Effect of thickness variations of lithium niobate on insulator waveguide on the frequency spectrum of spontaneous parametric down-conversion

We study the effect of waveguide thickness variations on the frequency spectrum of spontaneous parametric down-conversion in the periodically-poled lithium niobate on insulator (LNOI) waveguide. We analyze several variation models and our simulation results show that thickness variations in several nanometers can induce distinct effects on the central peak of the spectrum, such as narrowing, broadening, and splitting. We also prove that the effects of positive and negative variations can be canceled and thus lead to a variation-robust feature and an ultra-broad bandwidth. Our study may promote the development of on-chip photon sources in the LNOI platform, as well as opens up a way to engineer photon frequency state.     

基于无网格法的Timoshenko曲梁动力分析

曲梁具有外形美观、受力性能良好的优点,故在工程中得到广泛应用。本文基于移动最小二乘近似和一阶剪切变形理论,提出一种对Timoshenko曲梁自由振动和受迫振动进行分析的无网格方法。通过一系列离散点离散曲梁,建立曲梁无网格模型,然后推导曲梁势能和动能方程,通过哈密顿原理给出曲梁自由振动和受迫振动的控制方程,因为本文方法不能直接施加边界条件,所以使用完全转换法处理本质边界条件,最后求解方程得到频率和振动模态。文末通过算例验证了本文方法的有效性,且通过收敛性分析表明本文方法具有较好的收敛性,并进一步分析了不同边界条件、跨高比和变截面变曲率对曲梁自由振动和受迫振动的影响,将计算结果与文献解或ABAQUS解进行对比分析,表明本文方法具有较高的精度,且适用于实际工程情况。     

铌酸锂基光量子器件与集成技术：机遇与挑战

铌酸锂材料具有宽的透光范围和高的非线性光学、电光、声光、热光系数,且化学性能稳定,是理想的光子集成芯片的衬底材料。在量子光学领域,人们已经发展出一系列铌酸锂基集成器件,能够实现光子态的高效率产生、调控、频率转换、存储和异质集成的单光子探测,有望实现全集成的频率态操控、确定性多光子态制备和单光子间相互作用,最终形成全功能集成的有源光量子芯片,推动量子物理基础研究和光量子信息应用发展。文章回顾了基于铌酸锂基量子集成的研究进展,并对其在未来光量子信息时代的机遇与挑战进行探讨。     

Localization and Steering of Light in One-Dimensional Parity-Time Symmetric Photonic Lattices

We theoretically study the propagation dynamics of input light in one-dimensional mixed linear-nonlinear photonic lattices with a complex parity-time symmetric potential. Numerical computation shows simultaneous localization and steering of the optical beam due to the asymmetric scatter and interplay between Kerr-type nonlinearity and PT symmetry. This may provide a feasible measure for manipulation light in optical communications, integrated optics and so on.     

Ultra-broadband enhanced nonlinear saturable absorption for Mo0.53W0.47Te2 nanosheets

Alloying in two-dimension has been a hot spot in the development of new,versatile systems of optics and electronics.Alloys have been demonstrated to be a fascinating strategy to modulate the chemical and electronic properties of two-dimensional nanosheets.We firstly reported ultra-broadband enhanced nonlinear saturable absorption of Mo0.53W0.47Te2 alloy at 0.6,1.0,and 2.0μm.The nonlinear saturable absorption of Mo0.53W0.47Te2 saturable absorber(SA)was measured by the open aperture Z-scan technique.Compared to MoTe2 and WTe2 SAs,the Mo0.53W0.47Te2 SA showed five times deeper modulation depth,8.6%lower saturable intensity,and one order larger figure of merit.Thus,our research provides a method of alloys to find novel materials with more outstanding properties for optics and optoelectronic applications.     

面内变刚度薄板弯曲问题的挠度?弯矩耦合神经网络方法

发展了一种求解面内变刚度功能梯度薄板弯曲问题的神经网络方法. 面内变刚度薄板弯曲问题的偏微分控制方程为一复杂的4阶偏微分方程, 传统的基于强形式的神经网络解法在求解该偏微分方程时可能会遇到难以收敛、边界条件难以处理的情况. 本文基于Kirchhoff薄板弯曲理论, 提出了一种直角坐标系下任意面内变刚度薄板弯曲问题的神经网络解法. 神经网络模型包含挠度网络与弯矩网络, 分别用于预测薄板的挠度与弯矩, 从而将求解4阶偏微分方程转换为求解一系列二阶偏微分方程组, 通过对挠度、弯矩试函数的构造可使得神经网络计算结果严格满足边界条件. 在误差的反向传播中, 根据本文提出的误差函数公式计算训练误差并结合Adam优化算法更新模型的内部参数. 求解了不同边界条件、形状的面内变刚度薄板弯曲问题, 并将所得计算结果与理论解、有限元解进行对比. 研究表明, 本文模型对于求解面内变刚度薄板弯曲问题具备适应性, 虽然模型中的弯矩网络收敛较挠度网络要慢, 但本文方法在试函数的构造上更为简单、适应性更强.      

Enhanced saturable absorption of MoS_2 black phosphorus composite in 2 μm passively Q-switched Tm: YAP laser

We report the fabrication of an MoS_2 black phosphorus(BP) composite saturable absorber by liquid phase exfoliation and the spin-coating method and further exploitation to build a 2 μm passively Q-switched Tm:YAP laser. Such a composite based Q-switched laser with a duration of 488 ns and corresponding peak power of 85.9 W is obtained, which shows an improved saturable absorption effect than that of single MoS_2(616 ns,68.7 W) and BP(932 ns, 22.4 W). The results indicate that simple and reasonable fabrication of the vertical composite from two-dimensional atomic layer materials opens up the possibility to create an unprecedented saturable absorber with exciting properties.