Ricerc@Sapienza

We show that Kerr beam self-cleaning results from parametric mode mixing instabilities that generate a number of nonlinearly interacting modes with randomized phases - optical wave turbulence, followed by a direct and inverse cascade towards high mode numbers and condensation into the fundamental mode, respectively. This optical self-organization effect is an analogue to wave condensation that is well known in hydrodynamic 2D turbulence.

Narrowband Raman lasing in a polarization-maintaining two-core fiber (TCF) is demonstrated. Femtosecond point-by-point inscription of fiber Bragg gratings (FBGs) in individual cores produces a half-open cavity with random distributed feedback. The laser linewidth in the cavity with a single FBG inscribed in one core of the TCF reduced by ∼2 times with respect to the cavity with a fiber loop mirror. It is shown that the inscription of two FBGs in different cores leads to the formation of a Michelson-type interferometer, leading to the modulation of generation spectra near threshold.

We demonstrate thulium-doped fiber amplification of sub-nanosecond pulses generated at 1870 nm by exploiting spatiotemporal nonlinear dynamics in graded-index multimode fibers. The microjoule pulses at 1870 nm trigger supercontinuum generation in InF3 fiber.

We demonstrate self-induced high beam quality recovery in Er-Yb codoped multimode active fiber with parabolic refractive index profile of the core. Nonlinear beam cleanup is accompanied by Raman and parametric instability sideband generation.

We introduce the concept of distributed Kerr-lens mode-locking in GRIN fiber lasers. Our analysis demonstrates that proper control of spectral and spatial graded dissipation results in the self-emergence of stable dissipative solitons.

We experimentally demonstrate the fission of femtosecond pulses in a GRIN standard fiber, leading to high-energy multimode solitons that undergo huge Raman fre- quency shifts, and exhibit complex multisoliton dynamics

We experimentally demonstrate high-resolution mapping of the spatio-temporal dynamics of the beam cleaning process in graded index multimode fibers. This high-resolution characterization reveals the time-dependent nature of the beam self-cleaning process.

We demonstrate Kerr self-cleaning of beams in an Ytterbium doped multimode fiber taper with exponentially decreasing nonlinearity, with no accompanying frequency conversion or spectral broadening.

We show experimentally that geometric parametric instability in graded-index multimode fibers is composed by several multimode spectral components. The experimental observation is obtained by using a new 3D technique of high-resolution spatial and spectral analysis.

We report on the generation of third-order Riemann pulses in nonlinear optical fiber, obtained by tailoring the initial pulse in presence of high-order dispersion and Kerr nonlinearity. Analytical and numerical results show controllable pulse steepening and shock formation