Showing papers by "Piet Demeester published in 1999"

Resonant cavity LED's optimized for coupling to polymer optical fibers

Abstract: Planar resonant-cavity light-emitting diodes have been optimized to meet optical interconnect requirements The microcavity effect is exploited to increase the extraction efficiency into a given numerical aperture and to reduce the crosstalk in parallel optical interconnect applications Devices are fabricated with an overall quantum efficiency of 37% into a polymer optical fiber with a numerical aperture of 05 and a FWHM beam divergence angle of 105/spl deg/ at a drive current of 1 mA

Mobility Collapse in Undoped and Si-Doped GaN Grown by LP-MOVPE

Abstract: The room temperature carrier mobility in bulk GaN layers is found to improve drastically by up to a factor of 20 once the incorporated silicon is higher than a critical value. A theoretical model taking into account several scattering mechanisms has been developed to account for the temperature dependence of conduction band mobility m(T) and carrier density n(T) deduced from Van der Pauw Hall measurements. For significantly Si-doped layers, both m(T) and n(T) can be quite accurately reproduced. In lightly doped and undoped samples, m(T) cannot be explained just using this model. TEM observation shows the presence of a more diffuse distribution of threading dislocations in the Si-doped material compared to the undoped one. The grain boundaries in this latter case are likely to correspond to high energetic barriers that carriers can overcome only by some tunneling process resulting in very low mobility.

The optical and structural properties of InGaN epilayers with very high indium content

Abstract: We present the results of optical and structural investigations of InGaN epilayers grown by Metallorganic Vapour Phase Epitaxy (MOVPE). The peak energies of characteristic photoluminescence (PL) bands allow us to identify regions of crystal with different mean InN: (InN+GaN) fraction in the range from 0.1 to nearly 1 in selected samples. The PL peak energy and the optical absorption band edge are strongly intercorrelated, the Stokes’ shift and the Urbach tailing energy both increase with InN fraction. High-resolution energy dispersive X-ray analysis (EDX), coupled with scanning electron microscopy (SEM) and cathodoluminescence (CL) imaging, helps to establish striking microscale correlations between optical and structural properties. Finally, X-ray absorption fine structure (XAFS) at the In and Ga K-edges reveals characteristic local structure on the atomic scale for InGaN solid solutions over the available range of In:Ga composition ratios.

On the design of an integrated management platform for an ADSL/ATM based access network using CORBA

Abstract: In this paper, we address the problem of the end-to-end management of a heterogeneous public network. In the case study, the access part of the network is based on the ADSL technology for the provisioning of high-speed IP over ATM to the customer and consists of ADSL network elements and ATM access switches. The core of the network is ATM-based and provides connectivity to retailers, which in this case are Internet service providers (ISP). We give an insight into the technological approach which consists of building a distributed platform, based on CORBA, that integrates existing element and network management systems and provides an end-to-end configuration, performance and fault management solution. The architecture of a generic resource adapter for SNMP devices as well as an automated SNMP-to-IDL mapping method are detailed.

Automated Design of Modular SNMP-CORBA Gateways and Their Application for the Development of an ADSL Access Network Manager

Abstract: In this paper we address the problem of the specification and design of extensible CORBA/SNMP gateways which allow to embed legacy SNMP managed devices into a Distributed Processing Environment (DPE). Our approach is that of a generic Resource Adapter (RA) which is staged in two layers. A first Layer-1 contains stateless CORBA-IDL/SMI-SNMP stubs and a second Layer-2, runs on top of Layer-1 and adds logical behavior to the gateway. The Layer-1 builds upon a fully new specification and interaction translation of the MIB, whose creation is automated via a tool chain called the MibCompiler platform. In outlining the informational, computational and engineering viewpoint of the Resource Adapter architecture according to the ODP framework, two extra servers called the Resource Adapter Factory (RAF) and the Resource Adapter Factory Dispatcher (RAFD) are introduced. These servers enhance the CORBA/SNMP mediation platform in both performance and scalability. The Resource Adapter approach has been applied for the design and implementation of an ADSL access network manager, which was used for the ACTS VITAL project. This ADSL access network manager is now integrated with a similar ATM access network manager in order to support an ADSL provisioning support tool for the Belgian Public Network Operator.

Internal connectivity of optical crossconnects in opaque networks

Abstract: The impact of the internal OXC connectivity on the network cost is investigated. As a result, full connectivity inside the OXC is not required for realistic cost scenarios of optical switches.

WDM network planning in a changing environment

Abstract: This paper studies the planning of survivable all-optical networks on a long-term basis (e.g., considering a planning horizon of two to five years). Due to rapid changes on both demand and technology side, a quite dynamic long-term. behaviour can be expected for such networks. This enforces a planning technique which takes the time-dependent nature of demand and cost data explicitly into account. Considering a particular WDM network planning problem, several techniques are presented to serve problem instances of realistic size. Extensive simulations are carried out to compare the performances of the proposed planning techniques. This allows us to infer some general guidelines for long-term network planning.

Cathodoluminescence from an InGaN/GaN MQW Grown on an Epitaxially Laterally Overgrown GaN Epilayer

Abstract: In this paper we report room temperature CL studies of a 5 period InGaN (3 nm)/GaN (7 nm) multiple quantum well (MQW) with a nominal indium concentration of 15%, grown on and off a 4.8 μm epitaxially lateral overgrown GaN (ELOG) epilayer. The ELOG epilayer was overgrown through a SiO2 striped mask with 3 μm window and SiO2 stripe widths oriented in the GaN 〈11-00〉 direction by metalorganic vapour phase epitaxy (MOVPE). We show that the luminescence efficiency of both the GaN and the MQW is improved for material lying above the stripes of the SiO2 mask compared to that above the windows of the mask or unpatterned material. Monochromatic CL images were acquired from both the GaN and MQW layers with the emission from the MQW layer being much brighter than that from the GaN. Marked differences are observed between corresponding CL images acquired at different electron beam energies.

Probing nitride thin films in 3-dimensions using a variable energy electron beam

Abstract: In this paper we illustrate the application of electron beam techniques to the measurement of strain, defect and alloy concentrations in nitride thin films. We present brief comparative studies of CL spectra of AlGaN and InGaN epilayers and EBSD patterns obtained from two silicon-doped 3 μm thick GaN epilayers grown on an on-axis (0001) sapphire substrate and a sapphire substrate misoriented by 10° toward the m-plane (1010).

Evolution Towards Photonic Networks

Abstract: This paper is an edited version of “Roadmap towards the Optical Communication Age” published by the HORIZON project within the ACTS Photonic Domain. This paper summarises possible evolution scenarios leading to photonic access and transport networks.