Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2001-05-31
2003-12-30
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S084000, C349S009000
Reexamination Certificate
active
06669343
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
This invention pertains to the field of image display systems, and more particularly to image projectors employing liquid crystal light valves.
2) Description of the Related Art
Projection-type image display systems are widely known. Examples of such systems, and in particular systems using liquid crystal light valves, are shown in U.S. Pat. Nos. 5,532,763, 5,786,934, 6,224,215 and 6,234,634 the entirety of each of which is hereby incorporated by reference for all purposes as if fully set forth herein. With reference to the following description, familiarity with conventional features of such systems will be assumed, so that only features bearing on the present invention will be described.
FIG. 1
shows relevant portions of an exemplary liquid crystal display (LCD) projector
100
. The LCD projector
100
is a single panel color LCD projector.
The LCD projector
100
comprises in relevant part: a lamp
102
; a first integrator
104
; a second integrator
105
; a polarization conversion system (PCS)
106
; a condenser lens
107
; first through fourth dichoic color filters
108
,
110
,
112
and
114
; first to third scanning prisms
116
,
118
and
120
; reflecting mirrors
122
and
124
; pre-polarizer
126
; polarizing beam splitter
128
; LCD
130
; analyzer
132
; and projection lens
134
.
The operation of the LCD projector
100
will now be explained. The LCD device
130
operates as a light valve or modulator and is adapted to receive an incident light and to impress a desired image upon the incident light which is then projected by the projection lens
134
onto a desired display area or screen. To produce a high quality image with a high contrast ratio, the LCD
130
requires that the incident light be substantially linearly polarized in a predefined direction. In the LCD projector
100
, the LCD device
130
is preferably a reflective-type LCD device such as a liquid crystal on silicon (LCOS) device. The operation of reflective-type LCD devices is well known, and may be found, for example in U.S. Pat. Nos. 6,023,309 and 6,052,165.
The exemplary LCD projector
100
shown in
FIG. 1
employs a scrolling color system. In a scrolling color system, white light is split into constituent red (R), green (G), and blue (B) colored light beams. The colored light beams illuminate the LCD panel as spatially separated stripes of light. The stripes of light scroll across the LCD from top to bottom. As one color scrolls off the bottom of the LCD, it appears immediately again at the top. All three colors (R, G and B) are present on the LCD at all times.
To create the color image, the LCD is effectively addressed at three different places simultaneously. Data for a given color (e.g., green), is written to a row just after the passing of the previous color (e.g., blue). The (green) band of colored light then illuminates the pixel. The panel is addressed at three places and these address rows shift downward in sync with the illumination pattern. A more detailed explanation of the operation of the scrolling color architecture may be found in “
Single Panel Reflective LCD Projector
,” J. A. Shimizu, Projection Displays V, Proceedings SPIE, Vol. 3634, pp. 197-206, (1999), the entirety of which is hereby incorporated by reference for all purposes as if fully set forth herein.
Turning once again to
FIG. 1
, the lamp
102
produces a high intensity, generally unpolarized light. The integrator
104
receives the light from the lamp
102
and shapes and homogenizes the distribution of the light to produce a generally rectangular beam. The integrators
104
and
105
are typically each comprised of a lens array. The integrators
104
and
105
produce multiple secondary light source images in a focal plane, F.
The PCS
106
is located in the focal plane F of the integrators and serves to substantially linearly polarize the light incident thereon.
FIG. 2
shows one embodiment of an integrator
105
, a PCS
106
, and a condenser lens
107
that may be used in the LCD projector
100
. The integrator
105
comprises a lens array. The PCS
106
comprises a polarizing beam splitter array
210
and a half wave plate
220
. The polarizing beam splitter array
210
includes an alternating arrangement of polarizing beam splitters
212
and mirrors
214
.
The PCS
106
is adapted to receive generally unpolarized light and to convert the generally unpolarized incident light into linearly polarized light, “P.” The polarized light may then be passed out through the condenser lens
107
. In contrast to a standard absorbing polarizer, which passes only roughly 50% of light incident thereon having a desired polarization (e.g., “P”), and which absorbs roughly 50% of the light incident thereon having an undesired polarization (e.g., “S”), the PCS
106
typically passes a much higher percentage of incident light than a polarizer (e.g., 80% of incident light) and absorbs a small fraction of the light energy typically absorbed in an absorbing polarizer. Thus, the PCS
106
may be used to polarize light in high intensity applications (e.g., greater than about several hundred lumens) where a standard absorbing polarizer cannot be used because the absorbed light energy would destroy it. On the other hand, the extinction ratio (Tp/Ts) for the PCS
106
is typically substantially lower than that for an absorbing polarizer, meaning the output light has a lower degree of polarization. An extinction ratio for a typical PCS
106
is less than 10 (e.g., 8.25).
In addition to polarizing the received light beam, the combination of polarizing beam splitter
212
, adjacent mirror
214
, and half wave plate
220
in the PCS
106
roughly doubles the etendue, or optical size, of the light beam. That is, the PCS
106
roughly doubles the etendue of an illumination system into which it is incorporated.
A more detailed explanation of the operation of the PCS
106
may be found in “
Ultra
-
High
-
Efficiency LC Projector Using a Polarized Light Illuminating System
,” Y. Itoh et al., 1997 Society of Information Display Digest, pp. 993-996 (1997), the entirety of which is hereby incorporated by reference for all purposes as if fully set forth herein.
Turning again to
FIG. 1
, the substantially polarized light from the PCS
106
is passed through the dichoic color filters
108
and
110
to separate the polarized light into a plurality of different colored light beams (e.g., three, labeled “R,” “G,” and “B”). Each of the colored light beams, red, green and blue, is provided to a corresponding rotating prism
116
,
118
, or
120
, for scanning the color beam onto the LCD
130
in the scrolling color system. The dichoic color filters
112
and
114
direct the plurality of colored light beams to the pre-polarizer
126
.
The pre-polarizer
126
increases the extinction ratio of the colored light beams incident thereon to provide very highly polarized light to the LCD
130
. The pre-polarizer has in its plane both an absorbing direction and a non-absorbing direction, the absorbing direction being perpendicular to the non-absorbing direction. Light having a desired polarization “P” along the non-absorbing direction of the pre-polarizer
126
passes through the pre-polarizer
126
to the polarizing beam splitter
128
, and the remaining light is generally absorbed by the polarizer. The polarizer, being a non-ideal device, has a finite extinction ratio, and thus a small amount of the colored light beams having the undesired “S” polarization passes through the device.
The substantially polarized colored light beams from the pre-polarizer
126
are supplied to the polarizing beam splitter
128
. The polarizing beam splitter
128
directs the substantially polarized colored light beams to the LCD device
130
. Meanwhile, a small remnant of the colored light beams having the undesired “S” polarization is directed away from the LCD device
130
by the beam splitter
128
(e.g., passes through the device).
As briefly described above, the LCD device
130
imparts desired image information on the
Shahzad Khalid
Shimizu Jeffrey A.
Adams Russell
Koval Melissa J
LandOfFree
Image display system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image display system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image display system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3177943