Charge flipping of a vortex in a nonlinear photonic lattice

In this study of the evolution of a vortex beam on the lattice and its possible transformations such as the vortex charge flipping will provide the tools to control the transport of information (dislocation charge), as well as to manipulate it, e.g. erasing or reversing phase dislocations. In experiments, we use a biased photorefractive crystal, where the modulation of the refractive index is induced by periodically modulated partially coherent light. When being ordinary polarized, such an optical lattice propagates in the linear regime and it is not affected by interaction with a vortex. We refer to it as "fixed" lattice. When being extraordinary polarized, the lattice propagates in the nonlinear regime, and it experiences self-action together with the cross-phase modulation from the mutually incoherent signal beam. We call these nonlinear lattices "flexible" photonic structures, which may guide a signal vortex beam. The signal, on the other side, creates a defect in the lattice, significantly modifying its dynamics. Experimentally, in the case of flexible lattices, we observe the lattice deformation and twisting due to a transfer of the angular momentum carried by the vortex beam to the lattice.