It is well known that phase singularities, in general lines in space, are topologically stable features of a wave field. An exception is a pointlike singularity, which is unstable and deforms into a ring or disappears when a small perturbation is applied. Recently, Nye showed how such an event can be understood as an unfolding of a higher-order dislocation [J. Opt. Soc. Am. A (to be published)]. We present an optical implementation of this model and show experimentally that the focal region of a lens contains points of zero intensity on the optical axis that deform into rings when a small amount of spherical aberration is applied to the system.
© 1998 Optical Society of america
G. P. Karman, A. van Duijl, and J. P. Woerdman, "Unfolding of an unstable singularity point into a ring," Opt. Lett. 23, 403-405 (1998)