Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1999-03-29
2002-04-30
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
Reexamination Certificate
active
06379010
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type display using a light valve, particularly to a projection type display using a transmission type liquid crystal light valve.
2. Description of the Related Art
Among the projection type displays using the light valve for a light modulation, a projection type display using a liquid crystal light valve called a liquid crystal projector has the possibility to take the place of the CRT in the near future because the liquid crystal projector allows to display a fine and large image screen.
As the conventional projection type display used, there are a liquid crystal projector arranging a polarizing plate which has a transmission axis (or an absorption axis) oriented at 45 degrees diagonal with respect to the horizontal direction of a projection screen on the exiting side of a normally white type liquid crystal panel using a TN (twisted nematic) liquid crystal, and a liquid crystal projector having a transmission axis (or absorption axis) oriented parallel or perpendicular to the horizontal direction.
An exiting light from these conventional liquid crystal projectors is projected on the screen after being converted to a polarized light vibrating in the direction parallel to a major side or minor side of the display area of a rectangular shaped screen by a polarization converting device and so on. Also, one color of the three primary colors has a polarizing direction substantially orthogonal to the other two colors.
An example of a schematic structure of this conventional projection type display is briefly described with reference to FIG.
30
.
FIG. 30
shows the conventional projection type display using the transmission type liquid crystal light valve. A projection optical system of the projection type display is composed of a light source
1
, liquid crystal light valves
21
R,
21
G and
21
B, dichroic mirrors
4
and
6
, a dichroic prism
14
, a projection lens
16
and the like. The liquid crystal light valves
21
R,
21
G and
21
B having a structure, which sandwiches both surfaces of liquid crystal panels
20
R,
20
G and
20
B by polarizing plates, is used. The liquid crystal light valves
21
R,
21
G and
21
B shown in
FIG. 30
, provide polarizing plates
20
Rp,
20
Gp and
20
Bp on the exiting sides of the liquid crystal panels
20
R,
20
G and
20
B respectively. On the incident side, a common polarization converting device
2
is arranged in the vicinity of the light source
1
. Further, each of half-wave plates
20
Ri′,
20
Gi′ and
20
Bi′ is inserted on each incident side of the liquid crystal light valves
21
R,
21
G and
21
B respectively and each of half-wave plates
20
Ri,
20
Gi and
20
Bi is inserted on each of exiting sides respectively.
The three liquid crystal light valves
21
R,
21
G and
21
B form images by modulating the intensity of the three primary colors of red (R), green (G) and blue (B) respectively according to image signals and transmit the images to the dichroic prism
14
which is, for example, a color synthesizing optical system. The liquid crystal light valve
21
G is arranged at a position where the exiting light passes through the dichroic prism
14
and exits the prism
14
. The liquid crystal light valve
21
R is arranged at a position where the exiting light is reflected by a dichroic surface
14
b
of the dichroic prism
14
and exits the prism
14
. Also, the liquid crystal light valve
21
B is arranged at a position where the exiting light is reflected by a dichroic surface
14
a
of the dichroic prism
14
and exits the prism
14
.
In the projection type display shown in
FIG. 30
, a white light illuminated from the light source
1
is incident on the dichroic mirror
4
as a linearly polarized light (p-polarization) having a polarizing direction (shown by arrows in the diagram) parallel to this page, after passing through the polarization converting device
2
. The dichroic mirror
4
is structured so that a blue light is reflected thereby and other colors pass therethrough, where blue reflected by the dichroic mirror
4
is also reflected by a mirror
12
and is incident on the half-wave plate
20
Bi′. On the other hand, lights other than blue light pass through the dichroic mirror
4
and are incident on the next dichroic mirror
6
. The polarizing direction of the blue light, which is incident on the half-wave plate
20
Bi′, is rotated 45 degrees and then the blue light is incident on the liquid crystal panel
20
B which has substantially the same polarizing direction as the orientation direction of liquid crystal molecules on the incident side of the substrate side of the liquid crystal panel
20
B in the blue liquid crystal light valve
21
B.
On the other hand, the light passing through the dichroic mirror
4
is incident on the dichroic mirror
6
structured to reflect the green color and pass the red color. The green color reflected by the dichroic mirror
6
is incident on the half-wave plate
20
Gi′. The polarizing direction of the green color, which is incident on the half-wave plate
20
Gi′, is rotated 45 degrees by the half-wave plate
20
Gi′ and the green light is incident on the liquid crystal panel
20
G, which has a polarizing direction substantially the same as the orientation direction of liquid crystal molecules on the substrate side of the incident side of the liquid crystal panel
20
G in the liquid crystal light valve
21
G for green. Also, the red light passing through the dichroic mirror
6
is incident on the half-wave plate
20
Ri′ after reflected by mirrors
8
and
10
. The polarizing direction of the red light, which is incident on the half-wave plate
20
Ri′, is rotated 45 degrees by the half-wave plate
20
Ri′ and the red light is incident on the liquid crystal panel
20
R which has a polarizing direction substantially the same as the orientation direction of the liquid crystal molecules on the substrate side of the incident side of the liquid crystal panel
20
R in the liquid crystal light valve
21
R for red.
A substrate on each exiting side of the liquid crystal panel
20
R,
20
G and
20
B is rubbed in the direction orthogonal to the orientation direction of the liquid crystal molecules on the substrate side to which the light is incident. Therefore, a TN (twisted nematic) liquid crystal layer is formed on any of the liquid crystal panels
20
R,
20
G and
20
B. Also, each of the liquid crystal panels
20
R,
20
G and
20
B is an active matrix type liquid crystal panel, having a plurality of pixel areas where a p-Si TFT (a thin film transistor using poly-silicone for a channel layer) is formed as a switching device.
The blue light which is incident on the liquid crystal light valve
21
B for blue is modulated by driving the switching device at the liquid crystal panel
20
B and exits the polarizing plate
20
Bp. The transmission axis of the polarizing plate
20
Bp is set substantially in the same direction as the orientation direction of the liquid crystal molecules on the substrate side of the exiting side of the liquid crystal panel
20
B. Therefore, the liquid crystal panel
20
B is driven by a so-called normally white type, which obtains the greatest light transmission ratio under the condition where no voltage is applied to the TN liquid crystal layer of the pixel area. The blue light exiting the polarizing plate
20
Bp is in turn incident on the half-wave plate
20
Bi and the polarizing direction is converted to a polarizing direction perpendicular to this page, thereby being incident on the dichroic surface
14
a
as a s-polarized light and being reflected.
Similarly, the red light incident on the liquid crystal light valve
21
R for red is also modulated by the driving of the switching device in the liquid crystal panel
20
R and exits the polarizing plate
20
Rp. The transmission axis of the polarizing plate
20
Rp is also set substantially in the same direction as the orientation direction of the liquid crystal molecule
Gotoh Takeshi
Hamada Tetsuya
Hayashi Keiji
Kobayashi Tetsuya
Sugawara Mari
Dowling William
Fujitsu Limited
Greer Burns & Crain Ltd.
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