Contrast behavior of a field lens with a wire‐grid PBS

— In an LCOS projection system, a wire-grid PBS may be used to improve contrast and a field lens may be employed to simplify the projection lens. However, the combination of the two leads to a reduced contrast, which decreases with increasing field angle in one direction. In a representative arrangement, measured contrast with a mirror varied from over 10,000 in the center to 450 at the left and right edges. Contrast loss can be improved with a weaker field lens. The problem arises due to a phase delay between polarization states introduced by the wire grid. Polarization measurements show a +53-nm phase delay with an axis parallel to the wire-grid surface normal. Various compensation schemes are proposed in order to reduce the aforementioned loss of contrast.