Lattice of C points at intensity nulls.

The dependence of fringe contrast on the state of polarization (SOP) can be altered when more than two beams interfere, and it is possible to achieve high contrast fringes. We use a six-pinhole interferometer, in which a judicious choice (but not unique) of SOPs for the interfering beams is made to realize the lattice of C points at intensity nulls. These dark C points occur due to overlapping of singularities. These are not simply a minor variation of bright C points, in which the intensity dims to zero, but are poorly understood, unusual objects in their own right. A discussion on Stokes intensity degeneracy is presented. In the ellipticity distributions, it is shown that V points occur at nulls, whereas C points occur at extrema. It is shown that destructive interference of two right (left) handed bright C points can result in a left (right) handed dark C point.