双零色散光子晶体光纤中超连续谱的产生及控制

通过数值模拟飞秒脉冲在具有双零色散波长的光子晶体光纤中的传输过程,详细分析了超连续谱的产生和控制机制.结果表明:中心波长处于反常色散区的泵浦脉冲在高阶非线性和高阶色散等作用的调制下,将演化为基孤子和正常色散区的两个色散波;该色散波进而经与之相位匹配的基孤子相干加强而使频谱展宽形成超连续谱,同时两个色散波上出现了干涉引起的振荡现象.进一步对比三种结构的光子晶体光纤中超连续谱的特点,定量分析了两色散波对超连续谱的限制作用,阐述了结构参量对超连续谱的影响.基于上述结论,结合对色散波的中心波长与光子晶体光纤的色散曲线、结构参量之间关系的分析,提出了设计光子晶体光纤的结构来控制超连续谱的方法.作为例证,通过优化光子晶体光纤结构理论上实现了频谱分量覆盖可见光区的平坦超连续谱.     

Ultra broadband-flattened dispersion photonic crystal fiber for supercontinuum generation

We propose an improved design of photonic crystal fiber (PCF) with ultra broadband-flattened dispersion and ultra-low confinement loss in the telecommunication window.The design is considerably suitable for the generation of wideband supercontinuum spectrum.Numerical results reveal that the proposed PCF structure possesses a low dispersion of 0±1.5 ps/(nm·km) in the wavelengths ranging from 1.134 to 1.805 μm (approximately 700-nm bandwidth) with a confinement loss of less than 10 8 dB/km.In addition,a nonlinear coefficient greater than 11.47 (W·km) 1 and a dispersion slope of as low as 0.005694 ps/(nm 2 ·km) are obtained at 1.55-μm wavelength.Moreover,a symmetric flat supercontinuum spectrum with a 10-dB bandwidth of 190 nm is achieved in a 3-m-long fiber,verifying the excellent optical features of the innovative PCF.     

Thermal effect mechanism of magnetoresistance in p-type diamond films

Based on the analysis and the discussion of the influence of thermal ionization energy and various scatterings on magnetoresistance(MR) of p-type diamond films,a revised model of valence band split-off over temperature is put forward,and a corresponding calculation formula is given for the MR of p-type diamond films (Corbino discs).It is shown that the theoretical calculation that the MR of diamond films changes with temperature is consistent with the experiment.The influence of Fermi energy level on MR of diamond films is discussed.Additionally,the thermal effect mechanism of MR in p-type diamond films is also explored.     

Multiple Wavelength-Channels in SPP Waveguides for Optical Communication

Surface plasmon polaritons （SPPs） can be excited, meanwhile some peculiar optical phenomena will appear when light irradiates metal structures under some conditions. Based on photonie band gap theory, in this Letter we present a kind of SPP waveguide with multiple wavelength-channels. By using the Bragg effect and introducing some geometric defect layers into a quasi-periodic metal heterowaveguide, the multiple SPP forbidden bands （SPFBs） in a given waveband can be generated, and the multiple SPP pass bands （SPPBs） with narrow bandwidth in each SPFB can be realized. The SPP propagation in metal heterowaveguide is calculated by FDTD and transfer matrix methods. By selecting appropriate thickness, position and the number of defect layers, two SPPBs can be achieved in the SPFBs around 1.31 and 1.55μm simultaneously.     

Ba5-xLaxTixNb4-xO15和Ba5-xLaxTixTa4-xO15陶瓷的振动光谱和微波介电性能

采用高温固相合成法制备Ba5-xLaxTixNb4-xO15和Ba5-xLaxTixTa4-xO15(x=1,2,3)陶瓷,通过XRD、Raman测试方法表征其结构,并测试其微波介电性能。拉曼光谱显示:两体系中[NbO6]/[TaO6]氧八面体的A1g(O)模都随着x的增加向低波数移动,此模在铌酸盐体系中强度逐渐升高,在钽酸盐体系中峰劈裂加剧。介电性能结果显示:Nb/Ta体系样品的Q×f值随x增加而增加。因此:随La3 ,Ti4 取代量的增加,B位阳离子的结构有序度逐渐增加,Q×f值也随之增加,这都与[NbO6]/[TaO6]的伸缩振动频率A1g(O)的变化有关。     

更新随机指标分枝过程的大偏差

研究了时间指标为一般更新过程的随机指标分枝过程.在每个粒子至少有两个分枝(Bottcher情形)以及更新分布满足Cramer条件的情况下,得到了更新随机指标分枝过程的大偏差原理.     

一种基于Mumford-Shah模型的红外图像边缘检测方法

 Chan-Vese模型是一种优秀的简化Mumford-Shah模型。然而Chan-Vese模型是以两个同质区域为基础建立的，这并不符合红外图像的特点，导致直接应用该模型处理红外图像时可能失败。针对这一问题，提出了一种适用于红外图像边缘检测的改进Mumford-Shah模型，并对该模型中目标边缘的保持、停止准则的建立及算法速度的提高作了详细讨论。实验表明，改进Mumford-Shah模型能够克服Chan-Vese模型在对红外图像边缘检测时不能跨越过渡区域的缺点，有效地检测出目标边缘。     

类钙钛矿新铌酸盐Ba4LaTiNb3O15的合成、结构与介电特性

A new niobate compound Ba₄LaTiNb₃O₁₅ has been synthesized and characterized. Through Rietveld refinement of X-ray powder diffraction data, Ba₄LaTiNb₃O₁₅ is identified as the A₅B₄O₁₅ type cation-deficient perovskites with space group of P3m1(164) and lattice constants a=0.572 38(1) nm, c=1.169 48(1) nm, V=0.331 81(1) nm³, and Z=1. The crystal structure can be described as consisting of identical perovskite-like blocks, four corner-sharing (Ba,La)O₆ octahedra thick, separated by layers of vacant octahedral. The (Ba,La)-O bond lengths range from 0.267 to 0.321 nm and the (Ti,Nb)-O bond lengths range from 0.175 to 0.213 nm. The Ba₄LaTiNb₃O₁₅ ceramic has a high dielectric constant of 53.3, high quality factors (Q) 3 650 (at 6.402 5 GHz), and low temperature variation of resonant frequency (τ_f) +69.3 × 10^-6 K^-1.     

气氛氧压对PLD法生长Nd:LuVO4薄膜的性能影响

采用脉冲激光沉积技术在不同气氛和氧分压下, 在抛光石英片上生长了一系列(200)面择优取向的NdLuVO4薄膜. 利用X射线衍射(XRD)分析了所制备薄膜性能, 认为成膜较为适宜的气氛为氧气, 且氧分压为20 Pa时所得到的薄膜性能较好. 利用原子力显微镜(AFM)观察了NdLuVO4薄膜的表面形貌, 分析了氧分压的存在对薄膜表面质量的影响. 利用卢瑟福背散射(RBS)分析了薄膜的组成, 发现薄膜的成分组成与靶材的成分较为一致. 利用棱镜耦合法测得了该薄膜中每条模所对应的有效折射率为2.0044和1.7098.     

有机胺柱类钙钛矿型钽酸盐的制备与表征

采用分步交换法，合成了新型的正丙胺、正丁胺柱层状类钙钛矿型钽酸盐C3H7NH3-Sr2Ta3O10与C4H9NH3-Sr2Ta7O10，采用X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(IR)对该类化合物的结构与形貌进行了表征，并测定了其比表面积。