Time domain add-drop multiplexing scheme enhanced using a saw-tooth pulse shaper

We experimentally demonstrate the use of saw-tooth optical pulses, which are shaped using a fiber Bragg grating, to achieve robust and high performance time-domain add-drop multiplexing in a scheme based on cross-phase (XPM) modulation in an optical fiber, with subsequent offset filtering. As compared to the use of more conventional pulse shapes, such as Gaussian pulses of a similar pulse width, the purpose-shaped saw-tooth pulses allow higher extinction ratios for the add and drop windows and significant improvements in the receiver sensitivity for the dropped and added channels

All-optical pulse reshaping and retiming systems incorporating pulse shaping fiber Bragg grating

This paper demonstrates two optical pulse retiming and reshaping systems incorporating superstructured fiber Bragg gratings (SSFBGs) as pulse shaping elements. A rectangular switching window is implemented to avoid conversion of the timing jitter on the original data pulses into pulse amplitude noise at the output of a nonlinear optical switch. In a first configuration, the rectangular pulse generator is used at the (low power) data input to a nonlinear optical loop mirror (NOLM) to perform retiming of an incident noisy data signal using a clean local clock signal to control the switch. In a second configuration, the authors further amplify the data signal and use it to switch a (low power) clean local clock signal. The S-shaped nonlinear characteristic of the NOLM results in this instance in a reduction of both timing and amplitude jitter on the data signal. The underlying technologies required for the implementation of this technique are such that an upgrade of the scheme for the regeneration of ultrahigh bit rate signals at data rates in excess of 320 Gb/s should be achievable

Novel Fiber Design for Wideband Conversion and Amplification in Multimode Fibers

We propose an operating principle to achieve broadband and highly tunable mode conversion and amplification exploiting inter-modal four wave mixing in a multimode fiber. A bandwidth of 30 nanometers is demonstrated by properly designing a simple step-index silica fiber.Comment: Ecoc conference 201

Between Smartphones and Tablets: Improving Teacher Education Programmes through Mobile Devices

This research was conducted at the University of Genoa (Italy). The student teachers attended a course focused on the use of mobile devices at school. We tried to examine the impact of mobile learning on university activities for pre-service teachers, the changes in the organization of their studying, the changes in their learning strategies, and the changes in their interaction/cooperation levels. After the course, we administered a questionnaire with both closed-ended and open-ended questions, which highlighted important findings concerning the differences between smartphones and tablets in supporting these aspects of their learning. We found that both types of devices improved interaction and cooperation among students, and being able to search for information was useful for studying. However, changes in the organization of studying and the learning strategies were supported only by tablets and only for specific aspects of learning. This study suggests solutions to improve Italian teacher education programmes and the quality of university activitie

Using smartphones and tablets in higher education contexts: an exploratory study within a teacher education programme

Abstract This study aimed to analyse and explore the potential opportunities offered by mobile devices to improve the higher education scenario. In particular, the study was conducted within a teacher education programme. The students attended a course called Educational Technology, which focussed on the use of mobile devices (smartphones and tablets) inside and outside the classroom. We examined the impact of mobile learning on students’ university activities and the changes in the organisation of their studying activity, their learning strategies and their interaction/cooperation levels. After the course, we administered a questionnaire that highlighted some findings concerning the differences between smartphones and tablets in supporting these aspects. We found that both types of devices improved the interaction/collaboration among students and the search for information, which was useful for studying. However, the organisation of studying and the learning strategies were supported only by tablets and for specific aspects of learning. This exploratory research suggests, on the one hand, some possible solutions to improve the quality of university activities, and on the other, it underlines some difficulties that will be analysed more thoroughly in further studies.</jats:p

Gridsemble: Selective Ensembling for False Discovery Rates

In this paper, we introduce Gridsemble, a data-driven selective ensembling algorithm for estimating local false discovery rates (fdr) in large-scale multiple hypothesis testing. Existing methods for estimating fdr often yield different conclusions, yet the unobservable nature of fdr values prevents the use of traditional model selection. There is limited guidance on choosing a method for a given dataset, making this an arbitrary decision in practice. Gridsemble circumvents this challenge by ensembling a subset of methods with weights based on their estimated performances, which are computed on synthetic datasets generated to mimic the observed data while including ground truth. We demonstrate through simulation studies and an experimental application that this method outperforms three popular R software packages with their default parameter values\unicode{x2014}common choices given the current landscape. While our applications are in the context of high throughput transcriptomics, we emphasize that Gridsemble is applicable to any use of large-scale multiple hypothesis testing, an approach that is utilized in many fields. We believe that Gridsemble will be a useful tool for computing reliable estimates of fdr and for improving replicability in the presence of multiple hypotheses by eliminating the need for an arbitrary choice of method. Gridsemble is implemented in an open-source R software package available on GitHub at jennalandy/gridsemblefdr.Comment: 12 pages, 3 figures (+ references and supplement). For open-source R software package, see https://github.com/jennalandy/gridsemblefdr. For all code used in the simulation studies and experimental application, see https://github.com/jennalandy/gridsemble_PAPE

All-optical 160 Gbit/s RZ data retiming system incorporating a pulse shaping fibre Bragg grating

We characterize a 160Gbit/s retimer based on flat-topped pulses shaped using a superstructured fibre Bragg grating. The benefits of using shaped rather than conventional pulse forms in terms of timing jitter reduction are confirmed by bit-error-rate measurements

Ultrafast photodoping and effective Fermi-Dirac distribution of the Dirac particles in Bi2Se3

We exploit time- and angle- resolved photoemission spectroscopy to determine the evolution of the out-of-equilibrium electronic structure of the topological insulator Bi2Se. The response of the Fermi-Dirac distribution to ultrashort IR laser pulses has been studied by modelling the dynamics of the hot electrons after optical excitation. We disentangle a large increase of the effective temperature T* from a shift of the chemical potential mu*, which is consequence of the ultrafast photodoping of the conduction band. The relaxation dynamics of T* and mu* are k-independent and these two quantities uniquely define the evolution of the excited charge population. We observe that the energy dependence of the non-equilibrium charge population is solely determined by the analytical form of the effective Fermi-Dirac distribution.Comment: 5 Pages, 3 Figure