65 research outputs found
A Potential of Incoherent Attraction Between Multidimensional Solitons
We obtain analytical expressions for an effective potential of interaction
between two- and three-dimensional (2D and 3D) solitons (including the case of
2D vortex solitons) belonging to two different modes which are incoherently
coupled by cross-phase modulation. The derivation is based on calculation of
the interaction term in the full Hamiltonian of the system. An essential
peculiarity is that, in the 3D case, as well as in the case of 2D solitons with
unequal masses, the main contribution to the interaction potential originates
from a vicinity of one or both solitons, similarly to what was recently found
in the 2D and 3D single-mode systems, while in the case of identical 2D
solitons, the dominating area covers all the space between the solitons. Unlike
the single-mode systems,_stable_ bound states of mutually orbiting solitons are
shown to be possible in the bimodal system.Comment: latex, no figures, submitted to Physics Letters
Families of Bragg-grating solitons in a cubic-quintic medium
We investigate the existence and stability of solitons in an optical
waveguide equipped with a Bragg grating (BG) in which nonlinearity contains
both cubic and quintic terms. The model has straightforward realizations in
both temporal and spatial domains, the latter being most realistic. Two
different families of zero-velocity solitons, which are separated by a border
at which solitons do not exist, are found in an exact analytical form. One
family may be regarded as a generalization of the usual BG solitons supported
by the cubic nonlinearity, while the other family, dominated by the quintic
nonlinearity, includes novel ``two-tier'' solitons with a sharp (but
nonsingular) peak. These soliton families also differ in the parities of their
real and imaginary parts. A stability region is identified within each family
by means of direct numerical simulations. The addition of the quintic term to
the model makes the solitons very robust: simulating evolution of a strongly
deformed pulse, we find that a larger part of its energy is \emph{retained} in
the process of its evolution into a soliton shape, only a small share of the
energy being lost into radiation, which is opposite to what occurs in the usual
BG model with cubic nonlinearity.Comment: 15 pages, 4 figures, Physics Letters A (in press
Turning light into a liquid via atomic coherence
We study a four level atomic system with electromagnetically induced
transparency with giant and susceptibilities of
opposite signs. This system would allow to obtain multidimensional solitons and
light condensates with surface tension properties analogous to those of usual
liquids
Controlling pulse propagation in optical fibers through nonlinearity and dispersion management
In case of the nonlinear Schr\"odinger equation with designed group velocity
dispersion, variable nonlinearity and gain/loss; we analytically demonstrate
the phenomenon of chirp reversal crucial for pulse reproduction. Two different
scenarios are exhibited, where the pulses experience identical dispersion
profiles, but show entirely different propagation behavior. Exact expressions
for dynamical quasi-solitons and soliton bound-states relevant for fiber
communication are also exhibited.Comment: 4 pages, 5 eps figure
Stability of spinning ring solitons of the cubic-quintic nonlinear Schrodinger equation
We investigate stability of (2+1)-dimensional ring solitons of the nonlinear
Schrodinger equation with focusing cubic and defocusing quintic nonlinearities.
Computing eigenvalues of the linearised equation, we show that rings with spin
(topological charge) s=1 and s=2 are linearly stable, provided that they are
very broad. The stability regions occupy, respectively, 9% and 8% of the
corresponding existence regions. These results finally resolve a controversial
stability issue for this class of models.Comment: 10 pages, 5 figures, accepted to Phys. Lett.
Partially incoherent optical vortices in self-focusing nonlinear media
We observe stable propagation of spatially localized single- and
double-charge optical vortices in a self-focusing nonlinear medium. The
vortices are created by self-trapping of partially incoherent light carrying a
phase dislocation, and they are stabilized when the spatial incoherence of
light exceeds a certain threshold. We confirm the vortex stabilization effect
by numerical simulations and also show that the similar mechanism of
stabilization applies to higher-order vortices.Comment: 4 pages and 6 figures (including 3 experimental figures
On the theory of adiabatic field dynamics in the Kerr medium with distributed gain and dispersion
A general theory is presented for the adiabatic field evolution in a nonlinear Kerr medium with distributed amplification and varying dispersion. Analytical expression is derived linking parameters of the adiabaticity, gain distribution, and dispersion profile. As a particular example, an optical pulse compressor based on the adiabatic dynamics is examined
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 ring vortex solitons in Bessel optical lattices
Stable ring vortex solitons, featuring a bright-shape, appear to be very rare
in nature. However, here we show that they exist and can be made dynamically
stable in defocusing cubic nonlinear media with an imprinted Bessel optical
lattice. We find the families of vortex lattice solitons and reveal their
salient properties, including the conditions required for their stability. We
show that the higher the soliton topological charge, the deeper the lattice
modulation necessary for stabilization.Comment: 14 pages, 4 figures, submitted to Physical Review Letter
Non-quantum liquefaction of coherent gases
We show that a gas-to-liquid phase transition at zero temperature may occur
in a coherent gas of bosons in the presence of competing nonlinear effects.
This situation can take place both in atomic systems like Bose-Einstein
Condensates in alkalii gases with two and three-body interactions of opposite
signs, as well as in laser beams which propagate through optical media with
Kerr (focusing) and higher order (defocusing) nonlinear responses. The
liquefaction process takes place in absence of any quantum effect and can be
formulated in the frame of a mean field theory, in terms of the minimization of
a thermodynamic potential. We also show numerically that the effect of linear
gain and three-body recombination also provides a rich dynamics with the
emergence of self-organization behaviour.Comment: 6 pages, 5 figures. Submitted to Physica D: Nonlinear Phenomen
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