Medicalex (France)

Introduction: La vidéocapsule endoscopique (VCE) est le moyen non irradiant le moins invasif d'explorer l'intestin grêle chez l'enfant. Chez les moins de 6 ans, la VCE peut être déposée dans le duodénum par endoscopie sous anesthésie générale (AG). Nous avons étudié l'impact de cette AG sur la faisabilité et le l'efficacité diagnostique de la VCE.

High-performance tunable low-noise amplifiers for 38-42.5 GHz applications are presented based on a fully stabilized GaAs pseudomorphic high electron mobility transistor (PHEMT) 0.2 μm technology. A single 1.5×3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> chip, incorporating six amplifying stages, shows a measured gain of 36-42 dB depending on the center frequency. Both maximum gain frequency and input impedance of the amplifier are accurately tunable on the chip. This means that the amplifier provides a narrow-band filtering function and can be matched to a fast p-i-n photodiode as well as to a 50 /spl Omega/ load. This is the first time such performances are reported for single chip narrow-band tunable amplifiers using a GaAs PHEMT technology.

A new Schiff-base ligand based on the condensation of diaminomaleonitrile and 4-(diethylamino)salicylaldehyde is reported with its copper, nickel, and zinc complexes. Their second-order nonlinear optical properties are investigated by electric field induced second harmonic (EFISH) and ZINDO quantum-chemical calculations to probe the role of the metal center in the nonlinearity. All the complexes exhibit a second-order nonlinear response that is larger than that of the ligand with an hyperpolarizability (β) value of 400 (±100) 10-30 cm5 esu-1 for the zinc derivative at 1.34 μm. Theoretical calculations indicate that the two-level model is inadequate to describe the nonlinearity in such systems.

A semi-empirical expression for the refractive index, which takes excitonic effects correctly into account, is given for direct bandgap semiconductors in the vicinity of the absorption threshold. This expression, which can be useful even at low temperatures, is compared with previous models and applied to the case of gallium arsenide.

Laser diodes exhibiting a dip-free FM response will be key devices for future coherent FSK systems. We studied (both theoretically and experimentally) the thermal contribution to the FM response of a laser. It turns out that the agreement is good enough to validate the Fourier transform approach. This enables us to propose schemes to reduce the thermal FM response: decrease the heat generated in the laser and/or its thermal resistance by episide-down mounting. >

A model is proposed to optimize the design of a laser monolithically integrated with a transparent waveguide by an evanescent field. A five-layer structure is shown to be so sensitive to the growth parameters that the threshold current and coupled into the waveguide are basically uncontrollable. The model makes it clear that separate-confinement structures, in which the active layer is attached to a thicker waveguide, are more suitable. The increase of threshold current in these configurations can be efficiently offset by depositing high-reflectivity coatings on the facets of the devices. Moreover, these coatings are shown to further reduce the sensitivity of the devices to technological fluctuations. The use of a single quantum well embedded into a single-mode guide is proposed to obtain very low threshold currents while maintaining a low sensitivity to growth fluctuations. >

In the optical fiber telecommunication systems, the emission and reception modules contain optoelectronic components such as laser diodes and photodiodes. Beside the laser whose task and complexity are obvious, the photodiode, the mechanism of which is quite straightforward, becomes a sophisticated device when optimized for 1.3–1.55 µm fiber window. For photodetection, the photodiode is always associated to a preamplifier obtained from a transistor. For a given link, the performances of the receiver straightly depend on those of the photodiode and of the transistor. Different types of photodetectors are suitable for 1.3 µm and 1.55 µm transmissions. This paper surveys the different semiconductors materials and device structures encountered nowadays, pointing out the respective merits of each solution. Comparisons between photoreceivers outline the importance of matching the photodiode to the transistor, whether dealing with hybrid or monolithic circuits.

ABSTRACTAluminum lines have been drawn at a writing speed of 3.8 μm/s on (100) p-type Si by UV laser-assisted chemical processing, from a flow of TMA diluted in H2. These results are the experimental proof of direct writing at room temperature due to a single-step deposition process induced by a single light source. The useful (30 μQ-cm) ohmic-type resistivity obtained depends strongly on the photolytic process parameters.