The 1-chip DLP engine design uses two back-to-back prisms to allow light to couple light in and out of the DMD chip. The design is quite mature but it has an inherent contrast limitation. A revised design evaluated by The National Chiao Tung University in Taiwan was described in paper 35.4.
The new paper builds upon a 3-prism design proposed earlier, but rearranges the prisms as shown in the figure below. The paper describes the optical ray tracing and performance metrics, but the bottom line is that there is about a 5% increase in contrast over the previous 3-prism design. Unfortunately, the author did not provide a contrast reference measurement for the standard two-prism design.
The results are shown in the table below. While contrast increased a little, efficiency also decreased a little.