Thesis of Adrien Kraych

Amphithéâtre Pierre Glorieux (CERLA) Thesis defense of Adrien Kraych - laboratory Phlam PhD supervisor : Stéphane Randoux Co-PhD supervisor : Pierre Suret Modulation Instability in a recirculating fiber loop Abstract :
This thesis work deals with the modulation instability in a recirculating fiber
loop. Modulational instability (called Benjamin-Feir instability in hydrodynamics) is
responsible for the exponential amplification of weak perturbations of a plane wave,
which leads to the plane wave destabilization and the emergence of intense coherent
structures localized in space and time. The rich and complex spatio-temporal dynamic
resulting from this mechanism is the source of important interest in several fields of
physics where the nonlinear Schrödinger equation plays an important role. In order to
study this phenomenon, we set up a recirculating fiber loop allowing us to measure the
spatio-temporal evolution of a light wave propagating in an optical fiber. The spatiotemporal
dynamics resulting from the modulation instability differ according to the nature
of the perturbation which destabilizes the plane wave. We have used the recirculation
fiber loop to study the dynamics of two types of perturbations: local and stochastic. In
the case of local perturbation, we have demonstrated, for the first time, the emergence of
oscillating nonlinear structures predicted within the framework of certain mathematical
theories. In the case of a random perturbation, our work falls within the field of integrable
turbulence. We were able to observe spatio-temporal dynamics until then only revealed
by numerical simulations and to confront the statistical properties of our experimental
results with numerical simulations of the nonlinear Schrödinger equation.
Keywords: nonlinear optics, solitons; optical fibers; integrable turbulence; nonlinear
statistical optics; nonlinear schrödinger equation
Laboratoire de Physique des Lasers, Atomes et Molécul