Monitoring and all-optical signal processing techniques for transparent networks

Optical networks are under constant evolution. The growing demand for dynamism require devices that can accommodate different types of traffic. Thus the study of transparent optical networks arises. This approach makes optical networks more "elegant" , due to a more efficient use of network resources. In this thesis, the author proposes devices that intend to form alternative approaches both in the state of art of these same technologies both in the fitting of this technologies in transparent optical networks. Given that full transparency is difficult to achieve with current technology (perhaps with more developed optical computing this is possible), the author proposes techniques with different levels of transparency. On the topic of performance of optical networks, the author proposes two techniques for monitoring chromatic dispersion with different levels of transparency. In Chapter 3 the proposed technique seems to make more sense for long-haul optical transmission links and high transmission rates, not only due to its moderate complexity but also to its potential moderate/high cost. However it is proposed to several modulation formats, particularly those that have a protruding clock component. In Chapter 4 the transparency level was not tested for various modulation formats, however some transparency is achieved by not adding any electrical device after the receiver (other than an analog-digital converter). This allows that this technique can operate at high transmission rates in excess of 100 Gbit / s, if electro-optical asynchronous sampling is used before the optical receiver. Thus a low cost and low bandwidth photo-detector can be used. In chapter 5 is demonstrated a technique for simultaneously monitoring multiple impairments of the optical network by generating novel performance analysis diagrams and by use of artificial neural networks. In chapter 6 the author demonstrates an all-optical technique for controlling the optical state of polarization and an example of how all-optical signal processing can fully cooperate with optical performance monitoring.

Estudo da degradação do tempo de vida das fibras óticas e o seu impacte no desempenho das redes de comunicações

Este trabalho focou-se no estudo do impacte das condições ambientais, de instalação e de utilização na degradação da fibra ótica, que frequentemente resultam na redução do desempenho das fibras óticas. Entre este fatores, foram estudados os efeitos de ambientes agressivos para o revestimento da fibra, nomeadamente no tempo de vida e resistência. Foi também estudado o efeito da propagação de sinais óticos de elevadas potências em curvaturas apertadas e a sua influência na degradação do desempenho da fibra ótica. Ainda neste âmbito, foi também estudado o desempenho de fibras óticas insensíveis a curvtura e fibras dopadas com Érbio, sendo analisada a dinâmica do efeito rastilho nestas fibras. Como parte integrante das redes óticas, os conetores óticos são de extrema importância na sua estrutura. O seu desempenho será refletido na qualidade do serviço da rede, e por isso é determinante estudar os fatores que contribuem para a sua degradação e mau funcionamento. Assim, este trabalho apresenta um estudo do comportamento de conetores óticos perante situações de mau manuseamento (como são limpeza insuficiente e degradação física da face final). Em adição foi também dado ênfase à reutilização de fibra danificada pelo efeito rastilho no desenvolvimento de sensores, passíveis de serem utilizados na monitorização de índice de refração, pressão hidrostática, tensão ou alta temperatura. Este procedimento surge como uma solução de baixo custo para o desenvolvimento de sensores em fibra ótica a partir de fibra danificada e inutilizável para as suas habituais aplicações em transmissão e/ou reflexão de sinais óticos.

Channel modelling for MIMO systems

Systems equipped with multiple antennas at the transmitter and at the receiver, known as MIMO (Multiple Input Multiple Output) systems, offer higher capacities, allowing an efficient exploitation of the available spectrum and/or the employment of more demanding applications. It is well known that the radio channel is characterized by multipath propagation, a phenomenon deemed problematic and whose mitigation has been achieved through techniques such as diversity, beamforming or adaptive antennas. By exploring conveniently the spatial domain MIMO systems turn the characteristics of the multipath channel into an advantage and allow creating multiple parallel and independent virtual channels. However, the achievable benefits are constrained by the propagation channel’s characteristics, which may not always be ideal. This work focuses on the characterization of the MIMO radio channel. It begins with the presentation of the fundamental results from information theory that triggered the interest on these systems, including the discussion of some of their potential benefits and a review of the existing channel models for MIMO systems. The characterization of the MIMO channel developed in this work is based on experimental measurements of the double-directional channel. The measurement system is based on a vector network analyzer and a two-dimensional positioning platform, both controlled by a computer, allowing the measurement of the channel’s frequency response at the locations of a synthetic array. Data is then processed using the SAGE (Space-Alternating Expectation-Maximization) algorithm to obtain the parameters (delay, direction of arrival and complex amplitude) of the channel’s most relevant multipath components. Afterwards, using a clustering algorithm these data are grouped into clusters. Finally, statistical information is extracted allowing the characterization of the channel’s multipath components. The information about the multipath characteristics of the channel, induced by existing scatterers in the propagation scenario, enables the characterization of MIMO channel and thus to evaluate its performance. The method was finally validated using MIMO measurements.

Post-synthetic modification of metal–organic frameworks

Post-synthetic modification (PSM) of metal-organic frameworks encompassing the chemical transformation of the linker present is a promising new route for engineering optical centres and tuning the light emission properties of materials, both in the visible and in the near infrared (NIR) spectral regions. Here, PSM of isoreticular metal-organic framework-3 (IRMOF-3) with ethyl oxalyl monochloride, ethyl acetoacetate, pentane-2,4-dione, 3-(2- hydroxyphenyl)-3-oxopropanal, 2-chloroacetic acid, glyoxylic acid, methyl vinyl ketone and diethyl (ethoxymethylene)malonate followed by chelation of trivalent lanthanide ions afforded intriguing near infrared (Nd3+) and visible (Eu3+, Tb3+) light emitters. IRMOF-3 was used as a case in point due to both its highly porous crystalline structure and the presence of non-coordinating amino groups on the benzenedicarboxylate (bdc) linker amenable to modification. The materials were characterised by elemental analysis, powder X-ray diffraction, optical, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, and liquid and solid-state nuclear magnetic resonance. The solid-state luminescence properties of Ln-modified-IRMOF-3 were investigated at room temperature. The presence of the bdc aromatic ring, β– diketonate and oxalate enhanced the Ln3+ sensitization via ligand-to-metal energy transfer (anthena effect). As far as photocalysis is concerned, we have synthesized metal−organic frameworks (Cr-MIL-125-AC, Ag-MIL-125-AC) by a green method (solid–vapors reactions). The resulting functionalized materials show a photocatalytic activity for methylene blue degradation up to 6.52 times larger than that of the commercial photocatalyst hombikat UV-100. These findings open the door for further research for improving the photocatalytic performance of metal-organic frameworks.