Nonblocking photonic switch networks

A practical algorithm is described, with examples, for deciding whether or not a given network of 2×2 photonic switches is truly unblocking. Nonblocking photonic networks with specific additional properties, e.g. planarity, short path length, are also discussed, and specific networks, which have advantages over the square networks so far fabricated, are described. It is also shown that a correspondence can be set up between classical switch networks and networks of 2×2 switches, so that the classical results on blocking can be carried over to these networks     

Tree-type photonic switching networks

The enormous bandwidth offered by optical systems makes photonic switching a very attractive solution for broadband communications. Tree-type architectures play an important role in the design of photonic switching networks. The authors present and discuss all known tree-type space-division photonic switching networks architectures in a unified framework, and propose a number of new solutions. The discussed networks can be implemented with guided-wave-based switching elements, or laser diodes and passive splitters and combiners. The following network types are considered: conventional, simplified, and two-active stage networks. Techniques for improving SNR as well as waveguide crossover minimization are presented and discussed     

Non-coherent photonic frequency-multiplexed access networks

Noncoherent WDMA/FDMA (wavelength-division multiaccess/frequency-division multiaccess) networks that use tunable filters to select channels are considered. They have the same sensitivity as direct-detection networks, which is about 10 dB less than coherent networks. However, the noncoherent networks are much less complicated, which makes them interesting for multiaccess applications, where cost is more important than sensitivity. The direct-detection sensitivity is sufficient to allow as many as 1000 channels. Some recent research network experiments and progress on essential components for realizing noncoherent FDMA networks are reviewed     

Architectural considerations for photonic switching networks

Photonic technologies are reviewed that could become important components of future telecommunication systems. Photonic devices and systems are divided into two classes according to the function they perform. The first class, relational, refers to devices, that map the input channels to the output channels under external control. The second class, logic, perform some type or combination of Boolean logic functions. Some of the strengths and weaknesses of operating in the photonic domain are presented. Relational devices and their applications are discussed. Optical logic devices and their potential applications are reviewed     

Predeployment of resources in agile photonic networks

This paper shows that the main challenge in remotely configurable optical networks lies in how networks should be designed and sized for dynamic traffic in the face of uncertain forecasts, so as to minimize capital expenses, predominantly due to the need to predeploy (or overprovision) resources in preparation for the next connection request. In addition, this paper demonstrates how the operational savings promised by such capabilities measure up against the added capital expenses. Consequently, new ways to provision resources in the network to minimize these expenses are proposed. The results are based on real-world long-haul networks and costs.     

A class of directional-coupler-based photonic switching networks

A class of photonic switching networks composed of directional couplers is proposed. These networks require only two switching stages containing active elements. Both point-to-point and multicast architectures are presented. Various characteristics of the networks are compared to those of networks previously known with respect to insertion loss, SNR, number of crossovers, and number of active elements     

Wavelength switching components for future photonic networks

This article provides a review of integrated laser and semiconductor optical amplifier components that have been configured to provide a variety of all-optical functions such as wavelength conversion, routing, signal regeneration, and add-drop multiplexing. The components have been devised so that they can be reliably and simply used within a multiwavelength network. The article introduces the components by outlining the current leading techniques for wavelength conversion using SOAs, namely by way of cross-gain modulation, cross-phase modulation, and four-wave mixing. The integrated SOA distributed feedback laser is then shown to provide excellent regeneration properties, not only overcoming fiber dispersion limitations but also polarization mode dispersion. Finally, the devices are shown to make possible a regenerative wavelength switching node where routing is achieved using a tunable laser to provide regenerative wavelength conversion followed by an arrayed waveguide router. This switch shows promise for use in future photonic packet switching architectures     

Modified dilated Benes networks for photonic switching

A modified dilated Benes (1965) network composed of directional couplers is proposed. This structure is introduced to improve the signal-to-noise ratio (SNR) characteristics of dilated Benes networks. A new estimation of the SNR for dilated Benes networks is derived, and it is shown that this SNR is much worse than that previously known. The SNR for modified dilated Benes networks is estimated and compared to dilated Benes and other network architectures. Some other properties including the number of switching elements required, number of crossovers, and system attenuation are also derived and analyzed. Most of the characteristics are shown to be similar to dilated Benes networks and better than those of other well-known networks fabricated in Ti:LiNbO ₃     

光子晶体光纤在全光网中的应用

光子晶体光纤(PCF)以其独特的光学特性和灵活设计的特点,而成为近年来研究的热点.随着各种新型PCF的问世以及研究的深入,使其应用领域不断扩大.文章对PCF在全光网中的各项应用进行了分析,重点对PCF在光纤光栅和光纤激光器、放大器、光开关、波长变换器方面的研究进展进行了介绍.     

Design of photonic rearrangeable networks with zero first-orderswitching-element-crosstalk

The development of optical cross-connect architectures is a very important topic today. We consider here in particular the class of optical space-division switching fabrics configured as multistage structures built with 2×2 optical switching elements (SEs) and derived from a combination of vertical replication and horizontal expansion of Banyan networks. We determine the necessary and sufficient conditions for these matrices to be rearrangeably nonblocking and free of first-order crosstalk in SEs. This impairment is one of the major limitations in optical cross-connect performance. We focus on rearrangeable matrices since they have lower complexity than their strict-sense nonblocking counterparts. Given the current high cost of optical SEs, the rearrangeable solution looks attractive today     

Paired block line codes for pure photonic networks

New line coding schemes called paired block codes (PBC) are investigated for application in future pure photonic networks. The first block of each pair utilises coding rule violations to simplify transmission frame structures to facilitate frame processing to complement limited capabilities of photonic logic devices. The second block is provided with sufficient redundancies to attain photonic clock recovery through logical processing. An upper bound efficiency of this type code is 75%.<>     

A photonic knockout switch for high-speed packet networks

A high-performance packet switch is discussed which uses a photonic interconnect fabric to route very-wideband data packets from input to output. Packet contention is accomplished using a much slower electronic controller, based on the knockout principle operating in parallel with the optical interconnect. Specifically, the use of a wavelength-division-multiplex fabric whereby high-speed (2-4 Gb/s) packets are regenerated before modulating a single-frequency laser at each switch input. The optical signals from various inputs are summed in a star coupler and then broadcast to the different coupler outputs. Each coupler is equipped with a small number (L) of tunable receivers arranged in a parallel manner, each preceded by a power splitter so that up to L simultaneous packets can be received by each output. The L packets so received are stored in an L-input one-output first-in first-out (FIFO) buffer so that the FIFO packet sequence is always guaranteed. Not only does this architecture achieve the best delay-throughput performance, but, remarkably, modularity is such that the optical complexity grows linearly with the number of switch ports./     

Low-complexity multiple access protocols for wavelength-divisionmultiplexed photonic networks

Media access control protocols for an optically interconnected star-coupled system with preallocated wavelength-division multiple-access channels are discussed. The photonic network is based on a passive star-coupled configuration in which high topological connectivity is achieved with low complexity and excellent fault tolerance. The channels are preallocated to the nodes with the proposed approach, and each node has a home channel it uses either for data packet transmission or data packet reception. The performance of a generalized random access protocol is compared to an approach based on interleaved time multiplexing. Semi-Markov analytic models are developed to investigate the performance of the two protocols. The analytic models are validated through extensive simulation. The performance is evaluated in terms of network throughput and packet delay with variations in the number of nodes, data channels, and packet generation rate     

PCE-based fast path control in multi-domain photonic networks

We discuss issues for controlling an optical path in large-scale photonic networks, and introduce an inter-domain path control system based on Path Computation Elements (PCEs). In the system, maximum flow information enables the load balancing of traffic, and Path Key scheme preserve the confidentiality of internal topology information among carrier networks. Based on the experimental results, we show the path setup in the introduced system is significantly faster than the manual path setup among domains in current carriers' networks. For the additional reduction of the path setup time, we propose the domain-wise paralleled signaling method. We also show that decreasing the number of nodes per domain makes path setup faster in the introduced system with deployment of the proposed signaling method.     

基于WDM技术的未来光传输网络

讨论了光技术的潜在用途并确定它们在基础传输网功能中的基本任务。实践证明,光层的引入不仅在传输能力和路由节点的吞吐量上同时带来巨大飞跃,而且允许不同信号格式和协议的有效融合。文章给出了大容量WDM系统的传输能力,讨论了光纤放大器和非线性效应的影响最后阐述了实现可靠通信所需的技术,论述了光网络保护的策略。     

A coherent photonic wavelength-division switching system forbroad-band networks

A coherent photonic wavelength-division (WD) switching system, utilizing a coherent wavelength switch (λ switch), is proposed. In the proposed coherent λ switch, the tunable wavelength filter function is accomplished using coherent optical detection with a wavelength tunable local oscillator. The coherent photonic WD switching system has the following features; (1) low crosstalk switching for dense WDM signal, and (2) large line capacity capability. Design considerations show that 32 wavelength division channels can be available with a coherent λ switch. It is also shown that a broadband metropolitan-area-network with over 1000 line capacity is possible, using a multistage connection in the coherent λ switches. The switching function of the coherent λ switch is demonstrated in a two-channel wavelength-synchronized switching experiment, using 8-GHz-spaced, 280-Mb/s optical FSK signals     

Future photonic transport networks based on WDM technologies

It is expected that the explosion in Internet traffic implies a paradigm shift from a voice network to a data-centric network. The first and most important requirement of future transport networks is the large bandwidth transport capability which enables the paradigm shift. In addition, requirements for new service attributes are becoming more tangible. Furthermore, high reliability will be indispensable because the multimedia network will be the basis for the information society. To develop the robust and efficient networks that satisfy the requirements above, new network architectures and technologies should be developed. Photonic networks employing dense WDM technologies appear to be the solution. In this article, first the basic concept of the future photonic network is depicted. Next, the capability of large-capacity fiber transmission is shown. The critical degradation factor of fiber nonlinearity is analyzed, and the effectiveness of distributed amplification is quantitatively demonstrated. Furthermore, advances in fiber amplifiers which greatly widen the usable fiber window are shown. Other key technologies such as absolute frequency referencing and multiple channel frequency management techniques are also discussed     

A universal analytic model for photonic Banyan networks

One of the important considerations in designing waveguide-based photonic switching networks is to avoid crosstalk. Two approaches have been proposed which dilate a network in the space and time domains, respectively, to establish crosstalk-free connections. The space-domain dilation uses more hardware, representing cost in space, while the time-domain dilation uses more rounds (or time slots), representing cost in time. In order to evaluate the space-time tradeoffs involved in these two approaches, an analytical model is developed. We describe a recursive procedure which calculates the probability that a new connection can be established without crosstalk in a Banyan (or dilated Banyan) network by taking into consideration the dependency between traffic distributions at different stages. A Markov process based on such probabilities is then used to determine the average number of rounds needed for a set of one-to-one random connections. The model is applicable to both Banyan and dilated Banyan networks, with either stage or individual control. Simulation results are also obtained and compared to the analytic results. We show that the time-domain approach can achieve better space-time tradeoffs than the space-domain approach. One of the practical implications of this result is that a multiplane Banyan network may be more cost-effective than a dilated Banyan in avoiding crosstalk     

智能光开关——实现全光网的关键

在光纤传输系统中,应用ＤＷＤＭ技术的目的是为了满足Ｉｎｔｅｒｎｅｔ及其它电信业务对带宽的爆炸性需求。单根光纤可同时传输的波长数已从几年前普通ＷＤＭ的８个波长增长到国前ＤＷＤＭ的约１６０个波长,其增加的容量相当于数十万路电话的容量。 然而,人们对容量和带宽的需求是永无尽头的,最终的目标是建设一个能达到以Ｔｂ／ｓ速率传输的全光通信网。 全光网络的关键要素是“透明”,即网络中的光交叉连接与光分插复用器件应与所传输的数据格式、比特率以及所使用的协议无关。有几种类型的光开关提供了这种透明性。 这种光开关不需…     

Highly reliable optical bidirectional path switched ring networks applicable to photonic IP networks

The reliability of the optical bidirectional path switched ring (OBPSR) network is studied by using optical networking equipment (ONE) with microelectromechanical system (MEMS)-based optical switching fabrics. The reliability of the wavelength path in OBPSR networks is shown to be highly dependent on redundant schemes of switching fabrics in the ONE. This study proposes a new redundant scheme utilizing optical couplers together with controlled switch fabrics without using active selectors, and shows that reliability of the wavelength path can be remarkably improved. A fast redundant switching operation of 10 ms was experimentally confirmed with a prototype of the ONE based on the proposed redundant switching fabrics. Furthermore, interworking operations in terms of the protection and restoration between the optical layer and the Internet protocol (IP) layer are experimentally investigated. In a 500-km optical ring network, fast wavelength path protection switching was confirmed without reconfiguring the link state database of the IP layer, and the measured protection time in the IP layer was as short as 21 ms.