Crossover regime of optical vortices generation via electro-optic nonlinearity: the problem of optical vortices with the fractional charge generated by crystals.

In this work, we analyze the behavior of topological defects of optical indicatrix orientation induced by a conically shaped electric field in crystals in a crossover regime that appears at intermediate fields separating the regimes of prevailing Pockels and Kerr electro-optic nonlinearities. We have found that increases in the electric voltage applied to a crystal induce neither topological defects, with the strengths being not multiples of ½, or the optical vortices with fractional charges. Instead, there appear some additional topological defects of the optical indicatrix orientation, the behavior of which we have studied in detail.