4 research outputs found
Energy-efficient design of optical transport networks
Energy efficiency is becoming a key factor in the design and operation of telecommunications networks as a way to reduce operational expenditures and the carbon footprint associated to telecom operators. This Ph.D. thesis evaluates and proposes novel energy-efficient approaches in three design areas of optical transport networks: (1) Network architectures and operation modes; (2) Resilience schemes; and (3) Optical amplifier placements. The solutions proposed in these areas are shown to significantly reduce the power consumption in realistic deployment scenarios and could be applied by telecom operators in the near and medium-term future to enhance the energy efficiency of optical transport networks
Domain/Multi-Domain Protection and Provisioning in Optical Networks
L’évolution récente des commutateurs de sélection de longueurs d’onde (WSS -Wavelength Selective Switch) favorise le développement du multiplexeur optique d’insertionextraction reconfigurable (ROADM - Reconfigurable Optical Add/Drop Multiplexers) à plusieurs degrés sans orientation ni coloration, considéré comme un équipement fort prometteur pour les réseaux maillés du futur relativement au multiplexage en longueur d’onde (WDM -Wavelength Division Multiplexing ). Cependant, leur propriété de commutation asymétrique complique la question de l’acheminement et de l’attribution des longueur d’ondes (RWA - Routing andWavelength Assignment). Or la plupart des algorithmes de RWA existants ne tiennent pas compte de cette propriété d’asymétrie.
L’interruption des services causée par des défauts d’équipements sur les chemins
optiques (résultat provenant de la résolution du problème RWA) a pour conséquence la
perte d’une grande quantité de données. Les recherches deviennent ainsi incontournables afin d’assurer la survie fonctionnelle des réseaux optiques, à savoir, le maintien des services, en particulier en cas de pannes d’équipement. La plupart des publications antérieures portaient particulièrement sur l’utilisation d’un système de protection permettant de garantir le reroutage du trafic en cas d’un défaut d’un lien. Cependant, la conception de la protection contre le défaut d’un lien ne s’avère pas toujours suffisante en termes de survie des réseaux WDM à partir de nombreux cas des autres types de pannes devenant courant de nos jours, tels que les bris d’équipements, les pannes de deux ou trois liens, etc. En outre, il y a des défis considérables pour protéger les grands réseaux optiques multidomaines composés de réseaux associés à un domaine simple, interconnectés par des liens interdomaines, où les détails topologiques internes d’un domaine ne sont généralement pas partagés à l’extérieur.
La présente thèse a pour objectif de proposer des modèles d’optimisation de grande
taille et des solutions aux problèmes mentionnés ci-dessus. Ces modèles-ci permettent de générer des solutions optimales ou quasi-optimales avec des écarts d’optimalité mathématiquement prouvée. Pour ce faire, nous avons recours à la technique de génération de colonnes afin de résoudre les problèmes inhérents à la programmation linéaire de
grande envergure.
Concernant la question de l’approvisionnement dans les réseaux optiques, nous proposons
un nouveau modèle de programmation linéaire en nombres entiers (ILP - Integer
Linear Programming) au problème RWA afin de maximiser le nombre de requêtes acceptées
(GoS - Grade of Service). Le modèle résultant constitue celui de l’optimisation
d’un ILP de grande taille, ce qui permet d’obtenir la solution exacte des instances RWA
assez grandes, en supposant que tous les noeuds soient asymétriques et accompagnés
d’une matrice de connectivité de commutation donnée. Ensuite, nous modifions le modèle
et proposons une solution au problème RWA afin de trouver la meilleure matrice de
commutation pour un nombre donné de ports et de connexions de commutation, tout en
satisfaisant/maximisant la qualité d’écoulement du trafic GoS.
Relativement à la protection des réseaux d’un domaine simple, nous proposons des
solutions favorisant la protection contre les pannes multiples. En effet, nous développons
la protection d’un réseau d’un domaine simple contre des pannes multiples, en utilisant
les p-cycles de protection avec un chemin indépendant des pannes (FIPP - Failure Independent
Path Protecting) et de la protection avec un chemin dépendant des pannes
(FDPP - Failure Dependent Path-Protecting). Nous proposons ensuite une nouvelle formulation
en termes de modèles de flots pour les p-cycles FDPP soumis à des pannes
multiples. Le nouveau modèle soulève un problème de taille, qui a un nombre exponentiel
de contraintes en raison de certaines contraintes d’élimination de sous-tour. Par
conséquent, afin de résoudre efficacement ce problème, on examine : (i) une décomposition
hiérarchique du problème auxiliaire dans le modèle de décomposition, (ii) des
heuristiques pour gérer efficacement le grand nombre de contraintes.
À propos de la protection dans les réseaux multidomaines, nous proposons des systèmes
de protection contre les pannes d’un lien. Tout d’abord, un modèle d’optimisation
est proposé pour un système de protection centralisée, en supposant que la gestion du
réseau soit au courant de tous les détails des topologies physiques des domaines. Nous
proposons ensuite un modèle distribué de l’optimisation de la protection dans les réseaux
optiques multidomaines, une formulation beaucoup plus réaliste car elle est basée
sur l’hypothèse d’une gestion de réseau distribué. Ensuite, nous ajoutons une bande pasiv
sante partagée afin de réduire le coût de la protection. Plus précisément, la bande passante
de chaque lien intra-domaine est partagée entre les p-cycles FIPP et les p-cycles
dans une première étude, puis entre les chemins pour lien/chemin de protection dans une
deuxième étude. Enfin, nous recommandons des stratégies parallèles aux solutions de
grands réseaux optiques multidomaines.
Les résultats de l’étude permettent d’élaborer une conception efficace d’un système
de protection pour un très large réseau multidomaine (45 domaines), le plus large examiné
dans la littérature, avec un système à la fois centralisé et distribué.Recent developments in the wavelength selective switch (WSS) technology enable
multi-degree reconfigurable optical add/drop multiplexers (ROADM) architectures with
colorless and directionless switching, which is regarded as a very promising enabler for
future reconfigurable wavelength division multiplexing (WDM) mesh networks. However,
its asymmetric switching property complicates the optimal routing and wavelength
assignment (RWA) problem, which is NP-hard. Most of the existing RWA algorithms
do not consider such property.
Disruption of services through equipment failures on the lightpaths (output of RWA
problem) is consequential as it involves the lost of large amounts of data. Therefore,
substantial research efforts are needed to ensure the functional survivability of optical
networks, i.e., the continuation of services even when equipment failures occur. Most
previous publications have focused on using a protection scheme to guarantee the traffic
connections in the event of single link failures. However, protection design against single
link failures turns out not to be always sufficient to keep the WDM networks away from
many downtime cases as other kinds of failures, such as node failures, dual link failures,
triple link failures, etc., become common nowadays. Furthermore, there are challenges
to protect large multi-domain optical networks which are composed of several singledomain
networks, interconnected by inter-domain links, where the internal topological
details of a domain are usually not shared externally.
The objective of this thesis is to propose scalable models and solution methods for
the above problems. The models enable to approach large problem instances while producing
optimal or near optimal solutions with mathematically proven optimality gaps.
For this, we rely on the column generation technique which is suitable to solve large
scale linear programming problems.
For the provisioning problem in optical networks, we propose a new ILP (Integer
Linear Programming) model for RWA problem with the objective of maximizing the
Grade of Service (GoS). The resulting model is a large scale optimization ILP model,
which allows the exact solution of quite large RWA instances, assuming all nodes are
asymmetric and with a given switching connectivity matrix. Next, we modify the model
and propose a solution for the RWA problem with the objective of finding the best switching
connectivity matrix for a given number of ports and a given number of switching
connections, while satisfying/maximizing the GoS.
For protection in single domain networks, we propose solutions for the protection
against multiple failures. Indeed, we extent the protection of a single domain network
against multiple failures, using FIPP and FDPP p-cycles. We propose a new generic
flow formulation for FDPP p-cycles subject to multiple failures. Our new model ends
up with a complex pricing problem, which has an exponential number of constraints due
to some subtour elimination constraints. Consequently, in order to efficiently solve the
pricing problem, we consider: (i) a hierarchical decomposition of the original pricing
problem; (ii) heuristics in order to go around the large number of constraints in the
pricing problem.
For protection in multi-domain networks, we propose protection schemes against
single link failures. Firstly, we propose an optimization model for a centralized protection
scheme, assuming that the network management is aware of all the details of the
physical topologies of the domains. We then propose a distributed optimization model
for protection in multi-domain optical networks, a much more realistic formulation as it
is based on the assumption of a distributed network management. Then, we add bandwidth
sharing in order to reduce the cost of protection. Bandwidth of each intra-domain
link is shared among FIPP p-cycles and p-cycles in a first study, and then among paths
for link/path protection in a second study. Finally, we propose parallel strategies in order
to obtain solutions for very large multi-domain optical networks.
The result of this last study allows the efficent design of a protection scheme for a
very large multi-domain network (45 domains), the largest one by far considered in the
literature, both with a centralized and distributed scheme
Processamento ótico de sinal para sistemas de comunicações óticas
Doutoramento em Engenharia FĂsicaO processamento Ăłtico de sinal Ă© uma alternativa possĂvel para melhorar o desempenho e eficiĂŞncia de sistemas de comunicações Ăłticas, mas o seu estágio atual de desenvolvimento Ă© ainda insuficiente para aplicações em sistemas reais. De forma a inverter esta situação, novas estratĂ©gias e pos-sibilidades para processamento Ăłtico de sinal sĂŁo aqui investigadas, com ĂŞnfase em conversĂŁo de comprimento de onda, regeneração de fase e amplificação sensĂvel Ă fase em dispositivos de niobato de lĂtio com inversĂŁo periĂłdica dos domĂnios ferroelĂ©tricos e fibras fortemente nĂŁo-lineares. Um novo mĂ©todo para o desenho do perfil de inversĂŁo dos domĂnios fer¬roelĂ©tricos nos dispositivos de niobato de lĂtio de acordo com um espetro de conversĂŁo alvo Ă© investigado nesta tese. O mĂ©todo proposto Ă© validado numericamente e atravĂ©s da produção de um dispositivo real com largura de banda de conversĂŁo de 400 GHz. O dispositivo produzido Ă© utilizado para conversĂŁo de onda multicanal de oito sinais modulados em fase, com a possibilidade adicional de sintonizar o comprimento de onda dos sinais con¬vertidos. Observa-se a existĂŞncia de um compromisso entre elevada largura de banda de conversĂŁo e eficiĂŞncia do dispositivo.
SĂŁo tambĂ©m investigadas nesta tese conversĂŁo e permuta de comprimento de onda tolerantes ao ruĂdo de fase adicionado por fontes de bombeamento. Demonstra-se neste trabalho que a utilização de fontes de bombeamento coerentes permite evitar a adição de ruĂdo de fase aos sinais convertidos. Nesta tese Ă© tambĂ©m analisada analĂtica e numericamente amplificação sensĂvel a fase baseada em dispositivos de niobato de lĂtio com inversĂŁo periĂłdica dos domĂnios ferroelĂ©tricos para configurações de amplificadores de um, dois ou quatro modos. É ainda avaliada a possibilidade de ge¬rar ondas correlacionadas e de realizar amplificação sensĂvel a fase num Ăşnico dispositivo com propagação bidirecional. Com base neste esquema, demonstra-se regeneração de fase de sinais modulados em fase, porĂ©m com ganho limitado devido Ă baixa eficiĂŞncia de conversĂŁo dos dispositivos e com desempenho afetado por instabilidades tĂ©rmicas e foto refrativas. Mo¬tivado por estas limitações, demonstra-se amplificação de elevado ganho num amplificador sensĂvel Ă fase de quatro modos, construĂdo com uma fibra fortemente nĂŁo-linear em vez de um dispositivo de niobato de lĂtio. Por fim, Ă© efetuada uma análise numĂ©rica do impacto de utilizar amplifica¬dores sensĂveis Ă fase em vez de amplificadores de fibra dopada com Ă©rbio no alcance em transmissĂŁo ponto a ponto de sinais e na amplificação e regeneração em redes Ăłticas. Demonstra-se que amplificadores sensĂveis Ă fase sĂŁo mais vantajosos para formatos de modulação avançados e siste¬mas compostos por ligações Ăłticas longas. As simulações assumem mode¬los simplificados para o ganho e ruĂdo dos amplificadores, bem como uma versĂŁo modificada do modelo de ruĂdo Gaussiano para estimar a potĂŞncia das distorções nĂŁo-lineares em sistemas com compensação total da dispersĂŁo cromática no final de cada segmento de fibra entre amplificadores.All-optical signal processing techniques are a possible way to improve the performance and efficiency of optical communication systems, but the cur¬rent stage of development of such techniques is still unsatisfactory for real- world implementation. In order to invert this situation, new strategies and possibilities for all-optical signal processing are investigated here, with a particular focus on wavelength conversion, phase regeneration and phase- sensitive amplification in periodically poled lithium niobate waveguides and highly nonlinear fibers.
A new and flexible method to design the poling pattern of periodically poled lithium niobate devices according to a target conversion spectrum is inves¬tigated in this work. The proposed method is validated through numerical simulations and by producing a real device with broad conversion bandwidth of 400 GHz. The device is then used for multichannel wavelength conversion of eight phase-modulated signals, with the additional possibility to tune the wavelength of the converted signals. A trade-off between high conversion bandwidth and conversion efficiency is observed.
Advanced wavelength conversion and wavelength exchange tolerant to the phase noise added by the pump lasers are also investigated. It is shown that the additional phase noise transferred to the converted signals is eliminated by using coherent pumps, generated from the same light source. Phase-sensitive amplification based on periodically poled lithium niobate devices is also investigated in this thesis by numerically comparing the gain properties for one-, two- and four-mode configurations. The possibility to si¬multaneously generate correlated waves and observe phase-sensitive amplifi¬cation in a single device with bidirectional propagation is also demonstrated. Using such scheme,"black-box" phase regeneration of phase-encoded sig¬nals is experimentally demonstrated, albeit with limited net gain due to the low conversion efficiency of the device, and the limited reliability due to thermal and photorefractive instabilities. Motivated by such limitations, high-gain amplification in a four-mode phase-sensitive amplifier built with a highly nonlinear fiber instead of a periodically poled lithium niobate is demonstrated.
Finally, the impact of using phase-sensitive amplifiers instead of common erbium-doped fiber amplifiers on the reach in point-to-point transmission and on the amplification and regeneration requirements in optical transport networks is numerically investigated. The calculations show that phase- sensitive amplifiers are particularly advantageous when considering high- order modulation formats and for transport networks comprised by long links. The numerical simulations are performed using simplified models for the gain and noise properties of the amplifiers, and a modified enhanced Gaussian noise model to estimate the power of the nonlinear distortions in systems with full dispersion compensation at the end of each span of fiber
Analysis and optimisation of semiconductor reflective modulators for optical networks
Reflective modulators based on the combination of an electroabsorption modulator (EAM) and semiconductor optical amplifier (SOA) are attractive devices for applications in long reach carrier distributed passive optical networks (PONs) due to the gain provided by the SOA and the high speed and low chirp modulation of the EAM. Integrated R-EAM-SOAs have experimentally shown two unexpected and unintuitive characteristics which are not observed in a single pass transmission SOA: the clamping of the output power of the device around a maximum value and low patterning distortion despite the SOA being in a regime of gain saturation. In this thesis a detailed analysis is carried out using both experimental measurements and modelling in order to understand these phenomena. For the first time it is shown that both the internal loss between SOA and R-EAM and the SOA gain play an integral role in the behaviour of gain saturated R-EAM-SOAs. Internal loss and SOA gain are also optimised for use in a carrier distributed PONs in order to access both the positive effect of output power clamping, and hence upstream dynamic range reduction, combined with low patterning operation of the SOA Reflective concepts are also gaining interest for metro transport networks and short reach, high bit rate, inter-datacentre links. Moving the optical carrier generation away from the transmitter also has potential advantages for these applications as it avoids the need for cooled photonics being placed directly on hot router line-cards. A detailed analysis is carried out in this thesis on a novel colourless reflective duobinary modulator, which would enable wavelength flexibility in a power-efficient reflective metro node