Redes ópticas de acesso de nova geração : tecnologias e economia

Doutoramento em Engenharia Eletrotécnica - TelecomunicaçõesThe work presented herein, studies Next Generation Optical Access Networks (NG-OAN) economically (e.g. energy consumption) and technologically (e.g. rate, reach and dedicated/shared bandwidth). The work is divided into four main topics: energy efficiency in optical access architectures, novel spectrally efficient Long-Reach Passive Optical Networks (LR-PON), crosstalk impacts in heterogeneous and homogenous access networks and hybrid optical wireless transmissions. We investigate the impact of user profiles, optical distribution network topologies and equipment characteristics on resource sharing and power consumption in LR-PON. To have a clear vision on the energy consumption evolution of each part of NG-OAN, a model is proposed to evaluate the energy efficiency of optical access technologies. A spectrally efficient bidirectional Ultra-Dense Wavelength Division Multiplexing (UDWDM) PON architecture is developed using Nyquist shaped 16-ary quadrature amplitude modulation, offering up to 10 Gb/s service capabilities per user or wavelength. Performance of this system in terms of receiver sensitivity and nonlinear tolerance under different network transmission capacity conditions are experimentally optimized. In bi-directional transmis-sion, using frequency up/down-shifting of Nyquist pulse shaped signal from optical carrier, a full bandwidth allocation and easy maintenance of UDWDM networks as well as reduction of Rayleigh back-scattering are achieved. Moreover, self-homodyne detection is used to relax the laser linewidth requirement and digital signal processing complexity at the optical network unit. Simplified numerical model to estimate the impact of Raman crosstalk of multi-system next generation PONs in video overlay is proposed. Coexistence of considered G.98X ITU-T series and coherent multi-wavelength systems is considered and assessed. Additionally, the performances of bidirectional hybrid optical wireless coherent PONs over different optical distribution network power budgets and hybrid splitting ratios are evaluated.O trabalho aqui apresentado estuda redes óticas de acesso de próxima geração (NG-OAN) nas vertentes económica (consumo de energia) e tecnológica (taxa, alcance e largura de banda dedicada/partilhada). O trabalho está dividido em quatro grandes temas de investigação: a eficiência energética em arquiteturas de acesso ótico, as redes óticas passivas de longo alcance (LR-PON) com nova eficiência espetral, o impacto da diafonia em redes de acesso heterogéneas e homogéneas e as transmissões ópticas híbridas com tecnologias sem fio. Investiga-se o impacto dos perfis dos utilizadores, as tipologias da rede de distribuição ótica, as características do equipamento de partilha de recursos e o consumo de energia em LR-PON. Para se ter uma visão clara sobre o consumo de energia de cada parte das NG-OAN, é proposto um modelo para avaliar a eficiência energética das tecnologias de acesso óticas. Desenvolve-se uma arquitetura PON bi-direcional com elevada eficiência espetral, recorrendo a multiplexagem por divisão de comprimento de onda ultra-densa (UDWDM), modulação de amplitude em quadratura com formato de impulso de Nyquist, oferecendo até 10 Gb/s por utilizador/comprimento de onda. O desempenho deste sistema em termos de sensibilidade do recetor e da tolerância à resposta não linear do canal de comunicação, sob diferentes condições de transmissão, é avaliado experimentalm-ente. Em transmissão bi-direcional, utilizando desvio de frequência (cima/baixo) do impulso com formato de Nyquist relativo à portadora ótica conseguiu-se uma alocação de largura de banda completa e uma manutenção mais simplificada de redes UDWDM, bem como a redução do espalhamento de Rayleigh. Além disso, a deteção auto-homodina é usada para relaxar o requisito de largura de linha do laser e a complexidade do processamento digital de sinal nas unidades da rede ótica. Propõe-se um modelo numérico simplificado para estimar o impacto da diafonia de Raman em sistemas PON de próxima geração, com sobreposição do sinal de vídeo. É analisada a coexistência da série G.98X ITU-T e são considerados e avaliados sistemas coerentes multi-comprimento de onda. Adicionalmente avaliam-se os desempenhos de PONs bi-direcionais híbridas, considerando tecnologia coerente e propagação por espaço livre, para diferentes balanços de potência e taxas de repartição na rede ótica de distribuição

Design and optimization next generation passive all-optical networks

Doutoramento em Engenharia Electrotécnica/TelecomunicaçõesEste trabalho investiga novas metodologias para as redes óticas de acesso de próxima geração (NG-OAN). O trabalho está dividido em quatro tópicos de investigação: projeto da rede, modelos numéricos para efeitos não lineares da fibra ótica, impacto dos efeitos não lineares da fibra ótica e otimização da rede. A rede ótica de acesso investigada nesse trabalho está projetado para suprir os requisitos de densidade de utilizadores e cobertura, isto é, suportar muitos utilizadores ( 1000) com altas velocidades de conexão dedicada ( 1 Gb/s) ocupando uma faixa estreita do espectro ( 25 nm) e comprimentos de fibra ótica até 100 km. Os cenários são baseados em redes óticas passivas com multiplexagem por divisão no comprimento de onda de alta densidade (UDWDM-PON) utilizando transmissores/receptores coerentes nos terminais da rede. A rede é avaliada para vários ritmos de transmissão usando formatos de modulação avançados, requisitos de largura de banda por utilizador e partilha de banda com tecnologias tradicionais de redes óticas passivas (PON). Modelos numéricos baseados em funções de transferência das séries de Volterra (VSTF) são demonstrados tanto para a análise dos efeitos não lineares da fibra ótica quanto para avaliação do desempenho total da rede. São apresentadas as faixas de potência e distância de transmissão nas quais as séries de Volterra apresentam resultados semelhantes ao modelo referência Split-Step Fourier (SSF) (validado experimentalmente) para o desempenho total da rede. Além disso, um algoritmo, que evita componentes espectrais com intensidade nulo, é proposto para realizar cálculos rápidos das séries. O modelo VSTF é estendido para identificar unicamente os efeitos não lineares da fibra ótica mais relevantes no cenário investigado: Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM) e Four-Wave Mixing (FWM). Simulações numéricas são apresentadas para identificar o impacto isolado de cada efeito não linear da fibra ótica, SPM, XPM e FWM, no desempenho da rede com detecção coerente UDWDM-PON, transportando canais com modulação digital em fase (M-ária PSK) ou modulação digital em amplitude (M-ária QAM). A análise numérica é estendida para diferentes comprimentos de fibra ótica mono modo (SSMF), potência por canal e ritmo de transmissão por canal. Por conseguinte, expressões analíticas são extrapoladas para determinar a evolução do SPM, XPM e FWM em função da potência e distância de transmissão em cenários NG-OAN. O desempenho da rede é otimizada através da minimização parcial da interferência FWM (via espaçamento desigual dos canais), que nesse caso, é o efeito não linear da fibra ótica mais relevante. Direções para melhorias adicionas no desempenho da rede são apresentados para cenários em que o XPM é relevante, isto é, redes transportando formatos de modulação QAM. A solução, nesse caso, é baseada na utilização de técnicas de processamento digital do sinal.This work investigates novel methodologies and models for Next-Generation Optical Access Networks (NG-OAN). The work is divided into four main topics of research: network design, numerical models for fiber nonlinear effects, impact of fiber nonlinear effects and network optimization. The used case optical access network is designed to cope with high user density over extended reach, i.e. support large number of users ( 1000) with high speed dedicated connections ( 1 Gb/s) in a narrow bandwidth ( 25 nm) distributed up to 100 km. The scenarios rely on Ultra-Dense Wavelength-Division Multiplexing Passive Optical Networks (UDWDM-PON) employing coherent transceivers in the network terminals. The network is evaluated for various transmission rates using advanced modulation formats, transmitters and receivers specifications, user bandwidth requirements and coexistence with legacy Passive Optical Network (PON) technologies. Numerical models based on Volterra Series Transfer Function (VSTF) are demonstrated for both the analysis of fiber nonlinear effects and evaluation of the overall network performance. It is presented the power and transmission ranges that Volterra series provides accurate results, compared to the reference model Split-Step Fourier (SSF) (experimentally validated), for the overall network performance. Moreover, an algorithm is proposed to provide fast numerical calculations of the series by avoiding zero intensity signal frequency components. The VSTF model is extended to identify the sole effect of the most relevant fiber nonlinearities in UDWDM-PON network scenarios: Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM) and Four-Wave Mixing (FWM). Numerical simulations are performed to identify the impact of each nonlinear effect, SPM, XPM and FWM, on the performance of coherent UDWDMPON transporting either M-ary PSK (Phase-Shift Keying) or M-ary QAM (Quadrature Amplitude Modulation) modulated channels. The analysis is extended to different lengths of Standard Single-Mode Fibers (SSMF), power per channel and bit rate per channel. From that, analytic expressions are extrapolated to find the evolution of SPM, XPM and FWM with power and transmission distance for NG-AON scenarios. The performance of the network is optimized by mitigating some of the FWM crosstalk (unequally spaced channels), which in this case is the most relevant fiber nonlinear effect. The directions for further performance improvements are pointed out for scenarios in which XPM is enhanced, i.e. networks transporting QAM signaling. The solution in this case is based on digital signal processing techniques

Design and Analysis of Binary Driven Coherent M-ary Qam Transmitter for Next Generation Optical Networks

This work presents a design for a binary driven optical square M-ary quadrature amplitude modulation (QAM) transmitter for high speed optical networks. The transmitter applies tandem quadrature phase shift keying (QPSK) modulators to eliminate the need for linear broadband amplifiers and high-resolution digital to analog converters (DACs), which are both required by conventional transmitters. The transmitter design could be scaled to any order of square M-ary QAM by simply adding more QPSK modulators in tandem. It also provides a Gray coded symbol constellation, insuring the lowest bit error rate possible during symbol recovery. We also provide the design for the coupling ratios of the optical couplers that take into account the insertion loss of the optical components, in order to generate a proper 16-QAM and 64-QAM symbol constellation with equally-spaced symbols. Additionally, we analyze the impact of coupling ratio errors as well as phase errors on the bit error rate (BER) performance and constellation diagrams. The performance is tested using the OptiSystem simulation at 50 Gbaud and under presence of additive white Gaussian noise (AWGN), which demonstrated high quality symbol constellation and a BER performance similar to theoretical expectations. For 16-QAM, a BER better than 10-4 and power penalty of about 2 dB are achieved for coupling ratio errors less than 10 %, or phase errors within ±7 degrees. The 64-QAM transmitter, on the other hand, demonstrated a BER better than 10-4 and power penalty of about 1 dB for coupling ratio errors less than 4%, or phase errors within ±2 degrees. Adviser: Lim Nguye

Transparent heterogeneous terrestrial optical communication networks with phase modulated signals

This thesis presents a large scale numerical investigation of heterogeneous terrestrial optical communications systems and the upgrade of fourth generation terrestrial core to metro legacy interconnects to fifth generation transmission system technologies. Retrofitting (without changing infrastructure) is considered for commercial applications. ROADM are crucial enabling components for future core network developments however their re-routing ability means signals can be switched mid-link onto sub-optimally configured paths which raises new challenges in network management. System performance is determined by a trade-off between nonlinear impairments and noise, where the nonlinear signal distortions depend critically on deployed dispersion maps. This thesis presents a comprehensive numerical investigation into the implementation of phase modulated signals in transparent reconfigurable wavelength division multiplexed fibre optic communication terrestrial heterogeneous networks. A key issue during system upgrades is whether differential phase encoded modulation formats are compatible with the cost optimised dispersion schemes employed in current 10 Gb/s systems. We explore how robust transmission is to inevitable variations in the dispersion mapping and how large the margins are when suboptimal dispersion management is applied. We show that a DPSK transmission system is not drastically affected by reconfiguration from periodic dispersion management to lumped dispersion mapping. A novel DPSK dispersion map optimisation methodology which reduces drastically the optimisation parameter space and the many ways to deploy dispersion maps is also presented. This alleviates strenuous computing requirements in optimisation calculations. This thesis provides a very efficient and robust way to identify high performing lumped dispersion compensating schemes for use in heterogeneous RZ-DPSK terrestrial meshed networks with ROADMs. A modified search algorithm which further reduces this number of configuration combinations is also presented. The results of an investigation of the feasibility of detouring signals locally in multi-path heterogeneous ring networks is also presented

Investigation of high bit rate optical transmission systems employing a channel data rate of 40 Gb/s

Das Ziel dieser Doktorarbeit war eine detaillierte Untersuchung von hoch bit ratigen optischen Übertragungssystemen mit einer Kanaldatenrate von 40 Gbit/s, die als wavelength division multiplexing (WDM) Systeme realisiert sind. Die Erkenntnisse, die durch umfangreiche numerische Untersuchungen gewonnen worden sind, wurden für die Erarbeitung von Designkriterien für die Übertragungssysteme der nächsten Generation verwendet. Der Schwerpunkt der Arbeit liegt dabei an 40 Gbit/s basierten WDM Systemen mit amplitudenmodulierten optischen Signalen. Nach einer umfangreichen Beschreibung der Funktionsweise und des Standes der Technik von Systemkomponenten, die in optischen Übertragungssystemen zum Einsatz kommen, wurden die Übertragungseffekte (z.B. chromatische Dispersion, Kerr-Effekt) erklärt und beschrieben, die eine störungsfreie Übertragung von optischen Pulsen in Übertragungsstrecken beeinträchtigen. Wegen der Fokussierung der Arbeit auf amplitudenmodulierte Systeme, wurden Erzeugungsmethoden und Spektraleneigenschaften von zahlreichen amplitude-shift-keying (ASK) basierten Modulationsformaten erklärt. Die untersuchten Modulationsformate wurden in drei Gruppen unterteilt: Non-return-to-zero (NRZ) basierende Formate, Return-to-zero (RZ) basierende Formate und neue Modulationsformate. Zu der Gruppe von NRZ basierten Modulationsformaten gehören konventionelles NRZ und Duobinary Modulation. In der Gruppe von RZ basierten Formaten wurden konventionelles RZ, Carrier-suppressed RZ (CSRZ) und Single-side-band RZ (SSB-RZ) eingeführt. Die Gruppe der neuen Formate beinhaltet Modulationsformate, die vom Autor im Rahmen der Arbeit vorgeschlagen und weiterentwickelt worden sind: Alternate-chirped NRZ (alCNRZ), Novel-chirped RZ (nCRZ), Alternate-polarized NRZ (alPNRZ) und Alternate-polarized RZ (alPRZ). Die Anforderungen, die bei der Entwicklung von neuen Modulationsformaten berücksichtigt worden sind, waren die Verbesserung der nichtlinearen Übertragungseigenschaften (z.B. nichtlineare Toleranz) der Übertragungsstrecke und eine effizientere Ausnutzung der zur Verfügung stehenden Systembandbreite (z.B. Erhöhung der spektralen Effizienz), wobei die vorgeschlagenen Modulationsformate kompatibel mit herkömmlichen Systemkonfigurationen (z.B. Empfänger) sein sollten. Aufgrund numerischer Natur der Arbeit wurden diverse Auswertekriterien eingeführt, die eine genaue Evaluierung der Übertragungsqualität ermöglichen und im Rahmen der Arbeit verwendet worden sind. Die Vor- und Nachteile der Auswertekriterien wie Bitfehlerrate (BER), Q-Faktor, optischer Signalrauschabstand (OSNR) und Augendiagramme wurden erläutert, und ein Vergleich zwischen allen Kriterien ist gemacht worden. Die 40 Gbit/s basierten numerischen Untersuchungen wurden für Einkanal- und Mehrkanalübertragungssysteme durchgeführt. Dabei wurde im Mehrkanalfall zwischen WDM-Systemen mit einer spektralen Effizienz von 0.4 bit/s/Hz und effizienteren dense WDM (DWDM) Systemen mit einer spektralen Effizienz von 0.8 bit/s/Hz unterschieden. Das Ziel dieser Untersuchungen war eine 40 Gbit/s Systemoptimierung durch Bestimmung von optimalen Übertragungsfasern, optimalen Dispersionskompensationsschemen und optimalen Leistungsbereichen, in denen die zukünftigen Systeme betrieben werden sollen. Dabei wurden alle Untersuchungen unter Berücksichtigung von unterschiedlichen Modulationsformaten durchgeführt, um einen Vergleich zwischen den Modulationsformaten gewährleisten zu können. Die Ergebnisse der Einkanaluntersuchungen haben gezeigt, dass NRZ basierten Modulationsformate durch eine hohe Dispersionstoleranz (ca. ±50 ps/nm) und eine niedrige nichtlineare Toleranz charakterisiert sind, was eine Beschränkung der maximaler Übertragungslänge verursacht. Die wichtigsten Störeffekte stellen in diesem Fall Selbstphasenmodulation (SPM) und die Interaktion zwischen SPM und chromatischer Dispersion dar. Die RZ basierten Verfahren zeichnen sich durch eine reduzierte Dispersionstoleranz (ca. ±25 ps/nm) aus, aber ermöglichen wegen erhöhter nichtlinearer Toleranz eine Verbesserung der maximalen Übertragungslänge verglichen zu NRZ Formaten. Die limitierenden Effekte in einer RZ basierten Übertragung sind Intrakanaleffekte (z.B. Intrakanalkreuzphasenmodulation IXPM), die bei höheren Signalleistungen von SPM begleitet sind. Die wichtigste Eigenschaft der neuen Modulationsverfahren ist die große nichtlineare Toleranz, die besonders bei alternierend polarisierten Modulationsverfahren (z.B. alPNRZ, alPRZ) zur Geltung kommt. Es wurde gezeigt, dass in allen untersuchten Fällen die Übertragungsqualität von eine mittleren Faserdispersion (ca. 4-8 ps/nm·km) profitiert und dass Dispersionskompensationsschemen mit einem bestimmten Prozent (variiert von Format zu Format) der Vorkompensation das Optimum darstellen. Die Mehrkanaluntersuchungen haben gezeigt, dass solange die spektrale Effizienz eines 40 Gbit/s basierten WDM systems klein (£ 0.4 bit/s/Hz) ist, die Einkanaleffekte (z.B. SPM, IXPM) die dominierenden Effekten sind. Demzufolge haben WDM und Einkanalsysteme ähnliche optimale Systemparameter, was ein einfaches System- und Kapazitätsupgrade ermöglichen würde. Des weiteren wurde gezeigt, dass für die Realisierung von DWDM Systemen eine schmalbandige optische Filterung sowohl am Sender als auch am Empfänger notwendig ist, deren Folge die Zerstörung der RZ Pulsform ist, wodurch die untersuchten RZ und NRZ basierten Modulationsformate identische Übertragungseigenschaften in DWDM Systemen aufweisen. Eine ähnliche Tendenz wurde auch bei manchen neuen Formaten (z.B. alCNRZ) beobachtet, was mit einem breiten Signalspektrum zu erklären ist. Auf der anderen Seite zeigten alternierend polarisierte Modulationsverfahren (z.B. alPNRZ) auch in DWDM Systemen eine Verbesserung hinsichtlich Filtertoleranz und Toleranz zu Mehrkanaleffekten (z.B. XPM), und empfählen sich als optimaler Kandidat für die zukünftigen 40 Gbit/s Systeme. Es wurde gezeigt, dass der optimale Fasertyp für eine DWDM Übertragung weitgehend unabhängig vom Modulationsformat ist und dass Faser eine möglichst hohe Dispersion besitzen sollen, um eine Unterdrückung der Mehrkanaleffekte ermöglichen zu können. Um zu erkennen, wie eine weitere Verbesserung der Übertragungseigenschaften in 40 Gbit/s Systemen ermöglicht werden könnte, wurden Verfahren wie orthogonal polarisierte Kanäle sowie phase shift keying (PSK) basierte Modulationsformate (z.B. DPSK, DQPSK) untersucht. Es wurde gezeigt, dass die orthogonale Polarisation zwischen den Kanälen als eine Verbesserungsmethode auf eine Übertragungslänge von ca. 200 km begrenzt ist. PSK-Formate ermöglichen eine Verbesserung der Übertragungseigenschaften der Strecke, wobei die notwendigen komplizierten Sender- und Empfängerrealisierungen vom Nachteil sein könnten.The focus of this work was set on 40 Gb/s based optical transmission systems with a varying number of channels and various spectral efficiencies in order to investigate the potential of 40 Gb/s technologies for the implementation in the next generation optical transmission networks. The results of this work can be used as design guidelines enabling a better understanding of propagation limitations in high bit rate transmission systems and give useful insights needed for the capacity upgrade of existing transmission lines. Using conventional amplitude-shift-keying (ASK) based modulation formats and by the author proposed novel modulation formats, the optimization of the system settings is performed in 40 Gb/s based single channel, wavelength division multiplex (WDM) and dense WDM (DWDM) transmission lines, in order to enable a comparison between different modulation formats in terms of the total transmission distance and the maximum achievable spectral efficiency. The signal generation and dominant transmission characteristics of various conventional non return-to-zero (NRZ), return-to-zero (RZ), duobinary, single side band RZ (SSB-RZ), carrier suppressed RZ (CSRZ) - and novel modulation formats alternate chirped NRZ (alCNRZ), novel chirped RZ (nCRZ), alternate polarized (N)RZ (alP(N)RZ) were introduced. The idea behind the development of novel modulation formats was the performance improvement of the existing transmission lines with possibly low signal generation complexity, employing conventional ASK-based receiver configuration for the signal detection. Dividing all modulation formats in two groups NRZ- and RZ-based - their tolerances to linear and nonlinear transmission disturbances are investigated in single channel transmission, indicating that an implementation of NRZ-based modulation formats provides a better dispersion tolerance, but suffers from strong nonlinear limitations. The use of novel NRZ-based formats enables a significant improvement of nonlinear transmission characteristics at the cost of a slightly increased transmitter complexity. RZ-based formats are characterized by an increased sensitivity to residual dispersion and a significant nonlinear tolerance. It is shown that an additional phase or polarization modulation of RZ pulses enables more compact signal spectra and a further improvement of nonlinear transmission robustness, thus enlarging the maximum transmission distance. Strong intra-channel limitations were indicated as the dominant transmission limitation especially in RZ-based formats characterized by strong interactions of consecutive pulses within the bit stream, due to the fast broadening of short optical pulses at 40 Gb/s. This effect is accompanied by self-phase modulation (SPM) group velocity dispersion (GVD) interplay, which becomes evident in both format groups at larger channel powers. It is shown that the dominance of intra-channel effects requires implementation of transmission fibers with moderate dispersion values. Furthermore, it was shown, that as long as intra-channel effects dominate transmission performance, the best dispersion compensation scheme is characterized by a small amount of dispersion pre-compensation, due to suppression of interactions between adjacent pulses. Thereby, right amount of dispersion pre-compensation is dependent on the modulation format in use, because of the interplay between the pulse internal chirp induced during modulation and the local dispersion in transmission line. The importance of pre-compensation increases in long-haul transmission lines employing dispersion compensation on a span-by-span basis, because of constructive superposition of intrachannel cross-phase modulation (IXPM) contributions in each span. The modulation formats employing polarization switching between consecutive pulses were identified as best solution for the performance enhancement in 40 Gb/s single channel based transmission lines. The 40 Gb/s based WDM systems with spectral efficiency of 0.4 bit/s/Hz showed identical transmission behavior as in single channel transmission for all modulation formats, which can be explained by the dominance of single-channel effects in 40 Gb/s systems with a channel spacing of 100 GHz. This leads to the conclusion that a system upgrade from single channel to WDM at 40 Gb/s channel data rate can be made using identical transmission infrastructure. As in the single channel case, RZ-based formats indicated a significant robustness to nonlinear propagation effects, which could be further improved by the use of novel modulation formats. Basically, RZ-based modulation formats outperform the NRZ-based ones in 40 Gb/s single channel and WDM transmissions, and transmission advantages of RZ based formats become even more evident with an increased transmission distance. It was shown that an increase of spectral efficiency to 0.8 bit/s/Hz in 40 Gb/s based DWDM systems results in increased pulse distortions, because of the reduced tolerance to implemented narrow-band filtering and larger impact of multi-channel nonlinearities (particularly XPM). The differences between RZ- and NRZ-based modulation formats vanish in DWDM transmissions, because of the distortion of RZ pulse shape due to narrow-band filtering needed at the transmitter side. It was shown that transmission performance of DWDM systems could profit from implementation of transmission fibers with a large chromatic dispersion, due to suppression of multi-channel effects independently of the modulation format in use. Accordingly, already deployed fibers (e.g. G.652) can be further used in next generation of DWDM transmission systems. Furthermore, considering concatenation of identical spans in a DWDM transmission line, it was observed that XPM-induced impacts superpose constructively from span to span independently of the implemented dispersion compensation scheme, resulting in an transmission penalty, which is in high power regime proportional to number of concatenated spans. This behavior enables together with already know transmission rules (e.g. Pmax) an efficient estimation of the maximum transmission performance and maximum transmission distance in 40 Gb/s DWDM systems. This work is completed by representation of some promising technologies, e.g. polarization orthogonality between the channels or phase-shift-keying (PSK) based modulation formats, which enable a further increase of spectral efficiency (beyond 0.8 bit/s/Hz) and an enhanced maximum transmission distance. The investigations of PSK-based modulation formats showed that not all recently proposed PSK-based system could compete with ASK-based formats for implementation in DWDM systems. Differential quadrature PSK (DQPSK) based modulation formats were identified as a potential candidate for the implementation in future spectrally efficient DWDM systems

Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications

The rapid proliferation of the Internet has been driving communication networks closer and closer to their limits, while available bandwidth is disappearing due to an ever-increasing network load. Over the past decade, optical fiber communication technology has increased per fiber data rate from 10 Tb/s to exceeding 10 Pb/s. The major explosion came after the maturity of coherent detection and advanced digital signal processing (DSP). DSP has played a critical role in accommodating channel impairments mitigation, enabling advanced modulation formats for spectral efficiency transmission and realizing flexible bandwidth. This book aims to explore novel, advanced DSP techniques to enable multi-Tb/s/channel optical transmission to address pressing bandwidth and power-efficiency demands. It provides state-of-the-art advances and future perspectives of DSP as well

Transparent heterogeneous terrestrial optical communication networks with phase modulated signals

This thesis presents a large scale numerical investigation of heterogeneous terrestrial optical communications systems and the upgrade of fourth generation terrestrial core to metro legacy interconnects to fifth generation transmission system technologies. Retrofitting (without changing infrastructure) is considered for commercial applications. ROADM are crucial enabling components for future core network developments however their re-routing ability means signals can be switched mid-link onto sub-optimally configured paths which raises new challenges in network management. System performance is determined by a trade-off between nonlinear impairments and noise, where the nonlinear signal distortions depend critically on deployed dispersion maps. This thesis presents a comprehensive numerical investigation into the implementation of phase modulated signals in transparent reconfigurable wavelength division multiplexed fibre optic communication terrestrial heterogeneous networks. A key issue during system upgrades is whether differential phase encoded modulation formats are compatible with the cost optimised dispersion schemes employed in current 10 Gb/s systems. We explore how robust transmission is to inevitable variations in the dispersion mapping and how large the margins are when suboptimal dispersion management is applied. We show that a DPSK transmission system is not drastically affected by reconfiguration from periodic dispersion management to lumped dispersion mapping. A novel DPSK dispersion map optimisation methodology which reduces drastically the optimisation parameter space and the many ways to deploy dispersion maps is also presented. This alleviates strenuous computing requirements in optimisation calculations. This thesis provides a very efficient and robust way to identify high performing lumped dispersion compensating schemes for use in heterogeneous RZ-DPSK terrestrial meshed networks with ROADMs. A modified search algorithm which further reduces this number of configuration combinations is also presented. The results of an investigation of the feasibility of detouring signals locally in multi-path heterogeneous ring networks is also presented.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Investigation of performance issues affecting optical circuit and packet switched WDM networks

Optical switching represents the next step in the evolution of optical networks. This thesis describes work that was carried out to examine performance issues which can occur in two distinct varieties of optical switching networks. Slow optical switching in which lightpaths are requested, provisioned and torn down when no longer required is known as optical circuit switching (OCS). Services enabled by OCS include wavelength routing, dynamic bandwidth allocation and protection switching. With network elements such as reconfigurable optical add/drop multiplexers (ROADMs) and optical cross connects (OXCs) now being deployed along with the generalized multiprotocol label switching (GMPLS) control plane this represents the current state of the art in commercial networks. These networks often employ erbium doped fiber amplifiers (EDFAs) to boost the optical signal to noise ratio of the WDM channels and as channel configurations change, wavelength dependent gain variations in the EDFAs can lead to channel power divergence that can result in significant performance degradation. This issue is examined in detail using a reconfigurable wavelength division multiplexed (WDM) network testbed and results show the severe impact that channel reconfiguration can have on transmission performance. Following the slow switching work the focus shifts to one of the key enabling technologies for fast optical switching, namely the tunable laser. Tunable lasers which can switch on the nanosecond timescale will be required in the transmitters and wavelength converters of optical packet switching networks. The switching times and frequency drifts, both of commercially available lasers, and of novel devices are investigated and performance issues which can arise due to this frequency drift are examined. An optical packet switching transmitter based on a novel label switching technique and employing one of the fast tunable lasers is designed and employed in a dual channel WDM packet switching system. In depth performance evaluations of this labelling scheme and packet switching system show the detrimental impact that wavelength drift can have on such systems