Research interest: In recent years we have seen the emergence of commercial applications at high frequencies, such as the top part of the microwave band and the millimeter and sub-millimeter bands, and it is expected a big increase in the coming years. This growing demand requires a rapid development of low-cost technology with good performance at these frequencies, where common technologies, such as microstrip and standard waveguides, have some shortcomings. In particular, existing solutions for high-gain planar scanning antennas at these frequencies su er from the disadvantages of these technologies giving rise to high-cost products not suitable for high volume production. Objectives: The main objective of this thesis is to study the feasibility of a new proposal to improve existing solutions to date for low-cost high-gain planar scanning antennas at high frequencies. This overall objective has resulted in another central objective of this thesis, which is the research of new quasi-TEM waveguides that are more appropriate than current technologies for the realization of circuits and components at these frequency bands. These guided solutions make use of periodic or arti cial surfaces in order to con- ne and channel the elds within these waveguides. Methodology: The work follows a logical sequence of speci c tasks aimed at achieving the main objective of this thesis. Chapter 2 presents the proposed guiding solution and shows its performance numerical and experimentally. The optimized design of high-gain antennas based on waveguide slot arrays requires the development of e cient ad-hoc codes. The implementation and validation of this code is presented in Chapter 3, where a new method for the analysis of corrugated surfaces is proposed, and in Chapter 4, which extends this code to the analysis of waveguide slot arrays. The process design and optimization of a two-dimensional array is described in Chapter 5, where a preliminary experimental validation is also described. Moreover, the proposed guiding solution has inspired the development of a new guiding technology of wider bandwidth and more versatile for the realization of circuits and components at high frequencies. Chapter 6 presents the contributions to the study of this technology and its application to the design of circuits. / Alfonso Alós, E. (2011). New quasi-TEM waveguides using artificial surfaces and their application to antennas and circuits [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/11073

I present photonics applications of PbS quantum-dot-doped (QD-doped) glasses. The dissertation consists of two major parts: bulk material applications (Cr:forsterite laser modelocking, bleaching dynamics, optical gain, and photoluminescence) and the fabrication of QD-doped ion-exchanged waveguides.When this work began, these PbS QD-doped glasses were the state-of-the-art in QD glasses due to their narrow size distribution. Modelocking of a Cr:forsterite laser using this glass as a saturable absorber had been demonstrated, with little understanding of the dynamics. This work began by studying the dynamics of the saturable absorber to explain the ps-pulse width.In the bulk measurements, I functioned as secondary researcher. In the laser modelocking and bleaching measurements, my contribution was laser cavity alignment, sample preparation, collecting autocorrelation traces, and aiding in the setup and data collection for the bleaching measurements. On this work, I coauthored one refereed journal article in Applied Physics Letters [1] and one refereed conference paper [2], for which I am third and second author, respectively.For the gain measurements, I aided in the setup and data collection, whereas I set-up and took most of the luminescence data. The gain measurements resulted in one second-author refereed journal article in Applied Physics Letters [3] and I presented the luminescence results at CLEO2000 [4].I took the lead role in the waveguide fabrication and characterization and authored refereed journal articles in Applied Physics Letters [5], Journal of Applied Physics [6], and Journal of the Optical Society of America B [7]. I also presented an invited talk at Photonics West [8] and presented at CLEO2004 [9]. Additionally, I have been a coauthor of presentations at the Nanotechnology Symposium (2006), American Ceramic Society [10], and Photonics Europe (2006) [11]. A book chapter in The Photonics Handbook, 2nd edition [12] also discusses this work.The next step is to focus on reducing the waveguide losses. This requires new, circular wafers with better surface quality and glass homogeneity. I suggest using silver-film ion exchange followed by a field-assisted burial to eliminate the surface interaction.

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This thesis describes a detailed investigation into the process of laser-wakefield acceleration (LWFA) for the generation of high-energy electron beams using the hydrogen-filled capillary discharge waveguide. In only the second experiment to be performed using the newly commissioned Astra-Gemini laser at the Rutherford Appleton Laboratory, electron beams were accelerated to energies greater than 0.5 GeV by laser pulses of energy 2.5J and peak power of 30T\~T. The injec- tion and acceleration of electron beams was seen to depend on the state of the plasma channel for axial electron densities less than 2.5 x 1018 cm -3. With the aid of simulations performed using the code WAKE it was found that the plasma channel allows the laser pulse to maintain its self-focussed spot size along the length of the capillary even below the critical power for self-guiding. It was found that the threshold laser energy required for the production of elec- tron beams was reduced by the use of an aperture placed early in the laser system. This was attributed to the increased energy contained in the central part of the focal spot of the laser. A short paper on this work was published in Physical Review Special Topics - Accelerators and Beams and a longer paper was published in the New Journal of Physics. Transverse interferometry was used to measure the electron density of the plasma channel used in the Astra-Gemini experiments. An imaging system was devised which used cylindrical optics to increase the field of view of the capillary longitudinally, whilst maintaining the trans- verse resolution. The measured properties were consistent with previous measurements made by Gonsalves et al. [J]. The observed longitudinal variations in the plasma channel parameters were not found to be significant enough to affect the injection process.

A study is hereby presented on system embedded photonic interconnect technologies, which would address the communications bottleneck in modern exascale data centre systems driven by exponentially rising consumption of digital information and the associated complexity of intra-data centre network management along with dwindling data storage capacities. It is proposed that this bottleneck be addressed by adopting within the system electro-optical printed circuit boards (OPCBs), on which conventional electrical layers provide power distribution and static or low speed signaling, but high speed signals are conveyed by optical channels on separate embedded optical layers. One crucial prerequisite towards adopting OPCBs in modern data storage and switch systems is a reliable method of optically connecting peripheral cards and devices within the system to an OPCB backplane or motherboard in a pluggable manner. However the large mechanical misalignment tolerances between connecting cards and devices inherent to such systems are contrasted by the small sizes of optical waveguides required to support optical communication at the speeds defined by prevailing communication protocols. An innovative approach is therefore required to decouple the contrasting mechanical tolerances in the electrical and optical domains in the system in order to enable reliable pluggable optical connectivity. This thesis presents the design, development and characterisation of a suite of new optical waveguide connector interface solutions for electro-optical printed circuit boards (OPCBs) based on embedded planar polymer waveguides and planar glass waveguides. The technologies described include waveguide receptacles allowing parallel fibre connectors to be connected directly to OPCB embedded planar waveguides and board-to-board connectors with embedded parallel optical transceivers allowing daughtercards to be orthogonally connected to an OPCB backplane. For OPCBs based on embedded planar polymer waveguides and embedded planar glass waveguides, a complete demonstration platform was designed and developed to evaluate the connector interfaces and the associated embedded optical interconnect. Furthermore a large portfolio of intellectual property comprising 19 patents and patent applications was generated during the course of this study, spanning the field of OPCBs, optical waveguides, optical connectors, optical assembly and system embedded optical interconnects.

Dans cette thèse, nous étudions les propriétés spectrales des guides d'onde quantiques tridimensionnels (les tubes) perturbés. Nous considérons, principalement deux types différents de perturbation : Dans le premier type, il s’agit de la perturbation d’une déformation géométrique. Plus précisément, nous étudions l’opérateur de Laplace de Dirichlet défini dans un tube déformé à l’aide d’une torsion constante perturbée localement par une fonction de même signe (torsion répulsive).Le deuxième type de perturbation consiste à changer localement les conditions aux bords imposées sur la frontière du guide d’onde. En effet, il s’agit de l’étude du Laplacien avec des conditions aux bords mixtes.Nous imposons des conditions aux bords de Dirichlet par tout sur la frontière du guide d’onde, sauf sur une partie bornée où nous considérons des conditions aux bords de Neumann. D’une part, nous examinons les tubes droits (sans déformations géométriques) dans le but de comprendre l’effet de la perturbation des conditions aux bords. D’autre part, nous étudions les tubes torsadés afin d’établir une comparaison entre les effets opposés des deux perturbations (géométrique et des conditions aux bords). / In this thesis we study the spectral properties of perturbed 3D quantum waveguides (tubes). We mainly consider two types of perturbation:The first type is a geometric perturbation. More precisely, we study the Laplace operator with Dirichlet boundary conditions defined in a twisted tube. The twist that we consider is a constant one that has been locally perturbed by a function of same sign (a repulsive twist). The second type of perturbation is done by changing locally the boundary conditions. In fact, we study the Laplacian operator with Dirichlet conditions everywhere on the boundary of the tube except on a bounded part where we consider the Neumann conditions. In one hand we study the straight tubes (with no geometric perturbations) to figure out the effect of perturbation that occurred in the boundary conditions. In the other hand we study the twisted tubes to establish a comparison between the opposite effects of these two types of perturbation (the geometric one and the change that we imposed on the boundary conditions).

Dispensed organic polymer optical waveguides suitable for single-mode operation were recently fabricated. Different dispensing pressures, polymers, and dispensing tips were used in the drawing method. The waveguides were measured to be approximately 16[mu] wide and 0.8[mu] tall. This is significantly smaller than previously reported dimensions of 300[mu] x 3.5[mu] waveguides fabricated with a similar dispensed polymer method. The waveguides were also found to be suitable for single-mode operation through a series of approximate calculations . This is also something previously not achieved with the larger waveguides. This novel approach to waveguide fabrication could reduce the expense and time of creating single mode waveguides for rapid development applications. It will also allow the waveguides to be fabricated to be flexible as well as doped to be active devices.