Symmetry and optical transition rule for low-dimensional semiconductor system with spin-orbit interaction and magnetic field

Starting from effective mass Hamiltonian, we systematically investigate the symmetry of low-dimensional structures with spin-orbit interaction and transverse magnetic field. The position-dependent potentials are assumed to be space symmetric, which is ever-present in theory and experiment research. By group theory, we analyze degeneracy in different cases. Spin-orbit interaction makes the transition between Zeeman sub-levels possible, which is originally forbidden within dipole approximation. However, a transition rule given in this paper for the first time shows that the transition between some levels is forbidden for space symmetric potentials. (C) 2009 Elsevier Ltd. All rights reserved.

Numerical and theoretical analysis of the crosstalk in linear optical amplifiers

The dynamic characteristics, including the crosstalk and relaxation oscillation, of linear optical amplifiers (LOAs) are investigated by small-signal analysis under an averaging carrier density approximation and compared with the results of numerical simulation. The good agreement between the numerical simulation and the small-signal analysis indicated the averaging carrier density is an appropriate approximation for analyzing LOAs. Theoretical analyzes also show that the dynamic properties of the vertical laser fields dominate the dynamic performance of LOAs. Based on the small-signal analysis, a concise equation for the crosstalk under high bit rate was derived, which can be applied to measure the differential gain of LOAs.

Temperature dependence of the optical properties of InAs/GaAs self-organized quantum dots with bimodal size distribution

In this work we report the optical and microscopic properties of self-organized InAs/GaAs quantum dots grown by molecular beam epitaxy on (1 0 0) oriented GaAs substrates. A distinctive double-peak feature of the PL spectra from quantum dots has been observed, and a bimodal distribution of dot sizes has also been confirmed by scanning tunneling microscopy (STM) image for uncapped sample. The power-dependent photoluminescence (PL) study demonstrates that the distinctive PL emission peaks are associated with the ground-state emission of islands in different size branches. The temperature-dependent PL study shows that the PL quenching temperature for different dot families is different. It is shown that the coupling between quantum dots plays a key role in unusual temperature dependence of QD photoluminescence. In addition, we have tuned the emission wavelength of InAs QDs to 1.3 mu m at room temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

基于场景的笔式界面设计工具的设计和实现

设计实现了一个基于数字笔的用户界面设计工具，该工具以面向笔式界面领域，基于场景的设计思想来设计系统中的界面场景组织关系以及场景之间的动态切换方式，设计者与工具间的交互自然流畅、快捷高效。通过手势识别技术，该工具可以将场景的设计结果转换为内部的界面描述语言，并通过相应的解释最终构造生成笔式用户界面。该工具可以快速生成界面原型，从而有效地提高了笔式交互系统的设计和开发效率。

子午岭植被恢复对土壤饱和导水率的影响

通过对子午岭林区不同植被的土壤性质进行实验室测定和野外调查,对饱和土壤水分运动的重要参数之一土壤饱和导水率(Ks)及其相关因子进行了多元分析和通径分析,揭示了植被恢复提高土壤水分传输性能的机理,主要结论如下:土壤有机质是子午岭林区九种植被下土壤饱和导水率提高的主要驱动因子。不同植被下的土壤饱和导水率均随深度的增加而迅速降低,尽管草地和先锋草地在5～10cm深度有一强透水层。土壤饱和导水率在剖面上的平均值,从辽东栎、早期森林、灌丛、先锋草地、弃耕地到草地依次降低。灌丛与草地、弃耕地的差异达到显著水平,辽东栎顶级群落的饱和导水率最高,植被的恢复明显提高了土壤饱和导水率。土壤容重、毛管孔隙度、>0.25mm团聚体含量及粘粒含量直接影响土壤饱和导水率。土壤有机质含量的提高能够改善容重、毛管孔隙度、团聚体含量等物理性质。

铜的多元复合物组成、结构和电学性质的研究

本论文包括三个部分的内容，第一部分研究了Y-Ba-Cu-O材料中，钙、钾、氟离子的掺入对材料结构和电、磁学性质的影响。1、在Y_(1-x)Ca_xBa_2Cu_3O_(7-y)系列中，当x ≤ 0.15时，钙离子进入了YBa_2Cu_3O_(7-y)晶格中钇离子的位置，使晶胞参数略为增大，但没有引起正交 → 四方相变。钙离子渗入导致123相中Cu~(3+)含量上升，同时材料的监界超导转变温度下降。因此，Cu~(3+)含旱管高可能是对超导电性不利的。由于钇离子位置紧邻着Cu(2)-O平面而与Cu(1)-O链相隔较远。因此，钇离子被钙离子替代时主要影响了Cu(2)-O平面的性质。少量钙离子的渗入即明显影响材料的超导电性，这说明Cu(2)-O平面的性质与超导电性密切相关，并可能起着关键的作用。2、在Y(Ba_(1-x)Ca_x)_2Cu_3O_y系的研究中，当x = 1，YCa_2Cu_3O_y是一个单一的化合物，文献未见报道，本文研究了它的结构，电学性质与热学性质，确定它的结构属正交晶系，a = 5.286 A、b = 7.636 A、c = 9.286 A。热分析表明YCa_2Cu_3O_y在1080 ℃分解，分解前于380 ℃ 和608 ℃出殃失氧现象。这个化合物是黑色n型半导体。室温电阻率1.2 * 10~5Ω·cm。与热分析中的失氧温度相对应，lnρ-1/T曲线上在370 ℃、620 ℃ 出现两个转折点。3、在Y-Ba-Cu-O材料中渗入钾离子能细化材料晶粒，降低超导转变宽度，提高零电阻温度，但由于KOH、K_2CO_3等强吸湿性杂质的存在也降低了材料的稳定性。4、在Y-Ba-Cu-O材料中间时掺入钾和氟离子时，材料的超导电性的变化与仅掺钾时相似。这种变化可能主要是钾离子的影响造成的。第二部分中，我们研究了Ca-Sr-Ca-O系的相图和新化合物Sr_3Cu_5O_(8+x)、CaSrCu_3O_(5+x)的结构和电学性质。在第三部分中，广泛研究了组成为Bi_tSr_vCa_wCu_zO_y超导材料的制备，结构和超导电性。铋系超导材料的形成貌与YBa_2Cu_3O_y材料有较大差异，前者是片状层叠的晶粒堆积而成，后者是球状小颗粒堆积而成的。我们合成的材料最高起始转变温度124K，最高零电阻温度112K，与国际上已达到的最高Tc值一致。Jc值达到131A/cm~2。

高功率VCSEL中应变补偿量子阱的理论设计

利用模型固体理论、k．p理论和Pikus-Bir理论，研究了InGaAs／GaAsP应变补偿量子阱，得出了较为简单通用的设计方法；进而研究了阱宽、InGaAs中In组分和GaAsP中P组分等参数对跃迁波长的影响。理论计算发现，与InGaAs／GaAs普通量子阱相比，InGaAs／GaAsP应变补偿量子阱能提供更深的载流子阱和更大的增益。按照提出的理论设计方法，研制了含InGaAs／GaAsP应变补偿量子阱的垂直腔面发射激光器（VCSEL），理论计算和实验结果相吻合。

高密度排列大功率垂直腔面发射激光器列阵

报道了980nm高密度排列大功率垂直腔面发射激光器列阵的研制.列阵单元为蜂窝状密堆积排列,单元台面直径为70μm,氧化孔径为30μm,相邻单元间隔为100μm.制作了含7,19,37个单元的列阵,讨论了它们的阈值电流和远场特性.在室温连续工作条件下,3种列阵的最大输出功率分别为0.26,0.5和0.6W.其中含37个单元的列阵在6A脉冲电流(脉宽30μs,重复频率100Hz)激发下,输出功率达到1.4W.