Architectures and techniques for all-optical networks

Abstract

Some recent results on all-optical packet-switching and broadcasting networks are presented. The performance evaluation problem of packet-switching transparent optical networks with deflection routing is addressed. Transmission error arguments show how, for a given optical bit rate, the size of an all-optical nonregenerative multishop network is limited by the accumulation of noise and distortion in the optical fiber channel. Time-domain multiple access techniques are exploited in novel architectures based on recently proposed all-optical sampling gates to realize the matching of the ultrahigh optical speed allowed by the large bandwidth of the fiber with the lower speed of the electronic components needed at the user ends. These architectures allow great simplification of the node structure in the considered all-optical multihop and broadcast networks.     

Cutting-Edge Technologies on Broadband and Scalable Photonic-Network—Packet switched networks based on all-optical label processing—

Ultra-high speed all-optical label processing methods are proposed and experimentally demonstrated. These methods dramatically increase the label processing capability. Optical packet switch (OPS) systems and networks based on OPS nodes are expressed as an application of optical processing technologies. First, the 40 Gbit/s/port OPS prototype with all-optical label processor, optical switch, optical buffer, and electronic scheduler is described. The feasibility of OPS networks is verified by experimental demonstrations.     

0.73～1.7μm超宽带微纳光纤波导全光调制器

提出了单层石墨烯包裹双锥形微纳光纤复合波导结构,构建了730~1 700nm超宽带微纳光纤波导全光调制器。通过火焰拉锥法将一根标准的通信单模光纤拉成具有双锥形的微纳光纤,在保证通光率的前提下可以极大的提升微纳光纤处的倏逝波与物质的相互作用。利用石墨烯的"超级特征",即单原子层厚度、线性色散的能带结构、超强的载流子带间跃迁及极短的弛豫时间和超宽带光与物质相互作用等,将单层石墨烯作为可饱和吸收体,包裹在双锥形微纳光纤波导的锥体上,以增强该复合波导表面倏逝波与石墨烯的相互作用。静态和动态全光调制实验中采用传统808nm低功率LD作为泵浦光,对谱宽为480~1 700nm的超连续谱探测光实现了光光调制,其泵浦光功率低于50mW,调制深度大于5.7dB,调制速率达到~4kHz。该微纳光纤波导全光调制器,在保证调制深度的情况下,用更低的泵浦功率实现了超宽带的全光调制,以简单、有效、廉价的方式兼容了当前高速光纤通信网络,打开了一扇未来对微纳超快光信号处理的大门。     

O-RPR网络中622 Mbps光上路源的研制

基于全光缓存器的光弹性分组交换环(O-RPR)是一种全光分组交换网络,能够克服目前RPR存在的电子瓶颈。为了模拟这种网络解决竞争的能力和解决网络的帧同步不丢失的问题,设计了一种基于FPGA的光上路源。它由数据包(帧)生成、并串变换和电光转换三部分组成,其包长、包内伪随机序列长度、及通信速率均可变,具有结构简单、成本低廉和操作方便的优点,已成功应用于O-RPR实验网络中。     

研制超宽带全光取样示波器设备

全光取样示波器是研究与开发超高速光通信系统和光子交换网络的关键性测试仪器设备. 本文简介了我们自行设计和研制出的超宽带全光取样示波器设备的实验样机系统, 并报道了我们已取得的初步实验结果. 采用自主研发的高稳定性被动锁模飞秒光纤激光器作为该光学示波器的光脉冲取样源, 我们通过利用高度非线性光纤中的四波混频效应, 成功地实现了对脉宽为1.8ps、重复频率分别为10GHz和40GHz的光脉冲信号的全光取样. 然后通过数字信号处理和计算机图形处理, 得到了再现后的超短光脉冲信号波形, 并测出了其脉冲宽度值为2.3ps. 借助于该光学取样示波器实验样机, 我们还成功地完成了对脉宽为1.8ps、经过伪随机数据序列调制后的10Gbit/s和40Gbit/s光数据信号眼图的精确测量. 这是我国首次报道有关超宽带全光取样示波器设备的实际研制工作及其相应的实验测试结果. 所得到的有关超短光脉冲信号波形的测试结果也与用70GHz宽带电子示波器和超快光电探测器组成的常规光电测量系统所获得的结果进行了比较, 清楚地表明了我们研制出的全光取样示波器实验样机比后者具有更高的时间分辨率和更大的测量带宽.     

光交叉连接结构的分类和推演

光交叉连接(OXC)是波分复用(WDM)全光网的核心节点技术,其结构直接决定了其性能,严格无阻塞是最根本的要求.对于已经提出的多种多样的OXC结构,本文归纳出四种最基本的无阻塞结构,在此基础上具体推演分析其它OXC结构,这样便清晰地论证了OXC结构的阻塞性.对部分阻塞结构提出了消除阻塞的修正方法.     

基于注入锁定法布里-珀罗激光器的光学双稳态及光存储研究

研究基于注入锁定法布里-珀罗激光器的全光双稳态效应及其在全光存储中的应用. 进行了法布里-珀罗激光器的注入锁定的实验研究, 对注入锁定的法布里-珀罗激光器的输出功率特性进行实验分析, 得到了不同注入光波长失谐量对迟滞曲线的门限宽度和消光比的影响. 进一步, 通过对控制信号功率的合理设置, 实现了对10 Gb/s输入信号的2.5 GHz光存储验证了利用注入锁定法布里-珀罗激光器实现高速全光存储的可行性, 在高速光纤通信领域具有极大的应用价值.     

An all-optical comparison scheme between two multi-bit data with optical nonlinear material

Over the last few decades, several all-optical circuits have been proposed to meet the need of high-speed data processing. In some information processing architectures, the role of various analog and digital data comparisons is very important. In this letter, we proposed a multi-bit data comparison scheme. The scheme is based on the switching property of optical nonlinear material. Ultrafast operational speed larger than gigahertz can be expected from this all-optical scheme.OCIS codes: 190.0190, 200.0200, 200.1130, 200.3760.     

基于光纤中四波混频效应的全光串-并转换研究

 为了实现高速信号的降速处理,设计并通过实验演示了一种高速全光串-并转换系统。在方案中,利用时钟脉冲自身的频谱宽度和光纤中四波混频的高速响应特性,可以从一个光分频时钟脉冲出发,利用光纤中群速度色散（GVD）致脉冲展宽效应,把一个重复频率为10 GHz的时钟窄脉冲在时域上展宽,并通过光纤中的四波混频过程,将一路40 Gb/s 的归零（RZ）码信号转换成为4路10 Gb/s信号,完成串-并转换功能。该方案响应速率高,对波长和码率透明,并具有很大的转换路数可拓展性。     

一种覆盖全通信波段的新型宽带偏振无关双芯光纤定向耦合器的研究

提出了一种新型的双芯光子晶体光纤, 应用全矢量有限元方法分析了光纤各种结构参数对光纤宽带特性和偏振无关特性的影响. 在此基础上优化设计了一种50:50的双芯光子晶体光纤耦合器, 在1.225—1.675 μm波长范围内实现分光比小于1%、两偏振态之间的分光比差小于0.5%的优良特性. 由于引入了仅对偏振特性影响明显的相对独立的中心调制区, 不仅降低了光纤的优化设计难度, 而且实现了与普通单模光纤相匹配的模场特性, 能有效地降低耦合器的接续损耗与制作难度. 研究成果为研制接续损耗低、超宽工作带宽、偏振不敏感等特性的新型光定向耦合器提供了理论基础.     

Wavelength conversion in optical transport networks

The introduction of optical technology in the path layer of a transport network is analyzed; in particular, the impact of all-optical wavelength conversion is examined. Two basic optical cross-connect schemes based on space switching and on wave-length switching, respectively, and two types of wavelength converters are considered. The wavelength converters are, respectively, based on four-wave miring (FWM) in semiconductor optical amplifiers (SOAs) and on cross-phase modulation (XPM) obtained by two SOAs put in an interferometric configuration. An analysis of transmission performances of optical transport networks employing both types of wavelength conversion and both the node architectures is reported. The performances are evaluated by means of a system modeling that facilitates considering physical phenomena occurring during transmission and all the important transmission impairments. The analysis reveals that both the types of converters can be employed with different features and limitations, according to the considered network and switching architecture.     

SOA-assisted Sagnac switch and investigation of its roadmap from 10 to 40 GHz

Future broadband optical communications networks will rely on all-optical switches to perform a set of processing functions exclusively in the optical domain. Interferometric optical switches using semiconductor optical amplifier (SOA) nonlinearities can perform efficient optical switching with few tens of fJ control energies and short fiber lengths allowing for monolithic integration. In this paper we present work performed with a three terminal SOA-assisted Sagnac interferometer. We review all-optical Boolean AND and XOR logic results at 10 GHz and 10 Gb/s for full duty cycle and pseudo-random data pattern operation, respectively, achieved with adequate contrast ratios, remarkably low switching energies and low pattern dependence. The ability of the device to be cascaded was proved up to 10 GHz by recirculating stably for hours arbitrary pattern profiles. Finally, and in view of the extension of photonic networks single channel data rates beyond 40 Gb/s, the performance of the switch was simulated in terms of its critical parameters. The obtained results showed that full switching operation at 40 GHz or higher is feasible either by deploying gain recovery reduction techniques in bulk and quantum well SOAs or alternatively other technologically advanced optical devices, such as quantum dot SOAs.     

Ultra-high speed all-optical shift registers and their applications in OTDM networks

All-optical shift registers are basic building modules for the development of ultra-high speed optical time division multiplexing networks. In this paper, we review the progress that has been made in this cutting-edge technology, focusing on implementations that exploit the attractive features of semiconductor optical amplifier (SOA)-based interferometric configurations. We present regenerative storage performed with an all-optical recirculating shift register with an inverter at 10 Gb/s using a SOA-assisted Sagnac switch and a second SOA to provide feedback. We demonstrate also an all-optical memory based on the SOA-assisted Ultrafast Nonlinear Interferometer capable of reading/writing 20 Gb/s packets of variable length without data inversion. These registers can find application in the development of two nontrivial complex all-optical circuits of enhanced functionality. The first is an all-optical pseudorandom binary sequence generator for which we describe an efficient design algorithm and propose ways for monitoring and verification. The second is an all-optical error counter for which we address the error detection and evaluation issues using a novel sampling technique. These circuits are key elements for the implementation of a high-speed, all-optical bit error rate tester (BERT), which has the potential to outperform its electronic equivalent and constitute a possible new product for the telecommunications industry.     

Turbo-switched Mach-Zehnder interferometer performance as all-optical signal processing element at 160 Gb/s

Two variations of the active Mach-Zehnder interferometer (MZI) that incorporate the recently proposed turbo-switch effect are introduced to carry out three key functionalities in forthcoming high-speed optical telecommunication networks, namely, all-optical wavelength conversion, photonic XOR gating and optical time-division demultiplexing. Their performance is numerically investigated at 160 Gb/s using a sophisticated semiconductor optical amplifier (SOA) model. The more practical of the two proposed geometries shows error-free operation as XOR Boolean gate, low patterning as wavelength converter, and poor performance as demultiplexer. For comparison, results derived from well-accepted (or typical) schemes are also presented, and the role of the required extra SOAs as distinguishing elements of the new architectures is investigated.     

全光地址识别机理的研究

在面向分组业务的全光交换系统中,采用全光地址处理技术可以减少处理时延,大大提高信息处理速度和网络吞吐量,对全光网络的研究具有重要意义。分析了光正交码的自相关性与互相关性,并将其特性应用于全光传送网中,以针对未来基于光分组业务的全光环网为例,提出了一种光分插复用器的新型结构,给出了总体应用设计规则,重点研究和分析了全光地址识别机理和相关的应用设计方法,给出了针对全光环网组网规模的仿真分析结构和基本实验结果。结果表明采用所提出的设计原则和设计方法来实现全光地址识别是可行的。     

All-optical switch and limiter based on nonlinear polarization in Mach-Zehnder interferometer coupled with a polarization-maintaining fiber-ring resonator

A novel all-optical switch based on nonlinear polarization mechanism using polarization-maintaining fiber ring with a polarization rotator is proposed. Optical switching with low threshold of mW order and optical limiting with broader limiting range, less fluctuation, higher damage threshold and response speed are demonstrated numerically. The deterioration of switching and the improvement of limiting originating from losses are also studied. Considering the tradeoff between switching power and bandwidth, the way to increase bandwidth is discussed.     

半导体光放大器的稳态增益饱和特性

高速全光逻辑门是实现光分组交换、光计算和未来高速大容量光传输的关键器件,近年来受到广泛的关注。半导体光放大器（SOA）因为具备体积小、工作波长范围宽、响应时间短及良好的非线性特性等优点,成为研制高速全光逻辑器件的首选。采用分段模型分析了SOA的稳态增益饱和特性,通过数值求解载流子速率方程和光传输方程对其特性进行了仿真实现。结果表明,SOA在入射光功率不同时会表现出明显的非线性;在一定范围内增加光功率,SOA增益持续增加,继续增加入射光功率,SOA逐渐进入饱和吸收状态,增益反而降低。     

Numerical investigation on buffer performance based on acoustic excitation by stimulated Brillouin scattering in an As2Se3 fiber

Buffer performance of a 2.5 Gb/s bit stream with non-return-to-zero format is investigated based on acoustic excitation by stimulated Brillouin scattering in an As₂Se₃ fiber. The storage process and the retrieval process of the bit stream are separately controlled by a “Write” pulse and a “Read” pulse. The research results show that the output signal-to-noise ratio and the readout efficiency of the buffer are agreeable, and the pulse distortion is low, if both the “Write” and the “Read” pulses are with high enough peak power and spectrum wider than that of the signal pulse. Buffering of a consecutive 10-bit-long 2.5 Gb/s NRZ bit stream has also been demonstrated in the As₂Se₃ fiber with length of only 0.5 m. The storage of a long bit stream, such as the data packet containing about 1000 bits in the telecommunications, is limited by the high loss in the As₂Se₃ fiber. However, the development of the special optical fiber with high Brillouin gain coefficient, long acoustic lifetime and low loss can make this technology applicable for all-optical buffering in high speed optical networks.