Strain induced polarization chaos in a solitary VCSEL.

Physical curiosity at the beginning, optical chaos is now attracting increasing interest in various technological areas such as detection and ranging or secure communications, to name but a few. However, the complexity of optical chaos generators still significantly hinders their development. In this context, the generation of chaotic polarization fluctuations in a single laser diode has proven to be a significant step forward, despite being observed solely for quantum-dot vertical-cavity surface-emitting lasers (VCSELs). Here, we demonstrate experimentally that a similar polarization dynamics can be consistently obtained in quantum-well VCSELs. Indeed, by introducing anisotropic strain in the laser cavity, we successfully triggered the desired chaotic dynamics. The simplicity of the proposed approach, based on low-cost and easily available components including off-the-shelf VCSELs, paves the way to the wide spread use of solitary VCSELs for chaos-based applications.

Physical random bit generation from chaotic solitary laser diode.

We demonstrate the physical generation of random bits at high bit rates (> 100 Gb/s) using optical chaos from a solitary laser diode and therefore without the complex addition of either external optical feedback or injection. This striking result is obtained despite the low dimension and relatively small bandwidth of the laser chaos, i.e. two characteristics that have been so far considered as limiting the performances of optical chaos-based applications. We unambiguously attribute the successful randomness at high speed to the physics of the laser chaotic polarization dynamics and the resulting growth rate of the dynamical entropy.

Bistability of time-periodic polarization dynamics in a free-running VCSEL.

We report experimentally a bistability between two limit cycles (i.e. time-periodic dynamics) in a free-running vertical-cavity surface-emitting laser. The two limit cycles originate from a bifurcation on two elliptically polarized states which exhibit a small frequency difference and whose main axes are symmetrical with respect to the linear polarization eigenaxes at threshold. We demonstrate theoretically that this peculiar behavior can be explained in the framework of the spin-flip model model by taking into account a small misalignment between the phase and amplitude anisotropies.

Hopf bifurcation to square-wave switching in mutually coupled semiconductor lasers.

Using advanced continuation techniques for dynamical systems, we elucidate the bifurcations leading to asymptotically stable square-wave pulsing and polarization mode switching in semiconductor lasers with mutual time-delayed and polarization rotating coupling. We find that the increase of coupling strength leads to a cascade of Hopf bifurcations on a mixed-mode steady state up to a transcritical bifurcation on a so-called pure-mode steady state where both lasers emit with the injected polarization state. From these successive Hopf bifurcations emerge time-periodic solutions that have a period close to the laser relaxation oscillation for weak coupling but a period close to twice the time delay for large coupling strength. The wave form of the time-periodic solutions also evolves from harmonic pulsing up to square-wave pulsing as has been observed recently in experiments.

[Spontaneous rhinorrhea of a rare etiology (apropos of empty sella turcica)]. / Rhinorrhée spontanée d'étiologie rare (à propos d'un cas de selle turcique vide).

The authors report a case of non traumatic rhinorrhea due to an empty sella turcica. Such an intra sellar arachnoidocele compress the pituitary gland against the posterior wall, erode the floor and lead to CSF rhinorrhea through the sphenoidal sinus. Diagnosis and treatment are best accomplished by a team approach involving otolaryngologist, neurosurgeon and neuroradiologist. CT Scan and IRM explain the diagnosis. Treatment can be accomplished by a transeptal transphenoidal approach with localization and repair of the leak in the absence of increased intracranial pressure.

[New tympanomastoid repair in open technics: Galea's flap]. / Nouvel aménagement tympano-mastoïdien dans les techniques ouvertes: le lambeau de Galéa.

After an anatomical review, the authors describe the method for obtaining the temporo-parietal facial flap and its particularities in the rehabilitation of the canal down technic. The main indications of this flap are: the rehabilitation of unstable cavities, a Palva's flap alternation, a solution to the filling up after petrectomy or enlarged canal down technic.

[Current status of the treatment of nasal septal perforations]. / Etat actuel du traitement des perforations de la cloison nasale.

If the most part of the patients with septal perforation have an history of previous surgery, only few of them present symptoms and require surgical repair in spite of the various techniques described in the literature. Bilateral naso-septal mucosal flaps with temporalis fascia interposition graft give the best results. That's why the use of more complicated process remain the exception. Owing to the dubiousness of these reconstructions, it seems advisable to point out the value of preventive actions in order to preserve the nasal physiology.

Craniofacial lesions by grindstone wheels.

The authors report two new cases of craniofacial lesions due to the explosion of grindstone wheels and consider, after a short technological introduction, the specific features of these lesions diagnostically and therapeutically. These wheels are subject to mechanical shocks, may be run too fast for their capabilities, and may become overheated during use. In explosions, fragments may penetrate deeply, and are frequently small and difficult to see on X-rays because they are not very radio-opaque. Prevention of these injuries is most important: when they happen, surgeons must search carefully for all fragments.