分类： 光学 >> 量子光学 提交时间： 2023-02-21
摘要： Silicon carbide (SiC) recently emerged as a promising photonic and quantum material owing to its unique material properties. Here, we carry out an exploratory investigation of the electro-optic effect in high-quality-factor 4H-SiC microresonators. Our findings confirm the existence of the Pockels effect in 4H-SiC for the first time. The extracted Pockels coefficients show certain variations among 4H-SiC wafers from different manufacturers, with the magnitudes of $r_{13}$ and $r_{33}$ estimated to be in the range of (0.3-0.7) pm/V and (0-0.03) pm/V, respectively.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The unique material property of silicon carbide (SiC) and the recent demonstration of low-loss SiC-on-insulator integrated photonics platform have attracted considerable research interests for chip-scale photonic and quantum applications. Here, we carry out a thorough investigation of the Kerr nonlinearity among 4H-SiC wafers from several major wafer manufacturers, and reveal for the first time that their Kerr nonlinear refractive index can be significantly different. By eliminating various measurement errors in the four-wave mixing experiment and improving the theoretical modeling for high-index-contrast waveguides, the best Kerr nonlinear refractive index of 4H-SiC wafers is estimated to be approximately four times of that of stoichiometric silicon nitride in the telecommunication band. In addition, experimental evidence is developed that the Kerr nonlinearity in 4H-SiC wafers can be stronger along the c-axis than that in the orthogonal direction, a feature that was never reported before.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Silicon carbide has recently emerged as a promising photonics material due to its unique properties, including possessing strong second- and third-order nonlinear coefficients and hosting various color centers that can be utilized for a wealth of quantum applications. Here, we report the design and demonstration of octave-spanning microcombs in a 4H-silicon-carbide-on-insulator platform for the first time. Such broadband operation is enabled by optimized nanofabrication achieving >1 million intrinsic quality factors in a 36-$\mu$m-radius microring resonator, and careful dispersion engineering by investigating the dispersion properties of different mode families. For example, for the fundamental transverse-electric mode whose dispersion can be tailored by simply varying the microring waveguide width, we realized a microcomb spectrum covering the wavelength range from 1100 nm to 2400 nm with an on-chip power near 120 mW. While the observed comb state is verified to be chaotic and not soliton, attaining such a large bandwidth is a crucial step towards realizing $f$-2$f$ self-referencing. In addition, we have also observed coherent soliton-crystal state for the fundamental transverse-magnetic mode, which exhibits stronger dispersion than the fundamental transverse-electric mode and hence a narrower bandwidth.
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-05-08
摘要： Accurate and efficient online parameter identification and state estimation are crucial for leveraging Digital Twin simulations to optimize the operation of near-carbon-free nuclear energy systems. In previous studies, we developed a reactor operation digital twin (RODT). However, non-differentiabilities and discontinuities arise when employing machine-learning-based surrogate forward models, challenging traditional gradient-based in verse methods and their variants. This study investigated deterministic and metaheuristic algorithms and developed hybrid algorithms to address these issues. An efficient modular RODT software framework that incorpo rates these methods into its post-evaluation module is presented for comprehensive comparison. The methods were rigorously assessed based on convergence profiles, stability with respect to noise, and computational performance. The numerical results show that the hybrid KNNLHS algorithm excels in real-time online applications, balancing accuracy and efficiency with a prediction error rate of only 1% and processing times of less than 0.1 s. Contrastingly, algorithms such as FSA, DE, and ADE, although slightly slower (approximately 1 s), demonstrated higher accuracy with a 0.3% relative L2 error, which advances RODT methodologies to harness machine learning and system modeling for improved reactor monitoring, systematic diagnosis of off-normal events, and lifetime management strategies. The developed modular software and novel optimization methods presented offer pathways to realize the full potential of RODT for transforming energy engineering practices.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a catalog of 948,216 stars with mass label and a catalog of 163,105 red clump (RC) stars with mass and age labels simultaneously. The training dataset is cross matched from the LAMOST DR5 and high resolution asteroseismology data, mass and age are predicted by random forest method or convex hull algorithm. The stellar parameters with high correlation with mass and age are extracted and the test dataset shows that the median relative error of the prediction model for the mass of large sample is 0.03 and meanwhile, the mass and age of red clump stars are 0.04 and 0.07. We also compare the predicted age of red clump stars with the recent works and find that the final uncertainty of the RC sample could reach 18\% for age and 9\% for mass, in the meantime, final precision of the mass for large sample with different type of stars could reach 13\% without considering systematics, all these are implying that this method could be widely used in the future. Moreover, we explore the performance of different machine learning methods for our sample, including bayesian linear regression (BYS), gradient boosting decision Tree (GBDT), multilayer perceptron (MLP), multiple linear regression (MLR), random forest (RF) and support vector regression (SVR). Finally we find that the performance of nonlinear model is generally better than that of linear model, and the GBDT and RF methods are relatively better.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Yu-Sheng Wang
Kai-Bo Li
Chao-Feng Chang
Tan-Wen Lin
Jian-Qing Li
Shih-Si Hsiao
Jia-Mou Chen
Yi-Hua Lai
Ying-Cheng Chen
Yong-Fan Chen
Chih-Sung Chuu
Ite A. Yu
摘要： We report the generation of biphotons, with a temporal full width at the half maximum (FWHM) of 13.4$\pm$0.3 $\mu$s and a spectral FWHM of 50$\pm$1 kHz, via the process of spontaneous four-wave mixing. The temporal width is the longest, and the spectral linewidth is the narrowest up to date. This is also the first biphoton result that obtains a linewidth below 100 kHz, reaching a new milestone. The very long biphoton wave packet has a signal-to-background ratio of 3.4, which violates the Cauchy-Schwarz inequality for classical light by 4.8 folds. Furthermore, we demonstrated a highly-tunable-linewidth biphoton source and showed that while the biphoton source's temporal and spectral width were controllably varied by about 24 folds, its generation rate only changed by less than 15\%. A spectral brightness or generation rate per pump power per linewidth of 1.2$\times$10$^6$ pairs/(s$\cdot$mW$\cdot$MHz) was achieved at the temporal width of 13.4 $\mu$s. The above results were made possible by the low decoherence rate and high optical depth of the experimental system, as well as the nearly phase-mismatch-free scheme employed in the experiment. This work has demonstrated a high-efficiency ultranarrow-linewidth biphoton source, and has made a substantial advancement in the quantum technology utilizing heralded single photons.
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