Observation of bandgap guidance of optical vortices in a tunable negative defect

We experimentally demonstrate linear bandgap guidance of optical vortices as high-gap defect modes (DMs) in two-dimensional induced photonic lattices. We show that donut-shaped vortex beams can be guided in a tunable negative (lower-index) defect, provided that the defect strength is set at an appropriate level. Such vortex DMs have fine features in the "tails" associated with the lattice anisotropy and can be considered as a superposition of dipole DMs. Our numerical results find good agreement with experimental observations.