Kerr effect

The non-linear multimode optical fibers are opened a new window to study the spectral, spatial and temporal degrees of freedom of light beams that has been received a great fundamental and applicative interest during the last decades. In this article, we demonstrate spatial beam self-cleaning and supercontinuum generation in a new type of multimode fiber amplifier, consisting of a Ytterbium-doped (Yb-doped) multimode fiber taper with parabolic index refractive and doping profile, and a length of 9.5 m with a core diameter exponentially decreasing along its length from 120 to 40 microns. The beam self-cleaning, a bell-shaped output beam profile, has been achieved in passive configuration with an input beam peak power threshold of 20 kW and further increasing the input power causes no significant frequency conversion that can be attributed to the first Raman Stokes sideband. In active configuration, the gain leads to combine self-cleaning with supercontinuum generation, spanning from the visible to the mid-infrared (520-2600 nm), which is due to the geometric parametric instability and the Raman stokes sideband. In both configurations, the self-beam cleaning in the tapered fiber can be ascribed to the accelerated self-imaging. Finally, we studied the evolution of self-cleaning and super continuum generation as a function of taper length in active configuration to analyze the spatial and spectral beam dynamics resulting accelerated self- imaging. We observed that the speckled output spatial distribution in the first meters evolved into a dual lobe, LP11 mode, and finally into the fundamental mode (LP01). The results obtained confirm the combination of accelerated self-imaging with landscape dissipative in the tapered Yb-doped multimode fiber with graded index profile that leads to control spectral and spatial light beams in the active mode.

Ultra-high-Q microresonators can confine extremely large amounts of optical energy in tiny mode volumes. This talk will focus on recent realizations of nonlinear interaction of counterpropagating light in these resonators. Particularly, above a certain threshold power, light of a given frequency can only circulate in one direction. Experimental and theoretical results show spontaneous symmetry breaking that follows from the interaction of the counterpropagating light. The resulting nonreciprocity of the light propagation in the microresonators can be used for novel applications including integrated photonic isolators and circulators.

Nonlinear propagation of optical pulses in multimode fibers is subject to complex spatio-temporal phenomena. We outline different strategies for the control and optimization of nonlinear mode coupling. The first approach involves transverse wavefront shaping of the input beams, which permits to launch an optimized mode combination, that results in the generation of a stable nonlinear mode alphabet at the fiber output. The second approach involves the longitudinal variation of the core diameter of multimode active and passive tapers, which leads to tailored supercontinuum generation with high spatial beam quality.