Ann Ackaert

Thickness variations during MOVPE growth on patterned substrates

Experiments have been carried out to investigate thickness variations between epitaxial layers grown on ridges or channels and the surrounding planar surface. Results show a remarkable variation in growth velocity, even for relatively wide channels and ridges. Using these findings, a novel laser/waveguide coupling technique, which uses a single epitaxial growth step, is proposed.

Routing in an AWG-Based Optical Packet Switch

For the next generation of the optical internet, focus is now moving from circuit switched networks, which occupy a wavelength continuously regardless of the demand at that time, towards optical packet/burst switching. By only occupying a wavelength when data is to be transmitted, a more efficient utilization of bandwidth in optical fibers is strived for. As bandwidth in fibers keeps increasing, the bottleneck of the optical network is now moving towards the switching node, since evolution of electronic routers cannot follow the speed of bandwidth increase. Thus a key component in these novel networks is the optical node. Through this node we want to switch traffic very fast and reliably, preferably transparent. Lack of efficient and practically realizable optical buffer, however, makes migration from electronic routers to optical routers a non-straightforward transition. In most optical nodes payload traffic can be switched transparently, whilst control information (e.g., in a header, on a control channel) is still converted to the electronic domain in every node, since optical processing is far from mature. In this paper we present a possible architecture for such a node, array waveguide gratings and all-optical tuneable wavelength converters. The concept of this switch is explained and the node is evaluated in terms of loss rate. We will see that an inherent problem of this switch is its internal blocking. This drawback can be greatly overcome by using an intelligent and efficient wavelength assignment algorithm within the node. Simulation of slotted operation will give some numerical results.

Relaxed lattice-mismatched growth of III–V semiconductors

Abstract The fast increase in complexity of electronic and optoelectronic systems has created a need for high performance and multifunctional integrated circuits. One of the major restrictions is the lattice matching condition which severely limits the number of possible material combinations that can be used. This paper will review recent developments in the relaxed combination of III–V semiconductors with lattice mismatched substrates. Emphasis will be put on the problems encountered, the possible solutions and the device applications. The material combinations which will be discussed are: GaAs/AlGaAs on Si and InP substrates and InP/InGaAsP on Si and GaAs substrates.

Fabrication of high-radiance LEDs by epitaxial lift-off

Fully processed A1GaAs/GaAs LEDs were lifted off their GaAs substrates and grafted to various host substrates. Due to a metallic back reflector beneath the epitaxial structure, the LED output power was 2 to 3 times increased compared to LEDs still on a GaAs substrate. Output power and spectral responses were significantly influenced by the thermal properties of the host material.

Crack formation and thermal stress relaxation of GaAs on Si growth by metalorganic vapor phase epitaxy

In this letter we report on the use of selective metalorganic vapor phase epitaxy growth as an original tool to alleviate the problem of random formation of microcracks in thick GaAs‐on‐Si heteroepitaxial layers. Through the use of a special mask design including the definition of sharp wedges in the SiO2 mask material, the thermally induced stress in the GaAs‐on‐Si layers preferentially relaxes at precisely located sites on the substrate. The influence of mask configuration, wedge shape, wedge orientation, and layer thickness on microcrack formation has been investigated. Results obtained show that small‐area SiO2 wedges are useful for the definition of microcrack location, and thus eventually for optoelectronic device processing.

Towards a social and context-aware multi-sensor fall detection and risk assessment platform

For elderly people fall incidents are life-changing events that lead to degradation or even loss of autonomy. Current fall detection systems are not integrated and often associated with undetected falls and/or false alarms. In this paper, a social- and context-aware multi-sensor platform is presented, which integrates information gathered by a plethora of fall detection systems and sensors at the home of the elderly, by using a cloud-based solution, making use of an ontology. Within the ontology, both static and dynamic information is captured to model the situation of a specific patient and his/her (in)formal caregivers. This integrated contextual information allows to automatically and continuously assess the fall risk of the elderly, to more accurately detect falls and identify false alarms and to automatically notify the appropriate caregiver, e.g., based on location or their current task. The main advantage of the proposed platform is that multiple fall detection systems and sensors can be integrated, as they can be easily plugged in, this can be done based on the specific needs of the patient. The combination of several systems and sensors leads to a more reliable system, with better accuracy. The proof of concept was tested with the use of the visualizer, which enables a better way to analyze the data flow within the back-end and with the use of the portable testbed, which is equipped with several different sensors.

Performance improvement of an internally blocking optical packet/burst switch

Optical packet/burst switching is considered a promising technique to improve the performance of optical networks. Key components in these technologies are the optical switching nodes. Some of these node architectures suffer from internal blocking. Synchronous operation allows overcoming most of the problems introduced by this internal blocking. However, in asynchronous networks internal blocking can have a more pronounced effect. In this paper, we propose a windowing technique to improve the performance of internally blocking optical switching nodes in asynchronous operation. Simulations will show significant improvements can be made.

TV-kiosk: an open and extensible platform for the wellbeing of an ageing population

The ageing population is becoming a growing challenge to society. User-centered ICT solutions adapted to elderly can play a prime role in dealing with these challenges. This paper presents TV-kiosk, an open and extensible TV-based platform that aims to stimulate social interaction, avoid isolation and deliver information. One of its distinguishing features is the underlying decentralized network communication approach based on advanced technology to securely and automatically interconnect devices and the TV-based user interface specifically designed for elderly. The openness and extensibility of the platform make it possible to easily integrate all kinds of new and existing e-services. Currently, a field trial is ongoing in a care center where TV-kiosk is being used by elderly, their family and caregivers.

Economic Viability of eCare Solutions

Provisioning of good quality care to the elderly population and at the same time reducing the pressure on the health care expenditures is a challenging issue for governments today. Many ICT supported, distant care systems (eCare) have been proposed but few have found their way to the market. The problem is to provide a viable business case for each actor involved (including eCare platform, health care and finance providers) when offering eCare services. We have constructed a model for evaluating the (socio-)economic viability of different business models when introducing eCare solutions. A multi-actor approach has been implemented, calculating and evaluating the business case for each actor involved. For a Belgian case we will show (socio)-economic advantages to participate in an eCare ecosystem.

The Innovation Binder Approach: A Guide Towards a Social-Technical Balanced Pervasive Health System

Pervasive health systems aim to support society with the many challenges our healthcare system is facing today.