Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2001-06-28
2002-12-10
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C359S619000
Reexamination Certificate
active
06491397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination optical system that converts non-polarized light rays emitted from a light source into one type of linearly polarized light beams having a substantially fixed direction of polarization. The present invention also pertains to a projector that utilizes the illumination optical system to display bright images.
2. Description of the Related Art
The projector modulates illumination light transmitted to an electro-optical device called ‘light valve’ according to image information regarding an image to be displayed and projects the modulated light on a screen to display the resulting image. A liquid crystal light valve utilizing the functions of a liquid crystal panel is generally used for the electro-optical device.
It is naturally desirable to display bright images by the projector. For this purpose, the illumination light emitted from an illumination optical system incorporated in the projector preferably has the high utilization efficiency. The liquid crystal light valve included in the projector generally utilizes only one type of linearly polarized light beams. In the case of an illumination optical system that emits non-polarized light beams, light beams having a certain direction of polarization are not utilized in the liquid crystal light valve. This worsens the utilization efficiency of the illumination light emitted from the illumination optical system. For the enhanced utilization efficiency of the illumination light by the liquid crystal light valve, some proposed illumination optical systems use a polarization conversion optical system that converts the non-polarized light beams emitted from a light source into one type of linearly polarized light beams.
FIG. 13
is a plan view schematically illustrating the structure of a main part of a prior art illumination optical system. In the description below, the direction of advance of light is defined as a z-axis direction (direction in parallel with a system optical axis SX of the illumination optical system), the direction of 12 o'clock relative to the direction of advance of light is defined as a y-axis direction (vertical direction), and the direction of 3 o'clock relative to the direction of advance of light is defined as an x-axis direction (horizontal direction). The illumination optical system includes a light source
1110
, a first lens array
1120
, a second lens array
1130
, a polarization conversion optical system
1140
, and a superimposing lens
1150
, which are arranged sequentially along the system optical axis SX. The first lens array
1120
has a plurality of minute lenses
1122
. The second lens array
1130
has a plurality of minute lenses
1132
, which respectively correspond to the plurality of minute lenses
1122
of the first lens array
1120
.
The polarization conversion optical system
1140
includes plural pairs of mutually parallel polarizing separation films
1142
and reflection films
1144
, which are arranged sequentially in the x-axis direction. The polarizing separation films
1142
and the reflection films
1144
are inclined to have a fixed angle relative to the z-axis direction. &lgr;/2 phase plates
1148
are attached to the outgoing faces of the respective polarizing separation films
1142
.
Substantially parallel light rays emitted from the light source
1110
are divided into a plurality of sub-beams by the plurality of minute lenses
1122
of the first lens array
1120
. The condensing functions of the respective minute lenses
1122
of the first lens array
1120
and the minute lenses
1132
of the second lens array
1130
cause the plurality of sub-beams to be condensed in the vicinity of the polarizing separation films
1142
in the polarization conversion optical system
1140
. An optical axis LX of the light source
1110
is displaced in a −x-axis direction from the system optical axis SX of the illumination optical system by a predetermined amount of displacement Dp (=Wp/2), in order to allow the plurality of sub-beams emitted from the first lens array
1120
to efficiently enter the polarizing separation films
1142
of the polarization conversion optical system
1140
. Here Wp denotes the distance between the polarizing separation film
1142
and the reflection film
1144
.
Out of the light beams condensed in the vicinity of the polarizing separation films
1142
, one type of linearly polarized light beams (for example, p-polarized light beams) are mostly transmitted by the polarizing separation films
1142
, whereas the other type of linearly polarized light beams (for example, s-polarized light beams) are mostly reflected by the polarizing separation films
1142
. The other type of linearly polarized light beams reflected by the polarizing separation films
1142
are further reflected by the reflection films
1144
and enter the superimposing lens
1150
. One type of linearly polarized light beams transmitted by the polarizing separation films
1142
, on the other hand, enter the &lgr;/2 phase plates
1148
to be converted to linearly polarized light beams having the same direction of polarization as that of the other type of linearly polarized light beams, and subsequently enter the superimposing lens
1150
. The plurality of sub-beams entering the superimposing lens
1150
are substantially superimposed on an area LA to be illuminated. The prior art illumination optical system thus enables the area to be illuminated with substantially one type of linearly polarized light beams.
FIG. 14
shows drawbacks of the prior art illumination optical system.
FIG. 14A
shows the optical path of the light transmitted by the polarizing separation film
1142
(hereinafter may be simply referred to as the ‘transmitted light’).
FIG. 14B
shows, on the other hand, the optical path of the light reflected by the polarizing separation film
1142
and the reflection film
1144
(hereinafter may be simply referred to as the ‘reflected light’). For the simplicity of explanation, in the illustration of
FIGS. 14A and 14B
, the optical path of the reflected light by the polarizing separation film
1142
and the reflection film
1144
is replaced by an equivalent linear optical path, and deflection of light by the superimposing lens
1150
is neglected.
As shown in
FIGS. 14A and 14B
, in the prior art illumination optical system, out of the light beams entering the polarizing separation film
1142
, an optical path length of the reflected light between the polarizing separation film
1142
and the area LA is greater than an optical path length L
2
of the transmitted light by the distance Wp between the polarizing separation film
1142
and the reflection film
1144
. The difference in optical path length makes the size of a second region W
2
on the area LA, which is illuminated with the reflected light, greater than the size of a first region W
1
on the area LA, which is illuminated with the transmitted light. This causes the illuminating efficiency with the reflected light to be lower than the illuminating efficiency with the transmitted light, thus significantly reducing the total illuminating efficiency in the illumination optical system.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a technique that prevents the significant reduction of the illuminating efficiency occurring in the prior art illumination optical system that utilizes the polarization conversion optical system.
At least part of the above and the other related objects is attained by an illumination optical system that emits illumination light. The illumination optical system includes: a light source that emits non-polarized light; a polarization conversion optical system that has at least one pair of a polarizing separation film and a reflection film, which are arranged to be mutually in parallel with each other and to be inclined relative to a predetermined direction, the polarization conversion optical system converting incident non-polarized light into linearly pol
Akiyama Koichi
Ogawa Yasunori
Yamakawa Hidemasa
Adams Russell
Sever Andrew
LandOfFree
Illumination optical system and projector using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Illumination optical system and projector using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Illumination optical system and projector using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2984166