Optical vortices in low-mode fibers: I. Angular momentum of field

Results of the study of the angular momentum of fields of circular (CV) and instability (IV) vortices perturbed by the field of the fundamental circul arly polarized HE11 mode are presented. The action of the field of the HE11 mode removes degeneracy of coordinates of dislocations of longitudinal and transverse components of the strengths of electric and magnetic fields. Fo r CV, this perturbation results in the formation of an induced vortex of th e field of the vector of momentum density, which rotates about the field of the main vortex. Perturbation of IV leads to the formation of two partial vortices with opposite circulations of polarization and topological charges exchanging energy. In the process of propagation, one of partial vortices is periodically forced out of the fiber core. As a result, torsional mechan ical stresses appear in the fiber.