Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
2002-07-17
2004-12-14
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
C353S031000, C353S020000, C349S009000
Reexamination Certificate
active
06831706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection image display apparatus using an image display element.
2. Related Background Art
A reflection image display element such as a reflection LCD panel reflects incident illumination light and forms image light by performing modulation in accordance with an image signal. For example, Japanese Patent Application Laid-Open No. 2000-284228 discloses a projection image display apparatus which performs color separation/synthesis and projecting an image by using such a reflection image display element, a color selective retardation plate for rot 90° the polarization direction of only light in a given wavelength region, and a polarizing beam splitter having a polarization split surface having the properties of reflecting S-polarized light and transmitting P-polarized light.
FIG. 15
shows an arrangement of a conventional projection image display apparatus. This apparatus includes a light source
101
, polarizing plate
102
, color selective retardation plates
103
,
104
, and
105
, polarizing beam splitters
106
,
107
,
108
and
109
, reflection liquid crystal display elements
110
R,
111
B, and
112
G, and projection lens
113
.
The unpolarized light emitted from the light source
101
is converted into linearly polarized light (P-polarized light) by the polarizing plate
102
, and the polarization direction of only red (R) light is rotated by 90° by the color selective retardation plate
103
to convert the red light into S-polarized light. The red light which is S-polarized light is incident on the polarizing beam splitter
106
and reflected, and green (G) light and blue (B) light, other than the red light, which are P-polarized light, are transmitted through the polarizing beam splitter
106
. With this operation, the unpolarized light is color-separated into red light, and green light and blue light.
The red light is reflected by the polarizing beam splitter
108
and incident on the reflection liquid crystal display element
110
R. The green light and blue light are incident on the polarizing beam splitter
104
, by which the polarization direction of only the blue light is rotated by 90° to convert the light into S-polarized light.
The polarizing beam splitter
107
reflects the blue light which is S-polarized light and transmits the green light which is P-polarized light, thereby color-separating these light components. The blue light and green light are then incident on the reflection liquid crystal display elements
111
B and
112
G, respectively.
Of the red light modulated by the reflection liquid crystal display element
110
R, the S-polarized light component is reflected by the polarizing beam splitter
108
and returns to the light source
101
side, and the P-polarized light component is transmitted through the polarizing beam splitter
108
to become projection light.
Of the light modulated by the reflection liquid crystal display element
111
B, the S-polarized light component is reflected by the polarizing beam splitter
107
and returns to the light source
101
side, and the P-polarized light component is transmitted through the polarizing beam splitter
107
to become projection light.
Of the light modulated by the reflection liquid crystal display element
112
G, the P-polarized light is transmitted through the polarizing beam splitter
107
and returns to the light source
101
side, and the S-polarized light is reflected by the polarizing beam splitter
107
to become projection light.
The blue light and green light both comprising projection light are incident on the color selective retardation plate
105
, by which the polarization direction of the blue light is rotated by 90°, thereby uniformly converting both the blue light and the green light into S-polarized light.
The blue light and green light which have become S-polarized light are reflected by the polarizing beam splitter
109
, whereas the red light which is P-polarized light is transmitted through the polarizing beam splitter
109
. With this operation, the red light, green light, and blue light are synthesized into one light. This light is then projected through the projection lens
113
to display a color image.
In general, a polarizing beam splitter (i.e., a polarization split surface) exhibits ideal polarization split performance as shown in
FIG. 16
with respect to light incident on this polarization split surface at 45°, but exhibits imperfect characteristics as shown in
FIG. 17
with respect to light incident at angles deviating from 45°.
This is because since an optical thin film forming a polarization split surface acts on optical performance at n·dcos&thgr; where n is the refractive index of the thin film, d is the thickness of the thin film, and &thgr; is the incident angle of light, the optical performance changes in accordance with a change in the incident angle &thgr;.
As shown in
FIG. 2
, as an illumination system for a projection image display apparatus, an illumination system designed to uniformly illuminate the reflection image display element is widely used.
The light emitted from a light source
1
is incident on a point on a reflection liquid crystal display element R with a divergent angle 2&ohgr; through a condenser lens system
5
and field lens system
7
. For this reason, light is incident on the polarization split surface in the range from (45−&ohgr;)° to (45+&ohgr;)°. Therefore, light incident on the polarization split surface at an angle deviating from 45° is not perfectly separated into a P-polarized light component and S-polarized light component.
In this case, since the polarization direction of light reflected by a reflection liquid crystal display element ready to display black is the same as that of light incident on the reflection image display element, the light reflected by the reflection image display element must be returned to the light source side through the polarizing beam splitter and detected by the polarizing beam splitter.
However, since the light reflected by the reflection image display element ready to display black is incident on the polarizing beam splitter with a spread corresponding to the incident angle 2&ohgr;, light incident at an angle deviating from 45° is not detected by the polarizing beam splitter and becomes so-called leakage light, which is projected through the projection lens. As the amount of leakage light increases, displayed black appears as if it was floating, and the contrast of an image may decrease.
SUMMARY OF THE INVENTION
For preventing above situation, one aspect of the present invention is to provide a projection image display apparatus comprising an illumination optical system which illuminates an image display element with light from a light source and a projection optical system which projects light from the image display element through two,polarization split surfaces, wherein when an occurrence ratio of leakage light on one polarization split surface with respect to a light ray having a wavelength &lgr; is represented by analysis performance K(&lgr;), relative visibility of the human eye is represented by Y(&lgr;), and a wavelength region of light rays incident on the one polarization split surface is represented by a range of &lgr;
1
to &lgr;
2
, a value M given by
M
=
∫
λ
1
λ
2
Y
(
λ
)
K
(
λ
)
ⅆ
λ
/
∫
λ
1
λ
2
Y
(
λ
)
ⅆ
λ
is set as a leakage light amount on the polarization split surface, of the light rays incident on one of the two polarization split surfaces which is located on the image display element side whose angles with respect to an optical axis correspond to 55% of a maximum angle of the incident light rays with respect to the optical axis, light lays of which incident angle with respect to said image display element is larger is set as first light ray and light rays of which incident angle with respect to said image display element is smal
Abe Masayuki
Ohtaka Keiji
Okuyama Atsushi
Canon Kabushiki Kiasha
Morgan & Finnegan , LLP
Ton Toan
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