Fundamentals and applications of spatial dissipative solitons in photonic devices : [Chapter 6]

We review the properties of optical spatial dissipative solitons (SDS). These are stable, self‐localized optical excitations sitting on a uniform, or quasi‐uniform, background in a dissipative environment like a nonlinear optical cavity. Indeed, in optics they are often termed “cavity solitons.” We discuss their dynamics and interactions in both ideal and imperfect systems, making comparison with experiments. SDS in lasers offer important advantages for applications. We review candidate schemes and the tremendous recent progress in semiconductor‐based cavity soliton lasers. We examine SDS in periodic structures, and we show how SDS can be quantitatively related to the locking of fronts. We conclude with an assessment of potential applications of SDS in photonics, arguing that best use of their particular features is made by exploiting their mobility, for example in all‐optical delay lines

Enabling solar electricity with electric vehicles in future energy systems

Tese de doutoramento, Sistemas Sustentáveis de Energia, Universidade de Lisboa, Faculdade de Ciências, 2015Climate change is on the agenda of many world leaders and policy makers, and its containment is of exceptional importance. Within this frame, ambitious environmental targets have been established by the European Union, including the reduction in greenhouse gases emissions by 80-95% until 2050. To do so, energy systems will require a large share of renewable energies, particularly solar photovoltaic power, since it appears to have the greatest potential for decarbonized electricity generation. However, relying on such renewable energy sources is expected to generate a mismatch between production and consumption, namely considerable excess solar electricity during day time. This excess power may be conveniently used to power electric mobility, taking advantage of the battery capacity of the electric vehicles acting as distributed controllable storage. In this thesis, based on 2050 scenarios for the case study of Portugal, the synergy between photovoltaics and electric vehicles is explored, determining the minimum penetration levels that allow fulfilling the climate and energy targets. It is analyzed the extent to which photovoltaic energy can further transport electrification integration, and vice-versa. The technical impacts on the electricity system are determined quantitatively, as well as the required penetration of one technology that enables the deployment of the other. Model results show that CO2 emissions targets can only be achieved with high levels of photovoltaics and electric vehicles, reinforcing the need for day time charging infrastructures, presumably at or near work facilities. It is shown that a 100% renewable energy based electricity supply is possible for certain combinations of these technologies and that the environmental targets to reduce CO2 emissions can only be reached with at least 40% of electric vehicles market share. The present thesis contributes to the literature on integration of high levels of renewable energy sources on the electric grid and on interactions between renewable energy and electric vehicles deployment.As alterações climáticas estão na agenda dos líderes mundiais e dos decisores políticos, pois contê-las é fundamental. Neste quadro, a União Europeia traçou metas ambientais exigentes, como a redução das emissões de gases com efeito de estufa em 80-95% até 2050. Para isso, os sistemas de energia terão de assentar em energias renováveis, particularmente em energia fotovoltaica, uma vez que no futuro esta parece ser a forma com maior potencial de geração de electricidade limpa. Porém, esta situação contribuirá para o desfasamento entre a produção e o consumo, com geração de energia solar em excesso durante o dia. Esta energia em excesso pode ser convenientemente canalizada para a mobilidade eléctrica, aproveitando a capacidade das baterias dos veículos eléctricos a funcionar como armazenamento controlável e distribuído. Na presente tese, com base em cenários do ano 2050 para o caso de Portugal, exploram-se as sinergias entre a energia fotovoltaica e os veículos eléctricos, determinando-se os níveis mínimos de penetração que permitem o cumprimento das metas na área do ambiente. Analisa-se em que medida a energia fotovoltaica permite uma maior integração do veículo eléctrico, e vice-versa. Os impactos na rede de energia eléctrica são determinados quantitativamente, assim como a penetração necessária de uma tecnologia que permite a implantação da outra. Os resultados do modelo mostram que as metas para as emissões de CO2 só podem ser alcançadas com elevadas penetrações de energia fotovoltaica e veículos eléctricos, o que reforça a necessidade da existência de infraestruturas para carregamento dos veículos durante o dia, tal como nos locais de trabalho. Mostra-se que 100% de energia eléctrica renovável é possível com determinadas combinações entre as duas tecnologias e que as metas ambientais para redução de emissões de CO2 são apenas alcançáveis com pelo menos 40% de penetração de veículos eléctricos no mercado. A presente tese contribui para a literatura sobre a integração na rede eléctrica de elevados níveis de energia renovável e sobre a interacção entre energia renovável e veículos eléctricos.Fundação para a Ciência e a Tecnologia (FCT), SFRH/BD/51130/201

The role of energy storage for mini-grid stabilization

48 pagesMini-grids may be designed to operate autonomously with or without connection to a central grid. While operating autonomously, they cannot rely on the central grid to provide stabilization to control the line voltage and frequency, balance supply and demand of power and manage real or reactive power. Energy storage can provide stabilization in a mini-grid as follows: when the system works autonomously, storage provides or absorbs power to balance supply and demand, to counteract the moment to moment fluctuations in customer loads and unpredictable fluctuations in generation. When grid connected, energy storage systems also can provide ancillary services to improve power quality such as voltage and frequency regulation, harmonic filtering, and fault clearing (i.e. supply of short circuit current). This is named the power use of energy storage, contrary to the usual energy use of energy storage

Roadmap of ultrafast x-ray atomic and molecular physics

X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm−2) of x-rays at wavelengths down to ~1 Ångstrom, and HHG provides unprecedented time resolution (~50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ~280 eV (44 Ångstroms) and the bond length in methane of ~1 Ångstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Ångstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Ångstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science

Bifurcation analysis of a semiconductor laser with filtered optical feedback

We study the dynamics and bifurcations of a semiconductor laser with delayed filtered optical feedback, where a part of the output of the laser reenters after spectral filtering. This type of coherent optical feedback is more challenging than the case of conventional optical feedback from a simple mirror, but it provides additional control over the output of the semiconductor laser by means of choosing the filter detuning and the filter width. This laser system can be modeled by a system of delay differential equations with a single fixed delay, which is due to the travel time of the light outside the laser. In this paper we present a bifurcation analysis of the filtered feedback laser. We first consider the basic continuous wave states, known as the external filtered modes (EFMs), and determine their stability regions in the parameter plane of feedback strength versus feedback phase. The EFMs are born in saddle-node bifurcations and become unstable in Hopf bifurcations. We show that for small filter detuning there is a single region of stable EFMs, which splits up into two separate regions when the filter is detuned. We then concentrate on the periodic orbits that emanate from Hopf bifurcations. Depending on the feedback strength and the feedback phase, two types of oscillations can be found. First, there are undamped relaxation oscillations, which are typical for semiconductor laser systems. Second, there are oscillations with a period related to the delay time, which have the remarkable property that the laser frequency oscillates while the laser intensity is almost constant. These frequency oscillations are only possible due to the interaction of the laser with the filter. We determine the stability regions in the parameter plane of feedback strength versus feedback phase of the different types of oscillations. In particular, we find that stable frequency oscillations are dominant for nonzero values of the filter detuning. © 2007 Society for Industrial and Applied Mathematics

Microwave techniques and applications for semiconductor quantum dot mode-locked lasers

Semiconductor mode-locked lasers (MLLs) are important as compact and cost-effective sources of picosecond or sub-picosecond optical pulses with moderate peak powers. They have potential use in various fields including optical interconnects for clock distribution at an inter-chip/intra-chip level as well as high bit-rate optical time division multiplexing (OTDM), diverse waveform generation, and microwave signal generation. However, there are still several challenges to conquer for engineering applications. Semiconductor MLLs sources have generally not been able to match the noise performance and pulse quality of the best solid-state mode-locked lasers. For improving the characteristics of semiconductor mode-locked lasers, research on both the material/device design and stabilization mechanism is necessary. In this dissertation, by extending the net-gain modulation phasor approach based on a microwave photonics perspective, a convenient, yet powerful analytical model is derived and experimentally verified for the cavity design of semiconductor two-section passive MLLs. This model will also be useful in designing the next generation quantum dot (QD) MLL capable of stable operation from 20°C to 100°C for optical interconnects applications. The compact optical generation of microwave signals using a monolithic passive QD MLL is investigated. Relevant equations for the efficient conversion of electrical to optical to electrical (EOE) energy are derived and the device principles are described. In order to verify the function of a QD MLL as an RF signal generator, the integration with a rectangular patch antenna system is also studied. Furthermore, combined with the reconfigurable function, the multi-section QD MLL will be a promising candidate of the compact, efficient RF signal source in wireless, beam steering, and satellite communication applications. The noise performance is a key element for semiconductor MLLs in OTDM communications. The external stabilization methods to improve the timing stability in passive MLLs have been studied and an all-microwave measurement technique has also been developed to determine the pulse-to-pulse rms timing jitter. Compared to the conventional optical cross-correlation technique, the new method provides an alternative and simple approach to characterize the timing jitter in a passive MLL. The average pulse-to-pulse rms timing jitter is reduced to 32 fs/cycle under external optical feedback stabilization

Guanabara Bay: For all hopes to a new awakening of paradise

Abstract: Exclusion Territories are geographical areas under the action of degenerative environmental phenomena of anthropogenic origin, which compromise quality of life in general. One of the greatest examples of such areas is the Guanabara Bay and its surroundings, the scene of some of the worst disastrous incidents and locale of frequent episodes of human misery. This article presents a brief description of the main characteristics of the region, providing some technological suggestions of biogeographic recovery to be adopted by public policies that intend to align themselves with the good practices of ecological economy, sustainability and quality of life. The work falls within the context of macro-engineering cum eco-innovation applied to the preservation and management of water sources and water bodies that serve productive purposes as natural niches and breeding grounds.Key words: Exclusion Territories, Guanabara Bay, waste management, quality of life.=================================================================== Resumo: Territórios de Exclusão são áreas geográficas sob ação de fenômenos ambientais degenerativos de origem antropogênica, os quais comprometem a qualidade de vida em geral. Um dos maiores exemplos de zonas desse tipo é a Baía de Guanabara e seu entorno, palco de alguns dos piores incidentes desastrosos e de frequentes episódios da miséria humana. O presente artigo descreve sumariamente as principais características da região, fornecendo algumas sugestões tecnológicas de recuperação biogeográfica a serem adotadas por políticas públicas que pretendam alinhar-se às boas práticas de economia ecológica, sustentabilidade e qualidade de vida. O trabalho se insere no contexto da macroengenharia cum eco-inovação aplicada à preservação e à gestão das fontes hídricas e dos corpos de água que servem a propósitos produtivos como nichos naturais e criadouros.Palavras-chave: Territórios de Exclusão, Baía de Guanabara, gestão de resíduos, qualidade de vida.=================================================================== Abstrakt: Ausschlussgebiete sind geografische Regionen, in denen degenerative Umweltphänomene anthropogenen Ursprungs auftreten, die im Allgemeinen die Lebensqualität beeinträchtigen. Eines der besten Beispiele für solche Gebiete ist die Guanabara-Bucht und die Umgebung, Schauplatz einiger der schlimmsten katastrophalen Vorfälle und Schauplatz häufiger Episoden menschlichen Elends. Dieser Artikel enthält eine kurze Beschreibung der Hauptmerkmale der Region sowie einige technologische Vorschläge für die biogeografische Erholung, die die öffentliche Politik zur Angleichung an bewährte Praktiken in Bezug auf ökologische Ökonomie, Nachhaltigkeit und Lebensqualität annehmen sollte. Die Arbeit fällt in den Kontext von Makrotechnik und Öko-Innovation, die auf die Erhaltung und Bewirtschaftung von Wasserquellen und Gewässern angewendet werden, die als natürliche Nischen und Brutstätten für produktive Zwecke dienen.Schlüsselwörter: Ausschlussgebiete, Guanabara-Bucht, Abfallwirtschaft, Lebensqualität