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.