  In order to explore electric-field-induced transformations of polarization
singularities in the polarization-resolved angular (conoscopic) patterns
emerging after deformed helix ferroelectric liquid crystal (DHFLC) cells with
subwavelength helix pitch, we combine the transfer matrix formalism with the
results for the effective dielectric tensor of biaxial FLCs evaluated using an
improved technique of averaging over distorted helical structures. Within the
framework of the transfer matrix method, we deduce a number of symmetry
relations and show that the symmetry axis of L lines (curves of linear
polarization) is directed along the major in-plane optical axis which rotates
under the action of the electric field. When the angle between this axis and
the polarization plane of incident linearly polarized light is above its
critical value, the C points (points of circular polarization) appear in the
form of symmetrically arranged chains of densely packed star-monstar pairs. We
also emphasize the role of phase singularities of a different kind and discuss
the enhanced electro-optic response of DHFLCs near the exceptional point where
the condition of zero-field isotropy is fulfilled.
