双包层光纤吸收效率影响因素的研究

泵浦光的吸收效率是影响双包层光纤激光器输出功率的重要因素.在对双包层光纤的掺杂离子浓度、纤芯直径、内包层形状和尺寸、光纤弯曲和缠绕、外包层的背底损耗等因素对吸收效率的影响进行分析的基础上,分析了改变上述因素来提高吸收效率过程中,会出现的制约因素和需要注意的问题.     

弯曲双包层光纤吸收效率的理论分析

以耦合功率理论为基础,提出了一种分析弯曲结构双包层光纤吸收效率的新方法.在双包层光纤内,由于弯曲结构引起在内包层中传输的泵浦光发生模式间的耦合,通过分析居于主要地位的模式间发生耦合的情况,计算耦合功率的大小.然后根据此功率的大小,判断弯曲结构双包层光纤内掺杂纤芯吸收泵浦光功率能力的强弱,并通过计算实例,分析弯曲结构对吸收效率的影响.最后结合侧面泵浦耦合技术,提出了一种新的大功率双包层光纤激光器的设计模型.     

缺陷型内包层双包层光纤吸收效率研究

缺陷型内包层双包层光纤由于其特殊的内包层横截面结构,对于光波的吸收效率要比理想圆型内包层双包层光纤提高许多.由于射线法在分析光波在光纤中的场分布、传播功率等情况时有其局限性,因此,文章改用波动理论对缺陷型内包层双包层光纤进行分析,试图找出不同类型的缺陷型内包层双包层光纤单位距离内吸收效率的差异.     

用边界反射原理计算双包层光纤的吸收效率

以双包层光纤(DCF)中内外包层分界面上的点作为研究对象,对于分界面上的任意一点运用边界反射原理,确定在内包层截面中,能发出被掺杂纤芯吸收的光线的点源所占有的面积,将此面积与内包层总截面积作一比较,算出这一点对双包层光纤吸收效率的贡献。按该方法计算内外包层分界面上每一点对吸收效率的贡献并取平均,最后可求得双包层光纤的总吸收效率。讨论了双包层光纤的圆对称和偏心两种情况,结果与已有文献中的结论完全一致,但这种方法的计算过程更为简便。     

新型螺旋型内包层双包层光纤吸收效率分析

提出一种新型的内包层横截面边界为螺旋曲线的双包层光纤结构,并给出一种分析双包层光纤吸收效率的新方法:它以射线法为基础,采用概率理论计算出光纤内部传播的光线每次被内包层边界反射后能够被纤芯直接吸收的概率,并以此概率来衡量内包层横截面形状对光纤吸收效率的影响.最后用这种方法对螺旋型双包层光纤进行分析,得出它比一般缺陷型双包层光纤优异的结论.     

双包层光纤内包层形状对吸收效率的影响分析

在理想情况下，用二维几何光学对双包层光纤中的泵浦光传输路线进行分析，从而得出不同内包层形状下的吸收效率。圆形内包层有最低的吸收效率，破坏同心圆的圆对称性后吸收效率显著提高，如偏心圆结构有比同心圆大的吸收效率，矩形和D形内包层可以达到理论上100％的吸收效率。     

用耦合功率理论分析缺陷双包层光纤吸收效率

当泵浦光在内包层有缺陷的双包层光纤(DCF)内传输时,只有在光纤中心处有场强的LP0n模才能直接被单模掺杂纤芯吸收;但根据耦合模扩散理论,与LP0n模对应的一组亮环最邻近的2n个亮环所携带的功率能耦合进LP0n模,被纤芯吸收。运用耦合功率理论中的功率耦合系数方程,算得2n个亮环与相应LP0n模间的2n个功率耦合系数,将之相加得到总的功率耦合系数。根据此系数的大小,可以判断单位长度内掺杂纤芯吸收光功率能力的强弱。运用这种方法计算内包层为D型、有双重缺陷和矩形的DCF的功率耦合系数,可以发现,在内包层缺陷面积相等的前提下,前者的吸收效率更大,这结果用基于射线法的等亮度定理是得不到的。     

渐变折射率双包层光纤吸收效率的波动理论分析

用已知的积分公式计算了光纤中的总模数;用WKN方法推导了2个积分,分别用以计算两部分不能被双包层光纤(DCF)纤芯吸收的模式数量;最后将不被吸收的模式数与光纤总传播模式数作比较,得出渐变折射率DCF的吸收效率。给出了计算实例．讨论了吸收效率与渐变折射率参数及纤芯偏心距离之间的关系。     

双包层光纤放大器研究

双包层光纤放大器输出功率高,可用于密集波分复用系统、光纤CATV系统以及空间光通信系统中。本文采用分段方法,利用光子数平衡原理建立了半数值双包层掺稀土光纤放大器理论模型。利用本模型可以对双包层光纤放大器进行优化设计。     

1310nm FP TO-CAN偏心封装耦合效率的研究

文章应用ZEMAX软件模拟了管芯与光纤在不同偏移量下的耦合效率,并进行了实验验证.结果表明,6.5 mm焦距的TO-CAN(晶体管外壳封装)与端面倾斜8°的光纤,在管芯偏移100μm时,耦合效率最大,模拟值为21.9％,实验值为21.32％;5.8 mm焦距的TO-CAN与端面倾斜6°的光纤,在管芯偏移80 μm时,耦...     

Analysis and Optimization of the Energy Efficiency in the 802.11 DCF

This paper introduces an analytical model to investigate the energy efficiency of the IEEE 802.11 distributed coordinated function (DCF). This model not only accounts for the number of contending nodes, the contention window, but also the packet size, and the channel condition. Based on this model, we identify the tradeoff in choosing optimum parameters to optimize the energy efficiency of DCF in the error-prone environment. The effects of contention window and packet size on the energy efficiency are examined and compared for both DCF basic scheme and DCF with four-way handshaking. The maximum energy efficiency can be obtained by combining both the optimal packet size and optimal contention window. To validate our analysis, we have done extensive simulations in ns-2, and simulation results seem to match well with the presented analytical results. The Ohio Board of Regents Doctoral Enhancements Funds and the National Science Foundation under Grant CCR 0113361 have supported this work. Xiaodong Wang received his B.S. degree in communication engineering from Beijing Information Technical Institute of China in 1995, and his M.S. degree in electric engineering from Beijing University of Aeronautics and Astronautics of China in 1998. He joined China Telecom in 1998 where he worked on communication protocols for telecommunication. From June 2000 to July 2002, he worked on GSM base station software development at Bell-labs China, Beijing, China. Currently he is a Ph.D. student in Computer Engineering at University of Cincinnati. His research activities include wireless MAC protocols, energy saving for wireless sensor networks. He is a student member of the IEEE. Jun Yin received the BS degree in automatic control from Dalian Railway Institute of China in 1997, and the MS degree in flight control from Beijing University of Aeronautics and Astronautics of China in 2001. Since 2001 she has been a Ph.D. student in the OBR Research Center for Distributed and Mobile Computing at the University of Cincinnati. Her research interests include performance evaluation of 802.11 MAC protocol, wireless ad hoc networks and sensor networks. She is a student member of the IEEE. Dharma P.Agrawal IEEE Fellow, 1987; ACM Fellow, 1998; AAAS Fellow, 2003 Dr. Agrawal is the Ohio Board of Regents Distinguished Professor of Computer Science and Computer Engineering in the department of Electrical and Computer Engineering and Computer Science, University of Cincinnati, OH. He has been a faculty member at Wayne State University, (1977–1982) and North Carolina State University (1982–1998). He has been a consultant to the General Dynamics Land Systems Division, Battelle, Inc., and the U. S. Army. He has held visiting appointment at AIRMICS, Atlanta, GA, and the AT&T Advanced Communications Laboratory, Whippany, NJ. He has published a number of papers in the areas of Parallel System Architecture, Multi computer Networks, Routing Techniques, Parallelism Detection and Scheduling Techniques, Reliability of Real-Time Distributed Systems, Modeling of C-MOS Circuits, and Computer Arithmetic. His recent research interest includes energy efficient routing, information retrieval, and secured communication in ad hoc and sensor networks, effective handoff handling and multicasting in integrated wireless networks, interference analysis in piconets and routing in scatternet, use of smart directional antennas (multibeam) for enhanced QoS, Scheduling of periodic real-time applications and automatic load balancing in heterogeneous workstation environment. He has four approved patents and three patent filings in the area of wireless cellular networks.     

基于效用最大化的IEEE 802.11 DCF性能分析及改进

针对802.11 DCF在系统负载较大时不能有效利用带宽资源的缺点,该文提出一种基于效用函数的DCF优化机制(U-DCF)。通过设置站点吞吐量的对数效用函数,将带宽资源的有效利用问题建模为系统效用最大化问题;应用最优化理论将此系统问题等效为可分布式求解的用户问题,即各站点只须独立选择最大化其净效用的竞争参数(CWmin),则系统整体效用也获得最大化。仿真结果表明：与标准DCF相比,U-DCF通过预估系统的当前平均分组长度和竞争站点数来调整竞争参数CWmin,能够显著提高系统的饱和吞吐量,减小分组发送时延和丢帧率。     

无线局域网DCF性能分析与仿真

主要分析了在无线局域网中应用比较广泛的MAC协议DCF(分布式协调功能)协议的性能.从DCF的基本接入模式和RTS/CTS模式出发,分析了不同的节点数下分别在低速、中速、高速下两种接入模式吞吐量和延时方面的比较.通过仿真验证了低速状态下RTS/CTS在大多数情况下比基本接入模式无论在吞吐量和延时方面都更加有效,而且节点数越多的时候,情况越明显.而在高速状态下,基本接入模式要比RTS/CTS方式有效.     

IEEE802.11 DCF容量分析与讨论

本文介绍了IEEE802.11DCF(分布式协作功能)及分析其容量的3种方法,根据分析及仿真结果重点研究了网络容量与活跃结点数的关系,表明活跃结点数过多或过少时网络容量不理想的主要原因是当前所采用退避算法本身的局限性所致,退避算法仍需进一步改进。     

DCF光纤拉曼放大器的实验研究

DCF(dispersion compensating fibre)光纤具有较高的拉曼增益系数,利用这一点可以用较短长度的DCF光纤制成分立式的光纤拉曼放大器,作为传输线路上的损耗补偿.本文在测量并计算了DCF光纤的拉曼增益系数的基础上,对分立式的DCF放大器的开关增益和噪声指数进行了测量和分析,并将分立式FRA和分布式FRA在开关增益和噪声指数方面做了比较。介绍了用不同的测量方法所造成的实验结果的差异.实验结果表明,放大介质为5 km的DCF光纤所构成的放大器,在抽运功率为800 mW的条件下,最大增益可达14.77dB,3 dB带宽为35 nm,满足作为损耗补偿的要求.     

The Impact of RTS Threshold on Capacity of IEEE 802.11 DCF

Distributed coordination function (DCF) is the fundamental medium access control (MAC) mechanism in IEEE 802.11[1]. There are essentially two MAC techniques in DCF: a basic access method that uses two-way handshaking (DATA-ACK) and a RTS/CTS variant that uses Request-To-Send and Clear-To-Send messages in a four-way handshake (RTS-CTS-DATA-ACK). In a hybrid system, there is a preconfigured RTS threshold. Packet with payload longer than this threshold is transmitted in RTS/…     

A Novel Event Model for Performance Analysis of IEEE 802.11 DCF

After considering the memory effect among series events occurring on the channel, we propose a novel event model to analyze the channel status more precisely. The memory effect is caused by the backoff freezing regulation of IEEE 802.11 Distributed coordination function （DCF）, which has been ignored before and thus resulted in the inaccurate evaluation of the network performance. Based on our new event model, the network performance of IEEE 802.11 DCF, including throughput, packet delay distribution and energy efficiency is analyzed. Simulation results show that our model is highly accurate.