  Vector optical vortices exhibit complex polarisation patterns due to the
interplay between spin and orbital angular momenta. Here we demonstrate, both
analytically and with simulations, that certain polarisation features of
optical vortex beams maintain constant transverse spatial dimensions
independently of beam divergence due to diffraction. These polarisation
features appear in the vicinity of the phase singularity and are associated
with the presence of longitudinal electric fields. The predicted effect may
prove important in metrology and high resolution imaging applications.
