance. Therefore, retina-like mechanisms and sensors have received considerable attention in recent years. This paper provides a review of state-of-the-art retina-like imaging techniques and applications. First, we introduce the principle and implementing methods, including software and hardware, and describe the comparisons between them. Then, we present typical applications combined with retina-like imaging, including three-dimensional acquisition and reconstruction, target tracking, deep learning, and ghost imaging. Finally, the challenges and outlook are discussed to further study for practical use. The results are beneficial for better understanding retina-like imaging. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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13 pages, 4415 KiB

Open AccessFeature PaperReview

Key Technologies of Photonic Artificial Intelligence Chip Structure and Algorithm

by Li Pei, Zeya Xi, Bing Bai, Jianshuai Wang, Xiaoyan Zuo, Tigang Ning, Jingjing Zheng and Jing Li

Appl. Sci. 2021, 11(12), 5719; https://doi.org/10.3390/app11125719 - 20 Jun 2021

Cited by 3 | Viewed by 3314

Abstract

Artificial intelligence chips (AICs) are the intersection of integrated circuits and artificial intelligence (AI), involving structure design, algorithm analysis, chip fabrication and application scenarios. Due to their excellent ability in data processing, AICs show a long-term industrial prospect in big data services, cloud [...] Read more.

Artificial intelligence chips (AICs) are the intersection of integrated circuits and artificial intelligence (AI), involving structure design, algorithm analysis, chip fabrication and application scenarios. Due to their excellent ability in data processing, AICs show a long-term industrial prospect in big data services, cloud centers, etc. However, with the conceivable exhaustion of Moore’s Law, the size of traditional electronic AICs (EAICs) is gradually approaching the limit, and an architectural update is highly required. Photonic artificial intelligence chips (PAIC) utilize light beam propagation in the silicon waveguide, contributing to a high parallelism configuration, fast calculation speed and low latency. Due to light manipulation, PAICs perform well in anti-electromagnetic interference and energy conservation. This invited paper summarized the recent research on PAICs. The characteristics of different hardware structures are discussed. The current widely used training algorithm is given and the Photonic Design Automatic (PDA) simulation platform is introduced. In addition, the authors’ related work on PAICs is presented and we believe that PAICs may play a critical role in the deployment of data processing technology. Full article

(This article belongs to the Special Issue State-of-the-Art Laser Measurement Technologies)

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