Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2000-12-19
2004-06-01
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S034000, C353S037000, C353S082000, C353S098000, C349S009000, C348S751000
Reexamination Certificate
active
06742897
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid crystal projector device incorporating a reflection type liquid crystal panel designed for realizing a greater compactness by reducing the number of parts.
BACKGROUND ART
The conventional liquid crystal projector device using the reflection type liquid crystal panel is designed so that, for example as shown in
FIG. 1
, a white light from a light source
1
is condensed by lens arrays
2
,
5
and a lens
6
; the condensed light is separated into the lights for three colors coming within a red color range, a green color range and a blue color range respectively; s-polarized light components of the different color ranges are separated by polarizing beam splitters (PBS)
44
R,
44
G and
44
B to be incident on reflection type liquid crystal panels
41
,
42
and
43
for the ranges of red color, green color and blue color
10
R,
10
G and
10
B respectively; image-forming lights having p-polarized light components of different color ranges, which have been modulated and reflected to be output, are synthesized by a cross dichroic prism
45
to be projected on a screen through a projection lens
11
. It is essential for such a conventional liquid crystal projector device not only to provide three PBS's and a costly cross dichroic prism but also to lay out the reflection type liquid crystal panels
10
R,
10
G and
10
B on the optical paths of the light rays of red color range, green color range and blue color range respectively so that these light rays will not interfere with one another, preventing the use of a more compact casing.
The present invention was made in consideration of such a problem and designed not only to reduce the dimensions of the device by providing an optical block having a dichroic reflection characteristic and a retarding characteristic so that the plane of polarization of the light ray of the specified wavelength range can be rotated by 90° to reduce the number of parts that results in the reduction of the dimensions of the device and also makes the three reflection type liquid crystal panels compatible with one another by using a ½ retarding plate.
DISCLOSURE OF THE INVENTION
According to the liquid crystal projector device of the present invention, which is primarily designed so that the white light, coming from the light source, is separated into the lights of red color range, green color range and blue color range and polarized respectively; the separated and polarized light rays are made to be incident on three pieces of reflection type liquid crystal panels for red color range, green color range and blue color range respectively; the image-forming lights modulated and reflected by the reflection type liquid crystal panels are synthesized for projection; wherein an optical unit designed for rotating by 90° the plane of polarization of a specified light ray out of those of the three color ranges is provided so that either the light ray of a color range, whose plane of polarization has been rotated 90°, outputted from the optical unit or the light ray of a color range, whose plane of polarization has not been rotated, is made to be incident on each of the reflection type liquid crystal panels.
The optical unit comprises a first dichroic layer, which permits the transmission of the light ray of a specified color range and reflects the light rays of other color ranges, a retarding layer for rotating by 90° the plane of polarization of the light ray, which is allowed to pass through the first dichroic layer, and a total reflection layer for totally reflecting the light ray from the retarding layer.
Further, the optical unit may comprise a second dichroic layer designed for transmitting the light ray of a specified color range while reflecting the light rays of other color ranges, a retarding layer, for rotating by 90° the plane of polarization of the light rays which has passed through the second dichroic layer and a third dichroic layer having a predetermined gradient dichroic characteristic for reflecting the light rays coming from the retarding layer so that the difference in dichroic characteristics resulting from the difference in the angle of incidence to the second dichroic layer owing to being not parallel to the incident light.
Then, a reflection unit comprising a dichroic layer having a dichroic characteristic similar to that of the first dichroic layer or the second dichroic layer, a transmission layer, which will not cause a phase difference corresponding to the above-mentioned retarding layer, and a total reflection layer is provided before the optical unit in order to correct the optical path difference occurring in the optical unit.
Further, the first dichroic layer for s-polarization or the second dichroic layer for the same is used for a high transmittance characteristic that contributes to an effective utilization of the light rays.
Further, a ½ retarding plate for rotating by 90° the plane of polarization of incident light is provided before the reflection type liquid crystal panel, which is similar to the other two reflection type liquid crystal panels, for receiving the light ray reflected by the first dichroic layer or the second dichroic layer, whereby the common reflection type liquid crystal panels can be used.
Further, a polarization beam splitter provided for reflecting a light ray of a color range whose plane of polarization is not rotated by the optical unit while transmitting the light rays of other two color ranges whose planes of polarization are rotated by 90° respectively, a dichroic prism provided for making the light ray of one color range reflected by the polarization beam splitter incident on one of the reflection type liquid crystal panels, while transmitting one light ray of one color range out of the two light rays which have passed through the polarization beam splitter and reflecting the other so that the two light rays of the two different color ranges are incident on the two reflection type liquid crystal panels respectively, and the image-forming light rays, which are modulated and reflected by the two reflection type liquid crystal panels, synthesized by the dichroic prism and reflected by the polarization beam splitter to be projected on a screen through a projection lens together with an image-forming light ray, which has passed through the polarization beam splitter and then modulated and reflected by the one reflection type liquid crystal panel, are primary constituents, wherein the dichroic prism is designed so that the reflected light ray is given on the opposite side to the projection lens, and a corresponding liquid crystal panel is provided at the corresponding position for easy mounting of the projection lens flange.
Further, the first dichroic layer or the second dichroic layer is one for reflecting the light ray of green color range and capable of making the characteristic of the dichroic prism milder.
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Adams Russell
Cruz Magda
Fujitsu General Limited
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