Unlocking Spectral Versatility from Broadly-Tunable Quantum-Dot Lasers

Wavelength−tunable semiconductor quantum−dot lasers have achieved impressive performance in terms of high−power, broad tunability, low threshold current, as well as broadly tunable generation of ultrashort pulses. InAs/GaAs quantum−dot−based lasers in particular have demonstrated significant versatility and promise for a range of applications in many areas such as biological imaging, optical fiber communications, spectroscopy, THz radiation generation and frequency doubling into the visible region. In this review, we cover the progress made towards the development of broadly−tunable quantum−dot edge−emitting lasers, particularly in the spectral region between 1.0–1.3 µm. This review discusses the strategies developed towards achieving lower threshold current, extending the tunability range and scaling the output power, covering achievements in both continuous wave and mode−locked InAs/GaAs quantum−dot lasers. We also highlight a number of applications which have benefitted from these advances, as well as emerging new directions for further development of broadly−tunable quantum−dot lasers

Double-pass amplification of picosecond pulses with a tapered semiconductor amplifier

Double-pass amplification of picosecond pulses is demonstrated and compared with single-pass amplification. This was achieved using a two-section tapered semiconductor optical amplifier with a chirped quantum-dot active region and a mode-locked laser diode as a seed. Across the range of biasing conditions common to both configurations, an enhancement in signal gain of up to 7 dB and output power by a factor of 4.1 was seen in the double-pass amplifier, compared to the single-pass. Only marginal increases in pulse duration were observed in the double-pass regime compared to the single-pass amplifier, meaning that enhancements in output power were well translated into peak power. Furthermore, the two-section contact layout of the SOA allowed the pulse duration to be optimised for a given fixed output power, giving additional flexibility to the amplifier. These results demonstrate the suitability of this simple and versatile technique, which could become the new standard in amplification of ultrashort pulses

Wide and tunable spectral asymmetry between narrow and wide facet outputs in a tapered quantum-dot superluminescent diode

A wide spectral asymmetry between the front and rear facets of a tapered chirped quantum dot multi-section superluminescent diode is reported. The spectral asymmetry between the two facet outputs was found to be tunable and highly dependent on the bias asymmetry between the two contact sections, with a spectral mismatch of up to 14 nm. Numerical simulations confirmed a relationship between this spectral asymmetry and the non-uniform filling of the quantum dots’ confined states when different current densities are applied to the device electrodes. The results from this investigation open up an additional degree of freedom for multi-section superluminescent diodes, which could pave the way for optical bandwidth engineering via multiplexing the spectral output from both facets, using only a single device

Influence of Copper on the Catalytic Activity of Supported Rhodium Catalysts in the Reactions of CO Oxidation and NO Reduction

The catalytic activity of Cu, Rh, and Rh/Cu, catalysts supported on Al2O3, CeO2 and CeO2/Al2O3 in reactions of CO oxidation and NO reduction has been studied in temperature-programmed regime. Addition of Cu to Rh catalysts decreases temperature at which 5 and 50% degree of conversion, while end of reaction temperature is not influenced by presence of Cu. The presence of Cu has positive effect on the activity of Rh containing catalysts in the low temperature region. Cu has noticeable promoting effect mainly for the catalytic activity in the reaction of CO oxidation and in smaller extent for the reaction of NO reduction. Preliminary redox treatment of the catalysts decreases the light off temperature in the reactions of CO oxidation and in NO reduction. Thermal treatment at temperatures up to 973 K does not have sensible effect on the catalytic activities of all studied catalysts. Calcination at 1073 K, however, strongly decreases the catalytic activity of Rh/Cu/CeO2/Al2O3 catalysts

Exploring New Ultrafast Operation Regimes in Quantum Dot Lasers and Amplifiers

We will present our recent results, harnessing the flexibility of quantum dot materials towards the development of increasingly versatile regimes of ultrashort pulse generation and amplification in edge-emitting devices

Anos 2006-07 : Pinhal-Novo - Palmela : dispersão / concentração

A cidade / [coordenação de] Victor Manuel Canedo Neves. - Lisboa : Universidade Lusíada, 2011. - P. 155-164

Aprendizagem Colaborativa e Informal do Espanhol - Língua Estrangeira (ELE) nas Redes Sociais: o Caso do Grupo no Facebook «Alunos de Espanhol (RC)»

O presente trabalho de projeto apresenta um estudo sobre a utilização das redes sociais enquanto meio de aprendizagem colaborativa e informal do Espanhol - Língua Estrangeira (ELE). Partindo da análise de um grupo privado no Facebook, denominado «Alunos de Espanhol (RC)», procura-se compreender quais são as vantagens da aprendizagem informal e colaborativa nas redes sociais e até que ponto poderão estas beneficiar os aprendentes, servindo de complemento, ou até mesmo alternativa, à aprendizagem formal de uma língua estrangeira. Procura-se, do mesmo modo, obter dados que ajudem a compreender que percepção têm os aprendentes acerca do papel do tutor/mediador nos grupos de aprendizagem informal e colaborativa nas redes sociais; qual é a realidade deste grupo especificamente; e como melhorar a aprendizagem do espanhol na sua página do Facebook. Este trabalho segue o modelo metodológico de Estudo de Caso e uma metodologia mista, na qual se conjugam as análises quantitativa e, maioritariamente, qualitativa. A análise dos resultados demonstra qual é a realidade do grupo em análise, inclusive no que diz respeito à aprendizagem informal e colaborativa em redes sociais, apontando meios de resolução de pontos menos positivos que podem influenciar negativamente a aprendizagem no seio do grupo, e deixa evidente a necessidade de realizar outros estudos, sobretudo no que à aprendizagem linguística diz respeito e à análise da figura do tutor/mediador em grupos análogos.This practical project presents a study about the use of social networks as a mean to the collaborative and informal learning of Spanish - Foreign Language (SFL). From the analysis of a private group on Facebook, named “Alunos de Espanhol (RC)”, we try to understand what are the advantages of informal and collaborative learning in social networks and to what extent these may benefit learners, serving as a complement, or even an alternative, to the formal learning of a foreign language. We try, in the same way, to obtain information that may help us understand the perception learners have about the role of the tutor/moderator in groups of informal and collaborative learning in social networks; what is the reality of this group in particular; and how to improve the learning of Spanish in its Facebook page. This work follows the case study methodology and a mixed method approach of research design, in which the quantitative and, above all, qualitative approaches combine. The analysis of the results show the reality of the studied group, inclusively in what concerns to the informal and collaborative learning in social networks, indicating means to solve some problems that can affect learning, in this group, in a negative manner, and clearly shows the need to conduct further studies, especially in what concerns to language learning and to the analysis of the tutor/moderator figure in similar groups

Four patients with a history of acute exacerbations of COPD: implementing the CHEST/Canadian Thoracic Society guidelines for preventing exacerbations

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Stratification of COPD patients by previous admission for targeting of preventative care

SummaryBackgroundHospital admissions for exacerbations of chronic obstructive pulmonary disease (COPD) impact considerably on disease evolution and healthcare provision. Building on previous studies, this study postulated that COPD patients could be stratified by risk of admission to determine which groups provide the greatest burden on resources, and how interventions should be targeted to prevent admissions.MethodsCOPD admissions during 1997–2003 in three Strategic Health Authorities in England were analysed (n=80,291). Patients admitted during winter (1 November–31 March) were stratified into three groups according to the number of admissions during the previous year: 0 (NIL), 1–2 (MOD) or ≥3 (FRQ). Winter weeks were classified as “average”, “above average”, “high”, or “very high” risk, compared with the long-term mean.ResultsThe risk of admission during winter for FRQ and MOD patients was 40% and 12% respectively. NIL patients contributed to 70% of winter admissions, and 90% of the variation between “average” and “very high” weeks, versus 9% and 1% for MOD and FRQ.ConclusionsPatients with no previous admissions have lower individual risk, but contribute to a high overall utilisation of health care resources and should be targeted to prevent admissions. Focusing upon high-risk patients (frequent attenders or more severe) may only reduce a small proportion of admissions, and therefore clinicians should ensure that all COPD patients receive appropriate therapy to reduce risk of exacerbations