Simulation of a high-speed demultiplexer based on two-photon absorption in semiconductor devices

In this paper, we present a theoretical model of an all-optical demultiplexer based on two-photon absorption in a specially designed semiconductor micro-cavity for use in an optical time division multiplexed system. We show that it is possible to achieve error-free demultiplexing of a 250 Gbit/s OTDM signal (25 × 10 Gbit/s channels) using a control-to-signal peak pulse power ratios of around 30:1 with a device bandwidth of approximately 30 GHz

All-optical sampling utilising two-photon absorption in semiconductor microcavity

A highly-efficient optical sampling system based on Two-Photon Absorption in a semiconductor micro-cavity is presented. The sensitivity of the sampling system is calculated to be 0.1mW² with a temporal resolution of 2ps

Dispersion monitoring for high-speed WDM networks via two-photon absorption in a semiconductor microcavity

Due to the continued demand for bandwidth, network operators have to increase the data rates at which individual wavelengths operate at. As these data rates will exceed 100 Gbit/s in the next 5-10 years, it will be crucial to be able to monitor and compensate for the amount of chromatic dispersion encountered by individual wavelength channels. This paper will focus on the use of the novel nonlinear optical-to-electrical conversion process of two-photon absorption (TPA) for dispersion monitoring. By incorporating a specially designed semiconductor microcavity, the TPA response becomes wavelength dependent, thus allowing simultaneous channel selection and monitoring without the need for external wavelength filterin

Romanticism and Periodisation: A Roundtable

"‘Eternity is in love with the productions of time’. This original edited volume takes William Blake’s aphorism as a basis to explore how British Romantic literature creates its own sense of time. It considers Romantic poetry as embedded in and reflecting on the march of time, regarding it not merely as a reaction to the course of events between the late-eighteenth and mid-nineteenth centuries, but also as a form of creative engagement with history in the making. The authors offer a comprehensive overview of the question of time from a literary perspective, applying a diverse range of critical approaches to Romantic authors from William Blake and Percy Shelley to John Clare and Samuel Rodgers. Close readings uncover fresh insights into these authors and their works, including Frankenstein, the most familiar of Romantic texts. Revising current thinking about periodisation, the authors explore how the Romantic poetics of time bears witness to the ruptures and dislocations at work within chronological time. They consider an array of topics, such as ecological time, futurity, operatic time, or the a-temporality of Venice. As well as surveying the Romantic canon’s evolution over time, these essays approach it as a phenomenon unfolding across national borders. Romantic authors are compared with American or European counterparts including Beethoven, Irving, Nietzsche and Beckett. Romanticism and Time will be of great value to literary scholars and students working in Romantic Studies. It will be of further interest to philosophers and historians working on the connections between philosophy, history and literature during the nineteenth century.

Shape control of QDs studied by cross-sectional scanning tunneling microscopy

In this cross-sectional scanning tunneling microscopy study we investigated various techniques to control the shape of self-assembled quantum dots (QDs) and wetting layers (WLs). The result shows that application of an indium flush during the growth of strained InGaAs/GaAs QD layers results in flattened QDs and a reduced WL. The height of the QDs and WLs could be controlled by varying the thickness of the first capping layer. Concerning the technique of antimony capping we show that the surfactant properties of Sb result in the preservation of the shape of strained InAs/InP QDs during overgrowth. This could be achieved by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick, and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure

Shape control of QDs studied by cross-sectional scanning tunneling microscopy

In this cross-sectional scanning tunneling microscopy study we investigated various techniques to control the shape of self-assembled quantum dots (QDs) and wetting layers (WLs). The result shows that application of an indium flush during the growth of strained InGaAs/GaAs QD layers results in flattened QDs and a reduced WL. The height of the QDs and WLs could be controlled by varying the thickness of the first capping layer. Concerning the technique of antimony capping we show that the surfactant properties of Sb result in the preservation of the shape of strained InAs/InP QDs during overgrowth. This could be achieved by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick, and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure

Recent changes in the abundance of Common Pochard Aythya ferina breeding in Europe

National accounts suggest that the Common Pochard Aythya ferina was an uncommon breeding bird throughout western Europe before 1850. Extensions to the breeding range in the late 19th century were potentially aided by the rapid development of managed fish-ponds in eastern Europe, which provided suitable novel habitat at that time. Expansion into western Europe followed in subsequent decades. Wetland and waterbody eutrophication throughout Europe, which likely provided food and cover for the birds, may have accelerated the rapid expansion from the 1950s until the early 1980s. Widespread declines in the last 30 years, especially in eastern Europe, where breeding numbers are highest, are possibly linked to intensification and/or abandonment of freshwater fish farming and changes in water quality. Studies show that Pochard gain fitness benefits from nesting in Black-headed Gull Chroicocephalus ridibundus colonies and hence has been affected by major losses of European gull colonies in the last 30 years. The spread of alien fish species such as the Carp Cyprinus carpio, which compete with Pochard for food resources, is a problem in the Mediterranean region. Changing predation pressures (in some cases linked to invasive alien mammals) are also implicated in some areas. Relatively modest numbers breeding in the UK, France and the Netherlands have remained stable or increased over the same recent span of years, confirming that different factors currently affect Pochard breeding abundance throughout its range. We urgently need better information relating to key factors affecting Pochard breeding success and abundance, which is currently showing an unfavourable conservation status throughout much of EuropePeer reviewe

Réalisation d’un laser à faible courant de seuil, avec des boites quantiques InAs/InP organisées et couplées latéralement

Nous présentons ici la réalisation d’un laser à faible courant de seuil avec des boites quantiques (QDs) organisées et couplées InAs/InP sur subsstrat (311)B pour une émission à 1.55 m. En effet, pour des hautes densités de QDs, une organisation périodique apparaît dans le plan. Cette organisation renforce le couplage latéral inter-boites. Des expériences de magnéto-photoluminescence permettent de mettre en évidence ces effets de couplage. Ce couplage améliore l’injection des porteurs. Une émission laser avec des faibles courants de seuil est obtenue avec de telles boites

Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption

For dissipation-free photon-photon interaction at the single photon level, we analyze one-photon transition and two-photon transition induced by photon pairs in three-level atoms using two-photon wavefunctions. We show that the two-photon absorption can be substantially enhanced by adjusting the time correlation of photon pairs. We study two typical cases: Gaussian wavefunction and rectangular wavefunction. In the latter, we find that under special conditions one-photon transition is completely suppressed while the high probability of two-photon transition is maintained.Comment: 6 pages, 4 figure

Optical properties and morphology of InAs ∕ InP (113)B surface quantum dots

We report on long-wavelength photoluminescence(PL) emission at room temperature from self-organized InAssurfacequantum dotsgrown by gas-source molecular beam epitaxy on a GaInAsP∕InP (113)B substrate. The influence of arsenic pressure conditions during growth on the PL emission of surfacequantum dots is detailed as well as oxide/contamination layer formation after growth. Experimental results are in good agreement with six-band k⋅p theory in the envelope function approximation.This work was supported by the SANDIE European Network of Excellence