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Indefinite metacavities coupled to a mirror:bound states in the continuum with anomalous resonance scaling

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Photonics Research 2024年第3期12卷 598-607页

作者： QIANG ZHANG PEIXIANG LI ZHIYUAN GU SHAODING LIU ZEJUN DUAN College of Electronic information and optical Engineering Taiyuan University of TechnologyTaiyuan 030024China key laboratory of Advanced Transducers and Intelligent Control System Ministry of EducationTaiyuan University of TechnologyTaiyuan 030024China

Indefinite metacavities(IMCs)made of hyperbolic metamaterials show great advantages in terms of extremely small mode volume due to large wave vectors endowed by the unique hyperbolic dispersion.However,quality(Q)factors of IMCs are limited by Ohmic loss of metals and radiative loss of leaked waves.Despite the fact that Ohmic loss of metals is inevitable in IMCs,the radiative loss can be further suppressed by leakage engineering.Here we propose a mirror coupled IMC structure which is able to operate at Fabry–Pérot bound states in the continuum(BICs)while the hyperbolic nature of IMCs is retained.At the BIC point,the radiative loss of magnetic dipolar cavity modes in IMCs is completely absent,resulting in a considerably increased Q factor(>90).Deviating from the BIC point,perfect absorption bands(>0.99)along with a strong near-field intensity enhancement(>1.8×10^(4))appear when the condition of critical coupling is almost fulfilled.The proposed BICs are robust to the geometry and material composition of IMCs and anomalous scaling law of resonance is verified during the tuning of optical responses.We also demonstrate that the Purcell effect of the structure can be significantly improved under BIC and quasi-BIC regimes due to the further enhanced Q factor to mode volume ratio.Our results provide a new train of thought to design ultra-small optical nanocavities that may find many applications benefitting from strong light–matter interactions.

关键词： hyperbolic mirror definite

Causal reasoning in typical computer vision tasks

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Science China(Technological Sciences) 2024年第1期67卷 105-120页

作者： ZHANG KeXuan SUN QiYu ZHAO ChaoQiang TANG Yang key laboratory of Advanced Control and Optimization for Chemical Process Ministry of EducationEast China University of Science and TechnologyShanghai 200237China National key laboratory of Air based information Perception and Fusion Luoyang 471000China Luoyang Institute of Electro optical Equipment of Avic Luoyang 471000China

Deep learning has revolutionized the field of artificial intelligence.Based on the statistical correlations uncovered by deep learning-based methods,computer vision tasks,such as autonomous driving and robotics,are growing rapidly.Despite being the basis of deep learning,such correlation strongly depends on the distribution of the original data and is susceptible to uncontrolled factors.Without the guidance of prior knowledge,statistical correlations alone cannot correctly reflect the essential causal relations and may even introduce spurious correlations.As a result,researchers are now trying to enhance deep learningbased methods with causal theory.Causal theory can model the intrinsic causal structure unaffected by data bias and effectively avoids spurious correlations.This paper aims to comprehensively review the existing causal methods in typical vision and visionlanguage tasks such as semantic segmentation,object detection,and image captioning.The advantages of causality and the approaches for building causal paradigms will be summarized.Future roadmaps are also proposed,including facilitating the development of causal theory and its application in other complex scenarios and systems.

关键词： causal reasoning computer vision tasks vision-language tasks semantic segmentation object detection

Dynamic interactive bitwise meta-holography with ultra-high computational and display frame rates

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Opto-Electronic Advances 2024年第1期7卷 36-46页

作者： Yuncheng Liu Ke Xu Xuhao Fan Xinger Wang Xuan Yu Wei Xiong Hui Gao Wuhan National laboratory for Optoelectronics and School of optical and Electronic information Huazhong University of Science and TechnologyWuhan 430074China Optics Valley laboratory Wuhan 430074China

Interactive holography offers unmatched levels of immersion and user engagement in the field of future display.Despite of the substantial progress has been made in dynamic meta-holography,the realization of real-time,highly smooth interactive holography remains a significant challenge due to the computational and display frame rate limitations.In this study,we introduced a dynamic interactive bitwise meta-holography with ultra-high computational and display frame rates.To our knowledge,this is the first reported practical dynamic interactive metasurface holographic system.We spa-tially divided the metasurface device into multiple distinct channels,each projecting a reconstructed sub-pattern.The switching states of these channels were mapped to bitwise operations on a set of bit values,which avoids complex holo-gram computations,enabling an ultra-high computational frame rate.Our approach achieves a computational frame rate of 800 kHz and a display frame rate of 23 kHz on a low-power Raspberry Pi computational platform.According to this methodology,we demonstrated an interactive dynamic holographic Tetris game system that allows interactive gameplay,color display,and on-the-fly hologram creation.Our technology presents an inspiration for advanced dynamic meta-holography,which is promising for a broad range of applications including advanced human-computer interaction,real-time 3D visualization,and next-generation virtual and augmented reality systems.

关键词： interactive display meta-holography bitwise operation ultra-high frame rate

Bright/dark switchable mode-locked fiber laser based on alcohol

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Chinese Optics Letters 2024年第3期22卷 71-75页

作者：张文艳江慧洁杨坤刘楠楠耿利杰郝蕴琦贤天浩詹黎 Henan key laboratory of Magnetoelectronic information Functional Materials School of Physics and Electronic EngineeringZhengzhou University of Light IndustryZhengzhou 450002China State key laboratory of Advanced optical Communication Systems and Networks School of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China

A passively switchable erbium-doped fiber laser based on alcohol as the saturable absorber(SA)has been demonstrated.The SA is prepared by filling the gap between two optical patch cords with alcohol to form a sandwich structure.The modulation depth of the alcohol-SA is measured to be 6.4%.By appropriately adjusting the pump power and the polarization state in the cavity,three kinds of mode-locked pulse patterns can be achieved and switched,including bright pulse,bright/dark soliton pair,and dark pulse.These different soliton emissions all operate at the fundamental frequency state,with a repetition rate of 20.05 MHz and a central wavelength of~1563 nm.To the best of our knowledge,this is the first demonstration of a switchable soliton fiber laser using alcohol as the SA.The experimental results further indicate that organic liquid-like alcohol has great potential for constructing ultrafast lasers.

关键词： optical solitons fiber lasers alcohol pulsed lasers

Dual-band dynamic reconfigurable intelligent surface for signal enhancement in millimeter wave

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Science China(Technological Sciences) 2024年第4期67卷 1133-1138页

作者： YAO HuiMing DU XinRun WANG HengBin GAO Song PANG YaChen ZHENG HaiRong GONG HuiWen LI Yi XU JianChun ZHANG JianHua BI Ke State key laboratory of information Photonics and optical Communications School of ScienceBeijing University of Posts and TelecommunicationsBeijing 100876China Beijing key laboratory of Intelligent Telecommunications Software and Multimedia Beijing University of Posts and TelecommunicationsBeijing 100876China State key laboratory of Networking and Switching Technology Beijing University of Posts and TelecommunicationsBeijing 100876China

Millimeter wave with large bandwidth,high transmission rate,and low delay is considered a reliable alternative to cope with the spectrum shortage.However,the fast attenuation and narrow beam characteristics make it difficult to achieve long-distance or wide-range applications.Here,a 1-bit dual-band reflective reconfigurable intelligent surface(RIS)for signal enhancement in millimeter wave with 16×16 elements is designed,fabricated,and measured.Different from most existent RIS,dynamic programming is realized at two separate frequency bands by integrating the PIN diodes and field-programmable gate array(FPGA).Particularly,the beam deflection,dual-beam,and multi-beam are created based on the coding theory and convolution operation,proving the effectiveness of wavefront manipulation.Moreover,the far-field patterns and signal power with different coding sequences are measured and compared.It is indicated that the received signal power is 6–7 dB stronger than that without coding,which shows good agreement with the desired expectations.The proposed reconfigurable metasurface exhibits great potential in beam forming,making it a promising candidate for progressive wireless communication applications.

关键词： dual-band millimeter wave reconfigurable intelligent surface signal enhancement

Statistical Channel Modeling for Indoor VLC Communications Based on Channel Measurements

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China Communications 2024年第1期21卷 131-147页

作者： Shuo Liu Pan Tang Jianhua Zhang Yue Yin Yu Tong Baobao Liu Guangyi Liu Liang Xia State key laboratory of information Photonics and optical Communications Beijing University of Posts and TelecommunicationsBeijing 100876China State key laboratory of Networking and Switching Technology Beijing University of Posts and TelecommunicationsBeijing 100876China China Mobile Research Institute Beijing 100053China

Visible light communication(VLC)has attracted much attention in the research of sixthgeneration(6G)systems.Furthermore,channel modeling is the foundation for designing efficient and robust VLC systems.In this paper,we present extensive VLC channel measurement campaigns in indoor environments,i.e.,an office and a corridor.Based on the measured data,the large-scale fading characteristics and multipath-related characteristics,including omnidirectional optical path loss(OPL),K-factor,power angular spectrum(PAS),angle spread(AS),and clustering characteristics,are analyzed and modeled through a statistical method.Based on the extracted statistics of the above-mentioned channel characteristics,we propose a statistical spatial channel model(SSCM)capable of modeling multipath in the spatial domain.Furthermore,the simulated statistics of the proposed model are compared with the measured statistics.For instance,in the office,the simulated path loss exponent(PLE)and the measured PLE are 1.96and 1.97,respectively.And,the simulated medians of AS and measured medians of AS are 25.94°and 24.84°,respectively.Generally,the fact that the simulated results fit well with measured results has demonstrated the accuracy of our SSCM.

关键词： channel characteristics channel measurement channel modeling 6G spatial lobe VLC

Deep learning-based channel estimation for wireless ultraviolet MIMO communication systems

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Optoelectronics Letters 2024年第1期20卷 35-41页

作者： ZHAO Taifei SUN Yuxin Lü Xinzhe ZHANG Shuang Faculty of Automation and information Engineering Xi'an University of TechnologyXi'an 710048China Xian key laboratory of Wireless optical Communication and Network Research Xi'an 710048China

To solve the problems of pulse broadening and channel fading caused by atmospheric scattering and turbulence,multiple-input multiple-output(MIMO)technology is a valid way.A wireless ultraviolet(UV)MIMO channel estimation approach based on deep learning is provided in this paper.The deep learning is used to convert the channel estimation into the image processing.By combining convolutional neural network(CNN)and attention mechanism(AM),the learning model is designed to extract the depth features of channel state information(CSI).The simulation results show that the approach proposed in this paper can perform channel estimation effectively for UV MIMO communication and can better suppress the fading caused by scattering and turbulence in the MIMO scattering channel.

关键词： channel scattering MIMO

Excellent energy storage performance in Bi_(0.5)Na_(0.5)TiO_(3)-based lead-free high-entropy relaxor ferroelectrics via B-site modification

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Journal of Advanced Ceramics 2024年第3期13卷 345-353页

作者： Kaihua Yang Gengguang Luo Li Ma Ruoxuan Che Zhiyi Che Qin Feng Zhenyong Cen Xiyong Chen Jiajun Zhou Nengneng Luo State key laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures School of ResourcesEnvironment and MaterialsGuangxi UniversityNanning 530004China School of optical and Electronic information Key Lab of Functional Materials for Electronic Information(B)of Ministry of EducationHuazhong University of Science and TechnologyWuhan 430074China

Next-generation advanced high/pulsed power capacitors urgently require dielectric materials with outstanding energy storage performance.Bi_(0.5)Na_(0.5)TiO_(3)-based lead-free materials exhibit high polarization,but the high remanent polarization and large polarization hysteresis limit their applications in dielectric capacitors.Herein,high-entropy perovskite relaxor ferroelectrics(Na_(0.2)Bi_(0.2)Ba_(0.2)Sr_(0.2)Ca_(0.2))(Ti1-x%Zrx%)O_(3)are designed by adding multiple ions in the A-site and replacing the B-site Ti^(4+)with a certain amount of Zr^(4+).The newly designed system showed high relaxor feature and slim polarization-electric(P-E)loops.Especially,improved relaxor feature and obviously delayed polarization saturation were found with the increasing of Zr^(4+).Of particular importance is that both high recoverable energy storage density of 6.6 J/cm^(3) and energy efficiency of 93.5%were achieved under 550 kV/cm for the ceramics of x=6,accompanying with excellent frequency stability,appreciable thermal stability,and prosperous discharge property.This work not only provides potential dielectric materials for energy storage applications,but also offers an effective strategy to obtain dielectric ceramics with ultrahigh comprehensive energy storage performance to meet the demanding requirements of advanced energy storage applications.

关键词： energy storage density (Bi_(0.5)Na_(0.5))TiO_(3) high-entropy perovskite ceramics polarization saturation relaxor ferroelectrics(RFEs)

Recent advances on liquid intercalation and exfoliation of transition metal dichalcogenides: From fundamentals to applications

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Nano Research 2024年第3期17卷 2088-2110页

作者： Yan Tu Lingbin Xie Mengyang Zhang Shujuan Liu Zhongzhong Luo Longlu Wang Qiang Zhao State key laboratory of Organic Electronics and information Displays and Jiangsu key laboratory for Biosensors Institute of Advanced Materials(IAM)Nanjing University of Posts and TelecommunicationsNanjing 210023China College of Electronic and optical Engineering and College of Flexible Electronics(Future Technology) Jiangsu Province Engineering Research Center for Fabrication and Application of Special Optical Fiber Materials and DevicesNanjing University of Posts and TelecommunicationsNanjing 210023China

The weak van der Waals gap endows two dimensional transition metal dichalcogenides(2D TMDs)with the potential to realize guest intercalation and host exfoliation.Intriguingly,the liquid intercalation and exfoliation is a facile,low-cost,versatile and scalable strategy to modulate the structure and physiochemical property of TMDs via introducing foreign species into interlayer.In this review,firstly,we briefly introduce the resultant hybrid superlattice and disperse nanosheets with tailored properties fabricated via liquid intercalation and exfoliation.Subsequently,we systematically analyze the intercalation phenomenon and limitations of various intercalants in chemical or electrochemical methods.Afterwards,we intensely discuss diverse functionalities of resultant materials,focusing on their potential applications in energy conversion,energy storage,water purification,electronics,thermoelectrics and superconductor.Finally,we highlight the challenges and outlooks for precise and mass production of 2D TMDs-based materials via liquid intercalation and exfoliation.This review enriches the overview of liquid intercalation and exfoliation strategy,and paves the path for relevant high-performance devices.

关键词： two-dimensional transition metal dichalcogenides hybrid superlattice intercalation exfoliation