Francois Copie
maître de conférences
CNU : SECTION 30 - MILIEUX DILUES ET OPTIQUE
- Laboratoire / équipe
- Composantes, facultés
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Domaines de recherche
Nonlinear optics, fiber optics experiments, Ultra-fast dynamics, Instabilities
Francois Copie
maître de conférences
Présentation
Actualités
We study experimentally the early stages of integrable turbulence of unidirectional deep water gravity waves. By generating partially coherent waves in a 148−m-long wave flume, we observe the emergence of high-amplitude structures formed by nonlinear focusing, commonly referred to as rogue waves. This work confronts the experiment with two recent results obtained in the framework of the nonlinear Schrödinger equation (NLSE), namely that (i) these structures can be locally fitted by a Peregrine soliton and (ii) their emergence leaves a visible trace on the evolution of statistical parameters such as kurtosis. We show that (i) yields accurate results as long as the wave steepness remains moderate, whereas (ii) is very robust and remains valid beyond the assumption of integrability. Numerical simulations of the NLSE and of the fully nonlinear dynamical equations are also performed to support these results.
https://link.aps.org/doi/10.1103/PhysRevFluids.5.082801
We report water wave experiments performed in a long tank where we consider the evolution of nonlinear deep-water surface gravity waves with the envelope in the form of a large-scale rectangular barrier. Our experiments reveal that, for a range of initial parameters, the nonlinear wave packet is not disintegrated by the Benjamin-Feir instability but exhibits a specific, strongly nonlinear modulation, which propagates from the edges of the wave packet toward the center with finite speed. Using numerical tools of nonlinear spectral analysis of experimental data, we identify the observed envelope wave structures with focusing dispersive dam break flows, a peculiar type of dispersive shock waves recently described in the framework of the semiclassical limit of the 1D focusing nonlinear Schrödinger equation (1D-NLSE). Our experimental results are shown to be in a good quantitative agreement with the predictions of the semiclassical 1D-NLSE theory. This is the first observation of the persisting dispersive shock wave dynamics in a modulationally unstable water wave system.
https://link.aps.org/doi/10.1103/PhysRevFluids.5.034802
François a présenté les derniers résultats de mesure rapide du processus d'instabilité de modulation à Photonics West, San Francisco dans la session Real-time Measurements, Rogue Phenomena, and Single-Shot Applications.
We present two single-shot experiments devoted to the study of noise-induced modulation instability (MI) in optical fibers. The first one, performed in a recirculating fiber loop, enables the first observation of the space-time dynamics of MI. The second one uses a heterodyne version of time microscope (SEAHORSE) that enables the single-shot observation of the phase and of the amplitude of the nonlinear random waves. Our SEAHORSE has a subpicosecond resolution and allows observation within a window of observation of 160ps. Our observations provide new experimental insights into the fundamental problem of spontaneous MI.
We review the different dynamical mechanisms leading to the emergence of coherent structures in physical systems described by the integrable one-dimensional nonlinear Schrödinger equation (1DNLSE) in the focusing regime. In this context, localized and coherent structures are very often associated to rogue wave events. We focus on one-dimensional optical experiments and in particular on (single mode) optical fibers experiments. In the focusing regime of 1DNLSE, the so-called modulation instability (MI), arising from nonlocal perturbation of the plane waves, is the most common phenomenon. Alongside the standard MI, other mechanisms are responsible for the emergence of rogue waves. We classify the different scenarii by considering those induced by small perturbations of unstable stationary state (the plane waves) and the ones arising from the self-focusing of large pulses without any perturbation. In the former case, the perturbations can be local, global, random or deterministic. In the latter case, the self-focusing dynamics can be observed both with isolated pulses or with large initial fluctuations of the optical power. We review the dynamics of emergence of localized structures in all these different scenarii.