Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2002-10-30
2004-08-17
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S056000, C353S058000, C353S060000, C349S009000, C349S161000
Reexamination Certificate
active
06776489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color separation/combination optical system, an image display optical system, and a projection type image display apparatus which use polarization beam splitters to separate illumination light into respective color light components and/or to combine color light components modulated by image display elements.
2. Description of the Related Art
A projection type image display apparatus having a combination of reflection type liquid crystal display elements and polarization beam splitters is disclosed, for example, in U.S. Pat. No. 6,183,091. As shown in
FIG. 19
, the projection type image display apparatus according to that U.S. Pat. is configured to have four polarization beam splitters
218
,
220
,
224
,
228
and four color selecting phase plates
216
,
226
,
234
,
236
.
The color selecting phase plate has a function of converting the direction of polarization of light in a predetermined wavelength area by 90 degrees in the wavelength region of visible light but not converting the direction of light in the other wavelength areas.
In the projection type image display apparatus according to the aforementioned U.S. Patent, linearly polarized light (S-polarized light) from a light source
200
is incident on the first color selecting phase plate
216
which rotates only the polarization direction of light component for blue (B″) by 90 degrees (resulting in P-polarized light) before incidence on the first polarization beam splitter
218
. The first polarization beam splitter
218
transmits the light component for blue which is the P-polarized light and reflects light components for green (G″) and red (R″) (Yellow light (Y″)) which is the S-polarized light except the light component for blue, thereby performing color separation.
The light component for blue (P-polarized light) passes through the second polarization beam splitter
220
and reaches a reflection type liquid crystal display element
222
for blue. The light components for green and red are incident on the second color separating phase plate
226
which converts only the polarization direction of the light component for green by 90 degrees (resulting in P-polarized light) before incident on the third polarization beam splitter
228
. The third polarization beam splitter
228
transmits the light component for green which is the P-polarized light and reflects the light component for red which is the S-polarized light to perform color separation, so that the light component for green and the light component for red reach reflection type liquid crystal display elements
232
and
230
for green and red, respectively.
The P-polarized light component for blue modulated to image light by the reflection type liquid crystal display element
222
passes through the second polarization beam splitter
220
and returns toward the light source
200
. The S-polarized light component thereof is reflected by the second polarization beam splitter
220
and serves as projection light.
The S-polarized light component for red modulated to image light by the reflection type liquid crystal display element
230
is reflected by the third polarization beam splitter
228
and returns toward the light source
200
. The P-polarized light component thereof passes through the third polarization beam splitter
228
and serves as projection light.
The P-polarized light component for green modulated to image light by the reflection type liquid crystal display element
232
passes through the third polarization beam splitter
228
and returns toward the light source
200
. The S-polarized light component thereof is reflected by the third polarization beam splitter
228
and serves as projection light.
The projection light components for green and red are incident on the third color selecting phase plate
234
which rotates the polarization direction of the light component for green by 90 degrees to make both the light component for green and the light component for red P-polarized before transmission through the fourth polarization beam splitter
224
. On the other hand, the light component for blue which is the S-polarized light is reflected by the fourth polarization beam splitter
224
. The fourth color selecting phase plate
236
converts only the polarization direction of the light component for blue by 90 degrees and the resulting P-polarized light emanates therefrom. The light component for green and the light component for red which are the P-polarized light pass through the fourth color selecting phase plate
236
. Thus, the light components for RGB are combined into one and projected on a projection surface such as a screen, not shown, by a projection lens
238
.
In this configuration, it is expected that the illumination light from the light source
200
heats the reflection type liquid crystal display elements
222
,
230
, and
232
.
No problem arises if each reflection type liquid crystal display element is uniformly heated. In general, however, a temperature difference is often caused between the central portion and the peripheral portion of the reflection type liquid crystal display element such that the central portion of the reflection type liquid crystal display element is at a higher temperature than the peripheral portion.
In this case, since liquid crystal has V-T (voltage-transmittance) characteristics and transmittance in each color varies with temperature, the transmittance variations between the central portion and the peripheral portion of the reflection type liquid crystal display element cause uneven colors (color variations) in a projected image to present the disadvantage of reduced quality of the projected image.
As a measure to achieve a uniform temperature at the reflection type liquid crystal display elements, Japanese Patent Application Laid-Open No. 6-194621 proposes a method in which a cooling fan is provided around each reflection type liquid crystal display element to directly supply a cooling wind to the reflection type liquid crystal display element to minimize a temperature difference between the central portion and the peripheral portion of the reflection type liquid crystal display element, thereby reducing color variations in a projected image.
In addition, Japanese Patent Application Laid-Open No. 11-305203 proposes a method in which a heater is provided around a reflection type liquid crystal display element to heat the element to minimize a temperature difference between the central portion and the peripheral portion of the reflection type liquid crystal display element, thereby reducing color variations in a projected image.
Components which are expected to experience heating due to the illumination light include not only the reflection type liquid crystal display elements but also the polarization beam splitters. When the polarization beam splitter has a temperature difference therein, internal stress is produced in an optical glass material constituting the polarization beam splitter. As a result, birefringence which converts linearly polarized light incident thereon into elliptically polarized light (that is, produces an undesired polarized light component) under the influence of photoelasticity, so that a desired effect of polarized light separation (reflection and transmission) is not attained with reliability.
Consequently, there exists a problem that so-called light leakage which is not subjected to a desired polarized light separation effect reaches a projection surface to reduce contrast and quality of a projected image.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a color seperation/combination optical system, an image display optical system, and a projection type image display apparatus which allow a uniform temperature at the polarization beam splitters.
To achieve the aforementioned object, the present invention provides a color separation/combination optical system comprised of a polarization beam splitter which is formed in a prism shape h
Adams Russell
Koval Melissa J
LandOfFree
Color separation/combination optical system, image display... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color separation/combination optical system, image display..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color separation/combination optical system, image display... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3343411