In this study,a phase field model is established to simulate the microstructure formation during the solidification of dendrites by taking the Al-Cu-Mg ternary alloy as an example,and machine learning and deep learnin...In this study,a phase field model is established to simulate the microstructure formation during the solidification of dendrites by taking the Al-Cu-Mg ternary alloy as an example,and machine learning and deep learning methods are combined with the Kim-Kim-Suzuki(KKS)phase field model to predict the quasi-phase equilibrium.The paper first uses the least squares method to obtain the required data and then applies eight machine learning methods and five deep learning methods to train the quasi-phase equilibrium prediction models.After obtaining different models,this paper compares the reliability of the established models by using the test data and uses two evaluation criteria to analyze the performance of these models.This work find that the performance of the established deep learning models is generally better than that of the machine learning models,and the Multilayer Perceptron(MLP)based quasi-phase equilibrium prediction model achieves the best performance.Meanwhile the Convolutional Neural Network(CNN)based model also achieves competitive results.The experimental results show that the model proposed in this paper can predict the quasi-phase equilibrium of the KKS phase-field model accurately,which proves that it is feasible to combine machine learning and deep learning methods with phase-field model simulation.展开更多
Whispering-gallery-mode(WGM)microresonators can greatly enhance light-matter interaction,making them indispensable units for frequency conversion in nonlinear optics.Efficient nonlinear wave mixing in microresonators ...Whispering-gallery-mode(WGM)microresonators can greatly enhance light-matter interaction,making them indispensable units for frequency conversion in nonlinear optics.Efficient nonlinear wave mixing in microresonators requires stringent simultaneous optical resonance and phase-matching conditions.Thus,it is challenging to achieve efficient frequency conversion over a broad bandwidth.Here,we demonstrate broadband second-harmonic generation(SHG)in the x-cut thinfilm lithium niobate(TFLN)microdisk with a quality factor above 107by applying the cyclic quasi-phase-matching(CQPM)mechanism,which is intrinsically applicable for broadband operation.Broadband SHG of continuous-wave laser with a maximum normalized conversion efficiency of~15%/m W is achieved with a bandwidth spanning over 100 nm in the telecommunication band.Furthermore,broadband SHG of femtosecond lasers,supercontinuum lasers,and amplified spontaneous emission in the telecommunication band is also experimentally observed.The work is beneficial for integrated nonlinear photonics devices like frequency converters and optical frequency comb generator based on second-order nonlinearity on the TFLN platform.展开更多
In this paper,we demonstrate efficient spontaneous quasi-phase matched(SQPM)second harmonic generation(SHG)in a microracetrack resonator on X-cut thin film lithium niobate.Our approach does not involve poling,but expl...In this paper,we demonstrate efficient spontaneous quasi-phase matched(SQPM)second harmonic generation(SHG)in a microracetrack resonator on X-cut thin film lithium niobate.Our approach does not involve poling,but exploits the anisotropy of the crystals to allow the phase-matching condition to be fulfilled spontaneously as the TE-polarized light circulates in a specifically designed racetrack resonator.In experiment,normalized on-chip conversion efficiencies of 1.01×10-4/W and 0.43×10-4/W are achieved by 37th-order and 111th-order SQPM,respectively.The configurable SQPM will benefit the application of nonlinear frequency conversion and quantum source generation in chip-scale integrated photonics compatible with standard CMOS fabrication processes.展开更多
A deep understanding of the spectral gain characteristics of optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs) is important for a highly efficient optical parametric conversion. We numeric...A deep understanding of the spectral gain characteristics of optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs) is important for a highly efficient optical parametric conversion. We numerically calculated the spectral gain characteristics of a quasi-phase-matching (QPM) parametric conversion process using the periodically poled 6% (mol/mol) MgO doped LiNbO3 (PPMgLN) as the nonlinear crystal. In the simulation we utilized the approach of a transformative matrix of the periodically poled nonlinear medium, which results from the small-signal approximation of three-wave mixed nonlinear equations. Numerical simulation results show that: (1) The full width at half maximum (FWHM) of the spectral gain of the parametric process becomes wider with the increase of parametric wavelength and reaches the maximum at degeneration; (2) The gain coefficient decreases gradually with the increase of parametric wavelength; (3) The spectral gain bandwidth decreases correspondingly with the increase of the nonlinear material length; (4) There exists an optimal parametric wavelength band, which is most suitable for the high gain parametric conversion when pumped by a laser source with a wide wavelength band, such as the high power fiber laser.展开更多
补偿电流跟踪控制策略对有源电力滤波器(Active Power Filter,APF)的谐波治理能力有直接影响。在单相系统中,利用并联型APF进行谐波治理时,传统的电流比例积分(Proportional Integral,PI)控制方式具有较快的响应速度,但3次谐波电流不能...补偿电流跟踪控制策略对有源电力滤波器(Active Power Filter,APF)的谐波治理能力有直接影响。在单相系统中,利用并联型APF进行谐波治理时,传统的电流比例积分(Proportional Integral,PI)控制方式具有较快的响应速度,但3次谐波电流不能得到充分抑制。针对这一问题,文中采用准比例谐振(Quasi Proportional-resonant,QPR)控制策略对3次谐波电流进行跟踪控制。同时利用陷波滤波器对ip-iq谐波电流检测算法进行改进,提高谐波电流检测精度,消除数字低通滤波器输出侧直流信号中的低频波动问题。最后通过MATLAB/Simulink建立单相并联型APF谐波治理系统模型,验证了所提控制策略的可行性和有效性。展开更多
云贵高原的冻雨是中国南方冬季最严重的气象灾害。利用天气研究和预报模式(weather research and forecasting model, WRF),对云贵高原大地形进行了敏感性实验,模拟了不同地形高度对大气环流、云微物理参量及冻雨分布的影响,结果显示:...云贵高原的冻雨是中国南方冬季最严重的气象灾害。利用天气研究和预报模式(weather research and forecasting model, WRF),对云贵高原大地形进行了敏感性实验,模拟了不同地形高度对大气环流、云微物理参量及冻雨分布的影响,结果显示:随着云贵高原大地形的抬升,准静止锋的锋线一直维持在24°N附近,但锋面越来越陡,表明高原大地形是形成云贵准静止锋的主要因素,准静止锋长时间滞留在贵州中东部和湖南西部,是该区冻雨高发的原因。随着高原的抬升,从全境的云滴碰并增长逐渐在高原东部出现冰晶融化过程,高原主体上的冻雨以过冷暖雨机制为主,而低海拔的东部地区以融化机制为主。随着高原抬升,高空逆温层及冻雨区均从贵州西北向贵州中部及东部地区移动,逆温层的存在及其冷-暖-冷的垂直结构是冻雨形成非常重要的因子。当云贵高原降至原地形的一半时,冻雨量最大,其后随着高原抬升,冻雨量开始减少。该研究有助于更深入了解云贵高原大地形对冻雨形成、范围和强度的影响机制。展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos.52161002,51661020 and 11364024.
文摘In this study,a phase field model is established to simulate the microstructure formation during the solidification of dendrites by taking the Al-Cu-Mg ternary alloy as an example,and machine learning and deep learning methods are combined with the Kim-Kim-Suzuki(KKS)phase field model to predict the quasi-phase equilibrium.The paper first uses the least squares method to obtain the required data and then applies eight machine learning methods and five deep learning methods to train the quasi-phase equilibrium prediction models.After obtaining different models,this paper compares the reliability of the established models by using the test data and uses two evaluation criteria to analyze the performance of these models.This work find that the performance of the established deep learning models is generally better than that of the machine learning models,and the Multilayer Perceptron(MLP)based quasi-phase equilibrium prediction model achieves the best performance.Meanwhile the Convolutional Neural Network(CNN)based model also achieves competitive results.The experimental results show that the model proposed in this paper can predict the quasi-phase equilibrium of the KKS phase-field model accurately,which proves that it is feasible to combine machine learning and deep learning methods with phase-field model simulation.
基金supported by the National Natural Science Foundation of China(Nos.12074252,12192252,and 62022058)the National Key Research and Development Program of China(No.2022YFA1205101)+1 种基金the Shanghai Municipal Science and Technology Major Project(No.2019SHZDZX01-ZX06)and the Yangyang Development Fund。
文摘Whispering-gallery-mode(WGM)microresonators can greatly enhance light-matter interaction,making them indispensable units for frequency conversion in nonlinear optics.Efficient nonlinear wave mixing in microresonators requires stringent simultaneous optical resonance and phase-matching conditions.Thus,it is challenging to achieve efficient frequency conversion over a broad bandwidth.Here,we demonstrate broadband second-harmonic generation(SHG)in the x-cut thinfilm lithium niobate(TFLN)microdisk with a quality factor above 107by applying the cyclic quasi-phase-matching(CQPM)mechanism,which is intrinsically applicable for broadband operation.Broadband SHG of continuous-wave laser with a maximum normalized conversion efficiency of~15%/m W is achieved with a bandwidth spanning over 100 nm in the telecommunication band.Furthermore,broadband SHG of femtosecond lasers,supercontinuum lasers,and amplified spontaneous emission in the telecommunication band is also experimentally observed.The work is beneficial for integrated nonlinear photonics devices like frequency converters and optical frequency comb generator based on second-order nonlinearity on the TFLN platform.
基金supported by the National Key R&D Program of China(Grant No.2019YFB2203501)National Natural Science Foundation of China(Grant Nos.12134009,and 91950107)+1 种基金Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01-ZX06)Shanghai Jiao Tong University(SJTU)(Grant No.21X010200828)。
文摘In this paper,we demonstrate efficient spontaneous quasi-phase matched(SQPM)second harmonic generation(SHG)in a microracetrack resonator on X-cut thin film lithium niobate.Our approach does not involve poling,but exploits the anisotropy of the crystals to allow the phase-matching condition to be fulfilled spontaneously as the TE-polarized light circulates in a specifically designed racetrack resonator.In experiment,normalized on-chip conversion efficiencies of 1.01×10-4/W and 0.43×10-4/W are achieved by 37th-order and 111th-order SQPM,respectively.The configurable SQPM will benefit the application of nonlinear frequency conversion and quantum source generation in chip-scale integrated photonics compatible with standard CMOS fabrication processes.
基金supported by the National Natural Science Foundation of China (No. 60778001)the National Basic Research Program (973) of China (No. 2007CB307003)
文摘A deep understanding of the spectral gain characteristics of optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs) is important for a highly efficient optical parametric conversion. We numerically calculated the spectral gain characteristics of a quasi-phase-matching (QPM) parametric conversion process using the periodically poled 6% (mol/mol) MgO doped LiNbO3 (PPMgLN) as the nonlinear crystal. In the simulation we utilized the approach of a transformative matrix of the periodically poled nonlinear medium, which results from the small-signal approximation of three-wave mixed nonlinear equations. Numerical simulation results show that: (1) The full width at half maximum (FWHM) of the spectral gain of the parametric process becomes wider with the increase of parametric wavelength and reaches the maximum at degeneration; (2) The gain coefficient decreases gradually with the increase of parametric wavelength; (3) The spectral gain bandwidth decreases correspondingly with the increase of the nonlinear material length; (4) There exists an optimal parametric wavelength band, which is most suitable for the high gain parametric conversion when pumped by a laser source with a wide wavelength band, such as the high power fiber laser.
文摘补偿电流跟踪控制策略对有源电力滤波器(Active Power Filter,APF)的谐波治理能力有直接影响。在单相系统中,利用并联型APF进行谐波治理时,传统的电流比例积分(Proportional Integral,PI)控制方式具有较快的响应速度,但3次谐波电流不能得到充分抑制。针对这一问题,文中采用准比例谐振(Quasi Proportional-resonant,QPR)控制策略对3次谐波电流进行跟踪控制。同时利用陷波滤波器对ip-iq谐波电流检测算法进行改进,提高谐波电流检测精度,消除数字低通滤波器输出侧直流信号中的低频波动问题。最后通过MATLAB/Simulink建立单相并联型APF谐波治理系统模型,验证了所提控制策略的可行性和有效性。
文摘云贵高原的冻雨是中国南方冬季最严重的气象灾害。利用天气研究和预报模式(weather research and forecasting model, WRF),对云贵高原大地形进行了敏感性实验,模拟了不同地形高度对大气环流、云微物理参量及冻雨分布的影响,结果显示:随着云贵高原大地形的抬升,准静止锋的锋线一直维持在24°N附近,但锋面越来越陡,表明高原大地形是形成云贵准静止锋的主要因素,准静止锋长时间滞留在贵州中东部和湖南西部,是该区冻雨高发的原因。随着高原的抬升,从全境的云滴碰并增长逐渐在高原东部出现冰晶融化过程,高原主体上的冻雨以过冷暖雨机制为主,而低海拔的东部地区以融化机制为主。随着高原抬升,高空逆温层及冻雨区均从贵州西北向贵州中部及东部地区移动,逆温层的存在及其冷-暖-冷的垂直结构是冻雨形成非常重要的因子。当云贵高原降至原地形的一半时,冻雨量最大,其后随着高原抬升,冻雨量开始减少。该研究有助于更深入了解云贵高原大地形对冻雨形成、范围和强度的影响机制。
