Design of a dual‐f‐number illumination system and its application to DMD™ projection displays

Abstract

Abstract— A dual‐f/# optical system is evaluated and considered for illumination. Étendue theory has been employed to increase the optical throughput and collection efficiency. A classical Cooke triplet with a dual f/# is included for illustration. As a demonstration of the potential application to projection displays, an elliptically shaped illumination‐pupil system is proposed to increase the optical collection efficiency in the DMD™ (Digital Micromirror Device™)‐based projection system. With a dual‐f/# configuration, this design can eliminate the f/2.4 constraint that was caused by the light‐steering action of the narrow ±12° tilt angles on the DMD™. The percentage of increase in the optical collection efficiency is 6.2% in the dual f/2.0 × f/2.4 optical projection system by using ray‐tracing simulation. This method enables a lower than f/2.4 optical design with a high brightness and an adequate contrast ratio in the DMD™‐based projectors.