Abstract

An optical vortex is a distinctive waveform that has a dark circular core on a bright background. Seen from head on, a beam with an optical vortex appears as a bright doughnut of light. The dark core is the result of destructive interference caused by a 2׳rr phase ramp above the core, another characteristic of optical vortex. Very similar to hurricanes or tornadoes, optical vortices in linear medium¹ eventually dissipate. In other words, diffraction causes expansion of vortex core and washes away vortices. Owing to the special intensity profile of vortices, linear optical vortices have been used in trapping and guiding small particles.² In a nonlinear medium, such as self-defocusing Kerr material, the nonlinear refractive index induced by the vortex intensity profile counteracts diffraction. As a result, a stable and stationary core with well-defined size is formed inside a light beam. Because the core is immune from instability and its size remains constant with propagation distance, this optical vortex is the only known cylindrical soliton in Kerr media,³ so-called optical vortex solitons (OVSs).

© 1998 Optical Society of America