Modelling and design of a travelling-wave electro-optic modulator on InP

Based on a rigorous vectorial analysis, a fast travelling-wave Mach–Zehnder modulator is modelled and designed. The cross-section of the semiconductor layer stack and the lossy electrodes are carefully modelled using the method of lines in order to investigate propagation characteristics, velocity and losses. This yields an accurate microwave and optical field distribution to explain the behaviour of the component. In order to enhance the modulation efficiency, design curves are derived and the cross-sectional dimensions for minimum microwave loss are determined. The loss of the optimized modulator agrees very well with small-signal measurements up to 40 GHz and HFSS simulations. The layerstack of the fabricated device is suitable for integration with InP multi-wavelength lasers.     

Lein?l, Lein?lfirniss und Oelfarben

Ohne Zusammenfassung     

A parallel method for time discretization of parabolic equations based on Laplace transformation and quadrature

We consider the discretization in time of an inhomogeneous parabolicequation in a Banach space setting, using a representation ofthe solution as an integral along a smooth curve in the complexleft half-plane which, after transformation to a finite interval,is then evaluated to high accuracy by a quadrature rule. Thisreduces the problem to a finite set of elliptic equations withcomplex coefficients, which may be solved in parallel. The paperis a further development of earlier work by the authors, wherewe treated the homogeneous equation in a Hilbert space framework.Special attention is given here to the treatment of the forcingterm. The method is combined with finite-element discretizationin spatial variables.     

Diffusion Structural Analysis Study of Titania Films Deposited by Sol-Gel Technique on Silica Glass

The diffusion structural analysis (DSA) was used to characterize microstructure changes of hydrous titania gel films under in situ conditions of heating. TG and DTA were used in order to elucidate the processes controlling the formation of anatase film during heating of hydrous titania gel film. The annealing of porosity and near surface structure defects of the dehydrated titania films was indicated by DSA in the temperature range 255–700°C as the decrease of radon release rate. It was demonstrated that the annealing was enhanced on heating in oxygen in comparison with heating in argon. The DSA experimental results were compared with model curves describing the radon diffusion mobility and the annealing of radon diffusion paths.     

The kinetics of the light-induced defect creation in hydrogenated amorphous silicon – Stretched exponential relaxation

Our model for light-induced defect creation in hydrogenated amorphous silicon is applied to its kinetics, i.e., the growing curve of light-induced dangling bond density as a function of illumination time, which is fitted to a stretched exponential function. Two parameters β and τ involved in the function are estimated as functions of saturated dangling bond density in terms of our model. These are compared with two experimental results, i.e., our results obtained from ESR measurements and Shimakawa et al.’s results obtained from photoconductivity measurements. The saturated dangling bond density is also measured as a function of the generation rate of free carriers. The experimental results are compared with calculated results and discussed.     

Buckling of a stiff thin film on a compliant substrate in large deformation

A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically.     

Receiver set partitioning and sequencing for multicasting traffic in a WDM lightwave single-hop network

This paper considers a receiver set partitioning and sequencing problem in a wavelength division multiplexing single-hop lightwave network for multicasting traffic. The problem is analysed in the approach of uncapacitated single batch-processing machine scheduling. In the analysis, several solution properties are characterized with respect to a mean flow time measure, based upon which two heuristic algorithms are developed, along with a dynamic programming algorithm. Several numerical experiments show that the heuristic algorithms generate good schedules. The problem is extended to consider two measures simultaneously including the mean flow time and the number of transmissions, for which the proposed algorithms also perform well.     

Use of a range scaling method to determine alanine/water stopping power ratios

A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level).     

Application of INAA to reveal the chemical evolution of selected volcanic eruptiva from Santorini, Greece

The pumiceous products of the large-scale explosive eruptions at Santorini show a high grade of similarity in their optical appearance as well as in their chemical composition. The demand for a clear classification of these eruption products was raised from archaeological research, where pumice can be interpreted as a “post-eruption” time marker. The aim of this work was to find elements that underwent significant changes because of geochemical processes and that could be indicative for a distinction of pumice produced by the five major explosive eruptions. INAA of 25 elements allows a clear classification and contributes new information to the chemical evolution of Santorini volcano. This revised version was published online in July 2006 with corrections to the Cover Date.