Compound polarization beam splitters

A prism assembly which comprises an input prism, an output prism, and a polarizer between the input and output prisms, where:

• (A) the input prism comprises:
• (i) a first surface which is configured and arranged to receive polarized illumination light from an illumination system;
• (ii) a second surface which is configured and arranged to provide polarized illumination light to an imaging device and to receive modulated reflected light from the imaging device;
• and
• (iii) a third surface which faces the output prism;
• (B) the output prism comprises:
• (i) a first surface which faces the input prism and is parallel to the third surface of the input prism;
• and
• (ii) a second surface which is configured and arranged to provide light to a projection lens to form a projected image;
• and
• (C) the polarizer:
• (i) is between the third surface of the input prism and the first surface of the output prism;
• and
• (ii) reflects light having a first polarization direction and transmits light having a second polarization direction;
• wherein the polarized illumination light has an optical path which comprises:
• (i) inward transmission through the first surface of the input prism;
• (ii) total internal reflection at the second surface of the input prism;
• (iii) outward transmission through the third surface of the input prism;
• (iv) reflection from the polarizer;
• (v) inward transmission through the third surface of the input prism;
• and
• (vi) outward transmission through the second surface of the input prism.

A method for producing an image using a polarizer which reflects light of a first polarization and transmits light of a second polarization, said method comprising in order:

• (1) providing polarized illumination light having a first polarization direction;
• (2) introducing the polarized illumination light into a prism having a plurality of surfaces;
• (3) changing the direction of the polarized illumination light through total internal reflection at one of the prism's surfaces;
• (4) reflecting the polarized illumination light from the polarizer;
• (5) modulating the polarization of the polarized illumination light at a reflective imaging device by changing the polarization of selected portions of that light to the second polarization, said selected portions comprising the light which forms the image;
• and
• (6) transmitting the selected portions through the polarizer and to a projection lens to form the image.

A method for producing an image using a polarizer which reflects light of a first polarization and transmits light of a second polarization, said method comprising in order:

• (1) providing polarized illumination light having the second polarization direction;
• (2) transmitting the polarized illumination light through the polarizer;
• (3) modulating the polarization of the polarized illumination light at a reflective imaging device by changing the polarization of selected portions of that light to the first polarization, said selected portions comprising the light which forms the image;
• (4) reflecting the selected portions having the first polarization from the polarizer to form image light;
• (5) introducing the image light into a prism having a plurality of surfaces;
• (6) changing the direction of the image light through total internal reflection at one of the prism's surfaces;
• and
• (7) transmitting the image light to a projection lens to form the image.