By: Majid Taki
From: Université des Sciences et Technologies de Lille, France
At: Instituto de Investigação Interdisciplinar, B1-01
In the ocean, giant waves (also called killer waves, freak or rogue waves) are extremely rare and strong events. They are not well understood yet and the conditions, which favour their emergence, are unclear. Very recently, it was shown that the governing equations as well as the statistical properties of an optical pulse propagating inside an optical ﬁbre mimic very well these gigantic surface waves in the ocean. Here we generate both experimentally and numerically optical rogue waves in a photonic crystal ﬁber (microstructured ﬁber) with continuous wave (CW) pumps. This is relevant for establishing an analogy with rogue waves in an open ocean. After recalling fundamental rogue waves known as Akhmediev breathers that are solutions of pure nonlinear SchrÃ¶dinger (NLS) equation, we analytically demonstrate that a generalized NLS equation, which governs the propagation of light in the ﬁber, exhibits convective instability. The latter provides one of the main explanations of the optical rogue wave extreme sensitivity to noisy initial conditions at the linear stage of their formation. In the highly nonlinear regime, we provide the evidence that optical rogue waves result from soliton collisions leading to the rapid appearance/disappearance of a powerful optical pulse. Finally we report on an experimental observation of spatial rogue patterns in an optical feedback system. These patterns occur in a highly nonlinear regime characterized by a continuous space frequency spectrum associated with rare and intense localized peaks.