Generation of optical vortex beam by surface-processed photonic-crystal surface-emitting lasers.

An optical vortex beam possesses a phase singularity that causes a null intensity at the center of the beam, and can be explained as a superposition of a phase distribution along the azimuthal direction and a plane wave. Here, we process the surface of a photonic-crystal surface-emitting laser (PCSEL) to generate an optical vortex beam. By using an eight-segmented phase plate fabricated via three chemical etching steps, a beam having null intensity is obtained. From evaluation of the beam's polarization and interference patterns, we show that the null intensity comes from the phase singularity of the optical vortex.