Novel Insights into Orbital Angular Momentum Beams: From Fundamentals, Devices to Applications

It is well-known by now that the angular momentum carried by elementary particles can be categorized as spin angular momentum (SAM) and orbital angular momentum (OAM). In the early 1900s, Poynting recognized that a particle, such as a photon, can carry SAM, which has only two possible states, i.e., clockwise and anticlockwise circular polarization states. However, only fairly recently, in 1992, Allen et al. discovered that photons with helical phase fronts can carry OAM, which has infinite orthogonal states. In the past two decades, the OAM-carrying beam, due to its unique features, has gained increasing interest from many different research communities, including physics, chemistry, and engineering. Its twisted phase front and intensity distribution have enabled a variety of applications, such as micromanipulation, laser beam machining, nonlinear matter interactions, imaging, sensing, quantum cryptography and classical communications. This book aims to explore novel insights of OAM beams. It focuses on state-of-the-art advances in fundamental theories, devices and applications, as well as future perspectives of OAM beams

Mode division multiplexing in radio-over-free-space-optical system incorporating orthogonal frequency division multiplexing and photonic crystal fiber equalization

Radio over free space optics (Ro-FSO) is a revolutionary technology for seamlessly integrating radio and optical networks without expensive optical fiber cabling. RoFSO technology plays a crucial role in supporting broadband connectivity in rural and remote areas where current broadband infrastructure is not feasible due to geographical and economic inconvenience. Although the capacity of Ro-FSO can be increased by mode division multiplexing (MDM), the transmission distance and capacity is still limited by multipath fading and mode coupling losses due to atmospheric turbulences such as light fog, thin fog and heavy fog. The main intention of this thesis is to design MDM system for Ro-FSO for long and short haul communication. Orthogonal frequency division multiplexing (OFDM) is proposed for long haul communication to mitigate multipath fading and Photonic Crystal Fiber (PCF) is proposed for short haul communication to reduce mode coupling losses. The reported results of the proposed scheme for long haul communication show a significant 47% power improvement in deep fades from multipath propagation with the use of OFDM in MDM-Ro-FSO systems as compared to without OFDM. The results of the proposed scheme for short haul communication show 90.6% improvement in power in the dominant mode with the use of PCF in MDM-Ro-FSO as compared to without PCF. The reported results in the thesis show significant improvement in Ro-FSO systems as compared to previous systems in terms of capacity and transmission distance under clear weather conditions as well as under varying levels of fog. The contributions of this thesis are expected to provide seamless broadband services in remote areas

Mode division multiplexing based on ring core optical fibers

The unique modal characteristics of ring core fibers (RCFs) potentially enable the implementation of mode-division multiplexing (MDM) schemes that can increase optical data transmission capacity with either low-complexity modular multi-input multi-output (MIMO) equalization or no MIMO equalization. This paper attempts to present a comprehensive review of recent research on the key aspects of RCF-based MDM transmission. Starting from fundamental fiber modal structures, a theoretical comparison between RCFs and conventional step-index and graded-index multi-mode fibers in terms of their MDM capacity and the associated MIMO complexity is given first as the underlining rationale behind RCF-MDM. This is followed by a discussion of RCF design considerations for achieving high-mode channel count and low crosstalk performances in either MIMO-free or modular MIMO transmission schemes. The principles and implementations of RCF mode (de-)multiplexing devices are discussed in detail, followed by RCF-based optical amplifiers culminating in MIMO-free or modular-MIMO RCF-MDM data transmission schemes. A discussion on further research directions is also given

Optical angular momentum in air core fibers

As data consumption continues to grow, the backbone of the internet, comprising single mode fiber (SMF)-based infrastructure, is fundamentally limited by nonlinear optical effects. One strategy to address this bottleneck, space division multiplexing (SDM), utilizes multiple modes in a single fiber as independent data channels. Orbital Angular Momentum (OAM) carrying modes, which have twisting phase fronts tracing out helices as the beams propagate, have recently received tremendous attention as a means of achieving low-crosstalk, digital signal processing (DSP)-free transmission with enhanced capacity. Terabit-scale transmission using 4 OAM modes over 1.1km has been demonstrated, but questions remain – how many OAM modes can fibers support, and how stable is propagation over longer lengths? In this thesis, we investigate angular momentum carrying modes in a novel class of fibers featuring an air core. We find that high-order OAM states, although arising in degenerate pairs, counterintuitively resist mode coupling due to OAM conservation, pointing to a unique stability inherent to OAM modes in fibers. We achieve OAM propagation up to 13.4km lengths, and achieve mode purities greater than 15dB at data-center length-scales. We use these fibers to transmit wavelength-division multiplexed data with 25 GHz channel spacing, 10 GBaud rates and quadrature-phase-shift keyed modulation formats in 12 modes simultaneously, over 1.2km, and over a large number of wavelengths across the C-band (1530-1565nm). However, transmission over every mode in every channel of the C-band was prevented by the accidental degeneracy of OAM states with undesired modes. To achieve a larger ensemble of stable modes over a larger wavelength range, we study new fiber designs that avoid this accidental degeneracy problem. We find that the most scalable modal eigenbasis is a set of states that carry non-integer amounts of average OAM, also called spin-orbit coupled modes in analogy with similar effects observed in atomic physics. We demonstrate excitation and transmission of 24 such modes over device lengths (10m). The achievement of a record number of uncoupled modes in fibers confirms the viability of angular momentum states as data carriers, and potential applications include links in data centers, high capacity optical amplifiers, and quantum communications links.2017-09-09T00:00:00

Design and modeling of optical fibers for spatial division multiplexing using the orbital angular momentum of light

Les besoins toujours croissants en terme de transfert de données numériques poussent au développement de nouvelles technologies pour accroître la capacité des réseaux, notamment en ce qui concerne les réseaux de fibre optique. Parmi ces nouvelles technologies, le multiplexage spatial permet de multiplier la capacité des liens optiques actuels. Nous nous intéressons particulièrement à une forme de multiplexage spatial utilisant le moment cinétique orbital de la lumière comme base orthogonale pour séparer un certain nombre de canaux. Nous présentons d’abord les notions d’électromagnétisme et de physique nécessaires à la compréhension des développements ultérieurs. Les équations de Maxwell sont dérivées afin d’expliquer les modes scalaires et vectoriels de la fibre optique. Nous présentons également d’autres propriétés modales, soit la coupure des modes, et les indices de groupe et de dispersion. La notion de moment cinétique orbital est ensuite introduite, avec plus particulièrement ses applications dans le domaine des télécommunications. Dans une seconde partie, nous proposons la carte modale comme un outil pour aider au design des fibres optiques à quelques modes. Nous développons la solution vectorielle des équations de coupure des modes pour les fibres en anneau, puis nous généralisons ces équations pour tous les profils de fibres à trois couches. Enfin, nous donnons quelques exemples d’application de la carte modale. Dans la troisième partie, nous présentons des designs de fibres pour la transmission des modes avec un moment cinétique orbital. Les outils développés dans la seconde partie sont utilisés pour effectuer ces designs. Un premier design de fibre, caractérisé par un centre creux, est étudié et démontré. Puis un second design, une famille de fibres avec un profil en anneau, est étudié. Des mesures d’indice effectif et d’indice de groupe sont effectuées sur ces fibres. Les outils et les fibres développés auront permis une meilleure compréhension de la transmission dans la fibre optique des modes ayant un moment cinétique orbital. Nous espérons que ces avancements aideront à développer prochainement des systèmes de communications performants utilisant le multiplexage spatial.The always increasing need for digital data bandwidth pushes the development of emerging technologies to increase network capacity, especially for optical fiber infrastructures. Among those technologies, spatial multiplexing is a promising way to multiply the capacity of current optical links. In this thesis, we are particularly interested in current spatial multiplexing using the orbital angular momentum of light as an orthogonal basis to distinguish between a few optical channels. We first introduce notions from electromagnetism and physic needed for the understanding of the later developments. We derive Maxwell’s equations describing scalar and vector modes of optical fiber. We also present other modal properties like mode cutoff, group index, and dispersion. Orbital angular momentum is briefly explained, with emphasis on its applications to optical communications. In the second part, we propose the modal map as a tool that can help in the design of few mode fibers. We develop the vectorial solution of the ring-core fiber cutoff equation, then we extend those equations to all varieties of three-layer fiber profiles. Finally, we give some examples of the use of the modal map. In the third part of this thesis, we propose few fiber designs for the transmission of modes with an orbital angular momentum. The tools that were developed in the second part of this thesis are now used in the design process of those fibers. A first fiber design, characterized by a hollow center, is studied and demonstrated. Then a second design, a family of ring-core fibers, is studied. Effective indexes and group indexes are measured on the fabricated fibers, and compared to numerical simulations. The tools and the fibers developed in this thesis allowed a deeper comprehension of the transmission of orbital angular momentum modes in fiber. We hope that those achievements will help in the development of next generation optical communication systems using spatial multiplexing

Design and characterization of few-mode fibers for space division multiplexing on fiber eigenmodes

La croissance constante et exponentielle de la demande de trafic de données Internet conduit nos réseaux de télécommunications optiques, principalement composés de liaisons de fibre monomode, à une pénurie imminente de capacité. La limite non linéaire de la fibre monomode, prédite par la théorie de l'information, ne laisse aucune place à l'amélioration de la capacité de communication par fibre optique. Dans ce contexte, la prochaine technologie de rupture dans les transmissions optiques à haute capacité devrait être le multiplexage par répartition spatiale (SDM). La base du SDM consiste à utiliser différents canaux spatiaux d'une seule fibre optique pour transmettre des données indépendantes. Le SDM fournit ainsi une augmentation de la capacité de transport de données d'un facteur qui dépend du nombre de chemins spatiaux qui sont établis. Une façon de réaliser le SDM consiste à utiliser des fibres faiblement multimodes (FMF) spécialisées, conçues pour présenter un couplage faible entre les modes guidés. Un traitement MIMO réduit peut alors être utilisé pour annuler le couplage résiduel des modes. Dans cette thèse, nous donnons tout d'abord un aperçu des progrès récents du multiplexage par répartition de modes (MDM). Les modes à polarisation linéaire (LP), les modes de moment angulaire orbital (OAM) et les modes vectoriels représentent différentes bases de modes orthogonaux possibles dans la fibre. Nous comparons les travaux utilisant ces modes en termes de conception de fibre proposée, nombre de modes, complexité MIMO et résultats expérimentaux de transmission de données. Ensuite, nous introduisons la modélisation de la fibre optique réalisée avec les solveurs numériques de COMSOL Multiphysics, et nous discutons de quelques travaux utilisant cette modélisation de fibre. Nous proposons une nouvelle FMF, composée d'un noyau hautement elliptique et d'une tranchée adjacente ajoutée pour réduire la perte de courbure des modes d'ordre supérieur. La fibre est conçue et optimisée pour prendre en charge cinq modes spatiaux avec une dégénérescence de polarisation double, pour un total de dix canaux. La fibre proposée montre une différence d'indice effectif entre les modes spatiaux supérieure à 1 × 10-3sur la bande C. Ensuite, nous fabriquons la fibre avec un procédé standard de dépôt chimique en phase vapeur modifié (MCVD), et nous caractérisons la fibre en laboratoire. La caractérisation expérimentale a révélé que la fibre présente une propriété de maintien de polarisation. Ceci est obtenu grâce à la combinaison de la structure centrale asymétrique et de la contrainte thermique introduite lors de la fabrication. Nous mesurons la biréfringence avec une technique de réseau de Bragg inscrit dans la fibre (FBG). En incluant la contrainte thermique dans notre modélisation de fibre, un bon accord est obtenu entre la biréfringence simulée et mesurée. Nous avons réussi à effectuer la première transmission de données sur la fibre proposée, en transmettant deux signaux QPSK sur les deux polarisations de chaque mode spatial, sans utiliser de traitement MIMO. Enfin, nous présentons une amélioration d'une technique d'interférométrie hyperfréquence (MICT) précédemment proposée, afin de mesurer expérimentalement la perte en fonction du mode (MDL) des groupes de modes FMF. En conclusion, nous résumons les résultats et présentons les perspectives d'avenir de cette recherche. En résumé, de nouveaux FMF doivent être étudiés si nous voulons résoudre la pénurie imminente de capacité de nos technologies système. Les résultats de cette thèse indique que le FMF à maintien de polarisation proposée dans cette recherche représente une amélioration significative dans le domaine des systèmes de transmission MDM sans MIMO pour des liaisons de communication courtes ; c’est-à-dire distribuant des données sur une longueur inférieure à 10 km. Nous espérons que ce travail conduira au développement de nouveaux composants SD Mutilisant cette fibre, tels que de nouveaux amplificateurs à fibre, ou de nouveaux multiplexeurs/démultiplexeurs, comme par exemple des coupleurs en mode fibre fusionnée ou des dispositifs photoniques au silicium.The constant and exponential growth of Internet data traffic demand is driving our optical telecommunication networks, mainly composed of single-mode fiber links, to an imminent capacity shortage. The nonlinear limit of the single-mode fiber, predicted by the information theory, leave no room for optical fiber communication capacity improvements. In this direction, the next disruptive technology in high-capacity communication transmissions is expected to be Space Division Multiplexing (SDM). The basic of SDM consists of using different spatial channels of a single optical fiber to transmit information data. SDM thus provides an increase in the data-carrying capacity by a factor that depends on the number of spatial paths that are established. A way to realize SDM is through the use of specialty few-mode fibers (FMFs), designed to have a weak coupling between the guided modes. A reduced MIMO processing can be used to undo the residual mode coupling. In this thesis, we firstly give an overview of the recent progress in mode division multiplexing (MDM). Linearly polarized (LP) modes, orbital angular momentum (OAM) modes and vector modes represent the possible orthogonal modes guided into the fiber. We compare works, making use of those modes, in terms of proposed fiber design, number of modes, MIMO complexity and data transmission experiments. After that, we introduce the optical fiber modelling performed with the numerical solvers of COMSOL Multiphysics, and we discuss some works making use of this fiber modelling. Next, we propose a novel FMF, composed of a highly elliptical core and a surrounding trench added to reduce the bending loss of the higher order modes. The fiber is designed and optimized to support five spatial modes with twofold polarization degeneracy, for a total of ten channels. The proposed fiber shows an effective index difference between the spatial modes higher than 1×10-3 over the C-band. Afterwards, we fabricate the fiber with standard modified chemical vapor deposition (MCVD) process, and we characterize the fiber in the laboratory. The experimental characterization revealed the polarization maintaining properties of the fiber. This is obtained with the combination of the asymmetric core structure and the thermal stress introduced during the fabrication. We measure the birefringence with a fiber Bragg grating (FBG) technique, and we included the thermal stress in our fiber modelling. A good agreement was found between the simulated and measured birefringence. We successfully demonstrate the first data transmission over the proposed fiber, by transmitting two QPSK signals over the two polarizations of each spatial mode, without the use of any MIMO processing. Lastly, we present an improvement of a previously proposed microwave interferometric technique (MICT), in order to experimentally measure the mode dependent loss (MDL) of FMF mode groups. Finally, we present the conclusions and the future perspectives of this research. To conclude, novel FMFs need to be investigated if we want to solve the imminent capacity shortage of our system technologies. We truly believe that the polarization-maintaining FMF proposed in this research represents a significant improvement to the field of MIMO-free MDM transmission systems for short communication links, distributing data over length less than 10 km. We hope that this work will drive the development of new SDM components making use of this fiber, such as new fiber amplifiers, or new mux/demux, as for example fused fiber mode couplers or silicon photonic devices

Spatially integrated erbium-doped fiber amplifiers enabling space-division multiplexing

L'augmentation exponentielle de la demande de bande passante pour les communications laisse présager une saturation prochaine de la capacité des réseaux de télécommunications qui devrait se matérialiser au cours de la prochaine décennie. En effet, la théorie de l’information prédit que les effets non linéaires dans les fibres monomodes limite la capacité de transmission de celles-ci et peu de gain à ce niveau peut être espéré des techniques traditionnelles de multiplexage développées et utilisées jusqu’à présent dans les systèmes à haut débit. La dimension spatiale du canal optique est proposée comme un nouveau degré de liberté qui peut être utilisé pour augmenter le nombre de canaux de transmission et, par conséquent, résoudre cette menace de «crise de capacité». Ainsi, inspirée par les techniques micro-ondes, la technique émergente appelée multiplexage spatial (SDM) est une technologie prometteuse pour la création de réseaux optiques de prochaine génération. Pour réaliser le SDM dans les liens de fibres optiques, il faut réexaminer tous les dispositifs intégrés, les équipements et les sous-systèmes. Parmi ces éléments, l'amplificateur optique SDM est critique, en particulier pour les systèmes de transmission pour les longues distances. En raison des excellentes caractéristiques de l'amplificateur à fibre dopée à l'erbium (EDFA) utilisé dans les systèmes actuels de pointe, l'EDFA est à nouveau un candidat de choix pour la mise en œuvre des amplificateurs SDM pratiques. Toutefois, étant donné que le SDM introduit une variation spatiale du champ dans le plan transversal de la fibre, les amplificateurs à fibre dopée à l'erbium spatialement intégrés (SIEDFA) nécessitent une conception soignée. Dans cette thèse, nous examinons tout d'abord les progrès récents du SDM, en particulier les amplificateurs optiques SDM. Ensuite, nous identifions et discutons les principaux enjeux des SIEDFA qui exigent un examen scientifique. Suite à cela, la théorie des EDFA est brièvement présentée et une modélisation numérique pouvant être utilisée pour simuler les SIEDFA est proposée. Sur la base d'un outil de simulation fait maison, nous proposons une nouvelle conception des profils de dopage annulaire des fibres à quelques-modes dopées à l'erbium (ED-FMF) et nous évaluons numériquement la performance d’un amplificateur à un étage, avec fibre à dopage annulaire, à ainsi qu’un amplificateur à double étage pour les communications sur des fibres ne comportant que quelques modes. Par la suite, nous concevons des fibres dopées à l'erbium avec une gaine annulaire et multi-cœurs (ED-MCF). Nous avons évalué numériquement le recouvrement de la pompe avec les multiples cœurs de ces amplificateurs. En plus de la conception, nous fabriquons et caractérisons une fibre multi-cœurs à quelques modes dopées à l'erbium. Nous réalisons la première démonstration des amplificateurs à fibre optique spatialement intégrés incorporant de telles fibres dopées. Enfin, nous présentons les conclusions ainsi que les perspectives de cette recherche. La recherche et le développement des SIEDFA offriront d'énormes avantages non seulement pour les systèmes de transmission future SDM, mais aussi pour les systèmes de transmission monomode sur des fibres standards à un cœur car ils permettent de remplacer plusieurs amplificateurs par un amplificateur intégré.The exponential increase of communication bandwidth demand is giving rise to the so-called ‘capacity crunch’ expected to materialize within the next decade. Due to the nonlinear limit of the single mode fiber predicted by the information theory, all the state-of-the-art techniques which have so far been developed and utilized in order to extend the optical fiber communication capacity are exhausted. The spatial domain of the lightwave links is proposed as a new degree of freedom that can be employed to increase the number of transmission paths and, subsequently, overcome the looming ‘capacity crunch’. Therefore, the emerging technique named space-division multiplexing (SDM) is a promising candidate for creating next-generation optical networks. To realize SDM in optical fiber links, one needs to investigate novel spatially integrated devices, equipment, and subsystems. Among these elements, the SDM amplifier is a critical subsystem, in particular for the long-haul transmission system. Due to the excellent features of the erbium-doped fiber amplifier (EDFA) used in current state-of-the-art systems, the EDFA is again a prime candidate for implementing practical SDM amplifiers. However, since the SDM introduces a spatial variation of the field in the transverse plane of the optical fibers, spatially integrated erbium-doped fiber amplifiers (SIEDFA) require a careful design. In this thesis, we firstly review the recent progress in SDM, in particular, the SDM optical amplifiers. Next, we identify and discuss the key issues of SIEDFA that require scientific investigation. After that, the EDFA theory is briefly introduced and a corresponding numerical modeling that can be used for simulating the SIEDFA is proposed. Based on a home-made simulation tool, we propose a novel design of an annular based doping profile of few-mode erbium-doped fibers (FM-EDF) and numerically evaluate the performance of single stage as well as double-stage few-mode erbium-doped fiber amplifiers (FM-EDFA) based on such fibers. Afterward, we design annular-cladding erbium-doped multicore fibers (MC-EDF) and numerically evaluate the cladding pumped multicore erbium-doped fiber amplifier (MC-EDFA) based on these fibers as well. In addition to fiber design, we fabricate and characterize a multicore few-mode erbium-doped fiber (MC-FM-EDF), and perform the first demonstration of the spatially integrated optical fiber amplifiers incorporating such specialty doped fibers. Finally, we present the conclusions as well as the perspectives of this research. In general, the investigation and development of the SIEDFA will bring tremendous benefits not only for future SDM transmission systems but also for current state-of-the-art single-mode single-core transmission systems by replacing plural amplifiers by one integrated amplifier

Processamento ótico e digital de sinal em sistemas de transmissão com multiplexagem por divisão espacial

The present thesis focuses on the development of optical and digital signal processing techniques for coherent optical transmission systems with spacedivision multiplexing (SDM). According to the levels of spatial crosstalk, these systems can be grouped in the ones with and the ones without spatial selectivity; drastically changing its operation principle. In systems with spatial selectivity, the mode coupling is negligible and therefore, an arbitrary spacial channel can be independently routed through the optical network and post-processed at the optical coherent receiver. In systems without spatial selectivity, mode coupling plays a key role in a way that spatial channels are jointly transmitted and post-processed at the optical coherent receiver. With this in mind, optical switching techniques for SDM transmission systems with spatial selectivity are developed, whereas digital techniques for space-demultiplexing are developed for SDM systems without spatial selectivity. With the purpose of developing switching techniques, the acoustic-optic effect is analyzed in few-mode fibers (FMF)s and in multicore fibers (MCF)s. In FMF, the signal switching between two arbitrary modes using flexural or longitudinal acoustic waves is numerically and experimentally demonstrated. While, in MCF, it is shown that a double resonant coupling, induced by flexural acoustic waves, allows for the signal switching between two arbitrary cores. Still in the context of signal switching, the signal propagation in the multimodal nonlinear regime is analyzed. The nonlinear Schrödinger equation is deduced in the presence of mode coupling, allowing the meticulous analysis of the multimodal process of four-wave mixing. Under the right conditions, it is shown that such process allows for the signal switching between distinguishable optical modes. The signal representation in higher-order Poincaré spheres is introduced and analyzed in order to develop digital signal processing techniques. In this representation, an arbitrary pair of tributary signals is represented in a Poincaré sphere, where the samples appear symmetrically distributed around a symmetry plane. Based on this property, spatial-demultiplexing and mode dependent loss compensation techniques are developed, which are independent of the modulation format, are free of training sequences and tend to be robust to frequency offsets and phase fluctuations. The aforementioned techniques are numerically validated, and its performance is assessed through the calculation of the remaining penalty in the signal-to-noise ratio of the post-processed signal. Finally, the complexity of such techniques is analytically described in terms of real multiplications per sample.A presente tese tem por objectivo o desenvolvimento de técnicas de processamento ótico e digital de sinal para sistemas coerentes de transmissão ótica com multiplexagem por diversidade espacial. De acordo com a magnitude de diafonia espacial, estes sistemas podem ser agrupados em sistemas com e sem seletividade espacial, alterando drasticamente o seu princípio de funcionamento. Em sistemas com seletividade espacial, o acoplamento modal é negligenciável e, portanto, um canal espacial arbitrário pode ser encaminhado de forma independente através da rede ótica e pós-processado no recetor ótico coerente. Em sistemas sem seletividade espacial, o acoplamento modal tem um papel fulcral pelo que os canais espaciais são transmitidos e pós-processados conjuntamente. Perante este cenário, foram desenvolvidas técnicas de comutação entre canais espaciais para sistemas com seletividade espacial, ao passo que para sistemas sem seletividade espacial, foram desenvolvidas técnicas digitais de desmultiplexagem espacial. O efeito acústico-ótico foi analisado em fibras com alguns modos (FMF) e em fibras com múltiplos núcleos (MCF) com o intuito de desenvolver técnicas de comutação de sinal no domínio ótico. Em FMF, demonstrou-se numérica e experimentalmente a comutação do sinal entre dois modos de propagação arbitrários através de ondas acústicas transversais ou longitudinais, enquanto, em MCF, a comutação entre dois núcleos arbitrários é mediada por um processo de acoplamento duplamente ressonante induzido por ondas acústicas transversais. Ainda neste contexto, analisou-se a propagação do sinal no regime multimodal não linear. Foi deduzida a equação não linear de Schrödinger na presença de acoplamento modal, posteriormente usada na análise do processo multimodal de mistura de quatro ondas. Nas condições adequadas, é demonstrado que este processo permite a comutação ótica de sinal entre dois modos de propagação distintos. A representação de sinal em esferas de Poincaré de ordem superior é introduzida e analisada com o objetivo de desenvolver técnicas de processamento digital de sinal. Nesta representação, um par arbitrário de sinais tributários é representado numa esfera de Poincaré onde as amostras surgem simetricamente distribuídas em torno de um plano de simetria. Com base nesta propriedade, foram desenvolvidas técnicas de desmultiplexagem espacial e de compensação das perdas dependentes do modo de propagação, as quais são independentes do formato de modulação, não necessitam de sequências de treino e tendem a ser robustas aos desvios de frequência e às flutuações de fase. As técnicas referidas foram validadas numericamente, e o seu desempenho é avaliado mediante a penalidade remanescente na relação sinal-ruído do sinal pós-processado. Por fim, a complexidade destas é analiticamente descrita em termos de multiplicações reais por amostra.Programa Doutoral em Engenharia Eletrotécnic