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

Abstract

A dual-f/# optical system is evaluated and considered for illumination. Etendue 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(TM) (Digital Micromirror Device(TM))-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 degrees tilt angles on the DMD(TM). The percentage of increase in the optical collection efficiency is 6.2% in the dual f/2.0 x 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(TM)-based projectors.