Systems, methods and apparatus for improving the contrast ratio in reflective imaging systems utilizing color splitters
First Claim
1. A waveplate compensator for use in an image projection system which utilizes color splitting means for separating a polarized component of light into at least two separate color beams, the waveplate compensator comprising:
- a birefringent material having a thickness,said waveplate compensator having a retardance which is dependent on the birefringent material and the thickness of the birefringent material,said retardance being selected to retard a color beam by a wave value at which an approximate minimum occurs for both ellipticity and elliptical polarization orientation of the color beam as caused by polarization rotation of a portion of the color beam by a color splitting means,whereby placement of the waveplate compensator in the optical path between a color splitting means and an imaging means substantially eliminates any portion of light that undergoes polarization rotation by the color splitting means.
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Accused Products
Abstract
Methods and apparatus for enhancing the performance of reflective LCD systems. The high-contrast color-splitting prism system utilizes a "double-pass" prism assembly. Polarized light enters the prism assembly, is color-split and is emitted as separate colors to reflective imagers which reflect each color in accord with a desired image. The reflected light is passed, once again, through the prism assembly where the separate colors converge and the convergent light is emitted to a projection lens for display of the image on a screen. At least one zero-incidence waveplate compensator is positioned between one reflective imager and the prism assembly. The waveplate compensator effectively decreases the unwanted polarized light entering the prism assembly for the second pass-through, thereby increases the polarization purity of the light that is emitted from the prism assembly to the projection lens to yield a high-contrast projection image.
139 Citations
70 Claims
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1. A waveplate compensator for use in an image projection system which utilizes color splitting means for separating a polarized component of light into at least two separate color beams, the waveplate compensator comprising:
a birefringent material having a thickness, said waveplate compensator having a retardance which is dependent on the birefringent material and the thickness of the birefringent material, said retardance being selected to retard a color beam by a wave value at which an approximate minimum occurs for both ellipticity and elliptical polarization orientation of the color beam as caused by polarization rotation of a portion of the color beam by a color splitting means, whereby placement of the waveplate compensator in the optical path between a color splitting means and an imaging means substantially eliminates any portion of light that undergoes polarization rotation by the color splitting means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A waveplate compensator for use in an image projection system which utilizes color splitting means for separating a polarized component of light into at least two separate color beams, the waveplate compensator comprising:
a birefringent material having a thickness, said waveplate compensator having a retardance which is dependent on the birefringent material and the thickness of the birefringent material, said retardance being selected to retard a color beam by a wave value which corresponds with a calculated polarization rotation elimination retardance value, said calculated polarization rotation elimination retardance value being the value at which both ellipticity and elliptical polarization orientation of the color beam as caused by polarization rotation of a portion of the color beam by a color splitting means are both at approximately a minimum, whereby placement of the waveplate compensator in the optical path between a color splitting means and an imaging means substantially eliminates any portion of light that undergoes polarization rotation by the color splitting means. - View Dependent Claims (11, 12, 13, 14, 15)
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16. An image projection system comprising:
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(a) polarizing means for polarizing light to transmit a first polarized component of light in a first polarization state; (b) color splitting means for separating the first polarized component of light into three primary color beams including a red beam, a green beam, and a blue beam, (i) wherein each of the three beams exits primarily in the first polarization state from the color splitting means at three separate beam exit locations, (ii) wherein said color splitting means causes at least one of the three beams to have residual elliptical polarization due to polarization rotation of a portion of the beam such that at least one of the three beams has an ellipticity and an elliptical polarization orientation; (c) three imager means for modulating a polarization state of each of the three primary color lights, (i) wherein the three imager means are positioned such that each imager means receives one of the three primary color beams; and (d) at least one waveplate compensator means for retarding at least one of the three primary color beams to achieve a predetermined phase difference, (i) wherein the waveplate compensator means is positioned such that the waveplate compensator means is in an optical path between one of the three light exit locations of the color splitting means and one of the three imager means, (ii) wherein the waveplate compensator means has a retardance selected to retard the respective primary color beam by a wave value at which both the ellipticity and the elliptical polarization orientation of the respective beam are approximately at a minimum, thereby substantially eliminating any portion of light that undergoes polarization rotation by said color splitting means. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
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38. An image projection system comprising:
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(a) polarizer for polarizing light to transmit a first polarized component of light in a first polarization state; (b) color splitter for separating the first polarized component of light into three primary color beams including a red beam, a green beam, and a blue beam, (i) wherein each of the three beams exits primarily in the first polarization state from the color splitter at three separate beam exit locations, (ii) wherein said color splitter causes at least one of the three beams to have residual elliptical polarization due to polarization rotation of a portion of the beam such that at least one of the three beam has an ellipticity and an elliptical polarization orientation; (c) three reflective imagers for modulating a polarization state of each of the three primary color lights and for reflecting the beam thus modulated, (i) wherein the three reflective imagers are positioned such that each reflective imager receives one of the three primary color beams and reflects the respective beam in a second polarization state back into the color splitter; and (d) at least one waveplate compensator for retarding at least one of the three primary color beams to achieve a predetermined phase difference. (i) wherein the waveplate compensator is positioned in an optical path between one of the three light exit locations of the color splitter and one of the three reflective imagers, (ii) wherein the waveplate compensator has a retardance selected to retard the respective primary color beam by a wave value at which both the ellipticity and the elliptical polarization orientation of the respective beam are approximately at a minimum, thereby substantially eliminating any portion of light that undergoes polarization rotation by said color splitter. - View Dependent Claims (39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58)
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59. A method of manufacturing a waveplate compensator for use in an image projection system which utilizes color splitting means for separating a polarized component of light into at least two separate color beams, the method comprising:
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identifying a desired retardance value at which an approximate minimum occurs for both ellipticity and elliptical polarization orientation of light as caused by polarization rotation of a portion of the light by a color splitting means in an image projection system, and providing a waveplate compensator having a retardance value which corresponds with the desired retardance value identified as resulting in an approximate minimum for both the ellipticity and elliptical polarization orientation of the light. - View Dependent Claims (60, 61, 62)
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63. A method of manufacturing a waveplate compensator for use in an image projection system which utilizes color splitting means for separating a polarized component of light into at least two separate color beams, the method comprising:
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determining values, at retardance value intervals, for both ellipticity and elliptical polarization orientation of light as caused by polarization rotation of a portion of the light by a color splitting means in an image projection system, identifying a desired retardance value at which an approximate minimum occurs for both the ellipticity and the elliptical polarization orientation of the light, and providing a waveplate compensator having a retardance value which corresponds with the retardance value identified as resulting in an approximate minimum for both the ellipticity and elliptical polarization orientation of the light, whereby the waveplate compensator may be placed in an optical path between a color splitting means and an imaging means to substantially eliminate any portion of light that undergoes polarization rotation by the color splitting means. - View Dependent Claims (64, 65, 66, 67, 68, 69, 70)
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Specification