Roland Debrie

Fast and automatic stereo vision matching algorithm based on dynamic programming method

We consider that the matching problem in a stereo vision process can be treated as the problem of finding an optimal path on a two-dimensional (2D) search plane. To obtain this path, we consider a non-linear gain function which varies as a function of threshold values calculated during the preliminary statistical analysis of the right and left images.

Fast and self-adaptive image segmentation using extended declivity

In this paper we present a new fast self-adaptive image segmentation operator for real-time vision applications. It is based on the extended declivity which is obtained by extending the basic declivity — whose concept is recalled — using a similar principle to region growing. This non-linear operator is able to detect low contrasted region boundaries without any pre-processing such as low-pass filtering. Experimental results are produced with different types of image and compared with those obtained with the basic declivity operator and with the Deriche’s operator as a reference.RésuméDans cet article un nouvel opérateur rapide et autoadaptatif de segmentation d’images pour des systèmes de vision en temps réel est présenté. Il est basé sur la déclivité étendue qui est obtenue par extension de la déclivité de base — dont le concept est rappelé — selon un principe semblable à celui de la croissance de régions. Cet opérateur non linéaire permet de détecter des limites de régions faiblement contrastées sans aucun pré-traitement tel qu un filtrage passe-bas. Des résultats expérimentaux portant sur différents types d’images sont présentés et comparés avec ceux obtenus avec l’opérateur de déclivité de base ainsi qu’avec l’opérateur de Deriche en tant que référence.

Optimization of the coupling between a tapered fibre and a p-i-n photodiode

With increasing information flow, direct illumination of the photodiode intrinsic layer from the end of a fibre becomes a necessity. The active area size of the photodiode is much smaller than the spot size in the fibre. This paper proposes an optimized scheme for direct coupling between the fibre and the device. Different fibre extremities are investigated. It is shown that optical coupling could be optimized with an acid-etched taper ended by a lens of 13 mu m diameter or by a pulled and melted fibre with certain conditions of profiles.

3-D surface reconstruction using a polarization state analysis

Analysing the polarization state of reflected beams in a vision system provides essential informations concerning the observed surface orientations. In this paper, we present an original 3-D surface reconstruction method based on this principle. The polarimetric characterization of reflected beams in two stereoscopic images enables the determination, for every surface element of the analysed scene, of a normal vector to this surface element. In this aim, a specific stereoscopic image acquisition device including optical processors has been defined. The normal vectors to a surface elements are then involved in a specific integration process which yields the complete 3-D surface reconstruction. Results of this global treatment for real scenes are shown and discussed.

Rapid thermal annealing of magnesium implanted GaAs-GaAlAs heterostructures experimental and simulated distributions

The use of rapid thermal annealing (RTA) techniques to anneal ion implanted GaAs compounds is expected to have a significant impact on device technology. Due to the short duration of the heat treatment, the implanted impurities may be activated without significant diffusion. For heterojunction bipolar transistor (HBT) applications, high doses of p-type impurities are required to compensate the doping levels of N-GaAlAs emitter and n+ GaAs contact layers. Multi-implantations were chosen to maintain a flat profile down to the base layer. Energies of 30, 60, 150, and 340 keV with doses of 6 × 1013, 9 × 1013,6 × 1014, and 9 × 1014 cm−2, respectively, have been used. Annealing cycles with time durations of a few seconds and temperature in the range of 850–950°C are described. Electrical properties of the annealed samples have been investigated using an electrochemical measurement technique. It was found that hole concentrations as high as 4 × 1019 cm−3 and electrical activities near to 75 percent can be obtained. There is no evident indiffusion and no significant outdiffusion at the optimal annealing conditions. Simulation of multilayer implantations are also carried out by an accurate model available in TITAN 2D process simulator using Pearson IV laws and taking into account the diffusion effects on profile distribution caused by RTA. A first approximation using a simple model allows a rapid evaluation of the data fitting operation. In a second approach, concentration dependent diffusivity and the contribution of the electric field at the interface are covered to perform an improved data fitting of ion implanted and annealed dopant profiles. A comparative study shows a good agreement between experimental and simulated distributions.

Parametric investigations and simulations of ion beam etching and reactive ion etching mechanisms for GaAs compounds

Abstract This work introduces a comprehensive analytic model of the sputtering mechanism present in ion beam etching and reactive ion etching processes. Our final objective is to correlate the etch rate to the plasma reactor parameters. Experimental verifications for GaAs etching show a good agreement for ion beam etching. In the case of reactive ion etching, the non-perfect agreement is explained by the influence of effects such as flow rate and temperature not taken into account in the theoretical approach. We also present parametric investigations of GaAs etched in SiCl 4 plasma.

The study of the radiance variation between two pixels for their stereo vision matching

In the stereo vision system, the key problem is a search problem which finds the corresponding pixels in the two stereoscopic images. These pixels must satisfy a very strict photometric constraint. In our approach, we use a special configuration of the two cameras in order to speed up the stereo vision process. In this paper, a theoretical study of the radiance variation between two stereo vision matching pixels is presented. This study shows the efficiency and the limitation of the used photometric constraint. Furthermore, we show the influence of the maximum value of the disparity and the one of the focal length of the two cameras on the stereo vision process. Some experimental results obtained on real images are given in the end of this paper.

Analytic models and parametric investigations of IBE and RIE mechanisms for GaAs compounds

This work introduces a comprehensive analytic model of the sputtering mechanism present in ion beam etching and reactive ion etching processes. Our final objective is to correlate the etch rate to the plasma reactor parameters. Experimental verifications for GaAs etching show a good agreement for ion beam etching. In the case of reactive ion etching, the imperfect agreement is explained by the influence of effects such as flow rate and temperature not taken into account in the theoretical approach. We also present parametric investigations of GaAs etched in SiCl4 plasma.

Field power distribution in variable core radius of optical fiber for optimal coupling with photodiode

Many possibilities are offered to analyze the field in tapered fibers. We have used in this work the bpm method and the coupled-mode theory for a conical fiber. In the second case, it is shown by a length-scale criterion that some geometries should provide a good efficiency. The comparison between the quasi 3D numerical simulation and the local mode method is also performed. The complete resolution procedure is then dependent on certain essential approximations and simplifying hypothesis.

Modelization of field power distribution in specific singlemode optical fiber for optimal coupling in P-I-N photodiode

Many possibilities are offered to compute field. We have used in this work the bpm method and the local mode method for a conical fiber. In the second case, it is shown by a length-scale criterion that some geometry should provide a good efficiency. We examine the fiber end and show that an appropriate lens form makes it possible to adapt the power distribution between the optical fiber and the photodiode. Some taper shapes are suggested and the model accuracy is discussed according to the nature of the decrease criterion. We obtain in this case an assessment along this guide that is optimized. The comparison of this results with the quasi 3D numerical simulation of the guided optical propagation is also performed.