Optimal frequency conversion in the nonlinear stage of modulation instability

We investigate multi-wave mixing associated with the strongly pump depleted regime of induced modulation instability (MI) in optical fibers. For a complete transfer of pump power into the sideband modes, we theoretically and experimentally demonstrate that it is necessary to use a much lower seeding modulation frequency than the peak MI gain value. Our analysis shows that a record 95 % of the input pump power is frequency converted into the comb of sidebands, in good quantitative agreement with analytical predictions based on the simplest exact breather solution of the nonlinear Schr\"odinger equation

Modulational instability in dispersion-kicked optical fibers

We study, both theoretically and experimentally, modulational instability in optical fibers that have a longitudinal evolution of their dispersion in the form of a Dirac delta comb. By means of Floquet theory, we obtain an exact expression for the position of the gain bands, and we provide simple analytical estimates of the gain and of the bandwidths of those sidebands. An experimental validation of those results has been realized in several microstructured fibers specifically manufactured for that purpose. The dispersion landscape of those fibers is a comb of Gaussian pulses having widths much shorter than the period, which therefore approximate the ideal Dirac comb. Experimental spontaneous MI spectra recorded under quasi continuous wave excitation are in good agreement with the theory and with numerical simulations based on the generalized nonlinear Schr\"odinger equation

Nonlinear envelope equation for broadband optical pulses in quadratic media

We derive a nonlinear envelope equation to describe the propagation of broadband optical pulses in second order nonlinear materials. The equation is first order in the propagation coordinate and is valid for arbitrarily wide pulse bandwidth. Our approach goes beyond the usual coupled wave description of $\chi^{(2)}$ phenomena and provides an accurate modelling of the evolution of ultra-broadband pulses also when the separation into different coupled frequency components is not possible or not profitable

Heteroclinic structure of parametric resonance in the nonlinear Schr\"odinger equation

We show that the nonlinear stage of modulational instability induced by parametric driving in the {\em defocusing} nonlinear Schr\"odinger equation can be accurately described by combining mode truncation and averaging methods, valid in the strong driving regime. The resulting integrable oscillator reveals a complex hidden heteroclinic structure of the instability. A remarkable consequence, validated by the numerical integration of the original model, is the existence of breather solutions separating different Fermi-Pasta-Ulam recurrent regimes. Our theory also shows that optimal parametric amplification unexpectedly occurs outside the bandwidth of the resonance (or Arnold tongues) arising from the linearised Floquet analysis

CPAP after endoscopic procedures as add-on therapy for the treatment of tracheal stenosis: a case series

Tracheal stenosis represents a possible complication in intubated or tracheotomised patients. Tracheal resection is currently the gold standard for the treatment of complex stenosis while granulomas and simple stenosis (e.g., web-like) are often treated by endoscopic procedures, which do not consistently give satisfactory long-term results, due to frequent relapses. Administering continuous positive airway pressure (CPAP) after endoscopic procedures might represent a new add-on option for the treatment of this complication. In this case series are presented two patients with tracheal stenosis showed after the removal of tracheostomy tube, both treated with CPAP. The results were straightforward: CPAP treatment helped to keep stable the tracheal lumen, without adverse effects. No further endoscopic dilations were necessary thereafter, with a likely positive impact on patients' quality of life and on health expenditure

Soliton annihilation into a polychromatic dispersive wave

International audienceWe investigate the propagation of a soliton in an axially-varying optical fiber with a progressive change from anomalous to normal dispersion regimes. Spectral and temporal measurements provide evidence for a complete annihilation of the soliton, which explodes into a polychromatic dispersive wave. This interpretation is confirmed by numerical solution of the generalized nonlinear Schrödinger equation

PARISROC, a Photomultiplier Array Integrated Read Out Chip

PARISROC is a complete read out chip, in AMS SiGe 0.35 !m technology, for photomultipliers array. It allows triggerless acquisition for next generation neutrino experiments and it belongs to an R&D program funded by the French national agency for research (ANR) called PMm2: ?Innovative electronics for photodetectors array used in High Energy Physics and Astroparticles? (ref.ANR-06-BLAN-0186). The ASIC (Application Specific Integrated Circuit) integrates 16 independent and auto triggered channels with variable gain and provides charge and time measurement by a Wilkinson ADC (Analog to Digital Converter) and a 24-bit Counter. The charge measurement should be performed from 1 up to 300 photo- electrons (p.e.) with a good linearity. The time measurement allowed to a coarse time with a 24-bit counter at 10 MHz and a fine time on a 100ns ramp to achieve a resolution of 1 ns. The ASIC sends out only the relevant data through network cables to the central data storage. This paper describes the front-end electronics ASIC called PARISROC.Comment: IEEE Nuclear Science Symposium an Medical Imaging Conference (2009 NSS/MIC

Dynamics of Turing and Faraday instabilities in a longitudinally modulated fiber-ring cavity

International audienceWe experimentally investigate the roundtrip-to-roundtrip dynamics of the modulation instability spectrum in a passive fiber ring cavity presenting an inhomogeneous dispersion profile. By implementing a real-time spectroscopy technique we are able to record successive single-shot spectra, which display the evolution of the system toward a stationary state. We find that the two instability regimes (Turing and Faraday) that compete in this kind of inhomogeneous cavities not only differ by their characteristic frequency but also by their dynamical behaviour. The dynamic transition between those two regimes of instability is also presented

Bouncing of a dispersive wave in a solitonic cage

International audienceWe report the experimental observation of a weak dis-persive wave trapping within a cage formed by two solitons in an optical fiber. We show that the disper-sive wave bouncing is accompanied by a back and forth wavelength conversion of the probe to an idler wave. Besides, we observed the destruction of the soliton cage when dispersive wave power is increased, leading to the collision of the solitons