长周期光纤光栅中的包层模谐振

本文给出了光纤中包层模的电场形式,指出包层膜的电场形式与弱导光纤中导模的电场形式不同,对光纤中基模与包层模电场沿光纤横截面分布的重叠情况的分析表明,长周期光纤光栅除了能将HE₁₁导模耦合到HE_1p包层模外,也可以将其耦合到EH_1p包层模。基于耦合模理论的计算表明,耦合到EH_1p和EH_1,p-1包层模的耦合波长相近,对于典型的单模光纤,当p>4时耦合到这两个模式的耦合系数是可比的。     

非线性包层光纤中TE0模的传播特性分析

本文对具有Kerr非线性包层和线性匀芯的光纤在不同光功率下的传播特性进行了理论分析和数值计算.结果表明,在适当光功率下,当模折射率N等于芯折射率n_f时,芯场变得相当均匀,而包层场迅速衰减.对于自聚焦包层,当从N<n_f逐渐变到N>n_f时,芯场剖面越过N=n_f从凸变凹.在拐点,芯场成为均匀的.论文给出了模场分布和光功率与模折射率的关系.指出纤芯出现匀场预期会在光纤器件、光电子器件、光子器件中得到应用.     

均匀折射率包层铌酸锂单晶光纤远离截止区的模特性讨论

给出了具有均匀折射率包层铌酸锂单晶光纤的场强颁上和本征值方程，分析了远离截止区的模特性。     

光纤光栅温度传感的非线性现象

对光纤光栅温度传感反射波长相对漂移量与温度改变量的非线性问题进行了详细研究.通过对实验曲线的多项式拟合,求出了光纤光栅反射中心波长相对漂移量Δλ_C/λ_C与温度改变量ΔT的解析式,用对比法得到了温度灵敏度系数η表达式.取样计算表明:多项式能更好地反映Δλ_C/λ_C与ΔT的关系,证明了温度灵敏度系数η不是常量,而是随温度增加缓慢增大.     

高边模抑制比窄线宽的光纤光栅外腔半导体激光器

本文从耦合腔理论出发分析了光纤光栅外腔半导体激光器的模式选择,得到了为达到稳定的高主边模抑制比所需的短外腔、短光纤光栅的器件设计原则.制作了两只光纤光栅外腔半导体激光器,Q₁为短外腔(<2mm)、短光纤光栅(4mm)结构,Q₂为长外腔(20mm)、长光纤光栅(17mm)结构.测量Q₁的主边模抑制比为35dB,Q₂的主边模抑制比为10dB.     

光纤光栅的局域耦合模分析

本文运用矢量局域耦合理论分析了平均扰动折射率随Z轴变化的单模光纤光栅的纤芯模场分布、包层模场分布以及耦合系数,得到更为精确的光栅光谱特性.并分别计算了布喇格光栅和长周期光纤光栅在平均扰动折射率在Z轴有扰动时的光谱特性图.从而得出平均折射率随Z轴变化对光谱特性的危害性,并提出了解决方法.     

Formation of rippled surface morphology during Si/Si （100） epitaxy by ultrahigh vacuum chemical vapour deposition

The Si epitaxial films are grown on Si (100) substrates using pure Si2H6 as a gas source using ultrahigh vacuum chemical vapour deposition technology. The values of growth temperature T_g are 650 ℃, 700 ℃, 730 ℃, 750 ℃, and 800 ℃. Growth mode changes from island mode to step-flow mode with T_g increasing from 650 ℃ to 700 ℃. Rippled surface morphologies are observed at T_g = 700 ℃, 730 ℃, and 800 ℃, but disappear when T_g = 750 ℃. A model is presented to explain the formation and the disappearance of the ripples by considering the stability of the step-flow growth.     

单轴晶体包层光纤Bragg光栅反射谱特性模拟研究

本文推导了包层为单轴各向异性晶体的光纤理想正规模特征方程, 应用中值定理, 结合Matlab的数值求解, 提出了这一超越方程的一种求解算法, 并在此基础上, 对包层为单轴各向异性材料的光纤Bragg光栅的反射谱与包层折射率关系进行了模拟分析. 模拟结果表明, k_cl 对反射谱有很大的影响, 不同的k_cl 可以导致不同的光栅反射率和Bragg波长.     

抛物型折射率包层的铌酸锂单晶光纤

利用镁离子内扩散的方法，实现了铌酸锂单晶光纤具有抛物型折射率包层的波导结构。对扩散层中的镁离子浓度分布进行了理论模拟，理论和实验结果相符合。     

掺Er光纤飞秒激光器中高信噪比载波包络位相偏移频率获取的实验研究

在实验上分析了掺Er光纤光学频率梳中激光器与一级放大器之间光纤长度、 光纤扰动以及放大器抽运功率对倍频程光谱和载波包络位相偏移频率(f₀)信噪比的影响. 通过系统优化, 实现了40 dB信噪比的f₀输出, 为f₀的长期锁定和光纤光学频率梳的实现提供了技术保障.     

某些稀土氧化物的高温高压合成及其结构稳定性研究

 首次用高压高温方法，在3.2~4.0 GPa，1 000~1 300 ℃下，对CeO₂-R₂O₃（R=Eu，Gd），CeO₂-Tb₄O₁₁，Pr₆O₁₁-Tb₄O₇稀土氧化物进行合成实验，得到具有F型结构的CeEuO_3.5，CeGdO_3.5，CeTbO_3.5；B型结构的CeEuO₃，CeGdO₃，CeTbO₃，PrTbO₃和P型结构的PrTbO₃。PrTbO₃是迄今自然界尚未发现，文献未见报导过的新物质。对上面的产物和NdYbO₃、PrTmO₃，利用高、低温X射线衍射实验，检测了其结构的稳定性，结果指出：从300 ℃直到1 000 ℃，发生由B型CeRO_x向F型CeRO_x（R=Eu，Gd，Tb）、B型PrTbO₃向C型PrTbO₃的结构转变。F型CeRO_x属于氧缺位萤石型结构。     

高温超导体低温、高压下的物理性质的研究

 在3~20 GPa压力范围内，测量了含氧量较低的YBa₂Cu₃O_7-δ（δ=0.46）单晶压力增强效应（dT_c/dp=4.9KGPa^-1）；YBa₂Cu₃O₇（T_c0=90 K）单晶在压力下临界电流密度随压力变化；外磁场H=30 kO_e时，T_c与磁场、压力关系；压力达16.5 GPa下，Bi₂Sr₂CaCu₂O_x单晶T_c(p)关系（dT_c/dp=-0.4 KGPa^-1）。发现Y系高温超导体的温度压力导数dT_c/dp与T_c0中间呈dT_c/dp=b-mT_c0线性关系（b、m为常数）。结合压力下Y系超导体结构相变和含氧量对T_c影响，分析这类超导体T_c有很强的正压力效应的原因。把实验结果同几种超导电性微观理论模型进行了分析和比较。     

Blue-to-Orange Tunable Luminescence from Europium Doped Yttrium--Silicon--Oxide--Nitride Phosphors

Europium-doped yttrium-silicon-oxide-nitride phosphors are synthesized by carbothermal reduction and nitridation method. The crystal structure of the phosphors changed gradually from oxide Y2Si2O7 to nitride YSi3N5 state with increasing dosage of Si3N4 and carbon powder. The Y2Si2O7：Eu phosphor shows a blue emission at 465 nm with 300 nm excitation and a characteristic red emission of Eu^3＋ at 612 nm with 230 nm excitation. The YSi3N5：EU phosphor shows a broad emission band centred at 595nm with some sharp peaks of Eu^3＋ with 325nm excitation. The absorption of the studied phosphors increases from 450 to 700hm with an increment in nitrogen content. Blue-to-orange tunable luminescence is observed with 390 nm excitation.     

Adsorption Mechanism of Hydrogen on Boron-Doped Fullerenes

The C35BH-H2 complex and two other possible isomers, C34BCaH-H2 and C34BCbH-H2, are investigated using the local-spin-density approximation （LSDA） method. The results indicate that a single hydrogen molecule could be strongly adsorbed on two isomers, C34BCaH and C34BCbH, with binding energies of 0.42 and 0.47eV, respectively, and that these calculated binding energies are suitable for reversible hydrogen adsorption/desorption near room temperature. However, it is difficult for the H2 molecule to be firmly adsorbed on C35BH. We analyze the interaction between C34BCxH （x= a, b） and the H2 molecule using dipole moments and molecular orbitals. The charge analysis showed there was a partial charge （about 0.32e） transfer from 1-12 to the doped fullerenes. These calculation results should broaden our understanding of the mechanisms of hydrogen storage using borondoped fullerenes.     

Interface microstructure in epitaxial YBa2Cu3Ox/PrBa2Cu3Ox/YBa2Cu3Ox ramp-type Josephson junctions

The interfaces in ramp-type YBa₂Cu₃O_x/PrBa₂Cu₃O_x/YBa₂Cu₃O_x Josephson junctions with different ramp slopes were characterized electrically and structurally. From the cross-sectional TEM images, it has been found that the epitaxy remains through all layers even on the ramp surface, providing the ramp angle is less than 45°. No big defects such as grain boundaries and secondary phases occurred at the interface. The major defects which appeared at the interface are antiphase boundaries which were formed by lattice shifts with c/3 unit between PrBa₂Cu₃O_x and YBa₂Cu₃O_x. The interface between YBa₂Cu₃O_x base-layer and PrBa₂Cu₃O_x barrier is more defective in comparison with that between PrBa₂Cu₃O_x barrier and top-layer. Alteration of the ramp slope from 10° to 45° leads to a significant increase in the density of defects near the base-YBa₂Cu₃O_x/PrBa₂Cu₃O_x interface. The average roughness of the ramp surface created by ion milling is about 10 nm, which seems insensitive to the ramp slope. The damaged ramp surface could be repaired during the subsequent deposition process, leading to a negligible interface resistance.     

Preferential orientation of modified SrBi2Nb2O9 ferroelectric thin films prepared by pulsed laser deposition

We report on the deposition of SrBi₂Nb₂O₉ and Sr_1-xNa_xBi_2-xTe_xNb₂O₉ ferroelectric thin films on Pt/TiO₂/SiO₂/(100)Si substrates using the pulsed laser deposition technique. Deposition on substrates heated to 600-700 °C produces {11l} film texture and dense films with grain sizes up to about 500 nm. The recrystallization at 700 °C of amorphous films deposited at lower temperatures enhances the contribution of the {100} and {010} orientations. These films show smaller grain size, namely 50-100 nm. {11l}-oriented Sr_1-xNa_xBi_2-xTe_xNb₂O₉ films have remnant polarization P_rۆ 7C/cm², a coercive field E_c䏐 kV/cm and dielectric constant, )𪓴. The low value of P_r is probably related to the low fraction of grains with the ferroelectric axis in the direction of the applied field, E. The recrystallized films have more grains with the ferroelectric axis parallel to E; however, they have a low resistivity which so far has prevented electrical characterization.     

Phase-Transition and Magnetic Moment of the Gd3+ Ion in the Gd2Fe17 Compound

The structure and magnetic phase transitions of the Gd2Fe17 compound are investigated by using a differential thermal/thermogravimetric analyzer, x-ray diffraction, and magnetization measurements. The result shows that there are two phase structures for the Gd2Fe17 compound： the hexagonal Th2Nilr-type structure at high temperatures （above 1243℃）, and the rhombohedral Th2Zn17-type structure, respectively. A method to measure the magnetic moments of the Gd-sublattice and the Fe-sublattice in the Gd2Fe17 compound is presented. The moments of the Gd-sublattice and the Fe-sublattice in the Gd2Fe17 compound from 77 to 500 K are measured in this way with a vibrating sample magnetometer. A detailed discussion is presented.     

基于组分Ca2Pr2Cu5O10三元固溶区的范围和晶体结构

 利用X射线衍射分析和Rietveld结构精修方法研究了基于组分Ca₂Pr₂Cu₅O₁₀三元固溶区的范围和晶体结构。根据X射线分析结果和相消失法，为了保持Ca_2+xPr_2-xCu₅O₁₀结构单位晶胞中恒定的氧含量和电价平衡，基于组分Ca₂Pr₂Cu₅O₁₀的三元固溶区的范围可确定为：在Ca_2+xPr_2-xCu₅O₁₀固溶区的富Ca区（Ca/Pr>1），其表达式仍可以表示为一般的化学计量式Ca_2+xPr_2-xCu₅O₁₀（x=0.4, 0.2, 0）；在富Pr区（Ca/Pr<1），其表达式为Ca_1.7Pr_2.2·Cu₅O₁₀、Ca_1.4Pr_2.4Cu₅O₁₀，即：Ca_2+xPr_2-xCu₅O₁₀固溶区范围从Ca_2.4Pr_1.6Cu₅O₁₀至Ca_1.4Pr_2.4·Cu₅O₁₀。研究表明：基于组分Ca₂Pr₂Cu₅O₁₀的三元固溶体晶体结构可以看作是正交晶系NaCuO₂型亚晶胞的无公度相；Ca_2.4Pr_1.6Cu₅O₁₀亚晶胞的点阵常数为a₀=0.282 46(7) nm，b₀=0.636 93(1) nm，c₀=1.067 94(1) nm；其正交超结构的点阵常数为a=5a₀，b=b₀，c=5c₀。Ca_2.4Pr_1.6Cu₅O₁₀的结构也可以用单斜超晶胞来表述，该单斜超晶胞的空间群为P2₁/c，Z=4，a=5a₀，b=b₀，c=c₀/sin β，β=104.79°或136.60°，V=5a₀b₀c₀。在基于组分Ca₂Pr₂Cu₅O₁₀的三元固溶体晶体结构中，Ca和Pr之间在一定范围内是可以相互替代的，而且它们在结构中的占位是无序的。     

Compression Behaviour of Bulk Metallic Glasses and Binary Amorphous Alloy

The compression properties of Zr41Ti14Cu12.aNi10Be22.5, Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glasses and Ni77P23 binary amorphous alloy are investigated at room temperature up to 24 GPa, 39 GPa and 30.5 GPa, respectively, using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The pressure-volume relationship of Ni77P23 amorphous alloy is consistent well with the second order BirchMurnaghan （B-M） equation within the experimental pressure range. However, under higher pressure, the experimental data of Zr-based specimens deviate from the B-M equation. Compare to the binary amorphous alloy less excess free volume existing in the bulk metallic glass and multi-component atomic configuration results in a two-stage relationship between compressibility and pressure.     

An SU (3)_L×U(1)_X Electroweak Model

We studied an SU(3)_L×U(1)_X electroweak model. By requiring M2z1-M2w/ cos²θw to be less than experimental value we abtain a lower bound on M_Z′ The relation between M_Z′ and M_U (M_V) then gives a lower bound on M_U (M_V). We further consider the K_L－K_S mass difference due to Z′ exchange and obtain stronger lower bounds on M_Z′ and M_U (M_V).