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 circularly polarized C~+ and C~- disclinations and linearly polarized L_x and L_y disclinations are present in the field of a linearly polarized LP_(11) mode of a fiber with a stepwise profile of the refractive index. Scalar D_x and D_y dislocations appear at fiber lengths multiple of half the beating length of the LP_(11) mode. For remaining fiber lengths, the evolution of the LP_(11) mode is determined by the dynamics of interaction of C~+ and C~-, L_x and L_y disclinations. In the interference pattern of the LP_(11) mode with a smooth reference wave for a given fiber length and fixed conditions of excitation, both unit pure screw dislocations of both signs of the topological charge and unit pure edge dislocations can be separated. The conditions for the observation of unit dislocations are determined by the optical fiber length, the state of polarization of the reference wave, or the orientation of the axis of transmission of a polarization analyzer in the recording device.
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