**
Higher-order optical spatial (2+1)D vector solitons in a**

saturable nonlinear photorefractive medium

**Marcus Ahles**

*Institute of Applied Physics, Darmstadt University of Technology,*

Hochschulstraße 6, 64289 Darmstadt, Germany

**Abstract: **
Optical spatial (2+1)D solitons are solitary self-trapped light beams
that can form in a saturable Kerr-like nonlinear bulk medium. A
monochromatic and coherent light beam propagating through a
photorefractive SBN crystal induces a refractive index modulation which
under certain conditions counterbalances exactly the beam's natural
diffraction in both transverse directions. The light propagates as the
fundamental mode of its own self-induced waveguide. Self-focused light
structures that consist only of one optical field are denoted as scalar
solitons. In contrast, higher-order Hermite-Gaussian dipole-like or
Laguerre-Gaussian vortex-like transverse modes do not self-trap due to
their non uniform transverse phase distribution. But if they
co-propagate incoherently with a fundamental Gaussian beam of equal
total power, a stationary self-trapped state will form which is denoted
as a vector soliton.[1] Vector solitons are multicomponent self-focused
structures whose components interact only due to the mediums
nonlinearity.
Our aim is threefold. First, we demonstrate that the combination of a
Gaussian and a vortex beam with a topological charge of m=2 is unstable
and decays into two single-charged optical vortices that will decay into
a triple humped structure. Second, we show that this HG(0,2) mode-like
triple humped structure co-propagating with a Gaussian beam will
self-trap and form a vector soliton. Third, we even succeeded in
generating more complex structures consisting only of higher order modes
generating more complex structures consisting only of higher order modes
that trap mutually without any fundamental Gaussian beam. A
triple-humped structure as we mentioned above copropagating with a
HG(0,1) dipole-mode will form such a complex vector soliton.[2]
[1] C. Weilnau, W. Krolikowski, E.A. Ostrovskaya, M. Ahles, M. Geisser,
G. McCarthy, C. Denz, Y.S. Kivshar, B. Luther-Davies,
"Composite spatial solitons in a saturable nonlinear bulk medium",
Applied Physics B, accepted for publication.

[2] C. Weilnau, M. Ahles, C. Denz, A. Stepken, K. Motzek, F. Kaiser,
"Higher-order optical (2+1) dimensional spatial vector solitons in an
anisotropic medium", Phys. Rev. E, submitted.