Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2002-12-27
2004-09-28
Mathews, Alan A. (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S020000, C353S033000, C353S082000, C353S084000, C353S089000, C359S256000, C359S435000, C359S634000, C359S494010, C359S577000, C348S339000, C348S057000, C362S231000, C362S293000
Reexamination Certificate
active
06796657
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a projection type display apparatus normally called liquid crystal projector in which a liquid crystal light valve is used.
A projection type display apparatus in which a liquid crystal light valve is used is conventionally configured in such a manner as shown in FIG.
11
.
Referring to
FIG. 11
, the projection type display apparatus
90
shown includes an illumination unit (illumination optical system)
10
wherein part of non-polarized white light from a white light source
11
directly passes, but the remaining part of the non-polarized white light is first reflected by a reflector
12
and then passes, through a pair of multi-lens arrays
13
and
14
disposed in an opposing relationship to each other so that they are converted into a light flux which has an intensity distribution uniform within a fixed region on a plane perpendicular to the center axis of the light flux. Further, the light flux is converted from non-polarized light into linearly polarized light by a polarizing conversion element
15
and goes out from the illumination unit
10
through a condenser lens
16
.
The light flux going out from the illumination unit
10
is decomposed into red color light
3
R, green and blue color light
3
GB by a dichroic mirror
21
, and the red color light
3
R is reflected by a mirror
22
and introduced into a liquid crystal light valve
30
R for red through a condenser lens
28
R.
Meanwhile, the green and blue color light
3
GB is decomposed into green color light
3
G and blue color light
3
B by a dichroic mirror
23
, and the green color light
3
G is introduced into a liquid crystal light valve
30
G for green through a condenser lens
28
G while the blue color light
3
B is introduced into a liquid crystal light valve
30
B for blue through a relay lens
24
, a mirror
25
, another relay lens
26
, another mirror
27
and a condenser lens
28
B.
The liquid crystal light valves
30
R,
30
G and
30
B are each formed from a liquid crystal panel of the transmission type, and images are written into the liquid crystal light valves
30
R,
30
G and
30
B with red, green and blue color signals, respectively.
The decomposed color lights
3
R,
3
G and
3
B of red, green and blue are modulated and converted into image lights
4
R,
4
G and
4
B of red, green and blue by the liquid crystal light valves
30
R,
30
G and
30
B, respectively. The image lights
4
R,
4
G and
4
B of red, green and blue are synthesized by a dichroic prism
40
, and the image light
5
after the synthesis is projected in an enlarged scale on a screen
110
by a projection lens
50
.
While
FIG. 11
shows a display apparatus of the front projection type wherein the optical units from the illumination unit
10
to the projection lens
50
form the projection type display apparatus
90
separately from the screen
110
, also optical units of a display apparatus of the back projection type wherein the optical units from the illumination unit to the projection lens and the screen are disposed in a cabinet are formed similarly as in the projection type display apparatus
90
of FIG.
11
.
With the conventional projection type display apparatus described above, however, the contrast on the screen cannot be raised higher than a certain fixed value from a view angle of a liquid crystal panel which composes each of the liquid crystal light valves as described below.
FIG. 12
illustrates a manner wherein a light flux from the illumination unit
10
in the projection type display apparatus
90
of
FIG. 11
is introduced into a liquid crystal light valve
30
in principle with the decomposition optical system omitted. Here, the liquid crystal light valve
30
is the liquid crystal light valve
30
R,
30
G or
30
B for red, green or blue.
It is to be noted, however, that, while, in the projection type display apparatus
90
of
FIG. 11
, the lengths of the optical paths from the illumination unit
10
to the liquid crystal light valves
30
R,
30
G and
30
B are set such that the optical paths for the red color light
3
R and the green color light
3
G are equal to each other but the optical path for the blue color light
3
B is longer than those for the red color light
3
R and the green color light
3
G so that the length is unequal with regard to the blue color, it is assumed that, in
FIG. 12
, the optical path lengths from the illumination unit
10
to the liquid crystal light valve
30
are equal for the red, green and blue color lights for the convenience of description.
Usually, the size of the light exit of the illumination unit
10
is relatively greater than the aperture size of the liquid crystal light valve
30
. Therefore, light emitted from the illumination unit
10
is introduced into the liquid crystal light valve
30
while being condensed, and as viewed from the liquid crystal light valve
30
, the light is introduced from every direction within a certain angular range with respect to the direction of a normal
32
to the liquid crystal light valve
30
.
However, since TN (Twisted Nematic) liquid crystal of the twisted light mode wherein the major axis of a liquid crystal molecule is twisted by 90° between the top and the bottom of the liquid crystal layer is used for a liquid crystal panel which composes the liquid crystal light valve
30
, the light shutter characteristic differs depending upon the view angle.
As regards the view angle, as shown in
FIG. 13
, the angle &phgr; of outgoing light
33
b
from the liquid crystal panel
31
originating from incoming light
33
a
to the liquid crystal panel
31
with respect to a reference azimuth on an outgoing face
34
of the liquid crystal panel
31
is defined as an azimuth angle, and an angle &thgr; of the outgoing light
33
b
with respect to the normal
32
to the liquid crystal panel
31
is defined as a polar angle. As viewed on the display screen on the outgoing face
34
, &phgr;=0° corresponds to the rightward direction; &phgr;=90° corresponds to the upward direction; &phgr;=180° corresponds to the leftward direction; and &phgr;=270° corresponds to the downward direction.
FIG. 14
illustrates a result of measurement of the view angle dependency of the light cutoff rate which was performed while a certain liquid crystal panel was placed in an all-black state. The center of concentric circles corresponds to &thgr;=0; the circle denoted by numeral
5
corresponds to &thgr;=5°; the circle denoted by numeral
10
corresponds to &thgr;=10°; and the circle denoted by numeral
15
corresponds to &thgr;=15°.
The region indicated as “99% ~” is a view angle range within which light less then 1% is transmitted; the region indicated as “90% ~” is a view angle range within which light less than 10% is transmitted; the region indicated as “80% ~” and surrounded by a thick line is a view angle range within which light less than 20% is transmitted; and the region indicated as “70% ~” and surrounded by a broken line is a view angle range within which light less than 30% is transmitted.
Accordingly, with the liquid crystal panel shown, a sufficient light shutter function is exhibited and a high contrast is exhibited for any light flux
37
which penetrates the liquid crystal panel upwardly from below when the liquid crystal panel is viewed downwardly from above as indicated by an arrow mark
35
of
FIG. 12
as viewed from the outgoing face
34
side shown in FIG.
13
. However, the light shutter function is inferior and the contrast is low for any light flux
38
which penetrates the liquid crystal panel downwardly from above when the liquid crystal panel is viewed upwardly from below as indicated by an arrow mark
36
of FIG.
12
.
Since the contrast on the screen is given by an arithmetic mean of contrasts of light fluxes introduced into the liquid crystal light valve
30
, with the conventional projection type display apparatus described above, the contrast on the screen cannot be raised higher than a certain fixed value.
In order to solve
Shinoda Makoto
Sugihara Kenji
Cruz Magda
Frommer William S.
Frommer & Lawrence & Haug LLP
Mathews Alan A.
Polito Bruno
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