Alan Miller

Ultrafast electroabsorption dynamics in an InAs quantum dot saturable absorber at 1.3μm

The authors report a direct measurement of the absorption dynamics in an InAs p‐i‐n ridge waveguide quantum dot modulator. The carrier escape mechanisms are investigated via subpicosecond pump-probe measurements at room temperature, under reverse bias conditions. The optical pulses employed are degenerate in wavelength with the quantum dot ground state transition at 1.28μm. The absorption change recovers with characteristic times ranging from 62ps (0V)to∼700fs (−10V), showing a decrease of nearly two orders of magnitude. The authors show that at low applied fields, this recovery is attributed to thermionic emission while for higher applied fields, tunneling becomes the dominant mechanism.

A taxonomy of virtual worlds usage in education

Abstract Virtual worlds are an important tool in modern education practices as well as providing socialisation, entertainment and a laboratory for collaborative work. This paper focuses on the uses of virtual worlds for education and synthesises over 100 published academic papers, reports and educational websites from around the world. A taxonomy is then derived from these papers, delineating current theoretical and practical work on virtual world usage, specifically in the field of education. The taxonomy identifies rich veins of current research and practice in associated educational theory and in simulated worlds or environments, yet it also demonstrates the paucity of work in important areas such as evaluation, grading and accessibility. Practitioner notes What is already known about this topic • The use of virtual worlds for supporting education is widespread and increasing. • There are numerous studies on virtual worlds usage in education. • Virtual worlds are mainly used for collaborative- or simulation-based education. What this paper adds • An analysis and synthesis of over 100 academic papers and virtual worlds, multi-user virtual environments and virtual learning environments. • A taxonomic differentiation based upon population, educational activity and learning theory. • A balance sheet of the disadvantages and advantages of using virtual worlds in education. • Identification of under developed areas of research into virtual worlds in education. Implications for practice and/or policy • Motivates the use of virtual worlds to support experiential learning, where real world experiential learning is difficult to achieve due to barriers of time, cost and place. • Identification of difficulties and challenges in the educational use of virtual worlds. These may be overcome through future work or help identify where the use of virtual worlds is not appropriate. • Identification of where the current development or research focus is: pedagogy, collaboration, enquiry-based learning and identity, etc.

50-fs pulse generation from a self-mode-locked Cr:LiSrAlF6 laser.

The self-mode-locking of a Cr:LiSrAl6 laser has been demonstrated. With a pump power of 2 W from an argon-ion laser operating on the 476-nm line, 50-fs pulses were produced in the 800–920-nm tuning range at average powers of ∼150 mW. Although the mode-locking process was initiated by regenerative acousto-optic modulation, the self-mode-locking status of the Cr:LiSrAlF6 laser was readily confirmed by removal of the drive signal to the modulator.

Games Methodologies and Immersive Environments for Virtual Fieldwork

The construction and consolidation of knowledge through the practical application of concepts and processes can be difficult to support for subjects where practice is an integral component of competence and expertise in that domain. For example, participation in an archaeological excavation is not readily available to students, although a detailed understanding of what processes this involves is deemed to be core to the subject. The Laconia Acropolis Virtual Archaeology (LAVA) project has created a cooperative exploratory learning environment that addresses the need for students to engage with the complex practice of excavation. By leveraging the progressive nature of games methodologies and the immersive engagement provided by 3D multiuser virtual environments, LAVA facilitates the adoption of exploratory learning for excavation scenarios which have previously been inaccessible due to barriers of travel, time, and cost. A virtual environment based on real world data has been developed where groups of users are faced with a series of dynamic challenges with which they engage until such time that a certain level of competence is shown. Once a series of domain-specific objectives has been met, users are able to progress forward to the next level of the simulation. The excavation simulator enhances the student learning experience by providing opportunities for students to engage with the process in a customizable, virtual environment. Not only does this provide students with an opportunity to put the theories they are familiar with into practice, but it also allows students to gain experience in applying their skills in a bid to manage an excavation process, thereby making it possible for a greater emphasis to be placed on the practical application of knowledge that the excavation process necessitates. The potential of this approach has been confirmed by a positive user evaluation. LAVA contributes toward the progress of technology-enhanced learning by illustrating the instantiation of a framework which demonstrates how to integrate games methods with learning management systems and virtual worlds in order to support higher order learning behaviors such as applying, analyzing, evaluating, and creating.

Educationally enhanced virtual worlds

Virtual worlds continue to attract considerable interest as an innovative means of engaging students through the use of immersive, 3D, collaborative environments. They allow for the dynamic creation of content and for that content to be programmed. Second Life is the dominant virtual world technology in use, and whilst attractive in that it is a ready-made — albeit commercial — service, it was not designed for educational use and has significant social and technical drawbacks when used for that purpose. As such, we have been researching the serious use of OpenSim as an alternative virtual world for Computer Science education. OpenSim is a free, open source software development project which supports self-hosting and maintenance of virtual worlds. This paper explains our rationale for using OpenSim and reports on our experiences to date. It includes a feature comparison between OpenSim and Second Life as an aid for those wishing to exploit virtual worlds in the Computer Science curriculum.

Virtual worlds, real traffic: interaction and adaptation

Metaverses such as Second Life (SL) are a relatively new type of Internet application. Their functionality is similar to online 3D games but differs in that users are able to construct the environment their avatars inhabit and are not constrained by predefined goals. From the network perspective metaverses are similar to games in that timeliness is important but differ in that their traffic is much less regular and requires more bandwidth This paper contributes to our understanding of metaverse traffic by validating previous studies and offering new insights. In particular we analyse the relationships between application functionality, SLs traffic control system and the wider network environment. Two sets of studies have been carried out: one of the traffic generated by a hands-on workshop which used SL; and a follow up set of controlled experiments to clarify some of the findings from the first study. The interplay between network latency, SLs traffic throttle settings, avatar density, and the errors in the clients estimation of avatar positions are demonstrated. These insights are of particular interest to those designing traffic management schemes for metaverses and help explain some of the oddities in the current user experience.

802.11 wireless experiments in a virtual world

This paper describes the design and implementation of an 802.11 wireless laboratory within a Multi-User Virtual Environment (MUVE). The laboratory allows students and lecturers to create their own 802.11 scenarios by: i) selecting and placing components such as base stations and laptops within the immersive 3D landscape; ii) defining how traffic flows between these different network components; and iii) where appropriate specifying the movements of nodes. This information is sent outside of the MUVE and translated into a set of commands for the ns2 simulator, which then generates the simulation. The results of the simulation are sent back to the MUVE, where a 3D animation of the wireless communication is presented to learners interacting with the system. Learners are therefore able to set up and observe wireless phenomena such as the hidden and exposed node problems and to experiment by changing parameters such as packet loss and RTS/CTS threshold. The enabling framework behind the laboratory takes advantage of language independent, distributed resource management and stateful interaction through the use of web services.

Picosecond all-optical polarization switching in InGaAsP MQW's at 1.52 μm

An all-optical switch operating at a wavelength of 1.52 /spl mu/m is demonstrated. The switch makes use of electron spin polarization in a multiple-quantum-well semiconductor structure. The polarization change of a signal beam was observed to recover with a time constant of 20 ps determined by the spin relaxation time.

Exploring canons & cathedrals with Open Virtual Worlds: The recreation of St Andrews Cathedral, St Andrews day, 1318

St Andrews Cathedral is located on the East Coast of Scotland. Construction started in 1160 and spanned Romanesque and Gothic architectural styles. It was consecrated in 1318, four years after the battle of Bannockburn in the presence of King Robert I. For several hundred years, the Cathedral was one of the most important religious buildings in Europe and the centre of religious life in Scotland. During the Reformation, John Knox himself lead reformers in divesting the Cathedral of all its finery. Thereafter it fell into disuse and decline. Today the remains hint at its former glory. Here the use of Open Virtual Worlds (OVW) to support new modes of engagement with cultural heritage is presented through the example of St Andrews Cathedral. Open Virtual Worlds offer an extensible collaborative environment for developing historical scenes against which background material and intangible aspects of cultural heritage associated with a site may be explored. They offer the potential to reconstruct within a 3D computer environment both the physical structures of the past and important aspects of the lighting, sounds and lifestyles that once existed within those structures. Bringing together architecture, sculpture, illumination, stained-glass, music, procession and lighting into a scene, which can be explored from multiple spatial perspectives enables holistic appreciations to be developed.

Widely tunable, near- to mid-infrared femtosecond and picosecond optical parametric oscillators using periodically poled LiNbO/sub 3/ and RbTiOAsO/sub 4/

We describe the operation and characterization of Ti:sapphire laser-pumped femtosecond and picosecond optical parametric oscillators based the new quasi-phase-matched nonlinear materials of periodically poled LiNbO/sub 3/ and RbTiOAsO/sub 4/ with broad tunability in the near- to mid-infrared. We discuss the merits of the two materials for use in ultrafast optical parametric oscillators (OPOs) and compare and contrast their properties to the birefringent materials. We demonstrate an extended spectral coverage from 5 /spl mu/m, pump power thresholds as low as 45 mW, average mid-infrared output powers in excess of 100 mW, and pulse durations of 100-200 fs and 1-2 ps at /spl sim/80 MHz repetition rate. We also report the efficient operation of Ti:sapphire-pumped femtosecond OPOs in all-solid-state configurations by utilizing diode-laser-based input pump sources.