Illumination system for a colour image projection device and circular polarizer suitable for use in such a system.

摘要

The invention relates to an illumination system (7) for a colour image projection device (1). The illumination system (7) comprises a radiation source (3) for generating an unpolarized radiation beam (5) and at least a cholesteric mirror (9, 10, 11, 12, 13, 14) for wavelength-selective splitting of the radiation beam (5) into at least two sub-beams of different wavelengths. A composite circular polarizer (35) for directly converting the unpolarized radiation beam (5) into circularly polarized sub-beams jointly forming one beam is arranged in the path of the unpolarized radiation beam (5) between the radiation source (3) and the cholesteric mirror (9). The composite circular polarizer (35) comprises a polarization-sensitive beam splitter (43) which splits the unpolarized radiation beam (5) into two mutually perpendicularly and linearly polarized sub-beams, and a polarization converter (51, 53; 59, 61). The circularly polarized monochrome sub-beams are subsequently modulated, either or not after passage through a lambda /4 plate (63, 65, 67), by a corresponding number of image display panels (27, 29, 31) and projected as an image via a projection lens system (33).