Patent ID: 6511183
Filing Date: 2003-01-28
Classification: G02B,H04N

Abstract:
In a digital-image projector comprising:(a) an illumination-light source lamp for generating white-spectrum illumination light; (b) illumination-beam forming means for receiving illumination light generated by the source lamp and forming from such light a white-spectrum illumination beam; (c) color-band-separation means for dividing the input white-spectrum illumination beam into three spatially separated color-component illumination subbeams; (d) reflective digital-image-encoding polarization modulator means for spatially modulating the polarization of incident linearly polarized color-component illumination subbeams upon reflection of the subbeams in accordance with corresponding color-component images of a desired color digital image to form reflected color-component image-encoded-polarization subbeams; (e) projection lens means for projecting color-image bearing light rays for viewing the desired color image; and (f) a plate-supported, surface-mounted fixed-polarization-axis thin-polarizer polarizing beamsplitter for polarization-state-selectively directing illumination light rays incident upon the beamsplitter into dark-pixel-polarization-state polarized light rays for forming linearly polarized color-component illumination subbeams incident upon the reflective digital-image-encoding polarization modulator means and for polarization-state-selectively dividing image-encoded-polarization light rays incident upon the beamsplitter drawn from reflected color-component image-encoded-polarization subbeams from the reflective digital-image-encoding polarization modulator means into dark-pixel-polarization-state polarized negative-image bearing light rays and light-pixel-polarization-state polarized color-image bearing light rays for forming the desired color image, said polarizing beamsplitter comprising a transparent polarizer-support plate and a fixed-polarization-axis polarizer mounted on a substantially optically flat outer face of the polarizer-support plate which defines a polarizer-support face, the fixed-polarization axis polarizer being thin in a dimension perpendicular to the polarizer-support face, the polarizing beamsplitter having defined with respect thereto an illumination-beam-reception axis, a dark-pixel-polarization-state polarized beam axis, and a light-pixel-polarization-state polarized beam axis, the illumination light rays incident upon the beamsplitter propagating in a direction substantially parallel to the illumination-beam-reception axis, the image-encoded-polarization light rays incident upon the beamsplitter propagating in a direction substantially parallel to the dark-pixel-polarization-state polarized beam axis, and the light-pixel-polarization-state polarized color-image bearing light rays divided from the image-encoded-polarization light rays by the beamsplitter propagating in a direction substantially parallel to the light-pixel-polarization-state polarized beam axis, a polarizer-support-face normal being defined to project outwardly from the polarizer-support face of the polarizer-support plate in a direction perpendicular to the polarizer-support face; the improvement which comprises:positioning and orienting the fixed-polarization-axis polarizing beamsplitter with the dark-pixel-polarization-state polarized beam axis extending outwardly from the fixed-polarization-axis polarizer mounted on the polarizer-support face of the polarizer-support plate, a polarized-beam-axis angle being defined as an angle between the dark-pixel-polarization-state polarized beam axis and the polarizer-support-face normal, the polarized-beam-axis angle being substantially greater than zero degrees, the illumination-beam-reception axis extending in a direction effectively parallel to the direction of the dark-pixel-polarization-state polarized beam axis outwardly from a face of the polarizer-support plate opposing the polarizer-support face, the light-pixel-polarization-state polarized beam axis extending outwardly from the polarizer-support face of the polarizer-support plate in a plane of incidence defined by the dark-pixel-polarization-state polarized beam axis and the polarizer-support-face normal and making an angle of reflection with the polarizer-support-face normal equal to the polarized-beam-axis angle, the fixed-polarization-axis polarizing beamsplitter being oriented to receive the illumination light rays propagating towards the polarizing beamsplitter substantially parallel to the illumination-beam reception axis and through the transparent polarizer-support plate to the fixed-polarization-axis polarizer mounted on the polarizer-support face of the polarizer-support plate, to direct the dark-pixel-polarization-state light rays to propagate outwardly from the polarizer-support face substantially parallel to the dark-pixel-polarization-state polarized beam axis, to receive the image-encoded-polarization light rays propagating towards the beamsplitter substantially parallel to the dark-pixel-polarization-state polarized beam axis directly upon the fixed-polarization-axis polarizer mounted on the polarizer-support face of the polarizer-support plate without passing through the polarizer-support plate, to divide the image-encoded-polarization light rays into the dark-pixel-polarization-state polarized negative-image bearing light rays propagating through the transparent polarizer-support plate and away from the polarizing beamsplitter substantially parallel to the illumination-beam-reception axis and the light-pixel-polarization-state polarized color-image bearing light rays propagating away from the polarizer-support face substantially parallel to the light-pixel-polarization-state polarized beam axis without passing through the polarizer-support plate for projection by the projection lens means.