Layered switch architectures for high-capacity optical transport networks

Cataloged from PDF version of article.We propose and analyze layered switch architectures that possess high design flexibility, greatly reduced switch size, and high expandability. The improvement in loss and crosstalk due to the reduced switch size is also discussed. Theoretical models have been developed to compute the network blocking probability using these architectures. Low blocking probability and high network utilization are achieved because of the capability of communication between layers in adjacent switches. The results show that the proposed layered switch architectures are very attractive for high-capacity optical transport networks

Modeling all-optical space/time switching fabrics with frame integrity

All-optical networks have attracted significant attention because they promise to provide significant advantages in throughput, bandwidth, scalability, reliability, security, and energy efficiency. These six features appealed to optical transport-network operators in the past and, currently, to cloud-computing and data-center providers. But, the absence of optical processors and optical Random Access Memory (RAM) has forced the optical network designers to use optical-to-electrical conversion on the input side of every node so the node can process packet headers and store data during the switching operation. And, at every node’s output side, all data must be converted from its electronic form back to the optical domain before being transmitted over fiber to the next node. This practice reduces all six of those advantages the network would have if it were all-optical. So, to achieve a network that is all-optical end-to-end, many all-optical switching fabrics have been proposed. Many of these proposed switching fabrics lack a control algorithm to operate them. Two control algorithms are proposed in this dissertation for two previously-proposed switching fabrics. The first control algorithm operates a timeslot interchanger and the second operates a space/time switching fabric - where both these photonic systems are characterized by active Feed-Forward Fiber Delay Line (FF-FDL) and the frame-integrity constraint. In each case, the proposed algorithm provides non-blocking control of its corresponding switching fabric. In addition, this dissertation derives the output signal power from each switching fabric in terms of crosstalk and insertion loss

High capacity photonic integrated switching circuits

As the demand for high-capacity data transfer keeps increasing in high performance computing and in a broader range of system area networking environments; reconfiguring the strained networks at ever faster speeds with larger volumes of traffic has become a huge challenge. Formidable bottlenecks appear at the physical layer of these switched interconnects due to its energy consumption and footprint. The energy consumption of the highly sophisticated but increasingly unwieldy electronic switching systems is growing rapidly with line rate, and their designs are already being constrained by heat and power management issues. The routing of multi-Terabit/second data using optical techniques has been targeted by leading international industrial and academic research labs. So far the work has relied largely on discrete components which are bulky and incurconsiderable networking complexity. The integration of the most promising architectures is required in a way which fully leverages the advantages of photonic technologies. Photonic integration technologies offer the promise of low power consumption and reduced footprint. In particular, photonic integrated semiconductor optical amplifier (SOA) gate-based circuits have received much attention as a potential solution. SOA gates exhibit multi-terahertz bandwidths and can be switched from a high-gain state to a high-loss state within a nanosecond using low-voltage electronics. In addition, in contrast to the electronic switching systems, their energy consumption does not rise with line rate. This dissertation will discuss, through the use of different kind of materials and integration technologies, that photonic integrated SOA-based optoelectronic switches can be scalable in either connectivity or data capacity and are poised to become a key technology for very high-speed applications. In Chapter 2, the optical switching background with the drawbacks of optical switches using electronic cores is discussed. The current optical technologies for switching are reviewed with special attention given to the SOA-based switches. Chapter 3 discusses the first demonstrations using quantum dot (QD) material to develop scalable and compact switching matrices operating in the 1.55µm telecommunication window. In Chapter 4, the capacity limitations of scalable quantum well (QW) SOA-based multistage switches is assessed through experimental studies for the first time. In Chapter 5 theoretical analysis on the dependence of data integrity as ultrahigh line-rate and number of monolithically integrated SOA-stages increases is discussed. Chapter 6 presents some designs for the next generation of large scale photonic integrated interconnects. A 16x16 switch architecture is described from its blocking properties to the new miniaturized elements proposed. Finally, Chapter 7 presents several recommendations for future work, along with some concluding remark

Effect Of Reconfiguration On Ip Packet Traffic In Wdm Networks

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2007Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2007Günümüzde iletişim ağlarına erişen insan sayısı ve iletişim uygulamalarının ihtiyaç duyduğu band genişliği ihtiyacı hızla artmaya devam etmektedir. Artan trafik istekleri daha geniş band genişliği kullanımına olanak verebilen optik iletişim ağlarının tasarımını tetiklemektedir. Bir veya daha fazla sayıda optik fiberi kapsayabilen bir ışıkyolu alt katmanda yer alan optik altyapının üzerinde iletişim kanalları sağlamaktadır. Sanal topoloji tasarımı, verilen bir trafik matrisine göre bir grup ışık yolunun kurulması olarak tanımlanabilir. Trafikte meydana gelecek bir değişiklik yeniden konfigürasyon kararının alınmasına neden olabilir. Sanal topoloji yeniden konfigürasyonu, hem yeni sanal topolojinin belirlenmesini hem de bu yeni topolojiye geçişi içermektedir. Bu tez çalışmasında IP/WDM ağlarda sanal topoloji yeniden konfigürasyonunun IP paket trafiği üzerindeki etkileri incelenmiştir. Çalışma kapsamında, çeşitli yeniden kofigürasyon algoritmaları gerçeklenmiş ve Fishnet tabanlı bir IP simülatörü üzerinde test edilmiştir. Gerçeklenen sanal topoloji tasarım algoritmalarına ait paket gecikmeleri/kayıpları incelenmiş ve algoritmaların başarımları karşılaştırılmıştır.Today, both the amount of people accessing communication networks and new communication applications which require high data transfer rates are exponentially increasing. Growing traffic demands triggered the design of optical communication networks which will be able to provide larger bandwidth utilization. A lightpath, which can span multiple fiber links, provides communication channels over the underlying optical communication infrastructure. Virtual Topology Design (VTD) means establishment of a set of lightpaths under a given traffic pattern. A change in traffic pattern may trigger reconfiguration decision. Virtual Topology Reconfiguration (VTR) contains determination of a new virtual topology and migration between the old and new virtual topologies. In this thesis, the effects of virtual topology reconfiguration on Internet Protocol (IP) packet traffic on IP over WDM networks were studied. Various reconfiguration algorithms were implemented and tested on a Fishnet based IP simulator. Packet delays/losses are investigated during reconfiguration procedure for performance comparison of implemented reconfiguration algorithms.Yüksek LisansM.Sc

Energy Efficient High Port Count Optical Switches

The advance of internet applications, such as video streaming, big data and cloud computing, is reshaping the telecommunication and internet industries. Bandwidth demands in datacentres have been boosted by these emerging data-hungry internet applications. Regarding inter- and intra-datacentre communications, fine-grained data need to be exchanged across a large shared memory space. Large-scale high-speed optical switches tend to use a rearrangeably non-blocking architecture as this limits the number of switching elements required. However, this comes at the expense of requiring more sophisticated route selection within the switch and also some forms of time-slotted protocols. The looping algorithm is the classical routing algorithm to set up paths in rearrangeably non-blocking switches. It was born in the electronic switch era, where all links in the switches are equal. It is, therefore, not able to accommodate loss difference between optical paths due to the different length of waveguides and distinct numbers of crossings, and bends, leading to sub-optimal performance. We, therefore, propose an advanced path-selection algorithm based on the looping algorithm that minimises the path-dependent loss. It explores all possible set-ups for a given connection assignment and selects the optimal one. It guarantees that no individual path would have a sufficiently substantial loss, therefore, improve the overall performance of the switch. The performance of the proposed algorithm has been assessed by modelling switches using the VPI simulator. An 8×8 Clos-tree switch demonstrates a 2.7dB decrease in loss and 1.9dB improvement in IPDR with 1.5 dB penalty for the worst case. An 8×8 dilated Beneš shows more than 4 dB loss reduction for the lossiest path and 1.4 dB IPDR improvement for 1 dB power penalty. The improved algorithm can be run once for each switch design and store its output in a compact lookup table, enabling rapid switch reconfiguration. Microelectromechanical systems (MEMS) based optical switches have been fabricated with over 1,000 ports which meet the port count requirements in data centre networks. However, the reconfiguration speed of the MEMS switches is limited to the millisecond to microsecond timescale, which is not sufficient for packet switching in datacentres. Opto-electronic devices, such as Mach-Zehnder Interferometers (MZIs) and semiconductor optical amplifiers (SOAs) with nanosecond response time show the potential to fulfil the requirements of packet switching. However, the scalability of MZI switches is inherently limited by insertion loss and accumulated crosstalk, while the scalability of SOA switches is restricted by accumulated noise and distortion. We, therefore, have proposed a dilated Beneš hybrid MZI-SOA design, where MZIs are implemented as 1×2 or 2×1 low-loss switching elements, minimising crosstalk by using a single input, and where short SOAs are included as gain or absorption units, offering either loss compensation or crosstalk suppression though adding only minimal noise and distortion. A 4×4 device has been fabricated and exhibits a mere 1.3dB loss, an extinction ratio of 47dB, and more than 13dB IPDR for a 0.5dB power penalty. When operating with 10 Gb/s per port, 6pJ/bit energy consumption is demonstrated, delivering 20% reduced energy consumption compared with SOA-based switches. The tolerance of the current control accuracy of this switch is very broad. Within a 5 mA bias current range, the power penalty can be maintained below 0.2 dB for 8 dB IPDR and 12 mA for 10 dB IPDR with a penalty less 0.5 dB. The excellent crosstalk and power penalty performance demonstrated by this chip enable the scalability of this hybrid approach. The performance of 16×16 port dilated Beneš hybrid switch is experimentally assessed by cascading 4×4 switch chips, demonstrating an IPDR of 15 dB at a 1 dB penalty with a 0.6 dB power penalty floor. In terms of switches with port count larger than 16×16, the power penalty performance has been analysed with physical layer simulations fitted with state-of-the-art data. We assess the feasibility of three potential topologies, with different architectural optimisations: dilated Beneš, Beneš and Clos-Beneš. Quantitative analysis for switches with up to 2048 ports is presented, achieving a 1.15dB penalty for a BER of 10-3, compatible with soft-decision forward error correction.Cambridge Overseas Trust; China Scholarship Council

Advanced devices based on fibers, integrated optics and liquid crystals for WDM networks

The increment of bandwidth required for new services offered to users make necessary the use of optical fibres in data transmission. Glass optical fibres are widely used in long distance communications, and there are many devices implemented for using in these networks, but these technologies are sometimes expensive for their used in local loops. Different systems implemented over the established technology are used for increasing local loops bandwidth, but more services are demanded at home. Those applications require more bandwidth than the offered by the usual twisted copper pair. Multimode fibres (both silica and polymer) with larger core diameters and numerical aperture, allows for large tolerance on axial misalignments, which results in cheaper connectors as well as associated equipment, but with a bandwidth penalty with regards to their singlemode counterparts, mainly due to the introduction of modal dispersion. On the other hand, polymer optical fibre (POF) offers several advantages over conventional multimode optical fibre over short distances (ranging from 100m to 1000m) such as the even potential lower cost associated with its easiness of installation, splicing and connecting. This is due to the fact that POF is more flexible and ductile, making it easier to handle. Consequently, POF termination can be realized faster and cheaper than in the case of multimode silica fibre. Therefore, the number of applications that use POF is quickly increasing. POF is being used in video transmission in medical equipment, or in multimedia applications for civil aviation and high range cars, in-home and access networks, wireless LAN backbone or office LAN, and in intrinsic optical sensor networks among others. Even greater channel capacity can be available using a specific type of POF, perfluorinated Graded-Index POF (PF GIPOF), having low attenuation and large bandwidth from 650nm to 1300nm. Link lengths for in-building/home scenarios are short (less than 1 km), and thus the loss per unit length is of less importance. Transmission of 10Gbps data over 100m and transmission of 1.25Gbps Ethernet over 1 km have been experimentally demonstrated with PF GIPOF. On the other hand, combiners and multiplexers are basic elements in POF networks using Wavelength Division Multiplexing (WDM) and there are not that many already developed. It is important to have low losses devices and reconfiguration can be an additional feature in those networks. On the other hand, reconfigurable optical networks in critical applications demand devices able to have different functionalities, including switching. This work has focused in the development of different optical switches for a wide range of optical networks. Different switching technologies are available. Liquid crystals are widely used as displays, but they are also employed in telecommunications. Other common technology used in data routing is integrated optics. In this case, light propagates by means of a waveguide and the modification of its parameters makes possible switching operation. Micro-Electromechanical Mechanisms, MEMs, based in small mobile mirrors that can change the direction of the incident light when required are an important optical switching technology. The objective of the present work is the proposal of several optical switches using different technologies depending on the final application. Some of these structures have been experimentally tested whereas others have been simulated. Most of the presented switches use liquid crystals, having different functionalities and broadband operation range, so allowing wavelength division multiplexing. To these respect it has been developed an optical multiplexer/combiner and an advanced multifunctional optical switch (AMOS), both implemented with Nematic Liquid Crystal technology. It has also been developed a multiplexer/combiner based on Polymer Dispersed Liquid Crystals. The third kind of switches proposed are micro ring-resonators combined with liquid crystals. Micro ring-resonators consist of a circular waveguide attached to one or two straight waveguides acting like input and output ports. Light that passes through the structure can be filtered according to the ring resonator characteristics: ring length, coupling ratio, losses… The use of liquid crystal makes possible the tuning of the ring resonator filtering properties. The last proposed switch is made of a passive splitter and a Mach-Zehnder Interferometer. This kind of devices makes use of integrated optics and interference for switching purposes. The variation of the optical properties influencing the two light beam interference can be done in different ways: thermally, electrically… Finally, an automated optical characterization bench has been implemented in order to make easy the measurements. It is composed by a three axis translation stage with three actuators, several linear translation stages that allows the user to modify the bench structure for adapting it to his experiment, and different machinery for mounting the optics.The present research work has been supported by the following Spanish projects: TIC2003-038783 (DISFOTON), TEC2006-13273-C03-03-MIC (FOTOCOMIN) and TEC2009-14718-C03-03-MCI (DEDOS) of the Spanish Interministerial Commission on Science and Technology (CICYT), FACTOTEM-CM: S-005/ESP/000417, and FACTOTEM-II-CM: S2009/ESP-1781 and FENIS-CCG06-UC3M/TIC-619 of Comunidad Autónoma de Madrid. Additional financial support has been obtained form European Thematic Network SAMPA: Synclinic and Anticlinic Mesophases for Photonic Applications (HPRNCT- 2002-00202), carried out during the V Framework Program of the European Union, COST Action 299 FIDES: Optical Fibres Dedicated to Society, and from the European Network of Excellence: ePhoton/ONe+ (FP6-IST-027497), both carried out during the VI Framework Program of the European Union, and BONE: Building the Future Optical Network in Europe (FP7-ICT-216863) carried out during the VII Framework Program of the European Union

Advances in Optical Amplifiers

Optical amplifiers play a central role in all categories of fibre communications systems and networks. By compensating for the losses exerted by the transmission medium and the components through which the signals pass, they reduce the need for expensive and slow optical-electrical-optical conversion. The photonic gain media, which are normally based on glass- or semiconductor-based waveguides, can amplify many high speed wavelength division multiplexed channels simultaneously. Recent research has also concentrated on wavelength conversion, switching, demultiplexing in the time domain and other enhanced functions. Advances in Optical Amplifiers presents up to date results on amplifier performance, along with explanations of their relevance, from leading researchers in the field. Its chapters cover amplifiers based on rare earth doped fibres and waveguides, stimulated Raman scattering, nonlinear parametric processes and semiconductor media. Wavelength conversion and other enhanced signal processing functions are also considered in depth. This book is targeted at research, development and design engineers from teams in manufacturing industry, academia and telecommunications service operators