OPTICS OF SINGULARITIES OF THE FIELD OF A LOW-MODE FIBER - I - CIRCULAR DISCLINATIONS

The dynamics of vector singularities of lower modes of the field of an optical fiber is studied experimentally and theoretically It is shown that scalar linearly polarized D-x and D-y dislocations as well as ci rcularly polarized C+ and C- disclinations and linearly polarized L-x and L-y disclinations are present in the field of a linearly polarized LP11 mode of a fiber with a stepwise profile of the refractive index. Scaler D-x and D-y dislocations appear at fiber lengths multiple of h alf the beating length of the LP11 mode. For remaining fiber lengths, the evolution of the LP11 mode is determined by the dynamics of intera ction of C+ and C-, L-x and L-y disclinations. In the interference pat tern of the LP11 mode with a smooth reference wave for a given fiber l ength and fixed conditions of excitation, both unit pure screw disloca tions of both signs of the topological charge and unit pure edge dislo cations can be separated. The conditions for the observation of unit d islocations are determined by the optical fiber length, the state of p olarization of the reference wave, or the orientation of the axis of t ransmission of a polarization analyzer in the recording device.