2024

• Record 1 of
  
  Title:High repetition frequency tunability active Q-switched all-fiber laser by multi-gain sub-rings smoothing multipeak pulse and suppressing ASE self-saturation
  
  Author(s):Chen, Xuechun(1,2,3,4); Wang, Nan(1,2,3,4); He, Chaojian(2,3); Xu, Shuang(2,3,4); Ning, Chaoyu(2,3,4); Li, Xinyao(2,3,4); Dong, Zhiyong(2,3); Yang, Yingying(2,3); Yang, Guowen(1); Lin, Xuechun(2,3,4)
  Source: Optics Express  Volume: 32  Issue: 2  DOI: 10.1364/OE.515391  Published: January 15, 2024  
  Abstract:This paper provides a method to effectively suppress the severe ASE self-saturation when achieving high repetition frequency tunability with high output power and narrow pulse width in active Q-switched all-fiber lasers. By studying the regularity of the system’s multi-stable state, we first ensured that the laser system operated in a steady state. Then output avoids uneven distribution of pulse energy or missing pulses due to period bifurcation state or chaos state. By adding multiple gain sub-rings within the cavity, the sub-ring structure itself indirectly mitigates the ASE self-saturation while smoothing the pulse. The method will avoid the severe power loss caused by traditional smoothing methods by adjusting the AOM rising edge time. It will also avoid lowering the ASE lasing threshold at high repetition frequency. Meanwhile, the intra-cavity backward ASE can be effectively absorbed by inserting the gain fiber in the sub-rings to directly mitigate the ASE self-saturation. The system’s continuously adjustable repetition frequency can be as high as over 300 kHz. It ensures that output power above the watt level and a © 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
  Accession Number: 20240415421892
• Record 2 of
  
  Title:Metasurfaces-Empowered Optical Micromanipulation (Invited)
  
  Author(s):Xu, Xiaohao(1,2); Gao, Wenyu(1,2); Li, Tianyue(3,4); Shao, Tianhua(3,4); Li, Xingyi(5); Zhou, Yuan(1,2); Gao, Geze(3,4); Wang, Guoxi(1,2); Yan, Shaohui(1,2); Wang, Shuming(3,4); Yao, Baoli(1,2)
  Source: Guangxue Xuebao/Acta Optica Sinica  Volume: 44  Issue: 5  DOI: 10.3788/AOS231748  Published: March 2024  
  Abstract:Significance Optical micromanipulation utilizes optical force to dynamically control particles, which has the characteristics of non-contact and can be operated in a vacuum environment. Since the invention of optical tweezers in the 1980s, the field has experienced rapid development and has given rise to many emerging research directions, such as holographic optical tweezers, near-field evanescent wave optical tweezers, fiber optic tweezers, optoelectronic tweezers, and photo-induced temperature field optical tweezers, providing rich and powerful tools for fields such as biology, chemistry, nanoscience, and quantum technology. These methods can not only capture, separate, and transport small objects but also allow more precise manipulation, such as the rotation of small objects. However, traditional manipulation methods rely on tightly focused local light, greatly limiting the action range of optical force. In addition, in order to generate a structured light field, larger optical components such as spatial light modulators are usually required, making it difficult to miniaturize and integrate the optical manipulation system. In recent years, metasurfaces have emerged as integrated devices composed of subwavelength nanoantennas, promising new opportunities for optical micromanipulation. This ultra-thin artificial microstructure device can flexiblely control multiple degrees of freedom such as amplitude, phase, and polarization of light, by specially designing the geometric shape, size, and material of its own micro/nanostructure. Compared with traditional optical components such as liquid crystal spatial light modulators, gratings, and lenses, metasurfaces exhibit higher operating bandwidth, structural compactness, and integration. With the merits of miniaturization, integration, and excellent performance in light tailoring, optical metasurfaces have been extensively incorporated into the realm of optical micromanipulation. Especially, owing to their peculiar photomechanical properties, the metasurfaces hold the ability to be actuated by light fields, paving the way to the next generation of light-driven artificial micro-robots. The fast development of this subject indicates that the time is now ripe to overview recent progress in this cross-field. Progress We summarized principles of optical micromanipulation and metasurfaces (Fig. 1) and overviewed meta-manipulation devices, including metasurface-based optical tweezers (Fig. 2), tractor beams (Fig. 5), multifunctional micromanipulation systems (Fig. 3), and metamachines (Figs. 7 and 8). Furthermore, we provided a detailed discussion of novel mechanical effects, such as topological light manipulation, which stems from the topological characteristics of nanostructures (Fig. 6). Conclusions and Prospects We review the cutting-edge developments in the field of optical micromanipulation based on metasurfaces. The metasurface-based micromanipulation technology is expected to evolve toward higher temporal resolution, higher spatial accuracy, and lower manipulation power. To this end, more urgent requirements have been imposed on the underlying design scheme and experimental preparation standards of the metasurface. Although the introduction of metasurfaces has benefited micromanipulation systems and significantly reduced their sizes, there is still much room for further development and improvement in wide bands, multi-dimensional responses, and device thresholds. In terms of micromanipulation systems, the subwavelength-scale structure of metasurfaces will continue to be a key focus of research. Especially in the field of topological light manipulation, it is expected to further expand its research scope, combining non-Abelitan, non-Hermitian, and nonlinear effects to discover new physical phenomena. In the fields of biology and chemistry, metasurface technology is expected to be flexibly applied on smaller scales, even achieving manipulation of single molecule-level objects. This technology is expected to be further applied to the fields such as battery quality inspection and targeted therapy, bringing changes to the basic research and practical applications of energy and life sciences. Specifically, in the development of ultrafast optics, metasurfaces are gradually exhibiting unique advantages. Nanoscale superlattice enables high-resolution spectral measurements, and the design of nonlinear superlattice surfaces can be used to enhance nonlinear effects or generate high-order harmonics, making high time resolution transient micromanipulation technology possible. Overall, the technological evolution from traditional optical micromanipulation to meta-manipulation will continue to drive the vigorous development of nanophotonics. This technological paradigm not only meets the needs of various basic research but also arouses more innovative applications, opening up new prospects for branched sciences and technologies. © 2024 Chinese Optical Society. All rights reserved.
  Accession Number: 20241215789339
• Record 3 of
  
  Title:The role of eye movement signals in non-invasive brain-computer interface typing system
  
  Author(s):Liu, Xi(1,2,3); Hu, Bingliang(1,3); Si, Yang(4,5); Wang, Quan(1,3)
  Source: Medical and Biological Engineering and Computing  Volume:   Issue:   DOI: 10.1007/s11517-024-03070-7  Published: 2024  
  Abstract:Brain-Computer Interfaces (BCIs) have shown great potential in providing communication and control for individuals with severe motor disabilities. However, traditional BCIs that rely on electroencephalography (EEG) signals suffer from low information transfer rates and high variability across users. Recently, eye movement signals have emerged as a promising alternative due to their high accuracy and robustness. Eye movement signals are the electrical or mechanical signals generated by the movements and behaviors of the eyes, serving to denote the diverse forms of eye movements, such as fixations, smooth pursuit, and other oculomotor activities like blinking. This article presents a review of recent studies on the development of BCI typing systems that incorporate eye movement signals. We first discuss the basic principles of BCI and the recent advancements in text entry. Then, we provide a comprehensive summary of the latest advancements in BCI typing systems that leverage eye movement signals. This includes an in-depth analysis of hybrid BCIs that are built upon the integration of electrooculography (EOG) and eye tracking technology, aiming to enhance the performance and functionality of the system. Moreover, we highlight the advantages and limitations of different approaches, as well as potential future directions. Overall, eye movement signals hold great potential for enhancing the usability and accessibility of BCI typing systems, and further research in this area could lead to more effective communication and control for individuals with motor disabilities. Graphical Abstract: This article delves into three pivotal components of the BCI typing system: data, algorithms, and interaction. The system leverages eye movement and EEG data as inputs, which are processed through algorithms for data fusion, feature extraction, and classification to yield output results. Furthermore, it facilitates real-time interaction by providing visual feedback via an efficient user interface. (Figure presented.). © International Federation for Medical and Biological Engineering 2024.
  Accession Number: 20241215789908
• Record 4 of
  
  Title:Multispectral Image Quality Improvement Based on Global Iterative Fusion Constrained by Meteorological Factors
  
  Author(s):Shi, Yuetian(1,2); Fu, Bin(3); Wang, Nan(1,2); Chen, Yaxiong(4); Fang, Jie(5,6)
  Source: Cognitive Computation  Volume: 16  Issue: 1  DOI: 10.1007/s12559-023-10207-7  Published: January 2024  
  Abstract:It has been proven that the refractive index is related to meteorological parameters in physics. The temperature changes the atmospheric and lens refractive indices, resulting in image degradation. Image restoration aims to recover the sharp image from the degraded images. It is also the basis of many computer vision tasks. A series of methods have been explored and used in this area. Sometimes, meteorological factors cause image degradation. Most of the existing image restoration methods do not consider meteorological factors’ influence on image degradation. How meteorological factors affect image quality is not yet known. A multispectral image dataset with corresponding meteorological parameters is presented to solve the problem. We propose a novel multispectral image restoration algorithm using global iterative fusion. The proposed method firstly enhances image edge features through spatial filtering. Then, the Gaussian function is used to constrain the weights between each channel in the image. Finally, a global iterative fusion method is used to fuse image spatial and spectral features to obtain an improved multispectral image. The algorithm explores the impact of meteorological factors on image quality. It considers the impact of atmospheric factors on image quality and incorporates it into the image restoration process. Extensive experimental results illustrate that the method achieves favorable performance on real data. The proposed algorithm is also more robust than other state-of-the-art algorithms. In this paper, we present an algorithm for improving the quality of multispectral images. The proposed algorithm incorporates the influence of meteorological parameters into the image restoration method to better describe the relationship between different spectral channels. Extensive experiments are conducted to validate the effectiveness of the algorithm. Additionally, we investigate the impact of near-surface meteorological parameters on multispectral image quality. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
  Accession Number: 20234314934471
• Record 5 of
  
  Title:Saturable absorption properties and ultrafast photonics applications of HfS3
  
  Author(s):Li, Lu(1); Xue, Ze(1); Pang, Lihui(2); Xiao, Xusheng(3); Yang, Huiran(1); Zhang, Jinniu(1); Zhang, Yaming(1); Zhao, Qiyi(1); Liu, Wenjun(4)
  Source: Optics Letters  Volume: 49  Issue: 5  DOI: 10.1364/OL.513573  Published: March 1, 2024  
  Abstract:In this Letter, we focus on investigating the ultrafast photonics applications of two-layer HfS3 nanosheets. We prepared two-layer HfS3 nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two-layer HfS3-based saturable absorber exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two-layer HfS3 material. Furthermore, we utilized the two-layer HfS3 materials as SAs in an erbium-doped fiber cavity to generate mode-locked laser pulses. We measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio of 77 dB. Overall, our findings demonstrate that the two-layer HfS3 material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS3 materials and highlights their potential for advanced optoelectronic devices. © 2024 Optica Publishing Group.
  Accession Number: 20241015683562
• Record 6 of
  
  Title:Site-Selective Synthesis of Bilayer Graphene on Cu Substrates Using Titanium as a Carbon Diffusion Barrier
  
  Author(s):Song, Qiyang(1); Zhang, Youwei(1,2); Chen, Qiao(1); Wu, Su(1); Yan, Xin(3); He, Kai(3); Gao, Guilong(3); Chen, Qiao(4); Zhang, Butian(1); Wang, Shun(1)
  Source: SSRN  Volume:   Issue:   DOI: 10.2139/ssrn.4707698  Published: January 26, 2024  
  Abstract:Chemical Vapor Deposition (CVD) is a widely used method for graphene synthesis, but it struggles to produce large-area uniform bilayer graphene (BLG). This study introduces a novel approach to meet the demands of large-scale integrated circuit applications, challenging the conventional reliance on uniform BLG over extensive areas. We developed a unique method involving the direct growth of bilayer graphene arrays (BLGA) on Cu foil substrates using patterned Titanium (Ti) as a diffusion barrier. The use of the Ti layer can effectively control carbon atom diffusion through the Cu foil without altering the growth conditions or compromising the graphene quality, thereby showcasing its versatility. The approach allows for targeted BLG growth and achieved a yield of 100% for a 10×10 BLG units array. Then a 10×10 BLG memristor array was fabricated and a yield of 96% was achieved. The performances of these devices show good uniformity, evidenced by the set voltages concentrated around 4V, and a high resistance state (HRS) to low resistance state (LRS) ratio predominantly around 107, reflecting the spatial uniformity of the prepared BLGA. This study provides insight into the BLG growth mechanism and opens new possibilities for BLG-based electronics. © 2024, The Authors. All rights reserved.
  Accession Number: 20240051144
• Record 7 of
  
  Title:Duplex-Hierarchy Representation Learning for Remote Sensing Image Classification
  
  Author(s):Yuan, Xiaobin(1,2); Zhu, Jingping(1); Lei, Hao(3,4); Peng, Shengjun(5); Wang, Weidong(6); Li, Xiaobin(7)
  Source: Sensors  Volume: 24  Issue: 4  DOI: 10.3390/s24041130  Published: February 2024  
  Abstract:Remote sensing image classification (RSIC) is designed to assign specific semantic labels to aerial images, which is significant and fundamental in many applications. In recent years, substantial work has been conducted on RSIC with the help of deep learning models. Even though these models have greatly enhanced the performance of RSIC, the issues of diversity in the same class and similarity between different classes in remote sensing images remain huge challenges for RSIC. To solve these problems, a duplex-hierarchy representation learning (DHRL) method is proposed. The proposed DHRL method aims to explore duplex-hierarchy spaces, including a common space and a label space, to learn discriminative representations for RSIC. The proposed DHRL method consists of three main steps: First, paired images are fed to a pretrained ResNet network for extracting the corresponding features. Second, the extracted features are further explored and mapped into a common space for reducing the intra-class scatter and enlarging the inter-class separation. Third, the obtained representations are used to predict the categories of the input images, and the discrimination loss in the label space is minimized to further promote the learning of discriminative representations. Meanwhile, a confusion score is computed and added to the classification loss for guiding the discriminative representation learning via backpropagation. The comprehensive experimental results show that the proposed method is superior to the existing state-of-the-art methods on two challenging remote sensing image scene datasets, demonstrating that the proposed method is significantly effective. © 2024 by the authors.
  Accession Number: 20240815619383
• Record 8 of
  
  Title:Multi-Dimensional Fusion of Spectral and Polarimetric Images Followed by Pseudo-Color Algorithm Integration and Mapping in HSI Space
  
  Author(s):Guo, Fengqi(1,2); Zhu, Jingping(1); Huang, Liqing(2); Li, Feng(1); Zhang, Ning(3); Deng, Jinxin(1); Li, Haoxiang(1); Zhang, Xiangzhe(1); Zhao, Yuanchen(1); Jiang, Huilin(4); Hou, Xun(1)
  Source: Remote Sensing  Volume: 16  Issue: 7  DOI: 10.3390/rs16071119  Published: April 2024  
  Abstract:Spectral–polarization imaging technology plays a crucial role in remote sensing detection, enhancing target identification and tracking capabilities by capturing both spectral and polarization information reflected from object surfaces. However, the acquisition of multi-dimensional data often leads to extensive datasets that necessitate comprehensive analysis, thereby impeding the convenience and efficiency of remote sensing detection. To address this challenge, we propose a fusion algorithm based on spectral–polarization characteristics, incorporating principal component analysis (PCA) and energy weighting. This algorithm effectively consolidates multi-dimensional features within the scene into a single image, enhancing object details and enriching edge features. The robustness and universality of our proposed algorithm are demonstrated through experimentally obtained datasets and verified with publicly available datasets. Additionally, to meet the requirements of remote sensing tracking, we meticulously designed a pseudo-color mapping scheme consistent with human vision. This scheme maps polarization degree to color saturation, polarization angle to hue, and the fused image to intensity, resulting in a visual display aligned with human visual perception. We also discuss the application of this technique in processing data generated by the Channel-modulated static birefringent Fourier transform imaging spectropolarimeter (CSBFTIS). Experimental results demonstrate a significant enhancement in the information entropy and average gradient of the fused image compared to the optimal image before fusion, achieving maximum increases of 88% and 94%, respectively. This provides a solid foundation for target recognition and tracking in airborne remote sensing detection. © 2024 by the authors.
  Accession Number: 20241615921118
• Record 9 of
  
  Title:Monolithic PMN-39PT nanograting-assisted second harmonic generation enhancement
  
  Author(s):Li, Tianlun(1); Liu, Xin(2); Lu, Yang(3); Gao, Duorui(4); Zhang, Kai(3); Gan, Xuetao(1); Wei, Xiaoyong(2); Xu, Zhuo(2); Zhang, Lei(2)
  Source: Optics Express  Volume: 32  Issue: 6  DOI: 10.1364/OE.510869  Published: March 11, 2024  
  Abstract:Second harmonic generation plays a vital role in frequency conversion which mutually promotes the laser technology and allows the wavebands extension of new coherent source. The monolithic crystals are supposed to be a superior choice for harmonic generation due to long interaction distance, however, the phase-mismatch brought a sharp reduction in the conversion efficiency. Although birefringent phase-matching and quasi-phase-matching techniques are commonly utilized to fill the phase gap in monolithic crystals, these techniques are limited by the natural refractive index of crystal and the domain engineering, respectively. In recent years, subwavelength structures evolve as a flexible scheme to realize phase matching by engineering the geometry features of crystals. Here, structured nanogratings are designed and fabricated on a monolithic PMN-39PT (Pb(Mg1/3Nb2/3)O3-0.39PbTiO3) substrate, a novel ferroelectric crystal with promising optical prospect, for enhancing second harmonic generation, where birefringent or quasi phase-matching is hard to achieve. The nanograting-assisted second harmonic generation enhancement is observed which is not limited by the availability of thin crystalline films. Meanwhile, a boost in the second harmonic signal synchronously promotes the cascading third harmonic generation. This method may provide an alternative solution for enhanced harmonic generation on monolithic substrates and develop potential nonlinear optical materials for frequency conversion. © 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
  Accession Number: 20241215768412
• Record 10 of
  
  Title:Ultralow-Noise K-Band Soliton Microwave Oscillator Using Optical Frequency Division
  
  Author(s):Niu, Rui(1,2,3); Hua, Tian-Peng(2,4); Shen, Zhen(1,2,3); Wang, Yu(1,2,3); Wan, Shuai(1,2,3); Sun, Yu Robert(2,4); Wang, Weiqiang(5,6); Zhao, Wei(5,6); Guo, Guang-Can(1,2,3); Zhang, Wenfu(5,6); Liu, Wen(7); Hu, Shui-Ming(2,3,4); Dong, Chun-Hua(1,2,3)
  Source: ACS Photonics  Volume: 11  Issue: 4  DOI: 10.1021/acsphotonics.3c01247  Published: April 17, 2024  
  Abstract:Compact, low-noise microwave oscillators are required throughout a wide range of applications such as radar systems, wireless networks, and frequency metrology. Optical frequency division via an optical frequency comb provides a powerful tool for low-noise microwave signal generation. Here, we experimentally demonstrate an optical reference down to 26 GHz frequency division based on the dissipative Kerr soliton comb, which is generated on a CMOS-compatible, high-index doped silica glass platform. The optical reference is generated through two continuous wave lasers locked to an ultralow expansion cavity. The dissipative Kerr soliton comb with a repetition rate of 26 GHz acts as a frequency divider to derive an ultralow-noise microwave oscillator, with a phase noise level of −101.3 dBc/Hz at a 100 Hz offset frequency and −132.4 dBc/Hz at a 10 kHz offset frequency. Furthermore, the Allan deviation of the oscillator reaches 6.4 × 10-13 at a 1 s measurement time. Our system is expected to provide an ultralow-noise microwave oscillator for future radar systems and the next generation of wireless networks. © 2024 American Chemical Society.
  Accession Number: 20241215760586
• Record 11 of
  
  Title:Evaporation characteristics of Er3+-doped silica fiber and its application in the preparation of whispering gallery mode lasers
  
  Author(s):Li, Angzhen(1); Ward, Jonathan M.(2); Tian, Ke(3,4); Yu, Jibo(5); She, Shengfei(6); Hou, Chaoqi(6); Guo, Haitao(6); Chormaic, Síle Nic(4,7); Wang, Pengfei(3)
  Source: Optics Express  Volume: 32  Issue: 3  DOI: 10.1364/OE.509662  Published: January 29, 2024  
  Abstract:In this work, the concentration of rare-earth ions in doped silica whispering gallery lasers (WGLs) is controlled by evaporation. The fabrication of WGLs is used to experimentally evaluate the evaporation rate (mol/µm) and ratio (mol/mol) of erbium and silica lost from a doped fiber during heating. Fixed lengths of doped silica fiber are spliced to different lengths of undoped fiber and then evaporated by feeding into the focus of a CO2 laser. During evaporation, erbium ions are precipitated in the doped silica fiber to control the erbium concentration in the remaining SiO2, which is melted into a microsphere. By increasing the length of the undoped section, a critical point is reached where effectively no ions remain in the glass microsphere. The critical point is found using the spectra of the whispering gallery modes in microspheres with equal sizes. From the critical point, it is estimated that, for a given CO2 laser power, 6.36 × 10−21 mol of Er3+ is lost during the evaporation process for every cubic micron of silica fiber. This is equivalent to 1.74 × 10−7 mol of Er3+ lost per mol of SiO2 evaporated. This result facilitates the control of the doping concentration in WGLs and provides insight into the kinetics of laser-induced evaporation of doped silica. © 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
  Accession Number: 20240615502598
• Record 12 of
  
  Title:Enhancing the spatial resolution of time-of-flight based non-line-of-sight imaging via instrument response function deconvolution
  
  Author(s):Wang, Dingjie(1,2); Hao, Wei(1,3,4); Tian, Yuyuan(1,2); Xu, Weihao(1,2); Tian, Yuan(1,2); Cheng, Haihao(2,5); Chen, Songmao(1,3,4); Zhang, Ning(6); Zhu, Wen Hua(7); Su, Xiuqin(1,3,4)
  Source: Optics Express  Volume: 32  Issue: 7  DOI: 10.1364/OE.518767  Published: March 25, 2024  
  Abstract:Non-line-of-sight (NLOS) imaging retrieves the hidden scenes by utilizing the signals indirectly reflected by the relay wall. Benefiting from the picosecond-level timing accuracy, time-correlated single photon counting (TCSPC) based NLOS imaging can achieve theoretical spatial resolutions up to millimeter level. However, in practical applications, the total temporal resolution (also known as total time jitter, TTJ) of most current TCSPC systems exceeds hundreds of picoseconds due to the combined effects of multiple electronic devices, which restricts the underlying spatial resolution of NLOS imaging. In this paper, an instrument response function deconvolution (IRF-DC) method is proposed to overcome the constraints of a TCSPC system s TTJ on the spatial resolution of NLOS imaging. Specifically, we model the transient measurements as Poisson convolution process with the normalized IRF as convolution kernel, and solve the inverse problem with iterative deconvolution algorithm, which significantly improves the spatial resolution of NLOS imaging after reconstruction. Numerical simulations show that the IRF-DC facilitates light-cone transform and frequency-wavenumber migration solver to achieve successful reconstruction even when the system s TTJ reaches 1200 ps, which is equivalent to what was previously possible when TTJ was about 200 ps. In addition, the IRF-DC produces satisfactory reconstruction outcomes when the signal-To-noise ratio (SNR) is low. Furthermore, the effectiveness of the proposed method has also been experimentally verified. The proposed IRF-DC method is highly applicable and efficient, which may promote the development of high-resolution NLOS imaging. © 2024 Optica Publishing Group (formerly OSA). All rights reserved.
  Accession Number: 20241415837517