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We investigate the formation of collisionless shocks along the spatial profile of a Gaussian laser beam propagating in nonlocal nonlinear media. For defocusing nonlinearity the shock survives the smoothing effect of the nonlocal response, though its dynamics is qualitatively affected by the latter, whereas for focusing nonlinearity it dominates over filamentation. The patterns observed in a thermal defocusing medium are interpreted in the framework of our theory.

We investigate the self-trapping phenomenon in one-dimensional nonlinear waveguide arrays. We discuss various approximate analytical descriptions of the discrete self-trapped solutions. We analyze the packing, steering, and collision properties of these solutions, by means of a variational approach and soliton perturbation theory. We compare the analytical and numerical results

We investigate the propagation of a dark beam in a defocusing medium in the strong nonlinear regime. We observe for the first time a shock fan filled with noninteracting one-dimensional gray solitons that emanates from a gradient catastrophe developing around a null of the optical intensity. This scenario turns out to be very robust, persisting also when the material nonlocal response averages the nonlinearity over dimensions much larger than the emerging soliton filaments.

Optical fibres constitute a unique ground to investigate one of the most prolific and controversial discovery of modern physics, namely the Fermi-Pasta-Ulam (FPU) recurrence, which becomes manifest as the growth and decay cycles of a comb of sideband pairs from a weakly modulated pump, occurring via modulational instability (MI). To date, however, the genuine spontaneous symmetry-breaking nature of the MI recurrence was never observed (in any area of physics) due to intrinsic limitations of the experimental realizations. In this work, we overcome such limitations by implementing a novel experimental technique which allows us to reconstruct the longitudinal evolution in amplitude and phase of frequency modes via heterodyne detection of the backscattered light. As a result, we clearly observe how the control of the input modulation seed results into qualitatively different types of FPU recursive behavior associated with the spontaneously broken symmetry.

We observe the formation of an intense optical wavepacket fully localized in all dimensions, i.e. both longitudinally (in time) and in the transverse plane, with an extension of a few tens of fsec and microns, respectively. Our measurements show that the self-trapped wave is a X-shaped light bullet spontaneously generated from a standard laser wavepacket via the nonlinear material response (i.e., second-harmonic generation), which extend the soliton concept to a new realm, where the main hump coexists with conical tails which reflect the symmetry of linear dispersion relationship.PACS numbers: 03.50. De,42.65.Tg,05.45.Yv,42.65.Jx Defeating the natural spreading of a wavepacket (WP) is a universal and challenging task in any physical context involving wave propagation. Ideal particle-like behavior of WPs is demanded in applications, such as microscopy, tomography, laser-induced particle acceleration, ultrasound medical diagnostics, Bose-Einstein condensation, volume optical-data storage, optical interconnects, and those encompassing long-distance or high-resolution signal transmission. The quest for light WPs that are both invariant (upon propagation) and sufficently localized in all dimensions (3D, i.e., both transversally and longitudinally or in time) against spreading "forces" exerted by diffraction and material group-velocity dispersion (GVD,) has motivated long-standing studies, which have followed different strategies in the linear [1, 2, 3, 4, 5] and nonlinear [6,7] regime, respectively.In the linear case, to counteract material (intrinsic) GVD, one can exploit the angular dispersion (i.e., dependence of propagation angle on frequency) that stems from a proper WP shape. The prototype of such WPs is the X-wave [2], a non-monochromatic, yet non-dispersive, superposition of non-diffracting cylindrically symmetric Bessel J 0 (so-called conical or Durnin [1]) beams, experimentally tested in acoustics [3], optics [4] and microwave antennae [5]. Importantly, in the relevant case of WPs with relatively narrow spectral content both temporally (around carrier frequency ω 0 ) and spatially (around propagation direction z, i.e. paraxial WPs), X-waves require normally dispersive media (k ′′ > 0). In this case, a WP with disturbance E(r, t, z) exp, has a slowly-varying envelope E = E(r, t, z) obeying the standard wave equationLaplacian, where ∇ 2 ⊥ = ∂ 2 rr + r −1 ∂ r is the transverse Laplacian, and we limit our attention to luminal WPs traveling at light group-velocity 1/k ′ = dk/dω| introducing the retarded time t = T − k ′ z in the WP barycentre frame. Propagation-invariant waves E(r, t, z) = E(r, t, z = 0) exp(iβz) can be achieved whenever their input spatio-temporal spectra E(K, Ω, z = 0) lie along the characteristics of the dispersion relationship k ′′ Ω 2 /2 − K 2 /(2k 0 ) = β, which follows from Eq. (1) in Fourier space (K, Ω) (K is the transverse wavevector related to cone angle with z-axis θ ≃ sin θ = K/k 0 , and Ω = ω − ω 0 ). In the normal GVD regime (k ′′ > 0) these curves, displayed in Fig. 1(a), refl...

A synchronously pumped modulational-instability ring laser with a nonlinear dispersive fiber can be operated in both the anomalous and the normal dispersion regimes. We obtain simple analytical expressions for the sideband gain in the cavity by using an average pulse formalism. The numerical simulations indicate that stable stationary trains of pulses may be formed in the cavity. This is independent of the sign of the dispersion.