Some projection systems use a polarization beamsplitter (PBS) for coupling
light to and from an image-forming device. The PBS is typically formed
with a reflective polarizing layer disposed between glass covers. Stress
birefringence in the glass cover lying between the reflective polarizing
layer and the image-forming device can reduce the image contrast of the
projection system. A quarter-wave retarding element positioned between
the glass cover and the image-forming device is used to compensate for
the birefringence, at least in part. This permits the PBS to use glass
covers formed of a glass material having a higher stress optic
coefficient than before, while still maintaining high image contrast.