  We show that a super-resolution process with 100% visibility is characterized
by the formation of a point of phase singularity in free space outside the lens
in the form of a saddle with topological charge equal to -1. The saddle point
is connected to two vortices at the end boundary of the lens, and the two
vortices are in turn connected to another saddle point inside the lens. The
structure saddle-vortices-saddle is topologically stable. The formation of the
saddle point in free space explains also the negative flux of energy present in
a certain region of space outside the lens. The circulation strength of the
power flow can be controlled by varying the position of the object plane with
respect to the lens.

Optics