Illumination – Light modifier – Refractor
Reexamination Certificate
2000-02-22
2003-02-04
Tso, Laura K. (Department: 2875)
Illumination
Light modifier
Refractor
C362S019000
Reexamination Certificate
active
06513953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an illumination system that splits light from a light source into a plurality of light beams, converts the light beams to one type of polarized light in which the polarization is substantially in one direction, and superposes these beams of light on the same illumination region. The invention also relates to a projector that by using the illumination system is able to display images with uniform brightness.
2. Description of the Related Art
In a projection display system apparatus, light projected onto electro-optical devices called light valves is modulated in accordance with image information and the light thus modulated is projected onto a screen to thereby display images. Liquid crystal panels (liquid crystal light valves) are the electro-optical devices usually employed. It is desirable that images displayed by a projection display system be uniform and bright, and that the light emitted by the illumination system employed in the apparatus have a high utilization efficiency. Conventionally, integrator optical systems are used to ensure uniform illumination of a region by liquid crystal light valves. Also, in projectors employing liquid crystal light valves that use modulation of just one type of linearly polarized light, in order to raise the light utilization efficiency, a polarization conversion system is used to convert unpolarized light from the light source to one type of linearly polarized light.
FIG. 24
shows the configuration of a conventional illumination system. This illumination system comprises a light source
4120
, a first lens array
4130
, a second lens array
4140
, a polarization conversion system
4150
and a superposition lens
4160
. The two lens arrays
4130
and
4140
and the superposition lens
4160
constitute an integrator optical system.
The first lens array
4130
has a plurality of small lenses
4132
. The second lens array
4140
has a plurality of small lenses
4142
corresponding to the plurality of small lenses
4132
of the first lens array
4130
.
The polarization conversion system
4150
has a plurality of pairs of the polarization splitting film
4152
and reflecting film
4154
arrayed in parallel along the x axis. The polarization splitting film
4152
and reflecting film
4154
have a fixed slant in the direction of the x axis that inclines counterclockwise when viewed from the z axis. The exit side of each polarization splitting film
4152
is provided with a &lgr;/2 retardation film
4156
.
Substantially parallel light emitted by the light source
4120
is divided into a plurality of partial light beams by the plurality of small lenses
4132
. The condensing action of the small lenses
4132
and
4142
converges each of the partial light beams in the vicinity of the polarization splitting film
4152
of the polarization conversion system
4150
. The polarization splitting film
4152
transmits virtually all of one linearly polarized light component, such as p polarized light, for example, while reflecting virtually all of the other linearly polarized light components, such as s polarized light, for example. The linearly polarized light component reflected by the polarization splitting film
4152
is reflected by the reflecting film
4154
onto the superposition lens
4160
. The linearly polarized light component transmitted by the polarization splitting film
4152
falls incident on the &lgr;/2 retardation film
4156
, is converted to linearly polarized light having the same polarization direction as the other linearly polarized light component, and falls incident on the superposition lens
4160
. Thus, the multiple partial light beams incident on the superposition lens
4160
are converted into substantially one type of linearly polarized light and substantially superposed at the illumination region
4180
. This enables the illumination region
4180
to be illuminated substantially uniformly by substantially one type of linearly polarized light.
In the above conventional illumination system, the partial light beams formed by the first lens array
4130
are converged in the vicinity of the polarization splitting film
4152
, and as a result, the partial light beams that fall incident on the polarization splitting film
4152
are spatially separated. The reflecting film
4154
is positioned where there are no partial light beams, and reflects linearly polarized light reflected by the polarization splitting film
4152
. In this way, unpolarized light emitted by the light source is separated into two types of linearly polarized light by the polarization splitting film
4152
and the reflecting film
4154
.
If the light source
4120
emits a perfectly parallel beam, the partial light beams will be converged to substantially a point in the vicinity of the polarization splitting film
4152
. However, if in practice the beam from the light source
4120
is not perfectly parallel, the image will be formed with some degree of divergence. The width of the polarization splitting film
4152
and reflecting film
4154
along the x axis is set so that almost all of the light used to form the image falls effectively on the polarization splitting film
4152
.
An effective way of obtaining a brighter image with a projector is to increase the output of the light source lamp. Light source lamps that are used include metal halide lamps and mercury lamps. To increase the light output it is preferable to use a lamp having a long arc. Usually, however, the beam emitted by a long-arc lamp is less parallel than a beam emitted by a short-arc lamp. This means that even if a short-arc lamp used in an illumination system is simply replaced by a long-arc lamp, the decreased parallelism of the beam will result in a lower proportion of the light impinging on the polarization splitting film
4152
, reducing the polarization splitting efficiency. Thus, the problem is that even when the light source output is increased, there is not much of an increase in the effective output of the light used to illuminate the illumination region.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a technology that, in an illumination system that includes an integrator optical system and polarization conversion system that uses a light source lamp with a higher output than a conventional lamp, allows the light output to be increased without decreasing the utilization efficiency of the illumination system. Another object is to provide a projector that enables a brighter, more uniform projection image to be obtained.
At least part of the above and the other related object are attained by an illumination system that illuminates a light incident surface of an optical device as an illumination region. The system comprises: a light source that emits unpolarized light, a power variation optical relay system that changes a size of a light beam emitted by the light source, a superposition optical system that effects illumination of the illumination region by a given incident light beam, and a polarization conversion system that is provided at a selected position along a light path from an incident surface of the power variation optical relay system to an exit surface of the superposition optical system to convert an incident beam of unpolarized light to a light beam having a linearly polarized component with one type of polarization direction and emits the converted light beam. A size of a light beam entering the polarization conversion system is reduced in a prescribed direction by the power variation optical relay system.
In the illumination system of the present invention the size of a beam of light entering the polarization conversion system can be reduced in a prescribed direction by a power variation optical relay system, thereby improving the incident efficiency of light entering the polarization conversion system. As a result, the illumination region can be brightly and uniformly illuminated by one type of linearly polarized light with substantially uniform directions of polari
LandOfFree
Illumination system and projector 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 system and projector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Illumination system and projector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3140358