A 40 Gbit/s optical link on a 300-mm silicon platform.

We demonstrated 40 Gbit/s optical link by coupling a silicon (Si) optical modulator to a germanium (Ge) photo-detector from two separate photonic chips. The optical modulator was based on carrier depletion in a pn diode integrated in a 950-µm long Mach-Zehnder interferometer. The Ge photo-detector was a lateral pin diode butt coupled to a silicon waveguide. The overall loss, which is mainly due to coupling (3 grating couplers times ~4 dB) was estimated to be lower than 18 dB. That also included modulator loss (4.9-dB) and propagation loss (<1 dB/cm). Both optoelectronic devices have been fabricated on a 300-mm CMOS platform to address high volume production markets.

Low loss 40 Gbit/s silicon modulator based on interleaved junctions and fabricated on 300 mm SOI wafers.

We demonstrate high-speed silicon modulators based on carrier depletion in interleaved pn junctions fabricated on 300 mm-SOI wafers using CMOS foundry facilities. 950 µm-long Mach Zehnder (MZ) and ring resonator (RR) modulator with a 100 µm radius, were designed, fabricated and characterized. 40 Gbit/s data transmission has been demonstrated for both devices. The MZ modulator exhibited a high extinction ratio of 7.9 dB with only 4 dB on-chip losses at the operating point.

THz surface plasmon modes on planar Goubau lines.

The dispersion relation and confinement of terahertz surface plasmon modes propagating along planar Goubau lines are studied using guided-wave time domain spectroscopy. We demonstrate the radial nature of the surface plasmon mode known as the Goubau mode and the transverse confinement of the electric field over a few tenths of microns (~l/10). We experimentally and computationally observed a transition of the shape of the THz pulses from unipolar to bipolar as the propagation distance increases, indicating that the Goubau line acts as a high-pass filter. The deviation of the dispersion relation curve from a linear law above 600 GHz is discussed.

Current-driven vortex oscillations in metallic nanocontacts.

We present experimental evidence of subgigahertz spin-transfer oscillations in metallic nanocontacts that are due to the translational motion of a magnetic vortex. The vortex is shown to execute large-amplitude orbital motion outside the contact region. Good agreement with analytical theory and micromagnetics simulations is found.

Single-shot time-resolved measurements of nanosecond-scale spin-transfer induced switching: stochastic versus deterministic aspects.

Using high bandwidth resistance measurements, we study the single-shot response of tunnel junctions subjected to spin torque pulses. After the pulse onset, the switching proceeds by a ns-scale incubation delay during which the resistance is quiet, followed by a 400 ps transition terminated by a large ringing that is damped progressively. While the incubation delay fluctuates significantly, the resistance traces are reproducible once this delay is passed. After switching, the time-resolved resistance traces indicate micromagnetic configurations that are rather spatially coherent.

Emission characteristics of ion-irradiated In(0.53)Ga(0.47)As based photoconductive antennas excited at 1.55 microm.

We present a detailed study of the effect of the carrier lifetime on the terahertz signal characteristics emitted by Br(+)-irradiated In(0.53)Ga(0.47)As photoconductive antennas excited by 1550 nm wavelength femtosecond optical pulses. The temporal waveforms and the average radiated powers for various carrier lifetimes are experimentally analyzed and compared to predictions of analytical models of charge transport. Improvements in bandwidth and in average power of the emitted terahertz radiation are observed with the decrease of the carrier lifetime on the emitter. The power radiated by ion-irradiated In(0.53)Ga(0.47)As photoconductive antennas excited by 1550 nm wavelength optical pulses is measured to be 0.8 muW. This value is comparable with or greater than that emitted by similar low temperature grown GaAs photoconductive antennas excited by 780 nm wavelength optical pulses.

Photomixing at 1.55 microm in ion-irradiated In(0.53)Ga(0.47)As on InP.

We report the first demonstration of a terahertz photomixer made of ion-irradiated In(0.53)Ga(0.47)As lattice-matched to InP and fiber-optic coupled with the drive lasers. A continuous-wave radiation is generated at frequencies up to 0.8 THz by photomixing two continuous-wave laser diodes around 1.55 microm. The measured 3dB-down bandwidth of 300 GHz yields a carrier lifetime of 0.53 ps, in agreement with the value of 0.41 ps measured in pump probe experiments. The detected signal is at the most 15 dB lower than the one obtained from similar photomixers fabricated from low-temperature-grown GaAs.

Single-mode in-gap emission of medium-width photonic crystal waveguides on InP substrate.

In this paper, we present a numerical and experimental study of W3-4 photonic crystal (PhC) waveguide lasers fabricated on InP substrate. In such a PhC waveguide, the dispersion curve of the fundamental mode folds in the two-dimensional gap of the triangular lattice. Folding occurs at the Brillouin zone edge as in the case of genuine distributed feedback (DFB) lasers. Single-mode emission is presently observed in both electrical and optical pumping configurations. This behavior is attributed to the different levels of out-of-plane losses experienced by the two DFB mode components. Three-dimensional finite-difference-time-domain calculations are used to finely quantify the quality factors of the waveguide modes. The modal discrimination is shown to be reinforced when lasing occurs far from the conduction band edge. This trend is also predicted for other canonical waveguides in triangular PhCs as for instance W2-3 waveguides.

Phase coherent precessional magnetization reversal in microscopic spin valve elements.

We evidence multiple coherent precessional magnetization reversal in microscopic spin valves. Stable, reversible, and highly efficient magnetization switching is triggered by transverse field pulses as short as 140 ps with energies down to 15 pJ. At high fields a phase coherent reversal is found revealing periodic transitions from switching to nonswitching under variation of pulse parameters. At the low field limit the existence of a relaxation dominated regime is established allowing switching by pulse amplitudes below the quasistatic switching threshold.

[Cerebrospinal fluid shunting: anesthetic particularities]. / Les dérivations du liquide céphalorachidien: particularités anesthésiques.

The symptomatic treatment of hydrocephalus remains cerebrospinal fluid (CSF) drainage to an external reservoir (external CSF drainage) or to an internal cavity mainly the peritoneum or the right atrium via a unidirectional valve (internal CSF drainage) and finally by endoscopic ventriculocisternostomy. Local anaesthesia is adequate for external CSF drainage in adults and children above 10 years while general anaesthesia is required in all other cases. The main problems encountered in these patients are difficult intubation and full stomach associated with increased intracranial pressure. The anaesthetic approach should favour homeostasis. With the exception of ketamine and enflurane, the majority of anaesthetic drugs can be used. Anti-epileptic drug are mandatory. Antibioprophylaxis mainly against staphylococcus is systematic in internal CSF drainage. Rapid emergence from anaesthesia and extubation should be encouraged. Complications (infectious, mechanical and bleeding kinds) are frequent and are often the cause of reinterventions or revisions of the device, exposing the patients to iterative anaesthesia. Furthermore, patients with shunts are at risk of malfunction of the device when exposed to situations like pregnancy, magnetic resonance imaging, or laparoscopy. Under these circumstances, it is recommended to associate the neurosurgical team in the management of these patients and to verify that the shunt is working well before and after the procedure or event.

High-temperature superconducting surface coil for in vivo microimaging of the human skin.

A small, high-temperature superconducting (HTS) surface coil was used to improve the signal-to-noise ratio (SNR) for in vivo human skin microscopy at 1.5 T. The internal noise of the conventional copper coil limits the SNR for this application. Inductive measurements of the HTS coil parameters indicated that at 77 K its internal noise contributed about 4% of the total noise, and the predicted SNR gain was about 3.2-fold over that of a room-temperature copper coil. In vivo images of the human skin produced with the HTS coil showed highly resolved details and a 3.7-fold improvement in SNR over that obtained with the room-temperature copper coil. Magn Reson Med 45:376-382, 2001.

[Controlled hypertension and cerebral protection]. / Hypertension artérielle contrôlée et protection cérébrale.

Among the techniques of cerebral protection, the use of controlled arterial hypertension is based on the following arguments: 1) Cerebral ischaemia is the final common pathway of any insult to the brain, particularly through secondary lesions. Causes of secondary cerebral lesions include pressure under the brain retractors, temporary clipping, arterial hypotension, hypoxaemia, anaemia and hypercapnia. 2) In the brain, the critical lower value for cerebral blood flow is around 25 mL.100g-1.min-1, under which two types of ischaemic areas can be defined: the penlucida type where cerebral function is abolished, without permanent cerebral lesion and the penumbra type where cerebral tissue recovers only if flow is rapidly restored. In the latter case the duration of ischaemia is very important. 3) Cerebral blood flow is maintained stable within a large range of variations of mean arterial pressure through the autoregulation mechanisms, which is based on vasomotricity of the cerebral circulation, which implies major variations in cerebral blood volume. However, autoregulation needs several dozens of seconds to be achieved. Therefore, sudden variations in mean arterial pressure are associated with short lasting but major variations in cerebral blood volume. 4) In case of increased intracranial pressure, a decrease in cerebral perfusion pressure causes cerebral vasodilation through the autoregulation mechanism, with an increase in cerebral blood volume which will, in turn, increase intracranial pressure and thus decrease cerebral perfusion pressure, and so on. This is the vasodilatory cascade. The therapeutical increase in mean arterial pressure will correct this phenomenon and decrease intracranial pressure. This is called the vasoconstrictive cascade.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pharmacokinetics of pethidine after spinal anesthesia. Clinical implications]. / Pharmacocinétique de la péthidine après rachianesthésie. Implications cliniques.

Eleven male patients undergoing endoscopic resection for prostatic adenoma and bladder tumours under spinal anaesthesia received intrathecal pethidine 1 mg X kg-1. Plasma concentration and its evolution with time were assessed; pethidine plasma concentrations were determined by high performance liquid chromatography. Pethidine was rapidly and extensively absorbed. The peak plasma concentration of pethidine was 176 +/- 66 ng X ml-1 (range: 84-208) and the time to peak concentration was 2.3 +/- 1.4 h (range: 0.5-6 h). The terminal elimination half-life was 7.2 +/- 2.2 h (range: 4-11.5 h). The plasma concentrations of pethidine remained below 500-700 ng X ml-1, the minimum concentration necessary to obtain a systemic analgesic effect. Two patients required noramidopyrine as a complement at the 8th and 12th h respectively. No respiratory depression was observed. Intrathecal pethidine (1 mg X kg-1) was an effective agent for spinal anaesthesia: the prolonged postoperative analgesia was due to the drug acting on opioid receptors in the spinal cord. This led to the necessity of postoperative monitoring during 24 h after intrathecal pethidine administration.