272 research outputs found
Vortex soliton tori with multiple nested phase singularities in dissipative media
We show the existence of stable two- and three-dimensional vortex solitons
carrying multiple, spatially separated, single-charge topological dislocations
nested around a vortex-ring core. Such new nonlinear states are supported by
elliptical gain landscapes in focusing nonlinear media with two-photon
absorption. The separation between the phase dislocations is dictated mostly by
the geometry of gain landscape and it only slightly changes upon variation of
the gain or absorption strength.Comment: 17 pages, 5 figures, to appear in Physical Review
Topological light bullets supported by spatio-temporal gain
We reveal that the competition between diffraction, cubic nonlinearity,
two-photon absorption, and gain localized in both space and time results in
arrest of collapse, suppression of azimuthal modula-tion instabilities for
spatiotemporal wavepackets, and formation of stable three-dimensional light
bul-lets. We show that Gaussian spatiotemporal gain landscapes support bright,
fundamental light bullets, while gain landscapes featuring a ring-like spatial
and a Gaussian temporal shapes may support stable vortex bullets carrying
topological phase dislocations.Comment: 19 pages, 5 figures, to appear in Physical Review
Convection-induced nonlinear-symmetry-breaking in wave mixing
We show that the combined action of diffraction and convection (walk-off) in
wave mixing processes leads to a nonlinear-symmetry-breaking in the generated
traveling waves. The dynamics near to threshold is reduced to a Ginzburg-Landau
model, showing an original dependence of the nonlinear self-coupling term on
the convection. Analytical expressions of the intensity and the velocity of
traveling waves emphasize the utmost importance of convection in this
phenomenon. These predictions are in excellent agreement with the numerical
solutions of the full dynamical model.Comment: 5 page
Effects of a localized beam on the dynamics of excitable cavity solitons
We study the dynamical behavior of dissipative solitons in an optical cavity
filled with a Kerr medium when a localized beam is applied on top of the
homogeneous pumping. In particular, we report on the excitability regime that
cavity solitons exhibits which is emergent property since the system is not
locally excitable. The resulting scenario differs in an important way from the
case of a purely homogeneous pump and now two different excitable regimes, both
Class I, are shown. The whole scenario is presented and discussed, showing that
it is organized by three codimension-2 points. Moreover, the localized beam can
be used to control important features, such as the excitable threshold,
improving the possibilities for the experimental observation of this
phenomenon.Comment: 9 Pages, 12 figure
Strongly localized moving discrete dissipative breather-solitons in Kerr nonlinear media supported by intrinsic gain
We investigate the mobility of nonlinear localized modes in a generalized discrete Ginzburg-Landau-type model, describing a one-dimensional waveguide array in an active Kerr medium with intrinsic, saturable gain and damping. It is shown that exponentially localized, traveling discrete dissipative breather-solitons may exist as stable attractors supported only by intrinsic properties of the medium, i.e., in the absence of any external field or symmetry-breaking perturbations. Through an interplay by the gain and damping effects, the moving soliton may overcome the Peierls-Nabarro barrier, present in the corresponding conservative system, by self-induced time-periodic oscillations of its power (norm) and energy (Hamiltonian), yielding exponential decays to zero with different rates in the forward and backward directions. In certain parameter windows, bistability appears between fast modes with small oscillations and slower, large-oscillation modes. The velocities and the oscillation periods are typically related by lattice commensurability and exhibit period-doubling bifurcations to chaotically "walking" modes under parameter variations. If the model is augmented by intersite Kerr nonlinearity, thereby reducing the Peierls-Nabarro barrier of the conservative system, the existence regime for moving solitons increases considerably, and a richer scenario appears including Hopf bifurcations to incommensurately moving solutions and phase-locking intervals. Stable moving breathers also survive in the presence of weak disorder
Radially symmetric and azimuthally modulated vortex solitons supported by localized gain
We discover that a spatially localized gain supports stable vortex solitons
in media with cubic nonlinearity and two-photon absorption. The interplay
between nonlinear losses and gain in amplifying rings results in suppression of
otherwise ubiquitous azimuthal modulation instabilities of radially symmetric
vortex solitons. We uncover that the topology of the gain profile imposes
restrictions on the maximal possible charge of vortex solitons. Symmetry
breaking occurs at high gain levels resulting in the formation of necklace
vortex solitons composed of asymmetric bright spots.Comment: 11 pages, 4 figures, to appear in Optics Letter
Stable vortex and dipole vector solitons in a saturable nonlinear medium
We study both analytically and numerically the existence, uniqueness, and
stability of vortex and dipole vector solitons in a saturable nonlinear medium
in (2+1) dimensions. We construct perturbation series expansions for the vortex
and dipole vector solitons near the bifurcation point where the vortex and
dipole components are small. We show that both solutions uniquely bifurcate
from the same bifurcation point. We also prove that both vortex and dipole
vector solitons are linearly stable in the neighborhood of the bifurcation
point. Far from the bifurcation point, the family of vortex solitons becomes
linearly unstable via oscillatory instabilities, while the family of dipole
solitons remains stable in the entire domain of existence. In addition, we show
that an unstable vortex soliton breaks up either into a rotating dipole soliton
or into two rotating fundamental solitons.Comment: To appear in Phys. Rev.
Modulational instability in periodic quadratic nonlinear materials
We investigate the modulational instability of plane waves in quadratic
nonlinear materials with linear and nonlinear quasi-phase-matching gratings.
Exact Floquet calculations, confirmed by numerical simulations, show that the
periodicity can drastically alter the gain spectrum but never completely
removes the instability. The low-frequency part of the gain spectrum is
accurately predicted by an averaged theory and disappears for certain gratings.
The high-frequency part is related to the inherent gain of the homogeneous
non-phase-matched material and is a consistent spectral feature.Comment: 4 pages, 7 figures corrected minor misprint
BAIKAL experiment: status report
We review the present status of the Baikal Neutrino Project and present the
results obtained with the deep underwater neutrino telescope NT-200.Comment: 4 pages, 3 figures. Presented at TAUP 2001 (7th international
workshop on Topics in Astroparticle and Underground Physics), Sep. 2001,
Laboratori Nazionali del Gran Sasso, Assergi, Ital
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