Klaus David

Gain-coupled DFB lasers versus index-coupled and phase shifted DFB lasers: a comparison based on spatial hole burning corrected yield

A statistical yield analysis is presented for gain- and index-coupled distributed feedback (DFB) laser structures, allowing a comparison of their single longitudinal mode (SLM) yield capabilities. For the yield calculations, the threshold gain difference and the longitudinal spatial hole burning (SHB) are taken into account. By comparing the experimental and theoretical yield of index-coupled DFB lasers, the significance of SHB for correct yield predictions is illustrated. For the purpose of comparison, yield calculations for various lambda /4-shifted DFB lasers (with low facet reflectivities) are presented. The most emphasis, however, is on partly gain-coupled DFB lasers. Estimations of practical gain coupling coefficient values for gain and for loss gratings are discussed. >

Improved performance of AR-coated DFB lasers for the introduction of gain coupling

Antireflection (AR)-coated distributed-feedback (DFB) lasers with both gain- and index-coupled distributed feedback are studied numerically with respect to mode losses, mode suppression, and spatial hole burning. The mode losses and the spatial hole burning decrease with increasing gain coupling, while the mode suppression increases. It is shown that a large improvement in performance can already be obtained for small fractions of gain coupling.<<ETX>>

Supporting patient monitoring using activity recognition with a smartphone

In our work we envision the use of context awareness to complement and improve telemedicine services. One concrete example is the recognition of physical activity (PA) for therapies and treatments. The usage of context can provide newer services by assisting medical professionals and patients to obtain implicit information. We introduce the Context Aware Remote Monitoring Assistant (CARMA), an application implemented on the MATRIX telemedicine middleware platform. It enables activity recognition for patients using non-obtrusive devices. In this paper, a movement recognition approach is investigated using a smartphone with a built-in accelerometer. Experiments were carried out to compare the influences of classification algorithms, features and combinations for feature extraction conditions on the recognition accuracy. The obtained results indicated that the approach is viable and shows much potential.

A new DFB-laser diode with reduced spatial hole burning

An index coupled antireflection-coated distributed-feedback (DFB)-laser diode which theoretically exhibits a longitudinally uniform power density is proposed. The structure contains an amplitude modulated grating and is far more efficient in reducing spatial hole burning than multiphase-shift lasers. The laser can be expected to be single mode up to high power levels. It can be of interest when long lasers with a reduced linewidth and a flat FM response are to be used or as a laser with small modulation distortion in analog communication.<<ETX>>

Basic analysis of AR-coated, partly gain-coupled DFB lasers: the standing wave effect

A theoretical analysis of distributed feedback (DFB) lasers with mixed gain and index coupling (partly gain-coupled DFB) is given for perfect antireflection (AR) coatings. Analytical expressions for the threshold gain, facet loss, and the relative depth of the standing wave pattern are derived. At the same time the importance of the standing wave effect and its consideration by coupled mode equations is shown. For purely gain-coupled DFB lasers, simple expressions for the effective linewidth enhancement factor and the longitudinal spontaneous emission factor are derived. In addition, various approximations describing the performance of purely gain-coupled DFB lasers are given. >

An Alignment Approach for Context Prediction Tasks in UbiComp Environments

The authors detail the alignment prediction approach-a time-series-estimation technique applicable to both numeric and nonnumeric data-and compare it to four other prediction approaches to determine context-prediction accuracy in ubiquitous computing environments.

Theoretical investigation of the second-order harmonic distortion in the AM response of 1.55 mu m F-P and DFB lasers

Numerical calculations of the second-order harmonic distortion in the amplitude modulation-response of Fabry-Perot, and distributed feedback (DFB) lasers are presented, and the influence of several nonlinearities, such as longitudinal spatial hole burning, gain suppression, and relaxation oscillations are considered. This analysis is valid for modulation frequencies ranging from a few megahertz to well beyond the resonance frequency of the relaxation oscillation. The distortion of Fabry-Perot lasers for which the effects of spontaneous emission and gain suppression can be clearly illustrated is investigated. The distortion of DFB lasers where the emphasis is on the influence of spatial hole burning and its combination with other nonlinearities is discussed. Various effects are discussed. >

CAR-2-X and Pedestrian Safety

Traffic accidents involving pedestrians or cyclists cause thousands of fatalities and serious injuries every year. In this article, we present an innovative approach for a collision avoidance system that seeks to reduce these accidents. We also discuss the different architectural approaches utilizing ad hoc and/or cellular technologies and different processing setups and present a physical analysis of the system time available between detection, warning, and reaction to give an overview of the time constraint.

UPOS: User Profile Ontology with Situation-Dependent Preferences Support

Context-aware adaptive systems aim at automatically personalizing the users environment depending on the users situation, and hence, minimizing user interaction with the system. We present a novel user profile ontology that is dedicated to describe situation-dependent sub-profiles. This ontology can be used by context-aware adaptive service platforms for mobile communication and information services to automatically trigger the situation-dependent personalization of services. The design of this novel ontology also takes into consideration recommendations from the human factors research area. In particular, the ontology enables the easy specification of situational conditions and situation-dependent user sub-profiles.

On the distinctive features of gain coupled DFB lasers and DFB lasers with second-order grating

First, the two types of DFB lasers with gain cou- pling, true gain coupled lasers (with either a gain or loss grat- ing) and second-order index coupled lasers are shown to be equivalent, mathematically and to some extent also physically. The operation of these DFB lasers, partly based on the overlap of the standing wave pattern in the optical power density with the periodic gainlloss variation, is addressed. It is further shown in detail how this special feature also leads to important modifications in the expressions for the modal loss or threshold gain, the threshold gain difference, the efficiency and the line- width.