Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
2000-01-11
2003-05-06
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
C353S038000
Reexamination Certificate
active
06559900
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type display apparatus that projects an image by inputting a light beam emitted from the light source to a spatial light modulation device that is also called a light valve.
2. Description of the Related Art
In recent years, projection type TV receivers, projector apparatuses, computer display devices, etc. that use, for example, a liquid crystal display panel that is a spatial light modulation device have spread.
FIGS. 1A and 1B
show, among those apparatuses, a rear projection type TV receiver using a liquid crystal display panel. This rear projection type TV receiver
11
incorporates a projection type display apparatus
13
, a mirror
14
, a screen
15
, etc. in a cabinet
12
. A light beam
16
that is output from the projection type display apparatus
13
is reflected by the mirror
14
and shines on the back surface of the screen
15
, whereby a color or black-and-white image is displayed on the screen
15
. Therefore a viewer views the image on the screen
15
from the front side of the screen
15
.
FIGS. 2 and 3
show a color projection type display apparatus
13
. In this projection type display apparatus
13
, a light source
18
is detachably attached to an illumination optical system
17
and a rectangular-prism-shaped dichroic prism
21
is also attached to the illumination optical system
17
. Red, green, and blue liquid crystal panels
22
-
24
are opposed to three side faces of the dichroic prism
21
, respectively. In each of the liquid crystal display panels
22
-
24
, a polarizer and an analyzer are disposed on the incidence side and the exit side of a liquid crystal cell. Spatial light modulation is performed in such a manner that each pixel of the liquid crystal cell selectively rotates the polarization plane of incident light in accordance with a video signal.
A projection lens
25
, which is opposed to the remaining side face of the dichroic prism
21
, is detachably attached to the illumination optical system
17
. The projection lens
25
and the dichroic prism
21
have the liquid crystal display panels
22
-
24
and the screen
15
as conjugate points. The light source
18
has a parabolic mirror
18
a
and a lamp
18
b
that is disposed at the focal position of the parabolic mirror
18
a
. A metal halide lamp, a halogen lamp, or the like is used as the lamp
18
b.
A filter
28
, a lens array
29
, and a polarization conversion device
32
are disposed in succession on the optical axis of the light source
18
. The filter
28
passes only a light beam
27
in a visible range while interrupting unnecessary light beams in an infrared and ultraviolet ranges of a light beam
26
that is emitted from the light source
18
. The lens array
29
is configured in such a manner that a plurality of convex cell lenses
29
a
are arranged in matrix form. For example, the polarization conversion device
32
converts the light beam
27
that is output from the lens array
29
and generally includes P-waves and S-waves in mixture into a light beam
31
having only P-waves by converting S-waves into P-waves.
In the polarization conversion device
32
, a polarizing beam splitter passes P-waves while reflecting S-waves and a half-wave plate converts the reflected S-waves into P-waves. If the light beam
27
including P-waves and S-waves in mixture were input to the polarizers of the liquid crystal display panels
22
-
24
, the S-waves of the light beam
27
would be interrupted by the polarizers and hence the light beam
27
would not be utilized effectively. In contrast, if the light beam
31
having only P-waves is input to the polarizers of the liquid crystal display panels
22
-
24
, all of the light beam
31
passes through the polarizers and hence the light beam
31
is utilized effectively.
The incidence surface of a lens
33
is disposed in the vicinity of the focal plane of the image space of the lens array
29
. The incidence surface of the lens
33
is formed with a lens array
34
in such a manner that a plurality of convex cell lenses
34
a
are arranged so as to correspond to the respective cell lenses
29
a
. The exit surface of the lens
33
is formed with a condenser lens
35
that has a single convex shape and condenses, onto the liquid crystal display panels
22
-
24
, the light beam
31
that has passed through the lens array
34
. A dichroic mirror
36
that reflects red light R and passes,green light G and blue light B, a dichroic mirror
37
that reflects the green light G and passes the blue light B, a relay lens
38
, and a mirror
41
are disposed in succession downstream of the lens
33
.
A mirror
42
and a condenser lens
43
are disposed on the optical path between the dichroic mirror
36
and the liquid crystal display panel
22
. A condenser lens
44
is disposed on the optical path between the dichroic mirror
37
and the liquid crystal display panel
23
. A relay lens
45
, a mirror
46
, and a condenser lens
47
are disposed on the optical path between the mirror
41
and the liquid crystal display panel
24
. The liquid crystal display panels
22
-
24
are disposed on the focal planes of the image space of the lens array
34
. The condenser lenses
43
,
44
, and
47
are disposed in the vicinity of the respective liquid crystal display panels
22
-
24
.
The dichroic prism
21
is configured in such a manner that triangular-prism-shaped prisms
21
A-
21
D made of plastics or glass are bonded together via optical thin films
21
a
and
21
b
. The optical thin film
21
a
reflects red light R and passes green light G and blue light B. The optical thin film
21
b
reflects blue light B and passes red light R and green light G. Therefore, the dichroic prism
21
outputs a light beam
16
in which a red image, a green image, and a blue image are combined together. The light beam
16
shines on the back surface of the screen
15
via the projection lens
25
, whereby a color image is displayed on the screen
15
.
FIGS. 4 and 5
show how green light G of the light beam
27
that has passed through the filter
28
travels. Red light R and blue light B travel in the same manner as the green light G though their optical paths are different from the optical path of the green light G. In the light source
18
, the lamp
18
b
is disposed at the focal position of the parabolic mirror
18
a
. However, since the light emitting portion of the lamp
18
b
where arc discharge or the like occurs has a certain, limited size and hence the lamp
18
b
is not a complete point light source, not only light beams
27
shown in
FIG. 4
that are parallel with the optical axis but also light beams
27
shown in
FIG. 5
that are inclined with respect to the optical axis shine on the lens array
29
.
As shown in
FIG. 4
, light beams
27
that are emitted from the light source
18
parallel with the optical axis and shine on the lens array
29
are converged by the respective cell lenses
29
a
at their focal positions.
However, the lens array
34
is disposed in the vicinity of the focal plane of the image space of the lens array
29
and the cell lenses
34
a
of the lens array
34
correspond to the respective cell lenses
29
a
of the lens array
29
. Therefore, the light beams
27
that are emitted parallel with each other from the light source
18
and shine on the lens array
29
are converged at the central portions of the respective cell lenses
34
a
, and then condensed onto the liquid crystal display panel,
23
by the condenser lens
35
while receiving almost no lens action from the cell lenses
34
a
. The light beams
27
are condensed onto the input pupil E of the projection lens
25
by the condenser lens
44
that is disposed in the vicinity of the liquid crystal display panel
23
.
On the other hand, as shown in
FIG. 5
, the lens array
34
has, as an object plane, a plane that is located in the vicinity of the lens array
29
that is illuminated with the light source
18
, and the lens array
34
images this object plane onto the liquid cr
Kanamori Tatsuru
Kawai Tohru
Shinoda Makoto
Sugihara Kenji
Maioli Jay H.
Parker Kenneth
Sony Corporation
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