Color video projection system employing reflective liquid crystal display devices
View Patent ↗An image projector ( 8, 68 ) includes a light source ( 14 ) that illuminates a three-path reflective LCD assembly ( 25, 74 ) that produces images for projection by a projection lens ( 27 ). The light source produces S-polarized light rays that are received by a spectrally selective wave plate ( 36 ) that changes a first wavelength range of light to P-polarized light rays ( 34 ) and transmits without polarization change second and third wavelength ranges of light. A plate-type transflective polarizing beam splitter ( 40 ) transmits the P-polarized first wavelength range light rays and reflects S-polarized second and third wavelength range light rays ( 34 ). The P-polarized first wavelength range light rays transmit through a field lens ( 42 1 ) and impinge on a first reflective LCD light valve ( 26 1 ). The S-polarized second and third wavelength range light rays strike a pleochroic filter ( 48 ), which divides them into second and third wavelength range light rays ( 44, 46 ) that propagate through field lenses ( 42 2 , 42 3 ) and impinge on respective second and third LCD light valves ( 26 2 , 26 3 ). The light rays impinging on dark state pixels on the first LCD light valve are reflected without polarization direction change and return toward the light source along their original paths. However, the light rays impinging on illuminated state pixels on the first LCD light valve are reflected with a 90° change in polarization direction and are reflected toward the projection lens by the transflective polarizing beam splitter. The light rays impinging on illuminated state pixels on the second and third LCD light valves are reflected with a 90° change in polarization direction, are recombined by the pleochroic filter, and transmit through the transflective polarizing beam splitter toward the projection lens.
1. An apparatus comprising:
a light source to produce light in first, second and third wavelength bands in a second polarization direction;
a spectrally selective input device
to receive the first, second, and third wavelength bands of light from the light source;
to transmit the first wavelength band of light in a first polarization direction; and
to transmit the second and third wavelength bands of light in the second polarization direction;
a plate-type transflective polarizing beam splitter
to recieve the first, second and third wavelength bands of light,
to transmit, in a first polarization direction, the first wavelength band of light, and
to reflect, in a second polarization direction, the second and third wavelength bands of light;
a color filter
to recieve the second and third wavelength bands of light,
to transmit in second polarization direction, the second wavelength band of light, and
to reflect in the second polarization direction, the third wavelength band of light; and
first, second and third reflective liquid crystal light valves
to selectively reflect portions of the respective first, second and third wavelength bands of light toward a projection lens.
2. The apparatus of claim 1 , wherein at least a selected one of the reflective liquid crystal light valves includes a plurality of pixels selectively switchable between a clark polarization state and an illuminated polarization state.
3. The apparatus of claim 2 , wherein the pixels of the first reflective liquid crystal light valve are to be selectively switched to the dark polarization state to reflect selected portions of the first wavelength band of light, in the first polarization direction, back through the plate-type transflective polarizing beam splitter toward the light source.
4. The apparatus of claim 2 , wherein the pixels of the second reflective liquid crystal light valve are to be selectively switched to the dark polarization state to reflect selected portions of the second wavelength band of light, in the second polarization direction, back through the color filter, off the plate-type transflective polarizing beam splitter, toward the light source.
5. The apparatus of claim 2 , wherein the pixels of the second reflective liquid crystal light valve are to be selectively switched to the illuminated polarization state to reflect selected portions of the second wavelength band of light, in the first polarization direction, through the color filter and the plate-type transflective polarizing beam splitter toward the projection lens.
6. The apparatus of claim 2 , wherein the pixels of the third reflective liquid crystal light valve are to be selectively switched to the dark polarization state to reflect selected portions of the third wavelength band of light, in the second polarization direction, off the color filter and the plate-type transflective polarizing beam splitter toward the light source.
7. The apparatus of claim 2 , wherein the pixels of the third reflective liquid crystal light valve are to be selectively switched to the illuminated polarization state to reflect selected portions of the third wavelength band of light, in the first polarization direction, off the color filter through the plate-type transflective polarizing beam splitter toward the projection lens.
8. The apparatus of claim 1 , wherein the spectrally selective input device is of an optical retardation type.
9. The apparatus of claim 1 , further comprising:
one or more dichroic trim filters respectively associated with one or more of the first, second, and third light valves, to reflect selected wavelength bands of light without changing their polarization direction.
10. A system comprising:
a video unit to output a video signal; and
a projection system, coupled to the video unit, to receive the video signal and project video, said projection system comprising
a light source to produce light in first, second, and third wavelength bands;
a reflective light valve arrangement optically coupled to the light source, comprising
a plate-type transflective polarizing beam splitter selected from the group consisting of a wire grid device, a multi-layer thin film device, a cholesteric polymer liquid crystal device and a laminated polymer sheet device,
a color filter, and
first, second and third reflective liquid crystal light valves; and
a projection lens optically coupled to the reflective light valve arrangement.
11. The system of claim 10 , wherein
the plate-type transflective polarizing beam splitter is to receive the first, second, and third wavelength bands of light, to transmit, in a first polarization direction, the first wavelength band of light and to reflect in a second polarization direction the second and third wavelength bands of light;
the color filter is to receive the second and third wavelength bands of light, to transmit in the second polarization direction the second wavelength band of light, and to reflect in the second polarization direction the third wavelength band of light; and
the first, second, and third reflective liquid crystal light valves to selectively reflect portions of the respective first, second, and third wavelength bands of light toward the projection lens.
12. The system of claim 11 , in which the first and second polarization directions are substantially orthogonal linear polarization directions.
13. The system of claim 10 , wherein at least a selected one of the reflective liquid crystal light valves includes a plurality of pixels selectively switchable between a dark polarization state and an illuminated polarization state.
14. The system of claim 13 , further comprising:
a controller, coupled to the video unit, to selectively control the plurality of pixels of the first, second, and third reflective liquid crystal light valves.
15. The system of claim 10 , in which the first, second, and third wavelength bands of light each include a selected one of a green, a blue, and a red wavelength band.
16. The system of claim 10 , in which the light source emits the first, second, and third wavelength bands of light in a second polarization direction.
17. The system of claim 10 , further comprising:
each of the first, second, and third wavelength bands of light having selected ones of a first and second polarization direction; and
one or more dichroic trim filters respectively associated with one or more of the first, second, and third reflective liquid crystal light valves, to reflect selected wavelength bands of light without changing their polarization direction.
18. An apparatus comprising:
a light source to produce light in first, second and third wavelength bands;
a plate-type transflective polarizing beam splitter selected from the group consisting of a wire grid device, a multi-layer thin film device, a cholesteric polymer liquid crystal device, and a laminated polymer sheet device, the plate-type transflective polarizing beam splitter
to receive the first, second, and third wavelength bands of light,
to transmit, in a first polarization direction, the first wavelength band of light, and
to reflect, in a second polarization direction, the second and third wavelength bands of light;
a color filter
to receive the second and third wavelength bands of light,
to transmit in the second polarization direction, the second wavelength band of light, and
to reflect in the second polarization direction, the third wavelength band of light; and
first, second and third reflective liquid crystal light valves to selectively reflect portions of the respective first, second and third wavelength bands of light toward a projection lens.