Coupling coefficients of gratings with graded refractive index waveguides

In this paper, the effective coupling coefficient k(eff) and the self-coupling coefficient zeta(1) are introduced to describe the characteristic of gratings in a resonant situation when the effects of radiation and other partial waves coupling are considered. The dependence of these two coupling coefficients on grating tooth shapes and depths and the dimensions of graded refractive index (GRIN) waveguides is numerically analysed. The results show that the gratings with linear GRIN waveguides have the largest \k(eff)\. The possibility of realizing a complex-coupled DFB laser, even a pure gain or loss coupled DFB laser, employing only a real refractive index coupled grating is also discussed.

Coupling coefficients of gain-coupled distributed feedback lasers with absorptive grating

An effective coupling efficient is introduced for gain-coupled distributed feedback lasers with absorptive grating. When radiation and other partial wave coupling effects are considered, the effective coupling coefficient will change significantly. In some cases, it will become real, although both loss and index coupling are presented.

Theoretical Study on the Butt-coupling of Semiconductor Laser and Fiber Bragg Grating

The butt-coupling between a semiconductor laser diode and a fiber Bragg grating external cavity acts a key roll on the laser characteristics. The scatter matrix method considering the butt-coupling efficiency is used to analyze the butt-coupling between them. It is found that the butt-coupling distance and coupling efficiency determine the laser characteristics. For strong feedback, the single lasing wavelength changes in the reflection bandwidth of the effective reflectivity ( approximately the Bragg region of the fiber Bragg grating) as the distances change. For weak feedback condition, some different results are obtained. The SMSRs in the two conditions are presented and analyzed. These results can provide important design guidance of device parameters for the practical fabrication.

Design of a Tapered Lens for Semiconductor Laser to Single-Mode Fiber Coupling

The theoretical investigation of the coupling efficiency of a laser diode to a single mode fiber via a hemispherical lens on the tip of the tapered fiber in the presence of possible transverse offset and angular mismatch is reported.Without the misalignment,coupling efficiency increases with the decreasing of taper length.With the misalignment,this relation is that the coupling efficiency decreases with each kind of offset.

Optimal distance from high power laser diode to cylindrical microlens in a coupling system

In a practical coupling system, a cylindrical microlens is used to collimate the emission of a high powerlaser diode (LD) in the dimension perpendicular to the junction plane. Using passive alignment, the LD isplaced in the focus of the cylindrical microlens generally, regardless of the performance of the multimodeoptical fiber and the LD. In this paper, a more complete analysis is arrived at by ray-tracing technique,by which the angle θ of the ray after refraction is computed as a function of the angle θo of the ray beforerefraction. The focus of the cylindrical microlens is not always the optimal position of the LD. In fact, inorder to achieve a higher coupling efficiency, the optimal distance from the LD to the cylindrical microlensis dependent on not only the radius R and the index of refraction n of the cylindrical microlens, but alsothe divergence angle of the LD in the dimension perpendicular to the junction plane and the numericalaperture (NA) of the multimode optical fiber. The results of this discussion are in good agreement withexperimental results.

Fiber Optic Coupling of CW Linear Laser Diode Array

Based on a set of microoptics the output radiation from a continuous wave (CW) linear laser diode array is coupled into a multi-mode optical fiber of 400 ptm diameter. The CW linear laser diode array is a 1 cm laser diode bar with 19 stripes with 100 fxm aperture spaced on 500 (xm centers. The coupling system contains packaged laser diode bar, fast axis collimator, slow axis collimation array, beam transformation system and focusing system. The high brightness, high power density and single fiber output of a laser diode bar is achieved. The coupling efficiency is 65% and the power density is up to 1.03 * 10~4 W/cm~2.

Fiber Coupling of Laser Diode Bar to Multimode Fiber Array

A piece of multimode optical fiber with a low numerical aperture (NA) is used as an inexpensive microlens to collimate the output radiation of a laser diode bar in the high numerical aperture (NA) direction. The emissions of the laser diode bar are coupled into multimode fiber array. The radiation from individual ones of emitter regions is optically coupled into individual ones of fiber array. Total coupling efficiency and fiber output power are 75% and 15W, respectively.

Influence of interdot electronic coupling on photoluminescence spectra of self-assembled InAs/GaAs quantum dots

The influence of interdot electronic coupling on photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) has been systematically investigated combining with the measurement of transmission electron microscopy. The experimentally observed fast red-shift of PL energy and an anomalous reduction of the linewidth with increasing temperature indicate that the QD ensemble can be regarded as a coupled system. The study of multilayer vertically coupled QD structures shows that a red-shift of PL peak energy and a reduction of PL linewidth are expected as the number of QD layers is increased. On the other hand, two layer QDs with different sizes have been grown according to the mechanism of a vertically correlated arrangement. However, only one PL peak related to the large QD ensemble has been observed due to the strong coupling in InAs pairs. A new possible mechanism to reduce the PL linewidth of QD ensemble is also discussed.

Rashba and Dresselhaus spin-orbit coupling in GaN-based heterostructures probed by the circular photogalvanic effect under uniaxial strain

The spin splitting in GaN-based heterostructures has been investigated by means of circular photogalvanic effect experiments under uniaxial strain. The ratios of Rashba and Dresselhaus spin-orbit coupling coefficients (R/D ratios) have been measured in AlxGa1-xN/GaN heterostructures with various Al compositions. It is found that the R/D ratio increases from 4.1 to 19.8 with the Al composition of the AlxGa1-xN barrier varied from 15% to 36%. The Dresselhaus coefficient of bulk GaN is experimentally obtained to be 0.4 eV angstrom(3). The results indicate that the spin splitting in GaN-based heterostructures can be modulated effectively by the polarization-induced electric fields.

Sequential coupling transport for the dark current of quantum dots-in-well infrared photodetectors

The dark current characteristics and temperature dependence for quantum dot infrared photodetectors have been investigated by comparing the dark current activation energies between two samples with identical structure of the dots-in-well in nanoscale but different microscale n-i-n environments. A sequential coupling transport mechanism for the dark current between the nanoscale and the microscale processes is proposed. The dark current is determined by the additive mode of two activation energies: E-a,E-micro from the built-in potential in the microscale and E-a,E-nano related to the thermally assisted tunneling in nanoscale. The activation energies E-a,E-micro and E-a,E-nano decrease exponentially and linearly with increasing applied electric field, respectively.

多Agent群体行为中的扩散趋同综述

为了研究复杂系统及复杂性科学问题,人们提出多Agent模型进行建模和分析.多Agent的群体行为是复杂系统研究所必须解决的问题,而其中的扩散趋同更是相关领域的研究热点.文中首先介绍多Agent群体行为中的扩散趋同现象,然后根据Agent扩散趋同传递的方式、Agent的扩散趋同能力的分布情况和Agent扩散趋同所感知的范围,将相关研究成果中的扩散趋同机制分为3个方面:层次结构性扩散趋同与群集性扩散趋同、平滑扩散趋同与非平滑扩散趋同、邻域扩散趋同与全局扩散趋同.文中对每种模型的特点进行论述和比较分析,最后指出下一步的研究方向.

一种用于软件过程建模的适应性Agent协商

大多软件过程模型是预定义的.在变化的应用环境中,需要由相应人员进行适应性调整.提出一种用于软件过程建模的适应性多边协商模型——AMNM-PA,其采用Agent封装软件过程中所涉及的个体,包含组织、团队、个人等,通过Agent间的协商动态、适应地建立针对给定软件项目的软件过程模型.AMNM-PA基于非静态有限阶段Markov决策过程,采用模型无关的Q学习算法选取协商策略,因此能够支持动态、非预知环境下的适应性协商,从而满足软件过程建模对环境的适应性需求.AMNM-PA已经实施于软件过程管理系统——SoftPM.

一种适应性多边软件过程Agent协商模型研究

软件过程建模是指对软件过程建立模型，并且对模型建立和模型执行提供自动化支持。软件过程建模技术为软件过程的描述、表示、执行、分析、跟踪、变更以及改进提供了方法和工具，从而为软件组织实现软件开发过程的管理和改进提供了有力的支持，对于保证软件组织的软件产品质量，提高开发效率具有重要的理论和实践价值。 软件过程的一个重要特征是极大地依赖于软件开发人员，当软件过程面临各种变化时，正是作为软件过程的主体——软件开发人员的及时反应和应对，使得软件过程能够灵活适应各种软件开发的实际和变化状况；忽视软件开发人员在软件过程中的核心作用，是目前大多软件过程建模方法不适用于软件企业实际应用的原因之一。Agent技术主要基于对人的观察，其已被认识到是软件过程建模领域的重要研究方向之一。然而，相关研究工作并没有很好地体现人在软件过程中的核心作用，其根本原因在于其所采用或关注的是单Agent技术，而非多Agent系统技术。以互联为背景的多Agent系统能够很好地刻画人类的社会性，因此，对于当前以全球性、分布式多点等为主要特点的软件过程而言，采用多Agent系统技术，关注软件过程中所涉及的实体之间的协商、协作、竞争、承诺等特性是将Agent技术应用于软件过程的研究重点。 本文提出一种适应性多边软件过程Agent协商模型AMNM-PA。AMNM-PA基于软件开发者为软件过程中的核心要素并且软件过程为这些核心要素之间的相互协同关系的观点，将软件开发建模描述为代表软件开发者的自治的软件过程Agent（简称过程Agent）之间的协商；在协商中，过程Agent能够在变化的环境下针对各种不同实际应用，以及根据对环境的感知和所拥有的知识，适应、灵活地确立彼此间的协同关系，即建立软件过程。 本文在组织上采用了从模型要素及其相互关系定义、模型要素具体描述到模型实现及验证的逻辑结构。首先，本文给出AMNM-PA的模型定义，对过程Agent的协商所涉及的协商要素及其相互之间的关系进行描述。其次，本文详细描述协商要素中的决策过程，即过程Agent在协商中进行决策所依据的协商策略选择方法及各种可选协商策略；并以决策过程为基础，提出一种多边适应性协商算法，以此给出基于AMNM-PA的适应性多边协商过程的基本算法。随后，本文详细描述了另一协商要素——协商规则，其解决了协商过程的离线和在线灵活性问题，从而为软件过程建模的灵活性提供了解决方案。最后，本文实现了基于AMNM-PA的协商系统，并在该系统的支持下进行了实验研究，验证了AMNM-PA能够在变化的环境中适应性地建立面向实际软件项目的软件过程，并且该软件过程所包含的个体利益能够得到均衡、整体利益较高；同时很好地支持了软件过程建立和执行的灵活性。

软件过程Agent的知识生成方法研究

软件开发过程的不可见是软件项目失败的主要原因之一。为了提高软件开发过程的可见性，研究人员从软件开发过程的表示、软件开发知识的管理和软件开发数据的挖掘等方面提出了相应理论、方法和工具，这些理论、方法和工具对提高软件过程的可见性提供了一定的帮助，但却都有自己的局限性，难以全面覆盖提高软件开发过程可见性的要素。 为此，我们需要进一步融合软件过程建模、知识管理和数据挖掘等领域各自的研究成果，探索一种不但支持从过程资产库提取知识，而且支持对这些知识进行描述和管理，同时还能将这些知识直接用于建立符合组织能力的软件过程模型，并可以根据该软件过程模型生成符合组织中人的能力的软件开发项目计划的完整方法，为提高软件开发过程的可见性提供全面、有力的支持，从而有效保障软件开发的质量和效率。 本文给出一种根据组织的软件过程资产库生成软件过程Agent知识的方法，该方法生成的软件过程Agent知识可被用于建立一种基于组织实体能力的软件过程模型。基于该方法，本文实现了一个软件过程Agent自动生成工具，该工具可以根据指定的软件过程资产库自动生成软件过程Agent实例及其知识。同时本文在应用实例研究中进行了实验验证，证明了该方法的有效性。 本文研究是对基于组织实体能力的软件过程建模方法的扩展和补充。该方法和基于组织实体能力的软件过程建模方法的集成，可有效支持根据组织过程资产库生成组织的软件开发知识并将这些知识进行描述，使其能够被用于建立符合组织能力的软件开发模型，并最终根据特定目标生成符合组织实际能力软件开发项目计划。