Conception par la méthode des fréquences réelles d'amplificateurs monolithiques millimétriques pour les télécommunications à très haut débit

Cette thèse traite de la synthèse d'amplificateurs microondes monolithiques passe-bas dédiés aux liaisons SDH/ETDM sur fibre optique à 40 Gbit/s. Le premier chapitre expose le cahier des charges du driver situé dans le bloc d'émission pour ce type de liaison. Le deuxième chapitre détaille pour une technologie HEMT, les deux principales architectures MMIC qui satisfont aux spécifications exigeantes de tels amplificateurs: l'architecture distribuée et l'architecture dite « à forte désadaptation ». Nous proposons dans un premier temps d'étendre la bande passante d'un amplificateur à forte désadaptation incluant un étage suiveur, par superposition d'une cellule cascode. Nous proposons dans un second temps une variante contre-réactionnée qui permet de réduire l'ondulation dans la bande de l'amplificateur. Nous présentons dans le troisième chapitre la Méthode des Fréquences Réelles, une méthode basée sur l'optimisation d'égaliseurs passifs, dans le cadre d'une synthèse de circuit monolithique. Un premier exemple de synthèse à égaliseur unique utilisant la méthode sous forme quadripolaire est alors donné. L'amplificateur a été réalisé sur substrat microruban à partir de l'architecture à cellule cascode proposée. Nous donnons pour celui-ci des résultats de simulations électromagnétiques et des résultats de mesures. Un deuxième exemple de synthèse, basé sur l'architecture à cellule cascode contreréactionnée, est finalement donné. Pour l'optimisation du circuit, la Méthode des Fréquences Réelles est utilisée sous une forme octopolaire. Le circuit a été réalisé sur substrat coplanaire et l'égaliseur passif est alors inclus dans la boucle de contre-réaction. Des résultats de simulations sont donnés et sont comparés à ceux d'un amplificateur distribué, simulé dans la même technologie.This work is concerned with the monolithic microwave low-pass amplifier synthesis dedicated to SDH/ETDM optical fiber links at a bitrate of 40 Gbit/s. The first chapter describes the driver requirements for such a link. In the second part, the two principal topologies for a HEMT technology which comply with the specifications are detailed : the distributed architecture and the strong mismatch architecture. In a first time we propose to extend the bandwidth of a strong mismatch amplifier including a follower stage by superimposing a cascode cell. In a second time we propose to add a shunt feedback to the circuit for reducing the ripple over the band. We present in the third chapter the Real Frequency Technique, a synthesis method based on passive equalizer optimization, applied to the monolithic design. We give a first synthesis example involving a single passive equalizer. The amplifier has been realized on a microstrip substrate and it is based on the superimposed cascode cell architecture that we propose. For this, we give electromagnetic simulation and measurement results. A second synthesis example is then given, based on the proposed feedback architecture. In this example, we used the Real Frequency Technique under octopolar form for the circuit optimization. It allows to place the equalizer in the feedback loop. The amplifier has been realized on a coplanar substrate. Simulation results are given and are compared with those of a distributed amplifier realized in the same technology

Electronic/photonic interfaces for ultrafast data processing.

This report summarizes a 3-month program that explored the potential areas of impact for electronic/photonic integration technologies, as applied to next-generation data processing systems operating within 100+ Gb/s optical networks. The study included a technology review that targeted three key functions of data processing systems, namely receive/demultiplexing/clock recovery, data processing, and transmit/multiplexing. Various technical approaches were described and evaluated. In addition, we initiated the development of high-speed photodetectors and hybrid integration processes, two key elements of an ultrafast data processor. Relevant experimental results are described herein

Estudo dos limites na capacidade de transmissão em SCFO

Mestrado em Engenharia Electrónica e TelecomunicaçõesA constante necessidade de aumentar a capacidade de transmissão de dados nos sistemas ópticos impõe uma incessante procura do melhor desempenho, eficiência e qualidade possíveis, de modo a tirar o melhor proveito das potencialidades das fibras ópticas. Neste contexto, torna-se importante conhecer e comparar os principais formatos de modulação existentes, de modo a que, para uma dada situação de transmissão prática, com um determinado ritmo de transmissão e distância associada, seja possível fazer a melhor escolha do formato de acordo com as necessidades. Este é o principal objectivo deste trabalho. Os formatos estudados nesta dissertação são o Non Return to Zero (NRZ), Return to Zero (RZ), Duobinário (DB), Vestigial Side Band (VSB), Quadrature Phase Shift Keying (QPSK), Diferential Quadrature Phase Shift Keying (DQPSK) bem como o Quadrature Amplitude Modulation com 4 e 6 bits codificados por símbolo (16-QAM e 64-QAM respectivamente) e ritmos de transmissão de 2.5, 10, 20 e 40 Gbps, observando-se as distâncias máximas para cada caso. De modo a fazer o estudo comparativo entre estes formatos foram realizadas uma série de simulações, através do VPISystemsTM, sob as mesmas condições de frequência de funcionamento (nomeadamente o parâmetro da dispersão e PMD das fibras, extintion ratio dos moduladores Mach-Zehnder e potência óptica de saída dos lasers usados) de modo a caracterizar espectralmente os formatos e análise da penalidade de potência. Tendo como base os resultados obtidos destas simulações, foi possível concluir que a ocupância espectral apresentada por cada formato é um bom indicador do seu desempenho e que para ritmos de transmissão superiores a 10Gbps a diferença de resultados entre os formatos de modulação em intensidade e os demais tornam-se muito significativas. Destes últimos formatos destacam-se os formatos de modulação em amplitude e fase (16-QAM e 64-QAM) pelo seu desempenho superior face aos restantes. Destes, o 64-QAM apresenta os melhores resultados sugerindo que um maior número de bits codificados por símbolo poderá permitir melhores resultados. Isto é apoiado pelo facto de um maior número de bits codificados por símbolo se traduzir numa eficiência espectral superior. Tendo em conta os resultados em WDM, as conclusões são idênticas. Aqui, verificou-se uma diferença significativa de desempenho entre os formatos de em intensidade e os formatos em fase ou amplitude e fase. Estes últimos, demonstraram permitir um espaçamento entre canais muito mais reduzindo quando comparado com os formatos de intensidade (aproximadamente 10 GHz face aos 35 GHz dos formatos em intensidade). No entanto, dever-se-á ter sempre em consideração a potência óptica exigida pelo formato, que tende a aumentar significativamente com a complexidade do formato. Logo, terá sempre de ser encontrado o melhor compromisso entre desempenho e potência exigida para cada situação.The constant need for increased data transmission capacity in optic systems imposes an unending search for the best performance, efficiency and quality possible in order to take full advantage of the fiber optics’ potentialities. Keeping this in mind, it is important to know and compare the existing main modulation formats so that, in any given situation, the most informed decision can be made regarding one’s needs. This is this paper’s objective. The studied modulation formats are Non Return to Zero (NRZ), Return to Zero (RZ), Duobinary (DB), Vestigial Side Band (VSB), Quadrature Phase Shift Keying (QPSK), Diferential Quadrature Phase Shift Keying (DQPSK) as well as Quadrature Amplitude Modulation with 4 and 6 coded bits per symbol (16-QAM and 64-QAM respectively) and bit rates of 2.5, 10, 20 and 40Gbps observing the maximum distances achieved for each case. In order to undertake a comparative study between these modulation formats, a series of simulations where made, using VPISystemsTM, under similar circumstances characterizing the optical spectrum and power penalty of each modulation format (namely the fiber’s dispersion parameter and PMD, Mach-Zehnder modulators’ extintion ratio and the lasers’ optical output power).Basing on the simulation’s results, it was possible to conclude that the optical spectrum’s width is an important indicator of a modulation format´s performance and that for bit rates superior to 10Gbps, the difference in results between intensity modulation formats and all the others studied formats becomes meaningful. Considering these last formats, the ones showing the best results are the amplitude and phase modulation formats (16-QAM and 64-QAM). From these two it is the 64-QAM which shows the best performance suggesting that an increased number of encoded bits per symbol could lead to better results. This is supported by the fact that a superior number of encoded bits per symbol translates into a superior spectral efficiency. Considering the obtained results for WDM, the conclusions are identical. Here the performance gap between the intensity and phase or amplitude and phase formats is clear. These last formats allow for significantly inferior channel spacing when compared to the intensity modulation formats (approximately 10 GHz compared to 35 GHz from the intensity formats). However, one should keep in mind that the required optical power (even for a back-to-back situation) tends to increase with the complexity of the modulation format in cause. Therefore, the best compromise between required performance and required optical power should be found for each particular situation

Crosstalk mitigation techniques in multi-wavelength networks comprising photonic integrated circuits

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