Phase Dislocations in the Negative Curvature Hollow Core Fibres

The negative curvature hollow core fibres (NCHCFs) [1–3] have attracted recently a great deal of attention because of their potential for many practical applications ranging from optical communications to high power lasers and power delivery. In the NCHCFs light is strongly localized in the air core due to the mode field interaction with the limited portions of the core-cladding boundary. In our work [4] we observed that the light leakage from the hollow core in NCHCFs has features which indicate the formation of phase dislocations and optical vortices in the cladding elements. Here we demonstrate that there are lines in the cladding capillary walls along which the imaginary and real parts of the transverse components of the core mode electric field Ex and Ey are equal to zero and can cross each other (the zero — amplitude lines). The direction of the transverse component of the core mode electric field is uncertain in the vicinity of these lines. Such behaviour of the core mode fields and its polarization indicates the presence of optical vortices in the cladding capillary wall [5].