Building blocks for nonpolarizing optical coatings.

The problem of designing nonpolarizing beam splitters with as broad a spectral band as practical has not been clearly understood. The effort of the work reported here has been to glean understanding from the various results of a contest for such designs and further studies of what might be the underlying principles and behaviors that are involved in such designs. A few key layer patterns have been observed, and the importance of symmetry in these patterns has been discovered. Four-layer building blocks have been found that relate to the two quarter-wave optical thickness pairs used as building blocks in normal-incidence designs.