Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2002-05-17
2003-12-16
Spector, David N. (Department: 2872)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S640000, C359S638000
Reexamination Certificate
active
06665122
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a three-plate projection-type image display apparatus including light valves (e.g., liquid crystal panels), one each for red, green and blue light beams, as a modulation means so that display images of the respective light beams are combined in the apparatus and projected to form a magnified image on a screen.
2. Background Art
The projector market, especially for projection-type image display apparatuses using a transmission-type liquid crystal panel, now is growing rapidly. The trends of products can be divided into two major categories: higher brightness and smaller size. In particular, the diagonal size of an effective aperture of a liquid crystal panel is reduced from 1.3 inches, which has been a mainstream diagonal size, to 0.9 inches at present and is expected to be reduced further in the future. While reducing the effective aperture size, the transmission-type liquid crystal panel has a very small black matrix (BM) and a numerical aperture high enough to be comparable with that of a conventional liquid crystal panel that is one size larger than the above liquid crystal panel. With the implementation of such a small-size high-density liquid crystal panel, a color combination portion for combining display images on the liquid crystal panels also needs to provide higher accuracy.
Next, the configuration of a conventional projection-type image display apparatus using liquid crystal panels will be described. Three-plate projection-type image display apparatuses including liquid crystal panels, one each for red, green and blue light beams, can be classified roughly into two categories according to their characteristics in color combination: a cross-prism system and a mirror-sequential system.
FIGS. 7 and 8
schematically show the basic configurations of conventional projection-type image display apparatuses employing the cross-prism system and the mirror-sequential system, respectively. The following is an explanation for each of the configurations.
As shown in
FIG. 7
, a cross-prism projection-type image display apparatus
100
includes a light source portion
101
, a color separation optical system
102
, a relay optical system
103
, a light valve portion
104
, a color combination optical system
105
, and a projection optical system (a projection lens)
106
.
The light source portion
101
includes a light source
107
and a reflector
108
. The light source
107
forms an arc by discharge between electrodes to generate a randomly polarized light beam. The reflector
108
reflects the light beam from the light source
107
in one direction along its axis of rotational symmetry.
A light beam from the light source portion
101
enters a blue-reflection dichroic mirror
109
of the color separation optical system
102
, where a blue light beam of the incident light is reflected. Then, the blue light beam is reflected from a total reflection mirror
110
and passes through a condenser lens
111
into a blue light valve unit
112
. Green and red light beams are transmitted by the blue-reflection dichroic mirror
109
and enter a green-reflection dichroic mirror
113
, where the green light beam is reflected and passes through a condenser lens
114
into a green light valve unit
115
. The red light beam is transmitted by the green-reflection dichroic mirror
113
and enters the relay optical system
103
. Then, the red light beam passes through an entrance lens
116
, a total reflection mirror
117
, an intermediate lens
118
, a total reflection mirror
119
, and a condenser lens
120
into a red light valve unit
121
.
The light valve portion
104
includes the blue, green and red light valve units
112
,
115
and
121
, which are arranged in accordance with the respective light beams. Each of the light valve units
112
,
115
and
121
includes an entrance polarizing plate
122
, a liquid crystal panel
123
, and an exit polarizing plate
124
, as shown in FIG.
2
. The entrance polarizing plate
122
is rectangular in shape and designed, e.g., to transmit light polarized in the short side direction and to absorb light polarized in the direction perpendicular thereto. The light beam passing through the entrance polarizing plate
122
enters the liquid crystal panel
123
. The liquid crystal panel
123
has many pixels arranged in the form of an array and can change the polarization direction of the incident light at each pixel aperture with an external signal. In this example, when the pixels are not driven, the liquid crystal panel
123
transmits the incident light while rotating its polarization direction by 90 degrees; when the pixels are driven, the liquid crystal panel
123
transmits the incident light without changing its polarization direction. The exit polarizing plate
124
has polarization characteristics in the direction perpendicular to the entrance polarizing plate
122
. In other words, the exit polarizing plate
124
has a transmission axis in the long side direction of its rectangular outline and transmits light polarized in this direction. Therefore, the light beam that has entered the undriven pixel of the liquid crystal panel
123
and been transmitted with its polarization direction rotated by 90 degrees can pass through the exit polarizing plate
124
because it is polarized in the direction parallel to the transmission axis. On the other hand, the light beam that has entered the driven pixel of the liquid crystal panel
123
and been transmitted with its polarization direction unchanged is absorbed by the exit polarizing plate
124
because it is polarized in the direction perpendicular to the transmission axis.
The light beams thus transmitted through the light valve portion
104
enter the color combination optical system
105
. The color combination optical system
105
is a color combination prism formed by joining four triangular prisms so that a blue-reflection dichroic mirror surface
125
and a red-reflection dichroic mirror surface
126
cross at right angles. The blue and red light beams incident on the color combination optical system
105
are reflected from the blue-reflection dichroic mirror surface
125
and the red-reflection dichroic mirror surface
126
, respectively, and then enter the projection lens
106
, which acts as a projection optical system. The green light beam passes through the blue- and red-reflection dichroic mirror surfaces
125
,
126
and enters the projection lens
106
.
The projection lens
106
magnifies and projects the incident light onto a screen (not shown). In this manner, images of three light beams, each of which is formed in the light valve portion
104
, are combined and displayed as a color image.
As shown in
FIG. 8
, a mirror-sequential projection-type image display apparatus includes a light source portion
201
, a color separation optical system
202
, a light valve portion
203
, a color combination optical system
204
, and a projection optical system (a projection lens)
205
.
The light source portion
201
includes a light source
206
and a reflector
207
. The light source
206
forms an arc by discharge between electrodes to generate a randomly polarized light beam. The reflector
207
reflects the light beam from the light source
206
in one direction along its axis of rotational symmetry.
A light beam from the light source portion
201
enters a blue-reflection dichroic mirror
208
of the color separation optical system
202
, where a blue light beam of the incident light is reflected. Then, the blue light beam is reflected from a total reflection mirror
209
and passes through a condenser lens
210
into a blue light valve unit
211
. Green and red light beams are transmitted by the blue-reflection dichroic mirror
208
and enter a green-reflection dichroic mirror
212
, where the green light beam is reflected and passes through a condenser lens
213
into a green light valve unit
214
. The red light beam is transmitted by the green-reflection dichroic mirror
212
and passes through a condenser len
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Spector David N.
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