Abstract

We demonstrate all robust bound states in the continuum in photonic crystal slabs are vortex centers in the polarization directions of far-field radiation. They are robust because they carry quantized topological charges, which are conserved if the system is invariant under parity-time (PT) and up-down mirror flip operations. Also, we show lasing of these special states are vector beams. The order of the vector beam is given by the topological charge carried by these special modes. Using this rule, we can design lasers that are generically high-order vector beams.

© 2015 Optical Society of America