[Bilateral peroneal neuropathy following bariatric surgery]. / Neuropathie bilatérale du nerf fibulaire commun après chirurgie bariatrique.

We report the case of bilateral peroneal neuropathy following massive weight loss after bariatric surgery. A few months after a gastric by-pass, the patient developed sequentially within 6 months a L2-L3 herniated disc that required surgery, a severe right peroneal nerve palsy that led to decompressive surgery and finally contralateral peroneal nerve palsy also operated. The electrophysiological analysis confirmed the clinical suspicion of peroneal nerve compression at the fibular head. Postoperative course was favorable. Literature reports peroneal nerve palsy after slimming, mostly when weight loss is fast and marked although the issue is rarely bilateral.

20 THz-bandwidth continuous-wave fiber optical parametric amplifier operating at 1 µm using a dispersion-stabilized photonic crystal fiber.

We report the experimental demonstration of a continuous-wave all-fiber optical parametric amplifier in the 1 µm band with a record bandwidth of more than 20 THz and a peak gain of almost 40 dB. This is achieved by using a photonic crystal fiber with a high figure of merit and strongly reduced longitudinal dispersion fluctuations. Due to their unique bandwidth and gain characteristics, fiber parametric amplifiers at 1 µm provide an interesting alternative to solid-state or ytterbium-doped fiber amplifiers for ultrafast optical pulse and signal processing.

Grating-free Raman laser using highly nonlinear photonic crystal fiber.

We demonstrate a Raman laser made from a grating-free highly-nonlinear photonic crystal fiber. The laser threshold power is lower than 600 mW and laser power characteristics recorded in experiments are accurately described from the usual simplest model dealing only with stationary evolutions of total optical powers [J. Opt. Soc. Am. 69, 803-807 (1979)]. In our theoretical treatment, reflectivity coefficients are fixed parameters, in strong contrast with procedures usually implemented to describe Raman fiber lasers made with fiber Bragg gratings. Experimental investigations of the spectral properties of our grating-free Raman fiber laser evidence that the shape of the Stokes power spectrum remains remarkably Gaussian whatever the incident pump power. Increasing the incident pump power induces a drift of the Stokes wavelength together with a broadening of the Stokes optical spectrum. Investigations on the role of light polarization on laser characteristics show that our grating-free Raman fiber laser behaves as a Raman laser made with a standard polarization maintaining fiber.

Efficient Bragg gratings in phosphosilicate and germanosilicate photonic crystal fiber.

We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers. We then conducted a study of the thermal stability of the BGs in PCFs through 30 min of isochronal annealing. At the same time we discuss the role played by the microstructuration and the doping with regard to the grating contrast and the Bragg wavelength stability.

Light transmission in multiple or single subwavelength trefoil channels of microstructured fibers.

We evaluate the trefoil channels present between the holes of microstructured fibers as a potential dense array of small waveguides. In channels with an inner radius of 330nm, calculations indicate possible propagation with a mode waist of ~350nm at lambda=670nm, near to the diffraction limit. Actual measurements have been performed on a 1-meter fiber section, with injection by a microlensed fiber and mapping of output by near-field scanning optical microscopy. They show that light can be output in individual channels or in several of them, depending on the injection. The observed waist is ~500nm, possibly due to experimental widening. Estimated propagation losses are <20dB/m. Since each channel occupies only 2microm2, this structure opens a way to dense parallel optical processing.