Observation of slow light in the noise spectrum of a vertical external cavity surface emitting laser

The role of coherent population oscillations is evidenced in the noise spectrum of an ultra-low noise lasers. This effect is isolated in the intensity noise spectrum of an optimized single-frequency vertical external cavity surface emitting laser. The coherent population oscillations induced by the lasing mode manifest themselves through their associated dispersion that leads to slow light effects probed by the spontaneous emission present in the non-lasing side modes.Comment: accepted for publication in Phys. Rev. Let

Randomized trial of paroxetine in end-stage COPD

Background: Although the underlying pathology is initially confined to the lungs, the associated emotional responses to chronic obstructive pulmonary disease (COPD) contribute greatly to the resulting morbidity. The objective of this study was to examine the effect of an antidepressant drug on disease-specific quality of life in patients with end-stage COPD who present significant depressive symptoms. Methods: We conducted a 12-week, randomized double- blind placebo-controlled trial of Paroxetine in which quality of life measured by the Chronic Respiratory Questionnaire (CRQ), an evaluative COPD-specific quality-oflife questionnaire, was the primary outcome. Results: 23 patients were randomized and 15 completed the trial (8 on Paroxetine; 7 on placebo). In the per-protocol analysis, we observed statistically and clinically significant improvements favoring the active treatment in 2 of the 4 domains of the CRQ: emotional function (adjusted mean difference: 1.1; 95% confidence interval [CI]: 0.0 - 2.2) and mastery (difference: 1.1; CI: 0.4 - 1.8). Dyspnea and fatigue improved, but to an extent that did not reach statistical significance. In the intention-to-treat analysis, none of the differences in CRQ scores was significant. Paroxetine was not associated to any worsening of respiratory symptoms. Conclusions: The results of this small randomized trial indicated that patients with end-stage COPD may benefit from antidepressant drug therapy when significant depressive symptoms are present. This study underlined the difficulties in conducting experimental studies in frail and elderly patients with COPD

Network Defence Using Attacker-Defender Interaction Modelling

Network security is still lacking an efficient system which selects a response action based on observed security events and which is capable of running autonomously. The main reason for this is the lack of an effective defence strategy. In this Ph.D., we endeavour to create such a defence strategy. We propose to model the interaction between an attacker and a defender to comprehend how the attacker’s goals affect his actions and use the model as a basis for a more refined network defence strategy. We formulate the research questions that need to be answered and we discuss, how the answers to these questions relate to the proposed solution. This research is at the initial phase and will contribute to a Ph.D. thesis in four years

2D photonic-crystal optomechanical nanoresonator

We present the optical optimization of an optomechanical device based on a suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based on a 2D photonic-crystal geometry. We first identify by numerical simulation a set of geometrical parameters providing a reflectivity higher than 99.8 % over a 50-nm span. We then study the limitations induced by the finite value of the optical waist and lateral size of the NWG pattern using different numerical approaches. The NWG grating, pierced in a suspended InP 265 nm-thick membrane, is used to form a compact microcavity involving the suspended nano-membrane as end mirror. The resulting cavity has a waist size smaller than 10 $\mu$m and a finesse in the 200 range. It is used to probe the Brownian motion of the mechanical modes of the nanomembrane

Networks of nonlinear superconducting transmission line resonators

We investigate a network of coupled superconducting transmission line resonators, each of them made nonlinear with a capacitively shunted Josephson junction coupling to the odd flux modes of the resonator. The resulting eigenmode spectrum shows anticrossings between the plasma mode of the shunted junction and the odd resonator modes. Notably, we find that the combined device can inherit the complete nonlinearity of the junction, allowing for a description as a harmonic oscillator with a Kerr nonlinearity. Using a dc SQUID instead of a single junction, the nonlinearity can be tuned between 10 kHz and 4 MHz while maintaining resonance frequencies of a few gigahertz for realistic device parameters. An array of such nonlinear resonators can be considered a scalable superconducting quantum simulator for a Bose-Hubbard Hamiltonian. The device would be capable of accessing the strongly correlated regime and be particularly well suited for investigating quantum many-body dynamics of interacting particles under the influence of drive and dissipation.Comment: 18 pages, 3 figure

Heterogeneous integration and precise alignment of InP-based photonic crystal lasers to complementary metal-oxide semiconductor fabricated silicon-on-insulator wire waveguides

The integration of two-dimensional III-V InP-based photonic crystal and silicon wire waveguides is achieved through an accurate alignment of the two optical levels using mix-and-match deep ultraviolet (DUV)/electron beam lithography. The adhesively bonded structures exhibit an enhancement of light emission at frequencies where low group velocity modes of the photonic crystal line defect waveguides occur. Pulsed laser operation is obtained from these modes at room temperature under optical pumping. The laser light is coupled out of the Si waveguide via grating couplers directly to single mode fiber

Conceptually driven and visually rich tasks in texts and teaching practice: the case of infinite series

The study we report here examines parts of what Chevallard calls the institutional dimension of the students’ learning experience of a relatively under-researched, yet crucial, concept in Analysis, the concept of infinite series. In particular, we examine how the concept is introduced to students in texts and in teaching practice. To this purpose, we employ Duval's Theory of Registers of Semiotic Representation towards the analysis of 22 texts used in Canada and UK post-compulsory courses. We also draw on interviews with in-service teachers and university lecturers in order to discuss briefly teaching practice and some of their teaching suggestions. Our analysis of the texts highlights that the presentation of the concept is largely a-historical, with few graphical representations, few opportunities to work across different registers (algebraic, graphical, verbal), few applications or intra-mathematical references to the concept's significance and few conceptually driven tasks that go beyond practising with the application of convergence tests and prepare students for the complex topics in which the concept of series is implicated. Our preliminary analysis of the teacher interviews suggests that pedagogical practice often reflects the tendencies in the texts. Furthermore, the interviews with the university lecturers point at the pedagogical potential of: illustrative examples and evocative visual representations in teaching; and, student engagement with systematic guesswork and writing explanatory accounts of their choices and applications of convergence tests

Continuous-Wave Second-Harmonic Generation in Orientation-Patterned Gallium Phosphide Waveguides at Telecom Wavelengths

A new process to produce orientation-patterned gallium phosphide (OP-GaP) on GaAs with almost perfectly parallel domain boundaries is presented. Taking advantage of the chemical selectivity between phosphides and arsenides, OP-GaP is processed into suspended shallow-ridge waveguides. Efficient second-harmonic generation from telecom wavelengths is achieved in both Type-I and Type-II polarisation configurations. The highest observed conversion efficiency is 200% W–1 cm–2, with a bandwidth of 2.67 nm in a 1 mm-long waveguide. The variation of the conversion efficiency with wavelength closely follows a squared cardinal sine function, in excellent agreement with theory, confirming the good uniformity of the poling period over the entire length of the waveguide

Growing innovations for the bioeconomy

Agriculture is often viewed as a source of problems needing innovative solutions. But agriculture can actually be a source of innovations for the bioeconomy, if researchers embrace the cultural changes needed