Projection apparatus

Details Projection apparatus Projection apparatus

2002-08-30

2003-11-18

Fuller, Rodney (Department: 2851)

Optics: image projectors

Polarizer or interference filter

C348S750000, C348S758000, C349S009000, C353S081000, C359S634000, C359S640000

Reexamination Certificate

active

06648474

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a projection apparatus which uses an optical modulation element of the reflection type to modulate illumination light emitted from a light source and uses a lens to project the modulated illumination light as an image of an enlarged scale.
Conventionally, in order to make display on a large screen possible, a projection apparatus is used wherein illumination light from a lamp is irradiated on an optical modulation element such as a liquid crystal panel on which a pattern corresponding to an video signal inputted to the liquid crystal panel is displayed and reflected light from the liquid crystal panel is projected in an enlarged scale to project the pattern displayed on the liquid crystal panel in an enlarged scale.
Various optical systems for a projection apparatus wherein such a liquid crystal panel of the reflection type as described above is used have been proposed. An optical system for colors which uses a polarization rotating element having a function of rotating the polarization direction of light of a particular wavelength band by 90° and a polarization beam splitter (hereinafter referred to as PBS) is superior in both of the contrast and the brightness.
An exemplary one of projection apparatus in which such an optical system as just described is used is shown in FIG.
1
. Referring to
FIG. 1
, the projector apparatus
100
shown includes a lamp
101
for irradiating illumination light and a fly's eye integrator
102
, a PS conversion and multiplexing element
103
, a main condenser
104
, a field lens
105
, a pre-polarizing plate
106
, a G polarization rotating element
107
and an incoming PBS
108
disposed in order along a path of the light irradiated from the lamp
101
.
In the projector apparatus
100
described above, illumination light emitted from the lamp
101
is uniformized by the fly's eye integrator
102
so as to have a uniform illuminance distribution. Then, P polarized light of the illumination light is converted into S polarized light by the PS conversion and multiplexing element
103
so that the illumination light thereafter includes only S polarized light. Then, the illumination light is condensed by the main condenser
104
and the field lens
105
and adjusted by the pre-polarizing plate
106
so that it has an adjusted polarization plane. Then, the polarization plane of the light in a wavelength band of green from within the illumination light of the arranged polarization plane is rotated by 90° by the G polarization rotating element
107
so that the light is converted into P polarized light. Then, the P polarized light, that is, the light in the wavelength band of green, passes through the incoming PBS
108
while the other S polarized light, that is, the light in wavelength bands of red and blue, is reflected by a reflecting surface
108
a
of the incoming PBS
108
, which is inclined by 45° with respect to the light path, so that the advancing direction thereof is changed by 90°.
The projector apparatus
100
further includes a G-PBS
109
and a first liquid crystal panel
110
disposed in this order along the path of the illumination light which has passed through from the incoming PBS
108
and advanced straightforwardly.
The illumination light having passed through and advanced straightforwardly from the incoming PBS
108
is P polarized light in the wavelength band of green and therefore passes through the G-PBS
109
and is introduced to the first liquid crystal panel
110
. The illumination light is modulated and reflected to the incoming direction by the first liquid crystal panel
110
. The reflected light reflected by the first liquid crystal panel
110
is S polarized light in the wavelength band of green and is reflected by a reflecting surface
109
a
of the G-PBS
109
, which is inclined by 45° with respect to the light path, so that the advancing direction thereof is changed by 90°.
The projector apparatus
100
further includes a R polarization rotating element
111
and a RB-PBS
112
disposed in this order in the direction of the path of the illumination light reflected by the reflecting surface
108
a
of the incoming PBS
108
, a second liquid crystal panel
113
disposed in the advancing direction of the illumination light having passed through the RB-PBS
112
, and a third liquid crystal panel
114
disposed in the advancing direction of the illumination light reflected by a reflecting surface
112
a
of the RB-PBS
112
.
The illumination light reflected by the reflecting surface
108
a
of the incoming PBS
108
is S polarized light in the wavelength bands of red and blue, and the polarization plane of the light only in the wavelength band of red is rotated by 90° by the R polarization rotating element
111
. The light of the rotated polarization plane enters the RB-PBS
112
.
Of the illumination light entering the RB-PBS
112
, the P polarized light in the wavelength band of red passes through the RB-PBS
112
and advances straightforwardly so that it is introduced to the second liquid crystal panel
113
. Then, the P polarized light is modulated and reflected to the incoming direction by the second liquid crystal panel
113
. On the other hand, of the illumination light entering the RB-PBS
112
, the S polarized light in the wavelength band of blue is reflected by the reflecting surface
112
a
of the RB-PBS
112
, which is inclined by 45° with respect to the light path, so that the advancing direction thereof is changed by 90°. Consequently, the S polarized light is introduced to the third liquid crystal panel
114
and is modulated and reflected to the incoming direction by the third liquid crystal panel
114
.
The reflected light modulated and reflected by the second liquid crystal panel
113
is S polarized light in the wavelength band of red and is reflected by the reflecting surface
112
a
of the RB-PBS
112
, which is inclined by 45° degrees with respect to the light path, so that the advancing direction of the S polarized light is changed by 90°. Meanwhile, the reflected light modulated and reflected by the third liquid crystal panel
114
is P polarized light in the wavelength band of blue, and passes through the third liquid crystal panel
114
and advances straightforwardly.
The projector apparatus
100
further includes a R polarization rotating element
115
disposed in the advancing direction of the reflected light from the second liquid crystal panel
113
reflected by the reflecting surface
112
a
of the RB-PBS
112
and the reflected light from the third liquid crystal panel
114
having passed through the RB-PBS
112
.
The reflected light from the second liquid crystal panel
113
reflected by the reflecting surface
112
a
of the RB-PBS
112
is S polarized light in the wavelength band of red, and the polarization plane of the reflected light is rotated by 90° by the R polarization rotating element
115
so that the reflected light is converted into P polarized light. Meanwhile, the reflected light from the third liquid crystal panel
114
having passed through the RB-PBS
112
is P polarized light in the wavelength band of blue and passes through the R polarization rotating element
115
.
The projector apparatus
100
further includes an outgoing PBS
116
disposed in the advancing direction of the reflected light from the first liquid crystal panel
110
reflected by the reflecting surface
109
a
of the G-PBS
109
and in the advancing directions of the reflected light from the second liquid crystal panel
113
having the polarization plane rotated by 90° by the R polarization rotating element
115
and the reflected light from the third liquid crystal panel
114
having passed through the R polarization rotating element
115
.
The reflected light from the first liquid crystal panel
110
reflected by the reflecting surface
109
a
of the G-PBS
109
is S polarized light in the wavelength band of green and is reflected by a reflecting surface
116
a
of the outgoing PBS
116
, which is inclined by 45° with respect to the light

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