解决光突发交换竞争的新模型

针对光突发中的竞争问题，提出了一种分割反馈模型，相应地建立了数学分析模型，并进行了仿真与性能分析。结果表明这一模型是解决光突发交换中竞争问题的一个较佳方案。     

色散缓变光纤中五阶非线性调制不稳定性

在三五阶非线性共存时,研究了有损耗单模光纤中基于两光波交叉相位调制的不稳定条件和增益谱.在色散缓变光纤正色散区,分析了五阶非线性系数、色散纵向变化参量以及两扰动的频率大小关系对交叉相位调制不稳定增益谱的影响.结果表明,在五阶非线性下,色散的纵向渐减仍有利于展宽调制不稳定增益谱;正五阶非线性可使增益谱的谱宽和谱峰值增大,并使谱峰位置远离主波频率,负五阶非线性的作用则相反;两扰动频率大小关系不同,色散纵向参量的变化对增益谱的谱峰大小和位置的影响也不同,五阶非线性对交叉相位调制不稳定性的加强或抑制程度也不同.     

一种FDL和LRWC相结合的光分组交换网络的性能分析

研究了FDL和有限长波长转换器(LRWC)相结合的方法来解决异步变长的分组交换网中的冲突问题,对这种冲突解决方案建立了数学模型并进行了理论分析,提出了一个用于修正最佳延迟单元的公式,即在负载较大的情况下,我们要求延迟单元较小,这样可显著的降低在此交换网中的分组丢失率;对系统丢包率与负载、FDL数目和最佳延迟单元的关系进行了研究和讨论,结果表明:在同样的输入负载情况下,有限长波长转换器(LRWC)的引入可以降低缓存的数量;对延迟单元的修正可以大大降低丢包率,同时系统的性能较之单独使用FDL时有较大的改善。     

Performance of fiber delay‐line buffers in asynchronous packet‐based optical switching networks with wavelength conversion

A major challenge in asynchronous packet‐based optical networks is packet contention, which occurs when two or more packets head to the same output at the same time. To resolve contention in the optical domain, two primary approaches are wavelength conversion and fiber delay line (FDL) buffering. In wavelength conversion, a contending packet can be converted from one wavelength to another in order to avoid conflict. In FDL buffering, contending packets can be delayed for a fixed amount of time. While the performance of wavelength conversion and FDL buffering has been evaluated extensively in synchronous networks with fixed‐sized packets, in this paper, we study the performance of FDL buffers in asynchronous packet‐based optical networks with wavelength conversion. An analytical model is proposed to evaluate the performance in terms of packet loss probability and average delay. Extensive simulation and analytical results show that, with appropriate settings, FDL buffers can perform much better in switches with wavelength conversion than in switches with no conversion. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterization of the conjugated polymers tethered with dipolar side chains containing a benzothiadiazole entity for bulk heterojunction solar cells

New conjugated copolymers (P1?P3) containing dipolar side chains connected to the main chain via triphenylamine donors have been synthesized and characterized. The side chains of these polymers have an electron deficient benzothiadiazole moiety in the spacer, but with different acceptors at the end. By changing the acceptor moieties of the side chain, the absorption spectra and HOMO/LUMO gaps of the polymers can be fine-tuned, ranging from 1.86 to 1.59 eV. Solution processed bulk heterojunction (BHJ) solar cells using these polymers as the donor and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as the acceptor were fabricated and measured under 100 mW cm^?2 of AM 1.5 illumination. The cell based on the blend of P1/PCBM (1:1, w/w) exhibited the highest power conversion efficiency of 1.78%, with open circuit voltage (V_oc) = 0.79 V, short circuit current (J_sc) = 6.63 mA cm^?2 and fill factor (FF) = 0.34, respectively.     

Performance evaluation of throughput in optical burst switching

Optical burst switching (OBS) provides a promising solution to utilize the huge terahertz bandwidth of optical wavelength division multiplexing (WDM) transmission technology. To exploit this bandwidth, several reservation schemes have been proposed that include just‐in‐time (JIT) signaling, just‐enough‐time (JET) signaling and burst segmentation (BS). It is necessary to investigate the performance of these schemes under the same constraints for a prescribed OBS application. Accordingly, in this paper, we analyzed and compared the performance of JIT, JET and BS techniques under various scenarios such as network size, delay variation and load variation in an OBS network using various performance metrics, such as the offset time and switch configuration time. Also, the performance of the network under various switching delays was also investigated. The modified BS reservation scheme has been found to yield significantly better performance and better throughput compared with the JIT and JET reservation schemes. Test results show that the effect of varying loads as well as delays significantly impacts the performance of the OBS network. The results presented in this paper are expected to lead further performance improvements in OBS networks using the BS reservation scheme. Copyright © 2010 John Wiley & Sons, Ltd.     

QoS aware routing and wavelength allocation in optical burst switching networks using differential evolution optimization

The issue of burst losses imposes a constraint on the development of Optical Burst Switching (OBS) networks. Heavy burst losses strongly affect the Quality of Service (QoS) intended by end users. This article presents a QoS aware Routing and Wavelength Allocation (RWA) technique for burst switching in OBS networks. The RWA problem is modeled as a bi-objective Integer Linear Programming (ILP) problem, where objective functions are based on minimizing the number of wavelengths used and the number of hops traversed to fulfill the burst transmission requests for a given set of node pairs. The ILP model is solved using a novel approach based on a Differential Evolution (DE) algorithm. Analytical results show that the DE algorithm provides a better performance compared to shortest path routing, which is a widely accepted routing strategy for OBS networks.     

大模场单模增益光纤的研究进展

高功率光纤激光器的发展面临着各种非线性效应和输出模式和功率不稳定等技术瓶颈,而大 模场单模光纤被认为是解决该类问题的主要手段。 本文系统总结了各种典型的大模场单模增益光纤,阐述了各种光纤的 结构特点以及实现原理,重点分析 了光纤的模场面积、输出功率、抗弯曲特性、激光光束质量和制备难度等几项关键指标。最 后介绍了作者最新设计的新型异质包层螺旋侧漏大模场 单模光纤结构模型及其实现路径,该光纤芯径在50～200μm范围内 具有可调控性,且制备相对简单,有望成为大模场单模光纤 发展的一个新的方向。     

Polymorphism in Crystalline Microfibers of Achiral Octithiophene: The Effect on Charge Transport,Supramolecular Chirality and Optical Properties

Polymorphic crystalline microfibers from an achiral octithiophene with one S‐hexyl substituent per ring are separately and reproducibly grown with the same characteristics on various solid surfaces, including the interdigitated electrodes/SiO₂ surface of a bottomcontact field‐effect transistor. The arrangement of the same molecule in two diverse supramolecular structures leads to markedly different electronic, optical, and charge mobility properties. The microfibers—straight and yellow emitting or helical and red emitting—exhibit p‐type charge transport characteristics, with the yellow ones showing a charge mobility and on/off current ratio of one and three orders of magnitude, respectively, greater than the red ones. Both forms show circular dichroism signals with significant differences from one form to the other. DFT calculations show that the octithiophene exists in two different quasi‐equienergetic conformations aggregating with diverse orientations of the substituents. This result suggests that the observed polymorphism is conformational in nature. The self‐assembly, driven by sulfur–sulfur non‐bonding interactions, amplifies the small property differences between conformers, leading to quite different bulk properties.     

Fluorinated and non-fluorinated conjugated polymers showing different photovoltaic properties in polymer solar cells with PFNBr interlayers

Photovoltaic properties of the two polymers (named as PBQ-0F and PBQ-4F) were investigated by employing [6, 6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the acceptor and a water-alcohol-soluble polymer interlayer material (named as PFNBr) to fabricate photovoltaic devices. For the PBQ-0F:PC₇₁BM blend, the device using Ca/Al as cathode showed very similar efficiency as the device using PFNBr/Al as cathode, while for the PBQ-0F:PC₇₁BM blend, photovoltaic performance of the device can be distinctly improved by replacing Ca/Al with PFNBr/Al. As a result, the best PCE of the PBQ-4F:PC₇₁BM based devices reached 9.04%, which is much higher than that of the PBQ-0F:PC₇₁BM based devices. The results obtained from the quantum chemistry calculations and water contact angle measurements demonstrate that these two polymers are low polar materials, and also the films based on them have hydrophobic surfaces. Since PFNBr has an amphipathic structure (hydrophobic backbone and hydrophilic side chain) and the blend films of PBQ-4F:PC₇₁BM and PBQ-4F:PC₇₁BM have different surface energies, the PFNBr organization atop these two blend types of should be different, which will affect device photovoltaic performance.     

Modeling and performance analysis of IP access interface in optical transmission networks with packet switching

The article analyzes the influence of the Internet Protocol (IP) access interface on the packet loss probability and delay times in the optical packet switched network. The network and node model have been proposed, and the structure of the IP access interface, including assembler and holder, have been included in the analysis. It has been shown that the increase of the maximum optical packet sizes, as well as use of the holding feature as contention resolution mechanism, decrease the packet loss probability, but introduce delays at the optical network access points. Modeling and analysis were based on the discrete event simulation assuming self-similar traffic sources. IP packet lengths were modeled using empirical data. This work has been conducted while the author was affiliated with the Telecommunication Laboratory, Swiss Federal Institute of Technology (EPFL-STI-ITOP-TCOM), Lausanne, Switzerland     

高阶色散情况下光纤中基黑孤子传输特性的变分研究

本文从含修正项的非线性薛定谔方程出发,采用变分法,导出了光纤零色散附近高阶色散微扰影响下,基黑孤子脉冲参数随传输距离的演化方程组及其解析解。结果表明:高阶色散影响下,孤子脉宽比不存在高阶色散时加大,但振幅、频率、脉宽不随传输距离变化,因此基黑孤子能够保形传输,比明孤子具有更好的稳定性。     

基于同波长光纤延迟线集光突发交换结构及其性能分析

由于光突发交换机制本身就避免了光缓存的使用，但是现实中，光突发包之间竞争以及提供优先级服务又依靠光纤延迟线来解决。为此，我们设计了应用光纤延迟线的光突发交换网络核心节点结构。为了避免光纤延迟线色散引起的突发包输入排队缓存偏移，在该结构中设计了同波长光纤延迟线集。采用了空分交换矩阵，避免了波长转换的需要。为了有效运行该交换结构，我们提出了输入排队与自适应光缓存调度算法，而该算法不仅仅适用于光突发交换，也适合于光纤延迟线得到普遍应用的光分组交换。该调度算法能够提供优先级服务，避免队头阻塞，对该调度算法建立了严格的理论分析模型，并进行了仿真。仿真结果表明，与传统的延迟线竞争解决方案相比，这一调度算法能够改善交换性能1到2个数量级，是利用光纤延迟线解决光突发交换中竞争问题的一个较佳方案。     

半导体光放大器(SOA)皮秒增益和折射率非线性的数值模拟

从速率方程出发 ,采用分段模型对半导体光放大器 (SOA)的皮秒增益和折射率非线性进行了数值模拟 ,具体分析了注入光脉冲引起的载流子浓度的变化、输出光脉冲时域波形的畸变、注入光脉冲引起的增益和位相变化 ,以及输出光脉冲上的频率啁啾。     

Link budget calculation in optical LEO satellite downlinks with on/off-keying and large signal divergence: A simplified methodology

Direct-to-Earth transmissions with optical on/off-keying are becoming the method of choice to realize telemetry downlinks from low Earth orbit satellites at highest data-rates. Here, we review the calculation procedure for a practical assessment of the mean link budget in this space-ground data communication technology. We present a comprehensive survey of the dynamic orbital and beam-pointing effects as well as the impacts from atmospheric attenuation on the link performance. The paper provides an exhaustive review of the formulas commonly used and propounds a recipe to reliably estimate the received power on ground. An overview of typical data transmitter terminals, transmission channel parameters, and the according optical ground stations is provided. Comparison with measured received powers over transmitter elevation angle and the respective design estimates serves for verification.     

弹性光网络中结合预测的多维感知RSA算法

弹性光网络(EON)中的传统路由频谱分配(RSA)算法多考虑路由跳数或频谱资源占用情况,缺乏时域与相邻链路的信息有效利用.提出一种结合预测的多维感知RSA算法,对持续时间已知业务的历史时间信息通过后向传播神经网络预测未来业务的时间信息,在路由时综合考虑时间、频谱和相邻链路资源占用程度.仿真结果表明:与传统RSA算法相比...     

Study of the interfaces in resistive switching NiO thin films deposited by both ALD and e-beam coupled with different electrodes (Si, Ni, Pt, W, TiN)

Thin NiO films, included in a metal/resistive oxide/metal (MRM) stack, are receiving great interest, as they exhibit resistive switching when subjected to an external applied field, and can thus be implemented in a resistive random access memory (ReRAM). The electrical switching characteristic is seen to depend on the NiO/metal coupling. Therefore a characterization of the interface between NiO and the electrode is vital to optimize and get insights on the switching phenomena. In this work we deposited NiO thin films by atomic layer deposition (ALD) at 300 °C and electron beam deposition (e-beam) at 40 °C on Si, Ni, Pt, W and TiN substrates and we characterized them with X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and time of flight secondary ion mass spectrometry (ToF-SIMS). Depending on the growth process, we found an influence of the substrate on the NiO film roughness, which exhibits values in the 1.2-6.2 nm range. NiO electron density was 1.35-1.96 e⁻Å⁻³ spread around the nominal value of 1.83 e⁻ Å⁻³ for bulk cubic polycrystalline NiO. X-ray diffraction showed that NiO is polycrystalline in the cubic phase. ToF-SIMS profiles confirm NiO/Metal interface sharpness and the optimal uniformity of NiO layers. Intermixing phenomena are limited or absent and the presence of contaminants, such as C, F, and Cl is very low.