In the standard Turner Frustrated Total Reflection filter the pass bands occur in pairs which are oppositely polarized. The maximum theoretical transmission in any band is thus 50 percent. In this paper it is shown that if the high index layer of the filter is made of a birefringent material the oppositely polarized pass bands can be made to coincide so that the maximum theoretical transmission becomes 100 percent and the bands occur singly. Measurements are shown on a filter made with such a birefringent layer.
B. H. BILLINGS, "A Birefringent Frustrated Total Reflection Filter," J. Opt. Soc. Am. 40, 471-475 (1950)