Optimization of emerging extended FTTH WDM/TDM PONs and financial overall assessment

Optical access technology has experienced a boost in the last years, thanks to the continuously migrating multimedia services that are offered over the internet. Though the technologies used for deploying Fiber-To-The-x (FTTx) and Fiber-to-the-Home (FTTH) are mostly based on either Active solutions or as far as Passsive Optical Networks (PONs) is concerned, in Time Division Multiplexing (TDM), an evolution towards Hybrid solutions such as Wavelength Division Multiplexing/Time Division Multiplexing (WDM/TDM) can be foreseen. What needs to be researched and finally established are the exact designs for this important step of integration, which should be optimized in terms of transmission performance and cost, to address all requirements of next-generation passive optical networks. As the most critical elements in optical access network, the design and its cost are the main topics of this discussion. The covered topics span over a wide range and include cost estimation of several optical network technologies - architectures and their comparison and furthermore, subjects of design optimization. In this last category, in-line remote amplification, use of an alternative and an extended frequency band, dispersion compensation and equalization techniques have been examined as well as a combination of the aforementioned means of network optimization. Next to the principal proof of the proposed techniques, the benefits are highlighted in different case studies, while the most representative designs are further discussed

Integrated Optoelectronic Devices and System Limitations for WDM Passive Optical Networks

This thesis puts focus on the technological challenges for Wavelength Division Multiplexed Passive Optical Network (WDM-PON) implementation, and presents novel semiconductor optical devices for deployment at the optical network unit (ONU). The first-ever reported L-band Reflective semiconductor optical amplifier (RSOA) is presented based on InP-base material. A theoretical model is developed to estimate the optical gain and the saturation power of this device compared to a conventional SOA. Experiments on this device design show long-range telecom wavelength operation, with polarization-independent gain of greater than 20 dB, and low saturation output power of 0 dBm suitable for PON applications. Next, the effect of the amplified spontaneous emission noise of RSOA devices on WDM-PON system is investigated. It is shown through theoretical modeling and simulations that the RSOA noise combined with receiver noise statistics increase probability of error, and induce considerable power penalties to the WDM-PON system. By improving the coupling efficiencies, and by distributing more current flow to the input of these devices, steps can be taken to improve device noise characteristics. Further, in spectrally-spliced WDM-PONs deploying RSOAs, the effect of AWG filter shape on system performance is investigated. Simulation modeling and experiments show that deployment of Flat-band AWGs is critical for reducing the probability of error caused by AWG spectral shape filtering. Flat-band athermal AWGs in comparison to Gaussin-shape counterparts satisfy the maximum acceptable error probability requirements, and reduce the power penalty associated with filtering effect. In addition, detuning between two AWG center wavelengths impose further power penalties to the WDM-PON system. In the last section of this thesis, motivated by RSOA device system limitations, a novel injection-locked Fabry-Perot (IL-FP) device is presented which consists of a gain section monolithically integrated with a phase section. The gain section provides locking of one FP mode to a seed source wavelength, while the phase modulator allows for adjusting the wavelength of the internal modes by tuning bias current to maintain mode-locking. This device counters any mode drifts caused by temperature variations, and allows for cooler-less operation over a wide range of currents. The devices and the performance metrics subsequently allow for a hybrid integration platform on a silicon substrate and integrate many functionalities like reflective modulator with thin film dielectric filter and receiver on a single chip for deployment at the user-end of future-proof low cost WDM-PONs

Characterization and design of coherent optical OFDM transmission systems based on Hartley Transform

Nowadays, due to huge deployment of optical transport networks, a continuous increase towards higher data rates up to 100 Gb/s and beyond is observed. Furthermore, an evolution of the current optical networks is forecasted, acquiring new functionalities, e.g. elastic spectrum assignment for the optical signals. The target for these new challenges in transmission is to find techniques ready to deal with a growth of demand for bandwidth continuously asked by network operators, for whom the standard systems do not meet the new functionalities while higher rates are being set up. A solution for covering all of those needs is to adapt techniques capable to deal with such enormous data rates, and ensuring the same high efficiency for long distances and mitigate the optical impairments accumulated along the transmission path. Additionally, these transmission techniques are expected to provide some degree of flexibility, in order to enhance the network flexibility. A promising technology that can fully cope with those requires is the coherent optical orthogonal frequency division multiplexing (CO-OFDM). CO-OFDM provides several advantages, namely high sensitivity and spectral efficiency, simple integration and possibility to fully recover a signal in phase, amplitude and polarization. These systems are composed by digital signal processing (DSP) blocks that easily process data and can equalize and compensate the main impairments, providing high tolerance for dispersion effects. However, CO-OFDM systems are not free from drawbacks. Their high peak-to-average power ratio (PAPR) reduce their tolerance to nonlinearities. Furthermore, CO-OFDM systems are sensitive to any frequency shift and phase offset. Hence, a constant envelope optical OFDM (CE-OFDM) is proposed for significantly reducing the PAPR and solving high sensitivity to nonlinear impairments. It consists in a phase modulated discrete multi-tone signal, which is coherently detected at the receiver side. An alternative transform, the discrete Hartley transform, is proposed to speed up calculations in the DSP and eliminate the need to have a Hermitian symmetry. The optical CE-OFDM by its unique flexibility and rate scalability turns out as a great technology applicable to different configurations, ranging from access to core networks. In case of access solutions, several cases are investigated. First, the optical CE-OFDM is applied for radio access network signals delivery by means of a wavelength division multiplexing (WDM) overlay in deployed access architecture. A decomposed radio access network is deployed over an existing standard passive optical network (PON), capable to avoid interference and cross talks with access signals between network clients. The system exhibited narrow channel spacing, while reducing losses fed into the access equipment path. Next, a full duplex 10 Gb/s bidirectional PON transmission over a single wavelength with RSOA based ONU is investigated. The key point of that system is the upstream transmission, which is achieved re-modulating the phase of a downstream intensity modulated signal after proper saturation. The reported sensitivity performances show a power budget matching the PON standards and an OSNR easy to reach on non-amplified PON. Next, a flexible metropolitan area network of up to 100km with traffic add/drop using WDM is investigated. There the narrowing effect of the optical filters is studied. Finally, an elastic upgrade of the existing Telefonica model of the Spanish national core network is proposed. For that, the transceiver architecture is proposed to be operated featuring polarization multiplexing. Respect to the existing fixed grid, the flexible approach (enabled by the CE-OFDM transceiver) results into reduced bandwidth occupancy and low OSNR requirement.Hoy en día, debido al gran despliegue de las redes de ópticas de transporte, se espera un aumento continuado hacia mayores velocidades de datos, hasta 100 Gb/s y más allá. Por otra parte, la evolución que se prevé para las redes ópticas actuales, incluye la adquisición de nuevas funcionalidades, por ejemplo, la asignación del espectro de forma elástica para las señales ópticas. Por tanto, el claro desafío en cuanto a las tecnologías de transmisión es encontrar técnicas preparadas para hacer frente a un crecimiento de la demanda de ancho de banda; demanda que continuamente se incrementa por parte de los operadores de red, para quienes los sistemas estándar no se acaban de ajustar a las nuevas funcionalidades que esperan para la red. Una solución para cubrir todas estas necesidades es la adaptación de técnicas capaces de hacer frente a estas velocidades de datos enormes, y garantizar el mismo nivel de eficiencia para las largas distancias y mitigar las deficiencias ópticas acumuladas a lo largo de la ruta de transmisión. Además, se espera que estas técnicas de transmisión puedan proporcionar cierto grado de flexibilidad, a fin de mejorar y hacer más eficiente la gestión de la red. Una tecnología prometedora que puede hacer frente a estos requisitos es lo que se llama multiplexación por división de frecuencias ortogonales, combinado con la detección óptica coherente (CO-OFDM). CO-OFDM ofrece varias ventajas, entre otras: alta sensibilidad y eficiencia espectral y, sobre todo, la posibilidad de recuperar por completo de una señal en fase, la amplitud y la polarización. Estos sistemas están compuestos por bloques de procesado de señales digitales (DSP) que permiten detectar los datos fácilmente así como también compensar las principales degradaciones, proporcionando alta tolerancia a los efectos de dispersión. Sin embargo, los sistemas CO-OFDM no están exentos de inconvenientes. Su alta relación de potencia de pico a potencia media (PAPR) reduce sensiblemente la tolerancia no linealidades. Por otra parte, los sistemas CO-OFDM son sensibles a cualquier cambio de frecuencia y desplazamiento de fase. Por tanto, se propone un sistema OFDM de envolvente constante (CE-OFDM) para reducir significativamente la PAPR y solucionar la alta sensibilidad a las degradaciones no lineales. Consiste en una señal OFDM modulada en fase, que se detecta coherentemente en el receptor. Una transformada alternativa, la transformada discreta de Hartley, se propone para acelerar los cálculos en el DSP. El sistema CE-OFDM por su flexibilidad y escalabilidad única, resulta una tecnología aplicable a diferentes escenarios, que van desde las redes de acceso hasta las redes troncales. En el caso de las soluciones de acceso, se investigan varios casos. En primer lugar, el CE-OFDM aplica para el desarrollo y soporte de datos de una red radio, reutilizando una red óptica de acceso ya desplegada. A continuación, se investiga la transmisión bidireccional dúplex a 10 Gb / s sobre una sola longitud de onda empleando un RSOA a las unidades de usuario. El punto clave de este sistema es la transmisión en sentido ascendente, que se consigue re-modulando la fase de una señal de intensidad modulada después de saturar de forma adecuada. A continuación, se estudia una red de área metropolitana flexible de hasta 100 km. Concretamente el efecto de concatenación de filtros ópticos es el objetivo de este estudio. Finalmente, se propone una actualización elástica del modelo de Telefónica I+D para la red troncal española. Por ello, se propone operar el CE-OFDM en multiplexación de polarización. Los resultados muestran que esta combinación reduce sensiblemente el empleo de ancho de banda esto como los requisitos de los enlaces transmisión, reduciendo también los costes tanto de desarrollo como de operación y mantenimiento de la red.Avui dia, a causa del gran desplegament de les xarxes de òptiques de transport, s'espera un augment continuat cap a majors velocitats de dades, fins a 100 Gb/s i més enllà. D'altra banda, l'evolució que es preveu per a les xarxes òptiques actuals, inclou l'adquisició de noves funcionalitats, per exemple, assignació de l'espectre de forma elàstica per als senyals òptics. Per tant, el clar desafiament pel que fa a les tecnologies de transmissió és trobar tècniques preparades per fer front a un creixement de la demanda d'ample de banda; demanda que contínuament es fa per part dels operadors de xarxa, per als qui els sistemes estàndard no s'acaben d'ajustar a les noves funcionalitats que esperen per a la xarxa. Una solució per a cobrir totes aquestes necessitats és l'adaptació de tècniques capaces de fer front a aquestes velocitats de dades enormes, i garantir el mateix nivell d'eficiència per a les llargues distàncies i mitigar les deficiències òptiques acumulades al llarg de la ruta de transmissió. A més, s'espera que aquestes tècniques de transmissió puguin proporcionar cert grau de flexibilitat, per tal de millorar i tornar més eficient la gestió de la xarxa. Una tecnologia prometedora que pot fer front a aquests requisits és el que s'anomena multiplexació per divisió de freqüències ortogonals, combinat amb la detecció òptica coherent (CO-OFDM). CO-OFDM ofereix diversos avantatges, entre altres: alta sensibilitat i eficiència espectral i, sobretot, la possibilitat de recuperar per complet d'una senyal en fase, l'amplitud i la polarització. Aquests sistemes estan compostos per blocs de processament de senyals digitals (DSP) que permeten detectar les dades fàcilment així com també compensar les principals degradacions, proporcionant alta tolerància pels efectes de dispersió. No obstant això, els sistemes CO-OFDM no estan exempts d'inconvenients. La seva alta relació de potència de pic a potència mitjana (PAPR) redueix sensiblement la tolerància a no linealitats. D'altra banda, els sistemes de CO-OFDM són sensibles a qualsevol canvi de freqüència i desplaçament de fase. Per tant, es proposa un sistema OFDM d'envolvent constant (CE-OFDM) per a reduir significativament la PAPR i solucionar l'alta sensibilitat a les degradacions no lineals. Consisteix en un senyal OFDM modulat en fase, que es detecta coherentment en el receptor. Una transformada alternativa, la transformada discreta d'Hartley, es proposa accelerar els càlculs en el DSP. El sistema CE-OFDM per la seva flexibilitat i escalabilitat única, resulta una tecnologia aplicable a diferents escenaris, que van des de les xarxes d'accés fins a les xarxes troncals. En el cas de les solucions d'accés, s'investiguen diversos casos. En primer lloc, el CE-OFDM s'aplica per al desplegament i suport de dades d'una xarxa radio, reutilitzant una xarxa òptica d'accés ja desplegada. A continuació, s'investiga la transmissió bidireccional dúplex a 10 Gb/s sobre una sola longitud d'ona emprant un RSOA a les unitats d'usuari. El punt clau d'aquest sistema és la transmissió en sentit ascendent, que s'aconsegueix re-modulant la fase d'un senyal d'intensitat modulada després de saturar-la de forma adequada. A continuació, s'estudia una xarxa d'àrea metropolitana flexible de fins a 100 km. Concretament l'efecte de concatenació de filtres òptics és l'objectiu d'aquest estudi. Finalment, es proposa una actualització elàstica del model de Telefónica I+D per a la xarxa troncal espanyola. Per això, es proposa operar el CE-OFDM en multiplexació de polarització. Els resultats mostren que aquesta combinació redueix sensiblement l'ocupació d'ample de banda això com també els requisits dels enllaços transmissió, reduint també els costos tant de desplegament com d'operació i manteniment de la xarxa

Optical Network Design, Modelling and Performance Evaluation for the Upgraded LHC at CERN

This thesis considers how advances in optical network and optoelectronic technologies may be utilised in particle physics applications. The research is carried out within a certain framework; CERN's Large Hadron Collider (LHC) upgrade. The focus is on the upgrade of the "last-tier" data links, those residing between the last information-processing stage and the accelerator. For that purpose, different network architectures, based on the Passive Optical Network (PON) architectural paradigm, are designed and evaluated. Firstly, a Time-Division Multiplexed (TDM) PON targeting timing, trigger and control applications is designed. The bi-directional, point-to-multipoint nature of the architecture leads to infrastructure efficiency increase. A custom protocol is developed and implemented using FPGAs. It is experimentally verified that the network design can deliver significantly higher data rate than the current infrastructure and meet the stringent latency requirements of the targeted application. Consequently, the design of a network that can be utilised to transmit all types of information at the upgraded LHC, the High-Luminosity LHC (HL-LHC) is discussed. The most challenging requirement is that of the high upstream data rate. As WDM offers virtual point-to-point connectivity, the possibility of using a Wavelength-Division Multiplexed (WDM) PON is theoretically investigated. The shortcomings of this solution are identified; these include high cost and complexity, therefore a simpler architecture is designed. This is also based on the PON paradigm and features the use of Reflective Electroabsorption Modulators (REAM) at the front-end (close to the particle collision point). Its performance is experimentally investigated and shown to meet the requirements of a unified architecture at the HL-LHC from a networking perspective. Finally, since the radiation resistance of optoelectronic components used at the front-end is of major importance, the REAM radiation hardness is experimentally investigated. Their radiation resistance limits are established, while new insights into the radiation damage mechanism are gained

WDM/TDM PON bidirectional networks single-fiber/wavelength RSOA-based ONUs layer 1/2 optimization

This Thesis proposes the design and the optimization of a hybrid WDM/TDM PON at the L1 (PHY) and L2 (MAC) layers, in terms of minimum deployment cost and enhanced performance for Greenfield NGPON. The particular case of RSOA-based ONUs and ODN using a single-fibre/single-wavelength is deeply analysed. In this WDM/TDM PON relevant parameters are optimized. Special attention has been given at the main noise impairment in this type of networks: the Rayleigh Backscattering effect, which cannot be prevented. To understand its behaviour and mitigate its effects, a novel mathematical model for the Rayleigh Backscattering in burst mode transmission is presented for the first time, and it has been used to optimize the WDM/TDM RSOA based PON. Also, a cost-effective, simple design SCM WDM/TDM PON with rSOA-based ONU, was optimized and implemented. This prototype was successfully tested showing high performance, robustness, versatility and reliability. So, the system is able to give coverage up to 1280 users at 2.5 Gb/s / 1.25 Gb/s downstream/upstream, over 20 Km, and being compatible with the GPON ITU-T recommendation. This precedent has enabled the SARDANA network to extend the design, architecture and capabilities of a WDM/TDM PON for a long reach metro-access network (100 km). A proposal for an agile Transmission Convergence sub-layer is presented as another relevant contribution of this work. It is based on the optimization of the standards GPON and XG-PON (for compatibility), but applied to a long reach metro-access TDM/WDM PON rSOA-based network with higher client count. Finally, a proposal of physical implementation for the SARDANA layer 2 and possible configurations for SARDANA internetworking, with the metro network and core transport network, are presented

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

Caracterização de moduladores RSOA em ligações de radio sobre fibra

Doutoramento em Engenharia ElectrotécnicaIn this work physical and behavioral models for a bulk Reflective Semiconductor Optical Amplifier (RSOA) modulator in Radio over Fiber (RoF) links are proposed. The transmission performance of the RSOA modulator is predicted under broadband signal drive. At first, the simplified physical model for the RSOA modulator in RoF links is proposed, which is based on the rate equation and traveling-wave equations with several assumptions. The model is implemented with the Symbolically Defined Devices (SDD) in Advanced Design System (ADS) and validated with experimental results. Detailed analysis regarding optical gain, harmonic and intermodulation distortions, and transmission performance is performed. The distribution of the carrier and Amplified Spontaneous Emission (ASE) is also demonstrated. Behavioral modeling of the RSOA modulator is to enable us to investigate the nonlinear distortion of the RSOA modulator from another perspective in system level. The Amplitude-to-Amplitude Conversion (AM-AM) and Amplitude-to-Phase Conversion (AM-PM) distortions of the RSOA modulator are demonstrated based on an Artificial Neural Network (ANN) and a generalized polynomial model. Another behavioral model based on Xparameters was obtained from the physical model. Compensation of the nonlinearity of the RSOA modulator is carried out based on a memory polynomial model. The nonlinear distortion of the RSOA modulator is reduced successfully. The improvement of the 3rd order intermodulation distortion is up to 17 dB. The Error Vector Magnitude (EVM) is improved from 6.1% to 2.0%. In the last part of this work, the performance of Fibre Optic Networks for Distributed and Extendible Heterogeneous Radio Architectures and Service Provisioning (FUTON) systems, which is the four-channel virtual Multiple Input Multiple Output (MIMO), is predicted by using the developed physical model. Based on Subcarrier Multiplexing (SCM) techniques, four-channel signals with 100 MHz bandwidth per channel are generated and used to drive the RSOA modulator. The transmission performance of the RSOA modulator under the broadband multi channels is depicted with the figure of merit, EVM under di erent adrature Amplitude Modulation (QAM) level of 64 and 254 for various number of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers of 64, 512, 1024 and 2048.Nesta tese são propostos modelos físicos e comportamentais para o amplificador óptico semicondutor reflectivo (RSOA), tendo como objectivo a avaliação do seu desempenho quando utilizado como modulador em ligações de rádio sobre fibra (RoF). Os modelos propostos são capazes de prever o comportamento do dispositivo quando utilizado com sinais de banda larga bem como quando estimulado por sinais de elevada potência. Inicialmente propõe-se um modelo físico simplificado para o RSOA baseado nas equações de taxa e nas equações de propagação electromagnética. A implementação do modelo utiliza o ADS (Advanced Design Systems) e o bloco designado por dispositivo definido simbolicamente (SDD) para descrever as equações de taxa, assim como a propagação de fotões ao longo da cavidade. O modelo permite uma análise detalhada do ganho óptico, distorções harmônicas, intermodulação e seu desempenho de transmissão com portadoras RF modeladas. Foram também considerados modelos comportamentais. Um modelo baseado em rede neural artificial (ANN) e um modelo polinomial generalizado para banda base foram considerados tendo os parâmetros respectivos sido extraídos utilizando, para o efeito, dados obtidos experimentalmente. São demonstradas a característica da distorção resultante da conversão amplitude - amplitude (AM-AM) e conversão da fase - amplitude (AM-PM) no modulador RSOA. Um modelo baseado em parametros X, obtidos a partir do modelo físico, foi também analisado. Compensação da não-linearidade do modulador RSOA é realizada com base num modelo polinomial com memória. Demonstra-se que a distorção não linear do modulador RSOA pode ser compensada com sucesso. Com a compensação obtem-se uma redução de 17 dB da distorção introduzida pelos produtos de intermodulação de terceira ordem. O EVM (Error Vector Magnitude) apresenta uma melhoria de 6,1% para 2,0%. Na última parte deste trabalho considera-se uma configuração que representa a ligação ascendente por fibra de um sistema de antenas remoto a uma estação central de processamento. Com esta configuração pretendese demonstrar a possibilidade de implementação de uma tecnologia MIMO, suportada num sistema RoF. Baseado numa técnica de multiplexação subportadora (SCM), os sinais de quatro canais com largura de banda de 100 MHz por canal são multiplexados e utilizados para modelar o ganho do RSOA. O desempenho deste link óptico é caracterizado para modulações OFDM considerando diferentes números de sub-portadoras por símbolo (64, 512 , 1024 e 2048) assim como o formato QAM imposto sobre cada sub-portadora