Methods and apparatus for reducing ghost images in reflective imager-based projectors

In an image projection system, comprising:

• a polarized light source;
• a reflective spatial light modulator;
• a projection lens;
• an imager field lens positioned between the light source and the reflective imager, and also between the reflective imager and the projection lens system;
• whereby light from the polarized light source is directed to the imager field lens for modulation by the reflective spatial light modulator after passing in a first direction through the imager field lens, light modulated by the reflective spatial light modulator is directed back to the imager field lens into a pupil of the projection lens after passing in a second direction opposite to the first direction through the imager field lens, and a portion of the light directed from the light source to the imager field lens is reflected off the imager field lens into the pupil of the projection lens system;
• a quarter-wave retarder positioned between the imager field lens and the reflective spatial light modulator for retarding light from the light source that passes through the imager field lens to the reflective spatial light modulator and for retarding light from the reflective spatial light modulator that passes through the imager field lens to the projection lens system;
• and
• a linear polarizer positioned between the imager field lens and the projection lens;
• the linear polarizer acting to pass light retarded by the quarter-wave retarder while passing in the first direction from the light source through the imager field lens to the reflective spatial light modulator and again while passing in the second direction from the reflective spatial light modulator through the imaging field lens into the pupil of the projection lens, and to block at least a portion of light reflected off the imager field lens into the pupil of the projection lens system.

A method for image projection, comprising:

• directing light from a polarized light source in a first direction through an imager field lens and then through a quarter-wave retarder to be incident on a reflective spatial light modulator;
• wherein a portion of the light directed in the first direction is reflected off the imager field lens into a pupil of a projection lens;
• modulating light incident on the reflective spatial light modulator;
• and
• directing the modulated light from the reflective spatial light modulator in a second direction opposite to the first direction through the quarter-wave retarder and then through the imager field lens into the pupil of the projection lens for projection;
• wherein a linear polarizer positioned between the imager field lens and the projection lens passes light passed in the first direction from the light source through the imager field lens and quarter-wave retarder to the reflective spatial light modulator and also passed in the second direction from the reflective spatial light modulator through the quarter-wave retarder and the imaging field lens into the pupil of the projection lens, and blocks at least part of the portion of light reflected off the imager field lens traveling into the pupil of the projection lens.