On the asymptotic behavior of some algorithms

A simple approach is presented to study the asymptotic behavior of some algorithms with an underlying tree structure. It is shown that some asymptotic oscillating behaviors can be precisely analyzed without resorting to complex analysis techniques as it is usually done in this context. A new explicit representation of periodic functions involved is obtained at the same time. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2005     

DPSK色散管理线性和类孤子系统传输的简约解

采用简化法分别研究了差分相移键控（DPSK）色散管理线性和类孤子系统的传输特性,得出较为简洁明了的脉宽以及脉冲啁啾随距离演化的方程组.研究的结果发现,线性的DPSK系统只有在色散完全补偿的情形下是一种临界的稳定,而类孤子的DPSK系统即使在欠补偿情形下,系统也是完全的稳定,啁啾的演化是独特的闭合曲线.其完全稳定性的物理实质来自于非线性效应引入的自束缚势.从而说明DPSK色散管理类孤子系统良好的传输性能.     

光极限探测技术在空间通信中的应用

光是人类最早的科学研究对象之一,光子是光的最小能量单元,具备量子的基本特征。随着科学技术发展,人类已经能够实现对单个光子的极限探测。光的常规探测已经普遍应用于地面光纤通信中,而光的极限探测则在空间量子通信及深空超远距离光通信中具备重要的应用价值。文章介绍了光极限探测技术在空间量子科学实验、空间光子通信中的典型应用及涉及的核心技术。     

A convolution formula for time‐invariant linear communication systems

For every linear and time‐invariant time‐discrete (communication) system T : l^∞ → l^∞, formally, the following convolution formula can be derived: \input amssym.def $$(Tf)(n)=\sum_{k \in {\Bbb Z}} h(n‐k) f(k),\quad n \in {\Bbb Z}, f \in l^{\infty},$$ where h = Tδ is the delta impulse response. This paper is concerned with the question under which assumptions linear and time‐invariant time‐discrete systems T : l^∞ → l^∞ can be characterized by this formula. For this purpose we derive a convolution formula in a more general situation which also leads to a well‐known convolution formula in the time‐continuous case. Copyright © 1999 John Wiley & Sons, Ltd.     

AN采用FBG温度机械合成调谐技术的光滤波器

报道了一种采用特别设计的调节结构,并与温度机械相结合的方法来调谐FBG的中心波长的新颖光滤波器,它在温度变化60°范围内波长可线性调节9nm以上,线性度达0.9999.     

Comprehensive self-consistent three-dimensional simulation of an operation of the GaAs-based oxide-confined 1.3-μm quantum-dot (InGa)As/GaAs vertical-cavity surface-emitting lasers

In the paper, a comprehensive fully self-consistent three-dimensional simulation of an operation of the GaAs-based oxide-confined long-wavelength 1.3-m quantum-dot (QD)(InGa)As/GaAs vertical-cavity surface-emitting diode lasers is demonstrated. The model has been intentionally prepared for the PC-class microcomputers to enable its easy application in designing optimal structures of the above devices with desired performance characteristics. An impact of some structure parameters on QD VCSEL room-temperature (RT) continuous-wave (CW) lasing thresholds is discussed. A stable RT CW operation on a single fundamental mode has been found to be possible in modern QD VCSELs with active regions containing more uniform and more dense QDs in stacks of QD layers. The desired single fundamental-transverse-mode operation is possible for smaller active regions of diameters not exceeding 8 m. In the case of larger active regions, on the other hand, higher-order transverse modes of an increasing order are excited first because of increasingly more non-uniform optical-gain distributions.     

星间激光通讯中的精跟踪研究

星间激光通讯中，精跟踪起着十分重要的作用，而精密偏转镜(FSM)是精跟踪系统中最为关键的部件.基于光学矢量反射定律，推导得到了FSM的精确光学特性，这一特性为精跟踪控制系统提供了精确的理论依据.设计了基于FSM精确光学特性的精跟踪控制系统，对系统整定所用的单纯形法进行了两点重要改进，并对所设计的精跟踪系统进行了数字模拟，由此实现了对FSM的精确控制，提高了精跟踪系统的精确性；将光学衍射超分辨原理应用到星间激光通讯中.利用三区位相光瞳滤波器的超分辨性能，改变光学系统的点扩散函数，从而改变接收端焦平面上的光强分布.由此减小接收衍射光斑的大小，提高系统的光学分辨能力，从而提高精跟踪系统的精确性. 关键词： 星间激光通讯 精跟踪 精密偏转镜(FSM) 超分辨 光瞳滤波器     

基于纠缠态的量子通信网络的量子信道建立速率模型

针对基于纠缠态的量子通信网络, 提出了网络模型. 基于网络模型, 首先分析了基础链路的量子信道建立速率. 然后根据基础链路的量子信道建立速率, 针对不同的量子信道建立方法, 对中继长链路上的量子信道建立速率进行分析, 得到在逐点方法和分段方法下所对应的量子信道建立速率. 最后, 利用逾渗模型, 对大规模纠缠态量子通信网络中任意两点间的量子信道建立速率进行分析, 推导出n个节点量子通信网络中, 量子信道建立速率为Ω (1/n).     

准共线集成声光模式转换器的性能分析与设计

报道了一种SiO2薄膜声波导和Ti∶LiNbO3光波导之间存在一个角度的准共线的模式转换器结构, 利用波导模式分析导出薄膜声波导的宽度限制; 利用模式耦合理论得出了声光模式转换特性和耦合系数的加权形式. 实现了对耦合系数的加权, 较好地抑制了旁瓣. 在综合考虑旁瓣和线宽的条件下, 设计了这种TE/TM声光模式转换器, 其旁瓣为－16.8 dB, －3 dB线宽和－10 dB线宽分别为1.37 nm和2.31 nm.     

Two-dimensional block partitionings for the parallel sparse Cholesky factorization

This paper presents a discussion on 2D block mappings for the sparse Cholesky factorization on parallel MIMD architectures with distributed memory. It introduces the fan-in algorithm in a general manner and proposes several mapping strategies. The grid mapping with row balancing, inspired by Rothberg's work (1994), is proved to be more robust than the original fan-out algorithm. Even more efficient is the proportional mapping, as shown by the experiments on a 32 processor IBM SP1 and on a Cray T3D. Subforest-to-subcube mappings are also considered and give good results on the T3D. This revised version was published online in August 2006 with corrections to the Cover Date.