Optical vortices near sub-wavelength structures

In this paper the phase singularities of the electromagnetic field near a sub-wavelength slit are studied. These phase singularities, such as optical vortices, are found in regular patterns, which can be created or annihilated under the conservation of certain topological quantities, when a parameter such as the slit width is changed. The connection between the phase singularities and the light transmission though the slit is considered.