Ricerc@Sapienza

Spatiotemporal light beam dynamics in multimode optical fibers (MMFs) has emerged in recent years as fertile research domain in nonlinear optics. Intriguing spatiotemporal wave propagation phenomena such as multimode optical solitons and parametric instabilities leading to ultra-wideband sideband series, although predicted quite a long time ago, have only been experimentally observed in MMFs in the last few years.

Spatiotemporal light beam dynamics in multimode opti- cal fibers (MMFs) has emerged as a fertile domain of scientific research in nonlinear optics and physics]. Intriguing spatiotemporal wave propagation phenomena such as multimode optical solitons, and parametric instabilities leading to ultra-wideband sideband series [3] have only been experimentally observed in MMFs over the last few years. Among these, we are interested to study here the phenomenon of spatial self-condensation or self-cleaning of multimode light beams in MMFs.

We overview experiments associated with nonlinear beam propagation in multimode optical fibers. We show that complex spatio-temporal phenomena permit to control the nonlinear beam reshaping across its spatial, temporal and spectral dimensions.

Recent experiments have shown that nonlinear wave propagation in multimode optical fibers leads to complex spatio-temporal phenomena. In this talk, we introduce new approaches for the control and optimization of nonlinear beam reshaping in the spatial, temporal and spectral dimensions. The first approach applies to spatial beam self-cleaning the technique of transverse wavefront shaping, which permits to launch an optimized input mode combination, that results in the stable generation of a whole nonlinear mode alphabet at the fiber output.

We provide a perspective overview of the emerging field of nonlinear optics in multimode optical fibers. These fibers enable new methods for the ultrafast light-activated control of temporal, spatial, and spectral degrees of freedom of intense, pulsed beams of light, for a range of different technological applications.

Simple Riemann waves (RWs), solutions of the Inviscid Burgers’ Equation (IBE), are of fundamental importance to study shock formation in different physical frameworks beyond hydrodynamics [1]. Recently, RW signatures in time domain have been reported in the context of nonlinear optical fibres [2-4]. Nevertheless, only limited control was demonstrated on the propagation of these peculiar optical pulses [5]. Here, we describe a method to control the nonlinear dynamics of their spatial counterpart, i.e., Riemann beams (RBs).

In this paper, we numerically investigate the process of beam self-cleaning in a graded-index multimode optical fiber, by using the coupled-mode model. We introduce various models of random linear coupling between spatial modes, including coupling between all modes, or only between degenerate ones, and investigate the effects of random mode coupling on the beam self-cleaning process. The results of numerical investigations are in complete agreement with our experimental data.

We experimentally demonstrate the conservation of the average mode number in the process of Kerr beam self-cleaning in a graded-index multimode optical fiber, in analogy with wave condensation in hydrodynamic 2D turbulence.

We theoretically investigate the formation of frequency combs in a dispersive second-harmonic generation cavity system, and predict the existence of quadratic cavity solitons in the absence of a temporal walk-off.

We experimentally demonstrate polarization-dependent Kerr spatial beam self-cleaning into the LP11 mode of an Ytterbium-doped multimode optical fiber with parabolic gain and refractive index profiles.