Ricerc@Sapienza

We demonstrate beam self-cleaning in a tapered Ytterbium-doped graded- index multimode fiber in both active and passive configurations, without accompanying self-phase modulation induced spectral broadening or frequency conversion

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.

The buildup process of coherent structures and patterns from the composite balance between conservative and
dissipative effects is a universal phenomenon that occurs in various areas of physics, ranging from quantum
mechanics to astrophysics. Dissipative solitons are highly coherent solutions of nonlinear wave equations, and
provide an excellent research platform for ultrafast transient phenomena. Herein, by taking advantage of the fast
detection technique provided by the dispersive Fourier transform, we experimentally observe the spectral

We introduce a mechanism of stable spatiotemporal soliton formation in a multimode fiber laser. This is based
on spatially graded dissipation, leading to distributed Kerr-lens mode locking. Our analysis involves solutions of
a generalized dissipative Gross-Pitaevskii equation. This equation has a broad range of applications in nonlinear
physics, including nonlinear optics, spatiotemporal pattern formation, plasma dynamics, and Bose-Einstein
condensates. We demonstrate that the careful control of dissipative and nondissipative physical mechanisms

We experimentally demonstrate that spatial beam self-cleaning can be highly efficient when obtained with a few-mode excitation in graded-index multimode optical fibers. By using 160 ps long, highly chirped (6 nm bandwidth at -3dB) optical pulses at 1562 nm, we demonstrate a one-decade reduction of the power threshold for spatial beam self-cleaning, with respect to previous experiments using pulses with laser wavelengths at 1030-1064 nm. Self-cleaned beams remain spatio-temporally stable for more than a decade of their peak power variation.

We experimentally demonstrate spatial beam self-cleaning in an Yb-doped graded-index multimode fiber taper, both in passive and active configurations. The input laser beam at 1064 nm was injected for propagation from the small to the large core side of the taper, with laser diode pumping in a counterdirectional configuration. The Kerr effect permits to obtain high-beam quality amplification with no accompanying frequency conversions. As a result, our nonlinear taper amplifier may provide an important building block for multimode fiber lasers and amplifiers.

Optical frequency combs are one of the most remarkable inventions in recent decades.
Originally conceived as the spectral counterpart of the train of short pulses emitted by mode-locked
lasers, frequency combs have also been subsequently generated in continuously pumped
microresonators, through third-order parametric processes. Quite recently, direct generation of
optical frequency combs has been demonstrated in continuous-wave laser-pumped optical resonators
with a second-order nonlinear medium inside. Here, we present a concise introduction to such

A two-level iterative algorithm for finding stationary solutions of coupled nonlinear Schrödinger equations describing the propagation dynamics of an electromagnetic pulse in multimode and multicore optical fibers of various structures was developed and tested. Using as an example the proposed analytical soliton solution which is localized in space and time, test calculations were performed, and the convergence of the algorithm was demonstrated.

Continuously pumped passive nonlinear cavities can be harnessed for the creation of novel optical frequency combs. While most research has focused on third-order "Kerr" nonlinear interactions, recent studies have shown that frequency comb formation can also occur via second-order nonlinear effects. Here, we report on the formation of quadratic combs in optical parametric oscillator (OPO) configurations. Specifically, we demonstrate that optical frequency combs can be generated in the parametric region around half of the pump frequency in a continuously driven OPO.

We experimentally demonstrate simultaneous spatial and temporal compression in the propagation of light pulses in multimode nonlinear optical fibers. We reveal that the spatial beam self-cleaning recently discovered in graded-index multimode fibers is accompanied by significant temporal reshaping and up to fourfold shortening of the injected subnanosecond laser pulses.