Nonlinear Optics

Abstract

contrast with the 1D analogues of SieversTakeno and Page modes, respectively, both of the basic types are stable.1, 2 Experimentally, both the on-site7 and off-site6, 7 vortex lattice solitons have been observed. Typical results for an on-axis vortex beam are shown in the figure. At low intensity, the vortex beam simply diffracts across the crystal. An interferogram, formed by interfering the output with a plane wave, clearly shows the 0→2 phase structure of the vortex. In the nonlinear regime, self-focusing creates a steady-state soliton that keeps its profile. In the corresponding interferogram, changing the phase of the reference plane wave changes the site of destructive interference, proving that the lattice soliton keeps its vortex phase structure. This is a nontrivial result, since lattices break the continuous rotational symmetry of homogeneous media and do not generally conserve angular momentum (topological charge). In this case, a combination of “discrete” dynamics and nonlinearity allows the soliton to maintain its vortex phase. Note that it is also this combination that allows a stable ring structure, since bright rings (with or without topological charge) are unstable in homogeneous media with self-focusing nonlinearity. Nonlinear Optics